Journal articles on the topic 'Atmospheric circulation Pacific area'
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1
Nakamura, Mototaka, and Toru Miyama. "Impacts of the Oyashio Temperature Front on the Regional Climate." Journal of Climate 27, no. 20 (October 7, 2014): 7861–73. http://dx.doi.org/10.1175/jcli-d-13-00609.1.
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Abstract Impacts of a sea surface temperature front (SSTF) in the northwestern Pacific Ocean on the large-scale summer atmospheric state in the region are examined with a regional atmospheric circulation model developed at the International Pacific Research Center. Ensemble simulation experiments with various SSTF strengths and positions show that an SSTF does have strong impacts on the summer atmospheric circulation in the region. A meridional shift in the position of the SSTF generally shifts the tropospheric jet and brings temperature anomalies in the area affected by the shift.
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Hoell, Andrew, and Chris Funk. "The ENSO-Related West Pacific Sea Surface Temperature Gradient." Journal of Climate 26, no. 23 (December 2013): 9545–62. http://dx.doi.org/10.1175/jcli-d-12-00344.1.
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El Niño–Southern Oscillation (ENSO) events are accompanied by an anomalous zonal sea surface temperature (SST) gradient over the west Pacific Ocean, defined here as the west Pacific SST gradient (WPG). The WPG is defined as the standardized difference between area-averaged SST over the central Pacific Ocean (Niño-4 region) and west Pacific Ocean (0°–10°N, 130°–150°E). While the direction of the WPG follows ENSO cycles, the magnitude of the gradient varies considerably between individual El Niño and La Niña events. In this study, El Niño and La Niña events are grouped according to the magnitude of the WPG, and tropical SST, circulations, and precipitation are examined for the period 1948–2011. Until the 1980s the WPG showed little trend as the west and central Pacific warmed at similar rates; however, the west Pacific has recently warmed faster than the central Pacific, which has resulted in an increased WPG during La Niña events. The temporal evolution and distribution of tropical Pacific SST as well as the near-surface tropical Pacific zonal wind, divergence, and vertical velocity are considerably different during ENSO events partitioned according to the strength of the WPG. Modifications to the tropical circulation, resulting in changes to Indo– west Pacific precipitation, are linked to strong and consistent circulation and precipitation modifications throughout the Northern Hemisphere during winter.
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Gradov, Viacheslav S., Irina V. Borovko, and Vladimir N. Krupchatnikov. "IMPACT OF ARCTIC SEA ICE REDUCTION ON ATMOSPHERIC CIRCULATION PATTERNS." Interexpo GEO-Siberia 4, no. 1 (May 21, 2021): 103–10. http://dx.doi.org/10.33764/2618-981x-2021-4-1-103-110.
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This paper focuses on the effect of sea ice melting under the effect of the mechanism of decreasing albedo of dry and wet ice and snow on the structure of atmospheric circulation. In particular, the Impact on storm tracks in the Pacific and Atlantic Oceans is analyzed. Extreme weather events are usually associated with atmospheric blocking conditions. Blocking is such meteorological conditions in which a large anticyclonic atmospheric vortex is observed over an area for several days. The Molteni-Tibaldi blocking criterion and the magnitude of the local anticyclonic wave activity (LAWA) are used to estimate the number of blockings. Extreme values of LAWA may indicate the presence of atmospheric blockings. As a result, there is a weakening and eastward shift of Atlantic storm trajectories. There is almost no influence on the Pacific storm tracks.
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Jia, XiaoJing, Hai Lin, June-Yi Lee, and Bin Wang. "Season-Dependent Forecast Skill of the Leading Forced Atmospheric Circulation Pattern over the North Pacific and North American Region*." Journal of Climate 25, no. 20 (April 9, 2012): 7248–65. http://dx.doi.org/10.1175/jcli-d-11-00522.1.
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Abstract Multimodel ensemble (MME) seasonal forecasts are analyzed to evaluate numerical model performance in predicting the leading forced atmospheric circulation pattern over the extratropical Northern Hemisphere (NH). Results show that the time evolution of the leading tropical Pacific sea surface temperature (SST)-coupled atmospheric pattern (MCA1), which is obtained by applying a maximum covariance analysis (MCA) between 500-hPa geopotential height (Z500) in the extratropical NH and SST in the tropical Pacific Ocean, can be predicted with a significant skill in March–May (MAM), June–August (JJA), and December–February (DJF) one month ahead. However, most models perform poorly in capturing the time variation of MCA1 in September–November (SON) with 1 August initial condition. Two possible reasons for the models’ low skill in SON are identified. First, the models have the most pronounced errors in the mean state of SST and precipitation along the central equatorial Pacific. Because of the link between the divergent circulation forced by tropical heating and the midlatitude atmospheric circulation, errors in the mean state of tropical SST and precipitation may lead to a degradation of midlatitude forecast skill. Second, examination of the potential predictability of the atmosphere, estimated by the ratio of the total variance to the variance of the model forecasts due to internal dynamics, shows that the atmospheric potential predictability over the North Pacific–North American (NPNA) region is the lowest in SON compared to the other three seasons. The low ratio in SON is due to a low variance associated with external forcing and a high variance related to atmospheric internal processes over this area.
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Nobre, Paulo, Marta Malagutti, Domingos F. Urbano, Roberto A. F. de Almeida, and Emanuel Giarolla. "Amazon Deforestation and Climate Change in a Coupled Model Simulation." Journal of Climate 22, no. 21 (November 1, 2009): 5686–97. http://dx.doi.org/10.1175/2009jcli2757.1.
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Abstract The effects of Amazon deforestation on climate change are investigated using twin numerical experiments of an atmospheric general circulation model (AGCM) with prescribed global sea surface temperature and the same AGCM coupled to an ocean GCM (CGCM) over the global tropics. An ensemble approach is adopted, with 10-member ensemble averages of a control simulation compared with perturbed simulations for three scenarios of Amazon deforestation. The latest 20 yr of simulation from each experiment are analyzed. Local surface warming and rainfall reduction are simulated by both models over the Amazon basin. The coupled model presented a rainfall reduction that is nearly 60% larger compared to its control run than those obtained by the AGCM. The results also indicated that both the fraction of the deforested area and the spatial continuity of the vegetated area might be important for modulating global climate variability and change. Additionally, significant remote atmospheric responses to Amazon deforestation scenarios are detected for the coupled simulations, which revealed global ocean and atmosphere circulation changes conducive to enhanced ocean–atmosphere variability over the Pacific Ocean. This, in turn, is interpreted as a manifestation of enhanced El Niño–Southern Oscillation (ENSO) activity over the Pacific and a positive feedback contributing to the extra rainfall reduction over the Amazon on the coupled simulations.
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Hu, Zeng-Zhen, Arun Kumar, Bhaskar Jha, Jieshun Zhu, and Bohua Huang. "Persistence and Predictions of the Remarkable Warm Anomaly in the Northeastern Pacific Ocean during 2014–16." Journal of Climate 30, no. 2 (January 2017): 689–702. http://dx.doi.org/10.1175/jcli-d-16-0348.1.
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In this work, the evolution and prediction of the persistent and remarkable warm sea surface temperature anomaly (SSTA) in the northeastern Pacific during October 2013–June 2016 are examined. Based on experiments with an atmospheric model, the possible contribution of SSTAs in different ocean basins to the atmospheric circulation anomalies is identified. Further, through verifying the real-time forecasts, current capabilities in predicting such an extreme warm event with a state-of-the-art coupled general circulation model are assessed. During the long-lasting warm event, there were two warm maxima in the area-averaged SSTA around January 2014 and July 2015, respectively. The warm anomaly originated at the oceanic surface and propagated downward and reached about 300 m. Model experiments forced by observed SST suggest that the long persistence of the atmospheric anomalies in the northeastern Pacific as a whole may be partially explained by SST forcing, particularly in the tropical Pacific Ocean associated with a persistent warm SSTA in 2014/15 and an extremely strong El Niño in 2015/16, via its influence on atmospheric circulation over the North Pacific. Nevertheless, it was a challenge to predict the evolution of this warm event, especially for its growth. That is consistent with the fact that the SSTAs in extratropical oceans are largely a consequence of unpredictable atmospheric variability.
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Lim, Won-Il, and Kyong-Hwan Seo. "Physical–Statistical Model for Summer Extreme Temperature Events over South Korea." Journal of Climate 32, no. 6 (February 26, 2019): 1725–42. http://dx.doi.org/10.1175/jcli-d-18-0201.1.
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AbstractExtreme temperature events have a significant impact on human life and property. Since the Korean Peninsula is affected by the high variability of the East Asian summer monsoon system, it is difficult to predict extreme temperature events skillfully. Here, we construct an empirical model to investigate the interannual variation of the frequency of summer extreme temperature events over South Korea by identifying predictors (explanatory variables) from ocean boundary conditions. The selected explanatory variables are sea surface temperature anomalies (SSTAs) over the North Atlantic, the western North Pacific, and the eastern North Pacific. The cross-validated correlation skill of the statistical model constructed using a 23-yr dataset is estimated to be 0.77. A common feature that all three explanatory variables contain is the development of an anticyclonic circulation anomaly over the Korean Peninsula. The North Atlantic SSTA predictor acts as a forcing mechanism for the generation of Rossby wave trains downstream, developing an anticyclonic circulation anomaly in the lower and upper troposphere over the Korean Peninsula. The western North Pacific (WNP) warm SSTA predictor induces a cyclonic circulation anomaly over the WNP and an anticyclonic circulation anomaly over the Korean Peninsula, resembling the Pacific–Japan teleconnection mechanism that represents the northward Rossby wave propagation over the western Pacific. Through air–sea interaction, the tripolar SSTA pattern in the eastern North Pacific representing the North Pacific gyre oscillation induces two opposite precipitation anomalies in the equatorial Maritime Continent and the Philippine Sea. These diabatic anomalies excite northward-propagating Rossby waves that form a cyclonic circulation anomaly in the WNP area and an anticyclonic anomaly over the Korean Peninsula.
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Šácha, Petr, Friederike Lilienthal, Christoph Jacobi, and Petr Pišoft. "Influence of the spatial distribution of gravity wave activity on the middle atmospheric dynamics." Atmospheric Chemistry and Physics 16, no. 24 (December 21, 2016): 15755–75. http://dx.doi.org/10.5194/acp-16-15755-2016.
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Abstract. Analysing GPS radio occultation density profiles, we have recently pointed out a localised area of enhanced gravity wave (GW) activity and breaking in the lower stratosphere of the east Asian–northwestern Pacific (EA/NP) region. With a mechanistic model of the middle and upper atmosphere, experiments are performed to study the possible effect of such a localised GW breaking region on large-scale circulation and transport and, more generally, a possible influence of the spatial distribution of gravity wave activity on middle atmospheric dynamics.The results indicate the important role of the spatial distribution of GW activity for polar vortex stability, formation of planetary waves and for the strength and structure of zonal-mean residual circulation. Furthermore, a possible effect of a zonally asymmetric GW breaking in the longitudinal variability of the Brewer–Dobson circulation is analysed. Finally, consequences of our results for a variety of research topics (e.g. sudden stratospheric warming, atmospheric blocking, teleconnection patterns and a compensation mechanism between resolved and unresolved drag) are discussed.
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Chen, Tsing-Chang, Harryvan Loon, Kuang-Der Wu, and Ming-Cheng Yen. "Changes in the Atmospheric Circulation over the North Pacific-North America Area since 1950." Journal of the Meteorological Society of Japan. Ser. II 70, no. 6 (1992): 1137–46. http://dx.doi.org/10.2151/jmsj1965.70.6_1137.
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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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Fahad, Abdullah A., Natalie J. Burls, Erik T. Swenson, and David M. Straus. "The Influence of South Pacific Convergence Zone Heating on the South Pacific Subtropical Anticyclone." Journal of Climate 34, no. 10 (May 2021): 3787–98. http://dx.doi.org/10.1175/jcli-d-20-0509.1.
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AbstractSubtropical anticyclones and midlatitude storm tracks are key components of the large-scale atmospheric circulation. Focusing on the Southern Hemisphere, the seasonality of the three dominant subtropical anticyclones, situated over the South Pacific, South Atlantic, and south Indian Ocean basins, has a large influence on local weather and climate within South America, southern Africa, and Australia, respectively. Generally speaking, sea level pressure within the Southern Hemisphere subtropics reaches its seasonal maximum during the winter season when the Southern Hemisphere Hadley cell is at its strongest. One exception to this is the seasonal evolution of the South Pacific subtropical anticyclone. While winter maxima are seen in the South Atlantic and south Indian subtropical anticyclones, the South Pacific subtropical anticyclone reaches its seasonal maximum during local spring with elevated values extending into summer. In this study, we investigate the hypothesis that the strength of the austral summer South Pacific subtropical anticyclone is largely due to heating over the South Pacific convergence zone. Using added-cooling and added-heating atmospheric general circulation model experiments to artificially change the strength of austral summer diabatic heating over the South Pacific convergence zone, our results show that increased heating, through increased upper-level divergence, triggers a Rossby wave train that extends into the Southern Hemisphere midlatitudes. This propagating Rossby wave train creates a high and low sea level pressure pattern that projects onto the center of the South Pacific subtropical anticyclone to intensify its area and strength.
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Yun, Kyung-Sook, Axel Timmermann, and Malte F. Stuecker. "Synchronized spatial shifts of Hadley and Walker circulations." Earth System Dynamics 12, no. 1 (February 2, 2021): 121–32. http://dx.doi.org/10.5194/esd-12-121-2021.
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Abstract. The El Niño–Southern Oscillation (ENSO) influences the most extensive tropospheric circulation cells on our planet, known as Hadley and Walker circulations. Previous studies have largely focused on the effect of ENSO on the strength of these cells. However, what has remained uncertain is whether interannual sea surface temperature anomalies can also cause synchronized spatial shifts of these circulations. Here, by examining the spatiotemporal relationship between Hadley and Walker cells in observations and climate model experiments, we demonstrate that the seasonally evolving warm-pool sea surface temperature (SST) anomalies in the decay phase of an El Niño event generate a meridionally asymmetric Walker circulation response, which couples the zonal and meridional atmospheric overturning circulations. This process, which can be characterized as a phase-synchronized spatial shift in Walker and Hadley cells, is accompanied by cross-equatorial northwesterly low-level flow that diverges from an area of anomalous drying in the western North Pacific and converges towards a region with anomalous moistening in the southern central Pacific. Our results show that the SST-induced concurrent spatial shifts of the two circulations are climatically relevant as they can further amplify extratropical precipitation variability on interannual timescales.
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Chen, Wei. "A Decadal Weakening in the Connection between ENSO and the Following Spring SST over the Northeast Tropical Atlantic after the Mid-1980s." Journal of Climate 35, no. 9 (May 1, 2022): 2867–81. http://dx.doi.org/10.1175/jcli-d-21-0698.1.
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Abstract The north tropical Atlantic (NTA) displays significant sea surface temperature anomalies (SSTA) during the ENSO decaying spring. This study identifies a largely weakened impact of ENSO on the SSTA concentrated over the northeast tropical Atlantic (NETA) after the mid-1980s, while the impacts on the SSTA over the northwest tropical Atlantic (NWTA) are stable during the whole period. Different SST datasets can recognize this weakened connection between ENSO and the NETA SSTA, suggesting the robustness in this decadal variation. The El Niño–related teleconnections shift westward after the mid-1980s, and thus the anomalous southwesterly, leading to the positive NTA SSTA via the wind–evaporation–SST feedbacks, is restricted over the NWTA without extending eastward. As a result, the positive SSTA rises only over the NWTA but is diminished over the NETA. The regime shift in these circulation anomalies is due to the westward shift in the El Niño–induced convection and circulation anomalies from the eastern equatorial Pacific (EEP) to the central equatorial Pacific (CEP). Further analysis indicates that the intensified zonal SST gradient over the equatorial Pacific leads to a westward shift of Pacific Walker circulation after the mid-1980s. The westward shift of Walker circulation contributes to the convergent circulation anomalies over the CEP and thus results in the El Niño–induced precipitation anomalies concentrated there. Significance Statement Previous studies have indicated a positive connection between ENSO and the succeeding spring SSTA over the north tropical Atlantic (NTA), and this connection tends to be unstable. This study identifies a decadal weakening in the connection between ENSO and the SSTA actually concentrated over the northeast part of tropical Atlantic (NETA) after the mid-1980s. Further analysis indicates that the decadal changes in the ENSO–NETA connection are due to the westward shift in the ENSO-related convection and teleconnections, resulting from the westward shift of Pacific Walker circulation, induced by the intensified zonal SST gradient over the equatorial Pacific after the mid-1980s. The result implies a decadal change in NTA SSTA structure, which may bring different climate anomalies in the surrounding area.
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Zawislak, Jonathan. "Global Survey of Precipitation Properties Observed during Tropical Cyclogenesis and Their Differences Compared to Nondeveloping Disturbances." Monthly Weather Review 148, no. 4 (March 30, 2020): 1585–606. http://dx.doi.org/10.1175/mwr-d-18-0407.1.
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Abstract This study evaluates precipitation properties involved in tropical cyclogenesis by analyzing a multiyear, global database of passive microwave overpasses of the pregenesis stage of developing disturbances and nondeveloping disturbances. Precipitation statistics are quantified using brightness temperature proxies from the 85–91-GHz channels of multiple spaceborne sensors, as well as retrieved rain rates. Proxies focus on the overall raining area, areal coverage of deep convection, and the proximity of precipitation to the disturbance center. Of interest are the differences in those proxies for developing versus nondeveloping disturbances, how the properties evolve during the pregenesis stage, and how they differ globally. The results indicate that, of all of the proxies examined, the total raining area and rain volume near the circulation center are the most useful precipitation-related predictors for genesis. The areal coverage of deep convection also differentiates developing from nondeveloping disturbances and, similar to the total raining area, generally also increases during the pregenesis stage, particularly within a day of genesis. As the threshold convective intensity is increased, pregenesis cases are less distinguishable from nondeveloping disturbances. Relative to the western Pacific and Indian Oceans, the Atlantic and eastern North Pacific Oceans have less precipitation and deep convection observed during genesis and the smallest differences between developing and nondeveloping disturbances. This suggests that the total raining area and areal coverage of deep convection associated with tropical disturbances are better predictors of tropical cyclogenesis fate in the Pacific and Indian Oceans than in the Atlantic and eastern North Pacific.
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Mayer, Michael, Leopold Haimberger, and Magdalena A. Balmaseda. "On the Energy Exchange between Tropical Ocean Basins Related to ENSO*." Journal of Climate 27, no. 17 (August 28, 2014): 6393–403. http://dx.doi.org/10.1175/jcli-d-14-00123.1.
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Abstract Vast amounts of energy are exchanged between the ocean, atmosphere, and space in association with El Niño–Southern Oscillation (ENSO). This study examines energy budgets of all tropical (30°S–30°N) ocean basins and the atmosphere separately using different, largely independent oceanic and atmospheric reanalyses to depict anomalous energy flows associated with ENSO in a consistent framework. It is found that variability of area-averaged ocean heat content (OHC) in the tropical Pacific to a large extent is modulated by energy flow through the ocean surface. While redistribution of OHC within the tropical Pacific is an integral part of ENSO dynamics, variability of ocean heat transport out of the tropical Pacific region is found to be mostly small. Noteworthy contributions arise from the Indonesian Throughflow (ITF), which is anticorrelated with ENSO at a few months lag, and from anomalous oceanic poleward heat export during the La Niña events in 1999 and 2008. Regression analysis reveals that atmospheric energy transport and radiation at the top of the atmosphere (RadTOA) almost perfectly balance the OHC changes and ITF variability associated with ENSO. Only a small fraction of El Niño–related heat lost by the Pacific Ocean through anomalous air–sea fluxes is radiated to space immediately, whereas the major part of the energy is transported away by the atmosphere. Ample changes in tropical atmospheric circulation lead to enhanced surface fluxes and, consequently, to an increase of OHC in the tropical Atlantic and Indian Ocean that almost fully compensates for tropical Pacific OHC loss. This signature of energy redistribution is robust across the employed datasets for all three tropical ocean basins and explains the small ENSO signal in global mean RadTOA.
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Lee, Jae N., Drew T. Shindell, and Sultan Hameed. "The Influence of Solar Forcing on Tropical Circulation." Journal of Climate 22, no. 22 (November 15, 2009): 5870–85. http://dx.doi.org/10.1175/2009jcli2670.1.
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Abstract The response of the seasonal tropical circulation to an 11-yr solar cycle forcing is studied with the Goddard Institute for Space Studies (GISS) ModelE, which includes fully interactive atmospheric chemistry. To identify characteristic solar signals in the tropical circulation, the model experiments are carried out with certain imposed conditions: a doubly amplified solar forcing and the present-day and preindustrial greenhouse gases and aerosol conditions, with the mixed layer or fully coupled dynamic ocean model. In both the model and the NCEP reanalysis, tropical humidity increases in response to enhanced solar irradiance are found to be statistically significant in both solstice seasons. Changes are also found in the vertical velocities for both the Hadley and Walker circulations in some areas of the Pacific region. With present-day greenhouse gas and aerosol conditions, the ascending branch of the Hadley cell is enhanced near the equator, and the intertropical convergence zone (ITCZ) is shifted northward in response to solar forcing during the boreal winter. Enhancement of the meridionally averaged vertical velocity over the western Pacific indicates strengthening of the Walker circulation in response to solar forcing in both solstice seasons. In present-day conditions, the tropical circulation response to an 11-yr solar forcing is generally consistent with that derived from previous observational works.
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Romero-Centeno, Rosario, Jorge Zavala-Hidalgo, and G. B. Raga. "Midsummer Gap Winds and Low-Level Circulation over the Eastern Tropical Pacific." Journal of Climate 20, no. 15 (August 1, 2007): 3768–84. http://dx.doi.org/10.1175/jcli4220.1.
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Abstract The low-level seasonal and intraseasonal wind variability over the northeastern tropical Pacific (NETP), its relationship with other variables, and the connection with large- and middle-scale atmospheric patterns are analyzed using a suite of datasets. Quick Scatterometer (QuikSCAT) wind data show that the low-level circulation over the NETP is mainly affected by the northerly trades, the southerly trades, and the wind jets crossing through the Tehuantepec, Papagayo, and Panama mountain gaps. The seasonal and intraseasonal evolution of these wind systems determines the circulation patterns over the NETP, showing predominant easterly winds in winter and early spring and wind direction reversals in summer over the central region of the NETP. During summer, when southerly trades are the strongest and reach their maximum northward penetration, weak westerlies are observed in June, easterlies in July–August, despite that strong southerlies tend to turn eastward, and again westerlies in September–October. This circulation pattern appears to be related to the Tehuantepec and Papagayo jets, which slightly strengthen during midsummer favored by the westward elongation and intensification of the Azores–Bermuda high (ABH). This ABH evolution induces an across-gap pressure gradient over the Isthmus of Tehuantepec favoring the generation of the jet and a meridional sea level pressure (SLP) gradient in the western Caribbean that favors the funneling of the trade winds through the Papagayo gap. The SLP pattern causing the gap winds in winter is different than in midsummer, being the southeastward intrusion of high pressure systems coming from the northwest, the main cause of the large meridional SLP gradients in Tehuantepec and the western Caribbean. The westward low-level circulation observed over the central-eastern region of the NETP during midsummer induces westward moisture fluxes in the lower layers of the atmosphere, displaces convergence areas away from the coasts, and confines the relatively strong convergence in the easternmost NETP to the south of the area of influence of the wind jets and associated easterlies, contributing to the development of the midsummer drought observed in southern Mexico and Central America.
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Diamond, Howard J., Andrew M. Lorrey, and James A. Renwick. "A Southwest Pacific Tropical Cyclone Climatology and Linkages to the El Niño–Southern Oscillation." Journal of Climate 26, no. 1 (January 1, 2013): 3–25. http://dx.doi.org/10.1175/jcli-d-12-00077.1.
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Abstract The new South Pacific Enhanced Archive for Tropical Cyclones (SPEArTC) dataset provides an opportunity to develop a more complete climatology of tropical cyclones (TCs) in the southwest Pacific. Here, spatial patterns and characteristics of TCs for the 41-yr period beginning with the 1969/70 season are related to phases of the El Niño–Southern Oscillation (ENSO), taking into account the degree of ocean–atmosphere coupling. Twentieth-century reanalysis data and the coupled ENSO index (CEI) were used to investigate TC genesis areas and climate diagnostics in the extratropical transition (ETT) region at and south of 25°S during different CEI ENSO phases. This is the first study looking at CEI-based ENSO phases and the more detailed relationship of TCs to the coupling of the ocean and atmosphere during different ENSO phases. Consistent with previous findings, positive relationships exist among TCs, sea surface temperature, and atmospheric circulation. A statistically significant greater frequency of major TCs was found during the latter half of the study period (1991–2010) compared to the 1970–90 period, again consistent with the findings of other studies. Also found were significant and consistent linkages highlighting the interplay of TCs and sea surface temperature (SSTs) in the southwest Pacific basin west of 170°E and a closer connection to atmospheric circulation east of 170°E. Moreover, this study demonstrates subtle differences between a fully coupled El Niño or La Niña and atmospheric- or ocean-dominated phases, or neutral conditions.
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Rodríguez, José M., and Sean F. Milton. "East Asian Summer Atmospheric Moisture Transport and Its Response to Interannual Variability of the West Pacific Subtropical High: An Evaluation of the Met Office Unified Model." Atmosphere 10, no. 8 (August 10, 2019): 457. http://dx.doi.org/10.3390/atmos10080457.
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In this study, the atmospheric moisture transport involved in the East Asian summer monsoon (EASM) water cycle is examined. Observational estimates are contrasted with the Met Office Unified Model (MetUM) climate simulations to evaluate the model’s ability to capture this transport. We explore the role of large circulation in determining the regional water cycle by analyzing key systematic errors in the model. MetUM exhibits robust errors in its representation of the summer Asian-Pacific monsoon system, including dry biases in the Indian peninsula and wet biases in the tropical Indian Ocean and tropical West Pacific. Such errors are consistent with errors in the atmospheric moisture convergence in the area. Diabatic heating biases in the Maritime Continent domain are shown, via nudging sensitivity experiments, to play a crucial role in remotely forcing the model circulation and moisture transport errors in the East Asian area. We also examine changes in the regional water cycle in response to interannual variability of the West Pacific subtropical high (WPSH). It is shown by water budget analysis that, although the model in general is not able to faithfully reproduce the response on a month to month basis, it gives comparable seasonal trends in regional moisture convergence and precipitation associated with shifts of the WPSH.
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Zhao, Guijie, Gang Huang, Renguang Wu, Weichen Tao, Hainan Gong, Xia Qu, and Kaiming Hu. "A New Upper-Level Circulation Index for the East Asian Summer Monsoon Variability." Journal of Climate 28, no. 24 (December 15, 2015): 9977–96. http://dx.doi.org/10.1175/jcli-d-15-0272.1.
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Abstract The East Asian summer monsoon (EASM) and its variability involve circulation systems in both the tropics and midlatitudes as well as in both the lower and upper troposphere. Considering this fact, a new EASM index (NEWI) is proposed based on 200-hPa zonal wind, which takes into account wind anomalies in the southern (about 5°N), middle (about 20°N), and northern areas (about 35°N) of East Asia. The NEWI can capture the interannual EASM-related climate anomalies and the interdecadal variability well. Compared to previous indices, the NEWI shows a better performance in describing precipitation and air temperature variations over East Asia. It can also show distinct climate anomalous features in early and late summer. The NEWI is tightly associated with the East Asian–Pacific or the Pacific–Japan teleconnection, suggesting a possible role of internal dynamics in the EASM variability. Meanwhile, the NEWI is significantly linked to El Niño–Southern Oscillation and tropical Indian Ocean sea surface temperature anomalies. Furthermore, the NEWI is highly predictable in the ENSEMBLES models, indicating its advantage for operational prediction of the EASM. The physical mechanism of the EASM variability as represented by the NEWI is also explicit. Both warm advection anomalies of temperature by anomalous westerly winds and the advection of anomalous positive relative vorticity by northerly basic winds cause anomalous ascending motion over the mei-yu–changma–baiu rainfall area, and vice versa over the South China Sea area. Hence, this NEWI would be a good choice to study, monitor, and predict the EASM.
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Li, Yuanlong, Weiqing Han, Lei Zhang, and Fan Wang. "Decadal SST Variability in the Southeast Indian Ocean and Its Impact on Regional Climate." Journal of Climate 32, no. 19 (August 26, 2019): 6299–318. http://dx.doi.org/10.1175/jcli-d-19-0180.1.
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Abstract The southeast Indian Ocean (SEIO) exhibits decadal variability in sea surface temperature (SST) with amplitudes of ~0.2–0.3 K and covaries with the central Pacific (r = −0.63 with Niño-4 index for 1975–2010). In this study, the generation mechanisms of decadal SST variability are explored using an ocean general circulation model (OGCM), and its impact on atmosphere is evaluated using an atmospheric general circulation model (AGCM). OGCM experiments reveal that Pacific forcing through the Indonesian Throughflow explains <20% of the total SST variability, and the contribution of local wind stress is also small. These wind-forced anomalies mainly occur near the Western Australian coast. The majority of SST variability is attributed to surface heat fluxes. The reduced upward turbulent heat flux (QT; latent plus sensible heat flux), owing to decreased wind speed and anomalous warm, moist air advection, is essential for the growth of warm SST anomalies (SSTAs). The warming causes reduction of low cloud cover that increases surface shortwave radiation (SWR) and further promotes the warming. However, the resultant high SST, along with the increased wind speed in the offshore area, enhances the upward QT and begins to cool the ocean. Warm SSTAs co-occur with cyclonic low-level wind anomalies in the SEIO and enhanced rainfall over Indonesia and northwest Australia. AGCM experiments suggest that although the tropical Pacific SST has strong effects on the SEIO region through atmospheric teleconnection, the cyclonic winds and increased rainfall are mainly caused by the SEIO warming through local air–sea interactions.
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Wu, Bingyi, Kun Yang, and Jennifer A. Francis. "A Cold Event in Asia during January–February 2012 and Its Possible Association with Arctic Sea Ice Loss." Journal of Climate 30, no. 19 (September 6, 2017): 7971–90. http://dx.doi.org/10.1175/jcli-d-16-0115.1.
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Abstract Through both observational analyses and simulation experiments, this study investigates the intraseasonal evolution of atmospheric circulation anomalies associated with a persistent cold event in the Asian continent during late January–early February 2012, and the possible association with Arctic sea ice loss and Arctic atmospheric circulation during the preceding summer. The results suggest that the northeastern Pacific–Aleutian region and central Eurasia are two critical areas where the atmospheric circulation evolution contributed to the development of this cold event. A persistent increase in sea level pressure (SLP) over the Aleutian region was a predominant feature prior to the cold event, and then decreasing SLP over this region was concurrent with both occurrence of a polar blocking high aloft and rapid strengthening of the Siberian high, triggering outbreaks of Arctic air over the Asian continent. Consequently, the influence of the Aleutian region on this cold event (i.e., the downstream effect of the atmospheric circulation) played a critical role. Simulation experiments demonstrate that Arctic atmospheric circulation conditions in the summer of 2011 significantly enhanced a negative feedback of Arctic sea ice loss on atmospheric circulation over the Aleutian region and central Eurasia during the ensuing wintertime, which could have led to the favorable atmospheric circulation that facilitated the occurrence of cold events resembling the one in 2012. This study also implies that the Aleutian low and disturbances in the midlatitudes over the northeastern Pacific may provide precursors that could increase skill in predicting the intraseasonal evolution of extreme cold events over Eurasia.
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Robinson, Dennis P., and Robert X. Black. "Baroclinic Development in Observations and NASA GSFC General Circulation Models." Monthly Weather Review 134, no. 4 (April 1, 2006): 1161–73. http://dx.doi.org/10.1175/mwr3110.1.
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Abstract Comparative diagnostic analyses of developing synoptic-scale baroclinic disturbances in NCEP–NCAR reanalyses and the NASA–NCAR (NASCAR) and Aries [NASA’s Seasonal-to-Interannual Prediction Project (NSIPP)] general circulation model simulations are performed. In particular, lag composite analyses of wintertime cyclonic and anticyclonic events occurring in the North Pacific and North Atlantic storm tracks are constructed to pursue a synoptic and dynamic characterization of eddy development. The data are also seasonally stratified to study aspects of the North Pacific midwinter suppression phenomenon. Winter-averaged results indicate that the model-simulated events are generally too weak in amplitude, particularly in the upper troposphere. For the North Pacific storm track, model-simulated events are also anomalously distended in the meridional direction. The existing model biases in eddy structure and magnitude lead to anomalously weak baroclinic energy conversions for both cyclonic and anticyclonic events over the North Pacific. For the North Atlantic storm track the NASCAR model provides a very good representation of the structure of developing cyclonic events. However, growing North Atlantic cyclones in the NSIPP model are anomalously weak and horizontally too isotropic (meridionally retracted). These latter two characteristics are also observed in both models for developing anticyclonic flow anomalies over the North Atlantic. The relative weakness of NSIPP synoptic events over the North Atlantic region is largely responsible for the 50% deficiency in areal-averaged baroclinic energy conversions. Conversely, the NASCAR model climatology features anomalously strong temperature gradients over the western North Atlantic that provide local enhancements to the baroclinic energy conversion field. A seasonally stratified diagnostic analysis reveals that the simulated climatological storm tracks over the North Pacific undergo larger spatial migrations during the cool season compared to observations. It is further determined that the suppression of synoptic eddy activity observed in the Pacific storm track is associated with a relative midwinter weakness in the magnitude of the growing cyclonic anomalies. Specifically, during midwinter the cyclonic perturbations entering the Pacific storm track are deficient in magnitude compared to their early and late winter counterparts. It is also discovered that the midwinter suppression pattern over the North Pacific region has a clear organized extension upstream into Siberia, the region from which incipient upper-tropospheric short-wave features emanate. This behavior is found in both observations and the model simulations. The results herein support the idea that the North Pacific midwinter suppression phenomenon is linked to a midwinter weakness in the upstream formation of upper-level short waves, leading to anomalously weak “seeding” of baroclinic disturbances in the Pacific storm track.
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He, Shengping, and Huijun Wang. "Oscillating Relationship between the East Asian Winter Monsoon and ENSO." Journal of Climate 26, no. 24 (December 2, 2013): 9819–38. http://dx.doi.org/10.1175/jcli-d-13-00174.1.
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Abstract This work investigates the interdecadal variations of the relationship between the El Niño–Southern Oscillation (ENSO) and the East Asian winter monsoon (EAWM), further explores possible mechanisms, and finally considers a recent switch in the ENSO–EAWM relationship. The 23-yr sliding correlation between the Niño-3.4 index and the EAWM index reveals an obvious low-frequency oscillation with a period of about 50 yr in the ENSO–EAWM relationship. Warm ENSO events during high-correlation periods are associated with an unusually weak East Asian trough, a positive phase of the North Pacific Oscillation (NPO), significant southerly wind anomalies along coastal East Asia, and warmer East Asian continent and adjacent oceans. However, there are no robust and significant anomalies in the EAWM-related circulation during low-correlation periods. Because of the southeastward shift of the Walker circulation, the area of anomalously high pressure in the western Pacific retreats south of 25°N, confining it to the region of the Philippine Sea. In this sense, the Pacific–East Asian teleconnection is not well established. Consequently, ENSO’s impact on the EAWM is suppressed. Additionally, the low-frequency oscillation of the ENSO–EAWM relationship might be attributable to the combined effect of the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation owing to their modulation on the establishment of the NPO teleconnection. The observation of two full cycles of the ENSO–EAWM relationship, a transition to negative PDO in the early 2000s and an enhancement of the Walker circulation in the late 1990s, suggests a recovery of the ENSO–EAWM relationship.
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Xu, Qi, Zhaoyong Guan, Dachao Jin, and Dingzhu Hu. "Regional Characteristics of Interannual Variability of Summer Rainfall in the Maritime Continent and Their Related Anomalous Circulation Patterns." Journal of Climate 32, no. 14 (June 19, 2019): 4179–92. http://dx.doi.org/10.1175/jcli-d-18-0480.1.
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Abstract Using the NCEP–NCAR reanalysis and Global Precipitation Climatology Project monthly rainfall, we have investigated the regional features of interannual variations of rainfall in the Maritime Continent (MC) and their related anomalous atmospheric circulation patterns during boreal summer by employing the rotated empirical orthogonal function (REOF) analysis. Our results demonstrate that the rainfall variabilities in the MC are of very striking regional characteristics. The MC is divided into four independent subregions on the basis of the leading REOF modes; these subregions are located in central-eastern Indonesia (subregion I), the oceanic area to the west of Indonesia (subregion II+V), the part of the warm pool in the equatorial western Pacific Ocean (subregion III), and Guam (subregion IV+VI).The anomalous precipitation in different subregions exhibits different variation periodicities, which are associated with different circulation patterns as a result of atmospheric response to different sea surface temperature anomaly (SSTA) patterns in the tropical Indo-Pacific sector. It is found that rainfall anomalies in subregion I are induced by the Pacific ENSO, whereas those in subregion II+V are dominated by a triple SSTA pattern with positive correlations in the MC and negative correlation centers in the tropical Pacific and tropical Indian Ocean. Rainfall anomalies in subregion III mainly resulted from an SSTA pattern with negative correlations in the eastern MC and positive correlations in the western equatorial Pacific east of the MC. A horseshoe SSTA pattern in the central Pacific is found to affect the precipitation anomalies in subregion IV+VI. All of the results of this study are helpful for us to better understand both the climate variations in the MC and monsoon variations in East Asia.
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Gao, Mingxiang, Shuangyan Yang, and Tim Li. "The Spatio—Temporal Variation of Pacific Blocking Frequency within Winter Months and Its Relationship with Surface Air Temperature." Atmosphere 11, no. 9 (September 9, 2020): 960. http://dx.doi.org/10.3390/atmos11090960.
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The spatio–temporal evolution of the Pacific blocking frequency (PBF) that is based on a two–dimensional blocking index is investigated during the recent 40–winter (1979/80–2018/19) months (December–January–February). It is found that maximum PBF appears in January within the key area of 140° E–160° W, 50°–70° N. The key–area Pacific blocking in January is more active during the first (1980–1988) and the third (2009–2019) periods than during the second period (1989–2008). There is a positive 500 hPa–geopotential height (Z500) anomaly over the mid–latitude Pacific and a negative one over the high latitude area between the first two periods (second minus first). This pattern can cause an anomalous westerly circulation over the mid–high Pacific sector, which indicates a weakening of the Pacific blocking activity during the second period. This connects to a positive two–meter air temperature (T2m) anomaly over the northeastern Asia and mid–western Pacific, and a negative one over the high–latitude area. The difference of Z500 between the third and the second periods (third minus first) is opposite to that between the second and the first periods, which leads to more Pacific blocking events during the third period. This is related to a positive T2m anomaly over the high–latitude area and a negative one over the mid–latitude area of Asia and the western Pacific. Furthermore, the correlation coefficient between the variables (Z500, T2m, 200 hPa–zonal wind) and the key–area PBF confirms the above results.
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Larson, Kristin, and Dennis L. Hartmann. "Interactions among Cloud, Water Vapor, Radiation, and Large-Scale Circulation in the Tropical Climate. Part II: Sensitivity to Spatial Gradients of Sea Surface Temperature." Journal of Climate 16, no. 10 (May 15, 2003): 1441–55. http://dx.doi.org/10.1175/1520-0442-16.10.1441.
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Abstract The responses of the large-scale circulation, clouds, and water vapor to an imposed sea surface temperature (SST) gradient are investigated. Simulations compare reasonably to averaged observations over the Pacific, considering the simplifications applied to the model. The model responses to sinusoidal SST patterns have distinct circulations in the upper and lower troposphere. The upper circulation is sensitive to the heating from deep convection over the warmest SST. Stronger SST gradients are associated with stronger longwave cooling above stratus clouds in the subsidence region, stronger lower-tropospheric large-scale circulation, a reduction of the rain area, and larger area coverage of low clouds. A similar SST gradient with a warmer mean temperature produces slightly weaker lower-tropospheric circulation, and slightly reduced low cloud coverage. The outgoing longwave radiation (OLR) is not sensitive to the mean SST or the range of the imposed sinusoidal SST gradient. The positive feedbacks of water vapor and decreasing high cloud OLR compensate for the increase in longwave emission with increasing mean temperature in these simulations. As the SST gradient is increased keeping the mean SST constant, the positive high cloud feedback is still active, but the air temperature increases in proportion to the maximum SST in the domain, increasing the clear-sky OLR value and keeping the average OLR constant. The net absorbed shortwave radiation (SWI) is found to be extremely sensitive to the SST gradient. The stronger lower-tropospheric large-scale circulation produces a higher water content in the high and low clouds, increasing the absolute magnitude of the shortwave cloud forcing. A 25% increase in the maximum zonal mass flux of the lower circulation of the 300-K mean, 4-K SST range simulation leads to a 7.4 W m−2 decrease in SWI. Increasing the mean SST creates a positive feedback in these simulations because of the decrease in the lower-tropospheric large-scale circulation and the resultant decrease in cloud optical depth.
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Kuwano-Yoshida, Akira, and Shoshiro Minobe. "Storm-Track Response to SST Fronts in the Northwestern Pacific Region in an AGCM." Journal of Climate 30, no. 3 (January 20, 2017): 1081–102. http://dx.doi.org/10.1175/jcli-d-16-0331.1.
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Abstract The storm-track response to sea surface temperature (SST) fronts in the northwestern Pacific region is investigated using an atmospheric general circulation model with a 50-km horizontal resolution. The following two experiments are conducted: one with 0.25° daily SST data (CNTL) and the other with smoothed SSTs over an area covering SST fronts associated with the Kuroshio, the Kuroshio Extension, the Oyashio, and the subpolar front (SMTHK). The storm track estimated from the local deepening rate of surface pressure (LDR) exhibits a prominent peak in this region in CNTL in January, whereas the storm-track peak weakens and moves eastward in SMTHK. Storm-track differences between CNTL and SMTHK are only found in explosive deepening events with LDR larger than 1 hPa h−1. A diagnostic equation of LDR suggests that latent heat release associated with large-scale condensation contributes to the storm-track enhancement. The SST fronts also affect the large-scale atmospheric circulation over the northeastern Pacific Ocean. The jet stream in the upper troposphere tends to meander northward, which is associated with positive sea level pressure (SLP) anomalies in CNTL, whereas the jet stream flows zonally in SMTHK. A composite analysis for the northwestern Pacific SLP anomaly suggests that frequent explosive cyclone development in the northwestern Pacific in CNTL causes downstream positive SLP anomalies over the Gulf of Alaska. Cyclones in SMTHK developing over the northeastern Pacific enhance the moisture flux along the west coast of North America, increasing precipitation in that region.
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Funk, Chris C., and Andrew Hoell. "The Leading Mode of Observed and CMIP5 ENSO-Residual Sea Surface Temperatures and Associated Changes in Indo-Pacific Climate*." Journal of Climate 28, no. 11 (May 27, 2015): 4309–29. http://dx.doi.org/10.1175/jcli-d-14-00334.1.
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Abstract SSTs in the western Pacific Ocean have tracked closely with CMIP5 simulations despite recent hiatus cooling in the eastern Pacific. This paper quantifies these similarities and associated circulation and precipitation variations using the first global 1900–2012 ENSO-residual empirical orthogonal functions (EOFs) of 35 variables: observed SSTs; 28 CMIP5 SST simulations; Simple Ocean Data Assimilation (SODA) 25-, 70-, and 171-m ocean temperatures and sea surface heights (SSHs); and Twentieth Century Reanalysis, version 2 (20CRv2), surface winds and precipitation. While estimated independently, these leading EOFs across all variables fit together in a meaningful way, and the authors refer to them jointly as the west Pacific warming mode (WPWM). WPWM SST EOFs correspond closely in space and time. Their spatial patterns form a “western V” extending from the Maritime Continent into the extratropical Pacific. Their temporal principal components (PCs) have increased rapidly since 1990; this increase has been primarily due to radiative forcing and not natural decadal variability. WPWM circulation changes appear consistent with a Matsuno–Gill-like atmospheric response associated with an ocean–atmosphere dipole structure contrasting increased (decreased) western (eastern) Pacific precipitation, SSHs, and ocean temperatures. These changes have enhanced the Walker circulation and modulated weather on a global scale. An AGCM experiment and the WPWM of global boreal spring precipitation indicate significant drying across parts of East Africa, the Middle East, the southwestern United States, southern South America, and Asia. Changes in the WPWM have tracked closely with precipitation and the increase in drought frequency over the semiarid and water-insecure areas of East Africa, the Middle East, and southwest Asia.
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Girardin, Martin-Philippe, Jacques C. Tardif, Mike D. Flannigan, and Yves Bergeron. "Synoptic-Scale Atmospheric Circulation and Boreal Canada Summer Drought Variability of the Past Three Centuries." Journal of Climate 19, no. 10 (May 15, 2006): 1922–47. http://dx.doi.org/10.1175/jcli3716.1.
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Abstract Five independent multicentury reconstructions of the July Canadian Drought Code and one reconstruction of the mean July–August temperature were developed using a network of 120 well-replicated tree-ring chronologies covering the area of the eastern Boreal Plains to the eastern Boreal Shield of Canada. The reconstructions were performed using 54 time-varying reconstruction submodels that explained up to 50% of the regional drought variance during the period of 1919–84. Spatial correlation fields on the six reconstructions revealed that the meridional component of the climate system from central to eastern Canada increased since the mid–nineteenth century. The most obvious change was observed in the decadal scale of variability. Using 500-hPa geopotential height and wind composites, this zonal to meridional transition was interpreted as a response to an amplification of long waves flowing over the eastern North Pacific into boreal Canada, from approximately 1851 to 1940. Composites with NOAA Extended Reconstructed SSTs indicated a coupling between the meridional component and tropical and North Pacific SST for a period covering at least the past 150 yr, supporting previous findings of a summertime global ocean–atmosphere–land surface coupling. This change in the global atmospheric circulation could be a key element toward understanding the observed temporal changes in the Canadian boreal forest fire regimes over the past 150 yr.
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Sun, Haowei, Haiying Hu, Zhaoli Wang, and Chengguang Lai. "Temporal Variability of Drought in Nine Agricultural Regions of China and the Influence of Atmospheric Circulation." Atmosphere 11, no. 9 (September 16, 2020): 990. http://dx.doi.org/10.3390/atmos11090990.
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In recent decades, the severe drought across agricultural regions of China has had significant impact on agriculture. The standardized precipitation evapotranspiration index (SPEI) has been widely used for drought analyses; however, SPEI is prone to be affected by potential evapotranspiration (PET). We thus examined the correlations between soil moisture anomalies and the SPEI calculated by the Thornthwaite, Hargreaves, and Penman–Monteith (PM) equations to select the most suitable for drought research. Additionally, the Mann–Kendall and wavelet analysis were used to investigate drought trends and to analyze and the impact of atmospheric circulation on drought in China from 1961 to 2018. The results showed that (1) PET obtained from the PM equation is the most suitable for SPEI calculation; (2) there were significant wetting trends in Northern China and the whole Chinese mainland and most of the wetting mutation points occurred in the 1970s and 1980s and the significant inter-annual oscillations period in the Chinese mainland was 2–4 years; (3) the Chinese mainland and Northern China are strongly influenced by West Pacific Trade Wind, while Western Pacific Subtropical High Intensity and Pacific Subtropical High Area have primary impact on Southern China.
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Sun, Yue, and Jianping Li. "Synergistic effect of El Niño and the North Pacific Oscillation on wintertime precipitation over Southeastern China and the East China Sea Kuroshio area." Climate Dynamics 58, no. 5-6 (January 25, 2022): 1635–49. http://dx.doi.org/10.1007/s00382-021-05982-8.
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AbstractWintertime precipitation in China is most pronounced over the southeastern area, and the Kuroshio in the East China Sea anchors a prominent precipitation band over the warm side of the sea surface temperature front. Previous studies have suggested that many factors contribute to the interannual variation of the precipitation over southeastern China (SC), whereas less attention has been paid to precipitation variability over the East China Sea Kuroshio (ECSK) area. This study focuses on the interannual variation of wintertime precipitation over the SC and ECSK areas. Empirical orthogonal function analysis reveals a spatially uniform pattern from SC to the ECSK area. Composite analysis shows that an El Niño event intensifies wintertime precipitation over our target region, and this effect is tripled when an El Niño follows a positive North Pacific Oscillation (NPO) event in the previous winter. The positive NPO event in the previous winter intensifies the El Niño event via the Victoria mode ocean bridge and the subsequent Bjerknes feedback. In comparison with single-factor El Niño events, a much weaker Walker cell induced by the joint event induces a much weaker regional Hadley cell through anomalous descending motion over the western tropical Pacific. The weakened regional Hadley circulation over the western Pacific directly enhances the precipitation over the SC and ECSK area. In this study, the synergistic effect of an El Niño event and a positive NPO event indicates that the influence of the El Niño event can be amplified by the positive NPO event in the previous winter.
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Ko, Ken-Chung, and Jyun-Hong Liu. "Quasi-Periodic Behavior of the Pacific–Japan Pattern Affecting Propagation Routes of Summertime Wave Patterns and the Associated Tropical Cyclone Tracks over the Western North Pacific." Monthly Weather Review 144, no. 1 (January 1, 2016): 393–408. http://dx.doi.org/10.1175/mwr-d-15-0080.1.
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Abstract This study introduces a modified Pacific–Japan (PJ) index that exhibits a substantial periodicity of 5–16 days in the East Asian summer monsoon region. The quasi-periodic fluctuations of the PJ index can indicate changes in the large-scale circulation systems. In the PJ high phase, the wave pattern propagates northwestward from the western North Pacific tropics to an area near northern Luzon and is then forced to move westward because of a stationary, anomalous high pressure system over southern Japan. The tropical cyclones (TCs) associated with the anomalous low pressure systems tend to follow a straight-moving propagation route through the northern South China Sea. The anomalous cyclonic flow causes heavy rainfall in eastern Taiwan. However, in the PJ low phase, the wave pattern and TCs follow a recurving propagation route toward higher latitudes. The circulation pattern typically brings heavy rainfall to northern Taiwan in the PJ low phase. Therefore, wave patterns under the influence of the quasi-periodic fluctuations of the PJ pattern affect rainfall because of the changing propagation routes of the wave patterns, as well as the TC tracks.
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Zhan, Ruifen, Yuqing Wang, and Li Tao. "Intensified Impact of East Indian Ocean SST Anomaly on Tropical Cyclone Genesis Frequency over the Western North Pacific." Journal of Climate 27, no. 23 (December 1, 2014): 8724–39. http://dx.doi.org/10.1175/jcli-d-14-00119.1.
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Abstract A recent finding is the significant impact of the sea surface temperature anomaly (SSTA) over the east Indian Ocean (EIO) on the genesis frequency of tropical cyclones (TCs) over the western North Pacific (WNP). In this study it is shown that such an impact is significant only after the late 1970s. The results based on both data analysis and numerical model experiments demonstrate that prior to the late 1970s the EIO SSTA is positively correlated with the equatorial central Pacific SSTA and the latter produces an opposite atmospheric circulation response over the WNP to the former. As a result, the impact of the EIO SSTA on the TC genesis over the WNP is largely suppressed by the latter. After the late 1970s, the area coverage of the EIO SSTA is expanding. This considerably enhances the large-scale circulation response over the WNP to the EIO SSTA and significantly intensifies the impact of the EIO SSTA on TC genesis frequency over the WNP. The results from this study have great implications for seasonal prediction of TC activity over the WNP.
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Chen, Baohua, and Chuntao Liu. "Warm Organized Rain Systems over the Tropical Eastern Pacific." Journal of Climate 29, no. 9 (April 26, 2016): 3403–22. http://dx.doi.org/10.1175/jcli-d-15-0177.1.
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Abstract This study uses 16-yr Tropical Rainfall Measuring Mission (TRMM) radar precipitation feature (RPF) data to characterize warm rain systems in the tropics with large horizontal extensions, referred to as warm organized rain systems. The systems are selected by specifying the RPFs with minimum infrared brightness temperature warmer than 0°C and rain area greater than 500 km2. ERA-Interim atmospheric fields and SST from NOAA are analyzed to highlight the environmental characteristics of warm organized rain systems. Warm organized systems occur over specific oceanic regions, including the eastern Pacific ITCZ, the eastern part of the SPCZ, and coastal regions. In contrast with ubiquitous warm isolated RPFs, warm organized systems have greater near-surface radar reflectivity. The rainfall amounts generated by warm organized systems are greater in winter than in summer. Composite analyses indicate that warm organized RPFs prefer to coexist with a dry midtroposphere associated with a strong upper-level descent, an enhanced near-surface moisture convergence, and a strong low-level large-scale ascent. The shallow meridional circulation in the eastern Pacific is significantly stronger for warm organized RPFs compared to the circulation for warm isolated RPFs. Warm organized systems over the tropical eastern Pacific occur at warm SSTs with mean value of about 27°C and a strong SST meridional gradient. The warm organized RPFs in the tropical eastern Pacific are found to be at the southern edge of deep ITCZ cores. This is probably related to the meridional asymmetrical thermodynamic structure over the eastern Pacific ITCZ with a higher low-level humidity to the south. Similar favorable large-scale environments for the warm organized RPFs are also found over the SPCZ and other regions.
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Enciso, Angelica M., Olga Lucia Baquero, Daniel Escobar-Carbonari, Jeimar Tapasco, and Wilmar L. Cerón. "Variability of Precipitation Recycling and Moisture Sources over the Colombian Pacific Region: A Precipitationshed Approach." Atmosphere 13, no. 8 (July 30, 2022): 1202. http://dx.doi.org/10.3390/atmos13081202.
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This study assessed the precipitation recycling and moisture sources in the Colombian Pacific region between 1980–2017, based on the monitoring of moisture in the atmosphere through the Eulerian Water Accounting Model-2 layer (WAM2 layer) and the delimitation of the area contributing to terrestrial and oceanic moisture in the region is performed using the “precipitationshed” approach. The results indicate a unimodal precipitation recycling ratio for the North and Central Pacific and Patía-Mira regions, with the highest percentages between March and April, reaching 30% and 34%, respectively, and the lowest between September and October (between 19% and 21%). Moreover, monthly changes in the circulation of the region promote a remarkable variability of the sources that contribute to the precipitation of the study area and the spatial dynamics of the precipitationshed. From December to April, the main contributions come from continental sources in eastern Colombia and Venezuela, the tropical North Atlantic, and the Caribbean Sea, a period of high activity of the Orinoco Low-Level jet. In September, the moisture source region is located over the Pacific Ocean, where a southwesterly cross-equatorial circulation predominates, converging in western Colombia, known as the Choco Jet (CJ), decreasing the continental contribution. An intensified Caribbean Low-Level Jet inhibits moisture sources from the north between June and August, strengthening a southerly cross-equatorial flow from the Amazon River basin and the southeastern tropical Pacific. The March–April (September–October) season of higher (lower) recycling of continental precipitation is related to the weakening (strengthening) of the CJ in the first (second) half of the year, which decreases (increases) the contribution of moisture from the Pacific Ocean to the region, increasing (decreasing) the influence of land-based sources in the study area.
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Deng, Kaiqiang, Mingfang Ting, Song Yang, and Yaheng Tan. "Increased Frequency of Summer Extreme Heat Waves over Texas Area Tied to the Amplification of Pacific Zonal SST Gradient." Journal of Climate 31, no. 14 (June 22, 2018): 5629–47. http://dx.doi.org/10.1175/jcli-d-17-0554.1.
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Abstract Summer extreme heat waves (EHWs) over the Texas area and their trend are investigated using observations and atmospheric general circulation model (AGCM) output. There is a positive linear trend in Texas EHW days for the period 1979–2015. While the interannual variability of the Texas EHWs is linked to ENSO conditions, the upward trend in Texas EHWs is found to be significantly associated with the tropical Pacific zonal SST gradient (PZSSTG). The amplification of PZSSTG leads to both enhanced convection in the western Pacific and suppressed convection in the central-eastern Pacific (i.e., La Niña–like pattern), both of which can induce anomalous anticyclones over the Texas area through two distinct planetary wave trains in the antecedent spring. As a result, anomalously sinking motions and divergent water vapor flux appear over the Texas area, which reduce precipitation and increase downward solar radiation, leading to dry and hot soil that favors the occurrence of Texas summer EHWs. In addition, all AGCMs using observed SSTs as boundary conditions were able to simulate the observed decreasing trend in Texas summer precipitation and the observed increasing trend in Texas summer surface air temperature. The observed relationships between winter PZSSTG and the following spring–summer Texas precipitation/temperature were also reproduced by these models, where the intensified PZSSTG tended to reduce the Texas precipitation while increasing the surface air temperature.
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Jia, Zikang, Zhihai Zheng, Guolin Feng, and Mingjun Tong. "The Intraseasonal Variations of the Leading Mode of Summer Precipitation Anomalies in Meiyu Area of East Asia." Atmosphere 13, no. 2 (January 28, 2022): 217. http://dx.doi.org/10.3390/atmos13020217.
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The intraseasonal variations of summer precipitation anomalies in the Meiyu area of East Asia are analyzed by applying a combined empirical orthogonal function (CEOF) of the latest meteorological reanalysis data ERA5 of European Center for Medium-Range Weather Forecasts for the period from 1991 to 2020, and the circulation structures and sources of variability of CEOF are also investigated. The first mode of the intraseasonal variations shows an in-phase pattern over the Meiyu area in June, July, and August, accounting for 22.2% of the total variance in the intraseasonal variations of summer precipitation anomalies. The positive (negative) CEOF1 is accompanied by the negative (positive) East Asia/Pacific pattern, including strong westerly wind anomalies in the upper troposphere and southwest monsoon in the lower troposphere, and the Western Pacific Subtropical High extending westward and its ridge line slightly south. The positive CEOF1 is preceded by decay of El Niño episodes, including the abnormal warm sea surface temperature anomalies (SSTAs) in the equatorial Central-Eastern Pacific in spring and warm SSTAs in the equatorial Indian Ocean in summer. The second mode shows an opposite precipitation anomaly in June and July, and the distribution in August is not significant. The corresponding geopotential height circulation of positive CEOF2 shows the large negative anomaly in the region north of 40° N and a positive anomaly over Japan in June, whereas the pattern reverses in July. At the same time, there is a radical reversion from abnormal eastly to westly wind in the upper troposphere. The structure of CEOF2 is somewhat induced by local SSTAs over the Northern Indian Ocean and South China Sea.
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Shulski, Martha, John Walsh, Eric Stevens, and Richard Thoman. "Diagnosis of Extended Cold-Season Temperature Anomalies in Alaska." Monthly Weather Review 138, no. 2 (February 1, 2010): 453–62. http://dx.doi.org/10.1175/2009mwr3039.1.
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Abstract During the early winter of 2002 and late winter of 2007, the Alaskan sector of the North Pacific Ocean region experienced record-breaking temperature anomalies. The duration of these episodes was unusually long, with each lasting more than 1 month: 55 days for the warm anomaly of October–December 2002 and 37 days for the cold anomaly of February–March 2007. Temperature departures over each respective period were the largest for the continental climate of interior Alaska (>10°C) and the smallest for the maritime regions of Alaska (<4°C). Mean temperatures over the event periods in 2002 and 2007 easily ranked as the record warmest and coldest, respectively, for many surface observing stations. In addition, heating degree-day anomalies were on the order of 700 units for these periods. Atmospheric circulation patterns at the surface and upper levels for the circum-Arctic proved to be the driver for these persistent events. The 2002 warm anomaly was driven by enhanced southerly advection associated with an unusually strong Aleutian low and a positive Pacific decadal oscillation index, which resulted in a large area of anomalous temperatures in Alaska and northern Canada. The 2007 cold anomaly was driven by a weakening of the circulation pattern in the subpolar Pacific sector and a strengthening of the Siberian high, with the strongest temperature anomalies in Alaska and northwestern Canada.
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Wu, Renguang, and Zhuoqi He. "Two Distinctive Processes for Abnormal Spring to Summer Transition over the South China Sea." Journal of Climate 30, no. 23 (December 2017): 9665–78. http://dx.doi.org/10.1175/jcli-d-17-0215.1.
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The period from April to June signifies the transition from spring to summer over the South China Sea (SCS). The present study documents two distinct processes for abnormal spring to summer transition over the SCS. One process is related to large-scale sea surface temperature (SST) anomalies in the tropical Indo-Pacific region. During spring of La Niña decaying years, negative SST anomalies in the equatorial central Pacific (ECP) and the southwestern tropical Indian Ocean (TIO) coexist with positive SST anomalies in the tropical western North Pacific. Negative ECP SST anomalies force an anomalous Walker circulation, negative southwestern TIO SST anomalies induce anomalous cross-equatorial flows from there, and positive tropical western North Pacific SST anomalies produce a Rossby wave–type response to the west. Together, they contribute to enhanced convection and an anomalous lower-level cyclone over the SCS, leading to an advanced transition to summer there. The other process is related to regional air–sea interactions around the Maritime Continent. Preceding positive ECP SST anomalies induce anomalous descent around the Maritime Continent, leading to SST increase in the SCS and southeast TIO. An enhanced convection region moves eastward over the south TIO during spring and reaches the area northwest of Australia in May. This enhances descent over the SCS via an anomalous cross-equatorial overturning circulation and contributes to further warming in the SCS. The SST warming in turn induces convection over the SCS, leading to an accelerated transition to summer. Analysis shows that the above two processes are equally important during 1979–2015.
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Takahashi, Hiroshi G., Hatsuki Fujinami, Tetsuzo Yasunari, Jun Matsumoto, and Somchai Baimoung. "Role of Tropical Cyclones along the Monsoon Trough in the 2011 Thai Flood and Interannual Variability." Journal of Climate 28, no. 4 (February 11, 2015): 1465–76. http://dx.doi.org/10.1175/jcli-d-14-00147.1.
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Abstract The atmospheric circulation patterns that were responsible for the heavy flooding that occurred in Thailand in 2011 are examined. This paper also investigates the interannual variation in precipitation over Indochina over a 33-yr period from 1979–2011, focusing on the role of westward-propagating tropical cyclones (TCs) over the Asian monsoon region. Cyclonic anomalies and more westward-propagating TCs than expected from the climatology of the area were observed in 2011 along the monsoon trough from the northern Indian subcontinent, the Bay of Bengal, Indochina, and the western North Pacific, which contributed significantly to the 2011 Thai flood. The strength of monsoon westerlies was normal, which implies that the monsoon westerly was not responsible for the seasonal heavy rainfall in 2011. Similar results were also obtained from the 33-yr statistical analysis. The 5-month total precipitation over Indochina covaried interannually with that along the monsoon trough. In addition, above-normal precipitation over Indochina was observed when enhanced cyclonic circulation with more westward-propagating TCs along the monsoon trough was observed. Notably, the above-normal precipitation was not due to the enhanced monsoon westerly over Indochina. Therefore, the 2011 Thai flood was caused by the typical atmospheric circulation pattern for an above-normal precipitation year. It is noteworthy that the effect of sea surface temperature (SST) forcing over the western North Pacific and the Niño-3.4 region on total precipitation during the summer rainy season over Indochina was unclear over the 33-yr period.
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Bai, Lina, Hong-Li Ren, Yuntao Wei, Yuwen Wang, and Bin Chen. "Influence of Madden–Julian Oscillation on Precipitation over the Tibetan Plateau in Boreal Summer." Atmosphere 14, no. 1 (December 30, 2022): 70. http://dx.doi.org/10.3390/atmos14010070.
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The influence of the Madden–Julian oscillation (MJO) on precipitation over the Tibetan Plateau (TP) during boreal summer is investigated using observational and reanalysis data during 1980–2020. The results show that summer precipitation over most areas of the eastern TP increases (decreases) in MJO Phases 1–2 (5–6), especially when the eastward-propagating MJO active convection is located over the Indian Ocean (Western Pacific) in Phase 2 (6). The most significant negative precipitation anomalies in Phase 4 (8) are located over the southern (northeastern) TP. Moreover, MJO has a relatively weakened effect on the TP summer precipitation in Phases 3 and 7 when its convection migrates to the eastern Indian Ocean and the western–central Pacific, respectively. The MJO-phase dependence of the TP summer precipitation anomalies is closely associated with the anomalous atmospheric circulation and evolution of the horizontal moisture flux convergence directly induced by MJO. When the MJO convection centers are located over the western Indian Ocean and the Pacific, high-level anticyclonic and low-level cyclonic anomalous circulations over the TP are excited. In contrast, when MJO locates over the Indian Ocean and the Maritime Continent, its diabatic heating can inspire high-level cyclonic and low-level anticyclonic circulation anomalies over the TP. The vertical motions and moisture transport from the Bay of Bengal caused by the MJO-excited large-scale circulation can modulate the TP summer precipitation. This study advances the understanding of the TP intraseasonal variability.
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Christoudias, T., and J. Lelieveld. "Modelling the global atmospheric transport and deposition of radionuclides from the Fukushima Dai-ichi nuclear accident." Atmospheric Chemistry and Physics 13, no. 3 (February 5, 2013): 1425–38. http://dx.doi.org/10.5194/acp-13-1425-2013.
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Abstract. We modeled the global atmospheric dispersion and deposition of radionuclides released from the Fukushima Dai-ichi nuclear power plant accident. The EMAC atmospheric chemistry – general circulation model was used, with circulation dynamics nudged towards ERA-Interim reanalysis data. We applied a resolution of approximately 0.5 degrees in latitude and longitude (T255). The model accounts for emissions and transport of the radioactive isotopes 131I and 137Cs, and removal processes through precipitation, particle sedimentation and dry deposition. In addition, we simulated the release of 133Xe, a noble gas that can be regarded as a passive transport tracer of contaminated air. The source terms are based on Chino et al. (2011) and Stohl et al. (2012); especially the emission estimates of 131I are associated with a high degree of uncertainty. The calculated concentrations have been compared to station observations by the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO). We calculated that about 80% of the radioactivity from Fukushima which was released to the atmosphere deposited into the Pacific Ocean. In Japan a large inhabited land area was contaminated by more than 40 kBq m-2. We also estimated the inhalation and 50-year dose by 137Cs, 134Cs and 131I to which the people in Japan are exposed.
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Mignot, Juliette, and Claude Frankignoul. "The Variability of the Atlantic Meridional Overturning Circulation, the North Atlantic Oscillation, and the El Niño–Southern Oscillation in the Bergen Climate Model." Journal of Climate 18, no. 13 (July 1, 2005): 2361–75. http://dx.doi.org/10.1175/jcli3405.1.
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Abstract The link between the interannual to interdecadal variability of the Atlantic meridional overturning circulation (AMOC) and the atmospheric forcing is investigated using 200 yr of a control simulation of the Bergen Climate Model, where the mean circulation cell is rather realistic, as is also the location of deep convection in the northern North Atlantic. The AMOC variability has a slightly red frequency spectrum and is primarily forced by the atmosphere. The maximum value of the AMOC is mostly sensitive to the deep convection in the Irminger Sea, which it lags by about 5 yr. The latter is mostly forced by a succession of atmospheric patterns that induce anomalous northerly winds over the area. The impact of the North Atlantic Oscillation on deep convection in the Labrador and Greenland Seas is represented realistically, but its influence on the AMOC is limited to the interannual time scale and is primarily associated with wind forcing. The tropical Pacific shows a strong variability in the model, with too strong an influence on the North Atlantic. However, its influence on the tropical Atlantic is realistic. Based on lagged correlations and the release of fictitious Lagrangian drifters, the tropical Pacific seems to influence the AMOC with a time lag of about 40 yr. The mechanism is as follows: El Niño events induce positive sea surface salinity anomalies in the tropical Atlantic that are advected northward, circulate in the subtropical gyre, and then subduct. In the ocean interior, part of the salinity anomaly is advected along the North Atlantic current, eventually reaching the Irminger and Labrador Seas after about 35 yr where they destabilize the water column and favor deep convection.
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Wu, Bingyi, Renhe Zhang, and Rosanne D’Arrigo. "Distinct Modes of the East Asian Winter Monsoon." Monthly Weather Review 134, no. 8 (August 1, 2006): 2165–79. http://dx.doi.org/10.1175/mwr3150.1.
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Abstract Two distinct modes of the East Asian winter monsoon (EAWM) have been identified, and they correspond to real and imaginary parts of the leading mode of the EAWM, respectively. Analyses of these modes used the National Centers for Environment Prediction (NCEP) and National Center for Atmospheric Research (NCAR) monthly mean reanalysis datasets for the period 1968–2003, as well as the Southern Oscillation index (SOI), North Atlantic Oscillation index, and eastern equatorial Pacific sea surface temperature (SST) data. Results were obtained by resolving a complex Hermite matrix derived from 850-hPa anomalous wind fields, and determining the resulting modes’ associations with several climate variables. The first distinct mode (M1) is characterized by an anomalous meridional wind pattern over East Asia and the western North Pacific. Mode M1 is closely related to several features of the atmospheric circulation, including the Siberian high, East Asian trough, East Asian upper-tropospheric jet, and local Hadley circulation over East Asia. Thus, M1 reflects the traditional EAWM pattern revealed in previous studies. The second distinct EAWM mode (M2), which was not identified previously, displays dominant zonal wind anomalies over the same area. Mode M2 exhibits a closer relation than M1 to sea level pressure anomalies over the northwestern Pacific southeast of Japan and with the SOI and equatorial eastern Pacific SST. Unlike M1, M2 does not show coherent relationships with the Siberian high, East Asian trough, and East Asian upper-tropospheric jet. Since atmospheric circulation anomalies relevant to M2 exhibit a quasi-barotropic structure, its existence cannot simply be attributed to differential land–sea heating. El Niño events tend to occur in the negative phase of M1 and the positive phase of M2, both corresponding to a weakened EAWM. The Arctic Oscillation does not appear to impact the EAWM on interannual time scales. Although the spatial patterns for the two modes are very different, the two distinct modes are complementary, with the leading EAWM mode being a linear combination of the two. The results herein therefore demonstrate that a single EAWM index may be inappropriate for investigating and predicting the EAWM.
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Darmawan, Yahya, Huang-Hsiung Hsu, and Jia-Yuh Yu. "Characteristics of Large-Scale Circulation Affecting the Inter-Annual Precipitation Variability in Northern Sumatra Island during Boreal Summer." Atmosphere 12, no. 2 (January 22, 2021): 136. http://dx.doi.org/10.3390/atmos12020136.
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This study aims to explore the contrasting characteristics of large-scale circulation that led to the precipitation anomalies over the northern parts of Sumatra Island. Further, the impact of varying the Asian–Australian Monsoon (AAM) was investigated for triggering the precipitation variability over the study area. The moisture budget analysis was applied to quantify the most dominant component that induces precipitation variability during the JJA (June, July, and August) period. Then, the composite analysis and statistical approach were applied to confirm the result of the moisture budget. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Anaysis Interim (ERA-Interim) from 1981 to 2016, we identified 9 (nine) dry and 6 (six) wet years based on precipitation anomalies, respectively. The dry years (wet years) anomalies over the study area were mostly supported by downward (upward) vertical velocity anomaly instead of other variables such as specific humidity, horizontal velocity, and evaporation. In the dry years (wet years), there is a strengthening (weakening) of the descent motion, which triggers a reduction (increase) of convection over the study area. The overall downward (upward) motion of westerly (easterly) winds appears to suppress (support) the convection and lead to negative (positive) precipitation anomaly in the whole region but with the largest anomaly over northern parts of Sumatra. The AAM variability proven has a significant role in the precipitation variability over the study area. A teleconnection between the AAM and other global circulations implies the precipitation variability over the northern part of Sumatra Island as a regional phenomenon. The large-scale tropical circulation is possibly related to the PWC modulation (Pacific Walker Circulation).
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Satake, Yuya, Masaru Inatsu, Masato Mori, and Akira Hasegawa. "Tropical Cyclone Tracking Using a Neighbor Enclosed Area Tracking Algorithm." Monthly Weather Review 141, no. 10 (September 25, 2013): 3539–55. http://dx.doi.org/10.1175/mwr-d-12-00092.1.
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Abstract Tropical cyclone (TC) tracking is essential for calculating TC statistics from gridded datasets. A new method for TC tracking is presented here using neighbor enclosed area tracking (NEAT), which is based on the temporal overlap of enclosed areas above a vorticity threshold and differs from the widely used neighbor point tracking (NPT) method. The parameters of cyclone intensity, vertical-shear, and warm-core criteria were intensively tuned for NEAT and NPT. When these criteria were optimized for the typhoon tracks observed in the western North Pacific based on the Japanese 25-yr Reanalysis Project (JRA-25)/Japan Meteorological Agency (JMA) Climate Data Assimilation System (JCDAS) dataset, the NEAT and NPT algorithms captured approximately 85% of typhoons with little qualitative distortion in the spatial distribution and temporal variability of the TC track density. The grid system dependency of the algorithms was tested by applying NEAT and NPT to a high-resolution general circulation model output. The method presented here can also provide realistic statistics on the TC size, the extratropical transition timing, and the meridional heat transport.
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Fan, Lingli, Jianjun Xu, and Liguo Han. "Impacts of Onset Time of El Niño Events on Summer Rainfall over Southeastern Australia during 1980–2017." Atmosphere 10, no. 3 (March 14, 2019): 139. http://dx.doi.org/10.3390/atmos10030139.
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El Niño–Southern Oscillation (ENSO) has large impacts on Australia’s rainfall. A composite analysis technique was utilized to distinguish the impact of onset time of El Niño on summer rainfall over southeastern Australia. Summer rainfall tended to be lower than normal in austral autumn El Niño events during December–January–February (DJF) and higher than normal in austral winter El Niño events, in 1980–2017. During autumn El Niño events, the Walker circulation and meridional cells served as a bridge, linking the warmer sea surface temperature (SST) in the eastern equatorial Pacific (EEP) and lower summer rainfall over southeastern Australia. This physical process can be described as follows: During DJF, a positive SST anomaly in the EEP was concurrent with anomalous downdraft over southeastern Australia via zonal anomalous Walker circulation, meridional anomalous cells along 170° E–170° W, and a Pacific South American (PSA) teleconnection wave train at 500 hPa. In addition, an anomalous convergence at 200 hPa depressed the convection. Meanwhile, an 850 hPa abnormal westerly was not conducive to transport marine water vapor into this area. These factors resulted in below-normal rainfall. During winter El Niño events, a positive SST anomaly in the central equatorial Pacific (CEP) and the changes in Walker circulation and meridional cells were weaker. The PSA teleconnection wave train shifted westward and northward, and there was a low-level anomalous ascent over southeastern Australia. At the western flank of the anomalous anticyclone, northerly transported water vapor from the ocean to southeastern Australia resulted in a sink of water vapor over this area. The development of low-level convective activity and the plentiful water vapor supply favored more rainfall over southeastern Australia. Onset time of El Niño may be a useful metric for improving the low predictive skill of southeastern Australian summer rainfall.
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Kim, Hye-Mi, Daehyun Kim, Frederic Vitart, Violeta E. Toma, Jong-Seong Kug, and Peter J. Webster. "MJO Propagation across the Maritime Continent in the ECMWF Ensemble Prediction System." Journal of Climate 29, no. 11 (May 13, 2016): 3973–88. http://dx.doi.org/10.1175/jcli-d-15-0862.1.
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Abstract The characteristics of the MJO propagation across the Maritime Continent are investigated using a 20-yr reforecast dataset from the ECMWF ensemble prediction system. Analysis of the MJO events initialized over the Indian Ocean (phase 2) shows that the initial MJO amplitude and prediction skill relationship is not linear, particularly when the predictions start in moderate (between strong and weak) MJO amplitude category. To examine the key factors that determine the prediction skill, reforecasts in the moderate category are grouped into high- and low-skill events, and the differences in their ocean–atmospheric conditions as well as the physical processes during reforecast period are examined. The initial distribution of OLR anomalies in high-skill events shows a clear dipole pattern of convection with an enhanced convective anomalies over the Indian Ocean and strongly suppressed convective anomalies in the western Pacific Ocean. This dipole mode may support the MJO propagation across the Maritime Continent via the Rossby wave response and associated meridional moisture advection. Prominent ocean–atmosphere coupled processes are also simulated during the propagation of high-skill events. However, in low-skill events, the convective signal over the western Pacific is almost absent and less organized, and the ocean–atmosphere coupled processes are not simulated correctly. It is found that in both high- and low-skill events, the amplitude of the convective anomaly decreases significantly after about day 15, possibly due to the systematic mean model bias. A strong wet bias in the vicinity of the Maritime Continent, a cold SST bias in the equatorial Pacific, and associated circulation biases make the west Pacific area unfavorable for MJO propagation, thus limiting its prediction skill.
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Li, Tim, Ping Liu, X. Fu, B. Wang, and Gerald A. Meehl. "Spatiotemporal Structures and Mechanisms of the Tropospheric Biennial Oscillation in the Indo-Pacific Warm Ocean Regions*." Journal of Climate 19, no. 13 (July 1, 2006): 3070–87. http://dx.doi.org/10.1175/jcli3736.1.
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Abstract The observed structure and seasonal evolution characteristics of the tropospheric biennial oscillation (TBO) in the warm ocean areas of the Indo-Pacific region are explored using a seasonal-sequence EOF analysis approach. The major convective activity centers associated with the TBO appear in the southeast Indian Ocean (SEIO) and western North Pacific (WNP), accompanied by anticyclonic (or cyclonic) circulation patterns with a first-baroclinic-mode structure. The convection and circulation anomalies have distinctive life cycles in the SEIO and WNP: the former have a peak phase in northern fall and the latter persist from northern winter to subsequent summer. The mechanisms of the TBO in this region are investigated with a hybrid coupled GCM. Numerical results show that air–sea interaction in the warm ocean alone can support TBO variability that has many observed characteristics. Key processes involved in the TBO include the WNP monsoon variability and associated cross-equatorial flows, convective activity over Southeast Asia/the Maritime Continent and associated anomalous Walker circulation, and ocean dynamic responses to anomalous wind stress curl in the western Pacific. The coupled model experiment demonstrates that the essential element of the TBO in this region arises from the monsoon–warm ocean interaction. A possible connection between the TBO and ENSO variability is further studied in another model that excludes the delayed oscillator dynamics. The key in causing the biennial variability of ENSO arises from teleconnections between the tropical Pacific and Indian Oceans, with three “atmospheric bridges”: 1) the north–south teleconnection that connects the WNP monsoon and the SEIO, 2) the east–west teleconnection that connects the Indian Ocean and the Pacific cold tongue, and 3) the El Niño–WNP monsoon teleconnection.