Journal articles on the topic 'Australian Monsoon Experiment'
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Holland, Greg J., John L. McBride, Roger K. Smith, David Jasper, and Thomas D. Keenan. "The BMRC Australian Monsoon Experiment: AMEX." Bulletin of the American Meteorological Society 67, no. 12 (December 1986): 1466–72. http://dx.doi.org/10.1175/1520-0477(1986)067<1466:tbamea>2.0.co;2.
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Yu, Jin-Yi, Fengpeng Sun, and Hsun-Ying Kao. "Contributions of Indian Ocean and Monsoon Biases to the Excessive Biennial ENSO in CCSM3." Journal of Climate 22, no. 7 (April 1, 2009): 1850–58. http://dx.doi.org/10.1175/2008jcli2706.1.
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Abstract The Community Climate System Model, version 3 (CCSM3), is known to produce many aspects of El Niño–Southern Oscillation (ENSO) realistically, but the simulated ENSO exhibits an overly strong biennial periodicity. Hypotheses on the cause of this excessive biennial tendency have thus far focused primarily on the model’s biases within the tropical Pacific. This study conducts CCSM3 experiments to show that the model’s biases in simulating the Indian Ocean mean sea surface temperatures (SSTs) and the Indian and Australian monsoon variability also contribute to the biennial ENSO tendency. Two CCSM3 simulations are contrasted: a control run that includes global ocean–atmosphere coupling and an experiment in which the air–sea coupling in the tropical Indian Ocean is turned off by replacing simulated SSTs with an observed monthly climatology. The decoupling experiment removes CCSM3’s warm bias in the tropical Indian Ocean and reduces the biennial variability in Indian and Australian monsoons by about 40% and 60%, respectively. The excessive biennial ENSO is found to reduce dramatically by about 75% in the decoupled experiment. It is shown that the biennial monsoon variability in CCSM3 excites an anomalous surface wind pattern in the western Pacific that projects well into the wind pattern associated with the onset phase of the simulated biennial ENSO. Therefore, the biennial monsoon variability is very effective in exciting biennial ENSO variability in CCSM3. The warm SST bias in the tropical Indian Ocean also increases ENSO variability by inducing stronger mean surface easterlies along the equatorial Pacific, which strengthen the Pacific ocean–atmosphere coupling and enhance the ENSO intensity.
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Keenan, T. D., J. McBride, G. Holland, N. Davidson, and B. Gunn. "Diurnal Variations during the Australian Monsoon Experiment (AMEX) Phase II." Monthly Weather Review 117, no. 11 (November 1989): 2535–53. http://dx.doi.org/10.1175/1520-0493(1989)117<2535:dvdtam>2.0.co;2.
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Höller, H., H. D. Betz, K. Schmidt, R. V. Calheiros, P. May, E. Houngninou, and G. Scialom. "Lightning characteristics observed by a VLF/LF lightning detection network (LINET) in Brazil, Australia, Africa and Germany." Atmospheric Chemistry and Physics Discussions 9, no. 2 (March 6, 2009): 6061–146. http://dx.doi.org/10.5194/acpd-9-6061-2009.
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Abstract. This paper describes lightning characteristics as obtained in four sets of lightning measurements during recent field campaigns in different parts of the world from mid-latitudes to the tropics by the novel VLF/LF (very low frequency/low frequency) lightning detection network (LINET). The paper gives a general overview on the approach, and a synopsis of the statistical results for the observation periods as a whole and for one special day in each region. The focus is on the characteristics of lightning which can specifically be observed by this system like intra-cloud and cloud-to-ground stroke statistics, vertical distributions of intra-cloud strokes or peak current distributions. Some conclusions regarding lightning produced NOx are also presented as this was one of the aims of the tropical field campaigns TROCCINOX (Tropical Convection, Cirrus and Nitrogen Oxides Experiment) and TroCCiBras (Tropical Convection and Cirrus Experiment Brazil) in Brazil during January/February 2005, SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) and TWP-ICE (Tropical Warm Pool – International Cloud Experiment) during November/December 2005 and January/February 2006, respectively, in the Darwin area in N-Australia, and of AMMA (African Monsoon Multidisciplinary Analyses) in W-Africa during June–November 2006. Regional and temporal characteristics of lightning are found to be dependent on orographic effects (e.g. S-Germany, Brazil, Benin), land-sea breeze circulations (N-Australia) and especially the evolution of the monsoons (Benin, N-Australia). Large intra-seasonal variability in lightning occurrence was found for the Australian monsoon between the strong convection during build-up and break phases and the weak wet monsoon phase with only minor lightning activity. Total daily lightning rates can be of comparable intensity in all regions with the heaviest events found in Germany and N-Australia. The frequency of occurrence of such days was by far the largest in N-Australia. In accordance with radar observed storm structures, the intra-cloud stroke mean emission heights were found distinctly different in Germany (8 km) as compared to the tropics (up to 12 km in N-Australia). The fraction of intra-cloud strokes (compared to all strokes) was found to be relatively high in Brazil and Australia (0.83 and 0.74, respectively) as compared to Benin and Germany (0.67 and 0.69, respectively). Using stroke peak currents and vertical location information, lightning NOx (LNOx) production under defined standard conditions can be compared for the different areas of observation. LNOx production per standard stroke was found to be most efficient for the N-Australian and S-German thunderstorms whereas the yield from Brazilian and W-African strokes was nearly 40% less. On the other hand, the main NO contribution in Brazil was from intra-cloud (IC) strokes whereas in Benin it was due to cloud-to-ground (CG) components. For the German and Australian strokes both stroke types contributed similar amounts to the total NO outcome.
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Höller, H., H. D. Betz, K. Schmidt, R. V. Calheiros, P. May, E. Houngninou, and G. Scialom. "Lightning characteristics observed by a VLF/LF lightning detection network (LINET) in Brazil, Australia, Africa and Germany." Atmospheric Chemistry and Physics 9, no. 20 (October 20, 2009): 7795–824. http://dx.doi.org/10.5194/acp-9-7795-2009.
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Abstract. This paper describes lightning characteristics as obtained in four sets of lightning measurements during recent field campaigns in different parts of the world from mid-latitudes to the tropics by the novel VLF/LF (very low frequency/low frequency) lightning detection network (LINET). The paper gives a general overview on the approach, and a synopsis of the statistical results for the observation periods as a whole and for one special day in each region. The focus is on the characteristics of lightning which can specifically be observed by this system like intra-cloud and cloud-to-ground stroke statistics, vertical distributions of intra-cloud strokes or peak current distributions. Some conclusions regarding lightning produced NOx are also presented as this was one of the aims of the tropical field campaigns TROCCINOX (Tropical Convection, Cirrus and Nitrogen Oxides Experiment) and TroCCiBras (Tropical Convection and Cirrus Experiment Brazil) in Brazil during January/February 2005, SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) and TWP-ICE (Tropical Warm Pool-International Cloud Experiment) during November/December 2005 and January/February 2006, respectively, in the Darwin area in N-Australia, and of AMMA (African Monsoon Multidisciplinary Analyses) in W-Africa during June–November 2006. Regional and temporal characteristics of lightning are found to be dependent on orographic effects (e.g. S-Germany, Brazil, Benin), land-sea breeze circulations (N-Australia) and especially the evolution of the monsoons (Benin, N-Australia). Large intra-seasonal variability in lightning occurrence was found for the Australian monsoon between the strong convection during build-up and break phases and the weak active monsoon phase with only minor lightning activity. Total daily lightning stroke rates can be of comparable intensity in all regions with the heaviest events found in Germany and N-Australia. The frequency of occurrence of such days was by far the largest in N-Australia. In accordance with radar observed storm structures, the intra-cloud stroke mean emission heights were found distinctly different in Germany (8 km) as compared to the tropics (up to 12 km in N-Australia). The fraction of intra-cloud strokes (compared to all strokes) was found to be relatively high in Brazil and Australia (0.83 and 0.82, respectively) as compared to Benin and Germany (0.64 and 0.69, respectively). Using stroke peak currents and vertical location information, lightning NOx (LNOx) production under defined standard conditions can be compared for the different areas of observation. LNOx production per standard stroke was found to be most efficient for the N-Australian and S-German thunderstorms whereas the yield from Brazilian and W-African strokes was nearly 40% less. On the other hand, the main NO contribution in Brazil was from intra-cloud (IC) strokes whereas in Benin it was due to cloud-to-ground (CG) components. For the German and Australian strokes both stroke types contributed similar amounts to the total NO outcome.
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May, Peter T., Charles N. Long, and Alain Protat. "The Diurnal Cycle of the Boundary Layer, Convection, Clouds, and Surface Radiation in a Coastal Monsoon Environment (Darwin, Australia)." Journal of Climate 25, no. 15 (August 1, 2012): 5309–26. http://dx.doi.org/10.1175/jcli-d-11-00538.1.
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Abstract The diurnal variation of convection and associated cloud and radiative properties remains a significant issue in global NWP and climate models. This study analyzes observed diurnal variability of convection in a coastal monsoonal environment examining the interaction of convective rain clouds, their associated cloud properties, and the impact on the surface radiation and corresponding boundary layer structure during periods where convection is suppressed or active on the large scale. The analysis uses data from the Tropical Warm Pool International Cloud Experiment (TWP-ICE) as well as routine measurements from the Australian Bureau of Meteorology and the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program. Both active monsoonal and large-scale suppressed (buildup and break) conditions are examined and demonstrate that the diurnal variation of rainfall is much larger during the break periods and the spatial distribution of rainfall is very different between the monsoon and break regimes. During the active monsoon the total net radiative input to the surface is decreased by more than 3 times the amount than during the break regime—this total radiative cloud forcing is found to be dominated by the shortwave (SW) cloud effects because of the much larger optical thicknesses and persistence of long-lasting anvils and cirrus cloud decks associated with the monsoon regime. These differences in monsoon versus break surface radiative energy contribute to low-level air temperature differences in the boundary layer over the land surfaces.
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Lazić, L. "Eta model forecasts of tropical cyclones from Australian Monsoon Experiment: The model sensitivity." Meteorology and Atmospheric Physics 52, no. 3-4 (September 1993): 113–27. http://dx.doi.org/10.1007/bf01031870.
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Lazić, L. "Eta model forecasts of tropical cyclones from Australian Monsoon Experiment: Dynamical adjustment of initial conditions." Meteorology and Atmospheric Physics 52, no. 3-4 (September 1993): 101–11. http://dx.doi.org/10.1007/bf01031869.
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Xie, Shaocheng, Timothy Hume, Christian Jakob, Stephen A. Klein, Renata B. McCoy, and Minghua Zhang. "Observed Large-Scale Structures and Diabatic Heating and Drying Profiles during TWP-ICE." Journal of Climate 23, no. 1 (January 1, 2010): 57–79. http://dx.doi.org/10.1175/2009jcli3071.1.
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Abstract This study documents the characteristics of the large-scale structures and diabatic heating and drying profiles observed during the Tropical Warm Pool–International Cloud Experiment (TWP-ICE), which was conducted in January–February 2006 in Darwin during the northern Australian monsoon season. The examined profiles exhibit significant variations between four distinct synoptic regimes that were observed during the experiment. The active monsoon period is characterized by strong upward motion and large advective cooling and moistening throughout the entire troposphere, while the suppressed and clear periods are dominated by moderate midlevel subsidence and significant low- to midlevel drying through horizontal advection. The midlevel subsidence and horizontal dry advection are largely responsible for the dry midtroposphere observed during the suppressed period and limit the growth of clouds to low levels. During the break period, upward motion and advective cooling and moistening located primarily at midlevels dominate together with weak advective warming and drying (mainly from horizontal advection) at low levels. The variations of the diabatic heating and drying profiles with the different regimes are closely associated with differences in the large-scale structures, cloud types, and rainfall rates between the regimes. Strong diabatic heating and drying are seen throughout the troposphere during the active monsoon period while they are moderate and only occur above 700 hPa during the break period. The diabatic heating and drying tend to have their maxima at low levels during the suppressed periods. The diurnal variations of these structures between monsoon systems, continental/coastal, and tropical inland-initiated convective systems are also examined.
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LinHo, L. H., Xianglei Huang, and Ngar-Cheung Lau. "Winter-to-Spring Transition in East Asia: A Planetary-Scale Perspective of the South China Spring Rain Onset." Journal of Climate 21, no. 13 (July 1, 2008): 3081–96. http://dx.doi.org/10.1175/2007jcli1611.1.
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Abstract Analysis of observations from 1979 to 2002 shows that the seasonal transition from winter to spring in East Asia is marked with a distinctive event—the onset of the south China spring rain (SCSR). In late February, the reduced thermal contrast between ocean and land leads to weakening of the Asian winter monsoon as well as the Siberian high and the Aleutian low. Meanwhile, convection over Australia and the western Pacific Maritime Continent is suppressed on the passage of the dry phase of a Madden–Julian oscillation (MJO). In conjunction with the seasonal march of monsoon circulation in the Indonesian–Australian sector, this MJO passage weakens the local thermally direct cell in the East Asia–Australia sector. This development is further accompanied by a series of adjustments in both the tropics and midlatitudes. These changes include attenuation of the planetary stationary wave, considerable weakening of the westerly jet stream over much of the central Pacific adjacent to Japan, and reduction of baroclinicity near the East Asian trough. The influence of concurrent local processes in midlatitudes on the SCSR onset is also important. The weakened jet stream is associated with confinement of frontal activities to the coastal regions of East Asia as well as with rapid expansion of the subtropical Pacific high from the eastern Pacific to the western Pacific. A parallel analysis using output from an experiment with a GFDL-coupled GCM shows that the above sequence of circulation changes is well simulated in that model.
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Johnson, Richard H., Steven L. Aves, Paul E. Ciesielski, and Thomas D. Keenan. "Organization of Oceanic Convection during the Onset of the 1998 East Asian Summer Monsoon." Monthly Weather Review 133, no. 1 (January 1, 2005): 131–48. http://dx.doi.org/10.1175/mwr-2843.1.
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Abstract The organizational modes of convection over the northern South China Sea (SCS) during the onset of the summer monsoon are documented using radar and sounding data from the May–June 1998 South China Sea Monsoon Experiment (SCSMEX). The onset occurred in mid-May with a rapid increase in deep convection over a 10-day period, accompanied by a major shift in the circulation over the east Asian region. Analysis of Bureau of Meteorology Research Centre (BMRC) radar data from Dongsha Island reveals a wide range of organizational modes of convection over the northern SCS. Proximity sounding data indicate that lower- and middle-level vertical wind shears exerted a dominant control over the orientation of convective lines within mesoscale convective systems in this region, as has been found in the Australian monsoon region and the equatorial western Pacific. The results are consistent with the conceptual model of LeMone et al. based on the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE), except two new organizational modes have been identified: shear-parallel bands for strong low-level shear and weak midlevel shear when there is weak instability and the air is dry aloft, and shear-parallel bands for strong shears in both layers when the shear vectors are in the same direction. Midlatitude influences, namely, the passage of troughs over southern China, likely contributed to these two additional modes. The stratiform rain fraction from the convective systems during the monsoon onset period was relatively small (26%) compared to the estimated average of about 40% for the entire Tropics. This small fraction is attributed to the weak instability during the onset period and relatively dry air in the upper troposphere.
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Minh, Pham Thi, Bui Thi Tuyet, Tran Thi Thu Thao, and Le Thi Thu Hang. "Application of ensemble Kalman filter in WRF model to forecast rainfall on monsoon onset period in South Vietnam." VIETNAM JOURNAL OF EARTH SCIENCES 40, no. 4 (September 18, 2018): 367–94. http://dx.doi.org/10.15625/0866-7187/40/4/13134.
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This paper presents some results of rainfall forecast in the monsoon onset period in South Vietnam, with the use of ensemble Kalman filter to assimilate observation data into the initial field of the model. The study of rainfall forecasts are experimented at the time of Southern monsoon outbreaks for 3 years (2005, 2008 and 2009), corresponding to 18 cases. In each case, there are five trials, including satellite wind data assimilation, upper-air sounding data assimilation, mixed data (satellite wind+upper-air sounding data) assimilation and two controlled trials (one single predictive test and one multi-physical ensemble prediction), which is equivalent to 85 forecasts for one trial. Based on the statistical evaluation of 36 samples (18 meteorological stations and 18 trials), the results show that Kalman filter assimilates satellite wind data to forecast well rainfall at 48 hours and 72 hours ranges. With 24 hour forecasting period, upper-air sounding data assimilation and mixed data assimilation experiments predicted better rainfall than non-assimilation tests. The results of the assessment based on the phase prediction indicators also show that the ensemble Kalman filter assimilating satellite wind data and mixed data sets improve the rain forecasting capability of the model at 48 hours and 72 hour ranges, while the upper-air sounding data assimilation test produces satisfactory results at the 72 hour forecast range, and the multi-physical ensemble test predicted good rainfall at 24 hour and 48 hour forecasts. The results of this research initially lead to a new research approach, Kalman Filter Application that assimilates the existing observation data into input data of the model that can improve the quality of rainfall forecast in Southern Vietnam and overall country in general.References Bui Minh Tuan, Nguyen Minh Truong, 2013. 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Yan, Mi, Bin Wang, Jian Liu, Axing Zhu, Liang Ning, and Jian Cao. "Understanding the Australian Monsoon change during the Last Glacial Maximum with a multi-model ensemble." Climate of the Past 14, no. 12 (December 20, 2018): 2037–52. http://dx.doi.org/10.5194/cp-14-2037-2018.
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Abstract. The response of the Australian monsoon to external forcings and related mechanisms during the Last Glacial Maximum (LGM) are investigated by multi-model experiments in CMIP5–PMIP3. Although the annual mean precipitation over the Australian monsoon region decreases, the annual range, or the monsoonality, is enhanced. The precipitation increases in early austral summer and decreases in austral winter, resulting in the amplified annual range, but the main contribution comes from the decreased precipitation in austral winter. The decreased winter precipitation is primarily caused by weakened upward motion, although reduced water vapor also has a moderate contribution. The weakened upward motion is induced by the enhanced land–sea thermal contrast, which intensifies the divergence over northern Australia. The increased Australian monsoon rainfall in early summer, however, is an integrated result of the positive effect of local dynamic processes (enhanced moisture convergence) and the negative effect of thermodynamics (reduced moisture content). The enhanced moisture convergence is caused by two factors: the strengthened northwest–southeast thermal contrast between the cooler Indochina–western Indonesia and the warmer northeastern Australia, and the east–west sea surface temperature gradients between the warmer western Pacific and cooler eastern Indian Ocean, both due to the alteration of land–sea configuration arising from the sea level drop. The enhanced Australian monsoonality in the LGM is not associated with global-scale circulation change such as the shift of the Intertropical Convergence Zone; rather, it is mainly due to the change of regional circulations around Australia arising from the changes in land–sea contrast and the east–west SST gradients over the Indian and western Pacific oceans. This finding should be taken into account when investigating its future change under global warming. Our findings may also explain why proxy records indicate different changes in Australian monsoon precipitation during the LGM.
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Taschetto, Andréa S., Reindert J. Haarsma, Alexander Sen Gupta, Caroline C. Ummenhofer, Khalia J. Hill, and Matthew H. England. "Australian Monsoon Variability Driven by a Gill–Matsuno-Type Response to Central West Pacific Warming." Journal of Climate 23, no. 18 (September 15, 2010): 4717–36. http://dx.doi.org/10.1175/2010jcli3474.1.
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Abstract The objective of this study is to investigate the mechanisms that cause the anomalous intensification of tropical Australian rainfall at the height of the monsoon during El Niño Modoki events. In such events, northwestern Australia tends to be wetter in January and February when the SST warming is displaced to the central west Pacific, the opposite response to that associated with a traditional El Niño. In addition, during the bounding months, that is, December and March, there is below-average rainfall induced by an anomalous Walker circulation. This behavior tends to narrow and intensify the annual rainfall cycle over northwestern Australia relative to the climatology, causing a delayed monsoonal onset and an earlier retreat over the region. Observational datasets and numerical experiments with a general circulation model are used to examine the atmospheric response to the central west Pacific SST warming. It is shown here that the increase of precipitation, particularly in February, is phased locked to the seasonal cycle when the intertropical convergence zone is displaced southward and the South Pacific convergence zone is strengthened. An interaction between the interannual SST variability associated with El Niño Modoki events and the evolution of the seasonal cycle intensifies deep convection in the central west Pacific, driving a Gill–Matsuno-type response to the diabatic heating. The westward-propagating disturbance associated with the Gill–Matsuno mechanism generates an anomalous cyclonic circulation over northwestern Australia, leading to convergence of moisture and increased precipitation. The Gill–Matsuno-type response overwhelms the subsidence of the anomalous Walker circulation associated with Modoki events over Australia during the peak of the monsoon.
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Meehl, Gerald A., Aixue Hu, and Claudia Tebaldi. "Decadal Prediction in the Pacific Region." Journal of Climate 23, no. 11 (June 1, 2010): 2959–73. http://dx.doi.org/10.1175/2010jcli3296.1.
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Abstract A “perfect model” configuration with a global coupled climate model 30-member ensemble is used to address decadal prediction of Pacific SSTs. All model data are low-pass filtered to focus on the low-frequency decadal component. The first three EOFs in the twentieth-century simulation, representing nearly 80% of the total variance, are used as the basis for early twenty-first-century predictions. The first two EOFs represent the forced trend and the interdecadal Pacific oscillation (IPO), respectively, as noted in previous studies, and the third has elements of both trend and IPO patterns. The perfect model reference simulation, the target for the prediction, is taken as the experiment that ran continuously from the twentieth to twenty-first century using anthropogenic and natural forcings for the twentieth century and the A1B scenario for the twenty-first century. The other 29 members use a perturbation in the atmosphere at year 2000 and are run until 2061. Since the IPO has been recognized as a dominant contributor to decadal variability in the Pacific, information late in the twentieth century and early in the twenty-first century is used to select a subset of ensemble members that are more skillful in tracking the time evolution of the IPO (EOF2) in relation to a notional start date of 2010. Predictions for the 19-yr period centered on the year 2020 use that subset of ensemble members to construct Pacific SST patterns based on the predicted evolution of the first three EOFs. Compared to the perfect model reference simulation, the predictions show some skill for Pacific SST predictions with anomaly pattern correlations greater than +0.5. An application of the Pacific SST prediction is made to precipitation over North America and Australia. Even though there are additional far-field influences on Pacific SSTs and North American and Australian precipitation involving the Atlantic multidecadal oscillation (AMO) in the Atlantic, and Indian Ocean and South Asian monsoon variability, there is qualitative skill for the pattern of predicted precipitation over North America and Australia using predicted Pacific SSTs. This exercise shows that, in the presence of a large forced trend like that in the large ensemble, much of Pacific region decadal predictability about 20 years into the future arises from increasing greenhouse gases.
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Wu, Renguang. "Possible Role of the Indian Ocean in the In-Phase Transition of the Indian-to-Australian Summer Monsoon." Journal of Climate 21, no. 21 (November 1, 2008): 5727–41. http://dx.doi.org/10.1175/2008jcli2354.1.
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Abstract Analysis of observations shows that in-phase transitions from the Indian summer monsoon (ISM) to the Australian summer monsoon (ASM) have occurred both in El Niño–Southern Oscillation (ENSO) and non-ENSO years. The present study investigates possible roles of the Indian Ocean in the in-phase ISM-to-ASM transitions. It is shown that an anomalous ISM leads to sea surface temperature (SST) anomalies in the tropical Indian Ocean through wind–evaporation effects. The resultant Indian Ocean SST anomalies induce an anomalous ASM of the same sign as the ISM through an anomalous east–west circulation over the eastern Indian Ocean and the Maritime Continent–northern Australia. The results indicate that the in-phase ISM-to-ASM transitions in non-ENSO years can be accomplished through monsoon–Indian Ocean interactions. The results of observational analysis are confirmed with numerical model experiments.
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Krishnan, R., and P. Swapna. "Significant Influence of the Boreal Summer Monsoon Flow on the Indian Ocean Response during Dipole Events." Journal of Climate 22, no. 21 (November 1, 2009): 5611–34. http://dx.doi.org/10.1175/2009jcli2176.1.
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Abstract A majority of positive Indian Ocean dipole (IOD) events in the last 50 years were accompanied by enhanced summer monsoon circulation and above-normal precipitation over central-north India. Given that IODs peak during boreal autumn following the summer monsoon season, this study examines the role of the summer monsoon flow on the Indian Ocean (IO) response using a suite of ocean model experiments and supplementary data diagnostics. The present results indicate that, if the summer monsoon Hadley-type circulation strengthens during positive IOD events, then the strong off-equatorial southeasterly winds over the northern flanks of the intensified Australian high can effectively promote upwelling in the southeastern tropical Indian Ocean and amplify the zonal gradient of the IO heat content response. While it is noted that a strong monsoon cross-equatorial flow by itself may not generate a dipolelike response, a strengthening (weakening) of monsoon easterlies to the south of the equator during positive IOD events tends to reinforce (hinder) the zonal gradient of the upper-ocean heat content response. The findings show that an intensification of monsoonal winds during positive IOD periods produces nonlinear amplification of easterly wind stress anomalies to the south of the equator because of the nonlinear dependence of wind stress on wind speed. It is noted that such an off-equatorial intensification of easterlies over the SH enhances upwelling in the eastern IO off Sumatra–Java, and the thermocline shoaling provides a zonal pressure gradient, which drives anomalous eastward equatorial undercurrents (EUC) in the subsurface. Furthermore, the combination of positive IOD and stronger-than-normal monsoonal flow favors intensification of shallow transient meridional overturning circulation in the eastern IO and enhances the feed of cold subsurface off-equatorial waters to the EUC.
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Ueki, Iwao, Nobuhiro Fujii, Yukio Masumoto, and Keisuke Mizuno. "Data Evaluation for a Newly Developed Slack-Line Mooring Buoy Deployed in the Eastern Indian Ocean." Journal of Atmospheric and Oceanic Technology 27, no. 7 (July 1, 2010): 1195–214. http://dx.doi.org/10.1175/2010jtecho735.1.
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Abstract For the purpose of climate research and forecasting the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) in the Indian Ocean has been planned. Development of RAMA has been gradually accelerated in recent years as a multinational effort. To promote RAMA the authors have developed a small size buoy system, which uses the slack-line mooring method, intended for the easy handling of maintenance on a relatively small vessel. The authors have also conducted a field experiment of the simultaneous deployment of new slack-line mooring and conventional taut-line mooring in the eastern Indian Ocean. This paper describes the performance of the newly developed buoy system, especially the data consistency against the taut-line mooring system, which is usually used for a tropical moored buoy array. Although the slack-line mooring method has the advantage of downsizing the total mooring system, it also has the disadvantage of having relatively large vertical shifts of installed sensors produced by a large migration of the surface buoy. To offset this disadvantage to a certain extent, a data reconstruction method has been developed and evaluated. Through the data comparison between both mooring systems, it is confirmed that the reconstructed data of the newly developed buoy can basically capture the same features as that observed with a conventional taut-line mooring system. The maximum mean difference of −0.16°C and the maximum root-mean-square (RMS) difference of 0.58°C for temperature appeared within the thermocline layer, whereas the maximum mean difference of 0.02 and the maximum RMS difference of 0.09 for salinity appeared within the mixed layer. Considering a distance of 8 n mi between the two moorings, these values are acceptable for regarding that the two moorings can observe same feature. Results of this study support the introduction of various types of mooring systems for a multinational approach of RAMA and contribute to the further progress of RAMA, climate research, and forecasting.
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Ye, Bing, Anthony D. Del Genio, and Kenneth K.-W. Lo. "CAPE Variations in the Current Climate and in a Climate Change." Journal of Climate 11, no. 8 (August 1, 1998): 1997–2015. http://dx.doi.org/10.1175/1520-0442-11.8.1997.
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Abstract Observed variations of convective available potential energy (CAPE) in the current climate provide one useful test of the performance of cumulus parameterizations used in general circulation models (GCMs). It is found that frequency distributions of tropical Pacific CAPE, as well as the dependence of CAPE on surface wet-bulb potential temperature (Θw) simulated by the Goddard Institute for Space Studies’s GCM, agree well with that observed during the Australian Monsoon Experiment period. CAPE variability in the current climate greatly overestimates climatic changes in basinwide CAPE in the tropical Pacific in response to a 2°C increase in sea surface temperature (SST) in the GCM because of the different physics involved. In the current climate, CAPE variations in space and time are dominated by regional changes in boundary layer temperature and moisture, which in turn are controlled by SST patterns and large-scale motions. Geographical thermodynamic structure variations in the middle and upper troposphere are smaller because of the canceling effects of adiabatic cooling and subsidence warming in the rising and sinking branches of the Walker and Hadley circulations. In a forced equilibrium global climate change, temperature change is fairly well constrained by the change in the moist adiabatic lapse rate and thus the upper troposphere warms to a greater extent than the surface. For this reason, climate change in CAPE is better predicted by assuming that relative humidity remains constant and that the temperature changes according to the moist adiabatic lapse rate change of a parcel with 80% relative humidity lifted from the surface. The moist adiabatic assumption is not symmetrically applicable to a warmer and colder climate: In a warmer regime moist convection determines the tropical temperature structure, but when the climate becomes colder the effect of moist convection diminishes and the large-scale dynamics and radiative processes become relatively important. Although a prediction based on the change in moist adiabat matches the GCM simulation of climate change averaged over the tropical Pacific basin, it does not match the simulation regionally because small changes in the general circulation change the local boundary layer relative humidity by 1%–2%. Thus, the prediction of regional climate change in CAPE is also dependent on subtle changes in the dynamics.
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Notaro, Michael, Guangshan Chen, and Zhengyu Liu. "Vegetation Feedbacks to Climate in the Global Monsoon Regions*." Journal of Climate 24, no. 22 (November 15, 2011): 5740–56. http://dx.doi.org/10.1175/2011jcli4237.1.
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Abstract Vegetation feedbacks on climate, on the subannual time scale, are examined across six monsoon regions with a fully coupled atmosphere–ocean–ice–land model with dynamic vegetation. Initial value ensemble experiments are run in which the total vegetation cover fraction across the six monsoon regions is reduced and the climatic response assessed. Consistent responses among the regions include reductions in leaf area index, turbulent fluxes, and atmospheric moisture; enhanced subsidence; and increases in ground and surface air temperature. The most distinct changes in vertical motion, precipitable water, and precipitation occur along the flanks of the monsoon season, with small changes in midmonsoon rainfall. Unique responses to reduced vegetation cover are noted among the monsoon regions. While the monsoon is delayed and weaker over north Australia owing to diminished leaf area, it occurs earlier over China and the southwest United States. The subtropical monsoon regions are characterized by a larger decrease in sensible heat than latent heat flux, while the opposite is true for tropical monsoon regions. North Australia experiences the most substantial decline in both moisture flux convergence and precipitation.
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Yeung, Nicholas King-Hei, Laurie Menviel, Katrin J. Meissner, Andréa S. Taschetto, Tilo Ziehn, and Matthew Chamberlain. "Land–sea temperature contrasts at the Last Interglacial and their impact on the hydrological cycle." Climate of the Past 17, no. 2 (April 21, 2021): 869–85. http://dx.doi.org/10.5194/cp-17-869-2021.
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Abstract. Due to different orbital configurations, high northern latitude summer insolation was higher during the Last Interglacial period (LIG; 129–116 thousand years before present, ka) than during the pre-industrial period (PI), while high southern latitude summer insolation was lower. The climatic response to these changes is studied here with focus on the Southern Hemisphere monsoons, by performing an equilibrium experiment of the LIG at 127 ka with the Australian Earth System Model, ACCESS-ESM1.5, as part of the Paleoclimate Model Intercomparison Project 4 (PMIP4). Simulated mean surface air temperature between 40 and 60∘ N over land during boreal summer is 6.5 ∘C higher at the LIG compared to PI, which leads to a northward shift of the Intertropical Convergence Zone (ITCZ) and a strengthening of the North African and Indian monsoons. Despite 0.4 ∘C cooler conditions in austral summer in the Southern Hemisphere (0–90∘ S), annual mean air temperatures are 1.2 ∘C higher at southern mid-latitudes to high latitudes (40–80∘ S). These differences in temperature are coincident with a large-scale reorganisation of the atmospheric circulation. The ITCZ shifts southward in the Atlantic and Indian sectors during the LIG austral summer compared to PI, leading to increased precipitation over the southern tropical oceans. However, weaker Southern Hemisphere insolation during LIG austral summer induces a significant cooling over land, which in turn weakens the land–sea temperature contrast, leading to an overall reduction (−20 %) in monsoonal precipitation over the Southern Hemisphere's continental regions compared to PI. The intensity and areal extent of the Australian, South American and South African monsoons are consistently reduced in LIG. This is associated with greater pressure and subsidence over land due to a strengthening of the Southern Hemisphere Hadley cell during austral summer.
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Taschetto, Andréa S., Alex Sen Gupta, Harry H. Hendon, Caroline C. Ummenhofer, and Matthew H. England. "The Contribution of Indian Ocean Sea Surface Temperature Anomalies on Australian Summer Rainfall during El Niño Events." Journal of Climate 24, no. 14 (July 15, 2011): 3734–47. http://dx.doi.org/10.1175/2011jcli3885.1.
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Abstract This study investigates the impact of Indian Ocean sea surface temperature (SST) anomalies on the atmospheric circulation of the Southern Hemisphere during El Niño events, with a focus on Australian climate. During El Niño episodes, the tropical Indian Ocean exhibits two types of SST response: a uniform “basinwide warming” and a dipole mode—the Indian Ocean dipole (IOD). While the impacts of the IOD on climate have been extensively studied, the effects of the basinwide warming, particularly in the Southern Hemisphere, have received less attention. The interannual basinwide warming response has important implications for Southern Hemisphere atmospheric circulation because 1) it accounts for a greater portion of the Indian Ocean monthly SST variance than the IOD pattern and 2) its maximum amplitude occurs during austral summer to early autumn, when large parts of Australia, South America, and Africa experience their monsoon. Using observations and numerical experiments with an atmospheric general circulation model forced with historical SST from 1949 to 2005 over different tropical domains, the authors show that the basinwide warming leads to a Gill–Matsuno-type response that reinforces the anomalies caused by changes in the Pacific as part of El Niño. In particular, the basinwide warming drives strong subsidence over Australia, prolonging the dry conditions during January–March, when El Niño–related SST starts to decay. In addition to the anomalous circulation in the tropics, the basinwide warming excites a pair of barotropic anomalies in the Indian Ocean extratropics that induces an anomalous anticyclone in the Great Australian Bight.
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Cao, Jian, Bin Wang, and Libin Ma. "Attribution of Global Monsoon Response to the Last Glacial Maximum Forcings." Journal of Climate 32, no. 19 (September 5, 2019): 6589–605. http://dx.doi.org/10.1175/jcli-d-18-0871.1.
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Abstract Investigation of global monsoon (GM) responses to external forcings is instrumental for understanding its formation mechanism and projected future changes. Coupled climate model experiments are performed to assess how the individual and full Last Glacial Maximum (LGM) forcings change GM precipitation. Under the full LGM forcing, the annual and local summer-mean GM precipitation are reduced by 8.5% and 10.8%, respectively, compared to the results in the preindustrial control run; and the reduction of Northern Hemisphere (NH) summer monsoon (NHSM) precipitation is twice as large as its Southern Hemisphere (SH) counterpart (SHSM). The NH–SH asymmetric response is mainly caused by the monsoon circulation change–induced moisture convergence rather than the reduction of moisture content, but the root cause is the continental ice sheet forcing. The NHSM precipitation changes dramatically differ among various single-forcing experiments, while this is not the case for their SH counterparts. The moisture budget analysis indicates the NHSM is dynamically oriented, but SHSM is thermodynamically oriented. The markedly different NHSM circulation changes are caused by different forcing-induced sea surface temperature (SST) patterns, including the North Atlantic cooling pattern forced by the continental ice sheet, the mega–La Niña–like pattern resulting from the greenhouse gas forcing, and the Indian Ocean dipole–like SST pattern caused by the land–sea configuration forcing. Moreover, the distinctive change of “monsoonality” in the Australian–Indonesian monsoon is predominantly forced by the exposure of the land shelf, which enhances precipitation during early summer (November–December) but weakens it in the rest of the year.
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Wu, Renguang, and Ben P. Kirtman. "Roles of the Indian Ocean in the Australian Summer Monsoon–ENSO Relationship." Journal of Climate 20, no. 18 (September 15, 2007): 4768–88. http://dx.doi.org/10.1175/jcli4281.1.
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Abstract A negative correlation is observed between interannual variations of the Australian summer monsoon (ASM) and El Niño–Southern Oscillation (ENSO). This negative relationship is well simulated in the Center for Ocean–Land–Atmosphere (COLA) interactive ensemble coupled general circulation model (CGCM). The present study investigates roles of the Indian Ocean in the ASM–ENSO relationship through controlled numerical experiments with the COLA CGCM. It is found that air–sea coupling in the Indian Ocean plays an important role in maintaining the negative ASM–ENSO relationship. When the Indian Ocean is decoupled from the atmosphere, the ASM–ENSO relationship is significantly weakened or even masked by the internal atmospheric variability. This change in the ASM–ENSO relationship is related to complementary roles of Indian Ocean sea surface temperature (SST) anomalies in the ASM variability and feedbacks from the Indian Ocean on ENSO. Without a coupled Indian Ocean, the ENSO amplitude is reduced, leading to a decrease in the ENSO-induced ASM variability, and the constructive impacts of the Indian Ocean SST anomalies on the ASM variability are substantially reduced. This reduces the ASM variability related to ENSO. Consistent with the change in the ASM–ENSO relationship, the local air–sea relationship in the ASM region displays important differences with and without a coupled Indian Ocean. The long-term change in the ASM–ENSO relationship is related to that in ENSO amplitude in the interactive ensemble coupled model. A relatively higher (lower) negative correlation occurs in periods of larger (smaller) ENSO amplitude. This relationship, however, is not clear in the anomaly coupled model with only one atmospheric realization. This difference is attributed to changes in the signal-to-noise ratio in the ASM variability. A comparison is made with observations and the long-term change in the Indian summer monsoon (ISM)–ENSO relationship in the model.
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Frederick, Kaycee, and Courtney Schumacher. "Anvil Characteristics as Seen by C-POL during the Tropical Warm Pool International Cloud Experiment (TWP-ICE)." Monthly Weather Review 136, no. 1 (January 1, 2008): 206–22. http://dx.doi.org/10.1175/2007mwr2068.1.
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Abstract The Tropical Pacific Warm Pool International Cloud Experiment (TWP-ICE) took place in Darwin, Australia, in early 2006. C-band radar data were used to characterize tropical anvil (i.e., thick, nonprecipitating cloud associated with deep convection) areal coverage, height, and thickness during the monthlong field campaign. The morphology, evolution, and longevity of the anvil were analyzed, as was the relationship of the anvil to the rest of the precipitating system. The anvil was separated into mixed (i.e., echo base below 6 km) and ice-only categories. The average areal coverage for each anvil type was between 4% and 5% of the radar grid. Ice anvil thickness averaged 2.8 km and mixed anvil thickness averaged 6.7 km. Areal peaks show that mixed anvil typically formed out of the stratiform rain region. Peak production in ice anvil usually followed the mixed anvil peak by 1–3 h. Anvil typically lasted 4–10 h after the initial convective rain area peak. TWP-ICE experienced three distinct regimes: an active monsoon, a dry monsoon, and a break period. During the experiment (except the active monsoon period) there was a strong negative correlation between ice anvil thickness and ice anvil height, a strong positive correlation between ice anvil area and thickness, and a greater variance in ice anvil bottom than ice anvil top. These results have important implications for understanding how anvil affects the tropical atmosphere.
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Wapler, Kathrin, Todd P. Lane, Peter T. May, Christian Jakob, Michael J. Manton, and Steven T. Siems. "Cloud-System-Resolving Model Simulations of Tropical Cloud Systems Observed during the Tropical Warm Pool-International Cloud Experiment." Monthly Weather Review 138, no. 1 (January 1, 2010): 55–73. http://dx.doi.org/10.1175/2009mwr2993.1.
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Abstract Nested cloud-system-resolving model simulations of tropical convective clouds observed during the recent Tropical Warm Pool-International Cloud Experiment (TWP-ICE) are conducted using the Weather Research and Forecasting (WRF) model. The WRF model is configured with a highest-resolving domain that uses 1.3-km grid spacing and is centered over Darwin, Australia. The performance of the model in simulating two different convective regimes observed during TWP-ICE is considered. The first regime is characteristic of the active monsoon, which features widespread cloud cover that is similar to maritime convection. The second regime is a monsoon break, which contains intense localized systems that are representative of diurnally forced continental convection. Many aspects of the model performance are considered, including their sensitivity to physical parameterizations and initialization time, and the spatial statistics of rainfall accumulations and the rain-rate distribution. While the simulations highlight many challenges and difficulties in correctly modeling the convection in the two regimes, they show that provided the mesoscale environment is adequately reproduced by the model, the statistics of the simulated rainfall agrees reasonably well with the observations.
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Wu, Renguang, and Ben P. Kirtman. "Role of the Indian Ocean in the Biennial Transition of the Indian Summer Monsoon." Journal of Climate 20, no. 10 (May 15, 2007): 2147–64. http://dx.doi.org/10.1175/jcli4127.1.
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Abstract The biennial variability is a large component of year-to-year variations in the Indian summer monsoon (ISM). Previous studies have shown that El Niño–Southern Oscillation (ENSO) plays an important role in the biennial variability of the ISM. The present study investigates the role of the Indian Ocean in the biennial transition of the ISM when the Pacific ENSO is absent. The influence of the Indian and Pacific Oceans on the biennial transition between the ISM and the Australian summer monsoon (ASM) is also examined. Controlled numerical experiments with a coupled general circulation model (CGCM) are used to address the above two issues. The CGCM captures the in-phase ISM to ASM transition (i.e., a wet ISM followed by a wet ASM or a dry ISM followed by a dry ASM) and the out-of-phase ASM to ISM transition (i.e., a wet ASM followed by a dry ISM or a dry ASM followed by a wet ISM). These transitions are more frequent than the out-of-phase ISM to ASM transition and the in-phase ASM to ISM transition in the coupled model, consistent with observations. The results of controlled coupled model experiments indicate that both the Indian and Pacific Ocean air–sea coupling are important for properly simulating the biennial transition between the ISM and ASM in the CGCM. The biennial transition of the ISM can occur through local air–sea interactions in the north Indian Ocean when the Pacific ENSO is suppressed. The local sea surface temperature (SST) anomalies induce the Indian monsoon transition through low-level moisture convergence. Surface evaporation anomalies, which are largely controlled by surface wind speed changes, play an important role for SST changes. Different from local air–sea interaction mechanisms proposed in previous studies, the atmospheric feedback is not strong enough to reverse the SST anomalies immediately at the end of the monsoon season. Instead, the reversal of the SST anomalies is accomplished in the spring of the following year, which in turn leads to the Indian monsoon transition.
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Bringi, V. N., C. R. Williams, M. Thurai, and P. T. May. "Using Dual-Polarized Radar and Dual-Frequency Profiler for DSD Characterization: A Case Study from Darwin, Australia." Journal of Atmospheric and Oceanic Technology 26, no. 10 (October 1, 2009): 2107–22. http://dx.doi.org/10.1175/2009jtecha1258.1.
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Abstract Comparisons are made between the reflectivity Z, median volume diameter D0, and rain rate R from a dual-frequency profiler and the C-band polarimetric radar (C-POL), which are both located near Darwin, Australia. Examples from the premonsoon “buildup” regime and the monsoon (oceanic) regime are used to illustrate the excellent agreement between the dual-profiler retrievals and the polarimetric radar-based retrievals. This work builds on similar works that were limited in scope to shallow tropical showers and predominantly stratiform rain events. The dual-frequency profiler retrievals of D0 and R herein are based on ensemble statistics, whereas the polarimetric radar retrievals are based on algorithms derived by using one season of disdrometer data from Darwin along with scattering simulations. The latest drop shape versus D relation is used as well as the canting angle distribution results obtained from the 80-m fall bridge experiment in the scattering simulations. The scatterplot of D0 from dual-frequency profiler versus Zdr measurements from C-POL is shown to be consistent not only with the theoretical simulations and prior data but also within prior predicted error bars for both stratiform rain as well as convective rain. Based on dual-frequency profiler–retrieved gamma drop size distribution parameters, a new smoothly varying “separator” indexing scheme has been developed that classifies between stratiform and convective rain types, including a continuous “transition” region between the two. This indexing technique has been applied on a number of low-elevation-angle plan position indicator (PPI) sweeps with the C-POL from the two regime examples, to construct “unconditioned” histograms of D0 in stratiform and convective rain (to within the sensitivity of the radar). With reference to the latter, it is demonstrated that the distribution of D0 is different in the buildup example than in the monsoon example, because of the differences in both the microphysical and kinematic features between the two regimes. In particular, (i) the mean D0 is significantly larger in the buildup example than in the monsoon example, irrespective of rain type; (ii) the histogram width (or standard deviation) is much larger for the buildup example than the monsoon example, irrespective of rain type; and (iii) the histogram skewness is negative for the monsoon regime example because of a lack of larger D0 values, whereas the buildup histogram is positively skewed irrespective of rain type.
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Mills, Graham A., and Sixiong Zhao. "A Study of a Monsoon Depression Bringing Record Rainfall over Australia. Part I: Numerical Predictability Experiments." Monthly Weather Review 119, no. 9 (September 1991): 2053–73. http://dx.doi.org/10.1175/1520-0493(1991)119<2053:asoamd>2.0.co;2.
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Lau, Ngar-Cheung, and Mary Jo Nath. "Impact of ENSO on the Variability of the Asian–Australian Monsoons as Simulated in GCM Experiments." Journal of Climate 13, no. 24 (December 2000): 4287–309. http://dx.doi.org/10.1175/1520-0442(2000)013<4287:ioeotv>2.0.co;2.
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Meehl, Gerald A., Julie M. Arblaster, and Johannes Loschnigg. "Coupled Ocean–Atmosphere Dynamical Processes in the Tropical Indian and Pacific Oceans and the TBO." Journal of Climate 16, no. 13 (July 1, 2003): 2138–58. http://dx.doi.org/10.1175/2767.1.
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Abstract The transitions (from relatively strong to relatively weak monsoon) in the tropospheric biennial oscillation (TBO) occur in northern spring for the south Asian or Indian monsoon and northern fall for the Australian monsoon involving coupled land–atmosphere–ocean processes over a large area of the Indo-Pacific region. Transitions from March–May (MAM) to June–September (JJAS) tend to set the system for the next year, with a transition to the opposite sign the following year. Previous analyses of observed data and GCM sensitivity experiments have demonstrated that the TBO (with roughly a 2–3-yr period) encompasses most ENSO years (with their well-known biennial tendency). In addition, there are other years, including many Indian Ocean dipole (or zonal mode) events, that contribute to biennial transitions. Results presented here from observations for composites of TBO evolution confirm earlier results that the Indian and Pacific SST forcings are more dominant in the TBO than circulation and meridional temperature gradient anomalies over Asia. A fundamental element of the TBO is the large-scale east–west atmospheric circulation (the Walker circulation) that links anomalous convection and precipitation, winds, and ocean dynamics across the Indian and Pacific sectors. This circulation connects convection over the Asian–Australian monsoon regions both to the central and eastern Pacific (the eastern Walker cell), and to the central and western Indian Ocean (the western Walker cell). Analyses of upper-ocean data confirm previous results and show that ENSO El Niño and La Niña events as well as Indian Ocean SST dipole (or zonal mode) events are often large-amplitude excursions of the TBO in the tropical Pacific and Indian Oceans, respectively, associated with anomalous eastern and western Walker cell circulations, coupled ocean dynamics, and upper-ocean temperature and heat content anomalies. Other years with similar but lower-amplitude signals in the tropical Pacific and Indian Oceans also contribute to the TBO. Observed upper-ocean data for the Indian Ocean show that slowly eastward-propagating equatorial ocean heat content anomalies, westward-propagating ocean Rossby waves south of the equator, and anomalous cross-equatorial ocean heat transports contribute to the heat content anomalies in the Indian Ocean and thus to the ocean memory and consequent SST anomalies, which are an essential part of the TBO.
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Luffman, James J., Andréa S. Taschetto, and Matthew H. England. "Global and Regional Climate Response to Late Twentieth-Century Warming over the Indian Ocean." Journal of Climate 23, no. 7 (April 1, 2010): 1660–74. http://dx.doi.org/10.1175/2009jcli3086.1.
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Abstract The global and regional climate response to a warming of the Indian Ocean is examined in an ensemble of atmospheric general circulation model experiments. The most marked changes occur over the Indian Ocean, where the increase in tropical SST is found to drive enhanced convection throughout the troposphere. In the extratropics, the warming Indian Ocean is found to induce a significant trend toward the positive phase of the northern annular mode and also to enhance the Southern Hemisphere storm track over Indian Ocean longitudes as a result of stronger meridional temperature gradients. Convective outflow in the upper levels over the warming Indian Ocean leads to a trend in subsidence over the Indian and Asian monsoon regions extending southeastward to Indonesia, the eastern Pacific, and northern Australia. Regional changes in Australia reveal that this anomalous zone of subsidence induces a drying trend in the northern regions of the continent. The long-term rainfall trend is exacerbated over northeastern Australia by the anomalous anticyclonic circulation, which leads to an offshore trend in near-surface winds. The confluence of these two factors leads to a drying signal over northeastern Australia, which is detectable during austral autumn. The rapid, late twentieth-century warming of the Indian Ocean may have contributed to a component of the observed drying trend over northeastern Australia in this season via modifications to the vertical structure of the tropical wind field.
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Bowman, DMJS. "Environmental Determinants of Allosyncarpia ternata Forests That Are Endemic to Western Arnhem Land, Northern Australia." Australian Journal of Botany 39, no. 6 (1991): 575. http://dx.doi.org/10.1071/bt9910575.
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Allosyncarpia ternata S. T. Blake dominates closed forests on rugged sandstone escarpments on the western edge of the Arnhem Land Plateau, northern Australia. The forests occur in a floristic continuum between fire-protected wet monsoon forests in the base of canyons and frequently burnt, eucalyptdominated savannas that occur in all other topographic positions. An indirect gradient analysis of 69 quadrats from these three vegetation types at six different localities showed that no measured edaphic variable was correlated with this floristic transition. A detailed study of a single patch of Allosyncarpia on level terrain with rock-free, sandy soils showed that Allosyncarpia trees occur on sites with significantly deeper soils and higher concentrations of available K in the surface soil compared to surrounding eucalypt savannas. However, there was no significant difference in dry season surface soil moisture content between these communities. There is also evidence that there is no significant difference in subsoil moisture supply. Xylem pressure potential of Callitris intratropica (which is equally abundant in both Allosyncarpia and eucalypt communities) was found to be statistically similar at the beginning and end of the dry season. The Allosyncarpia forest was made up of a mosaic ranging from stands co-dominated by savanna species with grassy understoreys to stands co-dominated by monsoon forest species with dense understoreys. No measured environmental factors were significantly related to the patterning of these stands within the forest. Seed throw of Allosyncarpia is limited to several metres from the canopy edge and seedlings were only observed beneath the canopy. Field experiments demonstrated that seedling survival in the savanna can be enhanced by the provision of shade, and nursery experiments demonstrated that the growth of seedlings provided with ample water is suppressed by full sunlight. Dry season fires in grass fuels ranging from 2 to 8 t ha-1 were found to be lethal to seedlings <100 mm tall. Although most Allosyncarpia trees recover following fire damage, the present distribution of the species may be best explained as a consequence of wildfires. However, there is need for confirmation that the species range is contracting under current fire regimes. This is probably best derived by analysis of existing remote sensing data.
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Zhuang, Moran, and Anmin Duan. "Revisiting the Cross-Equatorial Flows and Asian Summer Monsoon Precipitation Associated with the Maritime Continent." Journal of Climate 32, no. 20 (September 12, 2019): 6803–21. http://dx.doi.org/10.1175/jcli-d-18-0749.1.
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Abstract This study uses an atmospheric general circulation model to examine the relative effects of Maritime Continent (MC) orography, surface roughness, and land–sea contrast on the three cross-equatorial flows (CEF) north of Australia, including the South China Sea (SCS), Celebes-Moluccas (CM), and New Guinea (NG) CEFs, and Asian monsoon precipitation during boreal summer. Four experiments are conducted: with islands, with islands without orography, with islands with ocean roughness and no orography, and with ocean only in the MC region. At the approximately 1° horizontal resolution of these sensitivity experiments, results indicate that the land–sea contrast and orography in the MC have complicated impacts on the CEFs. The land–sea contrast creates the three CEFs. The orography is dominant in deepening, concentrating, and strengthening the CM CEF and modulating the longitudinal location of the NG CEF. For the intensity and depth of the SCS and NG CEFs, the surface roughness over the flat MC and orography are both important. In addition, the MC modulates the monsoon rainfall in tropical Asia. The decreased rainfall (by roughly 57% and 21.4% over South Asia and the SCS, respectively) is dominated by the reduced moisture availability resulting from the presence of the land–sea contrast, thereby intercepting the westward propagating quasi-biweekly convection. The surface roughness over the MC is key in reducing precipitation through reducing moisture convergence over Sumatra, Borneo, and northeastern New Guinea. However, the orography controls the intense precipitation over southwestern New Guinea and the adjacent seas through enhancing the moisture transport carried by the CM and NG CEFs.
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Zeng, Xiping, Wei-Kuo Tao, Scott W. Powell, Robert A. Houze, Paul Ciesielski, Nick Guy, Harold Pierce, and Toshihisa Matsui. "A Comparison of the Water Budgets between Clouds from AMMA and TWP-ICE." Journal of the Atmospheric Sciences 70, no. 2 (February 1, 2013): 487–503. http://dx.doi.org/10.1175/jas-d-12-050.1.
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Abstract Two field campaigns, the African Monsoon Multidisciplinary Analysis (AMMA) and the Tropical Warm Pool–International Cloud Experiment (TWP-ICE), took place in 2006 near Niamey, Niger, and Darwin, Northern Territory, Australia, providing extensive observations of mesoscale convective systems (MCSs) near a desert and a tropical coast, respectively. Under the constraint of their observations, three-dimensional cloud-resolving model simulations are carried out and presented in this paper to replicate the basic characteristics of the observed MCSs. All of the modeled MCSs exhibit a distinct structure having deep convective clouds accompanied by stratiform and anvil clouds. In contrast to the approximately 100-km-scale MCSs observed in TWP-ICE, the MCSs in AMMA have been successfully simulated with a scale of about 400 km. These modeled AMMA and TWP-ICE MCSs offer an opportunity to understand the structure and mechanism of MCSs. Comparing the water budgets between AMMA and TWP-ICE MCSs suggests that TWP-ICE convective clouds have stronger ascent while the mesoscale ascent outside convective clouds in AMMA is stronger. A case comparison, with the aid of sensitivity experiments, also suggests that vertical wind shear and ice crystal (or dust aerosol) concentration can significantly impact stratiform and anvil clouds (e.g., their areas) in MCSs. In addition, the obtained water budgets quantitatively describe the transport of water between convective, stratiform, and anvil regions as well as water sources/sinks from microphysical processes, providing information that can be used to help determine parameters in the convective and cloud parameterizations in general circulation models (GCMs).
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Collis, Scott, Alain Protat, and Kao-Shen Chung. "The Effect of Radial Velocity Gridding Artifacts on Variationally Retrieved Vertical Velocities." Journal of Atmospheric and Oceanic Technology 27, no. 7 (July 1, 2010): 1239–46. http://dx.doi.org/10.1175/2010jtecha1402.1.
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Abstract This article investigates the source and impact of artifacts produced by ordered linear interpolation techniques on variationally retrieved updraft intensities. Qualitative reasoning for the generation of periodic perturbations in gridded products is presented, and a simple analytical investigation into the impact of gridding artifacts on updraft retrieval is carried out. By projecting a nonconvergent flow typical of Darwin, Australia, onto the viewing geometry of a scanning radar, a numerical assessment of the impact of gridding artifacts is carried out. A simple enhancement to ordered linear interpolation, mixed-order linear interpolation, is proposed to reduce gridding artifacts. Radial velocity grids produced using both techniques are used to investigate the generation of spurious updrafts, with the simple ordered linear interpolation technique producing erroneous updrafts on the order of 2 m s−1. To investigate the impact on vertical velocities retrieved from a real weather event, radar-derived measurements taken during the active monsoon phase of Tropical Warm Pool International Cloud Experiment are gridded using both techniques, and vertical velocities are retrieved and contrasted.
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Reale, Oreste, Deepthi Achuthavarier, Marangelly Fuentes, William M. Putman, and Gary Partyka. "Tropical Cyclones in the 7-km NASA Global Nature Run for Use in Observing System Simulation Experiments." Journal of Atmospheric and Oceanic Technology 34, no. 1 (January 2017): 73–100. http://dx.doi.org/10.1175/jtech-d-16-0094.1.
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AbstractThe National Aeronautics and Space Administration (NASA) nature run (NR), released for use in observing system simulation experiments (OSSEs), is a 2-yr-long global nonhydrostatic free-running simulation at a horizontal resolution of 7 km, forced by observed sea surface temperatures (SSTs) and sea ice, and inclusive of interactive aerosols and trace gases. This article evaluates the NR with respect to tropical cyclone (TC) activity. It is emphasized that to serve as an NR, a long-term simulation must be able to produce realistic TCs, which arise out of realistic large-scale forcings. The presence in the NR of the relevant dynamical features over the African monsoon region and the tropical Atlantic is confirmed, along with realistic African easterly wave activity. The NR Atlantic TC seasons, produced with 2005 and 2006 SSTs, show interannual variability consistent with observations, with much stronger activity in 2005. An investigation of TC activity over all the other basins (eastern and western North Pacific Ocean, north and south Indian Ocean, and Australian region), together with important elements of the atmospheric circulation, such as the Somali jet and westerly bursts, reveals that the model captures the fundamental aspects of TC seasons in every basin, producing a realistic number of TCs with realistic tracks, life spans, and structures. This confirms that the NASA NR is a very suitable tool for OSSEs targeting TCs and represents an improvement with respect to previous long simulations that have served the global atmospheric OSSE community.
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Dong, Buwen, Rowan T. Sutton, Len Shaffrey, and Nicholas P. Klingaman. "Attribution of Forced Decadal Climate Change in Coupled and Uncoupled Ocean–Atmosphere Model Experiments." Journal of Climate 30, no. 16 (August 2017): 6203–23. http://dx.doi.org/10.1175/jcli-d-16-0578.1.
Full textAbstract:
There is still no consensus about the best methodology for attributing observed changes in climate or climate events. One widely used approach relies on experiments in which the time periods of interest are simulated using an atmospheric general circulation model (AGCM) forced by prescribed sea surface temperatures (SSTs), with and without estimated anthropogenic influences. A potential limitation of such experiments is the lack of explicit atmosphere–ocean coupling; therefore a key question is whether the attribution statements derived from such studies are in fact robust. In this research the authors have carried out climate model experiments to test attribution conclusions in a situation where the answer is known—a so-called perfect model approach. The study involves comparing attribution conclusions for decadal changes derived from experiments with a coupled climate model (specifically an AGCM coupled to an ocean mixed-layer model) with conclusions derived from parallel experiments with the same AGCM forced by SSTs derived from the coupled model simulations. Results indicate that attribution conclusions for surface air temperature changes derived from AGCM experiments are generally robust and not sensitive to air–sea coupling. However, changes in seasonal mean and extreme precipitations, and circulation in some regions, show large sensitivity to air–sea coupling, notably in the summer monsoons over East Asia and Australia. Comparison with observed changes indicates that the coupled simulations generally agree better with observations. These results demonstrate that the AGCM-based attribution method has limitations and may lead to erroneous attribution conclusions in some regions for local circulation and mean and extreme precipitation. The coupled mixed-layer model used in this study offers an alternative and, in some respects, superior tool for attribution studies.
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Collis, Scott, Alain Protat, Peter T. May, and Christopher Williams. "Statistics of Storm Updraft Velocities from TWP-ICE Including Verification with Profiling Measurements." Journal of Applied Meteorology and Climatology 52, no. 8 (August 2013): 1909–22. http://dx.doi.org/10.1175/jamc-d-12-0230.1.
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AbstractComparisons between direct measurements and modeled values of vertical air motions in precipitating systems are complicated by differences in temporal and spatial scales. On one hand, vertically profiling radars more directly measure the vertical air motion but do not adequately capture full storm dynamics. On the other hand, vertical air motions retrieved from two or more scanning Doppler radars capture the full storm dynamics but require model constraints that may not capture all updraft features because of inadequate sampling, resolution, numerical constraints, and the fact that the storm is evolving as it is scanned by the radars. To investigate the veracity of radar-based retrievals, which can be used to verify numerically modeled vertical air motions, this article presents several case studies from storm events around Darwin, Northern Territory, Australia, in which measurements from a dual-frequency radar profiler system and volumetric radar-based wind retrievals are compared. While a direct comparison was not possible because of instrumentation location, an indirect comparison shows promising results, with volume retrievals comparing well to those obtained from the profiling system. This prompted a statistical analysis of an extended period of an active monsoon period during the Tropical Warm Pool International Cloud Experiment (TWP-ICE). Results show less vigorous deep convective cores with maximum updraft velocities occurring at lower heights than some cloud-resolving modeling studies suggest.
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Mantsis, Damianos F., Benjamin R. Lintner, Anthony J. Broccoli, and Myriam Khodri. "Mechanisms of Mid-Holocene Precipitation Change in the South Pacific Convergence Zone." Journal of Climate 26, no. 18 (September 9, 2013): 6937–53. http://dx.doi.org/10.1175/jcli-d-12-00674.1.
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Abstract The variability of the South Pacific convergence zone (SPCZ) during the mid-Holocene is investigated using models archived in the Paleoclimate Modelling Intercomparison Project Phase II (PMIP2) database. Relative to preindustrial conditions, mid-Holocene top-of-atmosphere insolation was relatively lower during austral summer [December–February (DJF)], which is the season when the SPCZ is at its peak intensity. In response to this perturbation, the PMIP2 models simulate a displacement of the SPCZ to the southwest. This SPCZ shift is associated with a sea surface temperature (SST) dipole, with increased rainfall collocated with warm SST anomalies. Decomposing the DJF precipitation changes in terms of a diagnostic moisture budget indicates that the SPCZ shift is balanced to leading order by a change in the mean moisture convergence. Changes to the broad area of upper-level negative zonal stretching deformation, where transient eddies can become trapped and subsequently generate deep convection, support the notion that the SPCZ shift in the subtropics is tied to eddy forcing. Idealized experiments performed with an intermediate-level complexity model, the Quasi-Equilibrium Tropical Circulation Model (QTCM), suggest that the mid-Holocene change in rainfall in the SPCZ region as well as the equatorial Pacific is dominated by a change in the underlying SST. The tropical portion of the SPCZ is further remotely affected by the orbitally induced weakening of the Australian monsoon, even though this effect is weaker compared to the effect from SSTs.
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Sperna Weiland, F. C., L. P. H. van Beek, J. C. J. Kwadijk, and M. F. P. Bierkens. "Global patterns of change in discharge regimes for 2100." Hydrology and Earth System Sciences 16, no. 4 (April 2, 2012): 1047–62. http://dx.doi.org/10.5194/hess-16-1047-2012.
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Abstract. This study makes a thorough global assessment of the effects of climate change on hydrological regimes and their accompanying uncertainties. Meteorological data from twelve GCMs (SRES scenarios A1B and control experiment 20C3M) are used to drive the global hydrological model PCR-GLOBWB. This reveals in which regions of the world changes in hydrology can be detected that have a high likelihood and are consistent amongst the ensemble of GCMs. New compared to existing studies is: (1) the comparison of spatial patterns of regime changes and (2) the quantification of notable consistent changes calculated relative to the GCM specific natural variability. The resulting consistency maps indicate in which regions the likelihood of hydrological change is large. Projections of different GCMs diverge widely. This underscores the need of using a multi-model ensemble. Despite discrepancies amongst models, consistent results are revealed: by 2100 the GCMs project consistent decreases in discharge for southern Europe, southern Australia, parts of Africa and southwestern South-America. Discharge decreases strongly for most African rivers, the Murray and the Danube while discharge of monsoon influenced rivers slightly increases. In the Arctic regions river discharge increases and a phase-shift towards earlier peaks is observed. Results are comparable to previous global studies, with a few exceptions. Globally we calculated an ensemble mean discharge increase of more than ten percent. This increase contradicts previously estimated decreases, which is amongst others caused by the use of smaller GCM ensembles and different reference periods.
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Sperna Weiland, F. C., L. P. H. van Beek, J. C. J. Kwadijk, and M. F. P. Bierkens. "Global patterns of change in discharge regimes for 2100." Hydrology and Earth System Sciences Discussions 8, no. 6 (December 13, 2011): 10973–1014. http://dx.doi.org/10.5194/hessd-8-10973-2011.
Full textAbstract:
Abstract. This study makes a thorough global assessment of the effects of climate change on hydrological regimes and their accompanying uncertainties. Meteorological data from twelve GCMs (SRES scenarios A1B, and control experiment 20C3M) are used to drive the global hydrological model PCR-GLOBWB. We reveal in which regions of the world changes in hydrology can be detected that are significant and consistent amongst the ensemble of GCMs. New compared to existing studies is: (1) the comparison of spatial patterns of regime changes and (2) the quantification of consistent significant change calculatesd relative to both the natural variability and the inter-model spread. The resulting consistency maps indicate in which regions likelihood of hydrological change is large. Projections of different GCMs diverge widely. This underscores the need of using a multi-model ensemble. Despite discrepancies amongst models, consistent results are revealed: by 2100 the GCMs project consistent decreases in discharge for southern Europe, southern Australia, parts of Africa and southwestern South-America. Discharge decreases are large for most African rivers, the Murray and the Danube. While discharge of Monsoon influenced rivers slightly increases. In the Arctic regions river discharge increases and a phase-shift towards earlier peaks is observed. Results are comparable to previous global studies, with a few exceptions. Globally we calculated an ensemble mean discharge increase of more than ten percent. This increase contradicts previously estimated decreases, which is amongst others caused by the use of smaller GCM ensembles and different reference periods.
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Wright, GC. "Furrow irrigation of grain sorghum in a tropical environment. I. Influence of period of inundation and nitrogen fertilizer on dry matter production, grain yield and soil aeration." Australian Journal of Agricultural Research 36, no. 1 (1985): 73. http://dx.doi.org/10.1071/ar9850073.
Full textAbstract:
An experiment was conducted during the dry season in monsoonal tropical Australia to determine the influence of applied nitrogen (N) and period of inundation during furrow irrigation on the growth and yield of grain sorghum. Water was run in the furrows for 3, 6, 12 and 24 h at all irrigations, which were applied every 7-10 days throughout the season. A sprinkler irrigated crop was used to represent zero inundation. Increasing the period of inundation from 0 to 24 h at each irrigation reduced grain yield by 43.8, 49.5 and 43.2% for crops supplied with 0, 80 and 170 kg N ha-1 respectively. This yield reduction was associated with fewer grains per plant, grain weight having only a small influence on final yield. Air-filled porosity of the soil recovered more slowly as the period of inundation increased. The time taken to reach an air-filled porosity of 0.10 at the 10-20 cm depth interval was highly correlated with grain yield. The results indicate that grain yield is strongly influenced by the duration of waterlogging associated with flood irrigation. To minimize yield losses crops should be irrigated and drained rapidly to reduce the duration and severity of soil anaerobiosis.
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Reddell, P., and AR Milnes. "Mycorrhizas and Other Specialized Nutrient-Acquisition Strategies: Their Occurrence in Woodland Plants From Kakadu and Their Role in Rehabilitation of Waste Rock Dumps at a Local Uranium Mine." Australian Journal of Botany 40, no. 2 (1992): 223. http://dx.doi.org/10.1071/bt9920223.
Full textAbstract:
The presence of mycorrhizas, proteoid roots and leguminous nodules was determined in a range of woodland species (from a variety of habitats in soils formed on different parent materials) in the Kakadu area in the monsoonal tropics of northern Australia. In addition, the chemical fertility and the occurrence of mycorrhizal fungi and rhizobia in rudimentary soils ('minesoils') forming in situ on waste rock dumps at a mine site in the region were compared with stockpiled topsoils from the mine area and undisturbed topsoils collected from the surrounding native woodland. A major aim of these investigations was to assess the feasibility of rehabilitating the waste rock dumps without spreading topsoils. More than 90% of the woodland flora examined had one or more specialised nutrient-gathering mechanism. Mycorrhizas were found on 82% of the species, with some 16% of species having both ecto and VA mycorrhizas, often on the same individual plant. Many of these observations are the first records of mycorrhizal infection in the particular genera and species involved. Soil baiting and dilution experiments showed that rhizobia and mycorrhizal fungi were ubiquitous components of the soil biota in all undisturbed woodland soils. However, they were absent or poorly represented in the stockpiled topsoils and in some of the rudimentary soils formed in waste rock at the mine site. The diversity of spore types and/or numbers of infective propagules of VAM fungi was lower in stockpiled topsoils and in minesoils than in the undisturbed woodland soils. Nutrient omission experiments identified that acute deficiency of P, and to a lesser extent N, was a limitation to growth of seedlings on all soils. Zn deficiency was detected in the only soil for which this was examined. A glasshouse experiment, using a young minesoil and application of basal nutrients, demonstrated that inoculation of Acacia holosericea seedlings with rhizobium could completely alleviate the effects of N deficiency. Under conditions of both N and P deficiency, dual inoculation of A. holosericea with rhizobium and spores of the VAM fungus, Glomus, only partly overcame the limitations of P deficiency on seedling growth. Induction of deficiencies of P and Zn in a second minesoil (through application of basal nutrients), demonstrated that inoculation of seedlings of Eucalyptus pellita with spores of the ectomycorrhizal fungus, Scleroderma, partly alleviated the effects of both deficiencies. Rehabilitation strategies implemented at the mine site using either soils forming in situ on the waste rock dumps, or by spreading stockpiled topsoils, will need to ensure deficiencies of P and other nutrients are alleviated and that viable populations of mycorrhizal fungi and rhizobia are introduced and maintained during early phases of vegetation establishment.
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Reddell, Paul, Victoria Gordon, and Michael S. Hopkins. "Ectomycorrhizas in Eucalyptus tetrodonta and E. miniata Forest Communities in Tropical Northern Australia and their Role in the Rehabilitation of these Forests Following Mining." Australian Journal of Botany 47, no. 6 (1999): 881. http://dx.doi.org/10.1071/bt97126.
Full textAbstract:
The importance of ectomycorrhizas in Eucalyptus tetrodonta F.Muell. and E. miniata Cunn. ex Schauer dominated forests and woodland communities in the monsoonal tropics of northern Australia was assessed. Ectomycorrhizas colonised between 24 and 54% of final order lateral roots in soil cores collected at 16 native forest sites. Only a minority of the plant species present formed ectomycorrhizas (mainly eucalypts and acacias) but these species contributed more than 75% of the basal area. More than 70 species of putative ectomycorrhizal fungi were collected, with three hypogeous taxa (Nothocastoreum, Hysterangium and an undescribed Boletaceae) most frequently encountered. Glasshouse inoculation experiments confirmed that a diverse range of fungi was capable of forming ectomycorrhizas with E. tetrodonta and E. miniata seedlings, and that the growth of both species could be substantially increased by inoculation with specific fungi. The fungi most effective in increasing seedling growth were generally those which most extensively colonised the seedling roots. A second component of this study investigated the requirements for ectomycorrhizal fungi in native forest rehabilitation following mining. Ectomycorrhizal infectivity was low in disturbed soils and mine spoil materials, with the intensity of disturbance and the presence of regrowth vegetation key determinants of the level of infectivity. Inoculation of seedlings of E. miniata with spores of ectomycorrhizal fungi increased both growth and leaf phosphorus concentrations by between two- and three-fold at 7 months after planting out on a waste rock dump devoid of native ectomycorrhizal propagules. The application of these findings to minesite rehabilitation in the region, and the feasibility of using spores for broad-scale inoculation, are discussed.
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Glatthor, N., T. von Clarmann, G. P. Stiller, B. Funke, M. E. Koukouli, H. Fischer, U. Grabowski, M. Höpfner, S. Kellmann, and A. Linden. "Source classification of upper tropospheric pollution by MIPAS HCN and C<sub>2</sub>H<sub>6</sub> global distributions." Atmospheric Chemistry and Physics Discussions 9, no. 4 (July 29, 2009): 16197–232. http://dx.doi.org/10.5194/acpd-9-16197-2009.
Full textAbstract:
Abstract. We present global upper tropospheric HCN and C2H6 amounts derived from MIPAS/ENVISAT limb emission spectra. HCN and C2H6 are retrieved in the spectral regions 715.5–782.7 cm−1 and 811.5–835.7 cm−1, respectively. The datasets we present consist of 54 days between September 2003 and March 2004. This period covers the peak and decline of the southern hemispheric biomass burning period and some months thereafter. HCN is a nearly unambiguous tracer of biomass burning with an assumed tropospheric lifetime of several months. Indeed, the most significant feature in the MIPAS HCN dataset is an upper tropospheric plume of enhanced values caused by southern hemispheric biomass burning, which in September and October 2003 extended from tropical South America over Africa, Australia to the Southern Pacific. The spatial extent of this plume agrees well with the MOPITT CO distribution of September 2003. Further there is good agreement with the shapes and mixing ratios of the southern hemispheric HCN and C2H6 fields measured by the ACE experiment between September and November 2005. The MIPAS HCN plume extended from the lowermost observation height (8 km) up to about 16 km altitude, with maximum values of 500–600 pptv in October 2003. It was still clearly visible in December 2003, but had strongly decreased by March 2004, confirming the assumed tropospheric lifetime. The main sources of C2H6 are production and transmission of fossil fuels, followed by biofuel use and biomass burning. The C2H6 distribution also clearly reflected the southern hemispheric biomass burning plume and its seasonal variation, with maximum amounts of 600–700 pptv. Generally there was good agreement between the southern hemispheric distributions of both pollution tracers, except for the region between Peru and the mid-Pacific. Here C2H6 was considerably enhanced, whereas the HCN amounts were low. Backward trajectory calculations suggested that industrial pollution was responsible for the elevated C2H6 in these particular air masses. Except for the Asian monsoon anticyclone in September 2003, there were only comparably small regions of enhanced HCN in the Northern Hemisphere. However, C2H6 showed an equally strong northern hemispheric signal between the equator and low midlatitudes, persisting over the whole observation period. Backward trajectory calculations for air masses from this region also pointed to industrial sources of this pollution. Generally, C2H6/HCN ratios between 1 and 1.5 indicate biomass burning and ratios larger than 1.5 industrial pollution. However, in March 2004 ratios of up to 2 were also found in some regions of the former southern biomass burning plume.
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Glatthor, N., T. von Clarmann, G. P. Stiller, B. Funke, M. E. Koukouli, H. Fischer, U. Grabowski, M. Höpfner, S. Kellmann, and A. Linden. "Large-scale upper tropospheric pollution observed by MIPAS HCN and C<sub>2</sub>H<sub>6</sub> global distributions." Atmospheric Chemistry and Physics 9, no. 24 (December 22, 2009): 9619–34. http://dx.doi.org/10.5194/acp-9-9619-2009.
Full textAbstract:
Abstract. We present global upper tropospheric HCN and C2H6 amounts derived from MIPAS/ENVISAT limb emission spectra. HCN and C2H6 are retrieved in the spectral regions 715.5–782.7 cm−1 and 811.5–835.7 cm−1, respectively. The datasets consist of 54 days between September 2003 and March 2004. This period covers the peak and decline of the southern hemispheric biomass burning period and some months thereafter. HCN is a nearly unambiguous tracer of biomass burning with an assumed tropospheric lifetime of several months. Indeed, the most significant feature in the MIPAS HCN dataset is an upper tropospheric plume of enhanced values caused by southern hemispheric biomass burning, which in September and October 2003 extended from tropical South America over Africa, Australia to the Southern Pacific. The spatial extent of this plume agrees well with the MOPITT CO distribution of September 2003. Further there is good agreement with the shapes and mixing ratios of the southern hemispheric HCN and C2H6 fields measured by the ACE experiment between September and November 2005. The MIPAS HCN plume extended from the lowermost observation height of 8 km up to about 16 km altitude, with maximum values of 500–600 pptv in October 2003. It was still clearly visible in December 2003, but had strongly decreased by March 2004, confirming the assumed tropospheric lifetime. The main sources of C2H6 are production and transmission of fossil fuels, followed by biofuel use and biomass burning. The C2H6 distribution also clearly reflected the southern hemispheric biomass burning plume and its seasonal variation, with maximum amounts of 600–700 pptv. Generally there was good spatial overlap between the southern hemispheric distributions of both pollution tracers, except for the region between Peru and the mid-Pacific. Here C2H6was considerably enhanced, whereas the HCN amounts were low. Backward trajectory calculations suggested that industrial pollution was responsible for the elevated C2H6 concentration in these particular air masses. Except for the Asian monsoon anticyclone in September 2003, there were only comparably small regions of enhanced HCN in the Northern Hemisphere. However, C2H6 showed an equally strong northern hemispheric signal between the equator and low midlatitudes, persisting over the whole observation period. Backward trajectory calculations for air masses from this region also point to industrial sources of this pollution. Generally, C2H6/HCN ratios between 1 and 1.5 indicate biomass burning and ratios larger than 1.5 industrial pollution. However, in March 2004 ratios of up to 2 were also found in some regions of the former southern biomass burning plume.
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Sekizawa, Shion, Hisashi Nakamura, and Yu Kosaka. "Interannual variability of the Australian summer monsoon sustained through internal processes: wind-evaporation feedback, dynamical air-sea interaction and soil moisture memory." Journal of Climate, October 20, 2022, 1–39. http://dx.doi.org/10.1175/jcli-d-22-0116.1.
Full textAbstract:
Abstract In northern Australia (NAUS), mean rainfall during the Australian summer monsoon (AUSM) season exhibits distinct interannual variability despite weak influence from tropical sea surface temperature (SST) variability. The present study investigates mechanisms for the strong and persistent rainfall anomalies throughout the AUSM season. When the AUSM is stronger than normal, the low-level monsoonal circulation intensifies in response to the stronger convective activity over NAUS. The intensified surface westerlies over the tropical southeastern Indian Ocean (SEIO) enhance oceanic evaporation locally and downstream moisture transport into NAUS. This wind-evaporation feedback is verified through a moist static energy budget analysis. For this feedback to work effectively, SST cooling due to the stronger AUSM should be weak enough not to suppress the oceanic evaporation in the tropical SEIO. Our mixed-layer heat budget analysis based on an ocean model hindcast experiment reveals that anomalous downwelling in the subsurface SEIO, which is induced dynamically by the intensified monsoon westerlies, partially offsets the SST cooling. The land-surface evaporation over the continental inland area is also enhanced significantly in the middle and later portions of the monsoon season associated with increased soil moisture, suggesting its memory effect for the persistence of rainfall anomalies. The AUSM variability can therefore be regarded as a self-sustaining internal variability in the atmosphere-ocean-land surface coupled system, rather than just an atmospheric internal variability.
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Sekizawa, Shion, Hisashi Nakamura, and Yu Kosaka. "Remote influence of the interannual variability of the Australian summer monsoon on wintertime climate in East Asia and the western North Pacific." Journal of Climate, September 22, 2021, 1–54. http://dx.doi.org/10.1175/jcli-d-21-0202.1.
Full textAbstract:
AbstractAnomalous convective activity in the Tropics forced by sea surface temperature (SST) variability exerts significant remote influence that provides a basis for seasonal prediction in the extratropics. In austral summer convective activity exhibits pronounced interannual variability over northern Australia (NAUS), which is, however, unlikely forced by SST anomalies but essentially a manifestation of internal variability of the Australian summer monsoon (AUSM) system. Based on observational data, the present study reveals its significant remote impacts on the wintertime climate in East Asia and the western North Pacific. The anomalous AUSM excites the Western Pacific (WP) pattern, as confirmed through an atmospheric general circulation model experiment. Through this cross-equatorial teleconnection, the enhanced AUSM leads to the strengthening of the East Asian winter monsoon with a colder winter over the Korean Peninsula and western Japan and reduced precipitation over southern China. The Okhotsk sea-ice extent decreases under warm anomalies and weakened offshore winds. The weakened AUSM leads to the same anomalies but with the opposite polarities. Our observational data analysis and numerical experiments reveal that the WP-like anomalies are excited by the propagation of stationary Rossby waves generated by anomalous upper-level divergent wind from NAUS that extends into the Northern Hemisphere subtropical jet. The climatological Hadley circulation is essential in this process. The concomitant anomalous diabatic heating over East Asia and feedback forcing by transient eddies along the Pacific stormtrack act to further amplify the WP-like response.
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"PREFACE." IOP Conference Series: Earth and Environmental Science 893, no. 1 (November 1, 2021): 011001. http://dx.doi.org/10.1088/1755-1315/893/1/011001.
Full textAbstract:
The seasonal atmospheric condition over the Maritime Continent is mainly driven by the Asian-Australian Monsoon. Precipitation over the Maritime Continent is highly influenced by the intra-seasonal Madden-Julian Oscillation (MJO), also highly affected by the El-Nino Southern Oscillation (ENSO) and Indian Ocean Dipole Mode (IOD). At an interannual time scale the Maritime Continent is also crossed by Indonesia Through Flow (ITF), as the artery connecting Tropical Pacific and Indian Oceans, and acting as a crucial link of the ocean general circulation that affects not only properties of these two oceans but also global climate. This complex mixture of land and sea interaction, with various atmospheric and oceanic phenomena within, makes the Maritime Continent as a unique, enigmatic and challenging area for scientific endeavor on tropical meteorology and atmospheric sciences. Various observations and research have been coordinated, campaigned, and conducted to better understand the atmospheric and oceanic condition over the tropics, especially the Maritime Continent. Many scientific discoveries have been found to enrich the knowledge of atmospheric science on the tropics, from the International Winter Monsoon Experiment in 1978, TOGA COARE in 1993, HARIMAU that ended in 2010, to CINDY/DYNAMO in 2011. The recent Year of Maritime Continent (YMC) during 2017 - 2020 aimed to improve understanding and prediction local multi-scale variability of the Maritime Continent weather-climate system and its global impact through observations and modelling exercises, was the state-of-art for such coordinated research on the tropics. As a part of YMC program, BMKG will also be involved in Measurements and Modelling of the Indonesian Throughflow International Experiment (MINTIE) which is collaborative research among countries including Indonesia BMKG and being led by Columbia University during 2019 – 2024. LIST OF Committee, Steering Committee, Organizing Committee Leader, Leader, Secretariat & Public Relations, Treasure, Event are available in this pdf.