Seminar: Dr. Ji Nie

Please join us as we welcome Dr. Ji Nie from the Lamont Doherty Earth Observatory at Columbia University for his seminar titled Triggers and Feedback in the 2010 Pakistan Flood: Modeling Extreme Precipitation with Interactive  Large-Scale Ascent. Refreshments will be served.

Abstract

The large-scale triggers and the convective heating feedback in the 2010 Pakistan extreme precipitation events are examined within the Column Quasi-Geostrophic framework, which allows modeling convection with interactive large-scale vertical motion. Forcing a cloud-revolving model with the large-scale forcings obtained from reanalysis data, we successfully reproduced the 2010 events. The positive feedback of convective heating to large-scale dynamics is essential in amplifying the precipitation intensity to the observed values. Orographic lift is the most important dynamical triggers in both events, while potential vorticity (PV) forcing also contributes to the triggering of the first event. Horizontal moisture advection modulates the extreme events mainly by setting the environment humidity, which controls the amplitude of responses of convection to the dynamic forcings. Representing convection by a single-column model (SCM) or an effective static stability leads to substantial discrepancies in simulation results. The SCM underestimates the triggering effects of the upper-level PV forcing and is subject to a much weaker sensitivity on environmental humidity. The effective static stability can be tuned to match extreme precipitation triggered by the upper-level PV forcing. However, it does not appropriately capture the triggering effects of orographic lift and lacks the dependencies of convection on environmental humidity.