A Moist Entropy Budget View of the South Asian Summer Monsoon Onset

Ding Ma, Adam H. Sobel, Zhiming Kuang, Martin S. Singh, Ji Nie

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Abstract

Using a high-resolution global model with explicit representation of convection, the physical processes involved in the abrupt onset of South Asian summer monsoon are investigated within a moist entropy budget framework. The monsoon onset is a two-stage transition. During the first stage, which starts around 2 months before onset, the source terms of column-integrated moist entropy gradually increase, while the export by the large-scale circulation slowly strengthens. The second stage is marked by a sudden increase of radiative heating and surface latent heat flux 10 days prior to the onset, followed by abrupt strengthening of large-scale export of moist entropy. When either cloud-radiative or wind-evaporation feedback is disabled in numerical experiments, the monsoon experiences much smoother and weaker onset. The evolution of the system in a gross moist stability plane demonstrates that these positive feedbacks destabilize the system and are responsible for the abruptness of the transition.

Original languageEnglish
Pages (from-to)4476-4484
Number of pages9
JournalGeophysical Research Letters
Volume46
Issue number8
DOIs
Publication statusPublished - 1 Jan 2019

Keywords

  • convection
  • energetic framework
  • gross moist stability
  • moist entropy
  • monsoon onset
  • South Asian monsoon

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