2018年冬季浙江连续阴雨天气东亚高空急流特征分析

利用欧洲中心ERA 5月平均资料和日资料分析2018年冬季浙江罕见连续阴雨寡照期间东亚高空副热带急流和温带急流的位置和强度特征,分析连阴雨异常天气期间东亚高空急流在位置和强度上的部分异常特征.结果表明:东亚高空急流活动区域以青藏高原上空为分界线,分为南北两支,南支副热带急流活动区域沿青藏高原南侧呈准纬向分布,北支温带急...     

冬季200 hPa西太平洋急流异常与海表加热和大气瞬变扰动的关系探讨

使用ERA40和NCEP/NCAR再分析资料探讨了冬季200 hPa东亚沿海到太平洋上空西风急流(WPJS)异常与北太平洋冬季海表加热和天气尺度瞬变扰动异常的关系。研究表明,东亚—北太平洋中纬度地区冬季海气系统与天气尺度瞬变扰动活动有十分密切的局地空间匹配型。通过进一步的诊断分析发现,与冬季200 hPa WPJS 3种不同的空间异常型相伴随的北太平洋海表加热异常型和天气尺度扰动异常型也截然不同:第1种空间异常型的西风异常主要发生于日界线以东的中东太平洋上空,而WPJS主体处却没有显著的异常发生,此时,在赤道中东太平洋和北太平洋海盆中部地区有异常的海表加热,西风异常区的瞬变扰动也发生异常变化;第2种空间异常型表现为WPJS主体区西风急流强度的变化,并与黑潮表面加热异常以及WPJS出口处的瞬变扰动活动异常有密切关系;第3种空间异常型显示出WPJS的南北移动,它与以35°N为界的西北太平洋南部和北部海区海表加热异常的正负对比有关系,与此同时,瞬变扰动活动也存在相应的南北移动。一个可能的联系是海表加热异常与大尺度平均气流异常密切关联,从而改变了中纬度大气斜压性,由此导致了瞬变扰动异常,后者通过大气内部动力过程对冬季WPJS异常起维持作用。     

夏季东亚西风急流扰动异常与副热带高压关系研究

利用1979—2003年NCEP/NCAR月平均再分析资料, 探讨夏季 (6—8月) 200 hPa东亚西风急流扰动异常与南亚高压和西太平洋副热带高压的关系。研究指出:夏季200 hPa东亚西风急流扰动动能加强 (减弱), 东亚西风急流位置偏南 (偏北)、强度偏强 (偏弱); 东亚西风急流扰动动能强弱不仅与北半球西风急流强弱和沿急流的定常扰动有关, 而且还与东亚地区高、中、低纬南北向的扰动波列有关, 亚洲地区是北半球中纬度环球带状波列异常最大的区域。夏季200 hPa东亚西风急流扰动动能加强 (减弱), 南亚高压的特征为位置偏东 (偏西)、强度加强 (减弱); 西太平洋副热带高压的特征为位置偏南 (偏北)。东亚环流特别是500 hPa西太平洋副热带高压对东亚西风带扰动异常的响应由高空东亚西风急流南侧的散度场及其对流层中下层热带和副热带地区的垂直速度距平场变化完成。     

冬季东亚副热带急流和温带急流协同变化与我国冷空气活动的关系

利用NCEP/NCAR再分析资料和地面台站气温观测资料,分析了冬季东亚副热带急流(EASJ)和东亚温带急流(EAPJ)强度变化特征及其与我国境内冷空气活动的关系。以(45°N~60°N,70°E~110°E)和(27.5°N~37.5°N,130°E~160°E)区域平均的300 hPa全风速分别表征冬季EAPJ和EASJ的强度,将两支急流的强度变化分为四种情况:EAPJ和EASJ同强(SS)、同弱(WW)、以及强弱(SW)、弱强(WS)。分析四种急流强度变化情形下中国境内冷空气活动强度、路径、持续时间以及源地的不同特征,发现当EAPJ和EASJ均强时,冷空气从内蒙古中东部入侵,主要影响华北、东北和东部沿海地区,强度较弱,持续时间短,冷空气源地位于新地岛以东的洋面及陆地上;当EAPJ和EASJ均弱时,冷空气从新疆北部入侵,影响我国大部分地区,强度强,持续时间长,冷空气源地位于巴尔喀什湖西部;当EAPJ强,EASJ弱时,冷空气从我国东北入侵,主要影响我国东北部,中国南部降温不明显,冷空气强度较强,持续时间短,冷空气源地位于中、西西伯利亚地带;当EAPJ弱,EASJ强时,冷空气从内蒙古中部入侵,进而影响华北和我国东部地区,但冷空气强度较弱,冷空气源地位于贝加尔湖的西侧。进一步分析急流强度四种变化情形下的环流特征发现,EAPJ、EASJ均弱时,西伯利亚高压偏强,阿留申低压偏弱,东亚大槽偏深,中国东部的偏北风强,而EAPJ弱、EASJ强时,尽管西伯利亚高压和阿留申低压偏强,东亚大槽偏深,但中国东部的偏北风并不是很强,而另两种情况时,西伯利亚高压较弱,东亚大槽也较弱,中国东部的偏北风偏弱。     

冬季东亚副热带急流和温带急流协同变化与我国冷空气活动的关系

利用NCEP/NCAR再分析资料和地面台站气温观测资料,分析了冬季东亚副热带急流（EASJ）和东亚温带急流（EAPJ）强度变化特征及其与我国境内冷空气活动的关系。以（45°N～60°N, 70°E～110°E）和（27.5°N～37.5°N,130°E～160°E）区域平均的300 hPa全风速分别表征冬季EAPJ和EASJ的强度,将两支急流的强度变化分为四种情况：EAPJ和EASJ同强（SS）、同弱（WW）、以及强弱（SW）、弱强（WS）。分析四种急流强度变化情形下中国境内冷空气活动强度、路径、持续时间以及源地的不同特征,发现当EAPJ和EASJ均强时,冷空气从内蒙古中东部入侵,主要影响华北、东北和东部沿海地区,强度较弱,持续时间短,冷空气源地位于新地岛以东的洋面及陆地上;当EAPJ和EASJ均弱时,冷空气从新疆北部入侵,影响我国大部分地区,强度强,持续时间长,冷空气源地位于巴尔喀什湖西部;当EAPJ强,EASJ弱时,冷空气从我国东北入侵,主要影响我国东北部,中国南部降温不明显,冷空气强度较强,持续时间短,冷空气源地位于中、西西伯利亚地带;当EAPJ弱,EASJ强时,冷空气从内蒙古中部入侵,进而影响华北和我国东部地区,但冷空气强度较弱,冷空气源地位于贝加尔湖的西侧。进一步分析急流强度四种变化情形下的环流特征发现,EAPJ、EASJ均弱时,西伯利亚高压偏强,阿留申低压偏弱,东亚大槽偏深,中国东部的偏北风强,而EAPJ弱、EASJ强时,尽管西伯利亚高压和阿留申低压偏强,东亚大槽偏深,但中国东部的偏北风并不是很强,而另两种情况时,西伯利亚高压较弱,东亚大槽也较弱,中国东部的偏北风偏弱。     

冬季东亚-西太平洋西风急流基本结构及其异常的诊断分析

利用ECMWF再分析资料ERA40中的逐月风场和温度场资料,对冬季位于东亚-西太平洋上空的西风急流(WJS)基本结构和异常特征进行了分析.结果表明,一年当中最为强盛的冬季200 hPa WJS主体稳定地分布于东亚至西太平洋上空,向上向下均迅速减小.在对流层中高层,从东亚沿海到太平洋上空的西风系统较为深厚,低层对应着显著的大气斜压区.通过对东亚-西太平洋地区冬季200 hPa纬向风异常的EOF分解得到三种异常空间分布型,第一模态的中纬度西风异常主要发生于日界线以东的中东太平洋上空,第二、三模态则分别对应WJS主体发生增强/减弱和位置的北/南移动.WJS的这三种空间异常形态与中纬度低层大气斜压性的三种异常分布型相对应.通过对冬季WJS长期趋势的初步分析发现,近二十年来,洋面上空西风急流有增强趋势,这是由于急流轴南侧洋面上空大气存在显著增暖趋势、而急流轴北侧洋面上空却有变冷的趋势所造成的.     

夏季东亚高空西风急流气候特征分析

利用NCEP/NCAR全球再分析风场资料定义了西风急流强度指数和位置指数,然后利用EOF方法对西风急流进行了进一步的分析,分析了高空西风急流的空间分布特征,从强度和位置两方面分析了西风急流与东亚环流及其与海温的关系。分析表明： EOF第一模态反映了东亚高空急流的位置指数,第二模态反映了高空急流的强度指数。东亚高空急流与对流层大气环流包括南亚高压,西太平洋副热带高压,东亚夏季风存在着密切关系,其气候变化与热带副热带东太平洋、印度洋海温密切相关。     

冬季东亚副热带西风急流变化及其与海表温度的关系

利用1957-2002年ERA-40月平均再分析资料以及不同海域(全球、热带外、热带、热带印度洋—太平洋、热带印度洋和热带太平洋等)1950-2000年逐月观测海表温度,驱动NCARCAM3全球大气环流模式,根据模拟结果,分析讨论了冬季东亚副热带西风急流的变化特征及其与海表温度异常的关系.表明:1957-2001年冬季东亚副热带西风急流有增强的趋势,且具有准3 a的显著周期.热带海表温度异常,特别是热带太平洋海表温度异常对东亚副热带西风急流变化有重要影响,即当热带太平洋海表温度升高时,东亚副热带西风急流增强.     

东亚—北太平洋大气环流和瞬变扰动的年代际变化

用NCEP/NCAR再分析资料,分析了东亚—北太平洋大气环流、大气斜压性和天气尺度瞬变扰动活动的年代际变化特征。东亚—北太平洋地区低层大气温度和比湿及高层的西风急流都存在明显的年代际变化。西风年代际异常与大气斜压性年代际异常之间有密切联系。夏季北太平洋北部到西伯利亚高原上空的天气尺度瞬变扰动活动年代际增强,但夏季低层瞬变热力和瞬变水汽强迫的年代际异常对北太平洋中纬度低层平均温度和比湿年代际异常的作用并不显著。冬季,西太平洋西风急流年代际增强与急流下方大气斜压性年代际增加相一致,使该地区瞬变扰动年代际增强,增强的瞬变扰动将更多能量传送给西风气流,巩固了西风急流的年代际异常。年代际尺度上冬季异常的瞬变热力强迫和瞬变水汽强迫对低层大气温度和比湿异常有显著的削弱作用。     

东亚副热带西风急流位置变化与亚洲夏季风爆发的关系

利用1961～2000年的NCEP/NCAR候平均再分析资料,初步探讨了季节转换期间东亚副热带西风急流南北和东西向位置变化与亚洲季风爆发之间的联系。结果表明,亚洲夏季风爆发伴随着东亚副热带西风急流轴线的北跳和急流中心西移,急流轴北跳至35°N以北的青藏高原上空,南支西风急流消失,亚洲季风环流形势建立。南海季风爆发早年,低纬的东风向北推进的时间早,到达的纬度偏北,中纬的西风急流强度偏弱,季风爆发晚年则相反。同时,南海夏季风爆发早年,青藏高原上空急流核出现较早,西太平洋上空急流核减弱较快,急流中心“西移”较早。而在南海夏季风爆发晚年,西太平洋上空的急流核减弱较迟,青藏高原上空急流核形成偏晚,急流中心“西移”较迟。此外,急流中心东西向位置和强度变化与江淮流域梅雨的开始和结束也有密切关系。     

Diagnostic Comparison of Wintertime East Asian Subtropical Jet and Polar-Front Jet: Large-Scale Characteristics and Transient Eddy Activities

Diagnostic comparison of the East Asian subtropical jet (EASJ) and polar-front jet (EAPJ) in winter season is carried out by using the ERA-40 dataset. The large-scale circulation characteristics and synopticscale transient eddy activities (STEAs) associated with the EASJ and EAPJ are examined. The results show that the EASJ and EAPJ in the upper-level monthly mean data have no clear geographical border, while the distribution of the numbers of jet cores from the daily data exhibits a distinct boundary at the latitudes of the northern Tibetan Plateau. The two areas with large numbers of jet cores correspond to the EASJ and EAPJ regions. The analysis of STEAs over the East Asian region shows a spatial match of STEAs with the EASJ and EAPJ in winter: the strong EASJ is located within the weak southern branch of the STEA while the relatively weak EAPJ appears within the active northern branch of the STEA, indicating that the EAPJ is the jet coexisting with the STEA. Further analysis shows two anomalous modes of the winter EAPJ: the anomalous anticyclonic/cyclonic circulation and the weakened/strengthened local westerly wind. The large-scale circulation anomalies in the Northern Hemisphere related to the first mode are concentrated in the Eurasian mid to high latitudes, and are also influenced by the anomalous circulation in the upstream area. When the local westerly wind over the EAPJ region is weakened/strengthened, the westerly jet in the eastern part of the EASJ and that in the western Pacific region show opposite variations. The corresponding anomalous atmospheric circulation demonstrates the Eurasian (EU) pattern. The EAPJ anomalies are also closely linked with the STEA anomalies over East Asia. The anomalies in the northern branch of the STEA propagate as a wave train along its axis into the East Asian coastal waters, and then migrate eastward to the oceanic region. However, the ones near the southern branch are trapped over the eastern part of East Asia and its coastal waters at 200 hPa.     

THE FEATURES OF EAST ASIAN JET STREAM IN PERSISTENT SNOWSTORM AND FREEZING RAIN PROCESSES OVER SOUTHERN CHINA IN EARLY 2008

Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) daily reanalysis data and the upper-level objective analysis data provided by the Meteorological Information Comprehensive Analysis and Process System (MICAPS), the feature of the spatio-temporal variation of the East Asian jet stream (EAJS) in persistent snowstorm and freezing rain processes over southern China in January 2008 have been investigated. Each of the storm events was closely linked with the extraordinarily abnormal variations of East Asian subtropical jet (EASJ) and East Asian polar front jet (EAPJ) at that time. The stronger EASJ with abnormally northward position of the jet axis corresponded to the more intense storm event with broader ranges and longer duration time. The heavy freezing-rain-and-snow event occurred over the region where a strong southerly wind of EASJ prevailed. Meanwhile, the westerly and northerly winds of the EAPJ were significantly intensified, which were also closely related to the beginning, enhancement, and ending of the heavy snowfall. The meridional component of the EAPJ was dominated by the northerly wind during the snowstorm. Thus, the intensification of the snowstorm was attributed to both the strengthening of the meridional wind of EAPJ and the southerly wind of EASJ. Further analysis indicated that wind speed and the zonal wind of the two jets exhibited precursory signals about half a month prior to this extreme event, and the precursory signals were found in the meridional components of the two jets about 20 days preceding the event. The sudden weakening of the meridional component of EASJ and the zonal component of EAPJ signified the ending of this persistent snowstorm.     

冬季东亚高空急流季节内协同变化及对我国东部降水的影响

利用ERA-Interim再分析资料,采用滤波和合成分析等统计方法,分析了冬季东亚高空急流的季节内协同变化以及对我国东部降水的影响,结果表明:在季节内尺度(10~90天)中,东亚地区冬季300 hPa逐日纬向风主要表现为准双周振荡(10~30天)。300 hPa低频纬向风异常整体向东传播,高纬的低频纬向风异常向南传播,低纬低频纬向风没有明显经向传播特征。伴随低频纬向西风从里海附近开始向东移动至西北太平洋上空,温带急流向东再向东南移动并且强度先增强再减弱,副热带急流位置没有明显变化,强度演变特征与温带急流变化相反。降水异常对300 hPa风场低频振荡有显著响应,低频降水主要出现在我国东部,随时间向东移动,移至西太平洋附近消失;受低频风场影响,温带急流偏强,副热带急流偏弱时,我国东部高空辐合,地面表现为低频高压,整层有较强下沉气流,地面为东北风控制,不易产生降水;温带急流偏弱,副热带急流偏强时,青藏高原北侧整层一致东风异常,南侧整层一致西风异常,使我国东部高空辐散,地面受低频低压控制,我国东部产生整层上升运动,并且有西南风水汽输送,水汽辐合,我国东部出现低频降水正异常。      

FGOALS-s2 simulation of upper-level jet streams over East Asia: Mean state bias and synoptic-scale transient eddy activity

Upper-level jet streams over East Asia simulated by the LASG/IAP coupled climate system model FGOALS-s2 were assessed, and the mean state bias explained in terms of synoptic-scale transient eddy activity (STEA). The results showed that the spatial distribution of the seasonal mean jet stream was reproduced well by the model, except that following a weaker meridional temperature gradient (MTG), the intensity of the jet stream was weaker than in National Centers for Environment Prediction (NCEP)/Department of Energy Atmospheric Model Inter-comparison Project Ⅱ reanalysis data (NCEP2). Based on daily mean data, the jet core number was counted to identify the geographical border between the East Asian Subtropical Jet (EASJ) and the East Asian Polar-front Jet (EAPJ). The border is located over the Tibetan Plateau according to NCEP2 data, but was not evident in FGOALS-s2 simulations. The seasonal cycles of the jet streams were found to be reasonably reproduced, except that they shifted northward relative to reanalysis data in boreal summer owing to the northward shift of negative MTGs. To identify the reasons for mean state bias, the dynamical and thermal forcings of STEA on mean flow were examined with a focus on boreal winter. The dynamical and thermal forcings were estimated by extended Eliassen-Palm flux (E) and transient heat flux, respectively. The results showed that the failure to reproduce the tripolar-pattern of the divergence of E over the jet regions led to an unsuccessful separation of the EASJ and EAPJ, while dynamical forcing contributed less to the weaker EASJ. In contrast, the weaker transient heat flux partly explained the weaker EASJ over the ocean.     

The effect of transient eddy on interannual meridional displacement of summer East Asian subtropical jet

Using ERA-40 reanalysis daily data for the period 1958-2002,this study investigated the effect of transient eddy(TE) on the interannual meridional displacement of summer East Asian subtropical jet(EASJ) by conducting a detailed dynamical diagnosis.The summer EASJ axis features a significant interannual coherent meridional displacement.Associated with such a meridional displacement,the TE vorticity forcing anomalies are characterized by a meridional dipole pattern asymmetric about the climatological EASJ axis.The TE vorticity forcing anomalies yield barotropic zonal wind tendencies with a phase meridionally leading the zonal wind anomalies,suggesting that they act to reinforce further meridional displacement of the EASJ and favor a positive feedback in the TE and time-mean flow interaction.However,The TE thermal forcing anomalies induce baroclinic zonal wind tendencies that reduce the vertical shear of zonal wind and atmospheric baroclinicity and eventually suppress the TE activity,favoring a negative feedback in the TE and time-mean flow interaction.Although the two types of TE forcing tend to have opposite feedback roles,the TE vorticity forcing appears to be dominant in the TE effect on the time-mean flow.     

夏季东亚高空急流与太平洋-日本遥相关型的关系

利用NCEP/NCAR和NOAA月平均资料,采用奇异值分解方法分析了夏季东亚高空纬向风场和西北太平洋海表温度(SST)的耦合关系,并据此研究了东亚副热带高空急流和太平洋-日本(Pacific-Japan,PJ)遥相关型的可能联系。合成分析结果表明,东亚副热带高空急流正模态年,急流偏南偏强,对流层上层南亚高压增强东进,中层西太平洋副热带高压加强西伸,菲律宾周边海域SST升高,中纬度黑潮延伸体区SST降低,菲律宾海和热带西太平洋地区对流活动偏弱,日本海和黑潮延伸体海区对流活动增强,对应PJ遥相关型的负位相;而东亚副热带高空急流负模态年,急流偏北偏弱,对流层上层南亚高压减弱西退,中层西太平洋副热带高压减弱东撤,菲律宾周边SST降低,中纬度黑潮延伸体区SST升高,菲律宾海和热带西太平洋地区对流活动强盛,日本海和黑潮延伸体海区对流活动减弱,对应PJ遥相关型的正位相。由于夏季东亚副热带高空急流活动与PJ遥相关型存在关联,PJ遥相关型可能是东亚副热带高空急流响应太平洋海温异常的纽带。     

The East Asian Upper-Tropospheric Jet Streams and Associated Transient Eddy Activities Simulated by a Climate System Model BCC_CSM1.1

In this paper, major features of the upper-tropospheric jet streams simulated by a coupled Climate System Model BCC_CSM1.1 are evaluated through comparison with the NCEP/NCAR reanalysis. The jet streams consist of the East Asian subtropical jet (EASJ) and the East Asian polar-front jet (EAPJ). Associated stationary wave and synoptic-scale transient eddy activities (STEA) are also examined. The results show that the climatological positions of the westerly jet streams are well captured by BCC_CSM1.1, but with slight intensity biases. Statistics from the 6-h model outputs reveal that the jet core number (JCN) of ESPJ is significantly underestimated. Examination of the simulated seasonal evolution of the westerly jet stream indicates that the model has produced a westward movement of the EASJ core in May, one month earlier than that in the reanalysis. Analysis of stationary wave activities shows that the overestimated meridional wind component may have caused considerable enhancement of meridional momentum and heat transport. The stationary Rossby wave represented by the wave activity flux at the southern flank of the Tibetan Plateau is favorable to the growth of asymmetric zonal wind and the multiple-center pattern of JCN. Unlike the stationary wave heat flux transport, the model tends to systematically generate weaker transient heat flux over East Asia. Further analysis of STEA exhibits a general consistent pattern between the simulation and the reanalysis, while the intensity of the northern STEA branch associated with the EAPJ is greatly reduced. The deficiencies of eddy momentum and heat flux transport and accompanied eddy forcing may contribute to the biases of the simulated upper-tropospheric jet streams, suggesting the potential importance of midlatitude internal atmospheric dynamics in shaping the tropospheric general circulation, which is not yet fully and accurately resolved in the current BCC_CSM1.1.     

江淮地区夏季持续性降水特征及其与东亚高空急流的联系

围绕1960—2011年江淮地区夏季持续性降水展开对单站和区域性持续4 d及以上降水的分析,并探讨其与东亚高空急流的联系。研究发现,近年来持续4 d及以上降水的频数有增多趋势,且在江淮地区其影响范围有逐渐扩大的趋势。持续4 d及以上单站降水频数EOF分析的前两个模态均与极锋急流和陆上副热带急流的协同作用有关。当极锋急流北移和陆上副热带急流南移时,冷暖空气易在江淮地区的西北部相遇,利于较长持续时间的单站降水在该地区发生,易于导致第一模态的全场一致变化。与第二模态相关的高空急流配置表现为陆上副热带急流的减弱和极锋急流的增强,两支急流的强弱配置通过影响水汽输送和上升运动导致江淮地区形成南湿北干的异常型。进一步研究了江淮地区持续4 d及以上区域性降水与急流协同作用的关系发现,在事件发生之前极锋急流显著增强,副热带急流略有增强。伴随着两支急流的变化,西北太平洋副热带高压和北风产生持续性异常,利于冷暖空气活动,导致持续时间较长的区域性降水发生