The Sensitivity of Convective Cloud Ensemble Statistics to Horizontal Grid Spacing in Idealized RCE Simulations.

Saved in:

Bibliographic Details
Title:	The Sensitivity of Convective Cloud Ensemble Statistics to Horizontal Grid Spacing in Idealized RCE Simulations.
Authors:	SAVRE, JULIEN¹ julien.savre@lmu.de, CRAIG, GEORGE¹
Source:	Journal of the Atmospheric Sciences. May2023, Vol. 80 Issue 5, p1267-1284. 18p.
Subjects:	Convective clouds, Statistical equilibrium, Poisson distribution, Distribution (Probability theory), Poisson regression, Statistics, Statistical mechanics
Abstract:	In this work, cloud ensemble statistics are extracted from idealized radiative-convective equilibrium simulations performed at horizontal grid spacings D ranging from 2 km to 125 m. At the coarsest resolution, convection remains randomly distributed in space such that the equilibrium statistical mechanics theory proposed by Craig and Cohen in 2006 (CC06; assumes Poisson distributed clouds and exponential mass flux distributions) remains valid. Using classical organization metrics, clustering is already observed at D 5 1 km, but substantial deviations between the simulated cloud ensemble statistics and CC06 are only observed for grid spacings D, 500 m. At these resolutions, the cloud mass flux distributions exhibit heavy tails and cloud counts become overdispersed (higher variance than a Poisson distribution). These changes in ensemble statistics are accompanied by a shift in subcloud organization patterns as well as with the fact that individual cloudy updrafts start to be resolved. Consequently, a horizontal grid spacing no larger than 250 m is recommended, not only to properly resolve the dynamics of individual convective clouds, but also to capture the mesoscale organization of the cloud ensemble. Finally, it is shown that the CC06 theory and our high-resolution results including mesoscale organization may be reconciled if one considers 1) areas smaller than approximately 2 km in size, corresponding roughly to the narrow bands along which clouds develop almost randomly; and 2) individual cloud cores instead of cloud objects, core mass fluxes being shown to generally follow exponential distributions. [ABSTRACT FROM AUTHOR]
	Copyright of Journal of the Atmospheric Sciences is the property of American Meteorological Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database:	Engineering Source

Description
Abstract:	In this work, cloud ensemble statistics are extracted from idealized radiative-convective equilibrium simulations performed at horizontal grid spacings D ranging from 2 km to 125 m. At the coarsest resolution, convection remains randomly distributed in space such that the equilibrium statistical mechanics theory proposed by Craig and Cohen in 2006 (CC06; assumes Poisson distributed clouds and exponential mass flux distributions) remains valid. Using classical organization metrics, clustering is already observed at D 5 1 km, but substantial deviations between the simulated cloud ensemble statistics and CC06 are only observed for grid spacings D, 500 m. At these resolutions, the cloud mass flux distributions exhibit heavy tails and cloud counts become overdispersed (higher variance than a Poisson distribution). These changes in ensemble statistics are accompanied by a shift in subcloud organization patterns as well as with the fact that individual cloudy updrafts start to be resolved. Consequently, a horizontal grid spacing no larger than 250 m is recommended, not only to properly resolve the dynamics of individual convective clouds, but also to capture the mesoscale organization of the cloud ensemble. Finally, it is shown that the CC06 theory and our high-resolution results including mesoscale organization may be reconciled if one considers 1) areas smaller than approximately 2 km in size, corresponding roughly to the narrow bands along which clouds develop almost randomly; and 2) individual cloud cores instead of cloud objects, core mass fluxes being shown to generally follow exponential distributions. [ABSTRACT FROM AUTHOR]
ISSN:	00224928
DOI:	10.1175/JAS-D-22-0164.1