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Characteristics of Western North Pacific Model Tropical Cyclogenesis

Camargo, Suzana J.; Sobel, Adam H.

"Tropical cyclogenesis" in a low-resolution Atmospheric General Circulation model is studied, focusing on the Western North Pacific region during the June-October typhoon season. Time-dependent composites of the cyclones are formed and analyzed, with a focus on the temporal evolution of quantities averaged in space around the storm centers. Day zero of each composite corresponds to the time at which the cyclone passes the criteria for detection. Some variables whose magnitude is related to cyclone intensity (such as low-level vorticity and surface wind speed) show similar temporal evolution, with a slight decrease up to a few days before day zero, a weak local minimum at that point, and a strong increase after that for a week or more. The relative humidity at low levels has its minimum somewhat later, at about day zero. The mean composite environmental vertical wind shear lacks a minimum and increases monotonically through the entire genesis period until a week after day zero. This variation is mostly due to the mean cyclone track's moving through regions of different climatological shear, which varies monotonically from easterly to westerly, crossing zero shortly after day zero, and would be consistent with a controlling role of the shear on model cyclogenesis. A signal in the skewness of the lower-level relative humidity distribution over the ensemble suggests that a dry lower troposphere can prevent development of a model cyclone. The local minimum in many variables' time series suggests the presence of an initial disturbance that is suddenly enhanced, becoming a model tropical cyclone, as has been noted in observations.

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More About This Work

Academic Units
International Research Institute for Climate and Society
Publisher
International Research Institute for Climate Prediction
Series
IRI Technical Report, 02-05
Published Here
May 21, 2010
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