Role of intra-seasonal oscillations on monsoon floods and droughts over India     

O. S. R. U. Bhanu Kumar  S. Ramalingeswara Rao  S. Ranganathan  S. S. Raju 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(1):21-28

Aim of this diagnostic study is to investigate the impact of intra-seasonal oscillations in terms of number, duration and intensity on rainfall during June through September, 1979–2006. Analysis of wavelet spectra for winds at 850 hPa field for monsoon period reveals number and duration of oscillations, which exercise profound influence on monsoon rainfall. Results indicate that four to six oscillations appear in normal rainfall or flood cases, while two or three oscillations are identified in the years of drought episodes. Though total duration of above oscillations is varied from 25 to 85 days, the duration is short (20 to 35 days) obviously in the years of less number of oscillations and also the number of oscillations are directly related to the monsoon rainfall. The coefficient of correlation between them is 0.56, which is significant at 1% level. To examine the strength of intra-seasonal oscillations in terms of different indices on seasonal rainfall is investigated. The Madden and Julian Oscillation Index shows an inverse relationship with rainfall, where as a direct relationship is noticed between Monsoon Shear Index and rainfall for the study period. Both results are significant at 5% level. To consolidate the above statistical relationships, seasonal circulation changes in the contrasting years of monsoon rainfall have been examined; present study reveals that anomaly negative outgoing longwave radiation is noticed over most of Arabian Sea, Indian sub-continent and the Bay of Bengal during June through September in flood year (1988). But opposite convective activity is true in drought year (2002). Similarly the spatial U-850 hPa field distribution showed much stronger monsoon winds in 1988, while zonal circulation was very weak in 2002. Such differences are observed in the anomaly zonal wind field at 200 hPa also. Over the monsoon region U-850 hPa field is almost a mirror image of U-200 hPa distribution of wind field. Finally annual cycles of U-850 and U-200 hPa fields reflect striking difference at 200 hPa level during the summer monsoon period in flood and drought years.  相似文献   

Preface to the Arctic Ocean special issue     

《Ocean Modelling》2013

  相似文献   

一种预测西北太平洋热带气旋逐月演变的新统计模型     

吕硕  胡轶佳  孙源  钟中 《气象科学》2024,44(1):59-72

本文提出一种月尺度西北太平洋热带气旋生成频数(Western North Pacific Tropical Cyclone Frequency, WNPTCF)预测的新方法。该方法利用全球次表层海温(Subsurface Sea Temperature Anomaly, SubSSTA)和中国气象局国家气候中心发布的130项监测指数,构建了既考虑热力强迫因子、又考虑大气动力因子,既考虑同期海洋强迫,又考虑前期海洋和大气影响的集成预测模型。利用该预测模型对2011—2020年6—10月逐月WNPTCF进行独立样本检验预测,准确率达70%以上,说明该预测模型对WNPTCF的逐月演变预测的效果良好。该预测模型对ENSO信号较强年份的WNPTCF预测效果要好于ENSO信号不强的年份,原因在于在ENSO信号不强的年份,SubSSTA可预报性较低,非线性变率大,海洋对WNPTC的强迫作用弱。  相似文献   

基于Argo历史观测的南海海盆尺度中层流场研究   总被引：1，自引：0，他引：1  

王晓慧  张卫民  王品强  杨俊  王辉赞 《海洋学报》2018,40(6):1-14

针对南海海域海流环境复杂、中层实测数据量少的现状，本文基于2006-2016年布放在南海海域的114个Argo剖面浮标的卫星定位等信息，采用基于背景流和惯性流外推的最小二乘方法，获取南海海域1 200 m深中层流场信息，并采用Divand变分插值的方法形成网格化季节流场。结果表明:（1）针对南海中层（1 200 m）流场，单个Argo浮标可以刻画出具体的中尺度结构，如越南沿岸的反气旋涡，半径约为120 km，最大流速约为9.6 cm/s，平均流速为5.3 cm/s；（2） Argo网格化流场表明海盆尺度中层流场南海南部为反气旋环流结构，北部为气旋式环流，同时在吕宋海峡口存在从南海至太平洋的水体交换；（3）将该流场信息与HYCOM和YoMaHa'07两种资料对比，吻合度较高，与HYCOM再分析资料的偏差分布趋近于正态分布，海流的东西向分量的均方根误差为3.28 cm/s，南北向分量的均方根误差为3.26 cm/s。总体而言，利用Argo轨迹资料能够有效地反演出南海地区海盆尺度的中层环流特征。  相似文献   

利用一种改进的算法对中国高分三号同极化SAR图像反演的有效波高的验证   总被引：1，自引：1，他引：0  

盛叶新  邵伟增  诸帅  孙建  袁新哲  李水清  史剑  左军成 《海洋学报(英文版)》2018,37(6):1-10

Chinese Gaofen-3(GF-3) is the first civilian satellite to carry C-band(5.3 GHz) synthetic aperture radar(SAR).During the period of August 2016 to December 2017, 1 523 GF-3 SAR images acquired in quad-polarization(vertical-vertical(VV), horizontal-horizontal(HH), vertical-horizontal(VH), and horizontal-vertical(HV)) mode were recorded, mostly around China's seas. In our previous study, the root mean square error(RMSE) of significant wave height(SWH) was found to be around 0.58 m when compared with retrieval results from a few GF-3 SAR images in co-polarization(VV and HH) with moored measurements by using an empirical algorithm CSAR_WAVE. We collected a number of sub-scenes from these 1 523 images in the co-polarization channel,which were collocated with wind and SWH data from the European Centre for Medium-Range Weather Forecasts(ECMWF) reanalysis field at a 0.125° grid. Through the collected dataset, an improved empirical wave retrieval algorithm for GF-3 SAR in co-polarization was tuned, herein denoted as CSAR_WAVE2. An additional 92 GF-3 SAR images were implemented in order to validate CSAR_WAVE2 against SWH from altimeter Jason-2, showing an about 0.52 m RMSE of SWH for co-polarization GF-3 SAR. Therefore, we conclude that the proposed empirical algorithm has a good performance for wave retrieval from GF-3 SAR images in co-polarization.  相似文献   

基于TIGGE资料的西太平洋热带气旋多模式集成预报方法比较   总被引：6，自引：2，他引：4  

张涵斌  智协飞  王亚男  陈静  张雷  李靖 《气象》2015,41(9):1058-1067

基于TIGGE资料中CMA、ECMWF、JMA和NCEP四中心2010、2011和2012年3年的资料,采用集合平均（EMN）、加权集合平均（WEMN）、消除偏差集合平均（BREM）和加权消除偏差集合平均（即超级集合,SUP）四种方法,对西太平洋地区热带气旋路径与中心气压进行时效为24、48、72、96和120 h的多模式集成预报,评估了不同单中心预报结果,并分析了不同多模式集成预报方法的特点,对比了不同多模式集成方法的效果。结果表明,对于热带气旋路径和中心气压预报,各中心预报技巧不同,其中3年的CMA预报效果均较差,2010、2011年的ECMWF预报和2012年的NCEP预报效果最优;总体上几种多模式集成方法在120 h预报时效内均优于单模式预报,其中EMN作为一种最简单的集成预报方法,具有一定的局限性,而WEMN由于给不同单模式预报赋予了权重,因此相对于EMN能够得到更好的多模式集成预报结果;BREM方案由于消除了模式预报中的系统性偏差,因此集成预报效果也优于EMN;由于去除了模式预报偏差,同时给不同模式赋予了权重,SUP方案得到的集成预报效果最优。  相似文献   

深度学习方法在北极海冰预报中的应用          下载免费PDF全文

刘泉宏  张韧  汪杨骏  闫恒乾 《大气科学学报》2022,45(1):14-21

在全球气候变暖背景下,北极海冰呈现出逐年消融的趋势.海冰的消融给北极的开发利用带来了重要机遇,例如北极航道通航潜力的显现.但北极航道开通还面临着诸多困难,尤其是海冰变化机理的复杂性和海冰预报的不确定性以及由此带来的航行安全风险.近年来,深度学习因其强大的非线性拟合能力,逐渐在海冰预报领域中崭露头角.本文对近年来深度学习...  相似文献   

Impacts of the Lowest Model Level Height on Tropical Cyclone Intensity and Structure简   总被引：1，自引：0，他引：1  

MA Zhanhong  FEI Jianfang  HUANG Xiaogang  and CHENG Xiaoping 《大气科学进展》2014,31(2):421-434

Variable thicknesses in the lowest half-ηmodel level （LML） are often used in atmospheric models to compute surface diagnostic fields such as surface latent and sensible heat fluxes.The effects of the LML on simulated tropical cyclone （TC）evolution were investigated in this study using the Weather Research and Forecasting （WRF） model.The results demonstrated notable influences of the LML on TC evolution when the LML was placed below 12 m.The TC intensification rate decreased progressively with a lowering of the LML,but its ultimate intensity change was relatively small.The maximum 10-m winds showed different behavior to minimum sea level pressure and azimuthally-averaged tangential winds,and thus the windpressure relationship was changed accordingly by varying the LML.The TC circulation was more contracted in association with a higher LML.Surface latent heat fluxes were enhanced greatly by elevating the LML,wherein the wind speed at the LML played a dominant role.The changes in the wind speed at the LML were dependent not only on their profile differences,but also the different heights they were taken from.Due to the enhanced surface heat fluxes,more intense latent heat release occurred in the eyewall,which boosted the storm＇s intensification.A higher LML tended to produce a stronger storm,and therefore the surface friction was reinforced,which in turn induced stronger boundary layer inflow together with increased diabatic heating.  相似文献   

西太平洋副高的东西进退与东亚夏季风系统的相互影响与关联   总被引：2，自引：1，他引：1  

余丹丹  ;张韧  ;赵越超  ;万雷  ;郭小璇 《南京气象学院学报》2014,(3):304-312

利用1980-2010年NCEP/NCAR再分析资料和美国NOAA向外长波辐射（outgoing longwave radiation,OLR）资料,根据关键区500 hPa位势高度的变化定义了西太平洋副高东西位置指标,利用该指标围绕东亚夏季风系统开展分析,详细对比了夏季6月、7月副高东西向活动异常时,季风区相应的环流及对流活动差异.结果表明：副高东西位置的年际变化反映了亚洲夏季风的强弱变化,副高偏西（东）年,南海夏季风偏弱（强）,副热带夏季风偏强（弱）;副高的东西进退与东亚夏季风系统成员之间相互影响、相互制约;副高偏西年,南亚高压偏东、偏强,季风槽不发展、强度偏弱,西风带长波槽发展加深,南半球马斯克林高压和澳大利亚高压减弱,越赤道气流减弱,而副高偏东年情况则反之.  相似文献   

地形强迫对大气长波调整的可能影响     

张立凤  余沛龙  黎爱兵  顾明逸 《大气科学》2014,38(4):804-812

地形作为大气的外部强迫,其动力和热力作用对波动结构演变及极端天气出现都有不能忽视的作用。本文通过数值求解考虑地形强迫的β平面正压准地转位势涡度方程,探讨了地形强迫作用对大气长波调整的可能影响,结果表明:同非线性作用和纬向非均匀基流作用一样,无基流情形下具有纬向差异的地形分布影响了大气长波结构的演变,也能强迫出大气长波调整现象。大气长波调整依赖于地形的高度和地形分布,地形越高,长波越容易出现波数的调整;地形波数越大,即地形结构复杂,越不易出现波数变化。大气长波调整还与纬度有关,纬度越高,β越小,地形强迫作用越突出,长波调整容易出现;反之,低纬度以β效应为主的线性波动不易出现波数调整。大气长波调整对波动初始波动的振幅不敏感,但依赖于波动的初始结构。此外,有基流作用时,地形强迫还是诱发定常波的重要因素,且定常波流场结构依赖于地形高度分布,与波动初始结构无关。  相似文献