Effect of the 1997 El Nino on the distribution of upper tropospheric cirrus

Geographical distributions of Halogen Occultation Experiment (HALOE) aeroso l extinction data for 1993-1998 are analyzed in the troposphere and stratos phere at pressures between 121 and 46 hPa. The El Nino conditions of 1997 i ncreased upper tropospheric cirrus over the mid-Pacific and decreased cirru s over Indonesia. Longitudinal centroids of cirrus in the Pacific and over Indonesia shifted eastward by 25 degrees in the troposphere in 1997. Longit udinal centroids of aerosol in the lower stratosphere do not exhibit longit udinal shifts in 1997, indicating that the effects of El Nino upon equatori al particle distributions are confined to the troposphere. The correlation of the longitudinal centroids of outgoing longwave radiation and HALOE exti nction confirms the spatial relationship between deep convective clouds and upper tropospheric cirrus. The number of cirrus events observed each year in 1993-1998 in the upper troposphere are quite similar for the region from the Indian Ocean to the mid-Pacific (30 degrees S to 30 degrees N, 50 degr ees to 240 degrees E).