Reexamining the Nonlinear Moisture‐Precipitation Relationship Over the Tropical Oceans

• Published in: Geophysical research letters Vol. 45; no. 2; pp. 1133 - 1140
• Main Authors: Rushley, S. S., Kim, D., Bretherton, C. S., Ahn, M.‐S.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.01.2018
• Subjects: Atmospheric models; Climate models; CMIP5 model evaluation; Herbivores; Humidity; Hydrologic data; Intercomparison; Moisture; moisture‐precipitation relationship; Oceans; Precipitation; Rainfall; Relative humidity; Satellite data; Satellites; Special Sensor Microwave Imager; Tropical atmosphere; Tropical climate
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL076296

Bretherton et al. (2004) used the Special Sensor Microwave Imager (SSM/I) version 5 product to derive an exponential curve that describes the relationship between precipitation and column relative humidity (CRH) over the tropical oceans. The curve, which features a precipitation pickup at a CRH of about 0.75 and a rapid increase of precipitation with CRH after the pickup, has been widely used in the studies of the tropical atmosphere. This study reexamines the moisture‐precipitation relationship by using the version 7 SSM/I data, in which several biases in the previous version are corrected, and evaluates the relationship in the Coupled Model Intercomparison Project phase 5 (CMIP5) models. In the revised exponential curve derived using the updated satellite data, the precipitation pickup occurs at a higher CRH (~0.8), and precipitation increases more slowly with CRH than in the previous curve. In most CMIP5 models, the precipitation pickup is too early due to the common model bias of overestimated (underestimated) precipitation in the dry (wet) regime. Key Points A revised exponential relationship between column relative humidity (CRH) and precipitation is obtained The precipitation pickup occurs at a higher CRH, and precipitation increases with CRH at a lower rate in the new relationship Most CMIP5 models exhibit a too early precipitation pickup bias