Vaisala IRIS, User Manual

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Example: Detecting Hail
The occurrence of 45 dBZ at 1.5 km above the freezing level is a good indicator of hail in
many mid-latitude locations. Assuming that the freezing level is at 4 km, and you run an
echo
TOPS product for the 45 dBZ contour, your pre-configured warning could check if:
• The TOPS product shows 45 dBZ tops at heights greater than 5.5 km. If yes, there is
a high probability of hail.
• To avoid issuing an alarm based on a single pixel, a "threshold region" parameter
checks if the region of hail signature at least 10 km
2
.
• The VIL for the same region (1 ... 10 km) is greater than 5 mm (or a value determined
from the local climatology of hail).
The WARN product automates this procedure in real time by searching the products for
significant weather, and alerts the operator when an event is detected. The following figure
shows how the
WARN product works.
IRIS Product and Display User Guide M211319EN-H
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