The transition to strong convection: temperature/moisture dependence and mesoscale clusters
Abstract
Recent work has shown that observations of tropical precipitation conform to a number of properties associated with critical phenomena in other systems (Peters and Neelin, 2006, Nature Phys.). Here some of these properties are used to probe the physics of tropical convection empirically in Tropical Rainfall Measuring Mission microwave and radar data. The power law pick-up of the ensemble-average precipitation as a function of column water vapor on tropospheric temperature is determined, and is found to differ from the simplest expectations from convective parameterizations. The empirically determined critical surface thus provides a new test against which convective parameterizations can be compared. The frequency of occurrence of strong precipitation has a characteristic sharp drop as the system approaches the critical point, with exponential decay above critical. A large fraction of the precipitation occurs near and above critical. Mesoscale convective cluster average size picks up sharply at critical, and the size distribution exhibits a scale-free range near critical. Sea surface temperature (SST) is shown not to have a strong effect on the critical pickup of precipitation. The effect of SST occurs instead via the fraction of time spent near critical over regions of warm SST. These new diagnostics are consistent with some assumptions of current convective parameterizations, but also suggest additional properties that should be included.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.H24C..04N
- Keywords:
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- 3265 Stochastic processes (3235;
- 4468;
- 4475;
- 7857);
- 3314 Convective processes;
- 3354 Precipitation (1854);
- 4425 Critical phenomena;
- 4480 Self-organized criticality