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| 1 | Planetary Wave Reflection and Its Impact on Tropospheric Cold Weather over Asia during January 2008显示文摘Reflection of stratospheric planetary waves and its impact on tropospheric cold weather over Asia during January 2008 were investigated by applying two dimensional Eliassen–Palm(EP) flux and three-dimensional Plumb wave activity fluxes. The planetary wave propagation can clearly be seen in the longitude–height and latitude–height sections of the Plumb wave activity flux and EP flux, respectively, when the stratospheric basic state is partially reflective. Primarily, a wave packet emanating from Baffin Island/coast of Labrador propagated eastward, equatorward and was reflected over Central Eurasia and parts of China, which in turn triggered the advection of cold wind from the northern part of the boreal forest regions and Siberia to the subtropics. The wide region of Central Eurasia and China experienced extreme cold weather during the second ten days of January 2008, whereas the extraordinary persistence of the event might have occurred due to an anomalous blocking high in the Urals–Siberia region. | Debashis NATH CHEN Wen WANG Lin MA Yin | 2014 | Advances in Atmospheric Sciences2014，31，4： | 8 |
| 2 | Impact of Planetary Wave Reflection on Tropospheric Blocking over the Urals–Siberia Region in January 2008显示文摘Planetary wave reflection from the stratosphere played a significant role in changing the tropospheric circulation pattern over Eurasia in mid-January 2008. We studied the 2008 event and compared with composite analysis(winters of 2002/2003,2004/2005, 2006/2007, 2007/2008, 2010/2011 and 2011/2012), when the downward coupling was stronger, by employing time-lagged singular value decomposition analysis on the geopotential height field. In the Northern Hemisphere, the geopotential fields were decomposed into zonal mean and wave components to compare the relative covariance patterns. It was found that the wavenumber 1(WN1) component was dominant compared with the wavenumber 2(WN2) component and zonal mean process. For the WN1 field, the covariance was much higher(lower) for the negative(positive) lag, with a prominent peak around +15 days when the leading stratosphere coupled strongly with the troposphere. It contributed to the downward coupling due to reflection, when the stratosphere exhibited a partially reflective background state. We also analyzed the evolution of the WN1 anomaly and heat flux anomaly, both in the troposphere and stratosphere, during January–March 2008. The amplitude of the tropospheric WN1 pattern reached a maximum and was consistent with a downward wave coupling event influenced by the stratospheric WN1 anomaly at 10 h Pa. This was consistent with the reflection of the WN1 component over Eurasia, which triggered an anomalous blocking high in the Urals–Siberia region. We further clarified the impact of reflection on the tropospheric WN1 field and hence the tropospheric circulation pattern by changing the propagation direction during and after the event. | Debashis NATH Wen CHEN | 2016 | Advances in Atmospheric Sciences2016，33，3： | 4 |
| 3 | Investigating the Dominant Source for the Generation of Gravity Waves during Indian Summer Monsoon Using Ground-based Measurements显示文摘Over the tropics,convection,wind shear(i.e.,vertical and horizontal shear of wind and/or geostrophic adjustment comprising spontaneous imbalance in jet streams) and topography are the major sources for the generation of gravity waves.During the summer monsoon season(June-August) over the Indian subcontinent,convection and wind shear coexist.To determine the dominant source of gravity waves during monsoon season,an experiment was conducted using mesosphere-stratosphere-troposphere(MST) radar situated at Gadanki(13.5 N,79.2 E),a tropical observatory in the southern part of the Indian subcontinent.MST radar was operated continuously for 72 h to capture high-frequency gravity waves.During this time,a radiosonde was released every 6 h in addition to the regular launch(once daily to study low-frequency gravity waves) throughout the season.These two data sets were utilized effectively to characterize the jet stream and the associated gravity waves.Data available from collocated instruments along with satellite-based brightness temperature(TBB) data were utilized to characterize the convection in and around Gadanki.Despite the presence of two major sources of gravity wave generation(i.e.,convection and wind shear) during the monsoon season,wind shear(both vertical shear and geostrophic adjustment) contributed the most to the generation of gravity waves on various scales. | Debashis NATH 陈文 | 2013 | Advances in Atmospheric Sciences2013，30，1： | 3 |
| 4 | Relationship Between Soil Temperature in May over Northwest China and the East Asian Summer Monsoon Precipitation显示文摘This study investigates the relationship between the soil temperature in May and the East Asian summer monsoon(EASM)precipitation in June and July using station observed soil temperature data over Northwest China from 1971 to 2000.It is found that the memory of the soil temperature at 80-cm depth can persist for at least 2 months,and the soil temperature in May is closely linked to the EASM precipitation in June and July.When the soil temperature is warmer in May over Northwest China,less rainfall occurs over the Yangtze and Huaihe River valley but more rainfall occurs over South China in June and July.It is proposed that positive anomalous soil temperature in May over Northwest China corresponds to higher geopotential heights over the most parts of the mainland of East Asia,which tend to weaken the ensuing EASM.Moreover,in June and July,a cyclonic circulation anomaly occurs over Southeast China and Northwest Pacific and an anticyclonic anomaly appears in the Yangtze and Huaihe River valley at 850 hPa.All the above tend to suppress the precipitation in the Yangtze and Huaihe River valley.The results also indicate that the soil temperature in May over Northwest China is closely related to the East Asia/Pacific(EAP)teleconnection pattern,and it may be employed as a useful predictor for the East Asian summer monsoon rainfall. | 王远皓 陈文 张井勇 Debashis NATH | 2013 | Acta meteorologica Sinica2013，27，5： | 2 |
| 5 | Impact of Drought on Agriculture in the Indo-Gangetic Plain,India显示文摘In this study, we investigate the spatiotemporal characteristics of drought in India and its impact on agriculture during the summer season(April–September). In the analysis, we use Standardized Precipitation Evapotranspiration Index(SPEI)datasets between 1982 and 2012 at the six-monthly timescale. Based on the criterion SPEI <-1, we obtain a map of the number of occurrences of drought and find that the humid subtropical Upper Middle Gangetic Plain(UMGP) region is highly drought-prone, with an occurrence frequency of 40%–45%. This UMGP region contributes at least 18%–20% of India's annual cereal production. Not only the probability of drought, but the UMGP region has become increasingly drought-prone in recent decades. Moreover, cereal production in the UMGP region has experienced a gradual declining trend from 2000 onwards, which is consistent with the increase in drought-affected areas from 20%–25% to 50%–60%, before and after 2000,respectively. A higher correlation coefficient(-0.69) between the cereal production changes and drought-affected areas confirms that at least 50% of the agricultural(cereal) losses are associated with drought. While analyzing the individual impact of precipitation and surface temperature on SPEI at 6 month timescale [SPEI(6)] we find that, in the UMGP region,surface temperature plays the primary role in the lowering of the SPEI. The linkage is further confirmed by correlation analysis between SPEI(6) and surface temperature, which exhibits strong negative values in the UMGP region. Higher temperatures may have caused more evaporation and drying, which therefore increased the area affected by drought in recent decades. | Reshmita NATH Debashis NATH Qian LI Wen CHEN Xuefeng CUI | 2017 | Advances in Atmospheric Sciences2017，34，3： | 2 |
| 6 | Long-Term Trend in Potential Vorticity Intrusion Events over the Pacific Ocean: Role of Global Mean Temperature Rise显示文摘In this study, we examine a long-term increasing trend in subtropical potential vorticity(PV) intrusion events over the Pacific Ocean in relation to the global mean temperature rise, based on multiple reanalysis datasets. The frequency of the PV intrusions is closely related to the upper-tropospheric equatorial westerly duct and the subtropical jet(STJ). An overall strengthening of the westerly duct and weakening of the STJ are found to be driven by the warming-induced strengthening of Walker circulation and regional changes in Hadley circulation on multi-decadal timescale, leading to an increase in the PV intrusion frequency over the tropics. The results are robust in all datasets.The multi-decadal strengthening in the Pacific Walker circulation is consistent with the global mean temperature rise.In this way, the PV intrusions are correlated with the warming related global mean temperuate rise. When the interannual variability of ENSO is removed from the intrusion time series, the long-term trend in PV intrusions due to external forcing associated with anthropogenic warming(global mean temperature rise) becomes clearer. The link between the global mean temperature rise and intrusion frequency is further verified by performing a correlation analysis between the two. The significant(> 95%) correlation coefficient is 0.85, 0.94, 0.84, 0.83, and 0.84 for ERA-40,ERA-Interim, NCEP-NCAR, JRA-55, and JRA-25, respectively. This unequivocally indicates that the global mean temperature rise can explain around 69%–88% of the variance related to the long-term increase in PV intrusion frequency over the Pacific Ocean. | Debashis NATH Wen CHEN Xiaoqing LAN | 2017 | Journal of Meteorological Research2017，31，5： | 1 |
| 7 | 大气非绝热加热在夏季风季引起的从里海向南亚和东亚的波列显示文摘本研究发现在夏季风季,存在从阿拉伯半岛北部和里海至印支恒河平原的一个波列,该波列进一步沿喜马拉雅山麓伸展到青藏高原东部。利用NCEP–NCAR再分析资料计算的大气非绝热加热通量(1000hPa至500hPa平均)在里海及其周围地区表现出从1979至2018年的显著的减少趋势。而海平面气压在里海地区则呈现出大约0.1hPayr^-1的增加趋势,并在该区域形成一个高压的辐散中心。这个辐散中心正与里海上空850hPa的一个反气旋环流趋势相配。减少的大气非绝热通量通过地面气压在辐散中心附近的增加可以调控当地的大气环流,并进而激发传播向南亚和东亚的波列。该波列可以将925 hPa的水汽从里海向东南输送到南亚季风和东亚季风区。 | CHOUDHURY Devanil NATH Debashis CHEN Wen | 2020 | Atmospheric and Oceanic Science Letters2020，13，5： | 0 |
| 8 | 基于静稳天气下气球探空实验的中国沙漠地区沙尘气溶胶的垂直分布(英文)显示文摘塔克拉玛干沙漠是亚洲沙尘气溶胶的重要源地。为探讨塔克拉玛干地区沙尘气溶胶的理化特性与时空变化,研究其环境与气候效应,本文分析了四个季节在中国敦煌(塔克拉玛干沙漠内)取得的探空气球观测数据,包括气溶胶的数浓度、粒径分布、质量浓度及在西风主导下的水平输送通量。气溶胶数浓度的垂直廓线显示,来自沙漠地区的矿物粒子对局地环境与气候有重要影响,且所有季节都存在长距离输送。粒子谱分布显示局地有大量粗粒子输入。结果说明,源于塔克拉玛干沙漠的沙尘气溶胶的背景输送有着重要的科学意义,需进一步研究其对东亚和西太平洋地区环境与气候的影响。 | HABIB Ammara CHEN Bin SHI Guangyu IWASAKA Yasunobu NATH Debashis KHALID Bushra TAN Saichun MAHMOOD Tariq JIAO Reguang NTWALI Didier | 2019 | Atmospheric and Oceanic Science Letters2019，12，1： | 0 |
| 9 | Improvement of a Snow Albedo Parameterization in the Snow–Atmosphere–Soil Transfer Model:Evaluation of Impacts of Aerosol on Seasonal Snow Cover显示文摘The presence of light-absorbing aerosols(LAA) in snow profoundly influence the surface energy balance and water budget.However,most snow-process schemes in land-surface and climate models currently do not take this into consideration.To better represent the snow process and to evaluate the impacts of LAA on snow,this study presents an improved snow albedo parameterization in the Snow–Atmosphere–Soil Transfer(SAST) model,which includes the impacts of LAA on snow.Specifically,the Snow,Ice and Aerosol Radiation(SNICAR) model is incorporated into the SAST model with an LAA mass stratigraphy scheme.The new coupled model is validated against in-situ measurements at the Swamp Angel Study Plot(SASP),Colorado,USA.Results show that the snow albedo and snow depth are better reproduced than those in the original SAST,particularly during the period of snow ablation.Furthermore,the impacts of LAA on snow are estimated in the coupled model through case comparisons of the snowpack,with or without LAA.The LAA particles directly absorb extra solar radiation,which accelerates the growth rate of the snow grain size.Meanwhile,these larger snow particles favor more radiative absorption.The average total radiative forcing of the LAA at the SASP is 47.5Wm^(-2).This extra radiative absorption enhances the snowmelt rate.As a result,the peak runoff time and 'snow all gone' day have shifted 18 and 19.5 days earlier,respectively,which could further impose substantial impacts on the hydrologic cycle and atmospheric processes. | efang zhong qian li shufen sun wen chen shangfeng chen debashis nath | 2017 | Advances in Atmospheric Sciences2017，34，11： | 0 |
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