Observing phase changes and 3.9µm reflectivity patterns on severe storm tops. (contd)
Unusually high 3.9 µm reflectivity patterns observed in mature storm tops.
Unusually bright patterns of 3.9µm reflectivity sometimes occur around the tops of mature or severe storms. This curious phenomena has been the subject of research in a joint project between the Czech Hydrometeorological Institute and NSSL ( (Setvak et al., 1996). You may also access their project homepage referred to as the MOST project (Multispectral Observations of Storm Tops).
There have been two broad classes high 3.9µm reflectivity patterns found at storm top:
- Small spots of high reflectivity found at anvil top, sometimes
observed over low WSR-88D reflectivity regions at stormtop.
These spots have also been observed over mesocyclones as shown in
in
figure 2 of Setvak et al. 1996.
- Larger plume-like features observed to form just downwind of
overshooting tops of strong thunderstorms. These features have
been observed over Eastern Europe (as seen here and over the Midwest shown in
figure 4
of Setvak et al. 1996. These features seem to be associated
with the 10.7µm warm wakes observed on top of updrafts that
remain quasi-steady state for at least tens of minutes.
To date, these high 3.9µm reflectivity features seem to be associated with strong thunderstorms. However, not all strong/severe storms have these features. No observations have been made over weakly forced convection either.
There are several explanations for the high 3.9µm reflectivity
features:
- Smaller than normal ice particles produced in a strong updraft.
- Much larger than normal ice particles.
- Jumping cirrus found above and downwind of overshoots. Here is
a photograph
.
