Tuesday, 16 January 2007: 5:00 PM
The water and energy budgets of hurricanes and implications for climate change
214D (Henry B. Gonzalez Convention Center)
To explore the role of hurricanes in the climate system, a detailed analysis is made of the bulk atmospheric moisture and related energy budgets using results based on several simulated storms, in particular, Katrina in August 2005. The simulations are with the Weather and Research Forecasting (WRF) model at 4 km resolution without parameterized convection. It is argued that a fundamental role of tropical cyclones in the climate system is to pump heat out of the tropical summer ocean and disperse it into the atmosphere mainly in the form of latent energy, providing evaporative cooling for the ocean. Surface fluxes of latent energy can exceed 1000 W m-2 in hurricanes. Based on simulations with Katina, empirical relationships are computed between the simulated maximum grid-point wind and the surface fluxes and precipitation averaged over 400 km radius. Then by making use of global 6-hourly global “best track” data on frequency of observed hurricanes at various strengths for 1970-2005, which include the maximum wind estimate, along with the empirical data from model runs, the total heat loss by the tropical ocean in hurricanes categories 1 to 5 within 400 km of the center of the storms is estimated to average about 0.531022 J per year (0.17 PW) for 1990 to 2005. The enthalpy loss due to hurricanes computed based on precipitation is about a factor of 3.4 greater than these numbers (0.58 PW), owing to the additional contribution from the surface fluxes outside 400 km radius and moisture convergence into the storms, typically from as far from the eye as 1600 km. Changes over time reflect basin differences and a prominent role for El Niño. Strong positive trends from 1970 to 2005 occur in these inferred surface fluxes and precipitation from hurricanes arising from increases in intensity of storms and also higher SSTs. The implied much heavier rainfalls (1.4% per year increase), escalate risk of flooding over land. This highlights the importance of surface energy exchanges from hurricanes in the global energetics of the climate system and indicates that climate models are markedly deficient by not adequately representing tropical cyclones.