A Tutorial on the Current Icing Product (CIP)
The Current Icing Product (CIP) combines sensor and numerical model
data to provide an hourly, three-dimensional diagnosis of the icing environment. Several
recent upgrades have resulted in a new suite of CIP variables including
calibrated icing probability and icing severity.
The new probability variable replaces the uncalibrated icing potential.
Probabilities range from 0% (no icing expected) to 85% (near certain
icing). Probabilities do not reach 100% because the data available to diagnose icing
do not allow for a diagnosis with absolute certainty at any given location in space.
Icing severity encompasses five categories (none, trace, light, moderate, and heavy).
SLD icing conditions are
characterized by water drops larger than 50 micrometers (diameter) which
includes freezing drizzle and freezing rain aloft. It has been
demonstrated that these conditions, which are
outside the icing certification envelopes (FAR Part 25 Appendix C) can
be particularly hazardous to some aircraft. Thus the information can
be valuable for flight planning.
CIP is output on a grid with pixels every 20 km in the horizontal
and 1000 feet in the vertical. ADDS displays every other level except on
the Flight Path Tool that provides access to all levels. To retrieve a CIP
graphic on the ADDS icing page, simply alter the desired
variable using the left-side pull-down menu
then select the desired altitude from a separate
pull-down menu to the right of the product list. The requested graphic should
appear as an image embedded directly in the icing page. Besides the individual
levels, you can select a composite, maximum value of all altitudes, labeled "max."
This image provides a quick overview of the regional icing threat.
On the icing probability
graphics (sample shown in Fig. 1), the scale is from 0 to 85%, using
cool to warm colors with warmer colors indicating higher icing likelihood.
On icing severity
graphics (sample shown in Fig. 2), the scale is from trace (very light blue) to heavy (dark
blue). By default, icing severity
is shown with red hatched regions indicating an SLD icing threat
(sample shown in Fig. 3). Icing severity can also be "masked" to
show points where the icing
probability is greater than 25% or 50%. Either of these options use a gray color to
mask the severity pixels where icing probability is less than the threshold value
(sample shown in Fig. 4).
Pilot reports (PIREPs) of icing are overlaid on the
single-level graphics (legend found at the bottom of each graphic)
if within 1000 feet vertically and 75 minutes temporally. On the
composite graphic, PIREPs for all altitudes are shown (except negative icing reports,
which are omitted for the sake of clarity).
Those interested to learn more details of the science used to create CIP are invited
to read the following paper:
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Bernstein, B.C., F. McDonough, M.K. Politovich, B.G. Brown, T.P. Ratvasky,
D.R. Miller, C.A. Wolff and G. Cunning, 2005: Current Icing Potential (CIP):
Algorithm description and comparison with aircraft observations. J. Appl.
Meteor., 44, 969-986.
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Fig.1: Icing probability
Fig.2: Icing severity
Fig.3: Severity with SLD overlay
Fig.4: Masked icing severity
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Example event: 16 Feb 2005
On 16 Feb 2005, a cold front moved through the Great
Lakes region and into the Appalachians leaving widespread
icing conditions in its wake. As part of the development work
behind the CIP product, researchers from NASA and NCAR purposefully
fly into known icing conditions. This event was chosen because a team
of researchers flew into the clouds and icing conditions
in the area around Cleveland, Ohio on this day. They encountered
primarily small supercooled water drops between 5500 and 6000 feet MSL
that produced periods of moderate icing. Photos of this
icing encounter are shown at right. Note the build-up of ice on the
leading edge of the wing of the NASA Glenn Research Center Twin Otter.
A series of graphics created from CIP data at 1500 UTC
are shown above. The small graphics here display the region around Cleveland
whereas clicking on the figure produces the graphic for the entire CIP domain.
Note the yellow and orange hues on Fig. 1 denoting the highest probability
for icing south and east of Cleveland. Likewise, note the region of moderate
icing severity in Fig. 2 but lower probability and decreased severity
to the north and west (over Lake Erie). When the Twin Otter briefly flew northwest
of Cleveland, the crew confirmed the sharp decrease in icing severity combined with
significantly less liquid water content but roughly constant temperature and droplet sizes.
The SLD product at the same altitude (not shown) did not depict any large drops
in the region around Cleveland and none was found by the research aircraft. A SLD plot
from 9000 feet seen in Fig. 3 shows SLD diagnosed well to the south and east
of Cleveland, but the research aircraft did not fly in those areas so it was not confirmed.
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Fig.5: Icing accumulates while in cloud. Photo credit: NASA Glenn Research Center
Fig.6: After ascending above cloud. Photo credit: NASA Glenn Research Center
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