1. Image Interpretation for Weather Analysis Part 2 26 October 2010 Dr. Steve Decker

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

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

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

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

6. Atmospheric Absorptivity

7. 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

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

9. 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)

12. 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

18. 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 in shortwave IR

19. Supercooled Example http://weather.msfc.nasa.gov/sport/goes_imager/goes_imager.html

20. 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.

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

24. Water Vapor Channel  Not an IR window –Does not see the ground (Exception) 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 Example

25. Identifying Jet Streams  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

28. 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 indicates “warm conveyor belt” immediately ahead of a surface cold front –Southern extent of solid band marks trough axis

33. Water Vapor Examples  Eddies Eddies  Cyclone development Cyclone development Cyclone development –Occlusion stage 1 2 1212  Mountain waves –Java example Java exampleJava example  Current weather

35. Many More Examples  CIMSS Satellite Blog CIMSS Satellite Blog CIMSS Satellite Blog