A Climatology of Warm-Season Cloud Patterns over East Asia Based on GMS Infrared Brightness Temperature Observations

摘要

In the present study, hourly infrared (IR) brightness temperatures observed by the Geostationary Meteorological Satellite (GMS) over the region 20°-40°N, 95°-145°E in May-August 1998-2001 are used to compile a climatology of warm-season cloud/precipitation episodes over east Asia. With a goal to better understand the characteristics of warm-season convection and the behavior of these episodes, results are compared with those obtained in North America using radar-derived data. The convection in east Asia, similar to that in North America, is shown to also exhibit coherent patterns and characteristics of propagating events in the longitude-time (Hovmoeller) space, with a preferred phase speed of ～ 10-25 m s~(-1), considerably faster than warm-season synoptic-scale waves. Near the eastern edge-of the Tibetan Plateau, convection was most active with a strong diurnal signal, peaking in late afternoon or early evening then propagating eastward. The zonal span and duration of episodes could reach 3000 km and 45 h, respectively, also well exceeding the scale of individual convective systems and thereby suggesting an intrinsic predictability. Beside the coherent patterns of propagation, effects/modulations of synoptic waves, monsoon circulations, mei-yu fronts, and tropical systems on the convection were also discernable. In east Asia, unlike North America, however, propagation was strongest in May-June and almost ceased in midsummer. Further studies are needed to clarify the reasons for this apparent difference. Based on the coherency of cloud/precipitation episodes, statistical methods can be developed in both North America and east Asia to aid precipitation forecasts in the future.