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Honeywell IntuVue RDR-4000 Pilot's Manual page 43

3-d automatic weather radar system with forward looking windshear detection for airbus sa/lr aircraft


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IntuVue RDR-4000 Weather Radar Pilot's Guide
In addition to reflectivity associated with convective weather, the radar
will typically display reflectivity associated with stratus, or stratiform,
weather. Whereas convection is characterized by localized towers with
updraft and downdraft features, stratiform precipitation results from
much more widespread and much less vigorous uplift. As a result,
stratus precipitation is more layered in form with much lower gradients
in radar reflectivity. However, the reflectivity of stratiform weather can
be sufficient to cause yellow and red on the radar display. These high
reflectivities result from relatively high rain rates, as well as from
enhancement of reflectivity due to melting of snow particles just below
the freezing level. High reflectivity of stratus weather does not indicate
any significant hazard (with the exception of any potential for icing, or
takeoff and landing performance issues associated with high rainfall
Updrafts in thunderstorms support abundant water; when carried above
the freezing level, this water becomes supercooled. As the temperature
in the upward current cools to about -15°C, much of the remaining water
vapor sublimates as ice crystals. Above this level, the amount of
supercooled water decreases.
Supercooled water freezes on impact with an aircraft. Clear icing can
occur at any altitude
above the freezing
level; but at high levels,
icing may be rime or
mixed rime and clear.
The abundance of
supercooled water
makes clear icing occur
very rapidly between
0°C and -15°C, and
encounters can be
frequent in a cluster of
Principles of Weather Radar Use
Rev 1, December 2014

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