Characteristics of mesoscale convective systems during the warm season over the Tibetan Plateau based on FY-2 satellite data sets

Abstract

Mesoscale convective systems (MCSs) often cause heavy precipitation events during the warm season over the Tibetan Plateau (TP). By using the 1-hr gridded data sets with the resolution of 0.1° × 0.1° from the geostationary satellites of Fengyun-2 series (FY-2C/2E), the characteristics of MCSs over the TP during the warm season (May–August) from 2005 to 2012 are analysed. Based on objective criteria, MCSs over the TP can be divided into six categories, namely mesoscale convection complexes (MCCs), persistent elongated convection systems (PECSs), meso-β circular convection systems (MβCCSs), meso-β elongated convection systems (MβECSs), smaller meso-β circular convection systems (SMβCCSs), as well as smaller meso-β elongated convection systems (SMβECSs). The results show that there are 1,465 MCSs occurring over the TP during the warm seasons of 2005–2012, and most MCSs occur in a banded area around 30°N with two high-frequency centres. The frequency of MCSs reaches a maximum in July, followed by August and June, while the lowest frequency occurs in May. The high-frequency centre is located in the northern part of the TP in May, and moves southward to the central and southern part of the TP from June to August. 82.3% of the MCSs over the TP belong to the elongated categories, out of which MβECSs account for the most. MCSs over the TP have significant diurnal variations, which usually initiate at around 1700 LST (LST, LST = UTC + 8 hr), then develop and reach maturity at 2000 LST, then weaken and dissipate at 2200 LST. The life cycles of MCSs are characterized by slow growth and rapid weakening. The larger the scale of MCSs over the TP is, the longer the duration will be.