Simulation of hurricane response to suppression of warm rain by sub-micron aerosols D. Rosenfeld1, A. Khain1, B. Lynn1, and W. L. Woodley2 1Institute of Earth Sciences, The Hebrew University of Jerusalem, Israel 2Woodley Weather Consultants, 11 White Fir Court, Littleton 80127, USA
Abstract. The feasibility of hurricane modification was investigated for hurricane
Katrina using the Weather Research and Forecasting Model (WRF). The possible
impact of seeding of clouds with submicron cloud condensation nuclei (CCN)
on hurricane structure and intensity as measured by nearly halving of the
area covered by hurricane force winds was simulated by "turning–off" warm
rain formation in the clouds at Katrina's periphery (where wind speeds were
less than 22 m s−1). This simplification of the simulation of aerosol
effects is aimed at evaluating the largest possible response. This resulted
in 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 a
shrinking of the eye and hence to some increase in the wind within the small
central area of the TC. Yet, the overall strength of the hurricane, as
defined by the area covered by hurricane force winds, decreased in response
to the suppressed warm rain at the periphery, as measured by a 25%
reduction in the radius of hurricane force winds. In a simulation with warm
rain suppression throughout the hurricane, the radius of the hurricane force
winds was reduced by more than 42%, and although the diameter of the eye
shrunk even further the maximum winds weakened. This shows that the main
mechanism by which suppressing warm rain weakens the TC is the low level
evaporative cooling of the un-precipitated cloud drops and the added cooling
due to melting of precipitation that falls from above.
Citation: Rosenfeld, D., Khain, A., Lynn, B., and Woodley, W. L.: Simulation of hurricane response to suppression of warm rain by sub-micron aerosols, Atmos. Chem. Phys., 7, 3411-3424, doi:10.5194/acp-7-3411-2007, 2007.