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Tornado Warning Guidelines Data Limitations |
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Data
Limitations |
In any meteorological study, it is important to understand the limitations of the data used. There are two primary sources of errors in the data used in this study; radar sampling limitations and errors in the tornado data base. As the radar beam moves away from the radar the beam width increases, and under normal atmospheric refraction, the elevation of the beam increases. At 60 n mi from the radar, the beam width increases to 1 n mi with a beam width of 2 n mi at 120 n mi. Under standard atmospheric conditions, the beam reaches a height of 1 n mi at a range of about 47 n mi. An actual tornado signature is rare and can only occur very close to the radar where the tornadic circulation is several beam widths wide (Brown 1998). As range increases, it becomes more and more difficult to resolve features associated with a tornadic thunderstorm, and the radar beam is likely to overshoot low-level features. Also, the maximum wind velocity depicted in Archive level IV data is 64 kt. The radar saves velocities greater than 64 kt as 64+ kt. In this study, when a velocity was indicated to be above the radar velocity limit, a simple empirical correction was used. Still, errors are likely when calculating rotational velocities and shears when either (or both) the inbound or (and) outbound velocities used in the calculation exceeded 64 kt. The availability of archived radar data and the quality of the data also was a problem. Initially, over 200 tornadoes were identified for potential study, but radar data was available for less than half of them. Even when radar data was available, there were many times when the data was incomplete due to missing volume scans or missing elevation slices. Storm Data (U.S. Department of Commerce 1993-1998) was used to identify tornadoes used in this study. Radar data suggest there may be errors in times assigned to several tornadoes and there were inconsistencies in a few reports. Also, it is possible that tornadoes in remote areas were never identified.
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