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contributor authorVuille, Mathias
contributor authorKeimig, Frank
date accessioned2017-06-09T16:23:25Z
date available2017-06-09T16:23:25Z
date copyright2004/09/01
date issued2004
identifier issn0894-8755
identifier otherams-6699.pdf
identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4208388
description abstractThe interannual variability of austral summer [December?January?February?March (DJFM)] convective activity and precipitation in the central Andes (15°?30°S) is investigated between 1983 and 1999 based on in situ rain gauge measurements, International Satellite Cloud Climatology Project (ISCCP) reduced radiance satellite data (the B3 dataset), and National Centers for Environmental Prediction?National Center for Atmospheric Research (NCEP?NCAR) reanalysis data. Twice-daily ISCCP-B3 calibrated infrared data, corrected for limb-darkening effects and representing equivalent blackbody temperatures Tb emitted by clouds are used to derive seasonal composites of fractional cold cloud coverage F*. Comparison of in situ rain gauge measurements with F* show a good correlation when a temperature threshold Tb = 240 K is used to derive F*. A rotated empirical orthogonal function (REOF) applied to the seasonal estimates of F* yielded three spatially separated modes of convective activity in the south, northwest, and northeast of the central Andes. Results indicate that precipitation variability in the central Andes shows less spatial coherence than previously thought, with many years showing an antiphasing of wet/dry conditions between the northern and southern part of the study area. Regression analyses confirm the crucial role of both intensity and location of upper-air circulation anomalies with easterly wind anomalies favoring wet conditions, and westerly winds producing dry conditions. Two different forcing mechanisms are identified as main causes of upper-air zonal wind anomalies in the northern and southern part of the central Andes, respectively. Easterly wind anomalies during wet summers in the northern part are in geostrophic balance with reduced meridional baroclinicity due to low-latitude (mid-latitude) cooling (warming), consistent with earlier studies. Farther to the south, easterly wind anomalies during wet summers are the result of an upper-air anticyclonic anomaly centered over southeastern South America, leading to a relaxation of the upper-air westerly winds and episodic easterly transport of humid air toward the subtropical Andes. This pattern is similar to one of the leading modes of intraseasonal variability, related to extratropical Rossby wave dispersion and modulation of the position of the Bolivian high. Correlation analysis of F* with near-surface specific humidity reveals that humidity variations in the lowlands to the east are not relevant on interannual time scales for the more humid northern part of the Altiplano. In the southern Altiplano, however, there is a significant correlation between convective activity and precipitation at high elevation and the low-level humidity content to the southeast of the Andes.
publisherAmerican Meteorological Society
titleInterannual Variability of Summertime Convective Cloudiness and Precipitation in the Central Andes Derived from ISCCP-B3 Data
typeJournal Paper
journal volume17
journal issue17
journal titleJournal of Climate
identifier doi10.1175/1520-0442(2004)017<3334:IVOSCC>2.0.CO;2
journal fristpage3334
journal lastpage3348
treeJournal of Climate:;2004:;volume( 017 ):;issue: 017
contenttypeFulltext


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