Activity 3A:

WEATHER SATELLITE IMAGERY

Do Now:

1. Print this file.
2. Print the Image 1 and Image 2 Files.
3. Staple this to the back of the classroom activity 3A.

10. On March 20, 2000 at 2:35 a.m., Spring will arrive. This is called the Vernal Equinox. September 21, 1999 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 0015Z on 23 SEP 1999 (8:15 PM Eastern Daylight Time), labeled across the upper margin ("Visible - Latest" on the meteorology homepage). This visible satellite image is for the time when sunset was occurring in the central US on that equinox day.

    The image shows a cloud pattern off the West Coast associated with a cold front approaching Washington State from the Pacific. Wide-spread convective cloudiness can also be seen across the Southwestern US and northern Mexico. (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 [(east) (west)]. Cloud conditions, if any, are not seen across the eastern half of the image because
    [(of nighttime conditions) (the satellite is beyond the horizon)].

     

11. At the Image 1 time of 0015Z it was sunset time at St. Cloud, Minnesota (7:15 PM at longitude 94.2 °W) and essentially sunset at Galveston, Texas (7:16 PM at longitude 94.8 °W). St. Cloud is approximately half-way across Minnesota just south of the border separating North and South Dakota. Galveston is located at the south side of the northernmost bay on the Texas Gulf Coast. Draw a line across the satellite view connecting these two cities. The line you drew represents the "terminator" or line separating the day from night side of the Earth 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 formed from north-south longitude lines.) This terminator - longitude line orientation changes throughout the year and will be discussed in this week's second activity.

     

12. Image 2 is the infrared satellite image ("Infrared - Latest") for the same time (0015Z 23 SEP 1999). 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.

The brightness of clouds in the infrared image associated with the northern and southern ends of the cold frontal band in the eastern US 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 cloud tops just off the East Coast of the Carolinas, behind the cold front, are generally [(warm) (cold)]. These clouds in the cold air behind the front are at [(lower) (higher)] levels.

15.  If you wished to create a 24-hour time-lapse of the cloud patterns across the US using 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.)