Joint Seminar: Representing deep convection in weather and climate models - new insights from observations

The representation of convection in weather and climate models remains one of the most difficult tasks in contemporary model development. Many of the well-known model errors including the poor simulation of the tropical mean precipitation patterns as well as errors in the representation of major modes of tropical variability ranging from ENSO to the Madden-Julian Oscillation to the diurnal cycle of precipitation have been shown to be associated with flaws in the representation of convection. By necessity convection in climate models is represented by means of parametrization, which inherently relies on the exploitation of relationships of large and small scales in a convecting atmosphere.

 

This presentation will shed new light on the large-to-convective scale relationships by using observations concurrently collected on both scales at Darwin in Northern Australia as well as globally by exploiting the International Satellite Cloud Climatology (ISCCP) data set. It will be shown that the common use of CAPE to determine the amount of convection in models is not supported by observations. Furthermore, it will be shown that much of the relationship between the large scales and convective rainfall is driven by the area that is precipitating, providing opportunities for new approaches to convection parametrization. The stochastic nature of the large-to-convective scale relationship will be investigated demonstrating that, contrary to currently used assumptions, the degree of stochastic behaviour is a function of the large-scale state itself. Finally, exploring the large-scale organization of convection beyond single grid boxes will show that the currently used diagnostic approach to cumulus parametrization does not fully capture the large-to-small scale relationships as memory on the small scales does influence the evolution of convection in similar large-scale conditions. 

Date

12.06.2012

Time

15:15 h

Place

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

Speaker

Christian Jakob, Monash University, Australia

Organizers

Bjorn Stevens

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