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Oscillation of High-Level Cirrus and Heavy Precipitation around Australian Region Tropical Cyclones

F. A. LajoieBureau of Meteorology, Department of Science and Technology, Melbourne, Victoria, Australia, 3000

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I. J. ButterworthBureau of Meteorology, Department of Science and Technology, Melbourne, Victoria, Australia, 3000

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Abstract

A study of 27 days of three-hourly GMS infrared data for 11 tropical cyclones in the Australian region has revealed that the area of the cirrus canopy executes a marked diurnal oscillation with maximum at +3 h of 0800 LMST Mean Solar Time (LMST) and minimum at ±3 h of 1800 LMST. In the mean, the ratio of maximum to minimum area is 1.7:1. This diurnal oscillation is 12 h out of phase with that in the North Atlantic.

A weaker daytime oscillation also exists on most days with minimum and maximum areas occurring most frequently at ±3 h of 0900 and 1200 LMST, respectively.

Heavy precipitation associated with tropical cyclones, measured on the only atoll in the Southwest Pacific with long rainfall records, has almost the same bi-modal oscillation as that of the area of the cirrus canopy.

There is some evidence that during and immediately after a stage of cyclone intensification the oscillation of the area of the cirrus canopy changes considerably.

Abstract

A study of 27 days of three-hourly GMS infrared data for 11 tropical cyclones in the Australian region has revealed that the area of the cirrus canopy executes a marked diurnal oscillation with maximum at +3 h of 0800 LMST Mean Solar Time (LMST) and minimum at ±3 h of 1800 LMST. In the mean, the ratio of maximum to minimum area is 1.7:1. This diurnal oscillation is 12 h out of phase with that in the North Atlantic.

A weaker daytime oscillation also exists on most days with minimum and maximum areas occurring most frequently at ±3 h of 0900 and 1200 LMST, respectively.

Heavy precipitation associated with tropical cyclones, measured on the only atoll in the Southwest Pacific with long rainfall records, has almost the same bi-modal oscillation as that of the area of the cirrus canopy.

There is some evidence that during and immediately after a stage of cyclone intensification the oscillation of the area of the cirrus canopy changes considerably.

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