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1.
亚——非季风区非绝热加热与夏季环流关系的诊断研究 总被引：4，自引：0，他引：4
基于热力适应理论,本文利用 ＮＣＥＰ／ ＮＣＡＲ再分析资料对撒哈拉沙漠、青藏高原和孟加拉湾地区的非绝热加热与夏季环流进行了诊断研究。在非洲撒哈拉沙漠地区,以感热输送为主的加热仅局限于近地面层,边界层以上的大气则以辐射冷却占优势。因而除了边界层内存在着浅薄的正涡度和微弱的上升运动以外,整个对流层几乎都维持负涡度并盛行下沉运动。对于青藏高原地区,强大的表面感热通量引起的垂直扩散是近地面大气加热的主要分量,与大尺度上升运动相关的凝结潜热对低层大气的加热也有一定的贡献。长波辐射造成的对流层中、上层大气的冷却则主要由深对流潜热释放来补偿。夏季高原地区总非绝热加热是正值,且最大加热率出现在边界层内。低空大气辐合产生正涡度,而中、高层大气辐散伴有较强的负涡度。因而高原盛行上升运动,最大上升运动位于近地面层。夏季孟加拉湾地区的深对流凝结潜热释放远大于长波辐的冷却作用,因而整个对流层几乎都保持较强的非绝热加热。４００ｈＰａ层附近的最大加热率引起３００－４００ｈＰａ最强的上升运动。对流层上层是负涡度区,而中、低层为正涡度区。结果还表明,垂直和水平辐散环流与大气的热源和热汇区密切相联：在高层,辐散气流从热源区流向热汇区;在低层则相 相似文献
2.
Utilizing data from NCEP/ NCAR reanalysis, the summertime atmospheric diabatic heating due to different physical processes
is investigated over the Sahara desert, the Tibetan Plateau, and the Bay of Bengal. Atmospheric circulation systems in summer
over these three areas are also studied. Thermal adaptation theory is employed to explain the relationship between the circulation
and the atmospheric diabatic heating.
Over the Sahara desert, heating resulting from the surface sensible heat flux dominates the near-surface layer, while radiative
cooling is dominant upward from the boundary layer. There is positive vorticity in the shallow boundary layer and negative
vorticity in the middle and upper troposphere. Downward motion prevails over the Sahara desert, except in the shallow near—surface
layer where weak ascent exists in summer. Over the Tibetan Plateau, strong vertical diffusion resulting from intense surface
sensible heat flux to the overlying atmosphere contributes most to the boundary layer heating, condensation associated with
large—scale ascent is another contributor to the lower layer heating. Latent heat release accompanying deep convection is
critical in offsetting longwave radiative cooling in the middle and upper troposphere. The overall diabatic heating is positive
in the whole troposphere in summer, with the most intense heating located in the boundary layer. Convergence and positive
vorticity occur in the shallow near—surface layer and divergence and negative vorticity exist deeply in the middle and upper
troposphere. Accordingly, upward motion prevails over the Plateau in summer, with the most intense rising occurring near the
ground surface. Over the Bay of Bengal, summertime latent heat release associated with deep convection exceeds longwave radiative
cooling, resulting in intense heating in almost the whole troposphere. The strongest heating over the Bay of Bengal is located
around 400 hPa, resulting in the most intense rising occurring between 300 hPa and 400 hPa, and producing positive vorticity
in the lower troposphere and negative vorticity in the upper troposphere. It is also shown that the divergent circulation
is from a heat source region to a sink region in the upper troposphere and vice versa in lower layers.
This work was jointly supported by “ National Key Program for Developing Basic Sciences” G1998040904 by NSFC projects 49805003,
49635170, 49823002, and 49825504. 相似文献
3.
冬季西伯利亚高压动力结构的研究 总被引：16，自引：1，他引：16
本文研究了冬季西伯利亚高压建立时期的动力结构。研究得到,在高压建立前期,对流层中以正涡度为主。低层和高层有弱的辐合,中层是辐散;相应在700hPa以下是上升,以上是下沉。但当反气旋发展时,高层为正涡度和辐合气流,低层为负涡度和辐散气流,整层为下沉运动。这表明对流层中、上层的强质量辐合是导致西伯利亚高压发展的一个重要因子。涡度方程的诊断表明,西伯利亚高压区负涡度的出现和加强是对流层中、上层负涡度平流和低层散度项的作用。 另外,西伯利亚高压热平衡计算表明,对流层有深厚的冷却层(热汇)。这种非绝热冷却将在对流层中导致深厚的下沉运动,从而引起中高层的辐合,低层的辐散,有利于高压的加强。因而西伯利亚高压是在动力和热力因子共同作用下形成的。 相似文献
4.
赤道反气旋的合成结构和涡度收支 总被引：1，自引：0，他引：1
本文通过普查1979—1983年7—9月在10°S—15°N、90°E—140°E范围内的赤道反气旋活动情况,从中选出15个强度和范围较接近的赤道反气旋进行综合分析,得到它们的平均三维结构特征。结果表明,赤道反气旋是一个暖性的中低层系统。反气旋环流与涡度、散度及垂直运动有较好的配合。在赤道反气旋的低层,环流中心为负涡度区和辐散区,并与下沉运动区相对应,四周为正涡度和辐合区,以及上升运动区。高层正好相反。加热场与垂直运动场有较好的对应关系,中心区是干绝热下沉增温区。对涡度收支的计算表明,中低层有负涡度积累,上层有正涡度积累,局地涡度变化主要决定于散度项、平流项和垂直输送项。 相似文献
5.
6.
初夏南海台风的结构分析 总被引：1，自引：0，他引：1
根据对8005号南海台风的结构分析,初步得到以下几点:1)南海台风各物理量的水平分布不对称。其湿度中心和暧中心分别位于700hPa和300—200hPa。垂直运动在台风迅速发展时达到极值。2)台风范围内的对流层高层和低层分别存在东北风和西南风大值区,U分量的垂直切变零线在台风发展阶级呈东西向穿过台风中心附近,随着台风加强切变加大。3)通过与西太平洋台风的比较,认为对流层高低层散度之差和涡度之差与南海台风发生发展的关系密切。4)积云对流造成的潜热释放是台风发展期的主要热源。 相似文献
7.
By employing the NCEP/NCAR reanalysis data sets (1000-10hPa, 2.5°×2.5°), the characteristics have been analyzed of the structure and evolution of an easterly vortex over the tropical upper troposphere relating to the east-west direction shift of the subtropical anticyclone over the Western Pacific Ocean. It is shown that there exists a westward shift simultaneously between the anticyclone and the vortex locating south of it. The anticyclone retreats eastward abnormally while the easterly encounters with the westerly around the same longitudes as they move from the opposite directions. The former is an upper weather system, extending from mid-troposphere to the height of 50 hPa with the center locating on 200 hPa.The vertical thermal distribution illustrates the characteristics of being "warm in the upper layer but cold in the lower layer". The divergence effect and the vertical motion change largely within the east and west sides of the easterly vortex and ascending branch transforms to descending branch near its center. 相似文献
8.
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
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
9.
北半球冬季副热带高压带维持的涡度机制 总被引：1，自引：0，他引：1
本文利用涡度平衡方程讨论北半球冬季副热带高压的维持,计算发现,30°N副热带高压带地区,大型扰动所造成的涡度输送的辐散是维持这地区反气旋涡度的主要因子,这种辐散作用所造成的反气旋涡度主要发生在对流层上层,平均经圈环流对地转祸度的输送可以把它引导到对流层下层来。此外,我们还根据涡度输送的计算,讨论了西风急流的维持。向北的扰动涡度输送在45°N上空达极大值,因此它对中纬度西风和纬向平均急流的维持起着重要作用。但30°N上空,扰动的涡度输送为零,而平均经圈环流对地转涡度和相对涡度的输送都比较大,因此,可以认为副热带急流是在平均经圈环流作用下维持的。 相似文献
10.
Based on composite analysis and numerical simulations using a regional climate model （RegCM3）, this paper analyzed the impact of the LHF anomaly in the tropical western Pacific on the precipitation over the south of China in June. The results are as follows. （1） Correlation analysis shows that the SC precipitation in June is negatively correlated with the LHF of the tropical western Pacific in May and June, especially in May. The SC precipitation in June appears to negatively correlate with low-level relative vorticity in the abnormal area of LHF in the tropical western Pacific. （2） The LHF anomaly in the tropical western Pacific is a vital factor affecting the flood and drought of SC in June. A conceptual model goes like this： When the LHF in the tropical western Pacific is abnormally increased （decreased）, an anomalous cyclone （anticyclone） circulation is formed at the low-level troposphere to its northwest. As a result, an anomalous northeast （southwest） air flow affects the south of China, being disadvantageous （advantageous） to the transportation of water vapor to the region. Meanwhile, there is an anomalous anticyclone （cyclone） at the low-level troposphere and an anomalous cyclone （anticyclone） circulation at the high-level troposphere in the region, which is advantageous for downdraft （updraft） there. Therefore a virtual circulation forms updraft （downdraft） in the anomalous area of LHF and downdraft （updraft） in the south of China, which finally leads to the drought （flood） in the region. 相似文献