engleski

Comparison and validation of satellite-based overshooting top detection methods

Overshooting convective cloud tops (OT), dome-like protrusions above a cumulonimbus anvil, indicate the location of vigorous updrafts where severe weather including heavy rainfall, hail, strong winds and tornadoes most often occurs. OTs are apparent in satellite data with a lumpy textured appearance in visible channel imagery. Since visible channel imagery is only available during daytime, meteorologists must also use the infrared (IR) channels for observing and objective detection of OTs. The aim of this investigation is to compare the detection characteristics and relative accuracy of several different satellite–based OT detection methods. Research by the authors has shown that OTs can be detected from the satellite data using the brightness temperature difference (BTD) of the water vapor and the IR channel (6.2–10.8 μm), BTD of the ozone and IR channel (9.7–10.8 μm) or BTD of carbon dioxide and IR channel (13.4–10.8 μm). A combination of the 6.2-10.8 μm and 9.7-10.8 μm BTDs can also be used. All these methods include thresholds for both IR brightness temperature and the BTD. A more complex method, called IRW-texture, includes a combination of infrared channel brightness temperature and spatial gradient criteria with a numerical weather prediction model tropopause temperature forecast to detect OT signatures at their characteristic spatial scale. The theoretical background of all mentioned methods will be explained and the results of detection will be compared with the High Resolution Visible (HRV) satellite images during day-time in order to validate each method.

overshooting tops; satellite-based detection methods

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