Geoscience Reference
In-Depth Information
Doppler radar is valued for measuring winds in hurricanes and detecting tornadoes that can
be imbedded in the bands. Combined with polarimetric capability, its utility greatly
increases because of improved quantitative measurement of rainfall. Observation of
hurricane Irene which swept the US East coast at the end of August 2011 is the case in point.
Rotation speed of over 110 km h
-1
is apparent in Fig. 18 where the color categories are too
coarse to estimate the maximum values. The cyan color captures well Irene's rotational
winds because they are aligned with radials. Color categories are coarse precluding precise
estimation of velocities but recorded values are quantized to 0.5 m s
-1
. Although the
unambiguous velocity is ~ 28 m s
-1
values more negative than -30 m s
-1
are displayed. These
and other outside the unambiguous interval have been correctly dealiased by imposing
spatial continuity to the field.
Fig. 18. Left: Rain rate in Hurricane Irene, obtained with a polarimetric algorithm using
differential phase and reflectivity factor (surveillance scan with unambiguous range of ~ 465
km). Right: Velocity field obtained with the SZ(2) phase code (Doppler scan with
unambiguous range of ~135 km and velocity ~ 28 m s
-1
). Elevation is 0.5
o
, time 12:26 UTC,
on Aug 27, 2011. The range circles are spaced 50 km apart. Color categories for rain rate are
in mm h
-1
and for velocity in m s
-1
. (Figure courtesy of Pengfei Zhang).
The rain rate field depicts Irene's bands some containing values larger than 100 mm h
-1
.
These are instantaneous measurements and over time accumulations caused significant
flooding which brought 43 deaths and ~ 20 billion $ damage to the NE coast of the USA. The
obviously large spatial extent of Irene amply justifies use of surveillance scan for maximum
storm coverage and Doppler scan for wind hazard detection.
Atmospheric biota is routinely observed with the WSR-88D network (Rinehart, 2010).
Examples are insects, birds, and bats. Many insects are passive wind tracers providing a
way to estimate winds in the planetary boundary layer (extending up to 2 km above
ground).
Biota can be tracked for ecological or other purposes. The radar can also provide location of
bird migrating paths, roosts, and other congregating places; this could be important for
aircraft safety. The three donut shaped features in Fig. 19 represent Doppler speeds of birds
