A diagnosis of rainfall over South America during 1997/98 El Niño and 1998/99 La Niña events: Comparison between TRMM PR and GPCP rainfall estimates

• Published in: Journal of Earth System Science Vol. 118; no. 3; pp. 193 - 207
• Main Authors: Franchito, Sergio H., Rao, V. Brahmananda, Vasques, Ana C., Santo, Clovis M. E., Conforte, Jorge C.
• Format: Journal Article
• Language: English
• Published: India Springer-Verlag 01.06.2009; Springer; Springer Nature B.V
• Subjects: Anomalies; Coastal zone; Convective rainfall; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; El Nino; El Nino events; El Nino phenomena; Estimates; Exact sciences and technology; Gauges; I.R. radiation; Infrared radiation; La Nina; La Nina events; Long wave radiation; Mean annual precipitation; Precipitation; Radiance; Rain gauges; Rainfall; Rainfall anomalies; Random errors; Satellite data; Satellite observation; Satellites; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; TRMM satellite; Tropical Rainfall Measuring Mission (TRMM); South America; Brazil; Brazil, Amazonia; ASW, Brazil; IS, Pacific; rainfall estimates over South America; TRMM PR data; GPCP data; satellites; coastal zone; rainfall; El Nino; radiation; anomalies; errors; La Nina; radiance
• ISSN: 0253-4126; 2347-4327; 0973-774X
• DOI: 10.1007/s12040-009-0013-x

A comparison between TRMM PR rainfall estimates and rain gauge data from ANEEL and combined gauge/satellite data from GPCP over South America (SA) is made. In general, the annual and seasonal regional characteristics of rainfall over SA are qualitatively well reproduced by TRMM PR and GPCP. It is found that over most of SA GPCP exceeds TRMM PR rainfall. The largest positive differences between GPCP and TRMM PR data occur in the north SA, northwestern and central Amazonia. However, there are regions where GPCP rainfall is lower than TRMM PR, particularly in the Pacific coastal regions and in southern Brazil. We suggest that the cause for the positive differences GPCP minus TRMM PR rainfall are related to the fact that satellite observations based on infrared radiation and outgoing longwave radiance sensors overestimate convective rainfall in GPCP and the cause for the negative differences are due to the random errors in TRMM PR. Rainfall differences in the latter phases of the 1997/98 El Niño and 1998/99 La Niña are analyzed. The results showed that the rainfall anomalies are generally higher in GPCP than in TRMM PR, however, as in the mean annual case, there are regions where the rainfall in GPCP is lower than in TRMM PR. The higher positive (negative) differences between the rainfall anomalies in GPCP and TRMM PR, which occur in the central Amazonia (southern Brazil), are reduced (increased) in the El Niño event. This is due to the fact that during the El Niño episode the rainfall decreases in the central Amazonia and increases in the southern Brazil. Consequently, the overestimation of the convective rainfall by GPCP is reduced and the overestimation of the rainfall by TRMM PR is increased in these two regions, respectively.