Dr. Brad Muller
The radar "bright band" is a phenomenon that shows up
higher reflectivity near the elevation of the melting layer
snow and rain.
As mentioned in conjunction with the radar
equation, the dielectric constant for ice is 0.197
is 0.93 for liquid water. This means that liquid water
considerably more reflective than ice for microwave
also know that the reflectivity factor is proportional to
the 6th power
of the particle size. Since snowflakes are usually
raindrops, their size compensates somewhat for the lack of
reflectivity, and they still show up pretty well on radar
previously mentioned, sometimes clear-air mode is used in
as to be able to better view details of the reflectivity).
The bright band occurs in the layer where snowflakes are
rain (following image borrowed from http://apollo.lsc.vsc.edu/classes/remote/lecture_notes/radar/conventional/bright_band.html:
Two effects are occurring. The first is that when the
first start to melt, they melt from the outside in, so at
have nearly the diameter of a snowflake (large) but are
liquid (high index of refraction), both combining for a high
reflectivity. The second effect is that as the
and shrink into liquid water drops, their terminal velocity
and they start to fall faster, leaving fewer of them in the
radar-sampled volume just below the melting layer.
bright band becomes a vertical maximum in the reflectivity.
The bright band is best seen on RHI displays (second panel):
It also can be seen in height-time plots of radar data from
On a PPI display, the bright band will be seen at the range
radar beam cuts through the vertical level of the melting
Since the radar is scanning at an angle upward, the
brightband in a PPI
appears as a bright ring around the radar location, fairly
close in to
the radar on the higher tilts.
Bright band at N3R from Goodland, Kansas.
Bright band at N3R from Portland, Oregon.
Bright band at N3R from Portland, Maine. Click here
To look for the bright band in real time, choose an
area with widespread stratiform precipitation falling at the
ground as rain (check NOAA's NEXRAD
page in comparison with NCAR's Surface Data
page.) Use Unidata's IDV (Integrated Data Viewer) to
access the radar data as described below:
Using the IDV to View the Radar Bright Band
NOAAPort does not disseminate radar reflectivity
from "tilts" other than the lowest one any more, so higher
tilts are best seen in the IDV (Integrated Data
Viewer). The IDV was originally a UNIX program, but
recently versions for Windows have become available. You can
get to the IDV for windows via the S: Drive => Courses
=> Outgoing => WX => wx-IDV => Start Menu Items
- Win 7 Integrated Data Viewer 3.0u2 and double click
on "Integrated Data Viewer."
The full address is S:\COURSES\OUTGOING\WX\wx-IDV\Start Menu
Items - Win7 - Integrated Data Viewer 3.0u2
Use the "Data" dropdown window to choose "NEXRAD Radar
Files" then on click on the "NEXRAD - Remote" tab on the
Dashboard to pull up a map of NEXRAD locations. Zoom
in with a rubber band box (left click, hold, and move the
cursor around), or unclick "Declutter" then zoom, to see
stations that may not show up at first. Click on the desired
station, then select some times to display (either relative
or absolute), then click "Add Source." Then select
"Reflectivity" from fields, and "Radar Sweep View in 3D"
from Displays, then click on "Create Display." The IDV
defaults to the 0.5 degree elevation angle, but on the
Dashboard you can select any elevation angle. The best
for views for seeing the bright band are usually
between about 2.4 and 6 degrees, but you'll have to
To take full advantage of the 3-D capabilities, right click
on the radar image, and hold down while moving the
cursor--prepare to be amazed! To reset to the original
plan view, look for the depiction of a 3-D rectangle with
its top face highlighted in blue at the upper left of the
display window, and click that icon.
The IDV is available for download to your own personal
computer from the Unidata
web page under the "Downloads" dropdown!
The IDV allows you to view products other than reflectivity
such as Radial Velocity and the new Dual Polarization
products using the Field Selector on the Dashboard. It
is best to clear out your previous data set before
selecting a new data set or station to display by clicking
the scissors icon or going to "Edit" then "Remove all Displays