EGU22-5574
https://doi.org/10.5194/egusphere-egu22-5574
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Low-level radiative cooling peaks in regimes of shallow convective organization

Benjamin Fildier1, Caroline Muller2, Robert Pincus3,4, and Stephan Fueglistaler5
Benjamin Fildier et al.
  • 1Laboratoire de Météorologie Dynamique (LMD)/Institut Pierre Simon Laplace (IPSL), École Normale Supérieure, Paris Sciences & Lettres (PSL) Research University, Sorbonne Université, École Polytechnique, CNRS, F-75005 Paris, France
  • 2Institute for Science and Technologie, Vienna, Austria
  • 3Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
  • 4NOAA Physical Sciences Laboratory, Boulder, Colorado, USA
  • 5Geosciences Department, Princeton University, Princeton, New Jersey, USA

In models, a local maximum of clear-sky radiative cooling in the lower troposphere often appears as a necessary condition for the development and persistence of convective organization. However, no robust understanding has been provided for the emergence and disappearance of lower-tropospheric cooling in the atmosphere. Here we propose a theoretical characterization of clear-sky radiative cooling peaks, recently calculated from over 2,000 soundings launched during the EUREC4A field campaign in various patterns of shallow organization. A suite of scaling approximations are developed from simplified spectral theory to connect the longwave cooling peak to the vertical humidity structure set by convection. Its height is controlled by local maxima in the vertical gradients of water vapor path, and its magnitude is mainly controlled by the ratio between column relative humidity above and below the peak. In contrast, the value of the Planck function and the spectral width of emission only weakly vary across soundings.  Water vapor spectroscopy implies that upper-level intrusions of moist air detrained from lower latitudes can substantially dim these peaks, possibly by reducing the range of the spectrum that effectively cools to space at the level of the peak. This work motivates future modeling work, formulating the hypothesis that "Fish" patterns, which embed the widest persisting dry areas, may be the most favorable conditions for radiative processes to organize convection. If at play, this radiative feedback would maintain these patterns that are efficient at cooling the tropics, a type of "dry radiator fins" which could mitigate the risk of runaway climate states.

How to cite: Fildier, B., Muller, C., Pincus, R., and Fueglistaler, S.: Low-level radiative cooling peaks in regimes of shallow convective organization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5574, https://doi.org/10.5194/egusphere-egu22-5574, 2022.

Comments on the display material

to access the discussion