On the use of PDF schemes to parameterize sub-grid clouds

Ping Zhu, Paquita Zuidema

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Using high resolution simulations of eight well-documented cloud cases in different climate regimes, this study investigated the statistical distributions of dynamic and thermodynamic variables in the cloud layer and examined various assumptions used by the current statistical cloud schemes. It is found that dynamic and thermodynamic variables skew differently in the cloud layer of shallow cumulus, stratocumulus, and deep convective clouds. Vertical velocity is positively skewed, but the skewed dynamic structure cannot account for the large skewness of positively skewed total mixing ratio q t and negatively skewed liquid water potential temperature θ l. It is, thus, not physically sound to assume that the sub-grid variation of different variables follows the same skewed PDF. The simulations further show that the weighted standard deviations of q t and θ l have the same order of magnitude in all types of clouds, indicating that the variations of temperature and moisture are the equally important factors for sub-grid clouds. Thus, neglecting either one of them in a statistical cloud scheme may introduce significant bias in the parameterized clouds.

Original languageEnglish (US)
Article numberL05807
JournalGeophysical Research Letters
Volume36
Issue number5
DOIs
StatePublished - Mar 16 2009

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grids
thermodynamics
stratocumulus
convective cloud
statistical distribution
skewness
potential temperature
cumulus
mixing ratio
simulation
mixing ratios
water temperature
statistical distributions
moisture
climate
standard deviation
liquid
temperature
acoustics
high resolution

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)
  • Geophysics

Cite this

On the use of PDF schemes to parameterize sub-grid clouds. / Zhu, Ping; Zuidema, Paquita.

In: Geophysical Research Letters, Vol. 36, No. 5, L05807, 16.03.2009.

Research output: Contribution to journalArticle

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