Stabilization of the Large-Scale Instability in the Tropics (Invited Presentation)

Raymond and Zeng (2000) proposed a tropical large-scale instability with a timescale of days, where cloud anvil from deep convection changes radiation that in turn changes large-scale vertical circulation. If a moving system removed the cloud anvil temporarily, the instability would abort if there were no stabilizer to maintain the instability. A common external stabilizers is the difference in SST (sea surface temperature), which usually maintains a large-scale upward motion over a warm region and downward one over a cool region.

This study proposes an internal stabilizer of the temperature lapse rate in the middle and upper troposphere. The lapse rate is modulated by large-scale vertical circulation. Meanwhile, it impacts the convective downdrafts in the mixed-phase region that in turn impact ICC (ice crystal concentration) there and further cloud anvil. The presentation, with the aid of Doppler radar observations and in situ sounding data, will show how the stabilizer works so as to reinforce the concept of the instability.