Deep convective clouds observed by ground-based radar over Naqu, Qinghai–Tibet Plateau

Abstract

The deep convective clouds (DCCs, 20 dBZ echo top exceeding 14 km) and intense DCCs (IDCCs, 40 dBZ echo top exceeding 10 km) over Naqu, a city featuring the most active convection in the central Qinghai–Tibet Plateau, were analyzed on the basis of data derived from the Naqu C-band radar within a radius of 100 km. The most frequent DCCs occur in July and at 15:00 LT (local time), in terms of monthly and diurnal variations, respectively. The geographic distribution of the DCCs seems to be related to the topography. The centers featuring the most frequent DCCs correspond to some certain hilly areas, while the ratio of IDCC to DCC is greater in some specific flat areas, which may be because the hilly topography is conducive to triggering convection but is unfavorable to the full accumulation of unstable energy. The DCCs (IDCCs) have average 20, 30 and 40 dBZ echo tops of approximately 15.8 (16.5), 12.3 (14.1) and 9.9 (11.3) km, and average areas of the regions with a composite reflectivity >20, 30 and 40 dBZ of approximately 120.3 (196.1), 37.4 (75.3) km2 and 9.2 (14.6) km2, respectively. The maximum reflectivity and horizontal extents of 20 and 30 dBZ radar echoes tend to occur at the level around −20 °C. The average horizontal extent of DCCs is much smaller than that suggested by the satellite-based radar data. In the diurnal variations in the vertical and horizontal extents of DCCs, the parameters related to 30 dBZ always increase more slowly and decrease more rapidly than those related to 20 dBZ in the afternoon, which is attributed to the generally weak convection characteristics of DCCs. The strongest convection may be around 16:00 LT in Naqu.