ATSC 5150 final 20%

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ATSC 5150 final (20)

• 12 questions in total,
• each question worth 1 2/3 pts
• A 13th question as extra credit

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Question 1. Here is a matched set of satellite
images, IR on the left and VIS on the right. Time
is 1845 UTC, date 26 Feb 02. Briefly explain
what you see at the lettered locations, in terms
of atmospheric properties (cloudiness, cloud
type, visibility, temperature ) and/or surface
properties (albedo, temperature ). a. b. c. d.
The dark areas surrounding the lighter
areas e. f.
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Location Ji Parana, southeastern Amazon Basin
Monthly total rainfall, Feb 1999, derived from 10
cm radar reflectivity-
Height above sea level (m)
Question 2 a. What echo on the rainfall map
(left) do you believe is an artifact of the
radar, i.e. what is not real? b. What kind of
rainfall (convective or stratiform) dominated,
and why? c. What insight does the topography map
(above) give about the spatial variability of
rainfall?
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Question 3. This is a vertical reflectivity
transect from a 2.5 cm radar across a mesoscale
convective system. The rainfall is classified, as
shown. What is the basis of the classification of
the stratiform precipitation? Explain the
microphysical mechanism.
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Question 4 a. What kind of satellite image is
this? b. What weather phenomenon are we looking
at? (hint the width of the image is 20 km)
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Question 5. Shown are 4 IR images, from 1115 UTC
thru 1715 UTC on 10 Dec 02. Focus on the belt
from MAF to OAX. The first two images suggest
that it is slightly warmer within this belt, and
the last image has this belt clearly colder than
the surroundings. Explain (hint A 12 Z sounding
at OAX is shown. )
OAX
MAF
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GOES west visible color, 12 Sept 1998
Question 6 a. What causes the brightness at
(a)? b. What kind of cloud system is (b)? c. What
kind of cloud is (c)? d. Estimate the image time
in UTC.
c
b
a
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Question 7. Use the graphs on the right to
discuss how the atmospheric profile of
temperature or water vapor can be derived by
spaceborne measurements of upwelling radiances at
a series of specific frequencies.
attenuation profile, for typical radiation
amounts emitted from various heights
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Question 8. (a) Explain why, in the absence of
rain, oceans appear so cold at 18 or 37 GHz.
(hint start with explaining the meaning of
brightness temperature) (a) If you had only an
18 GHz microwave receiver on your satellite,
where would you be able to estimate rainfall rate
best, over land or over oceans? Explain. (b) The
85 GHz channel is obviously quite useful to
estimate the heavy rainfall rates typical of deep
convection. Discuss why the 85 GHz brightness
temperature is so low over deep convection.
(hint explain what happens to the upwelling
radiation).
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Question 9. This image shows wind speed over the
ocean based on passive microwave radiation at two
frequencies. Can, at least in theory, passive
microwave radiation be used also to estimate wind
direction? Explain.
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Question 10. IR imagery has the advantage that it
works both day and night. This implies that
storms and clouds can be tracked 24 hrs a day.
The exception, perhaps, is fog. a. Why cant fog
be seen on IR imagery? b.The image below is an
example of the fog product, based on
geostationary satellite data at night. What is
the idea behind this product? c. Why doesnt this
concept work during the daytime?
fog
high/deep cloud
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Question 11. Water vapor imagery is supposed to
discriminate dry (high Tb) from humid airmasses
(low Tb). Discuss why region (a), right over
the Gulf of Mexico where the air usually is
muggy, is extremely dry in this image. Explain
why region (b) in N. Manitoba, where the winter
air is extremely dry, appears so humid in this
image. The coincident IR image may be of help.
b
a
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• Question 12.
• Plot the large-scale wind profile (use wind
  barbs) that produces this radial velocity
  pattern. Assume that the range rings correspond
  to heights of 2 and 4 km, with the maximum radius
  shown corresponding to 5 km AGL.
• The mean-wind profile you plotted is the essence
  of the VAD technique, which uses radar radial
  velocities at various elevation angles to
  calculate the mean wind profile on a circle
  surrounding the radar. Explain why the VAD
  technique (or single-Doppler radial velocities in
  general) cannot yield large-scale vorticity
  within the radar domain.

-35 kts
35 kts
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Question 13. Choose one of these two
questions a. How can geostationary IR imagery be
used to infer winds aloft? Hint look at this
loop. Discuss method, strengths, and
weaknesses. b. Discuss, in just a paragraph, the
challenge of rainfall estimation from satellite
IR imagery in the American West. The left image
below shows the true annual-mean precipitation,
as observed by raingauges etc. The right image
shows the global frequency of high clouds. High
clouds dominate the upwelling IR signal, on
account of their low skin temperature. In what
region (or season) does geostat IR imagery do
better in estimating rainfall totals?