Organization and Oscillations in Simulated Shallow Convective Clouds

Guy Dagan, Ilan Koren*, Alex Kostinski, Orit Altaratz

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Physical insights into processes governing temporal organization and evolution of cloud fields are of great importance for climate research. Here using large eddy simulations with a bin microphysics scheme, we show that warm convective cloud fields exhibit oscillations with two distinct periods (~10 and ~90 min, for the case studied here). The shorter period dominates the nonprecipitating phase, and the longer period is related to the precipitating phase. We show that rain processes affect the domain's thermodynamics, hence forcing the field into a low-frequency recharge-discharge cycle of developing cloudiness followed by precipitation-driven depletion. The end result of precipitation is stabilization of the lower atmosphere by warming of the cloudy layer (due to latent heat release) and cooling of the subcloud layer (by rain evaporation, creating cold pools). As the thermodynamic instability weakens, so does the cloudiness, and the rain ceases. During the nonprecipitating phase of the cycle, surface fluxes destabilize the boundary layer until the next precipitation cycle. Under conditions that do not allow development of precipitation (e.g., high aerosol loading), high-frequency oscillations dominate the cloud field. Clouds penetrating the stable inversion layer trigger gravity waves with a typical period of ~10 min. In return, the gravity waves modulate the clouds in the field by modifying the vertical velocity, temperature, and humidity fields. Subsequently, as the polluted nonprecipitating simulations evolve, the thermodynamic instability increases and the cloudy layer deepens until precipitation forms, shifting the oscillations from high to low frequency. The organization of cold pools and the spatial scale related to these oscillations are explored.

Original languageAmerican English
Pages (from-to)2287-2299
Number of pages13
JournalJournal of Advances in Modeling Earth Systems
Volume10
Issue number9
DOIs
StatePublished - Sep 2018
Externally publishedYes

Bibliographical note

Publisher Copyright:
©2018. The Authors.

Keywords

  • aerosol
  • clouds
  • gravity waves
  • self-organization
  • shallow convection
  • thermodynamic instability

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