Extended Abstract (68K)JP2.5
ENSO-based forecasting of seasonal tropical cyclone trends from historical analyses of genesis and OLR oscillations
Colin K. Kennedy, U.S. Naval Academy, Annapolis, MD; and D. R. Smith
Although a great deal of study has been carried out with regard to low frequency, long-term oscillations in the tropics, there remain numerous unanswered questions regarding higher frequency short-term oscillations. In particular the effects of high frequency intra-annual oscillations on regional and global tropical cyclogenesis have begun only recently to be examined in detail. A connection between low frequency oscillations such as the El Niņo/Southern Oscillation (ENSO) and higher frequency inter-basin oscillations is thought to exist in the tropics. Here, some characteristics of tropical cyclogenesis in the East Pacific and Atlantic basins are examined. Seasonal temporal positions of tropical cyclone genesis between 1950-1999 are recorded in both basins in a region confined from 5-45° N and 10-140° W. The genesis positions are separated into two datasets based on origin as either an East Pacific or North Atlantic system. Raw time series reveal the seasonal genesis frequencies for each region, and a subsequent interpretation yields a period of genesis oscillation between the two basins. This oscillation period is then compared to various index values of ENSO to determine what-if any-effects the state of ENSO has on genesis oscillation.
In subsequent tests, outgoing longwave radiation, a well-known means of approximating tropical convection, is analyzed for similar oscillations in order to substantiate the genesis analysis technique established above. In this case, daily OLR values are regionally averaged for the tropical seasons 1974-1999 (with the exception of 1978). For both the genesis and OLR frequency techniques, lagged cross-correlation tests are run to determine what effects the state of ENSO might have on the inter-basin oscillation of genesis and OLR anomalies. While the effect of ENSO on individual basin activity is well documented, this ENSO-based inter-basin periodicity represents potential cyclogenesis oscillations in both the Atlantic and East Pacific basins on annual timescales.
Joint Poster Session 2, Severe Local Storms Forecasting (Joint with 21SLS and 19WAF/15NWP) new
Tuesday, 13 August 2002, 3:00 PM-4:30 PM
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