A Low-level Gravity Wave Triggering Mechanism For Rainstorms In Warm Sector In South China

Observations and results simulated by high-resolution numerical model about a heavy rain occurred in warm sector in South China are analyzed, results show that hourly precipitation of frontal and warm sector assume wave train-like distribution, and 850hPa divergence appear acute oscillation about 1~2 hour before beginning of precipitation in frontal and warm sector, the oscillation of warm sector is late about 1h than frontal sector's;while rain, hourly divergence increment of grids among frontal and warm sector also assume evidence wave-like distribution;wavelet analysis confirm that disturbances in frontal and warm sector have same period but half phase difference, and wave period and wave length are belong to gravity wave range. Further analysis suggest that there already had a very thin low stable layer, which located among 950-850hPa, along frontal and warm sector before rainstorm in warm sector occurred;The appearance of the thin stable layer meet the condition that gravity wave propagation, cause low gravity wave propagate from frontal sector to warm sector along the stable layer, then trigger ascend movement of warm sector boost up sharply, and result in heavy rain in warm sector. Some studies have suggested that thin systems in boundary layer play an important role in heavy rains in South China, so low-level gravity wave triggering mechanism for rainstorm in South China may be of typical significance.