Journal articles: 'Equatorial middle atmosphere'

1

REDDY, C. A. "Equatorial Middle Atmosphere." Journal of geomagnetism and geoelectricity 43, Supplement2 (1991): 695–708. http://dx.doi.org/10.5636/jgg.43.supplement2_695.

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Fouchet, T., S. Guerlet, D. F. Strobel, A. A. Simon-Miller, B. Bézard, and F. M. Flasar. "An equatorial oscillation in Saturn’s middle atmosphere." Nature 453, no. 7192 (May 2008): 200–202. http://dx.doi.org/10.1038/nature06912.

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Sun, Chi-Rong, and Conway Leovy. "Ozone variability in the equatorial middle atmosphere." Journal of Geophysical Research 95, no. D9 (1990): 13829. http://dx.doi.org/10.1029/jd095id09p13829.

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4

Lieberman, Ruth S. "Nonmigrating Diurnal Tides in the Equatorial Middle Atmosphere." Journal of the Atmospheric Sciences 48, no. 8 (April 1991): 1112–23. http://dx.doi.org/10.1175/1520-0469(1991)048<1112:ndtite>2.0.co;2.

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Fechine, J., A. F. Medeiros, R. A. Buriti, H. Takahashi, and D. Gobbi. "Mesospheric bore events in the equatorial middle atmosphere." Journal of Atmospheric and Solar-Terrestrial Physics 67, no. 17-18 (December 2005): 1774–78. http://dx.doi.org/10.1016/j.jastp.2005.04.006.

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Teng, Chen-Ke-Min, Sheng-Yang Gu, Yusong Qin, and Xiankang Dou. "Impact of Solar Activity on Global Atmospheric Circulation Based on SD-WACCM-X Simulations from 2002 to 2019." Atmosphere 12, no. 11 (November 19, 2021): 1526. http://dx.doi.org/10.3390/atmos12111526.

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In this study, a global atmospheric model, Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (SD-WACCM-X), and the residual circulation principle were used to study the global atmospheric circulation from the lower to upper atmosphere (~500 km) from 2002 to 2019. Our analysis shows that the atmospheric circulation is clearly influenced by solar activity, especially in the upper atmosphere, which is mainly characterized by an enhanced atmospheric circulation in years with high solar activity. The atmospheric circulation in the upper atmosphere also exhibits an ~11 year period, and its variation is highly correlated with the temporal variation in the F10.7 solar index during the same time series, with a maximum correlation coefficient of up to more than 0.9. In the middle and lower atmosphere, the impact of solar activity on the atmospheric circulation is not as obvious as in the upper atmosphere due to some atmospheric activities such as the Quasi-Biennial Oscillation (QBO), El Niño–Southern Oscillation (ENSO), sudden stratospheric warming (SSW), volcanic forcing, and so on. By comparing the atmospheric circulation in different latitudinal regions between years with high and low solar activity, we found the atmospheric circulation in mid- and high-latitude regions is more affected by solar activity than in low-latitude and equatorial regions. In addition, clear seasonal variation in atmospheric circulation was detected in the global atmosphere, excluding the regions near 10−4 hPa and the lower atmosphere, which is mainly characterized by a flow from the summer hemisphere to the winter hemisphere. In the middle and low atmosphere, the atmospheric circulation shows a quasi-biennial oscillatory variation in the low-latitude and equatorial regions. This work provides a referable study of global atmospheric circulation and demonstrates the impacts of solar activity on global atmospheric circulation.

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Devanarayanan, S., and K. Mohanakumar. "Sunspot cycle and thermal structure of equatorial middle atmosphere." Journal of Geophysical Research 90, A6 (1985): 5357. http://dx.doi.org/10.1029/ja090ia06p05357.

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8

Semeniuk, Kirill, and Theodore G. Shepherd. "The Middle-Atmosphere Hadley Circulation and Equatorial Inertial Adjustment." Journal of the Atmospheric Sciences 58, no. 21 (November 2001): 3077–96. http://dx.doi.org/10.1175/1520-0469(2001)058<3077:tmahca>2.0.co;2.

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9

Vijayan, Lekshmi, and C. A. Reddy. "Radiative damping of equatorial waves in the middle atmosphere." Quarterly Journal of the Royal Meteorological Society 120, no. 519 (July 1994): 1323–43. http://dx.doi.org/10.1002/qj.49712051910.

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10

Harris, M. J., N. F. Arnold, and A. D. Aylward. "A study into the effect of the diurnal tide on the structure of the background mesosphere and thermosphere using the new coupled middle atmosphere and thermosphere (CMAT) general circulation model." Annales Geophysicae 20, no. 2 (February 28, 2002): 225–35. http://dx.doi.org/10.5194/angeo-20-225-2002.

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Abstract. A new coupled middle atmosphere and thermosphere general circulation model has been developed, and some first results are presented. An investigation into the effects of the diurnal tide upon the mean composition, dynamics and energetics was carried out for equinox conditions. Previous studies have shown that tides deplete mean atomic oxygen in the upper mesosphere-lower thermosphere due to an increased recombination in the tidal displaced air parcels. The model runs presented suggest that the mean residual circulation associated with the tidal dissipation also plays an important role. Stronger lower boundary tidal forcing was seen to increase the equatorial local diurnal maximum of atomic oxygen and the associated 0(1S) 557.7 nm green line volume emission rates. The changes in the mean background temperature structure were found to correspond to changes in the mean circulation and exothermic chemical heating.Key words. Atmospheric composition and structure (middle atmosphere – composition and chemistry) Meterology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

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11

Beig, Gufran, and S. Fadnavis. "In search of greenhouse signals in the equatorial middle atmosphere." Geophysical Research Letters 28, no. 24 (December 15, 2001): 4603–6. http://dx.doi.org/10.1029/2001gl013633.

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Beig, G., and S. Fadnavis. "Solar response in the temperature over the equatorial middle atmosphere." Journal of Atmospheric and Solar-Terrestrial Physics 71, no. 13 (September 2009): 1450–55. http://dx.doi.org/10.1016/j.jastp.2008.07.007.

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13

Burrage, M. D., R. A. Vincent, H. G. Mayr, W. R. Skinner, N. F. Arnold, and P. B. Hays. "Long-term variability in the equatorial middle atmosphere zonal wind." Journal of Geophysical Research: Atmospheres 101, no. D8 (May 1, 1996): 12847–54. http://dx.doi.org/10.1029/96jd00575.

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14

Krishna Murthy, B. V., S. P. Perov, and M. N. Sasi. "Diurnal and semi-diurnal tides in the equatorial middle atmosphere." Journal of Atmospheric and Terrestrial Physics 54, no. 7-8 (July 1992): 881–91. http://dx.doi.org/10.1016/0021-9169(92)90055-p.

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15

Koval, A. V., N. M. Gavrilov, A. I. Pogoreltsev, and E. N. Savenkova. "Experiments on sensitivity of meridional circulation and ozone flux to parameterizations of orographic gravity waves and QBO phases in a general circulation model of the middle atmosphere." Geoscientific Model Development Discussions 8, no. 7 (July 21, 2015): 5643–70. http://dx.doi.org/10.5194/gmdd-8-5643-2015.

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Abstract. Many atmospheric global circulation models have large biases in predicting meridional and vertical winds and fluxes of gas species in remote regions such as the middle and upper atmosphere. In this study, we make sensitivity simulations to recognize the role of vital processes associated with dynamical coupling between different atmospheric layers, namely dynamical and thermal impacts of mesoscale orographic gravity waves (OGWs) generated by the Earth's topography and changes from the easterly to westerly QBO phases in the lower equatorial atmosphere. We improved parameterizations of OGW dynamical and thermal effects and QBO flows and implemented them into a general circulation model of the middle and upper atmosphere used in different countries. With this model, we study the sensitivity of meridional circulation and vertical velocity to stationary OGWs and to changes in QBO phases at altitudes up to 100 km in January. We also considered respective changes in vertical ozone fluxes in the atmosphere. Accounting stationary OGW effects gives changes up to 40 % in the meridional velocity and associated ozone fluxes in the stratosphere. Transitions from the easterly to westerly QBO phase in tropics may significantly alter the meridional and vertical circulation of the middle atmosphere at middle and high latitudes: up to 60 % from the peak respective values. The improved parameterizations of OGW and QBO effects have impacts on other features of the general circulation model, improving the simulation of general circulation, planetary and tidal wave coupling in the lower, middle and upper atmosphere.

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16

Ramkumar, G., T. M. Antonita, Y. Bhavani Kumar, H. Venkata Kumar, and D. Narayana Rao. "Seasonal variation of gravity waves in the Equatorial Middle Atmosphere: results from ISRO's Middle Atmospheric Dynamics (MIDAS) program." Annales Geophysicae 24, no. 10 (October 20, 2006): 2471–80. http://dx.doi.org/10.5194/angeo-24-2471-2006.

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Abstract. Altitude profiles of temperature in the stratospheric and mesopheric region from lidar observations at NARL, Gadanki, India, during December 2002–April 2005, as part of ISRO's Middle Atmospheric Dynamics – "MIDAS (2002–2005)" program are used to study the characteristics of gravity waves and their seasonal variation. Month-to-month variation of the gravity wave activity observed during the period of December 2002–April 2005 show maximum wave activity, with primary peaks in May 2003, August 2004 and March 2005 and secondary peaks in February 2003 and November 2004. This month-to-month variation in gravity wave activity is linked to the variation in the strength of the sources, viz. convection and wind shear, down below at the tropospheric region, estimated from MST radar measurements at the same location. Horizontal wind shear is found to be mostly correlated with wave activity than convection, and sometimes both sources are found to contribute towards the wave activity.

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17

Harris, T. J., and R. A. Vincent. "The quasi-two-day wave observed in the equatorial middle atmosphere." Journal of Geophysical Research 98, no. D6 (1993): 10481. http://dx.doi.org/10.1029/93jd00380.

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18

Chakrabarty, D. K., G. Beig, J. S. Sidhu, and S. R. Das. "Fine scale structure and turbulence parameters in the equatorial middle atmosphere." Journal of Atmospheric and Terrestrial Physics 51, no. 1 (January 1989): 19–27. http://dx.doi.org/10.1016/0021-9169(89)90070-6.

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19

Heavens, Nicholas G., Alexey Pankine, J. Michael Battalio, Corwin Wright, David M. Kass, and Armin Kleinböhl. "A Multiannual Record of Convective Instability in Mars’s Middle Atmosphere from the Mars Climate Sounder." Planetary Science Journal 4, no. 6 (June 1, 2023): 101. http://dx.doi.org/10.3847/psj/acd69d.

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Abstract Gravity waves (GW) transfer energy and momentum from the lower to the middle and upper atmospheres of Earth and Mars. Momentum transfer can occur through the wave dissipative process of saturation associated with convective or shear instability. GW saturation both impacts the atmospheric circulation where saturation occurs and also mediates the GW flux above the level of saturation. It was previously demonstrated that convective instabilities are observable in Mars’s middle atmosphere. Here we characterize the seasonal, interannual, and dust event-driven variability in convective instability in Mars’s atmosphere using retrieved temperature profiles from more than 7 Martian yr of observations by the Mars Climate Sounder on board the Mars Reconnaissance Orbiter. The mean probability of convective instability in the middle atmosphere is <1%, except in the upper portions of the winter westerly jets (≈70 km altitude, 60°–75° N/S), near 30°–40° S and ≈60 km altitude on the dayside in southern summer, and in the tropics at 40–50 km altitude around northern fall equinox. Probabilities of convective instability in or near these three regions can increase by an order of magnitude during planetary-scale dust events and some regional-scale dust events. GW-driven drag on both the equatorial easterly jet and winter westerly jet therefore could increase by an order of magnitude during these dust events, as long as changes in GW properties and the local winds do not provide a compensating reduction of the drag.

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20

Mengel, J. G., H. G. Mayr, K. L. Chan, C. O. Hines, C. A. Reddy, N. F. Arnold, and H. S. Porter. "Equatorial oscillations in the middle atmosphere generated by small scale gravity waves." Geophysical Research Letters 22, no. 22 (November 15, 1995): 3027–30. http://dx.doi.org/10.1029/95gl03059.

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21

Hitchman, Matthew H., and Conway B. Leovy. "Diurnal Tide in the Equatorial Middle Atmosphere as Seen in LIMS Temperatures." Journal of the Atmospheric Sciences 42, no. 6 (March 1985): 557–61. http://dx.doi.org/10.1175/1520-0469(1985)042<0557:dtitem>2.0.co;2.

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22

Croskey, C. L., L. C. Hall, J. D. Mitchell, D. Muha, and N. C. Maynard. "A diurnal study of the electrical structure of the equatorial middle atmosphere." Journal of Atmospheric and Terrestrial Physics 47, no. 8-10 (August 1985): 835–44. http://dx.doi.org/10.1016/0021-9169(85)90058-3.

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23

Zülicke, Christoph, and Erich Becker. "Relation between Equatorial Mesospheric Wind Anomalies during Spring and Middle Atmosphere Variability Modes." SOLA 13A, Special_Edition (2017): 31–35. http://dx.doi.org/10.2151/sola.13a-006.

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24

Son, Jun-Hyeok, and Kyong-Hwan Seo. "Mechanisms for the Climatological Characteristics and Interannual Variations of the Guinea Coast Precipitation: Early Summer West African Monsoon." Atmosphere 11, no. 4 (April 16, 2020): 396. http://dx.doi.org/10.3390/atmos11040396.

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This study presents the climatological characteristics and physical mechanisms of Guinea Coast precipitation in June. Traditionally, the low-tropospheric air temperature and equivalent potential temperature ( θ e ) play crucial roles in the generation of monsoon precipitation through the following mechanisms: 1. Near-surface atmospheric front, depicted by steep ∂ θ e ∂ y , corresponds to the vertical motion in the lower troposphere. 2. Strong easterly wind in the middle troposphere (600–500 hPa), generated by a steep ∂ T ∂ y near the surface at 12° N, induces a positive vorticity to the south and vertical motion over the Guinea Coast (~5° N). Meanwhile, the strong Guinea Coastal precipitation, in association with the interannual variability, is mainly determined by the sea-surface temperature (SST) anomaly in the eastern equatorial Atlantic Ocean. In years of warm SST in the eastern equatorial Atlantic, ∂ θ e ∂ y in the lower troposphere is less pronounced than in normal years. However, the atmospheric buoyancy (moist static instability) increases, owing to a strong vertical θ e gradient ( ∂ θ e ∂ p ) arising from the increase in moisture and warm temperature in the lower troposphere over the warm SST area. Consequently, the eastern equatorial Atlantic warm SST modulates the Guinea Coastal thermodynamic structure, causing deep convection that increases precipitation south of the Guinea Coast. Forced by the eastern equatorial Atlantic warm SST anomaly, the strong precipitation and corresponding atmospheric structures are successfully simulated from the Geophysical Fluid Dynamics Laboratory global atmosphere model 2.1.

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25

Judt, Falko. "Atmospheric Predictability of the Tropics, Middle Latitudes, and Polar Regions Explored through Global Storm-Resolving Simulations." Journal of the Atmospheric Sciences 77, no. 1 (December 16, 2019): 257–76. http://dx.doi.org/10.1175/jas-d-19-0116.1.

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Abstract The predictability of the atmosphere has important implications for weather prediction, because it determines what forecast problems are potentially tractable. Even though our general understanding of error growth and predictability has been increasing, relatively little is known about the detailed structure of atmospheric predictability, such as how it varies between climate regions. The present study addresses this issue by exploring error growth and predictability in three latitude zones, using model output from a previous global storm-resolving predictability experiment by Judt published in 2018. It was determined that the tropics have longer predictability than the middle latitudes and polar regions (tropics, >20 days; middle latitudes and polar regions, a little over 2 weeks). Each latitude zone had distinct error growth characteristics, and error growth was broadly consistent with the underlying dynamics of each zone. Evidence suggests that equatorial waves play a role in the comparatively long predictability of the tropics; specifically, equatorial waves seem to be less prone to error growth than middle-latitude baroclinic disturbances. Even though the generality of the findings needs to be assessed in future studies, the overall conclusions agree with previous work in that current numerical weather prediction procedures have not reached the limits of atmospheric predictability, especially in the tropics. One way to exploit tropical predictability is to reduce model error, for example, by using global storm-resolving models instead of conventional models that parameterize convection.

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Deser, Clara, Robert A. Tomas, and Lantao Sun. "The Role of Ocean–Atmosphere Coupling in the Zonal-Mean Atmospheric Response to Arctic Sea Ice Loss." Journal of Climate 28, no. 6 (March 13, 2015): 2168–86. http://dx.doi.org/10.1175/jcli-d-14-00325.1.

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Abstract The role of ocean–atmosphere coupling in the zonal-mean climate response to projected late twenty-first-century Arctic sea ice loss is investigated using Community Climate System Model version 4 (CCSM4) at 1° spatial resolution. Parallel experiments with different ocean model configurations (full-depth, slab, and no interactive ocean) allow the roles of dynamical and thermodynamic ocean feedbacks to be isolated. In the absence of ocean coupling, the atmospheric response to Arctic sea ice loss is confined to north of 30°N, consisting of a weakening and equatorward shift of the westerlies accompanied by lower tropospheric warming and enhanced precipitation at high latitudes. With ocean feedbacks, the response expands to cover the whole globe and exhibits a high degree of equatorial symmetry: the entire troposphere warms, the global hydrological cycle strengthens, and the intertropical convergence zones shift equatorward. Ocean dynamics are fundamental to producing this equatorially symmetric pattern of response to Arctic sea ice loss. Finally, the absence of a poleward shift of the wintertime Northern Hemisphere westerlies in CCSM4’s response to greenhouse gas radiative forcing is shown to result from the competing effects of Arctic sea ice loss and greenhouse warming on the meridional temperature gradient in middle latitudes.

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27

Giorgetta, M. A., E. Manzini, E. Roeckner, M. Esch, and L. Bengtsson. "Climatology and Forcing of the Quasi-Biennial Oscillation in the MAECHAM5 Model." Journal of Climate 19, no. 16 (August 15, 2006): 3882–901. http://dx.doi.org/10.1175/jcli3830.1.

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Abstract The quasi-biennial oscillation (QBO) in the equatorial zonal wind is an outstanding phenomenon of the atmosphere. The QBO is driven by a broad spectrum of waves excited in the tropical troposphere and modulates transport and mixing of chemical compounds in the whole middle atmosphere. Therefore, the simulation of the QBO in general circulation models and chemistry climate models is an important issue. Here, aspects of the climatology and forcing of a spontaneously occurring QBO in a middle-atmosphere model are evaluated, and its influence on the climate and variability of the tropical middle atmosphere is investigated. Westerly and easterly phases are considered separately, and 40-yr ECMWF Re-Analysis (ERA-40) data are used as a reference where appropriate. It is found that the simulated QBO is realistic in many details. Resolved large-scale waves are particularly important for the westerly phase, while parameterized gravity wave drag is more important for the easterly phase. Advective zonal wind tendencies are important for asymmetries between westerly and easterly phases, as found for the suppression of the easterly phase downward propagation. The simulation of the QBO improves the tropical upwelling and the atmospheric tape recorder compared to a model without a QBO. The semiannual oscillation is simulated realistically only if the QBO is represented. In sensitivity tests, it is found that the simulated QBO is strongly sensitive to changes in the gravity wave sources. The sensitivity to the tested range of horizontal resolutions is small. The stratospheric vertical resolution must be better than 1 km to simulate a realistic QBO.

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28

Fleming, Eric L., and Sushil Chandra. "Equatorial Zonal Wind in the Middle Atmosphere Derived from Geopotential Height and Temperature Data." Journal of the Atmospheric Sciences 46, no. 6 (March 1989): 860–66. http://dx.doi.org/10.1175/1520-0469(1989)046<0860:ezwitm>2.0.co;2.

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29

Wang, Chia-Chi, Wei-Liang Lee, Yu-Luen Chen, and Huang-Hsiung Hsu. "Processes Leading to Double Intertropical Convergence Zone Bias in CESM1/CAM5." Journal of Climate 28, no. 7 (March 27, 2015): 2900–2915. http://dx.doi.org/10.1175/jcli-d-14-00622.1.

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Abstract The double intertropical convergence zone (ITCZ) bias in the eastern Pacific in the Community Earth System Model version 1 with Community Atmosphere Model version 5 (CESM1/CAM5) is diagnosed. In CAM5 standalone, the northern ITCZ is associated with inertial instability and the southern ITCZ is thermally forced. After air–sea coupling, the processes on both hemispheres are switched because the spatial pattern of sea surface temperature (SST) is changed. Biases occur during boreal spring in both CAM5 and the ocean model. In CAM5 alone, weaker-than-observed equatorial easterly in the tropical eastern South Pacific leads to weaker evaporation and an increase in local SST. The shallow meridional circulation overly converges in the same region in the CAM5 standalone simulation, the planetary boundary layer and middle troposphere are too humid, and the large-scale subsidence is too weak at the middle levels. These biases may result from excessive shallow convection behavior in CAM5. The extra moisture would then fuel stronger convection and a higher precipitation rate in the southeastern Pacific. In the ocean model, the South Equatorial Current is underestimated and the North Equatorial Countercurrent is located too close to the equator, causing a warm SST bias in the southeastern Pacific and a cold bias in the northeastern Pacific. These SST biases feed back to the atmosphere and further influence convection and the surface wind biases in the coupled simulation. When the convection in the tropical northeastern Pacific becomes thermally forced after coupling, the northern ITCZ is diminished due to colder SST, forming the so-called alternating ITCZ bias.

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30

Yamamoto, Masaru, and Masaaki Takahashi. "Superrotation Maintained by Meridional Circulation and Waves in a Venus-Like AGCM." Journal of the Atmospheric Sciences 63, no. 12 (December 2006): 3296–314. http://dx.doi.org/10.1175/jas3859.1.

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Fully developed superrotation—60 times faster than the planetary rotation (243 days)—is simulated using a Venus-like atmospheric general circulation model (AGCM). The angular momentum of the superrotation is pumped up by the meridional circulation with the help of waves, which accelerate the equatorial zonal flow. The waves generated by solar heating and shear instability play a crucial role in the atmospheric dynamics of the Venusian superrotation. Vertical and horizontal momentum transports of thermal tides maintain the equatorial superrotation in the middle atmosphere, while equatorward eddy momentum flux due to shear instability raises the efficiency of upward angular momentum transport by the meridional circulation in the lower atmosphere. In addition to the superrotation, some waves simulated in the cloud layer are consistent with the observations. The planetary-scale Kelvin wave identified as the near-infrared (NIR) oscillation with periods of 5–6 days is generated by the shear instability near the cloud base, and the temperature structure of the diurnal tide is similar to the infrared (IR) observation near the cloud top. Sensitivities to the bottom boundary conditions are also examined in this paper, since the surface physical processes are still unknown. The decrease of the equator–pole temperature difference and the increase of the surface frictional time constant result in the weaknesses of the meridional circulation and superrotation. In the cases of the weak superrotation, the vertical angular momentum transport due to the meridional circulation is inefficient and the equatorward eddy angular momentum transport is absent near 60-km altitude.

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31

Keckhut, P. "Mid-latitude summer response of the middle atmosphere to short-term solar UV changes." Annales Geophysicae 13, no. 6 (June 30, 1995): 641–47. http://dx.doi.org/10.1007/s00585-995-0641-7.

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Abstract. Temperature and wind data obtained with Rayleigh lidar since 1979 and Russian rockets since 1964 are analyzed to deduce the summer response of the middle atmosphere to short-term solar UV changes. The equivalent width of the 1083 nm He I line is used as a proxy to monitor the short-term UV flux changes. Spectral analyses are performed on 108-day windows to extract the 27-day component from temperature, wind and solar data sets. Linear regressions between these spectral harmonics show some significant correlations around 45 km at mid-latitudes. For large 27-day solar cycles, amplitudes of 2 K and 6 m s-1 are calculated for temperature data series over the south of France (44°N), and on wind data series over Volgograd (49°N), respectively. Cross-spectrum analyses have indicated correlations between these atmospheric parameters and the solar proxy with a phase lag of less than 2 days. These statistically correlative results, which provide good qualitative agreement with numerical simulations, are both obtained at mid-latitude. However, the observed amplitudes are larger than expected, with numerical models suggesting that dynamical processes such as equatorial or gravity waves may be responsible.

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Ramkumar, Geetha, and Veena Suresh Babu. "Climatology of Horizontal Winds in the Lower and Middle Atmosphere over an Equatorial Station - Thiruvananthapuram." Current Science 111, no. 3 (August 10, 2016): 500. http://dx.doi.org/10.18520/cs/v111/i3/500-508.

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33

Yamanaka, M. D., and S. Fukao. "A perspective of Middle-Atmosphere Dynamics (MAD) studies at the New International Equatorial Observatory (NIEO)." Advances in Space Research 10, no. 10 (January 1990): 155–59. http://dx.doi.org/10.1016/0273-1177(90)90023-s.

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34

Guillermic, Maxence, Sambuddha Misra, Robert Eagle, and Aradhna Tripati. "Atmospheric CO2 estimates for the Miocene to Pleistocene based on foraminiferal δ11B at Ocean Drilling Program Sites 806 and 807 in the Western Equatorial Pacific." Climate of the Past 18, no. 2 (February 2, 2022): 183–207. http://dx.doi.org/10.5194/cp-18-183-2022.

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Abstract. Constraints on the evolution of atmospheric CO2 levels throughout Earth's history are foundational to our understanding of past variations in climate. Despite considerable effort, records vary in their temporal and spatial coverage and estimates of past CO2 levels do not always converge, and therefore new records and proxies are valuable. Here we reconstruct atmospheric CO2 values across major climate transitions over the past 16 million years using the boron isotopic composition (δ11B) of planktic foraminifera from 89 samples obtained from two sites in the West Pacific Warm Pool, Ocean Drilling Program (ODP) Sites 806 and 807, measured using high-precision multi-collector inductively coupled plasma mass spectrometry. We compare our results to published data from ODP Site 872, also in the Western Equatorial Pacific, that goes back to 22 million years ago. These sites are in a region that today is near equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We show that δ11B data from this region are consistent with other boron-based studies. The data show evidence for elevated pCO2 during the Middle Miocene and Early to Middle Pliocene, and reductions in pCO2 of ∼200 ppm during the Middle Miocene Climate Transition, ∼250 ppm during Pliocene Glacial Intensification and ∼50 ppm during the Mid-Pleistocene Climate Transition. During the Mid-Pleistocene Transition there is a minimum pCO2 at marine isotopic stage (MIS) 30. Our results are consistent with a coupling between pCO2, temperature and ice sheet expansion from the Miocene to the late Quaternary.

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Furumoto, Jun-ichi, Toshitaka Tsuda, Satoshi Iwai, and Toshiaki Kozu. "Continuous Humidity Monitoring in a Tropical Region with the Equatorial Atmosphere Radar." Journal of Atmospheric and Oceanic Technology 23, no. 4 (April 1, 2006): 538–51. http://dx.doi.org/10.1175/jtech1868.1.

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Abstract A radar remote sensing technique that estimates humidity profiles using a wind profiler is applied to the equatorial atmosphere radar (EAR) to monitor detailed humidity variations in tropical regions. Turbulence echo power intensity is related to the vertical refractive index gradient squared (M2). Here, M is primarily determined by the vertical gradient of specific humidity in the lower troposphere. These relations are employed to estimate a humidity profile. EAR is a 47-MHz very high frequency (VHF) atmospheric radar installed at KotoTabang in West Sumatra, Indonesia. A humidity-profiling method, which was recently developed for the middle- and upper-atmosphere (MU) radar, was applied to EAR. The aim was to test this new method with a larger dataset observed in the tropical region, where detailed humidity variations have not been fully revealed. EAR observations were carried out in November 2002. Turbulence echoes from one vertical and four oblique beams were obtained with time and height resolutions of 3 min and 150 m, respectively. Spano and Ghebrebrhan's optimized 16-bit code was used for EAR in the entire height range in order to increase the signal-to-noise ratio of the turbulence observation. The effects of pulse compression and coherent and incoherent integrations were removed from the echo power intensity. Because the echo power intensity with the vertical beam was affected by partial reflection, M2 was averaged over four oblique beams. The humidity profiles were estimated using EAR at heights of 1.5–7.5 km. Below 3.0 km the sensitivity of the EAR receiver decreased and the radar-derived |M| was also reduced. Thus, the radar-derived |M| below 3.0 km was adjusted by multiplying the reduction factor calculated from the comparisons with radiosonde results in the campaign period. In this analysis, time-interpolated temperature profiles of radiosonde observations were used to estimate humidity profiles. Detailed variations of humidity corresponded well to rain distribution observed simultaneously with the L-band boundary layer radar (BLR) and the X-band radar, and to the cloud bottom height observed with a ceilometer.

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Hitchman, Matthew H., and Conway B. Leovy. "Evolution of the Zonal Mean State in the Equatorial Middle Atmosphere during October 1978-May 1979." Journal of the Atmospheric Sciences 43, no. 24 (December 1986): 3159–76. http://dx.doi.org/10.1175/1520-0469(1986)043<3159:eotzms>2.0.co;2.

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Dhaka, S. K., A. Kumar, and O. P. Nagpal. "Some studies of tropical/equatorial waves over Indian Tropical Middle Atmosphere: Results of tropical wave campaign." Meteorology and Atmospheric Physics 51, no. 1-2 (1993): 25–39. http://dx.doi.org/10.1007/bf01080878.

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Kishore, Pangaluru, Isabella Velicogna, Tyler C. Sutterley, Yara Mohajerani, Enrico Ciracì, and Gummadipudi Nagasai Madhavi. "A case study of mesospheric planetary waves observed over a three-radar network using empirical mode decomposition." Annales Geophysicae 36, no. 3 (June 21, 2018): 925–36. http://dx.doi.org/10.5194/angeo-36-925-2018.

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Abstract. In this paper an attempt is made to study equatorial Kelvin waves using a network of three radars: Kototabang (0.204∘ S, 100.320∘ E) meteor radar, Pameungpeuk (7.646∘ S, 107.688∘ E) medium-frequency radar, and Pontianak (0.003∘ S, 109.367∘ E) medium-frequency radar. We have used the continuous data gathered from the three radars during April–May 2010. Empirical mode decomposition (EMD), Lomb–Scargle periodogram (LSP) analysis, and wavelet techniques are used to study the temporal and altitude structures of planetary waves. Here, we used a novel technique called EMD to extract the planetary waves from wind data. The planetary waves of ∼ 6.5 and ∼ 3.6 days periodicity are observed in all three radar stations with peak amplitudes of about 12 and 11 m s−1, respectively. The 3.6-day wave has an average vertical wavelength from the three radars of about 42 km. The 3.6- and 6.5-day planetary waves are particularly strong in the zonal wind component. We find that the two waves are present at the 84–94 km height region. The observed features of the 3.6- and 6.5-day waves at the three tropical-latitude stations show some correspondence with the results reported for the equatorial-latitude stations. Keywords. Electromagnetics (wave propagation) – history of geophysics (atmospheric sciences) – meteorology and atmospheric dynamics (middle atmosphere dynamics)

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Garcia, Rolando R., and Jadwiga H. Richter. "On the Momentum Budget of the Quasi-Biennial Oscillation in the Whole Atmosphere Community Climate Model." Journal of the Atmospheric Sciences 76, no. 1 (December 18, 2018): 69–87. http://dx.doi.org/10.1175/jas-d-18-0088.1.

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Abstract This study documents the contribution of equatorial waves and mesoscale gravity waves to the momentum budget of the quasi-biennial oscillation (QBO) in a 110-level version of the Whole Atmosphere Community Climate Model. The model has high vertical resolution, 500 m, above the boundary layer and through the lower and middle stratosphere, decreasing gradually to about 1.5 km near the stratopause. Parameterized mesoscale gravity waves and resolved equatorial waves contribute comparable easterly and westerly accelerations near the equator. Westerly acceleration by resolved waves is due mainly to Kelvin waves of zonal wavenumber in the range k = 1–15 and is broadly distributed about the equator. Easterly acceleration near the equator is due mainly to Rossby–gravity (RG) waves with zonal wavenumbers in the range k = 4–12. These RG waves appear to be generated in situ during both the easterly and westerly phases of the QBO, wherever the meridional curvature of the equatorial westerly jet is large enough to produce reversals of the zonal-mean barotropic vorticity gradient, suggesting that they are excited by the instability of the jet. The RG waves produce a characteristic pattern of Eliassen–Palm flux divergence that includes strong easterly acceleration close to the equator and westerly acceleration farther from the equator, suggesting that the role of the RG waves is to redistribute zonal-mean vorticity such as to neutralize the instability of the westerly jet. Insofar as unstable RG waves might be present in the real atmosphere, mixing due to these waves could have important implications for transport in the tropical stratosphere.

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Debnath, Subhajit, and Uma Das. "Short-Term Variability of Non-Migrating Diurnal Tides in the Stratosphere from CMAM30, ERA-Interim, and FORMOSAT-3/COSMIC." Atmosphere 14, no. 2 (January 28, 2023): 265. http://dx.doi.org/10.3390/atmos14020265.

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The variability of non-migrating tides in the stratosphere is investigated using temperature data from Canadian Middle Atmosphere Model (CMAM30), ERA-interim reanalysis and Formosa Satellite-3 and Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) from 2006 to 2010 using a ±10-day window. CMAM30 and ERA results show that the amplitudes of non-migrating tides, DS0 and DW2, are negligible in the mid and high-latitude stratosphere, and the results from satellite datasets are significantly affected by aliasing in this region, in spite of using a smaller window size for analysis (±10 days). Significant short term variability ranging from 30 to 100 days is observed in DS0 and DW2 over the equatorial and tropical latitudes. These tides are seen as two prominent bands around the equator with DS0 maximising during boreal summers and DW2 maximising during boreal winters. These variabilities are compared with the variability in amplitude of the stationary planetary wave with wavenumber one (SPW1) in the high-latitude stratosphere using the continuous wavelet transform (CWT). It is found that during boreal winters, the variability of SPW1 at 10 hPa over 65° N is similar to that of DS0 and DW2 over the equator at 0.0007 hPa. This provides evidence that SPW1 from the high-altitude stratosphere moving upward and equator-ward could be interacting with the migrating diurnal tide and generating the non-migrating tides in the equatorial mesosphere and lower thermosphere (MLT). The variabilities, however, are not comparable during summers, with SPW1 being absent in the Northern Hemisphere. It is thus concluded that non-linear interactions could be a source of non-migrating tidal variability in the equatorial MLT region during boreal winters, but during summers, the tidal variabilities have other sources in the lower atmosphere. The anti-symmetric nature of the vertical global structures indicates that these tides could be the result of global atmospheric oscillations proposed by the classical tidal theory.

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Koval, Andrey V., Olga N. Toptunova, Maxim A. Motsakov, Ksenia A. Didenko, Tatiana S. Ermakova, Nikolai M. Gavrilov, and Eugene V. Rozanov. "Numerical modelling of relative contribution of planetary waves to the atmospheric circulation." Atmospheric Chemistry and Physics 23, no. 7 (April 5, 2023): 4105–14. http://dx.doi.org/10.5194/acp-23-4105-2023.

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Abstract. Using the general circulation model of the middle and upper atmosphere (MUAM), a number of numerical scenarios were implemented to study the impact of individual planetary waves (PWs) on the global atmospheric circulation, including zonal wind, temperature, and residual meridional circulation (RMC). The calculations were performed for the winter conditions of the Northern Hemisphere (January–February). We show the contribution to the formation of the dynamic and temperature regimes of the MUAM made by equatorial Kelvin waves propagating to the east, as well as atmospheric normal modes (NMs) with periods from 4 to 16 d. In particular, it is demonstrated that the impact of a 5 d PW and an ultra-fast Kelvin wave (UFKW) can change the speed of circulation flows by up to 6 % in the areas of their amplitude maxima. At the same time, this effect can be significantly enhanced in certain periods of time. The presented research results are important for a deeper understanding of the mechanisms of large-scale atmospheric interactions. Despite the obviousness and simplicity of the problem, such work has not been carried out yet.

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Ern, M., and P. Preusse. "Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature space-time spectra." Atmospheric Chemistry and Physics Discussions 9, no. 2 (March 3, 2009): 5623–77. http://dx.doi.org/10.5194/acpd-9-5623-2009.

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Abstract. The quasi-biennial oscillation (QBO) of the zonal mean zonal wind is one of the most important processes in the dynamics of the middle atmosphere in the tropics. Influences of the QBO can even be found at mid and high latitudes. It is widely accepted that the phase descent of alternating tropical easterlies and westerlies is driven by atmospheric waves of both global scale (equatorial wave modes like Kelvin, equatorial Rossby, Rossby-gravity, or inertia-gravity waves), as well as mesoscale gravity waves. However, the relative distribution of the different types of waves to the forcing of the QBO winds is highly uncertain. This is the case because until recently there were no high resolution long-term global measurements in the stratosphere. In our study we estimate Kelvin wave momentum flux and the contribution of zonal wind forcing by Kelvin waves based on space-time spectra determined from both Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements as well as temperatures from European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. Peak values of total Kelvin wave zonal wind forcing found are about 0.2 m/s/day. There is good agreement between SABER and ECMWF results. Global distributions are shown and the results are compared to the total wave forcing required to balance the background atmosphere. Sometimes Kelvin wave forcing is sufficient to explain almost the whole total wave forcing required for the momentum balance during the transition from QBO easterly to westerly winds. This is especially the case during the later parts of the periods of westerly wind shear at the equator between 20 and 35 km altitude. During other phases of the westerly wind shear periods, however, the contribution of Kelvin waves can be comparably low and the missing wave forcing, which is often attributed to mesoscale gravity waves or intermediate scale waves, can be the by far dominant contribution of the QBO forcing.

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Hauchecorne, A., P. Keckhut, and M. L. Chanin. "Interannual variability and long term changes in planetary wave activity in the middle atmosphere observed by lidar." Atmospheric Chemistry and Physics Discussions 6, no. 6 (November 14, 2006): 11299–316. http://dx.doi.org/10.5194/acpd-6-11299-2006.

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Abstract. The upwelling planetary wave activity (PW) from the troposphere controls the intensity of the equator to pole transport of stratospheric ozone by the Brewer-Dobson circulation and thereby modulates the total ozone content at mid- and high-latitudes. Rayleigh lidar temperature data obtained from 1981 to 2001 at mid-latitude were used to study the interannual variability of PW activity in winter (October to April). The spectrum of stratospheric temperature fluctuations exhibits 2 peaks corresponding to 2 dominant modes of free travelling Rossby waves known as 16 day- and 12 day-waves. The 12 day-wave activity is shown to be anticorrelated with the equatorial QBO wind at 40 hPa. During the period 1981–2000 the global PW activity shows a negative trend for months October to January and a positive trend in March and April.

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van Aalst, M. K., J. Lelieveld, B. Steil, C. Brühl, P. Jöckel, M. A. Giorgetta, and G. J. Roelofs. "Stratospheric temperatures and tracer transport in a nudged 4-year middle atmosphere GCM simulation." Atmospheric Chemistry and Physics Discussions 5, no. 1 (February 21, 2005): 961–1006. http://dx.doi.org/10.5194/acpd-5-961-2005.

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Abstract. We have performed a 4-year simulation with the Middle Atmosphere General Circulation Model MAECHAM5/MESSy, while slightly nudging the model’s meteorology in the free troposphere (below 113 hPa) towards ECMWF analyses. We show that the nudging 5 technique, which leaves the middle atmosphere almost entirely free, enables comparisons with synoptic observations. The model successfully reproduces many specific features of the interannual variability, including details of the Antarctic vortex structure. In the Arctic, the model captures general features of the interannual variability, but falls short in reproducing the timing of sudden stratospheric warmings. A 10 detailed comparison of the nudged model simulations with ECMWF data shows that the model simulates realistic stratospheric temperature distributions and variabilities, including the temperature minima in the Antarctic vortex. Some small (a few K) model biases were also identified, including a summer cold bias at both poles, and a general cold bias in the lower stratosphere, most pronounced in midlatitudes. A comparison 15 of tracer distributions with HALOE observations shows that the model successfully reproduces specific aspects of the instantaneous circulation. The main tracer transport deficiencies occur in the polar lowermost stratosphere. These are related to the tropopause altitude as well as the tracer advection scheme and model resolution. The additional nudging of equatorial zonal winds, forcing the quasi-biennial oscillation, sig20 nificantly improves stratospheric temperatures and tracer distributions.

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Li, Mingzhe, and Xinan Yue. "Statistically analyzing the effect of ionospheric irregularity on GNSS radio occultation atmospheric measurement." Atmospheric Measurement Techniques 14, no. 4 (April 22, 2021): 3003–13. http://dx.doi.org/10.5194/amt-14-3003-2021.

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Abstract. The Global Navigation Satellite System (GNSS) atmospheric radio occultation (RO) has been an effective method for exploring Earth's atmosphere. RO signals propagate through the ionosphere before reaching the neutral atmosphere. The GNSS signal is affected by the ionospheric irregularity including the sporadic E (Es) and F region irregularity mainly due to the multipath effect. The effect of ionospheric irregularity on atmospheric RO data has been demonstrated by several studies in terms of analyzing singe cases. However, its statistical effect has not been investigated comprehensively. In this study, based on the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO data during 2011–2013, the failed inverted RO events occurrence rate and the bending angle oscillation, which is defined as the standard deviation of the bias between the observed bending angle and the National Center for Atmospheric Research (NCAR) climatology model bending angle between 60 and 80 km, were used for statistical analysis. It is found that at middle and low latitudes during the daytime, the failed inverted RO occurrence and the bending angle oscillation show obvious latitude, longitude, and local time variations, which correspond well with the Es occurrence features. The F region irregularity (FI) contributes to the obvious increase of the failed inverted RO occurrence rate and the bending angle oscillation value during the nighttime over the geomagnetic equatorial regions. For high latitude regions, the Es can increase the failed inverted RO occurrence rate and the bending angle oscillation value during the nighttime. There also exists the seasonal dependency of the failed inverted RO event and the bending angle oscillation. Overall, the ionospheric irregularity effects on GNSS atmospheric RO measurement statistically exist in terms of failed RO event inversion and bending angle oscillation. Awareness of these effects could benefit both the data retrieval and applications of RO in the lower atmosphere.

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46

Pfeifer, Lily S., Gerilyn S. Soreghan, Stéphane Pochat, and Jean Van Den Driessche. "Loess in eastern equatorial Pangea archives a dusty atmosphere and possible upland glaciation." GSA Bulletin 133, no. 1-2 (June 19, 2020): 379–92. http://dx.doi.org/10.1130/b35590.1.

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Abstract Carboniferous–Permian strata in basins within the Central Pangean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (Pangea assembly, ice-age collapse, megamonsoon inception). The voluminous (∼1.5 km) succession of exclusively fine-grained red beds that comprises the Permian Salagou Formation (Lodève Basin, France) has long been interpreted to record either lacustrine or fluvial deposition, primarily based on a local emphasis of subaqueous features in the upper ∼25% of the section. In contrast, data presented here indicate that the lower-middle Salagou Formation is dominated by up to 15-m-thick beds of internally massive red mudstone with abundant pedogenic features (microscale) and no evidence of channeling. Up-section, limited occurrences of ripple and hummocky cross-stratification, and mudcracks record the intermittent influence of shallow water, but with no channeling nor units with grain sizes exceeding coarse silt. These data suggest that the most parsimonious interpretation for the Salagou Formation involves eolian transport of the sediment and ultimate deposition as loess in shallow, ephemeral lacustrine environments. Provenance analyses of the Salagou Formation indicate coarse-grained protoliths and, together with geochemical proxies (chemical index of alteration [CIA] and τNa) that correspond respectively to a low degree of chemical weathering and a mean annual temperature of ∼4 °C, suggest that silt generation in this case is most consistent with cold-weathering (glacial and associated periglacial) processes in the Variscan highlands. Together with previous studies that detailed voluminous Permian loess in western equatorial Pangea, this work shows a globally unique distribution of dust at low latitudes that can be linked either directly to glaciated alpine terranes or to reworked and deflated deposits of other types (e.g., fluvial outwash) where fine-grained material was originally generated from glacial grinding in alpine systems. These results further support a revised model for early Permian climate, in which extratropical ice sheets coexisted with a semiarid tropics that may have hosted significant ice at moderate elevation.

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Clemesha, Barclay R., Paulo Prado Batista, and Dale M. Simonich. "Comments on “In search of greenhouse signals in the equatorial middle atmosphere” by Gufran Beig and S. Fadnavis." Geophysical Research Letters 29, no. 16 (August 15, 2002): 57–1. http://dx.doi.org/10.1029/2002gl015097.

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48

Jackson, D. R., and L. J. Gray. "Simulation of the semi-annual oscillation of the equatorial middle atmosphere using the Extended UGAMP General Circulation Model." Quarterly Journal of the Royal Meteorological Society 120, no. 520 (October 1994): 1559–88. http://dx.doi.org/10.1002/qj.49712052007.

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Egito, Fabio, Ricardo Arlen Buriti, Amauri Fragoso Medeiros, and Hisao Takahashi. "Ultrafast Kelvin waves in the MLT airglow and wind, and their interaction with the atmospheric tides." Annales Geophysicae 36, no. 1 (February 21, 2018): 231–41. http://dx.doi.org/10.5194/angeo-36-231-2018.

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Abstract. Airglow and wind measurements from the Brazilian equatorial region were used to investigate the presence and the effects of the 3–4-day ultrafast Kelvin waves in the MLT. The airglow integrated intensities of the OI557.7 nm, O2b(0-1) and OH(6-2) emissions, as well as the OH rotational temperature, were measured by a multichannel photometer, and the zonal and meridional wind components between 80 and 100 km were obtained from a meteor radar. Both instruments are installed in the Brazilian equatorial region at São João do Cariri (7.4∘ S, 36.5∘ W). Data from 2005 were used in this study. The 3–4-day oscillations appear intermittently throughout the year in the airglow. They were identified in January, March, July, August and October–November observations. The amplitudes induced by the waves in the airglow range from 26 to 40 % in the OI557.7 nm, 17 to 43 % in the O2b(0-1) and 15 to 20 % in the OH(6-2) emissions. In the OH rotational temperature, the amplitudes were from 4 to 6 K. Common 3–4-day oscillations between airglow and neutral wind compatible with ultrafast Kelvin waves were observed in March, August and October–November. In these cases, the amplitudes in the zonal wind were found to be between 22 and 28 m s−1 and the vertical wavelength ranges from 44 to 62 km. Evidence of the nonlinear interaction between the ultrafast Kelvin wave and diurnal tide was observed. Keywords. Atmospheric composition and structure (airglow and aurora) – meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

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de Wit, R. J., R. E. Hibbins, P. J. Espy, and E. A. Hennum. "Coupling in the middle atmosphere related to the 2013 major sudden stratospheric warming." Annales Geophysicae 33, no. 3 (March 11, 2015): 309–19. http://dx.doi.org/10.5194/angeo-33-309-2015.

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Abstract. The previously reported observation of anomalous eastward gravity wave forcing at mesopause heights around the onset of the January 2013 major sudden stratospheric warming (SSW) over Trondheim, Norway (63° N, 10° E), is placed in a global perspective using Microwave Limb Sounder (MLS) temperature observations from the Aura satellite. It is shown that this anomalous forcing results in a clear cooling over Trondheim about 10 km below mesopause heights. Conversely, near the mesopause itself, where the gravity wave forcing was measured, observations with meteor radar, OH airglow and MLS show no distinct cooling. Polar cap zonal mean temperatures show a similar vertical profile. Longitudinal variability in the high northern-latitude mesosphere and lower thermosphere (MLT) is characterized by a quasi-stationary wave-1 structure, which reverses phase at altitudes below ~ 0.1 hPa. This wave-1 develops prior to the SSW onset, and starts to propagate westward at the SSW onset. The latitudinal pole-to-pole temperature structure associated with the major SSW shows a warming (cooling) in the winter stratosphere (mesosphere) which extends to about 40° N. In the stratosphere, a cooling extending over the equator and far into the summer hemisphere is observed, whereas in the mesosphere an equatorial warming is noted. In the Southern Hemisphere mesosphere, a warm anomaly overlaying a cold anomaly is present, which is shown to propagate downward in time. This observed structure is in accordance with the temperature perturbations predicted by the proposed interhemispheric coupling mechanism for cases of increased winter stratospheric planetary wave activity, of which major SSWs are an extreme case. These results provide observational evidence for the interhemispheric coupling mechanism, and for the wave-mean flow interaction believed to be responsible for the establishment of the anomalies in the summer hemisphere.

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Journal articles on the topic 'Equatorial middle atmosphere'

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