Topographic Controls on the Distribution of Summer Monsoon Precipitation over South Asia

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Abstract

We use a high-resolution (9 km) one-way nested regional climate modeling framework to systematically evaluate individual and aggregate roles of various components of topography in the precipitation distribution during South Asian Summer Monsoon (SASM). While it is not the arrival but the north-northwestward extent of summer monsoon precipitation that is regulated by the presence of elevated surfaces in South Asia, both the thermal and mechanical topographic forcing play a role. Topography not only provides mechanical uplifting and prevents dry air entrainment, it also helps regulate the strength of upper level anticyclone and tropical easterly jet, all of which are necessary to sustain a conducive environment for monsoon precipitation in the South Asian summer. In turn, precipitation feedbacks positively by accelerating the tropospheric diabatic warming through atmospheric latent heating and by maintaining the moisture supply through local recycling. Modifications in the topography, particularly the removal of the Tibetan Plateau, substantially modulates the moist flow in the lower troposphere and the anticyclonic circulation in the upper troposphere to an extent that the northern branch of SASM becomes substantially weaker. These changes give way to negative precipitation anomalies and eventually to an environment where the cycle of feedbacks that runs the process of monsoon progression over land becomes inefficient. The design of topographic modification experiments can influence precipitation response; therefore, we advise caution in the interpretation of these and previously reported results.

Original languageEnglish
Pages (from-to)667-683
Number of pages17
JournalEarth Systems and Environment
Volume4
Issue number4
DOIs
StatePublished - Dec 2020

Funding

We thank four anonymous reviewers for their feedback. This work is supported by the Department of Energy Office (DOE) of Science Biological and Environmental Research as part of Regional and Global Model Analysis program area within the Earth and Environmental Systems Modeling Program, and by the National Climate‐Computing Research Center, which is located within the National Center for Computational Sciences at the Oak Ridge National Laboratory and supported under a Strategic Partnership Project, 2316‐T849‐08, between DOE and NOAA. Support for data storage and analysis is provided by the Oak Ridge Leadership Computing Facility at ORNL. The WRF model code is publicly available from https://www2.mmm.ucar.edu/wrf/users/. The boundary forcing data are available from https://rda.ucar.edu/datasets/ds083.2/. MA would like to thank Danielle Touma and Rui Mei for their help in conducting the experiments. This manuscript has been co-authored by employees of Oak Ridge National Laboratory, managed by UT Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy. The publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan ). We thank four anonymous reviewers for their feedback. This work is supported by the Department of Energy Office (DOE) of Science Biological and Environmental Research as part of Regional and Global Model Analysis program area within the Earth and Environmental Systems Modeling Program, and by the National Climate‐Computing Research Center, which is located within the National Center for Computational Sciences at the Oak Ridge National Laboratory and supported under a Strategic Partnership Project, 2316‐T849‐08, between DOE and NOAA. Support for data storage and analysis is provided by the Oak Ridge Leadership Computing Facility at ORNL. The WRF model code is publicly available from https://www2.mmm.ucar.edu/wrf/users/ . The boundary forcing data are available from https://rda.ucar.edu/datasets/ds083.2/ . MA would like to thank Danielle Touma and Rui Mei for their help in conducting the experiments. This manuscript has been co-authored by employees of Oak Ridge National Laboratory, managed by UT Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy. The publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).

Keywords

  • South Asian summer monsoon
  • Tibetan Plateau
  • Topographic forcing

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