DataStreme Activity 4A:

TEMPERATURE AND AIR MASS ADVECTION


Notice: Figure 4.4, p. 63 of the Part A: Narrative (text) should have the shortwave reflected by clouds as 17 units. (A printed smudge mistakenly looks like a decimal.)


Do Now:

  1. Print this file.
  2. Print the Monday Image 1 File.
  3. Print (when available) the Tuesday, 3 October 2000, Daily Summary File.

To Do Activity:

  1. Read Chapter 4 in STUDY GUIDE, Part A: Narrative.
  2. Go to STUDY GUIDE, Part B: Applications. Start Activity 4A.
  3. Return here (Monday Activity A File) when told to do so.

Go to Study Guide - Activity 4A Now.


WELCOME BACK: Procedure continued from STUDY GUIDE.

  1. The on-going general decrease of solar insolation in the middle to high latitudes of the Northern Hemisphere coupled with the increasingly dominant outgoing radiation means cooling is taking place. This affects our weather in the progressively cooler air masses that invade the central US as we move from summer to winter months. The first dramatic example of these continental polar air masses was the beginning of last week, 24 - 26 September. Numerous record low temperatures were set from Texas to New England as this cold air moved southward into the central US.

    Image 1 is a map of reported surface weather conditions for 00Z 25 SEP 2000 (7 PM CDT 24 SEP) labelled U.S. - Data. The weather conditions are summarized at selected stations across the coterminous US in the surface station model introduced in Activity 2A. First, examine the temperature values across the map. (Temperature in degrees Fahrenheit is plotted in the "11 o'clock" position about the station circle.) Wichita, Kansas, where the air pressure at map time was 1021.7 mb, was reporting a temperature of _____°F, with a wind direction from the [(north-northwest) (south-southeast)] at about [(10) (25)] knots.

  2. On the Image 1 map, use the station temperature values to draw the position of the 80 °F isotherm across the Southeastern US from South Carolina through Texas. The isotherm would pass through stations where 80 °F occurred and be spaced proportionately between stations of temperature higher than and lower than 80 °F. Be sure to label both ends of the isotherm with its value, 80 °F. Then similarly draw the 70 °F isotherm across the US from the Middle Atlantic States to the New Mexico area and label it. Continue your temperature analysis by drawing the 60 °F and 50 °F isotherms from the East Coast to the New Mexico-Colorado area. (As an option, you may wish to complete all isotherms that would appear on the map.)

  3. The drawing of these isotherms reveals an important feature of the temperature pattern, called a temperature gradient. A temperature gradient is a measure of the change of temperature over distance. The gradient is relatively strong where the temperatures change rapidly over distance and weaker where the isotherms are farther apart. There is a strong temperature gradient as evidenced by the close spacing of isotherms from [(Kansas to north Texas) (Georgia to south Florida)].

    At map time the temperature at Wichita, Kansas was ______ °F. The temperature at San Antonio, Texas (south-central Texas) was ______ °F. The temperature difference between Wichita and San Antonio was ______ F°. The temperature difference between Atlanta, Georgia and Miami, Florida was ______ F°. These were comparable distances. Therefore, the temperature gradient, amount of change over distance, was stronger between [(Atlanta and Miami) (Wichita and San Antonio)].

  4. Where winds blow across isotherms, cold or warm air advection occurs. Cold air advection occurs at locations where winds blow across the isotherms from regions of lower temperature to regions of higher temperature. On the Image 1 map, compare wind directions and the isotherms you drew, at stations from northern Texas to Maine. The wind direction at these locations was generally [(parallel to) (at angles across)] the isotherms and from regions of [(higher) (lower)] temperatures. Cold air advection was occurring at these locations as the wind was blowing from colder to warmer regions.

  5. Warm air advection occurs at locations where winds blow across the isotherms from regions of higher temperature to regions of lower temperature. On the Image 1 map, compare wind directions along the 80-°F isotherm you drew in the region from LA to SC. The wind direction at these locations was generally [(parallel to) (at angles across)] the isotherms and from regions of [(higher) (lower)] temperatures. Warm air advection was occurring at these locations as the wind was blowing from warmer to colder regions.

  6. At map time a cold front was crossing the southern and eastern portions of the US. This front, the leading edge of the cold air intrusion, was located from the Canadian Maritime Provinces (at the Canadian Atlantic shoreline intersection with the top map boundary) to the central Virginia coast, to the middle of the Mississippi-Arkansas border, diagonally down to just south of San Antonio, and back up to El Paso, the point of western Texas. Mark this cold frontal position with a wide curving line. Add the appropriate cold frontal symbols to denote the direction of movement of the front.

  7. Compare the regions of cold and warm air advection you identified earlier on the map to the location of the cold frontal boundary. Generally the cold air advection was occurring [(behind, that is, northwest of) (ahead of, that is, southeast of)] the cold front. The warm air advection was occurring [(behind) (ahead of)] the cold front.

  8. An individual in Atlanta might have expected temperatures to [(rise or remain steady) (fall)] for a few hours due to warm air advection until the cold front passes. Then temperatures would be expected to [(rise) (fall)] following the frontal passage as cold air advection occurs. (One must also consider the normal daily cycle of daytime warming and nighttime cooling as well as advection processes in determining actual temperatures.)

Warm or cold air advection depends on the strength of the temperature gradient, the speed of the winds, and the angle of the wind across the isotherms. Light winds, as may occur overnight, or near the center of Highs, produce little temperature advection. As weather systems cross your region in the coming weeks and months, have your students call up DataStreme products to identify patterns of cold or warm air advection associated with these passing systems. The DataStreme homepage provides a map of station models and computer-analyzed isotherms ("Isotherms, Fronts, & Data") that aids in find warm or cold air advection.

The relatively warm temperatures from eastern Montana to the Dakotas show the warm air advection due to the effects of downsloping flow (Chinook). The wind directions (generally westerly) indicate the winds were coming down from higher elevations to the west. Such winds will be discussed in Chapter 10.


Hold this activity until you have completed all applications for this week. Instructions for faxing your LIT mentor will appear at the end of this week's Activity B.


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