JP3.21
Are tropical cyclones feeding more extreme rainfall events?
William K. M. Lau, NASA/GSFC, Greenbelt, MD; and Y. Zhou and J. H. -. T. Wu
We have conducted a study of the relationships between tropical cyclone (hurricane in the North Atlantic (NAT) and typhoon in the western North Pacific (WNP)) intensity and extreme rainfall events using TRMM and GPCP rainfall data, and Tropical Cyclone (TC) track data. Extreme rain events are defined in terms of percentile rain rate, and TC rain by the amount of rain associated with a named TC, within a radius of 500 km centered at the storm location during the northern hemisphere TC season, July through November (JASON). Analyses using TRMM data (1998-2005) show that climatologically, 8% of rain events and 17% of the total rain amount over the NAT were accounted by TCs, compared to 9% of rain events and 21% of rain amount in WNP. This means that while TCs occur with similar frequencies in both basin, in terms of latent heat energy (rainfall) the WNP TCs pack more punch than the NAT counterparts. The TC-rain contribution increases steadily as rain intensity increases, and for the top 5% heavy rain events, the TC contribution approaches to approximately 61% rain events and 64% rain amount for both ocean basins, indicating that even in the extreme rain categories, no less than 30% of rain amount may be due non-TC rains. In individual years, the percentage varies substantially.
Extending the analyses using GPCP pentad data to the period 1979-2005, we find that while there is a lack of significant trend signal in the total JASON rainfall over NAT and WNP, a clear positive trend in extreme heavy rainfall, T10 or higher rain rates can be found. The contribution by TC-rain to extreme rain increases far more rapidly for Atlantic hurricanes, compare to that for North Pacific typhoons. TC-rain amount shows significant positive trend in basin-total, with more rapid increase in extreme rain categories for both basins. For a given rain category, the NAT trend increases at a much faster rate than WNP. For example in T10, TC-rain fraction has increased from approximately 25% in the 1980-1990 to 50% in the mid-1990's to mid-2000's for NAT. The T10 TC rain contribution rises less rapidly from 65% to about 75% for the same periods in the WNP. The more rapid increase in TC contribution to extreme rain events in the NAT appears to be correlated with the larger fractional increase in the total warm pool area (defined by SST >28.5o C). The implication on the possible linkage of hurricanes to global warming is discussed.
Joint Poster Session 3, Tropical Cyclones and Climate Change Poster Session
Monday, 21 January 2008, 2:30 PM-4:00 PM, Exhibit Hall B
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