Abstract
Long-duration localized heavy rainfall (> 6 hours, < 10 km2) was recorded by raingauges on October 4, 2013 at mid-elevations (~1,500 m) in the Peruvian Andes, which was not apparent in infrared or microwave measurements from either geostationary or polar orbiting satellites. This spring event is investigated here through a numerical modeling study using the Weather and Research Forecasting (WRF) model, and examined in the context of the climatology of Cold Air Intrusions (CAIs) along the eastern flanks of the tropical Andes. The model results suggest significant precipitation enhancement from intense shallow convection at the CAI frontal boundary amplified by orographic lifting as it propagates northward latched to the slopes of Andes. Analysis of CAI mesoscale dynamics was conducted using four decades of European Center Medium-Range Weather Forecasts (ECMWF) reanalysis, Tropical Rainfall Measurement Mission (TRMM) data products, and rain-gauge observations with emphasis on characterizing year-round CAI frequency, CAI interactions with Andes topography, and their impact on orographic precipitation climatology. The data show a robust enhancement of the diurnal cycle of precipitation during CAI events in all seasons, and in particular increases in surface rainfall rate during early morning at intermediate elevations (~ 1,500 m), that is the eastern Andes orographic maximum. This link between CAI frequency and rainfall suggests that they play an important role in maintaining the Andes to Amazon year-round terrestrial connectivity through runoff production and transport by the river networks.
Highlights
The Andes mountain range is the most prominent topographic feature of South America and modulates the weather and climate of the continent (Garreaud, 2000, 2009)
In situ rainfall measurements are used for the first time together with the longest period of available climatology from European Center Medium-Range Weather Forecasts (ECMWF) ERAInterim reanalysis (1979–2017) to investigate the connection between the Cold Air Intrusions (CAIs) and orographic precipitation on the eastern flanks of the tropical Andes
A careful study of the vertical structure of atmospheric moisture content and vertical winds shows strong shallow convection associated with high values of precipitation at the intersection of the CAI front with the Andes terrain explaining the localized enhancement of surface rainfall
Summary
The Andes mountain range is the most prominent topographic feature of South America and modulates the weather and climate of the continent (Garreaud, 2000, 2009). The spatial organization of simulated precipitation (Figure 7A) is consistent overall with the spatial distribution of precipitation features from the TRMM satellite climatology along the eastern slopes of the Andes with negligible precipitation or very light rainfall at higher elevations above the tree line (e.g., ∼3,500 m) along the headwaters of the Amazon basin (Lowman and Barros, 2014).
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