1. More on Water Vapor/Clouds Satellite Meteorology/Climatology

2. January (M. King, our changing planet)

3. July

4. Water vapour evaluated in multiple infrared window channels where absorption is weak, so that  w = exp[- k w u] ~ 1 - k w u where w denotes window channel and d  w = - k w du What little absorption exists is due to water vapour, therefore, u is a measure of precipitable water vapour. RTE in window region u s I w = B sw (1-k w u s ) + k w  B w du o u s represents total atmospheric column absorption path length due to water vapour, and s denotes surface. Defining an atmospheric mean Planck radiance, then _ _ u s u s I w = B sw (1-k w u s ) + k w u s B w with B w =  B w du /  du o o Since B sw is close to both I w and B w, first order Taylor expansion about the surface temperature T s allows us to linearize the RTE with respect to temperature, so _ T bw = T s (1-k w u s ) + k w u s T w, where T w is mean atmospheric temperature corresponding to B w. (courtesy: Paul Mentzel)

5. For two window channels (11 and 12um) the following ratio can be determined. _ T s - T bw1 k w1 u s (T s - T w1 ) k w1 _________ = ______________ = ___ _ T s - T bw2 k w1 u s (T s - T w2 ) k w2 where the mean atmospheric temperature measured in the one window region is assumed to be comparable to that measured in the other, T w1 ~ T w2, Thus it follows that k w1 T s = T bw1 + [T bw1 - T bw2 ] k w2 - k w1 and T bw - T s u s =. _ k w (T w - T s ) Obviously, the accuracy of the determination of the total water vapour concentration depends upon the contrast between the surface temperature, T s, and _ the effective temperature of the atmosphere T w

6. Basic interpretation of water vapor imagery Comes from 6-7  m, part of the water vapor absorption channel Comes from 6-7  m, part of the water vapor absorption channel n Usually receiving radiation from 600-300 mb n The drier the column of air, the lower in the atmosphere that WV channel “sees” For very dry air may see some radiation from below 800mbFor very dry air may see some radiation from below 800mb n Does not depict low level moisture

7. Water vapor imagery n Acts as a tracer of atmospheric motion!! n Upper-level ridge/troughs n Mid-troposhperic vorticity maxima (rotation center) n Jet stream (sharp moisture gradient)

8. Water vapor imagery Upper Low Louie Grasso and Eric Hilgendorf, GOES-8 Channel 3 ( 6.7 micrometer water vapor channel ) http://www.cira.colostate.edu/ramm/picoday/980805.html

9. Where did it go?? GOES-8 channel 4 (10.7 micron IR) GOES-8 Visible

10. Water vapor imagery n A lower brightness temperature -- light tones -- means that the water vapor (the “optically thick layer”) is higher than a neighboring region with a higher brightness temperature -- dark tones.

11. Water vapor imagery Considered Saturated

12. Water vapor imagery n However, must also account for the temperature of the water vapor! Low temperatures may also appear bright in water vapor imageryLow temperatures may also appear bright in water vapor imagery

13. Water vapor imagery Bright = moist in mid trop?? Dark = dry?? Eric Hilgendorf and Jack Dostalek http://www.cira.colostate.edu/ramm/picoday/121297.html

14. Minnesota Florida

15. Water vapor imagery n Minnesota was not more humid, just colder

16. Water vapor imagery n Another way to think about “the vapor” A warmer temperature means that the water vapor (the “optically thick layer”) is lower than a neighboring cooler region at a fixed time.A warmer temperature means that the water vapor (the “optically thick layer”) is lower than a neighboring cooler region at a fixed time. So… If the temperature of a region is cooling (warming) that could imply that upward (downward) vertical motion is occurring.So… If the temperature of a region is cooling (warming) that could imply that upward (downward) vertical motion is occurring. However, another reason could be that the cooler/warmer region simply advected in from somewhere else.However, another reason could be that the cooler/warmer region simply advected in from somewhere else.

17. Water vapor imagery http://www.cira.colostate.edu/ramm/picoday/102397.html

18. Increased “dark” (red) implies downward motion. No dry air apparently advected.

19. WV gray shade interpretation n Very Light to Nearly White (lightest 10%) Cirrus clouds are likelyCirrus clouds are likely Pattern often recognizable by a textured appearance and relatively distinct edgesPattern often recognizable by a textured appearance and relatively distinct edges n Exceptions: Very cold winter continental air (rare)Very cold winter continental air (rare) Nearly saturated upper tropospheric moisture at tropical latitudes (relatviely common at low latitudes)Nearly saturated upper tropospheric moisture at tropical latitudes (relatviely common at low latitudes)

20. WV gray shade interpretation n Light to Very Light (75-90% of white) Significant moisture is present in the upper middle troposphereSignificant moisture is present in the upper middle troposphere –typically with single digit DD through a layer of at least 100 mb between 500 and 300 mb May be dry in the lower troposphereMay be dry in the lower troposphere n Exceptions: Very cold winter season continental airVery cold winter season continental air Combinations of middle clouds and moistureCombinations of middle clouds and moisture

21. WV gray scale interpretation n Medium Gray Shades (40 to 75% of whiteness scale) The vertical location of the moisture cannot be determined from the gray shades aloneThe vertical location of the moisture cannot be determined from the gray shades alone Numerous combinations of moisture conditions and clouds may produce the medium gray shadesNumerous combinations of moisture conditions and clouds may produce the medium gray shades

22. WV grey shade interpretation n Very Dark to Black (lower 40% of shades) Very dry air in the middle and upper trop.Very dry air in the middle and upper trop. Dry air probably extends down to 700 mbDry air probably extends down to 700 mb Deep dry conditions most likely if the dark area is becoming darker or expandingDeep dry conditions most likely if the dark area is becoming darker or expanding n Exceptions: Dark area is decreasing or becoming lighter with time- thin high moisture may be presentDark area is decreasing or becoming lighter with time- thin high moisture may be present

23. WV climatology from MODIS: example 1: Tibet

26. Global WV vs. T skin (over land only)

27. Is cirrus related to air traffic?