Investigation 3A

DataStr= eme Atmosphere Current Weather Studies 3A:

WEATHER SATELLITE IMAGERY

Do Now:

Print this file.
Print the Monday Image 1, Image 2 and Image 3 Files.
When available, answer the two Concept of the Day questions in the Tue= sday, 22 September 2009 Daily Weather Summary File.

To Complete Investigation:

Read Chapter 3 in the DataStreme Atmosphere textbook and respond to the Chapter Progress Questions in the DataStreme Atmosphere Study Guide Investigations binder. [Do not complete the Questions for Review and Critical Thinking Questions appearing in the = Weather Studies Investigations Manual].
Complete the introductory portion of Investigation 3A in the Weather Studies Investigations Manual, which ends when you reach the statement, "As direc= ted by your course instructor, complete this investigation by either: ---<= /b>." [Do not complete the Applications portion of the Investigation.= ]

Go to the Monday - CWS= A (Current Weather Studies A) link on the course website to complete this investigation.

At this writing, we are in the week of occurrence of the fall equinox [2= 118Z (5:18 PM EDT, etc.) Tuesday, 22 September this year] wh= en the daily periods of daylight and darkness are approximately equal. On t= he equinox they will be equal everywhere on Earth except at the poles (except = for the few minutes of added daylight due to atmospheric refraction). That means that on the fall equinox, Earth's Northern and Southern Hemispheres are equ= ally illuminated. And the local sunrise and sunset positions on your horizon are= due east and west, respectively, at the equinox.

1= .      Image 1 is the visible satellite display for Sunday evening, 0015Z on = 21 SEP 2009 (7:15 PM Central Daylight Time on 20 September), labelled across the upper margin "Visible Image" (listed "Visible - Latest" on the course website). The image is for the time when sunset = was occurring along a line stretching from eastern Texas= to Minnesota on Sunday evening.

The visible image shows the cloud patterns in= the western U.S. Major expanses of cloud cover the area from Saskatchewan Province in Canada to Arizona and New Mexico. As noted in the Daily Weat= her Summary for Monday, 21 September 2009, a cold front was crossing the northe= rn High Plains (central North and South Dakota and western Nebraska) accompani= ed by some severe weather with damaging thunderstorms containing large hail at about the same time as the visible image. Additional thunderstorms were occurring in central Texas. [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 U.S. from the general direction of [(east)(= west)].

2= .      Cloud conditions, if any existed at this time, are not seen across the eastern ha= lf of the image because [(the sun has already set leaving darkness)(the satellite is not aimed to view the surface= )].

3= .      Note the short marks located just beyond the upper and lower map boundaries. Dra= w a straight line across the satellite view connecting these two marks. The line you drew represents the "terminator" or line separating day and n= ight at the time of Image 1 (0015Z on 21 SEP 2009). Label this line "ter= minator". This can also be called the sunset line as it is progressing westward across Earth's surface as the planet rotates eastward. At the time sunset was occurring at International Falls, on the Minnesota-Canada border at longitu= de 93.4 °W, latitude 48.6 °N, and Beaumont, in eastern Texas at longit= ude 94.1 °W, latitude 30.1 °N.

The western borders of much of Missouri and Arkansas represent approximate north-south longitude lines. The terminator line you = drew is [(nearly parallel)(at a large angle)] to the north-south border longitude lines. The terminator's orientation relative to north-south longitude lines changes throughout the year and will be discussed in this week's second activity. Y= ou can also note that the longitudes of the sunset cities listed are within one degree of being equal.

4= .      Image 2 is the infrared satellite image (from "Infrared - Latest") for the same time (0015Z on 21 SEP 2009) as the visible image. This image shows much [(less)(<= i>more)] cloudiness in the eastern half of the country, particularly in a broad arc = from Wisconsin southeastward to Alabama and Georgia, and across southern Florida<= /st1:State> than was seen in the visible image. Infrared images are basically temperatu= re maps of the surfaces "seen" by the satellite sensor.

5= . Warm surfaces (land during most of the year and low clouds) appear relatively [(bright white)(dark)].

6= . Cold surfaces such as high cloud tops, emitting little infrared radiation appear= [(bright white)(dark)]. Surface= s with intermediate temperatures appear in gray shading= s.

7= . At 0015Z 21 SEP 2009 several areas of rain and showers were spread across much= of the U.S.= One particularly notable area of severe thunderstorms with damaging winds mentioned in the Summary was located in central Texas. That brightness of shading show= ed those cloud tops to be generally [("warm")("cold")].

You might also be able to see the "bumpy= " texture of those clouds in central Texas in the visible satellite image. This effect comes from the shadows produced from the towering thunderstorm tops on lower clouds to the east by the low = sun angle.

8= . Also, bright cloud tops associated with the curving cloud band from Saskatchewan to New Mexico were generally at [(low)(= high)] altitudes.

9= . Comparatively, the white area of clouds seen in the visible image located offshore from central and southern California were part of a relatively uniform gray ribb= on of shading all along the coastal Pacific in the infrared image. This mass of cloud tops offshore of Califo= rnia was relatively [("warmer")(<= /span>"colder")] than the thunderstorm tops and curved band over the High Plains. These offs= hore clouds were not evidenced in the infrared image because the tops of these coastal clouds were at lower altitudes, at temperatures near those of the w= ater surfaces.

1= 0. If you wished to create a complete 24-hour time-lapse of the cloud patterns across= the U.S. such as those routinely seen on television using the satellite images from = each hour, you should choose [(visible)(infrared)] images because the other type of images would appear black during nighttime hours.

1= 1. Image 3 is an enlarged image from the U.S. Naval Observatory web site, http://aa.usno.nav= y.mil/data/docs/earthview.php, at 7:15 PM CDT, the same time as the satellite images. The depiction in Ima= ge 3 is from a model showing the positions of the sunrise and sunset terminators= and the portions of the entire Earth's surface in sunlight and darkness at that time. Note the approximate positions of Internat= ional Falls and = Beaumont on the global map display.

The Image 3 sunset terminator line in North America [(did)(did not)] closely coincide with the sunset line you drew where suns= ets were 7:15 CDT.

1= 2. On the Image 3 map, dotted lines represent horizontal parallels of latitude at 30&= deg; intervals with the equator (0°) in the middle and vertical meridians of longitude also at 30° intervals with the 0° Prime Meridian at either edge and the 180° International Date Line i= n the middle. The lengths of the lighted portions of horizontal lines (latitudes)= at comparable distances north and south of the Equator, are proportional to the lengths of daylight at those latitudes (see for exa= mple 60° N and S latitudes). Their lengths infer that on the 22 September equinox, the daylight periods are [(longer in the Northern Hemisph= ere)(longer in the Southern Hemisphere)(= equal in both hemispheres)]. The Northern Hemisphere's summer season = is about to end with the fall equinox.

1= 3. The l= abel beneath the Image 3 map shows that at the time of the image, 0015Z 21 Septe= mber 2009, the sun was overhead at noon at 174.3° E longitude and [(23.5)(0.7)(17.4)] °N latitude. On the equinox, the noon sun will be directly over the equ= ator (0° latitude).

Based on different Image 3 model views, you can determine what portion of Earth would be illuminated on the equinox or the summer solstice (or any ot= her day of the year). Go to the Naval Observatory website listed above and enter the Year, Month, Day and time of day in Hours and Minutes Universal (Z) tim= e. Finally select a Grayscale or Color view. Lastly, click Show Earth Views= . In addition to the Mercator map view of the illuminated Earth at that time, there are polar views showing how the North and South polar regions are lit= and also the view of the globe as seen from either the sun or the moon (as if y= ou were vacationing on either site!)

Would the length of daylight change on the equator from day to day? Check day and night segments in Image 3 and then check day and night map views on= the Naval Observatory website for the upcoming solstice on 21 December 2009. Al= so, sunrise and sunset times, along with other astronomical information, can be obtained from another U. S. Naval Observatory site, http://aa.usno.nav= y.mil/data/docs/RS_OneDay.php.)

Routinely compare the latest satellite views with the latest analyzed surface map available via the course website. Compare what you see on-screen with your local weather. You can ask yourself such questions as: Are your s= kies 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 depiction= s of weather conditions.

The DataStreme Atmosphere website contains t= he link, "Infrared Surface Temperature Determination", under the Satellite section. Calling up this Java applet allows one to determine the temperature in degrees Celsius of cloud and ground surfaces related to their amounts of emitted infrared energy. Try comparing cloud surfaces of differi= ng brightnesses, or land and water surfaces in clear are= as. Another comparison may be the same land surface between early morning and l= ate afternoon as it responds to diurnal heating.

Place the answers to Current Weather Studies activities 3A and 3B on the= CWS Answer Form (provided from the DataStreme Atmos= phere website on Wednesdays).