The relationship between statistics of warm-season cloud episodes and synoptic weather regimes over the East Asian continent

In this study, the relationship between statistical properties (including zonal span, duration, and propagation speed) of warm-season cloud episodes in Hovmollder space and synoptic conditions over the East Asian continent is investigated for the period of May-July 1997-2002. Synoptic conditions are classified into four regimes: those with baroclinity only at lower level (L), only at upper level (U), at both lower and upper levels (B), or at neither level (N), and cloud streaks (i.e., episodes as identified through an automated procedure) in each regime are stratified based on their zonal span (length in the East-West direction). It is found that there exists a tendency for episodes in regime B to be larger than episodes in regime N. For larger and less frequent episodes with a zonal span more than about 1,400 km, low-level conditions appear to have slightly higher importance than upper-level conditions, as streaks in regime L tend to be larger than those in regime U. Overall, the results point to the possibility that both upper-level steering and low-level features are important for major episodes that propagate at the leeside of the Tibetan Plateau for long distances across the East Asian continent. A better understanding of the episode behavior in the area is important for future application to improve the quantitative precipitation forecasts in warm season.