DataStreme Activity 3A:

WEATHER SATELLITE IMAGERY

Do Now:

  1. Print this file.
  2. Print the Monday Image 1, Image 2 and Image 3 Files.
  3. Print (when available) the Tuesday, 26 September 2000, Daily Summary File

To Do Activity:

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

Go To STUDY GUIDE - Activity 3A Now


WELCOME BACK: Procedure continued from STUDY GUIDE.

  1. Last Friday, 22 September, was the autumnal or fall equinox when the Northern and Southern Hemispheres were equally illuminated by solar radiation. Image 1 is the visible satellite display for Monday morning, 0015Z on 25 SEP 2000 (7:15 PM Central Daylight Time on 24 September), labelled across the upper margin "Visible Image" (from "Visible - Latest" on the DataStreme Homepage). This visible satellite image is for the time when sunset was occurring across the central US on this day. [Due to data processing difficulties at COMET, this image is provided by another satellite imagery source.]

    The image shows the cloud pattern in the Western US. As described in the Monday, 25 September, Daily Weather Summary, most of the western US was experiencing fair weather. Some cloud patches remain in Colorado from the snowstorm of the previous day and thunderstorms in northern Mexico were associated with the southern end of the long cold front across the eastern US. (The surface map of these features is not shown.) [Note: The printed satellite image usually displays more detail than is seen on screen. The on-screen image may be enhanced by adjusting the screen brightness and/or contrast.]

    At the time of the visible satellite image, sunlight was reaching the US from the general direction of [(east) (west)]. Cloud conditions, if any existed at this time, are not seen across the eastern half of the image because [(of nighttime conditions) (the satellite is beyond the horizon)].

  2. At the Image 1 time of 0015Z it was approximately sunset time at Fargo, North Dakota (7:18 PM at longitude 96.8 °W, midway along the North Dakota-Minnesota border) and at Houston, Texas (7:15 PM at longitude 98.3 °W, in southeastern Texas). Draw a line between these two cities extending completely across the satellite image. The line you drew represents the "terminator" or line separating day and night at the time of Image 1.

    This line is [(approximately parallel) (at an angle)] to north-south lines of longitude. (The north-south line segment that is the Manitoba-Ontario border just north of Minnesota, and the north-south line segment of the Oklahoma-Arkansas border are longitude lines.) This terminator - longitude line orientation changes throughout the year and will be discussed in this week's second activity.

  3. Image 2 is the infrared satellite image ("Infrared - Latest") for the same time (0015Z 25 SEP 2000). This image showed much [(less) (more)] cloudiness, particularly in the eastern US, than was seen in the visible image. Infrared images are basically temperature maps of the surfaces "seen" by the satellite sensor. Warm surfaces (land during most of the year and low clouds) would appear relatively [(bright white) (dark)] and cold surfaces emitting little infrared radiation would appear [(bright white) (dark)]. Surfaces with intermediate temperatures appear in gray shadings.

  4. The surface weather map for essentially the same time as the images indicated that the major weather feature affecting the US was a cold front stretching from Virginia across the south central US to southeastern Texas and along the US - Mexican border to California. A large high-pressure system in southern Wyoming was influencing most of the western US.

    The brightness of clouds in the infrared image associated with the cold frontal system showed the cloud tops to be generally [(warm) (cold)]. This implies that the cloud tops associated with the convection along the front are generally very [(low) (high)]. The brightest white cloud tops from central Texas to northern Mexico are associated with towering thunderstorm tops. The cloud patch over northern Colorado and southern Wyoming are darker gray, and therefore are generally [(warmer) (colder)] than the clouds in central Texas. These CO-WY cloud tops generally are at [(lower) (higher)] levels than those in central TX.

  5. Now compare the Image 1 visible satellite view with the Image 2 infrared view. On the visible image, a patch of clouds appears generally bright white just off the southern Oregon border in the Pacific Ocean. In the infrared view, their shading is generally dark gray. This infrared shading implies these clouds were probably [(high) (low)] level clouds with relatively [(warm) (cold)] temperatures at cloud top level. In this way, the two types of satellite information complement each other.

  6. If you wished to create a 24-hour time-lapse of the cloud patterns across the US using the DataStreme satellite images from each hour, you should choose the [(visible) (infrared)] images because the [(visible) (infrared)] images would appear black during nighttime hours. (Most satellite images seen on television are infrared images.)

  7. Image 3 is an enlarged image from the web site, http://www.time.gov, at 13:37 CDT on 22 September, the equinox when the central US was in sunlight. This site gives the official time for the United States from the National Institute of Standards and Technology (formerly the National Bureau of Standards) in Boulder, Colorado. Selecting a time zone displays the current exact time and date for that zone, its relationship to UTC, and an image that is a smaller version of Image 3. The depiction in Image 3 is from a model showing the positions of the sunrise and sunset terminators and the portion of the entire Earth's surface that would be illuminated by the sun at that time.

    The Image 3 daylight portion of the map shows the equator to be about half illuminated. There are 12 hours of daylight everyday of the year at the equator. The daylight portion of the image is approximately equal width at all latitudes in both hemispheres. These widths imply that, at this time of the year, 22 September, the period of daylight is [(more than 12 hours in the Northern Hemisphere) (approximately 12 hours everywhere on Earth) (less than 12 hours in the Northern Hemisphere)].

Routinely compare the latest satellite views with the latest analyzed surface map available via the DataStreme Homepage. Compare what you see on-screen with your local weather. You can ask yourself such questions as: Are your skies clear or cloudy? Do the satellite views show the same? A sequence of these map and satellite views posted in your classroom or shared with other teachers allows everyone to relate information provided by these differing depictions of weather conditions.

(Sunrise times, along with other astronomical information, can be obtained from the U. S. Naval Observatory site, http://aa.usno.navy.mil/AA/data/docs/RS_OneDay.html.)


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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