第一届未来大气科学论坛

Over the middle reaches of the Yangtze River basin, there is an important type of mesoscale vortices, which are referred to as the Dabie vortex (DBV). DBV has formed a research focus for decades, as it frequently induces flash flood-producing rainstorms along their tracks. However, of all existing DBV-related studies, none have ever investigated DBVs’ long-term climatological features, and all the basic features of DBVs are obtained from short-term statistics and/or case studies. To partly fill these knowledge gaps, we conduct a 42-yr statistical study on the DBVs by using the hourly fifth major global reanalysis produced by European Centre for Medium-Range Weather Forecasts (ERA5) reanalysis data. New findings mainly include the following: On an interdecadal scale, from 1983 to 2016, DBVs’ occurrence frequency shows a significant increasing trend of ~0.3 DBV a^-1, which may correspond to the enhancing horizontal transport of vorticity by the intensifying summer monsoon (a trend of ~0.23 day^-1 in summer monsoon index). Monthly variation of DBVs’ occurrence/appearance frequency (maximizes in June) is consistent with monthly variations of summer monsoon and its as sociated divergence, which affect DBVs’ formation through vertical stretching. DBVs’ diurnal variation shows two peaks at 2200 UTC (~9.8% in proportion) and at 1000 UTC (~6.8%), respectively, with the former more stable than the latter. Both local diurnal variation and nonlocal forcings are crucial for producing these two peaks. As rainfall intensity grows, the relative importance of DBVs’ contribution increases from ~13.6% (accumulated precipitation) to ~71.5% (heaviest precipitation) within DBVs’ source region. Inside/outside the source region, ~15.2%/~1.4% of the strongest local hourly precipitation is directly related to the DBVs.

Mesoscale vortex,Heavy rainfall