Predicting convective rainfall over tropical oceans from environmental conditions

A cloud resolving model in spectral weak temperature gradient mode is used to explore systematically the response of mean convective rainfall to variations tropical environmental conditions. A very large fraction of the variance in modeled rainfall is explained by three variables, the surface moist...

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Bibliographic Details
Published in:Journal of advances in modeling earth systems 2016-06, Vol.8 (2), p.703-718
Main Authors: Raymond, David J., Flores, Marcos M.
Format: Article
Language:English
Subjects:
Atmospheric precipitations
Convection
Convective instability
Convective rainfall
Entropy
Environmental conditions
Gravitational waves
Heat
Instability index
Oceans
Precipitation
Rain
Rainfall
Rainfall forecasting
Relative humidity
Saturation
Scale models
Temperature gradients
Tropical climate
tropics
Variance analysis
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Summary:A cloud resolving model in spectral weak temperature gradient mode is used to explore systematically the response of mean convective rainfall to variations tropical environmental conditions. A very large fraction of the variance in modeled rainfall is explained by three variables, the surface moist entropy flux, the instability index (a measure of low to midlevel moist convective instability), and the saturation fraction (a kind of column‐averaged relative humidity). The results of these calculations are compared with the inferred rainfall from 37 case studies of convection over the tropical west Pacific, the tropical Atlantic, and the Caribbean, as well as in the NCEP FNL analysis and the ERA‐Interim reanalysis. The model shows significant predictive skill in all of these cases. However, it consistently overpredicts precipitation by about a factor of three, due possibly to simplifications made in the model. These calculations also show that the saturation fraction is not a predictor of rainfall in the case of strong convection. Instead, saturation fraction covaries with the precipitation as a result of a moisture quasi‐equilibrium process. Key Points: Rainfall in modeled tropical convection is predictable Stronger surface moist entropy flux increases rainfall Greater moist convective instability decreases rainfall
ISSN:1942-2466
1942-2466
DOI:10.1002/2015MS000595