Comprehensive Pattern of Deep Convective Systems over the Tibetan Plateau–South Asian Monsoon Region Based on TRMM Data

Abstract

Diurnal and seasonal variation, intensity, and structure of deep convective systems (DCSs; with 20-dBZ echo tops exceeding 14 km) over the Tibetan Plateau–South Asian monsoon region from the Tibetan Plateau (TP) to the ocean are investigated using 14 yr of Tropical Rainfall Measuring Mission (TRMM) data. Four unique regions characterized by different orography are selected for comparison, including the TP, the southern Himalayan front (SHF), the South Asian subcontinent (SAS), and the ocean. DCSs and intense DCSs (IDCSs; with 40-dBZ echo tops exceeding 10 km) occur more frequently over the continent than over the ocean. About 23% of total DCSs develop into IDCSs in the SHF, followed by the TP (21%) and the SAS (15%), with the least over the ocean (2%). The average 20-dBZ echo-top height of IDCSs exceeds 16 km and 9% of them even exceed 18 km. DCSs and IDCSs are the most frequent over the SHF, especially in the westernmost SHF, where the intensity—in terms of strong radar echo-top (viz., 40 dBZ) height, ice-particle content, and lightning flash rate—is the strongest. DCSs over the TP are relatively weak in convective intensity and small in size but occur frequently. Oceanic DCSs possess the tallest cloud top (which mainly reflects small ice particles) and the largest size, but their convective intensity is markedly weaker. DCSs and IDCSs show a similar diurnal variation, mainly occurring in the afternoon with a peak at 1600 local time over land. Although most of both DCSs and IDCSs occur between April and October, DCSs have a peak in August, whereas IDCSs have a peak in May.

Characteristics of Mesoscale Convective Systems over China and Its Vicinity Using Geostationary Satellite FY2

“…6d). Romatschke et al (2010) and Qie et al (2014) investigated the increase of extreme convection over the Tibetan Plateau during the monsoon season and indicated that the westerly winds and high relative humidity are likely related to the formation of systems in this region. During the monsoon season, westerly winds weaken gradually from May to August, and relative humidity increases westward from the eastern Tibetan Plateau.…”

“…The third type of monthly variation is the persistent high frequency of MCS occurrence, which means that there are regions where the MCS occurrences are persistently active during the warm seasons compared to the others. Those regions include the Bay of Bengal, regions south of the Himalayas, and the northern Indo-China (Houze 2007;Romatschke et al 2010;Xu and Zipser 2011;Qie et al 2014). Figure 7 illustrates the monthly variability of the six MCS types.…”

“…The availability of multiple satellite observations in recent years provides an opportunity to describe in detail the properties and characteristics of MCSs (e.g., Houze 2007;Romatschke et al 2010;Luo et al 2011;Xu and Zipser 2011;Xu 2013;Liu and Zipser 2013;Wu et al 2013;Qie et al 2014). The findings are particularly helpful to understand the structures of MCSs and their relationships with the environments as they evolve.…”

Vertical Characteristics of Reflectivity in Intense Convective Clouds using TRMM PR Data

“…Yuan and Qie (2008) explored the south China sea before and after the onset of the summer monsoon. Qie et al (2014) observed the deep and intense deep convective clouds over Tibetan Plateau-South Asian monsoon using 40 dBZ crossing 10 and 14 km altitude respectively. Bhat and Kumar (2015) observed a close similarity in vertical profiles over land and oceanic areas in cumulonimbus towers over south Asian areas during Indian summer monsoon.…”

“…Previous studies consider the 40 dBZ at and above 10 km to observe the vertical structure in convective precipitation (Houze et al, 2007;Qie et al, 2014;Romatschke & Houze, 2010;Romatschke et al, 2011a;2011b). Previous criteria underestimate some intense clouds, which evolve near the surface, but are not very deep (>10 km).…”