Study On Asian Overshooting Convections And Its Respondes To ENSO Using TRMM Satellite Data

Overshooting Convections (OCs) not only are often accompanied with severe weather events, such as heavy rain, hails, high winds, tornadoes and lightning flashes, but also play a crucial role in troposphere-stratosphere exchange. In this paper, the spatial-temporal distribution and intensity (i.e. radar reflectivity, microwave brightness temperature and lightning) of OCs over Asia and its responses to ENSO have been investigated by using the multi-sensor data based on TRMM satellite, furtherly the corresponding distribution of meteorological fields have been analized from the ECMWF reanalysis data (ERA-Interim). The main conclusions are as follows:(1) OCs Only account for2.6%of total cold cloud systems (cloud top IR brightness temperature less than235K) in Asian region, among which about2.2%and3.0%of cold cloud cystems penetrate the tropopause over the land and ocean, respectively. OCs are mainly distributed in the south of15°N, and nearly50%of OCs occur in summer, whose peak appears in August. The number of OCs over the ocean is higher than that over the land almost in every month, and volumetric precipitation rate and area of OCs over the ocean are higher than that over the land. The volume precipitation rate of OCs is an order of magnitude higher than Non Overshooting Convections (NOCs) over both land and ocean. The lightning frequency, microwave brightness temperature and radar echo top show that the strength of OCs is obviously stronger than NOCs, and the OCs over the land are stronger than that over the ocean. Strong OCs are mainly concentrated in the south slope of the Himalayas, eastern China and Southeast Asia, wherr the probability of occurrence of OCs is also higher.(2) It can be found that there are similar patterns of spatial distribution between OCs and thermaldynamic, kinematic and humidity parameters. The CAPE and specific humidity in the tropics are about400J/kg and11g/kg, both of which are higher than that in the subtropics, and the vertical wind shear is15m/s smaller (except for the Tibetan Plateau), which provide a favorable environmental conditions for OCs. A higher CAPE and specific humidity (the CAPE is greater than500J/kg, the specific humidity is greater than15g/kg) can be seen in the south slope of the Himalayas in summer, where the vertical wind shear is about3m/s, which is very favorable to the occurrence and development of strong convections. There are fewer, but stronger OCs in ther eastern-central China, where specific humidity and CAPE is bigger in summer than other seasons, and vertical wind shear is small (about5m/s), which is condictive to strong OCs.(3) During ENSO period, the frequency change of OCs is negatively correlated with intensity in most regions. The frequency of OCs has the most significant change in the maritime continent and northwestern Pacific, where decrease can be seen during El Nino episodes and increase during La Nina episodes (except for the northwestern Pacific in winter). OCs intensity appears to significantly vary in the south slope of the Himalayas and Tibet Plateau, where stronger OCs can be found during El Nino episodes and weaker OCs during La Nina episodes. Except for the summer, the change of OCs frequency is not obvious, but the significant change of OCs intensitycan be seen in eastern-central China during La Nina episodes. The seasonal anomaly variation of specific humidity, CAPE and vertical wind shear during El Nino appears to be opposite to that during La Nina periods. During El Nino periods, the seasonal anomaly variation of OCs frequency is similar to CAPE and specific humidity, but opposite to vertical wind shear. During La Nina periods, except for winter, the seasonal anomaly variations of OCs frequency and environmental conditions are the same as those in other seasons during El Nino period.