Interannual Meridional Displacement of the East Asian Upper-tropospheric Jet Stream in Summer

On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the data from the National Centers for Environmental Prediction-Department of Energy (NCEP/DOE) reanalysis-2 from 1979 to 2002, the authors investigate the interannual variations of the EAJS's meridional displacement in summer and their associations with the variations of the South Asian high (SAH) and the western North Pacific subtropical high (WNPSH), which are dominant circulation features in the upper and lower troposhere, respectively. The result from an EOF analysis shows that the meridional displacement is the most remarkable feature of the interannual variations of the EAJS in each month of summer and in summer as a whole. A composite analysis indicates that the summer (June-July-August, JJA) EAJS index, which is intended to depict the interannual meridional displacement of the EAJS, is not appropriate because the anomalies of the zonal wind at 200 hPa (U200) in July and August only, rather than in June, significantly contribute to the summer EAJS index. Thus, the index for each month in summer is defined according to the location of the EAJS core in each month. Composite analyses based on the monthly indexes show that corresponding to the monthly equatorward displacement of the EAJS, the South Asian high (SAH) extends southeastward clearly in July and August, and the western North Pacific subtropical high (WNPSH) withdraws southward in June and August.

Effects of the East Asian Summer Monsoon on Tropical Cyclone Genesis over the South China Sea on an Interdecadal Time Scale

Tropical cyclone （TC） genesis over the South China Sea （SCS） during 1965–2004 was analyzed. The locations of TC genesis display evident seasonal changes, with the mean position of formation situated north of 15 °N in summer （June–July–August） and south of 15 °N in autumn （September–October–November）. The TC genesis in summer underwent dramatic interdecadal variations, with more and less TC frequency during 1965–1974/1995–2004 and 1979–1993, respectively. In contrast, a significant interannual variation of TC genesis with a period of ～4 years was observed in autumn. This study investigated the relationship of SCS TC genesis to the East Asian jet stream （EAJS） and the western North Pacific subtropical high （WNPSH） on an interdecadal time scale. Analysis and comparison of the impacts of the EAJS and the WNPSH on vertical wind shear changes indicate that changes in the WNPSH and EAJS intensity rather than EAJS meridional location are responsible for changes in TC genesis on an interdecadal time scale. Corresponding to a weaker EAJS, anomalous Rossby wave energy at upper levels displays equatorward propagation at midlatitudes and poleward propagation in the subtropics. This induces anomalous convergence and divergence of wave activity fluxes in East Asia around 30 °N and the SCS, respectively. The anomalous divergence of wave activity fluxes reduces easterlies at upper levels over the SCS, which is favorable to TC genesis.

Surface and Upper-Level Features Associated with Wintertime Cold Surge Outbreaks in South Korea

The surface and upper-level features associated with a sharp drop ofwintertime daily temperature over South Korea is investigated in this study. This sharp drop indaily temperature is called a cold surge and is one of the most hazardous weather phenomena in EastAsian winters. An upper-level baroclinic wave of 60° wavelength propagating eastward at a phasespeed of 12° longitude per day across the continent of northern China from the west of Lake Baikaltoward the eastern coast of China causes the outbreak of cold air over South Korea. The coolingassociated with the upper-level baroclinic jvave is found at all altitudes under the geopotentialheight-fall center near the tropopause. The development in the ridge seems to derive the earlyevolution of the eastward-propagating sinusoidal wave, whereas the trough is connected directly withthe tropospheric temperature-drop. An enhancement of the wintertime East Asian jet stream after theoutbreak of a cold surge is a response to the steep temperature gradient associated with thedeveloping baroclinic wave.

On the Onset of the South China Sea Summer Monsoon in 1998

Through analyzing the NCEP/NCAR reanalysis data, the satellite observational data and the ATLAS-2 mooring buoy observational data, it is shown that May 21 is the onset date of the South China Sea summer monsoon in 1998. There were abrupt variations in the general circulation pattern at the lower troposphere and the upper troposphere, in upper jet stream location and in the convection and rainfall over the South China Sea region corresponding to the outbreak of the South China Sea summer monsoon. It is also indicated that there was rainfall in the southern China coastal region before onset of summer monsoon, but it resulted from the (cold) front activity and cannot be regarded as the sign of summer monsoon outbreak in the South China Sea. Key words Onset - South China Sea summer monsoon - General circulation pattern, Jet stream - Convection This work was supported by the State Key Project for Research—“ The South China Sea Monsoon Experiment”, CAS (KZ951-B1-408) and CNSF (49823002).

云南西双版纳2021年一次冬季暴雨天气浅析

利用ERA5再分析资料、高空探测和地面观测资料等对2021年2月7—9日云南西双版纳一次冬季暴雨天气进行分析。分析结果表明:(1)稳定持久位于90°E附近南支槽和脊线位于15°N附近西太平洋副热带高压(以下简称副高)、稳定维持经向型环流是有利的大尺度环流条件;(2)中低层切变线和700 hPa西南低空急流将充沛的水汽输送至西双版纳上空急剧辐合抬升是暴雨发生的主要机制;(3)逆温干暖盖储能作用使得水汽和热量积聚和500 hPa干冷空气侵入是有利的热力层结不稳定条件;(4)暴雨位于700 hPa急流核前沿辐合区内,暴雨移动路径与急流移动方向相一致;水汽强辐合区和暴雨落区有很好的对应关系。

夏季新疆降水异常与印度降水的关系

利用1960—2003年6~8月新疆75个气象站降水量、印度地区降水量和NCEP/NCAR再分析资料,分析了新疆夏季降水量与印度降水之间的关系,以及印度降水变化与新疆降水异常联系的可能的物理机制。研究表明,印度降水与新疆夏季降水量之间存在显著的反相关关系,它们之间的线性相关系数为-0.39。夏季印度降水变化与其西北侧的西亚—中亚地区对流层平均温度呈显著正相关,从而与对流层高层南亚高压中心东西振荡和高压西部强弱,西亚地区副热带西风急流（西亚急流）强度和南北位置振荡,500 hPa伊朗高压南北和东西振荡密切联系,夏季印度降水变化通过与这些影响新疆降水的系统联系而与新疆夏季降水呈显著的反相关关系。Eliassen-Palm通量（EP通量）的动力学诊断分析进一步表明,印度季风偏强（偏弱）导致南亚高压西侧由南向北进入亚洲西风急流入口处的波作用通量偏强（偏弱）,使得西亚急流偏强（偏弱）、偏北（偏南）。

华南前汛期盛期中国东部降水异常模态的环流特征及成因分析

根据1958-2011年中国东部（105°E以东）316站逐日降水观测资料及环流逐日再分析资料,利用统计分析、物理量诊断等方法,探讨华南前汛期盛期（5月21日至6月10日）中国东部降水异常模态及对应大气环流特征和可能成因。分析发现,华南前汛期盛期中国东部降水异常表现为两个相互独立的降水模态：第一模态为华南全区一致型,当其时间系数为正（负）时,整个华南降水偏多（少）,黄河中游降水偏少（多）;第二模态为华南沿海东部型,当其时间系数为正（负）时,华南沿海东部降水偏多（少）,而长江中下游降水偏少（多）。研究发现,造成华南前汛期盛期两个降水型的环流特征有明显差异：全区一致型降水主要受东亚高空西风急流南北偏移、副热带高压脊东西偏移及低层南海北部异常风场影响;沿海东部型降水主要由东亚高空西风急流强弱及位置异常、副热带高压强弱变化、低层日本以南西太平洋异常风场导致。此外,两个降水型对应环流异常的成因也各不相同。第一模态中高层环流异常由丝绸之路遥相关型导致,低层风场异常在5月下旬由阿拉伯海向下游传播的风场异常波列引起,在6月上旬则由西太平洋西移的异常反气旋（气旋）造成。第二模态的中高层环流异常先后由极地—欧亚遥相关型、环球遥相关型引起,低层风场异常由高层环流异常的动力作用造成。两降水型均存在整层深厚的垂直运动,但第一模态的垂直运动在高层闭合且对应显著的辐合辐散异常,第二模态则不具有上述特征。

索马里急流和南亚高压对印度夏季风爆发的协同作用

【目的】探讨索马里急流和南亚高压对印度夏季风(Indian Summer Monsoon,ISM)爆发产生的协同作用。【方法】基于ECMWF欧洲中期天气预报中心第五代再分析资料(ERA5)提供的逐日数据,结合印度气象局对ISM爆发日期(即印度次大陆最南端的喀拉拉邦降水骤升的日期)的统计数据采用功率谱分析、偏相关分析和滑动相关等统计学方法,分析索马里急流和南亚高压对ISM爆发的协同作用。【结果】ISM爆发前1候至当候,印度地区对流层高层南亚高压的范围和强度不断扩大,同时对流层低层索马里急流的强度和范围不断增强,使阿拉伯海地区的西南气流不断增强,将阿拉伯海地区大量水汽输送至印度大陆,在这样有利的条件下,印度南部降水量剧增,ISM爆发;当5月下旬的南亚高压、索马里急流以及阿拉伯海地区水汽通量和气旋性环流均显著偏强时,ISM会提前爆发,降水也会异常偏多。【结论】ISM爆发日期受到索马里急流和南亚高压两者协同作用的影响,而并非单独受到某个系统的影响。

广东前汛期一次锋前暖区暴雨触发机制分析

利用ECMWF的ERAdata再分析资料、Micaps实况等数据,对2015年5月22—24日的广东大范围强降雨过程进行分析,结果表明:该次过程是一次典型的华南前汛期降雨过程,过程中存在明显的两种性质降雨,即粤西北由南支短波槽、低涡、切变线造成的锋面型暴雨,而珠江口及其东侧的暖区暴雨主要是由西南低空急流脉冲引起的;珠江口及其东侧的暖区暴雨的触发机制主要为中尺度能量锋、地面辐合线以及地形等。

2012年3月新疆大范围暴雨雪天气诊断分析

2012年3月18—22日新疆出现了春季寒潮、大范围雨雪风沙天气,本文应用常规气象资料和NCEP1°X1°格点资料,从南北疆暴雨雪落区预报角度出发,诊断分析了乌鲁木齐周围暴雪、南疆西部山区持续暴雪和南疆西部多次明显降雨的高低空环流配置、热动力条件和水汽条件,初步归纳了上述雨雪落区的预报思路及其相应的预报指标。

0212号强热带风暴过程分析

02 1 2号强热带风暴“北冕”对闽南粤东地区造成严重影响。利用天气形势、T2 1 3数值预报产品和本站气象要素等资料 ,对“北冕”强热带风暴进行了综合分析。分析表明 ,引导气流的调整 ,高空辐散场的抽气作用使“北冕”路径改变 ,强度加强 ;低空偏南风急流的存在和维持源源不断输送水汽 ,强烈的辐合上升运动 。

南秦岭枇库沟地区铅锌矿矿床控矿因素分析

枇库沟铅锌矿地处南秦岭山柞镇旬多金属成矿区南秦岭公馆-回龙镇汞、锑、金、银、铅、锌多金属成矿带上,产于中泥盆统杨岭沟组炭质灰岩与上泥盆统落家河组炭质千枚岩的接触带中靠灰岩一侧,两种岩性之间呈断层接触。通过对区域地质、矿体地质、矿床成因以及控矿因素等方面的分析、研究,提出了铅锌矿矿床成因为喷流-沉积型,根据喷流-沉积型铅锌矿成矿理论及成矿元素的分带性理论指导找矿,结合目前钻探揭露情况及钡元素的分布范围,确定了该区铅锌矿目前处于顶部相,为寻找深部矿体、潜力区块提供了理论指导。

2016年华南地区一次持续性异常降水过程分析

为了解持续性异常降水的天气过程,利用NOAA提供的逐日降水数据和欧洲中心提供的逐日气象数据集,分析了2016年6月10-17日华南地区持续性降水过程的降水实况和相应的环流特征及物理量场。结果表明:(1)此次降水过程中,华南大范围地区累计降水量超过100 mm,相当于日总降水量在10 mm以上,逐日降水大值区从东南逐渐往西北方向移动;(2)200 hPa上南亚高压的东伸以及高空急流南侧气流拖曳产生的切变而形成反气旋,使华南地区高空处于辐散场中;500 hPa上西太平洋副热带高压(简称副高)缓慢北移,其西北侧与北上的暖湿气流汇合带动水汽在华南交汇,华南地区降水区位于副高西北侧;(3)700 hPa低层南支槽前暖湿气流稳定维持,整层水汽通量矢量的输送大值区与850 hPa西太平洋反气旋西北侧配合良好,孟加拉湾和南海为此次持续性降水过程提供了充足的水源;(4)高低空配置呈现为一深厚系统,有利于此次持续性异常降水的发生、发展和维持。

内蒙古河套地区久旱转雨诊断分析

2008年冬季至2009年初春,内蒙古中西部地区降水量持续偏少,农田土壤出现旱象。2009年3月1日,一个短波槽自新疆东部移入内蒙古西部地区,同时,低纬度地区的南支系统迅速建立,高空低槽与南风急流汇合,在内蒙古河套地区产生了小-中雨夹雪的降水过程,极大地缓解了内蒙古中西部地区的冬春旱情。文中利用常规高空、地面观测、数值产品等资料,对此次久旱转雨天气过程的机制进行了诊断分析。