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Remote Influence of Andean Convection on Amazonian Rainfall and Its Mechanisms

Journal Article · · Journal of Geophysical Research. Atmospheres
DOI:https://doi.org/10.1029/2025JD043465· OSTI ID:3000766
 [1];  [2];  [3];  [4];  [3];  [5]
  1. University of California Irvine Irvine CA USA; Now at University of Connecticut Storrs CT USA
  2. University of California Irvine Irvine CA USA
  3. Lawrence Livermore National Laboratory Livermore CA USA
  4. National Center for Atmospheric Research Boulder CO USA
  5. Earth System Research Laboratory Physical Sciences Division National Oceanic and Atmospheric Administration Boulder CO USA
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Models from Coupled Model Intercomparison Project Phase 6 produce too much precipitation over the Andes but too little over the Amazon or the Wet Andes-Dry Amazon (WADA) bias pattern. Unlike the conventional view that convection parameterization and land model deficiencies can contribute to Amazonian rainfall biases, we approach this long-standing biased model behavior through the lens of Andean convection. Using Community Earth System Model v1.1 and focusing on the wet season, our mechanism-denial experiments demonstrate that Andean convection notably reduces precipitation over the Amazon during austral summer. The Andean forced Amazonian response operates on weather timescale. Furthermore, the reduction of Amazonian rainfall is detectable within a few hours after initial Andean forcing. The precipitation response is primarily driven by variations in the moisture budget and is moderated by changes in convective available potential energy over the Amazon. Changes in the total advection of moisture over the Amazon are dominated by the vertical advection term and can be attributed to discrepancies in the dynamic omega field. In the experiments, the Andean east flank region is scrutinized where the vertical velocity and moisture fields play an intermediary role for the Andean driven WADA connection. The Andean forcing induces descending anomalies on the Andean east flank. The disturbances of wind and geopotential fields over the Andean east flank propagate eastward via Kelvin waves. Over the Amazon, descending anomalies and advective drying lead to reduction of mid-to-high level cloud, increase of shortwave cloud forcing and surface net radiation, and enhancement of themodynamic stability and rainfall reduction.
Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Atmospheric Radiation Measurement (ARM) User Facility; Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER); USDOE National Nuclear Security Administration (NNSA); Extreme Science and Engineering Discovery Environment
DOE Contract Number:
SC0012152; AC52-07NA27344; AC05-00OR22725
OSTI ID:
3000766
Report Number(s):
LLNL--JRNL-2015082
Journal Information:
Journal of Geophysical Research. Atmospheres, Journal Name: Journal of Geophysical Research. Atmospheres Journal Issue: 20 Vol. 130; ISSN 2169-8996; ISSN 2169-897X
Publisher:
American Geophysical Union; Wiley
Country of Publication:
United States
Language:
English

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Related Subjects

58 GEOSCIENCES
Amazon
Andes
bias
CMIP6
precipitation
simulations