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9.4: Homework Exercies

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  • 9.5.1. Broaden Knowledge & Comprehension

    B1. Access a surface weather map that shows station plot information for Denver, Colorado USA. Decode the plotted pressure value, and tell how you can identify whether that pressure is the actual station pressure, or is the pressure reduced to sea level.

    B2. Do a web search to identify 2 or more suggestions on how to reduce station pressure to sea level. Pick two methods that are different from the method described in this chapter.

    B3. Search the web for maps that show where METAR weather data are available. Print such a map that covers your location, and identify which 3 stations are closest to you.

    B13. Search the web for sites that give the ICAO station ID for different locations. This is the ID used to indicate the name of the weather station in a METAR.

    B4. Access the current METAR for your town, or for a nearby town assigned by your instructor. Try to decode it manually, and write out its message in words. Compare your result with a computer decoded METAR if available.

    B5. Search the web for maps that show where weather observations are made today (or recently), such as were shown in Figs. 9.2-13.16. Hint: If you can’t find a site associated with your own country’s weather service, try searching on “ECMWF data coverage” or “Met Office data coverage” or “FNMOC data coverage”.

    B6. For each of the different sensor types discussed in the section on Weather Observation Locations, use the web to get photos of each type of instrument: rawinsonde, dropsonde, AWOS, etc.

    B7. Search the web for a history of ocean weather ships, and summarize your findings.

    B8. Access from the web a current plotted surface weather map that has the weather symbols plotted around each weather station. Find the station closest to your location (or use a station assigned by the instructor), and decode the weather data into words.

    B9 Access simple weather maps from the web that print values of pressure or temperature at the weather stations, but which do not have the isopleths drawn. Print these, and then draw your own isobars or isotherms. If you can do both isobars and isotherms for a given time over the same region, then identify the frontal zone, and determine if the front is warm, cold, or occluded. Plot these features on your analyzed maps. Identify highs and lows and airmasses.

    B10. Use the web to access surface weather maps showing plotted station symbols, along with the frontal analysis. Compare surface temperature, wind, and pressure along a line of weather stations that crosses through the frontal zone. How do the observations compare with your ideas about frontal characteristics?

    9.5.2. Apply

    A1. Find the pressure “reduced to sea level” using the following station observations of pressure, height, and virtual temperature. Assume no temperature change over the past 12 hours.

    P (kPa) z (m) Tv(°C)
    a. 102 –30 40
    b. 100 20 35
    c. 98 150 30
    d. 96 380 30
    e. 94 610 20
    f. 92 830 18
    g. 90 980 15
    h. 88 1200 12
    i. 86 1350 5
    j. 84 1620 5
    k. 82 1860 2

    A2. Decode the following METAR. Hint: It is not necessary to decode the station location; just write its ICAO abbreviation followed by the decoded METAR. Do not decode the remarks (RMK).

    1. KDFW 022319Z 20003KT 10SM TS FEW037 SCT050CB BKN065 OVC130 27/20 A2998 RMK AO2 FRQ LTGICCG TS OHD MOV E-NE
    2. KGRK 022317Z 17013KT 4SM TSRA BKN025 BKN040CB BKN250 22/21 A3000 RMK OCNL LTGCCCG SE TS OHD-3SE MOV E
    3. KSAT 022253Z 17010KT 10SM SCT034 BKN130 BKN250 28/23 A2998 RMK AO2 RAE42 SLP133 FEW CB DSNT NW-N P0001 T02830233
    4. KLRD 022222Z 11015KT M1/4SM TSRA FG OVC001 24/23 A2998 RMK AO2 P0125 PRESRR
    5. KELD 022253Z AUTO 14003KT 4SM RA BR OVC024 23/21 A3006 RMK AO2 TSB2153E12 SLP177 T02280211 $
    6. KFSM 022311Z 00000KT 10SM TSRA SCT030 22/21 A3004 RMK AO2 P0000
    7. KLIT 022253Z 08009KT 7SM TS FEW026 BKN034CB OVC060 27/22 A3003 RMK AO2 RAB28E45 SLP169 OCNL LTGICCC OHD TS OHD MOV N P0000 T02720217
    8. KMCB 022315Z AUTO 34010KT 1/4SM +TSRA FG BKN005 OVC035 24/23 A3009 RMK AO2 LTG DSNT ALQDS P0091 $
    9. KEET 022309Z AUTO 05003KT 3SM -RA BR SCT024 BKN095 23/23 A3005 RMK AO2 LTG DSNT N AND E AND SW
    10. KCKC 022314Z AUTO 20003KT 2SM DZ OVC003 13/11 A3009 RMK AO2
    11. CYQT 022300Z 20006KT 20SM BKN026 OVC061 16/11 A3006 RMK SC5AC2 SLP185
    12. CYYU 022300Z 23013KT 15SM FEW035 BKN100 BKN200 BKN220 23/08 A3013 RMK CU2AS2CC1CI1 WND ESTD SLP207
    13. CYXZ 022300Z 00000KT 15SM -RA OVC035 14/11 A3021 RMK SC8 SLP239
    14. KETB 022325Z AUTO 10007KT 009V149 10SM -RA CLR 19/11 A3021 RMK AO2
    15. CYWA 022327Z AUTO 33004KT 9SM RA FEW027 FEW047 BKN069 19/12 A3016

    A3. Translate into words a weather glyph assigned from Table 9-11.

    Screen Shot 2020-02-27 at 4.54.49 PM.png
    Table 9-11. Weather-Glyph Exercises.

    A4 For a weather glyph from Table 9-11, write the corresponding METAR abbreviation, if there is one.

    A5. Using the station plot model, plot the weather observation data around a station circle drawn on your page for one METAR from exercise A2, as assigned by your instructor.

    A6. Using the USA weather map in Fig. 9.19, decode the weather data for the weather station labeled (a) - (w), as assigned by your instructor.

    A7. Photocopy the USA weather map in Fig. 9.19 and analyze it by drawing isopleths for:

    1. temperature (isotherms) every 5°F
    2. pressure (isobars) every 0.4 kPa
    3. dew point (isodrosotherms) every 5°F
    4. wind speed (isotachs) every 5 knots
    5. pressure change (isallobar) every 0.1 kPa

    Figure 9.21-i Temperature (°C). (These figures are shown out of order because there was space on this page for it.)

    Screen Shot 2020-02-27 at 5.10.20 PM.png

    Figure 9.21-ii Pressure (kPa). [The first 1 or 2 digits of the pressure are omitted. Thus, 9.5 on the chart means 99.5 kPa, while 0.1 means 100.1 kPa.]

    Screen Shot 2020-02-27 at 5.11.44 PM.png

    Screen Shot 2020-02-27 at 5.15.21 PM.png
    Figure 9.20 Canadian weather map courtesy of Environment Canada.
    (see previous page)
    Figure 9.21
    Screen Shot 2020-02-27 at 5.19.09 PM.png
    Figure 9.22 A surface weather map of central and eastern N. America. Units: T and Td (°F), visibility (miles), speed (knots), pressure and 3-hour tendency (see text), 6-hour precipitation (hundredths of inches). Extracted from a “Daily Weather Map” courtesy of the US National Oceanic and Atmospheric Administration (NOAA), National Weather Service (NWS), National Centers for Environmental Prediction (NCEP), Hydrometeorological Prediction Center (HPC). The date/time of this map is omitted to discourage cheating during map-analysis exercises.

    A8. Using the Canadian weather map of Fig. 9.20, decode the weather data for the station labeled (a) - (z), as assigned by your instructor.

    A9. Photocopy the Canadian weather map of Fig. 9.20, and analyze it by drawing isopleths for the following quantities.

    1. temperature (isotherms) every 2°C
    2. dew point (isodrosotherms) every 2°C
    3. pressure change (isallobar) every 0.1 kPa
    4. total cloud coverage (isonephs) every okta
    5. visibility every 5 km

    A10. Both of the weather maps of Fig. 9.21 correspond to the same weather. Do the following work on a photocopy of these charts:

    1. Draw isotherms and identify warm and cold centers. Label isotherms every 2°C.
    2. Draw isobars every 0.2 kPa and identify high and low pressure centers.
    3. Add likely wind vectors to the pressure chart.
    4. Identify the frontal zone(s) and draw the frontal boundary on the temperature chart.
    5. Use both charts to determine the type of front (cold, warm), and draw the appropriate frontal symbols on the front.
    6. Indicate likely regions for clouds and suggest cloud types in those regions.
    7. Indicate likely regions for precipitation.
    8. For which hemisphere are these maps?

    9.5.3. Evaluate & Analyze

    E1. Are there any locations in the world where you could get a reasonable surface weather map without first reducing the pressure to mean sea level? Explain.

    E2. What aspects of mean sea level reduction are physically unsound or weak? Explain.

    E3. One of the isoplething instructions was that an isopleth cannot end in the middle of the map. Explain why such an ending isopleth would imply a physically impossible weather situation.

    E4. Make a photocopy of the surface weather map (Fig. 9.22) on the next page, and analyze your copy by drawing isobars (solid lines), isotherms (dashed lines), high- and low-pressure centers, airmasses, and fronts.

    9.5.4. Synthesize

    S1. Suppose that you wanted to plot a map of thickness of the 100 to 50 kPa layer (see the General Circulation chapter for a review of thickness maps). However, in some parts of the world, the terrain elevation is so high that the surface pressure is lower than 100 kPa. Namely, part of the 100 to 50 kPa layer would be below ground.

    Extend the methods on sea-level pressure reduction to create an equation or method for estimating thickness of the 100 to 50 kPa layer over high ground, based on available surface and atmospheric sounding data.

    S2 What if there were no satellite data? How would our ability to analyze the weather change?

    S3. What if only satellite data existed? How would our ability to analyze the weather change?

    S4. a. Suppose that all the weather observations over land were accurate, and all the ones over oceans had large errors. At mid-latitudes where weather moves from west to east, discuss how forecast skill would vary from coast to coast across a continent such as N. America.

    b. How would forecast skill be different if observations over oceans were accurate, and over land were inaccurate?

    S5. Pilots flying visually (VFR) need a certain minimum visibility and cloud ceiling height. The ceiling is the altitude of the lowest cloud layer that has a coverage of broken or overcast. If there is an obscuration such as smoke or haze, the ceiling is the vertical visibility from the ground looking up.

    Use the web to access pilot regulations for your country to learn the ceiling and visibility needed to land VFR at an airport with a control tower. Then translate those values into the codes for a station plot model, and write those values in the appropriate box relative to a station circle.

    S6. In Fig. 9.4, notice that west of N. America is a large data-sparse region over the N.E. Pacific Ocean. This region, shown in Fig. 9.23 below, is called the Pacific data void. Although there is buoy and ship data near the surface, and aircraft data near the tropopause, there is a lack of mid-tropospheric data in that region.

    Although Figs. 9.2 - 9.12 show lots of satellite data over that region, satellites do not have the vertical coverage and do not measure all the meteorological variables needed to use as a starting point for accurate weather forecasts.

    Suppose you had an unlimited budget. What instruments and instrument platforms (e.g., weather ships, etc.) would you deploy to get dense spatial coverage of temperature, humidity, and winds in the Pacific data void? If you had a limited budget, how would your proposal be different?

    [Historical note: Anchored weather ships such as one called Station Papa at 50°N 145°W were formerly stationed in the N.E. Pacific, but all these ships were removed due to budget cutbacks. When they were removed, weather-prediction skill over large parts of N. America measurably decreased, because mid-latitude weather moves from west to east. Namely, air from over the data void regions moves over North America.]

    Screen Shot 2020-02-27 at 5.28.13 PM.png
    Figure 9.23 The “Pacific data void” & upper-air sounding locations (dots).

    A SCIENTIFIC PERSPECTIVE • Creativity in Engineering

    “Just as the poet starts with a blank sheet of paper and the artist with a blank canvas, so the engineer today begins with a blank computer screen. Until the outlines of a design are set down, however tentatively, there can be no appeal to science or to critical analysis to judge or test the design. Scientific, rhetorical or aesthetic principles may be called on to inspire, refine and finish a design, but creative things do not come of applying the principles alone. Without the sketch of a thing or a diagram of a process, scientific facts and laws are of little use to engineers. Science may be the theatre, but engineering is the action on the stage.”

    “Designing a bridge might also be likened to writing a sonnet. Each has a beginning and an end, which must be connected with a sound structure. Common bridges and so-so sonnets can be made by copying or mimicking existing ones, with some small modifications of details here and there, but such are not the creations that earn the forms their reputation or cause our spirits to soar. Masterpieces come from a new treatment of an old form, from a fresh shaping of a familiar genre. The form of the modern suspension bridge — consisting of a deck suspended from cables slung over towers and restrained by anchorages — existed for half a century before John Roebling proposed his Brooklyn Bridge, but the fresh proportions of his Gothic-arched masonry towers, his steel cables and diagonal stays, and his pedestrian walkway centered above dual roadways produced a structure that remains a singular achievement of bridge engineering. Shakespeare’s sonnets, while all containing 14 lines of iambic pentameter, are as different from one another and from their contemporaries as one suspension bridge is from another.”

    – Henry Petroski, 2005: Technology and the humanities. American Scientist, 93, p 305.