Extratropical Cyclone Clouds: Impact on Cyclone Strength and Climate

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Wednesday, 7 January 2015
James B. Polly, CREST/City College of New York, New York, NY; and W. B. Rossow

Clouds of extratropical cyclones (ECs) lie at the intersection of well-developed theory of dry baroclinic waves and nonlinear feedback on these dynamics due to the effects of moisture and radiation. Of all cloud regimes, EC clouds are the most effective at blocking short-wave radiation, while trapping heat within the troposphere via long-wave blocking. The net modulation of moist processes on the transient wave and the resulting climatological effects due to modified energy and water transports remain unclear. A novel cyclone tracking algorithm (NASA's MCMS) is used to identify ECs in the ERA-I reanalysis data and collect properties of each disturbance. A classification scheme based on cyclone radius and pressure depth is developed and compared to various strength metrics. Properties of resulting classes are analyzed, and composites of radiation (ISCCP FD) and precipitation (TRMM TMPA) are assembled for each class. At this stage of research each detected cyclonic disturbance is treated independently of its prior/future realizations or phase of development. Lifetime and temporal evolution will be considered in subsequent investigations. The depth—radius classes defined here meaningfully discriminate between over 106 extratropical disturbances and correspond with distinguishable regimes of precipitation and radiation. Seasonal variability of cyclone types and their diabatic heating are described as well as interesting interannual trends.