Simulation of hurricane response to suppression of warm rain by sub-micron aerosols

[摘要] The feasibility of hurricane modification was investigated for hurricaneKatrina using the Weather Research and Forecasting Model (WRF). The possibleimpact of seeding of clouds with submicron cloud condensation nuclei (CCN)on hurricane structure and intensity as measured by nearly halving of thearea covered by hurricane force winds was simulated by "turning–off" warmrain formation in the clouds at Katrina's periphery (where wind speeds wereless than 22 m s⁻¹). This simplification of the simulation of aerosoleffects is aimed at evaluating the largest possible response. This resultedin the weakening of the hurricane surface winds compared to the "non-seeded"simulated storm during the first 24 h within the entire tropical cyclone(TC) area compared to a control simulation without warm rain suppression.Later, the seeding-induced evaporative cooling at the TC periphery led to ashrinking of the eye and hence to some increase in the wind within the smallcentral area of the TC. Yet, the overall strength of the hurricane, asdefined by the area covered by hurricane force winds, decreased in responseto the suppressed warm rain at the periphery, as measured by a 25%reduction in the radius of hurricane force winds. In a simulation with warmrain suppression throughout the hurricane, the radius of the hurricane forcewinds was reduced by more than 42%, and although the diameter of the eyeshrunk even further the maximum winds weakened. This shows that the mainmechanism by which suppressing warm rain weakens the TC is the low levelevaporative cooling of the un-precipitated cloud drops and the added coolingdue to melting of precipitation that falls from above.

[学科分类] 大气科学