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Errors caused by draft fraction in cumulus parameterization
Author(s) -
Murata Akihiko
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl039100
Subject(s) - magnitude (astronomy) , fraction (chemistry) , cloud fraction , parameterized complexity , resolution (logic) , mathematics , statistics , mechanics , physics , computer science , astrophysics , algorithm , chemistry , organic chemistry , cloud computing , artificial intelligence , cloud cover , operating system
The assumption that the draft fraction is negligible in cumulus parameterization can be a major source of error in the parameterized tendencies of thermodynamic quantities. This study estimates the errors arising from this assumption based on an analysis of high‐resolution cloud‐resolving model output. The numerical results reveal a negative error associated with the assumption, indicating that the magnitude of the mean subgrid‐tendency of moist static energy is underestimated when the assumption is employed. The magnitude of the error is proportional to the draft fraction, and is independent of horizontal resolution. The results are confirmed by theoretical analyses, which support a linear relationship between error magnitude and draft fraction, and confirm that the error magnitude is independent of horizontal resolution. The resulting underestimates of moist static energy tendency should not be neglected in the case that the horizontal resolution is sufficiently fine to enable the frequent occurrence of large draft fractions.