SATELLITE INTERPRETATION DISCUSSION

October 31, 2001

Splitting Thunderstorms
Generally, when a thunderstorm is said to have “split,” the process implied is reminiscent of cell mitosis, that is, two separate thunderstorm updrafts form from one.  Numerical simulations suggest that one of the newly formed cells moves to the left of the mean (environmental) winds, and has an anticyclonically rotating updraft.  The other cell moves to the right of the mean winds, and has a cyclonically rotating updraft.  They are called the “left mover” and “right mover,” respectively. 
 

Loop 1
  

Figure 1

Click on images to start loops or enlarge figures.

The first loop contains visible satellite imagery of a storm that occurred over Nebraska on 17 May 1996 and is an example of such a split.  The diverging overshooting tops of the left and right movers are evident.  In an associated sequence of radar reflectivity images, the split, which has already begun as of 2213 UTC, is also evident.  Out of one >50 dBZ echo, come two >50 dBZ echos (Figure1). 

 
The second loop contains visible satellite imagery from 25 
May 1999.  As in the 17 May 1996 case, a left and right mover can be seen.  Unlike the first case, however, the transition from one thunderstorm to two does not occur as a mitosis-like process.  Rather, the left moving thunderstorm develops along the low level outflow boundary from the first thunderstorm, which was a right mover. 		  
Loop 2

 
Figure 2
   Another difference is seen in the radar reflectivity sequence (Figure 2).  The reflectivity core of the left moving cell strengthened as it propagated away from the right mover, rather than maintaining its strength during and immediately after the split.  Both the left moving and right moving thunderstorms of 25 May 1999 produced weak tornadoes, in addition to other severe weather.

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NOAA/NESDIS

Regional and Mesoscale Meteorology Team
Cooperative Institute for Research in the Atmosphere (CIRA)

We welcome your comments and discussion at ramsdis@comet.ucar.edu

The applet used for the loops was developed by Tom Whittaker of SSEC (his homepage is       http://www.ssec.wisc.edu/~tomw/index.html).  The Java applet is called AniS and it is freeware.  There is a link to a page describing it in detail from his homepage or you can go there directly at http://www.ssec.wisc.edu/visit/AniS/.

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