Meteorology 553- Mid-Term
Due: November 21
Purpose: (1) review basic fundamentals;
(2) apply linear Rossby wave theory;
(3) apply barotropic theory to the movement of weather systems;
(4) apply potential vorticity theory to the movement and development
of weather systems;
(5) figure out why last week's snow storm didn't materialize.
I will check in by phone
on Wednesday during class time (around 9:00 AM) to see
if there are any questions.
Do this exam on your own please; however, you may share information among
yourselves
regarding access to resources on mosaic.
Also share information related to how to print out graphics from xv.
Print them on the laser printer (lpr -s -P hplw), not the color printer.
Do not ask faculty, staff, or graduate students
who are not in this course for help .
Unlike the assignments, I want you to type your answers, print them out,
and turn them in with all figures
rather than emailing the text to me.
Fundamentals
(1) 5 points. Requires 2 700 mb maps for Nov 9 12z; use one map
as scratch copy and other to turn in. Question
pertains to western half of map only (west of 100W).
Correct the 700 mb temperature analysis from the ETA model, if you think it is necessary.
Shade areas of significant warm air advection in red and areas of significant
cold air advection in blue.
Estimate the magnitude of temperature advection at Salt Lake City in degrees C
per day.
(2) 5 points.
Crop and print out the 300 mb panel from the 24 hour forecast of the operational ETA
on Nov 9 12z. Do this by choosing the save option and selecting the postscript
format type. Follow the directions in xv and then type lpr -s -P hplw file_name .
Label areas of strong cyclonic curvature, strong cyclonic speed shear, and
anticylonic speed shear.
What is causing the strong convergence at 300 mb off the west coast of California? the strong divergence over southern Idaho and Utah?
Linear Rossby wave theory
(3) 10 points.
Write a Fortran (or C) program that computes the zonal mean wind speed required
for waves 1, 2, 3, ... 10 to remain stationary as a function of latitude (at
5 degree latitude intervals from 0-90).
Use the Rossby wave dispersion relationship as written in class or in a
standard text such as Holton.
Print out the resulting table of winds as a function of wavenumber (printed
horizontally) and latitude (printed down the page).
Describe very briefly the changes in wind speed required as (a)
the wave number increases and as (b) the latitude increases.
(4) 10 points. Run your Hovmuller program used in the first assignment to plot the amplitudes of
waves 1-10 as a function of time for Nov. 9 00z. The data file for this question is
/home/glory/v/research/nov0994/grid/94110900g027.grd . You will need to change
your scripts to reflect this change.
Describe briefly the evolution of the amplitudes of waves 1-3 during the
10 day forecast period.
Look at the temporal evolution of waves 1-3 by typing xanim /home/glory/v/research/nov0994/gif/MRF_WA* .
Relate the movement (retrogression/progression, etc.) forecast by the MRF model
to the
table developed as part of question 3.
Barotropic Theory
(5) 5 points. (a)
Assume that absolute vorticity is conserved.
An air parcel moves from 60N to 30N. At the initial time, the
air parcel has no relative vorticity. When it reaches 30N, by how much has
the relative vorticity increased or decreased?
(b) A vigorous short-wave trough is moving southward on the west side
of a deep long-wave trough. Explain schematically and briefly in words
what is likely to happen to the amplitude and position of the long-wave trough.
(6) 5 points. (a)
Use the vorticity equation including the divergence term for this question.
A short-wave ridge at 300 mb moves into a region of divergence. Will the
short-wave ridge amplify or decay? Why?
(b) Explain how when the vorticity equation is integrated vertically that the
effect of terrain on the movement of troughs and ridges can be taken into
consideration. Explain from this perspective why mean ridges in the
upper troposphere are common upstream of major mountain barriers.
(7) 10 points. Describe in turn the relative merits and drawbacks for
synoptic-scale dynamics of
the following vertical coordinates: height, pressure, potential termperature.
(8) 10 points. Assume that potential vorticity is conserved for a parcel moving
from 30N to 60N. At the initial time, the parcel has anticyclonic relative
vorticity of -5x10**-5/sec. Assuming that the parcel's initial depth is 100 mb,
what depth would the parcel have when it reaches 60N if its value of relative
vorticity remains unchanged? Would the parcel experience areal expansion or
contraction? Would the air motion likely be rising or sinking?
(9) 10 points. The mean flow immediately to the south of the equator (say 15S)
over
South America is from east to west in the upper troposphere.
The Andes Mountains represent a significant north-south mouontain barrier.
Assume that potential vorticity is conserved and that the height of the tropopause is unchanged in the east-west direction.
Sketch a vertical cross-section across the Andes and show the changes in depth,
horizontal extent and rotation of the parcel as it moves in this flow.
Sketch a horizontal surface to show the locations of troughs and ridges
that might be formed as a result of the effects of the terrain.
The Snow Storm that Wasn't
(10) 30 points. As you undoubtedly remember, the numerical forecasts
on November 9 at 00z indicated that a significant winter storm was likely
by November 11 at 00z. Based on the skill of the forecasts made for the
forecast contest for that day, none of us had a clue as to what was actually
going to happen. I want you to spend a few hours evaluating what led to
the poor forecasts by us ( and the NWS and the TV stations ...).
Some of the information is available in a somewhat
odd location. Go to the Meso-ETA forecasts page and then go to the case
study pages for Nov. 9 and Nov. 10.
There is a lot of information available to diagnose this storm, so I want
you to focus your efforts and not try to look at everything.
Choose either of the following periods:
9th 00z to 10th 12z or 9th 12z to 11th 00z.
Print out figures that seem relevant; but quality counts
for more than quantity.
If you think that something vital is missing, you may ask Rob Swanson for
assistance. But look around and think first, before asking for help.
Also, there is some overlap between this question and the 3rd homework assignment. I suggest you consider doing the homework assignment in parallel with answering
this question.
There are
a few key factors that you need to consider.
(a) What really happened? What was the observed evolution of temperature at the
surface or 700 mb? Where was the low-level baroclinic zone as a function of time?
What was the observed evolution of the upper level circulation?
(b) What was forecast? Where was the storm supposed to go?
What was different between the observed evolution and that forecast?
You may choose to look more extensively at a particular model or contrast
the forecasts from several different models.
Let me emphasize that you need to spend some time on this problem. I am more
interested in your attempts to explain what happened physically (even
if that may be in error) than simply describing figures.
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