Research and Application News
NASA sees inner-core structure of Typhoon Usagi persisted at landfall
24 September 2013
The radar on NASA and JAXA's Tropical Rainfall Measuring Mission (TRMM) satellite saw Typhoon Usagi maintaining some of its inner-core structure an hour before landfall on 22 September 2013. The data was used to create an image that showed the 3-D regions of heavy precipitation hiding under the circular cloud cover near Usagi's centre of rotation.
While the light precipitation regions had lost the appearance of organisation, the heavy precipitation regions showed what appeared to be a ~50 km/31.0 mile-radius eye wall, with multiple rain bands further away from the centre. There is even some evidence that the compact inner eye wall, seen in previous overflights, had not completely disappeared one hour before landfall. The yellow arrow on the left side of the image shows the orientation of the viewpoint in the zoom view on the right side of the image.
The heavy precipitation was indicated there using the 40 dBZ radar reflectivity signal, and that signal barely reached a 6 km/3.7 miles altitude, indicating updrafts fell somewhat short of what would be required for lightning to form in the inner core. (dBZ means "decibels relative to Z" and is a meteorological measure of "Z," the equivalent reflectivity of a radar signal reflected off a remote object- which is the principle of Doppler Radar).