Extended Abstract (952K)P2.24
Description of the seasonal cycle of low-level flows flanking the Andes and their interannual variability
Lee A. Byerle, Univ. of Utah, Salt Lake City, UT; and J. Paegle
There is much evidence for relatively long term fluctuation of low-level circulations east of the Andes. Some of these fluctuations may be connected to remote influences, such as ENSO, while others may result from long-term changes of local surface processes such as evapotranspiration. The central purpose of the present study is to quantify the variability of low-level circulations surrounding the Andes mountain range through diagnostic studies of monthly averaged reanalyses. The first step is to explore the climatological signal of the seasonal cycle in the vicinity of the Andes, and compare it to other mountainous regions such as North America and the Tibetan Plateau. The results suggest that all three regions have pronounced mechanical flow modifications associated with the deflecting effect of orography. Additionally, the Andean region possesses a strong monsoonal signature in the warm season including substantial vertical reversal of the flow. This monsoonal characteristic is much more pronounced over South America than over most of North America, and appears to contribute strongly to the active low-level jets that are observed east of the Andes in the warm season. Alternative explanations must be sought for low-level jets observed in other seasons, and preliminary study suggests that these may be due more directly to the mechanical effect of orography. For the case of the South American orography, this effect tends to produce an orographically bound cyclone in winter, with poleward low level flow located to the east of the mountains. Interannual variability of monthly averages is also described, including a discussion of the implication of this variability to field measurement activities.
Poster Session 2, Orographic Precipitation/Operational and Numerical Weather Prediction (with Coffee Break)
Wednesday, 19 June 2002, 9:15 AM-11:00 AM
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