对流层顶变化对上对流层/下平流层臭氧分布的影响

上对流层和下平流层(UT/LS),位于8—25km高度之间,是大气中一个很特殊的区域。大部分的臭氧分布在下平流层,在下平流层臭氧的含量发生一个很小的变化,就会对气候和地面的紫外辐射产生很大的影响。而作为气象参数的对流层顶,是充分混合、缺乏臭氧的上对流层和层结稳定、臭氧丰富的下平流层之间的边界或过渡层,其变化对臭氧总量和分布有直接和明显的影响。本文使用二维模式模拟研究对流层顶变化对臭氧在UT/LS分布的影响。模拟结果表明对流层顶的季节变化对UT/LS的臭氧分布有明显的影响,臭氧的局地变化可以超过10％。在冬季北半球中纬度对流层顶高度升高1km时,模式结果表明对臭氧分布的影响比较显著,局地变化可超过6％,但是对臭氧总量的影响较小,变化不超过5DU,小于观测资料统计分析的结果。

Atmospheric boundary layer sources for upper tropospheric air over the Asian summer monsoon region

Previous satellite measurements and model simulations have shown that the Asian summer monsoon（ASM） anticyclone is co-located with higher concentrations of pollutants, which are emitted in the continental atmospheric boundary layer（ABL）. Backward trajectory calculations show that the air at the 150-hPa level has the maximum frequency of ABL sources within 30 days over the most intensive convection regions and their downwind areas, which are not located within the ASM anticyclone,but rather at the southern flank or periphery of the ASM anticyclone. The upper tropospheric airs originated from the ABL sources include two parts： one from the ocean, which has the dominant impact to the south of 20°N, particularly over the South China Sea（SCS） and the west tropical Pacific Ocean; and another from the continent, which is dominant between 10°N and 30°N, particularly over the Bay of Bengal（BoB）, continental India, the Arabian Sea, and the Arabian Peninsula. It is the latter part that forms the higher pollutant concentration within the ASM anticyclone as shown by satellite measurements. Air in the ABL sources（both polluted and unpolluted） converges to the intensive convection region in the lower troposphere, and then traverses the middle troposphere through a wide group of upward pipes, and finally to the upper troposphere. These pipes in the middle troposphere are defined by the ASM intensive convections and cover the south of continental India,the BoB, the Tibetan Plateau, the Indochina Peninsula, the SCS, and the Philippine Sea.

A STUDY OF PARTITIONING Q VECTOR ON BACKGROUND CONDITIONS OF A TORRENTIAL RAINFALL OVER SHANGHAI,CHINA ON 25 AUGUST 2008

A rainfall that occurred during 0200–1400 Beijing Standard Time(BST)25 August 2008 shows the rapid development of a convective system,a short life span,and a record rate of 117.5 mm h-1for Xujiahui station since 1872.To study this torrential rainfall process,the partitioning method of Q vector is developed,in which a moist Q vector is first separated into a dry ageostrophic Q vector(DQ)and a diabatic-heating component.The dry ageostrophic Q vector is further partitioned along isothermal lines in the natural coordinate to identify different scale forcing in adiabatic atmosphere,and the large-scale and convective condensational heating in non-uniform saturated atmosphere,convective condensational heating, and Laplace of diabatic heating that includes radiative heating and other heating and cooling processes,are calculated to study the forcing from diabatic heating.The effects of the environmental conditions on the development of the rainfall processes are diagnosed by performing the partitioning of Q vector based on 6-hourly NCEP/NCAR Final Analysis(FNL)data with the horizontal resolution of 1°×1°.The results include the following:(1)a low-pressure inverted trough associated with the landfall of Typhoon Nuri (2008),a strong southwesterly jet along the western side of the subtropical high,and an eastward-propagating westerly low-pressure trough provide favorable synoptic conditions for the development of torrential rainfall;(2)the analysis of DQ vector showed that the upward motions forced by the convergence of DQ vector in the lower troposphere(1000–600 hPa)favor the development of torrential rainfall.When DQ vector converges in the upper troposphere(500–100 hPa),upward motions in the whole air column intensify significantly to accelerate the development of torrential rainfall;(3)the partitioning analysis of DQ vector reveals that large-scale forcing persistently favors the development of torrential rainfall whereas the mesoscale forcing speeds up the torrential rainfall;(4)the calculations of large-scale condensational heating in non-uniform saturated atmosphere,convective condensational heating, and Laplace of diabatic heating showed that the forcing related to diabatic heating has the positive feedback on the convective development,and such positive feedback decays and dissipates when the convective system propagates eastward and weakens.

Wind rotation characteristics of the upper tropospheric monsoon over the central and eastern tropical Pacific

In this study, to investigate whether the variation of wind direction in the upper tropospheric monsoon over the central and eastern tropical Pacific shows similar characteristics to the classical monsoon region, the authors introduced a wind vector angle methodology that describes the size of the angle of the wind direction variation, as well as the directed rotary angle, which includes not only the size of the angle but also how the wind vector rotates. On this basis, the authors utilized and improved the directed rotary angle methodology to investigate the evolution of wind direction in detail, and the study confirmed the presence of the same four rotation features in the upper tropospheric monsoon region. Furthermore, the authors also identified the precise variation of wind direction in pentads with seasonal evolution, and found the onset time of the upper tropospheric monsoon may be earlier than the classical monsoon while the termination time may be later. The results further support and supplement the theory of global monsoons, which unifies the low-level and upper tropospheric monsoon as one monsoon system.

Does a monsoon circulation exist in the upper troposphere over the central and eastern tropical Pacific?

Considering the central and eastern tropical Pacific （CETP） has important climate impacts, and its seasonal variability is also thought to be important, the authors used the monsoon investigation method named ＇dynamical normalized seasonality＇, which can precisely describe the wind vector direction over time, to analyze the upper-tropospheric circulation over the region. The authors discovered that there is a clear reversal of seasonal changes between winter and summer wind, just like the classic monsoon. Accordingly, the authors propose the new concept of the upper- troposphere monsoon over the CETP. The results extend the classical lower-troposphere monsoon region into the upper troposphere.