Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations

  • Louise NuijensEmail author
  • Kerry Emanuel
  • Hirohiko Masunaga
  • Tristan L’Ecuyer
Part of the Space Sciences Series of ISSI book series (SSSI, volume 65)


Space-borne observations reveal that 20–40% of marine convective clouds below the freezing level produce rain. In this paper we speculate what the prevalence of warm rain might imply for convection and large-scale circulations over tropical oceans. We present results using a two-column radiative–convective model of hydrostatic, nonlinear flow on a non-rotating sphere, with parameterized convection and radiation, and review ongoing efforts in high-resolution modeling and observations of warm rain. The model experiments investigate the response of convection and circulation to sea surface temperature (SST) gradients between the columns and to changes in a parameter that controls the conversion of cloud condensate to rain. Convection over the cold ocean collapses to a shallow mode with tops near 850 hPa, but a congestus mode with tops near 600 hPa can develop at small SST differences when warm rain formation is more efficient. Here, interactive radiation and the response of the circulation are crucial: along with congestus a deeper moist layer develops, which leads to less low-level radiative cooling, a smaller buoyancy gradient between the columns, and therefore a weaker circulation and less subsidence over the cold ocean. The congestus mode is accompanied with more surface precipitation in the subsiding column and less surface precipitation in the deep convecting column. For the shallow mode over colder oceans, circulations also weaken with more efficient warm rain formation, but only marginally. Here, more warm rain reduces convective tops and the boundary layer depth—similar to Large-Eddy Simulation (LES) studies—which reduces the integrated buoyancy gradient. Elucidating the impact of warm rain can benefit from large-domain high-resolution simulations and observations. Parameterizations of warm rain may be constrained through collocated cloud and rain profiling from ground, and concurrent changes in convection and rain in subsiding and convecting branches of circulations may be revealed from a collocation of space-borne sensors, including the Global Precipitation Measurement (GPM) and upcoming Aeolus missions.


Warm rain Shallow cumulus Congestus Circulations Climate 


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This paper arises from the International Space Science Institute (ISSI) workshop on Shallow clouds and water vapor, circulation and climate sensitivity. The first author wishes to express a special thanks to Reimar Luest and the Max Kade Foundation for the opportunity to spend a year at MIT. Thanks go to Ethan Nelson, Raphaela Vogel, Katrin Lonitz and Vivek Sant for their help in creating figures, and to Cathy Hohenegger, Chris Bretherton and Robert Pincus for insightful discussions. Lastly, we thank three reviewers for providing insightful feedback.


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Copyright information

© The Author(s) 2017

Authors and Affiliations

  1. 1.Delft University of TechnologyDelftNetherlands
  2. 2.Massachusetts Institute of TechnologyCambridgeUSA
  3. 3.Nagoya UniversityNagoyaJapan
  4. 4.University of Wisconsin-MadisonMadisonUSA

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