Abstract
The interactions between atmosphere and steep topography in the eastern south–central Andes result in complex relations with inhomogenous rainfall distributions. The atmospheric conditions leading to deep convection and extreme rainfall and their spatial patterns—both at the valley and mountain-belt scales—are not well understood. In this study, we aim to identify the dominant atmospheric conditions and their spatial variability by analyzing the convective available potential energy (CAPE) and dew-point temperature ( T d ). We explain the crucial effect of temperature on extreme rainfall generation along the steep climatic and topographic gradients in the NW Argentine Andes stretching from the low-elevation eastern foreland to the high-elevation central Andean Plateau in the west. Our analysis relies on version 2.0 of the ECMWF’s (European Centre for Medium-Range Weather Forecasts) Re-Analysis (ERA-interim) data and TRMM (Tropical Rainfall Measuring Mission) data. We make the following key observations: First, we observe distinctive gradients along and across strike of the Andes in dew-point temperature and CAPE that both control rainfall distributions. Second, we identify a nonlinear correlation between rainfall and a combination of dew-point temperature and CAPE through a multivariable regression analysis. The correlation changes in space along the climatic and topographic gradients and helps to explain controlling factors for extreme-rainfall generation. Third, we observe more contribution (or higher importance) of T d in the tropical low-elevation foreland and intermediate-elevation areas as compared to the high-elevation central Andean Plateau for 90th percentile rainfall. In contrast, we observe a higher contribution of CAPE in the intermediate-elevation area between low and high elevation, especially in the transition zone between the tropical and subtropical areas for the 90th percentile rainfall. Fourth, we find that the parameters of the multivariable regression using CAPE and T d can explain rainfall with higher statistical significance for the 90th percentile compared to lower rainfall percentiles. Based on our results, the spatial pattern of rainfall-extreme events during the past ∼16 years can be described by a combination of dew-point temperature and CAPE in the south–central Andes.
Highlights
The south–central Andes are characterized by steep gradients in topography, climate, and ecology supporting a diverse environment with economic significance
We find that the parameters of the multivariable regression using convective available potential energy (CAPE) and temperature on atmospheric humidity (Td) can explain rainfall with higher statistical significance for the 90th percentile compared to lower rainfall percentiles
The aim of our study is to identify the dominant atmospheric conditions and climatic variables leading to deep convection and rainfall extreme events in the south–central Andes by focusing on convective available potential energy (CAPE) and dew-point temperature (Td )
Summary
The south–central Andes are characterized by steep gradients in topography, climate, and ecology supporting a diverse environment with economic significance. This region is repeatedly affected by Atmosphere 2019, 10, 379; doi:10.3390/atmos10070379 www.mdpi.com/journal/atmosphere. The strong warm and dry upper-level westerlies that occur east of the Andes during the austral summer trigger deep convection in connection with low-level wind flow and associated shear that cause extreme rainfall in this region [9,10,11,12,13]; (3) the region lies at the climatic transition zone between the tropical and subtropical atmospheric circulation regimes. The tropics are regions characterized by more humidity and lower frequencies of storm formation; the sub-tropical regions have a higher frequencies of deep convective storms and higher seasonal rainfall
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