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.