NSSL SWAT Case Study - 14 April 1999:

Southern Hemisphere supercell - The Sydney Australia Hailstorm

On April 14 1999, a unique data set was collected which was the first of its kind. The 5-cm Doppler radar at Kurnell, Australia, near Sydney, was operating with a base data recorder for the first time that a severe storm passed within the radar domain. That storm was the great Sydney Australia hailstorm, that produced over one-billion dollars (Australian) damage to the eastern suburbs, making it the costliest Australian natural disaster in history.

The storm appeared to be a classic supercell storm. Since it occurred in the Southern Hemisphere, the radar appearance of the storm looks unique to many who are used to supercell
data from the United States and Canada.

Presented here are various radar images from the Kurnell Australia (KURN) 5-cm radar operated by the Bureau of Meteorology (with data decoding software supplied by NSSL). Included in some of the images is output from NSSL's Mesocyclone Detection Algorithm (MDA). A cyan circle represents a 2D vortex feature (from a constant elevation angle) as detected by the MDA. Yellow, and red-in-yellow circles represent 3D vortex detections. In order for the algorithm to properly identify the cyclonic vortices, we ran a version that looks for shear in a clockwise sense, which is basically our Anti-MDA or AMDA for short.

The KURN volume scans are 6 minutes long, but are updated every 10 minutes, as the additional 4 minutes are used for vertically pointing measurement and other algorothms. Also, the background maps have not been developed. The radar is located within the city limits of Sydney, so when the storm passes over the radar origin, it is in the city. Note the attenuation as well, which is common with 5-cm radars.

NOTE: This page is still under construction. The few radar images here do not have algorithm output overlaid on them yet. Look for more in the future.

A SOUTHERN HEMISPHERE SUPERCELL:

LOOP of left-moving supercell - Reflectivity Loop (0642-1012 UTC)
"REVERSED" (north and south) loop of the supercell - Reflectivity "Reverse" Loop (0642-1012 UTC)

Description: The storm has reflectivity characteristics of a typical Northern Hemisphere supercell, except that the N-S axis is reversed. The storm instead moves left (still equatorward), rotates clockwise (which is still cyclonic), and has a hook echo on the left (equator) side of the main core. This can be seen in the following reflectivity loop. We have created the same loop, but with "north and south flipped" to simulate the same storm as a Northern Hemisphere cyclonic supercell.

We have done a similar thing (but this time flipped east and west) with this case of a left (poleward) moving anti-cyclonic tornadic supercell near Sunnyvale California (4 May 1998). Note that in this case, the supercell is a left (poleward) moving clockwise supercell.

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