A mixed rain-snow storm associated with a strong burst of cold air and development of an extratropical cyclone occurred over North China from 3 to 5 November 2012.This early snowfall event was characterized by a dramatic drop in temperature,strong winds,high precipitation intensity,broad spatial extent,and coexistence of multi-phase precipitating hydrometeors.This study investigates the multi-scale interactions between the large-scale circulation background and the synoptic-scale weather systems associated with the storm.The results are as follows.（1） The Arctic Oscillation （AO） had been in its negative phase long before the event,leading to southward advection of cold air into North China in advance of the storm.（2）The large-scale atmospheric circulation experienced a decreased number of long waves upstream of North China prior to the storm,resulting in reduced wave velocity and an almost stagnant low pressure system （extratropical cyclone） over North China.（3） An Ω-shaped blocking high over East Asia and the western Pacific obstructed the eastward movement of an upstream trough,allowing the corresponding surface cyclone to stabilize and persist over Beijing and its neighboring areas.This blocking high was a major factor in making this event a historically most severe precipitation event in autumn in Beijing for the past 60 years.（4） Baroclinic instability at lower levels gave rise to rapid development of the cyclone under the classical ＂second type＂ development mechanism for extratropical cyclones.（5） Moisture originated from the Yellow Sea entered the slowly-moving cyclone in a steady stream,creating fairly favorable water vapor supply for the heavy rainfall-snowfall,especially during the later stage of the cyclone development.（6） Moisture transport and frontal lifting triggered low-level instability and updrafts.Intensification of the front enhanced the vertical wind shear,causing conditional symmetric instability （CSI） to expand upward within the unstable lower tropos
Effects of vertical wind shear, radiation, and ice clouds on cloud microphysical budget associated with torrential rainfall during landfall of severe tropical storm Bilis （2006） are investigated by using a series of analysis of two-day grid-scale sensitivity experiment data. When upper-tropospheric upward motions and lower-tropospheric downward motions occur on 15 July 2006, the removal of vertical wind shear and ice clouds increases rainfall contributions from the rainfall type （CM） associated with positive net condensation and hydrometeor loss/convergence, whereas the exclusion of cloud radiative effects and cloud-radiation in- teraction reduces rainfall contribution from CM. The elimination of vertical wind shear and cloud-radiation interaction increases rainfall contribution from the rainfall type （Cm） associated with positive net conden- sation and hydrometeor gain/divergence, but the removal of cloud radiative effects and ice clouds decreases rainfall contribution from Cm. The enhancements in rainfall contribution from the rainfall type （cM） as- sociated with negative net condensation and hydrometeor loss/convergence are caused by the exclusion of cloud radiative effects, cloud-radiation interaction and ice clouds, whereas the reduction in rainfall contri- bution from cM results from the removal of vertical wind shear. When upward motions appear throughout the troposphere on 16 July, the exclusion of all these effects increases rainfall contribution from CM, but generally decreases rainfall contributions from Cm and cM.
Mesoscale convective system (MCS) cloud clusters,defined using an objective recognition analysis based on hourly geostationary infrared satellite data over East Asia during the warm seasons of 1996-2008 (except 2004),were investigated in this study.The geographical pattern of MCS distribution over East Asia shows several high-frequency centers at low latitudes,including the Indo-China peninsula,the Bay of Bengal,the Andaman Sea,the Brahmaputra river delta,the south China coastal region,and the Philippine Islands.There are several middle-frequency centers in the middle latitudes,e.g.,the central-east of the Tibet Plateau,the Plateau of west Sichuan,Mount Wuyi,and the Sayan Mountains in Russia;whereas in Lake Baikal,the Tarim Basin,the Taklimakan Desert,the Sea of Japan,and the Sea of Okhotsk,rare MCS distributions are observed.MCSs are most intensely active in summer,with the highest monthly frequency in July,which is partly associated with the breaking out and prevailing of the summer monsoon in East Asia.An obvious diurnal cycle feature is also found in MCS activities,which shows that MCSs are triggered in the afternoon,mature in the evening,and dissipate at night.MCS patterns over East Asia can be characterized as small,short-lived,or elongated,which move slowly and usually lead to heavy rains or floods.
The CloudSat satellite data from June 2006 to April 2011 are used to investigate the characteristics of cloud vertical profiles over East Asia （20°-50°N, 80°- 120°E）, with particular emphasis on the profiles of precipitative clouds in comparison with those of nonprecipitative clouds, as well as the seasonal variations of these profiles. There are some obvious differences between the precipitative and nonprecipitative cloud profiles. Generally, precipitative clouds mainly locate below 8 km with radar refiectivity in the range of-20 to 15 dBZ and maximum values appearing within 2-4-km height, and the clouds usually reach the ground; while nonprecipitative clouds locate in the layers of 4 12 km with radar refiectivity between -28 and 0 dBZ and maximum values within 8-10-km height. There are also some differences among the liquid precipitative, solid precipitative, and possible drizzle precipitative cloud profiles. In precipitative clouds, radar reflectivity increases rapidly from 11 to 7 km in vertical, implying that condensation and collision-coalescence processes play a crucial role in the formation of large-size drops. The frequency distribution of temperature at -15℃ is consistent with the highest frequency of radar reflectivity in solid precipitative clouds, which suggests that the temperatures near -15℃ are conductive to deposition and accretion processes. The vertical profiles of liquid precipitative clouds show almost the same distributions in spring, summer, and autumn but with differences in winter at mainly lower levels. In contrast, the vertical profiles of solid precipitative clouds change from spring to winter with an alternate double and single high-frequency core, which is consistent with variations of the frequency distribution of temperature at 15℃. The vertical profiles of nonprecipitative clouds show a little change with season. The observations also show that the precipitation events over East Asia are mostly related to deep convective clouds and nimbostratus clouds. These results
The Infrared Atmospheric Sounding Interferometer (IASI) is a new-generation ultraspectral atmospheric sounding instrument mounted on the MetOp-A, the first operational polar-orbiting satellite developed by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). It is an ultrahigh spectral-resolution atmospheric detector which can detect atmospheric chemical composition, temperature, and humidity profiles with high accuracy and resolution. In the present study, through comparative analyses of the similarities and differences between the IASI and the radiosonde observation (RAOB) water vapor data, and between the IASI and the Aqua-AIRS water vapor retrievals, a detailed and systematic assessment of the credibility of the IASI water vapor retrievals over the plateau region was made. A comparison of the IASI retrievals with the AIRS retrievals and the RAOB measurements over the Tibetan Plateau revealed that the IASI retrieval data are reliable and can be used for conducting further studies.
