Satellite observations of the southeast Pacific intertropical convergence zone during 1993-1998

An intertropical convergence zone in the southeast Pacific Ocean is described from monthly mean 1° × 1° ocean vector wind, rainfall, sea surface temperature, and integrated water vapor measurements recorded from satellites. Time interval of the investigation was January 1993 to December 1998, when ocean and atmosphere conditions during 1993-1996 were normal compared to the 1997-1998 El Niño. The southeast Pacific intertropical convergence zone (SITCZ) occurred in March-April at 8° S-2° S, 130° W-90° W. During 1993-1996 the average March-April values of SITCZ surface wind convergence, rain rate, sea surface temperature, and integrated water vapor were 3.3 × 10^-6 s^-1, 3.3 mm d^-1, 27.3°C, and 45.3 mm, respectively. A statistical model of the monthly mean observations predicted rainfall greater than the 2 mm d^-1 threshold when surface wind convergence was greater than the 1.5 × 10^-6 s^-1 threshold and sea surface temperature was above 27°C. During non-El Niño conditions, SITCZ sea surface temperature was greater than sea surface temperature in the 2° S-2° N equatorial band, with maximum difference in March-April which would create a surface wind convergence larger in March-April compared to other months. The Intertropical Convergence Zone (ITCZ), which occurred north of the equator throughout the year, and the SITCZ were separated by divergent wind, low (<2 mm d^-1) rainfall, and cold (<27° C) surface water, except during the intense 1998 El Niño. The rain rate of the ITCZ was minimum in March-April during 1993-1996 and comparable to the SITCZ rain rate.