National Severe Storms Laboratory

Retrieving the cumulus entrainment rate remotely

Dr. Tim Wagner
Department of Atmospheric Sciences
Creighton University

10 July 2014, 10:00 AM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

The entrainment of environmental air into cumulus clouds can greatly influence the impact these clouds have on their environment. As cumuli are an important part of the climate system, these impacts must be accounted for in simulations but their small spatial extent means they must be parameterized. The parameterization of cumuli and the impact of entrainment upon them have proven to be difficult problems in part due to the lack of available observations of entrainment. Entrainment has been traditionally measured via direct penetration of clouds by instrumented aircraft but the expense and difficulty associated with this method means that the scope of the available entrainment observations is small.

To expand the number of observations of entrainment available for analysis, a remote retrieval method using ground-based instrumentation has been developed. This method, called the Entrainment Rate In Cumulus Algorithm (ERICA) retrieves the fractional entrainment rate through a Gauss-Newton optimal estimation retrieval. High temporal resolution observations of cumuli and their environment and a guess of the entrainment rate are ingested by a cloud parcel model, in this case the Explicit Mixing Parcel Model (EMPM). The entrainment rate is iteratively adjusted until the modeled cloud matches the observations. ERICA has been shown to correspond well with other methods of retrieving the entrainment rate. Results for both shallow continental cumulus and deep tropical convection will be shown.

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