A Statistical Forecast Model of Tropical Intraseasonal Convective Anomalies

Abstract

Tropical intraseasonal convective anomalies (TICAs) play a significant role in the coupled ocean?atmosphere system and the Madden?Julian oscillation (MJO) is the primary mode of this variability. This study describes statistical forecast models of intraseasonal variations. Twenty-four years of outgoing longwave radiation (OLR) and zonal components of the wind at 200 (U200) and 850 hPa (U850) are used. The models use the principal components (PCs) of combined EOF analysis of 20?90-day anomalies of OLR, U200, and U850 data. Forecast models are developed for each lead time from 1 to 10 pentads and for winter and summer seasons separately. The forecast models use a combination of the five most recent pentad values of the first five PCs of the combined EOF of (OLR, U200, U850) to predict the future values of a given PCK (k = 1, 5). The spatial structures are obtained by reconstructing the fields of OLR, U200, and U850 using the forecasts of PCK (k = 1, 5) and the associated EOFs. Verification with independent winter and summer data indicates useful forecasts of the first five PCs extending up to five pentads of lead time. The verification against 20?90-day anomalies indicates useful forecasts of the reconstructed fields of OLR, U200, and U850 extending up to four pentads of lead time over most of the Tropics. Furthermore, the statistical models provide useful forecasts of U200 and U850 intraseasonal anomalies up to two to three pentads of lead times in portions of the North Pacific region.