Project Report

A novel method increasing the sensitivity of implicit cumulus convection in climate models was developed and tested. The main thrust of this research was to examine how this modified scheme impacts the timing of precipitation over the course of the day. Many land areas tend to have the most rainfall in the evening, whereas many climate models produce the maximum rainfall around local noon. The modified scheme was shown to systematically delay the maximum rainfall until later in the day when compared to a control simulation. An alternate formulation of the model was used to show that this shift in the timing of rainfall was due to increased mixing between clouds and the environment only in the lower portions of the cloud. This most notable change in the model’s behavior occurred over the US Great Plains, where observations have shown that rainfall tend sot maximize after midnight. The control simulation produced the maximum rainfall around local noon, which is a deficiency found in many global atmospheric models. However, when using the modified cumulus parameterization rainfall over the Great Plains exhibited a maximum slightly after midnight similar to observations. Further investigation into what mechanisms were responsible for this did not yield conclusive results. Observations indicate that eastward propagating weather disturbances play a significant role in producing a nocturnal rainfall peak over the Great Plains. Eastward propagating disturbances were not evident in the simulations performed. Further investigation is needed to uncover the specific processes that contribute to the nocturnal maximum.

National Science Foundation (NSF)
Office of International and Integrative Activities (IIA)
Application #
Program Officer
Carter Kimsey
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Hannah Walter M
Fort Collins
United States
Zip Code