Resumo

RUIZ CARRASCAL, DANIEL. INDO-PACIFIC AND TROPICAL ATLANTIC EOF MODES: CONTRIBUTIONS TO THE ANALYSES OF CLOUD COVER CONDITIONS IN THE LOS NEVADOS NATURAL PARK. Rev.EIA.Esc.Ing.Antioq [online]. 2010, n.14, pp.39-52. ISSN 1794-1237.

Colombian paramos are experiencing an increase in their climatic stress. One of the key factors behind is the change in cloud cover conditions, which are dependent on both regional and local processes. This work aims to explore the degree of association between the year-to-year variability of sea surface temperatures (SSTs) observed in the tropical Indo-Pacific and Atlantic oceans, and the year-to-year changes in regional cloud cover conditions prevailing over the Colombian Central Cordillera, but focusing on the satellite grid pixel where Ruiz-Tolima Volcanic Massif, the Los Nevados Natural Park and their surroundings are located. Analyzed records include mean monthly SSTs observed in the El Niño 3.4 region of the equatorial Pacific, SST anomalies observed in the tropical Indo-Pacific and Atlantic basins, as well as all-type cloud cover and top pressure data observed over the northern Andes. Even though data of four "dry" months are processed, discussion focuses on January conditions when highaltitude environments of the Colombian Central Cordillera are exposed to sunshine maxima. Empirical orthogonal function (EOF)/principal component (PC) analyses are conducted to identify the major modes of variability in SSTs, such as the El Niño-Southern Oscillation (ENSO). The first EOF modes of January SST anomalies observed in the 30°S to 30°N and 15°S to 15°N Indo-Pacific regions represent, in particular, the mature phase of ENSO, and account for 30.7 % and 44.3 %, respectively, of the spatio-temporal variability of January SST anomalies. The first EOF mode of January SST anomalies observed in the 19°S to 29°N tropical Atlantic accounts for 32.0 % of the spatio-temporal variability of SST anomalies in this ocean region, and depicts the equatorial monopole structure. Simple correlation analyses are then conducted to explore linkages between the El Niño 3.4 SST anomalies, the Pacific ENSO mode, the Atlantic equatorial monopole structure, and the cloud cover conditions prevailing over the northern Andes; 59 % of the variance of January cloud cover conditions over the selected-high-altitude region is explained by the El Niño 3.4 SST anomalies; 72 % and 71 % are explained by the first PCs (PC1s) of January SST anomalies observed in the 30°S-to-30°N and 15°S-to-15°N belts of the Indo-Pacific region, respectively; finally, 28 % is explained by the PC1 of January SST anomalies observed in the 19°S to 29°N tropical Atlantic region. The PC1 of January SST anomalies in the 30°S-to-30°N belt of the Indo-Pacific region exhibits a statistically significant trend over the period 1942-2007 that shows more El Niño-like conditions during the last 28 years of the observational period. It also exhibits a statistically significant change in the mean that coincides with the regime shift that occurred in the tropical Pacific around 1976. Analyses suggest that there is likely to be a decrease in the January net cloud cover in the area of Ruiz-Tolima Volcanic Massif and its surroundings over the next 50 years. A decrease in all-type cloud amount of 6.8 %, relative to the period 1984-2001, is likely to happen by 2050 under "normal" conditions. A strong El Niño event would reduce this mean monthly cloud amount from an expected value of 68.7 % to an average value of 59.6 %. Predicted changes in cloud cover will probably worsen the current critical climatic conditions faced by Colombian high-altitude environments.

Palavras-chave : cloud cover; paramos; EOF/PC analyses; SST analyses.

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