1. Image Interpretation for Weather Analysis
Part 2
14 February 2007
Dr. Steve Decker

4. Improvement Example
Registration GOES-12 vs. GOES-13
Battery power

5. Severe Thunderstorm Detection
Severe thunderstorms often have notable overshooting tops
Vis: Shadow effects
IR: “Enhanced-V” signature
Example: Vis IR

6. Boundary Detection Boundary: Subtle separation between two air masses
Region of enhanced lifting
Clouds
Thunderstorms
Best seen in Vis
Lake Breeze example

7. Blowing Snow
Can produce whiteout conditions, even with no precipitation
Vis example

8. Common Channels Visible Infrared (IR) Water Vapor Shortwave IR
0.65 μm (red)
Infrared (IR)
10.7 μm
Water Vapor
6.7 μm
Shortwave IR
3.9 μm

9. Atmospheric Absorptivity

10. Shortwave IR An infrared window channel
Just like “longwave” IR
Also sees solar radiation (blackbody curve overlap)
Works best for warmer temps
> -30°C
Cold clouds (e.g., cirrus) look mottled
Good for fire detection
Fog detection
Supercooled vs. ice clouds
Snow vs. cloud

11. Fire Detection with Shortwave IR
Fires show up as “hot spots”
SoCal fire example

12. Fog Detection
Emissivity of liquid water cloud at 3.9 μm is less than at longer wavelengths.
Fog shows up as lower temperatures
Appears brighter
Opposite true for ice crystals (cirrus)

15. Fog Detection
Emissivity of liquid water cloud at 3.9 μm is less than at longer wavelengths.
Fog shows up at lower temperatures
Appears brighter
Differences can be maximized by taking the difference between the longwave and shortwave IR images

21. Supercooled Cloud Detection
Supercooled cloud droplets frequently occur for -20°C < T < 0°C
Detection method
Identify cloud-top temperatures conducive for supercooled droplets using longwave IR
Just like fog/stratus droplets, supercooled droplets emit less radiation

22. Supercooled Example

23. Snow vs. Cloud
During the day, low clouds will reflect more solar radiation than snow at 3.9 μm, so low clouds appear darker (more signal) than snow.

26. Urban Heat Islands
Shortwave IR is more sensitive to emissions from warmer temperatures
Urban heat islands show up better

27. Water Vapor Channel Not an IR window Absorbed/emitted by water vapor
Does not see the ground (Exception)
Absorbed/emitted by water vapor
Colder temperatures imply:
More moisture in the mid and upper troposphere
Possible regions of ascent
Temperature differences important; not their magnitudes
Example

28. Identifying Jet Streams
Ribbons of quickly moving air near the tropopause
Separate air masses
Support active weather
Vis: Band of cirrus clouds on equatorward side
Vapor: Strong moisture gradient
Dry air poleward
Moist air equatorward

31. Locating Ridges and Troughs
Upper tropospheric flow often contains a ridge/trough pattern
Clouds often occur downstream of troughs, but upstream of ridges
If ridge has small amplitude, clouds may “spill over” ridge
Cloud band ahead of trough often indicate “warm conveyor belt” immediately ahead of a surface cold front
Southern extent of solid band marks trough axis

36. Water Vapor Examples Eddies Cyclone development Mountain waves
Occlusion stage 1 2
Mountain waves
Java example
Current weather