Precipitation Structures of a Thermal Convective System Happened in the Central Western Subtropical Pacific Anticyclone   总被引：5，自引：1，他引：5       下载免费PDF全文

Fu Yunfei  Feng Jingyi  Zhu Hongfang  Li Rui  Liu Dong 《Acta Meteorologica Sinica》2006,20(2):232-243

In this paper, characteristics of precipitating clouds in a thermal convective system (TCS) occurred in the southeastern mainland of China at 15:00 BT (Beijing time) on August 2, 2003 in the central western subtropical Pacific anticyclone (WSPA) is studied by using TRMM tropical rainfallmeasuring mission PR (precipitution radar) and IR Infrared radiation measurements. The precipitating cloud structures in both horizontal and vertical, relationship among storm top, cloud top, and surface rain rate are particularly analyzed. Results show that a strong ascending air at 500 hPa and a strong convergence of moisture flux at 850 hPa in the central WSPA supply necessary conditions both in dynamics and moisture for the happening of the TCS precipitation. The TRMM PR observation shows that the horizontal scale of the most TCS precipitating clouds is about 30-40 km, their averaged vertical scale is above 10 km, and the maximum reaches 17.5 km. The maximum rain rate near surface of those TCS clouds is beyond 50 mm h-1. The mean rain profile of the TCS clouds shows that its maximum rain rate at 5 km altitude is 1 km lower than the estimated freezing level of the environment. Compared with the mesoscale convective system (MCS) of "98.7.20", both systems have the same altitude of the maximum rain rate displayed from both mean rain profiles, but the TCS is much deeper than the MCS. From the altitude of the maximum rain rate to near surface, profiles show that rain rate reducing in the TCS is faster than that in the MCS, which implies a strong droplet evaporation process occurring in the TCS. Relationship among cloud top, storm top, and surface rain rate analysis indicates a large variation of cloud top when storm top is lower. On the contrary, the higher the storm top, the more consistent both cloud top and storm top. And, the larger the surface rain rate, the higher and more consistent for both cloud top and storm top. At the end, results expose that area fractions of non-precipitating clouds and clear sky are 86% and 2%, respectively. The area fraction of precipitating clouds is only about 1/8 that of non-precipitating clouds.  相似文献   

一次200hPa辐散环流演变与海洋天气系统变化关系的分析     

孙世刚  喻世华 《海洋预报》1997,14(1):37-43

本文分析了１９８０年７月１７～２８日逐日２００ｈＰａ辐散环流的变化过程。讨论了辐散环流变化与西太平洋副热带高压、台风活跃与中断、南海赤道反气旋形成与消失之间的关系，揭示了一些有意义的事实  相似文献   

Large-scale Circulation Control of the Occurrence of Low-level Turbulence at Hong Kong International Airport     

Marco Y.T.LEUNG  Wen ZHOU  Chi-Ming SHUN  Pak-Wai CHAN 《大气科学进展》2018,35(4):435-444

This study identifies the atmospheric circulation features that are favorable for the occurrence of low-level turbulence at Hong Kong International Airport [below 1600 feet(around 500 m)]. By using LIDAR data at the airport, turbulence and nonturbulence cases are selected. It is found that the occurrence of turbulence is significantly related to the strength of the southerly wind at 850 h Pa over the South China coast. On the other hand, the east–west wind at this height demonstrates a weak relation to the occurrence. This suggests that turbulence is generated by flow passing Lantau Island from the south. The southerly wind also transports moisture from the South China Sea to Hong Kong, reducing local stability. This is favorable for the development of strong turbulence. It is also noted that the strong southerly wind during the occurrence of low-level turbulence is contributed by an anomalous zonal gradient of geopotential in the lower troposphere over the South China Sea. This gradient is caused by the combination of variations at different timescales. These are the passage of synoptic extratropical cyclones and anticyclones and the intraseasonal variation in the western North Pacific subtropical high. The seasonal variation in geopotential east of the Tibetan Plateau leads to a seasonal change in meridional wind, by which the frequency of low-level turbulence is maximized in spring and minimized in autumn.  相似文献   

Why Does Extreme Rainfall Occur in Central China during the Summer of 2020 after a Weak El Ni?o?     

Congxi FANG  Yu LIU  Qiufang CAI  Huiming SONG 《大气科学进展》2021,38(12):2067-2081

In summer 2020, extreme rainfall occurred throughout the Yangtze River basin, Huaihe River basin, and southern Yellow River basin, which are defined here as the central China (CC) region. However, only a weak central Pacific (CP) El Ni?o happened during winter 2019/20, so the correlations between the El Ni?o–Southern Oscillation (ENSO) indices and ENSO-induced circulation anomalies were insufficient to explain this extreme precipitation event. In this study, reanalysis data and numerical experiments are employed to identify and verify the primary ENSO-related factors that cause this extreme rainfall event. During summer 2020, unusually strong anomalous southwesterlies on the northwest side of an extremely strong Northwest Pacific anticyclone anomaly (NWPAC) contributed excess moisture and convective instability to the CC region, and thus, triggered extreme precipitation in this area. The tropical Indian Ocean (TIO) has warmed in recent decades, and consequently, intensified TIO basinwide warming appears after a weak El Ni?o, which excites an extremely strong NWPAC via the pathway of the Indo-western Pacific Ocean capacitor (IPOC) effect. Additionally, the ENSO event of 2019/20 should be treated as a fast-decaying CP El Ni?o rather than a general CP El Ni?o, so that the circulation and precipitation anomalies in summer 2020 can be better understood. Last, the increasing trend of tropospheric temperature and moisture content in the CC region after 2000 is also conducive to producing heavy precipitation.  相似文献   

1998年7月南亚高压影响西太平洋副热带高压短期变异的过程和机制   总被引：12，自引：0，他引：12  

任荣彩刘屹岷  吴国雄 《气象学报》2007,65(2):183-197

利用逐日NCEP/NCAR再分析资料,对1998年7月二度梅期间南亚高压影响西太平洋副热带高压短期变异的过程和作用机制进行了诊断。结果发现,梅雨间歇期副高单体异常向西、向北发展期间,高层南亚高压曾离开高原上空东移(伸)至120°E以东;南亚高压返回高原上空时,中层副热带高压减弱南落,两者有相向然后相背移动的趋势。进一步研究这两个高压系统密切关联的原因又发现,南亚高压通过两种作用机制影响中层副高的短期变异:南亚高压在东移过程中,高空负涡度平流动力强迫的下沉运动在中层副高区域产生辐散,从动力上影响副高内的负涡度发展;另一方面,强烈下沉运动伴随的绝热加热效应又有利于纬向温度梯度维持,有利于南北风发展,从热力上间接影响西太副高的发展。最后,利用R42L9/LASG大气环流模式进行敏感性数值试验,通过改变高空南亚高压东移产生的负涡度效应,发现中层副热带高压区确有强迫产生的动力辐散和绝热加热出现,并对应副高的异常加强,成功地验证了诊断所揭示的1998年夏季副高短期变异过程的两种机制。  相似文献   

夏季北印度洋海温异常对西北太平洋低层反气旋异常的影响   总被引：7，自引：0，他引：7  

黄刚  胡开明 《南京气象学院学报》2008,31(6):749-757

采用1957—2002年850 hPa风场的ERA-40再分析资料,分析得知西北太平洋低层环流存在着明显的年际变化。这种年际变化表征了西北太平洋夏季风的年际变化,并且会影响东亚夏季风的变化。用Hadley海表面气压以及海表温度资料诊断得到,这种夏季西北太平洋反气旋异常（WPAC,northwest Pacific anomalous anticyclone）的年际变化与北印度洋同期海表温度变化存在很好的相关。用偏相关方法消除N ino3.4信号的同期线性影响,这种同期相关更加显著,而西南热带印度洋的同期海温与WPAC的相关并不显著。数值试验结果表明,北印度洋存在正海温异常时,北印度洋降水偏多,同时伴随着西北太平洋反气旋异常。当只有西南热带印度洋有正海温异常时,北印度洋会出现东风异常且降水减少,而西北太平洋有弱的气旋异常。数值模式结果与观测数据的诊断结果相吻合,说明当夏季北印度洋海表温度为正异常时,可能会产生西北太平洋反气旋异常。  相似文献   

Three-Dimensional Structure and Low-Level Features of the North Pacific Storm Track from 1999 to 2005          下载免费PDF全文

FU Gang  BI Wei  GUO Jingtian 《Acta Meteorologica Sinica》2009,23(3):276-289

A storm track is a region in which synoptic eddy activities are statistically most prevalent and intense. At daily weather charts, it roughly corresponds to the mean trajectories of cyclones and anticyclones. In this paper, the recent QuikSCAT （Quick Scatterometer） satellite sea winds data with a 0.5°×0.5° horizontal resolution, and the NCEP （National Centers for Environmental Prediction） 10-m height Gaussian grid wind data and pressure-level reanalysis data, are employed to document the spatial structure of the North Pacific storm track in winter （January） and summer （July） from 1999 to 2005. The results show that in winter the North Pacific storm track is stronger, and is located in lower latitudes with a distinct zonal distribution. In summer, it is weaker, and is located in higher latitudes. Based on the horizontal distributions of geopotential height variance at various levels, three-dimensional schematic diagrams of the North Pacific storm track in winter and summer are extracted and presented. Analyses of the QuikSCAT wind data indicate that this dataset can depict the low-level storm track features in detail. The double storm tracks over the Southern Oceans found by Nakamura and Shimpo are confirmed. More significantly, two new pairs of low-level storm tracks over the North Pacific and the North Atlantic are identified by using this high-resolution dataset. The pair over the North Pacific is focused in this paper, and is named as the ＂subtropical storm track＂ and the ＂subpolar storm track＂, respectively. Moreover, statistical analyses of cyclone and anticyclone trajectories in the winters of 1999 to 2005 reveal as well the existence of the low-level double storm tracks over the North Pacific.  相似文献   

东风带扰动热力特征及其对西太副高东退影响的个例分析   总被引：1，自引：0，他引：1  

孙建元  朱伟军  姚秀萍 《高原气象》2013,32(3):707-717

利用NCEP/NCAR再分析资料,分析了2003年6月22—25日西太平洋副热带高压(下称西太副高)西伸东退时热带东风带扰动附近大气热源的分布和演变特征,以及对西太副高西伸东退的影响和机制。结果表明,高层东风带扰动附近的非绝热效应分布和强度的突变影响西太副高西伸东退,当扰动中心西侧非绝热加热加强,扰动中心东侧西太副高区域冷却加强时,西太副高东退;潜热释放造成的非绝热效应在高层变化最为明显,非绝热变化的主要影响因子是垂直运动。总结了西太副高东退过程与东风带扰动系统热力联系的可能概念模型:东风带扰动处大气热力结构变化引发经向风场异常,使东风带扰动西侧高层有北风发展和强烈的上升运动,扰动东侧有整层的南风发展,有助于西太副高异常东退。因此,西太副高的西伸东退与热带东风带扰动系统的热力作用密切关联。  相似文献   

惠州市5月高温特征及异常高温成因分析     

林汇丰  张玫  刘昌  陈雷文  刘建龙  陈芳丽  李明华  无 《气象研究与应用》2020,(1):16-20

利用1953-2018年NCEP/NCAR日平均再分析资料和惠州市区逐日气象要素数据,统计分析了惠州市5月高温的气候特征,及1963年和2018年异常高温的成因。结果表明,惠州市5月出现高温天气年频率为15%;近66a间,惠州市5月日极端最高和月平均气温年变化均呈不显著的增加变化趋势;1963年和2018年5月出现了罕见的持续长时间的高温酷热天气,1963年以15d和38.1℃位列第一;5月气温异常偏高主要成因为对流层高层南亚高压中心偏东偏北,副热带高压长时间控制广东上空,同时低层弱的西南气流影响,形成了对流层高层辐合-低层辐散的高低空配置,有利于惠州高温天气的形成和维持。  相似文献   

热力适应、过流、频散和副高Ⅱ．水平非均匀加热与能量频散   总被引：3，自引：2，他引：3  

刘屹岷  吴国雄等 《大气科学》2001,25(3):317-328

利用位涡方程和热力适应原理，讨论了因非绝热加热的空间不均匀性导致的大气动力特征的变化，进一步阐明了副热带地区的深对流凝结潜热加热的垂直非均匀性使副热带高压中低空出现在低源区以东，在高空出现在热源区以西。在此基础上，深入研究了水平非均匀加热对大气环流的影响。结果表明加热区以北，虽然非绝热加热消失，但存在加热的水平梯度在西风环流的背景下在高低层造成深厚的负涡度强迫。因而高层热源北部边界附近的西风向南偏转进入加热区，造成加热区北部边界及其以北发生次级辐散；低层热源区的南风发生反气旋偏转，汇入加热区外的西风气流中，造成低层加热区北部边界及其以北发生次级辐合。结果该区域产生了垂直上升运动及负的涡度强迫源，对应着异常强烈的反气旋环流。该负涡强度迫源还通过能量散射，在西风带中以Rossby波的形式向中高纬传播，影响中高纬地区的异常环流型。  相似文献