26th Conference on Hurricanes and Tropical Meteorology

Wednesday, 5 May 2004: 10:45 AM
Impact of CO2-induced warming on simulated hurricane intensity and precipitation: sensitivity to the choice of climate model and convective parameterization
Le Jardin Room (Deauville Beach Resort)
Thomas R. Knutson, NOAA/GFDL, Princeton, NJ; and R. E. Tuleya
Poster PDF (21.0 kB)
Our previous studies have found that idealized hurricanes, simulated under warmer, high CO2 conditions, are more intense and have higher precipitation rates than under present-day climate conditions. The present study explores the sensitivity of this result to the choice of climate model used to define the CO2-warmed environment and to the choice of convective parameterization used in the nested regional model that simulates the hurricanes. Approximately 1,300 five-day idealized simulations are performed using a higher-resolution version of the GFDL hurricane prediction system (grid spacing as fine as 9 km, with 42 levels). All storms were embedded in a uniform 5 m s-1 easterly background flow. The large-scale thermodynamic boundary conditions for these experiments--atmospheric temperature and moisture profiles and SSTs--are derived from nine different CMIP2+ climate models. The CO2-induced SST changes from the global climate models, based on 80-yr linear trends from +1%/yr CO2 increase experiments, range from about +0.8 to +2.4oC in the three tropical storm basins studied. Four different types of moist convection parameterization are tested in the hurricane model, including the use of no convective parameterization in the highest resolution inner grid. Nearly all combinations of climate model boundary condition and hurricane model convection scheme show a CO2-induced increase in both storm intensity and near-storm precipitation rates. The aggregate results, averaged across all experiments, indicate a 14% increase in central pressure fall, a 6% increase in maximum surface wind speed, and an 18% increase in the precipitation rate averaged within 100 km of the storm center. The fractional change in precipitation is more sensitive to the choice of convective parameterization than is the fractional change of intensity. Current hurricane potential intensity theories, applied to the climate model environments, yield an average increase of intensity (pressure fall) of 8% (Emanuel) to 16% (Holland) for the high CO2 environments. Convective Available Potential Energy (CAPE) is 21% higher on average in the high CO2 environments. One implication of the results is that if the frequency of tropical cyclones remains the same over the coming century, a greenhouse gas-induced warming may lead to a gradually increasing risk in the occurrence of highly destructive Category 5 storms.

Supplementary URL: http://www.gfdl.noaa.gov/~tk/manuscripts/hurr_cmip.pdf