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2012/09/04

Some more analysis of u/d lwir and clouds

Total / opaque cloud vs Temperature
No slope on the opaque cloud but a definite dip when teperatures are between 16 and 22C
 
The following plots limit RH to 20 to 40%. Day refers to time that cloud can be measured Night to when cloud is not measured.

D/U LWIR vs Temperature (night values - 0-100% cloud)

Both upward and downward LWIR linear proportional to temperature

D/U LWIR vs Temperature (day values cloud 0-100%)
Very similar to night - slopes are a bit different.

D/U LWIR vs Temperature (day values but limiting cloud to 20 to 40%) (note change in humidity limits

D/U LWIR vs Humidity Temp 22-24C cloud 40-50%
By constraining the temperature to a 2C band The temperature effects on IR are minimised whilst still returning a reasonable number  of results. Note that the ULWIR falls with increasing cloud but the DLWIR rises by 100w/sq m 

D/U LWIR vs Opaque Cloud cover temp 22-24C RH 35-40%
Temperature RH are constrained to minimise these effects. The DLWIR increases by approx 80 w/sqm
 
I think these last two plots conclusively prove relative humidity and cloud cover have a positive effect on the downward long wave ir (ir increases if cloud and/or RH increase)
 
Now how do you do this for CO2?

Data available from:
http://www.nrel.gov/midc/srrl_bms/

 



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2 comments:

  1. Anonymous14 November 2012 at 14:44:00 GMT

    Re: Now how do you do this for CO2?

    Can you do multiple MODTRAN runs for various levels of CO2 in your atmosphere, with your zenith angle set to either 0 or 180 degrees (I think the convention is zenith angle), using 8-12 microns (or whatever) for your band?

    The varied CO2 levels correspond to the opaque cloud cover, the two zenith angles give downward and upward respectively (if I have correctly remembered the convention).

    I am no expert on MODTRAN, but this seems like it would be a tractable modeling approach.

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  2. thefordprefect15 November 2012 at 02:32:00 GMT

    Unfortunately the data available from nrel does not give the dlwir ulwir for specific wavelengths - an overall w/sqm figure is all that is available.

    Available data is shown here
    http://www.nrel.gov/midc/srrl_bms/

    There are UV bands but not LW IR

    The idea with these plots was to remove "models" so hated by some. So it was just the measured values of interest.

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