Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
4.2 Satellite
4.2.1 Description Satellite is perhaps the single most important source of weather data worldwide, particularly over data sparse regions such as countries without organized weather data collection and the oceans.
GOES satellite imagery can be found on the NWS Aviation Digital Data Service (ADDS) website at: http://adds.aviationweather.noaa.gov/satellite/. Additional satellite imagery for Alaska can be found on the Alaska Aviation Weather Unit (AAWU) website at:
http://aawu.arh.noaa.gov/sat.php
4.2.2 Imagery Types Three types of satellite imagery are commonly used: Visible, infrared (IR), and water vapor.
Visible imagery is available only during daylight hours. IR and water vapor imagery are available day or night.
4.2.2.1 Visible Imagery Visible imagery (Figures 4-16 and 4-17) displays reflected sunlight from the Earth’s surface, clouds, and particulate matter in the atmosphere. These images are simply black and white pictures of the Earth from space. During daylight hours, visible imagery is the most widely used image type because it has the highest resolution and approximates what is seen with the human eye.
Gray shades displayed on visible imagery can be correlated with particular features. Assuming a high sun angle, thick clouds and snow will appear white, thin clouds will appear translucent gray, land appears gray, and deep bodies of water such as lakes and oceans will appear black.
AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-17
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 4-18. Visible Satellite Image – U.S. Example
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 4-19. Visible Satellite Image – Regional-Scale Example
4.2.2.1.1 Visible Image Data Legend The data legend (Figure 4-18) on a visible image displays albedo, or reflectance, expressed as a percentage. For example, an albedo of 72 means 72 percent of the sunlight which struck a feature was reflected back to space.
Figure 4-20. Visible Satellite Data Legend.
The gray shades (values) represent albedo or reflectance expressed as a percentage.
4.2.2.2 Infrared (IR) Imagery Infrared (IR) images (Figure 4-19 through 4-22) display temperatures of the Earth’s surface, clouds, and particulate matter. Generally speaking, the warmer an object, the more infrared energy it emits. The satellite sensor measures this energy and calibrates it to temperature using a very simple physical relationship.
AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-19
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Clouds that are very high in the atmosphere are generally quite cold (perhaps -50°C) whereas clouds very near the earth's surface are generally quite warm (perhaps +5°C). Likewise, land may be even warmer than the lower clouds (perhaps +20°C). Those colder clouds emit much less infrared energy than the warmer clouds and the land emits more than those warm clouds.
The data measured by satellite is calibrated and colorized according to the temperature. If the temperature of the atmosphere decreases with height (which is typical), cloud-top temperature can be used to roughly determine which clouds are high-level and which are low-level.
When clouds are present, the temperature displayed on the infrared images is that of the tops of clouds. When clouds are not present, the temperature is that of the ground or the ocean.
Figure 4-21. Infrared (Color) Satellite Image – U.S. Example The scale is in degrees Celsius. Blue/purple colors indicate colder temperatures, while orange/red colors indicate warmer temperatures.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) -68 -64 60 56 52 48 44 40 E36 E32 28 524 520 518 512 08 J 0 0 8 12 16 20 24 28 Figure 4-22. Infrared (Color) Satellite Image - Regional-Scale Example The scale is in degrees Celsius. Blue/purple colors indicate colder temperatures, while orange/red colors indicate warmer temperatures.
1-39-371-351-331-31-29 -27 -25 -23-21-191-171-15-131-11-9-71- Figure 4-23. Unenhanced Infrared (black and white) Satellite Image - U.S. Example The scale is in degrees Celsius. Lighter gray shades indicate colder temperatures, while darker gray shades indicate warmer temperatures.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 4-24. Unenhanced Infrared (black and white) Satellite Image – Regional- Scale Example The scale is in degrees Celsius. Lighter gray shades indicate colder temperatures, while darker gray shades indicate warmer temperatures.
4.2.2.2.1 Infrared Image Data Legends The data legend (Figure 4-23 and Figure 4-24) on an infrared image is calibrated to temperature expressed in degrees Celsius. The legend may vary based on the satellite image provider.
Figure 4-25. Infrared (Color) Satellite Image Data Legend.
The colors (values) represent temperature in degrees Celsius.
Figure 4-26. Unenhanced Infrared (black and while) Satellite Image Data Legend.
The gray shades (values) represent temperature in degrees Celsius.
4.2.3.3 Water Vapor Imagery The water vapor imagery (Figure 4-25 and Figure 4-26) displays the quantity of water vapor generally located in the middle and upper troposphere within the layer between 700 millibars (FL100) to 200 millibars (FL390). The actual numbers displayed on the water vapor images correspond to temperature in degrees Celsius. No direct relationship exists between these values and the temperatures of clouds, unlike IR imagery. Water Vapor imagery does not really "see" clouds but "sees" high-level water vapor instead.
The most useful information to be gained from the water vapor images is the locations and movements of weather systems, jet streams, and thunderstorms. Another useful tidbit is aided AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-22
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) by the color scale used on the images. In general, regions displayed in shades of red are VERY dry in the upper atmosphere and MAY correlate to crisp blue skies from a ground perspective.
On the contrary, regions displayed in shades of blue or green are indicative of lots of high-level moisture and may also indicate cloudiness. This cloudiness could simply be high-level cirrus types or thunderstorms. That determination cannot be gained from this image by itself but could easily be determined when used in conjunction with corresponding visible and infrared satellite images.
Figure 4-27. Water Vapor Satellite Image – U.S. Example The scale is in degrees Celsius. Blue/green colors indicate moisture and/or clouds in the mid/upper troposphere, while dark gray/orange/red colors indicate dry air in the mid/upper troposphere.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-24
Figure 4-28. Water Vapor Satellite Image – Regional-Scale Example The scale is in degrees Celsius. Blue/green colors indicate moisture and/or clouds in the mid/upper troposphere, while dark gray/orange/red colors indicate dry air in the mid/upper troposphere.
4.2.3.3.1 Water Vapor Image Data Legend The data legend (Figure 4-27) on a water vapor images is calibrated to temperature expressed in degrees Celsius. The actual data values on the water vapor images are not particularly useful. Interpretation of the patterns and how they change over time is more important. The legend may vary depending on the satellite image provider.
Figure 4-29. Water Vapor Satellite Image Data Legend.
The colors (values) represent temperature in degrees Celsius
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5 GRAPHICAL OBSERVATIONS AND DERIVED PRODUCTS
5.1 Surface Analysis Charts Surface Analysis charts are analyzed charts of surface weather observations. The chart depicts the distribution of several items including sea level pressure, the positions of highs, lows, ridges, and troughs, the location and character of fronts, and the various boundaries such as drylines, outflow boundaries, sea-breeze fronts, and convergence lines. Other symbols are often added depending upon the intended use of the chart. Pressure is referred to in mean sea level (MSL) on the surface analysis chart while all other elements are presented as they occur at the surface point of observation. A chart in this general form is commonly referred to as the weather map.
Figure 5-1. HPC Surface Analysis Chart Example
5.1.1 Issuance Five National Weather Service (NWS) offices issue surface analysis charts:
• The Hydrometeorological Prediction Center (HPC) in Camp Springs, Maryland is responsible for land areas of North America. The charts are available at o http://www.hpc.ncep.noaa.gov/html/sfc2.shtml o http://www.hpc.ncep.noaa.gov/html/avnsfc.shtml
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
• The Ocean Prediction Center (OPC) in Camp Spring, Maryland is responsible for the Atlantic and Pacific Oceans north of 30oN latitude. The charts are available at:
o http://www.opc.ncep.noaa.gov/
• The Tropical Prediction Center (TPC) in Miami, Florida is responsible for the tropical regions of the western hemisphere south of 30oN latitude and east of 160oE longitude.
The surface analysis charts are available at:
o http://www.nhc.noaa.gov/marine_forecasts.shtml
• The Alaskan Aviation Weather Unit (AAWU) in Anchorage, Alaska is responsible for the state of Alaska. The surface analysis chart is available at:
o http://aawu.arh.noaa.gov/surface.php
• The Weather Forecast Office in Honolulu, Hawaii (WFO HNL) is responsible for the tropical Pacific Ocean, south of 30oN latitude and west of 160oE longitude. The charts are available at:
o http://www.prh.noaa.gov/hnl/pages/analyses.php
Each office produces multiple versions of the surface analysis chart with varying formats.
5.1.2 HPC Surface Analysis Charts
• The Hydrometeorological Prediction Center (HPC) in Camp Springs, Maryland is responsible for land areas of North America. The charts are available at o http://www.hpc.ncep.noaa.gov/html/sfc2.shtml o http://www.hpc.ncep.noaa.gov/html/avnsfc.shtml
5.1.2.1 Issuance The Hydrometeorological Prediction Center (HPC) issues Surface Analysis Charts for North America eight times daily (Table 5-1).
Table 5-1. HPC Surface Analysis Charts Issuance Schedule Valid Time (UTC) 00 03 06 09 12 15 18 21
5.1.2.2 Analysis Symbols Figure 5-2 shows analysis symbols used on HPC surface analysis charts:
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
COLD FRONT - COLD FRONTOLYSIS WARM FRONT • WARM FRONTOLYSIS
STATIONARY FRONT STATIONARY
OCCLUDED FRONT FRONTOLYSIS
OCCLUDED FRONTOLYSIS
CHANGE OF FRONT TYPE
COLD FRONTOGENESIS HIGH PRESSURE CENTER
WARM FRONTOGENESIS LOW PRESSURE CENTER
STATIONARY TROPICAL (TRPL) WAVE
FRONTOGENESIS T.D.
TROUGH (TROF) OR XXX TROPICAL DEPRESSION
OUTFLOW BONDARY (OUTFLOW BNDRY) 6 TRPCL STORM TROPICAL STORM
DRYLINE
RIDGE HURCN HURRICANE
SQUALL LINE XXX Figure 5-2. HPC Surface Analysis Chart Symbols
5.1.2.3 Station Plot Models Land, ship, buoy, and C-MAN stations are plotted on the chart to aid in analyzing and interpreting the surface weather features. These plotted observations are referred to as station models. Some stations may not be plotted due to space limitations. However, all reporting stations are used in the analysis.
Figure 5-3 and 5-4 contain the most commonly used station plot models used in surface analysis charts:
Wind Sea-level pressure Temperature 57 107 Weather -→ • -6 56 Pressure trend (mb) Dew Point(F) Sky cover Figure 5-3. HPC Surface Analysis Chart Station Plot Model AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-3
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 5-4. HPC Surface Analysis Chart Ship/Buoy Plot Model
HPC also produces surface analysis charts specifically for the aviation community. Figure 5-5 contains the station plot model for these charts:
Figure 5-5. HPC Surface Analysis Chart for Aviation Interests Station Plot Model
5.1.2.3.1 Station Identifier The format of the station identifier depends on the observing platform.
• Ship -- Typically 4 or 5 characters. If 5 characters, then the fifth will usually be a digit.
• Buoy -- Whether drifting or stationary, a buoy will have a 5-digit identifier. The first digit will always be a 4.
• C-MAN -- Stands for Coastal-Marine Automated Network, and are usually close to coastal areas. Their identifier will appear like a 5-character ship identifier, however the 4th character will identify off which state the platform is located.
• Land -- Land stations will always be 3 characters, making them easily distinguishable from ship, buoy, and C-MAN observations.
5.1.2.3.2 Temperature The air temperature is plotted in whole degrees Fahrenheit.
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