Place an X here to count exam double! Name: ______
Final Examination, MEA 443 Fall 2009, Lackmann
If you wish to have the final exam count double and replace your midterm score, place an “X” in the box above. As always, you are allowed to ask me questions during the exam if you require clarification on a given problem. Good luck!
1.) Consider the three hypothetical 500-mb ensemble mean/spread plots shown below (taken from the COMET module). The contours show the ensemble mean, while the shading shows the spread. Match these plots with the most likely situation below: a.) A secondary cluster of solutions that differ from the majority: _____ b.) Large uncertainty in the forecasted amplitude of trough: _____ c.) Large uncertainty in the forecasted location of trough: _____
B A C
2.) List three advantages or types of information provided by ensemble predictions that are not obtainable from a single deterministic model forecast.
i.)
ii.)
iii.)
3.) Consider the following statements concerning a typical ensemble spaghetti diagram of 500-mb height. Which are true? Choose all that apply. ___ a.) The diagram provides a sense of the distribution of ensemble forecasts for only one or a few contour values at a time. ___ b.) The diagram presents information about all contour values of all ensemble members. ___ c.) Small distances between the height contours indicate strong wind speeds. ___ d.) The diagram allows forecasters to see if there is more than one likely solution.
4.) Ensemble True/False: ___ a.) A plume diagram for temperature can show multiple solutions for the timing of a cold frontal passage through a model grid box. ___ b.) Using different model boundary conditions can be a way of generating ensemble members. ___ c.) An ensemble “probability of exceedance” diagram is another name for a spaghetti plot of a given contour threshold, such as the 1.0” QPF line. ___ d.) “Targeted observations” are bad data identified by a data assimilation quality control system.
5.) a.) Based only on the sea-level pressure analysis shown below, is Appalachian cold-air damming taking place at the time of the analysis? _____ (yes or no).
b.)
If the answer above is “yes”, then how would you classify this event? (circle one) i.) Classical ii.) Hybrid iii.) In-Situ
If the answer is “no”, then explain why not.
6.) This semester, we have often utilized the potential vorticity as a means of quantifying the impact of diabatic processes and examining upper-tropospheric troughs and ridges. The mathematical expression for the Ertel (non-QG form) of the PV is PV g f , where is the relative p vorticity, and other symbols have their usual meanings. Using this expression: a.) Determine the MKS “units” of the PV,
b.) Determine the approximate scale of this quantity for typical synoptic-scale, tropospheric conditions.
7.) General meteorological analysis and scale analysis questions. Be sure to include units where appropriate, and show your work. a.) Write a mathematical expression for vertical potential temperature advection, with height (z) as the vertical coordinate. For synoptic-scale motions, what is the typical magnitude of this quantity?
b.) What is a typical value for the 900-mb geopotential height in the midlatitudes during winter? ______meters c.) What is the typical height of the tropopause over Miami, FL in winter? ______km d.) What is the typical height of the tropopause over Minneapolis, MN in winter? ______km
8.) The plot below shows an east-west oriented cross section, displaying the section-normal isotachs, with negative values dashed.
u g vg Thermal Wind Relations: z y z x a.) Sketch 3 isentropes, one each in the lower, middle, and upper portion of the section.
b.) Indicate with letters “T” and “R” the approximate location of any trough or ridge axes.
c.) Sketch a dotted line that corresponds approximately with the dynamic tropopause (a line separating large PV from smaller values).
9.) The plot below shows sea-level pressure (gray lines) with 500-mb height (darker lines). At each of the points A-D, indicate the sense of the temperature advection (cold, warm, or weak). A:______B: ______C: ______D: ______
B
D A
C
10.) A plot of sea-level pressure from the GFS model is shown below. Below it, there are 4 different 500-mb height maps. Based on your knowledge of QG dynamics, and the relation of upper waves to surface cyclones and anticyclones, which of the 500-mb map corresponds to this SLP map? _____
a.) b.)
c.) d.)
11.) A forecast of sea-level pressure (solid) and 850-mb temperature (dashed contours) is shown at left below, and a GFS-forecast sounding for Kalamazoo, MI is shown at right (the location of Kalamazoo is indicated with a diamond on the left diagram). The forecast is valid Saturday; Lake Michigan temperatures are ~35F.
a.) Based on the information available, do you expect lake-effect snow to occur in the Kalamazoo area at this time? ______(yes or no).
b.) If you do not expect lake-effect snow to be taking place, explain the reason. If you do expect it, what type of banding would be most likely for Lake Michigan?
12.) Below are two analyses of pressure and wind on the 308K isentrope for a recent weather event. The isentropes were observed to be moving towards the east at ~10 m/s. One of the plots shows storm-relative winds (V-c), and the other shows the full observed wind (V). a.) From which panel would you infer weaker ascent for the Carolinas? ______(a.) or (b.) b.) Which panel shows the storm-relative winds? ______(a.) or (b.)
a.) b.)
13.) Which of the following are true of barotropic and baroclinic energy conversions in the QG kinetic energy framework? Check all that are true. ____ a.) Barotropic energy conversions do not involve the generation of new kinetic energy, just a conversion of existing jet energy into or out of disturbance kinetic energy. ____ b.) A thermally indirect circulation converts kinetic energy to potential energy. ____ c.) At the latitude of the mean jet stream core, barotropic energy conversions are largest. ____ d.) Cyclones, on average, gain a large portion of their kinetic energy from baroclinic conversion.
14.) The diagram below shows a cross-sectional view through a region of latent heat release in a midlatitude cyclone. For each of the processes or characteristics mentioned below, match the location (A-C) on the diagram where that characteristic is relevant.
______a.) Height falls due to diabatic heating ______b.) Height rises due to diabatic heating ______c.) Positive PV anomaly due to diabatic heating ______d.) Negative PV anomaly due to heating ______e.) Development of cyclonic relative vorticity ______f.) Little or no height tendency.
C
B Maximum heating at “B”
up A
15.) True/False questions (1 point each) ___ a.) Q-vector convergence is the same as convergence of the wind field. ___ b.) Positive vorticity advection is always associated with rising air motion. ___ c.) If the large-scale flow is frontogenetical, a thermally indirect ageostrophic circulation will arise.
16.) Suppose that you are viewing historical model data for North Carolina in GEMPAK format, using GARP. A particular graphic you plot has the following date/time label: 941203/1800V036. a.) At what time is the image valid? ______b.) What do you know about the model forecast aspect? ______c.) What time of day, local time, is the image valid? ______
17.) One of the key terms in the QG equations is the vorticity advection. This process, or its vertical derivative, appears in both the height-tendency and omega equation. a.) Write a mathematical expression for the advection of absolute vorticity.
b.) What are the MKS units of this quantity (the vorticity advection)?
c.) What is the typical magnitude of this term for midlatitude, synoptic scale motions?
___ d.) At which of the following locations would you most expect to observe a large, positive value of this term? i.) Behind a strong upper-level trough ii.) At the center of a strong upper trough iii.) Immediately ahead of a strong upper-level trough iv.) At the center of a strong jet streak.
___ 18.) Suppose that you are forecasting during a severe weather outbreak in which you expect supercell thunderstorms to occur over the forecast area. You are examining output from the GFS model to assess the situation. Which of the following best represents the relation between the GFS vertical motion (omega) field and the expected supercell thunderstorms.
a.) If the model shows areas of strong ascent, we can assume that it is capturing the supercells themselves. b.) Ascent in the model would be environmental, and would not coincide to the actual convective storms. c.) The model may generate convective (parameterized) precipitation, but to do so would not result in any grid-scale ascent, so the storms could happen in the model but not show up in omega. d.) All of the above e.) Both b.) and c.)
___ 19.) Why is it necessary for numerical models to parameterize cumulus convection? a.) Because models would otherwise require an unrealistically long time to develop precipitation. b.) Because the atmosphere would become too unstable due to the neglect of the stabilizing action of sub-grid scale cumulus convection. c.) Because models must account for the effects of convective precipitation for a more realistic precipitation forecast. d.) All of the above e.) Only b.) and c.)
20.) Which convective scheme is used in the NAM model, the Kain-Fritsch or the Betts-Miller-Janjic scheme? ______
___ 21.) Which of the examples below best describes the concept of “forcing” and “response” in the form of linked “primary” and “secondary” atmospheric circulations? a.) Primary circulation: Ascending air at a front; Secondary circulation: Shearing frontogenesis. b.) Primary circulation: Geostrophic advections in a jet exit region; Secondary circulation: Thermally indirect ascent in left exit, descent in right exit. c.) Primary circulation: Strong land breeze over lake Michigan. Secondary circulation: Rising air in a lake-effect snow band. d.) Primary circulation: The jet stream. Secondary circulation: Embedded shortwave troughs.
22.) The top two images below are the NAM (211 grid) 24-h forecast valid for 12 UTC today. The upper left panel has SLP and 10-m winds, the upper right also as 2-m temperature added (dashed lines). The lower left panel is the same as the upper right, but zoomed in on NC. The lower right panel shows surface observations from 12 UTC today. a.) Compare panels c.) and d.) What physical processes might be responsible for the model errors in this case? List and briefly discuss.
b.) Sketch isotherms at 5F intervals on the lower right panel, and analyze any prominent frontal boundaries.
___ c.) What is/are the main frontogenetical mechanisms evident in the observational analysis? i.) shearing ii.) tilting iii.) confluence iv.) differential diabatic
Don’t forget to forecast for STL today and tomorrow. Happy Holidays!