Global Energy and Water Budgets

Global Energy and Water Budgets

1 40 10 30 Pressure (hpa) 100 Pure radiative equilibrium Dry adiabatic adjustment 20 Altitude (km) 6.5 C/km adjustment 10 1000 0 180 220 260 300 340 Temperature (K)

Tropopause

Cloud Radiative Effects

https://www.atmos.washington.edu/~dennis/321/ Global Physical Climatology by Dennis Hartmann Clouds and Earth s Temperature! All the previous results were for clear skies, but clouds have Cloud a substantial Radiative effect Effects on the TOA energy balance.

0: solar constant (incoming solar flux, 1367 W m 2 ). p: planetary albedo (0.30). ( ): outgoing longwave (IR) radiation at TOA (234 W m 2 ).

Heuristic Model of Cloud Radiative Effect (CRE)! TOA Energy Balance a.k.a. Cloud Forcing R TOA = S 0 4 (1! " p )! F # ($)!R TOA = R cloudy " R clear =!Q abs "!F # ($)! Cloud Radiative Effect Add Clouds, what changes?!q abs = S 0 4 (1" # cloudy ) " S 0 4 (1" # clear ) = S 0 4 (# cloudy " # clear ) = " S 0 4!# p

Heuristic Model of Cloud Radiative Effect (CRE) a.k.a. Cloud Forcing Cloud Radiative Effect Add Clouds, what changes?!r TOA = R cloudy " R clear =!Q abs "!F # ($) Shortwave bit Longwave bit!q abs = S 0 4 (1" # cloudy ) " S 0 4 (1" # clear ) = S 0 4 (# cloudy " # clear ) = " S 0 4!# p!f " (#) = F " cloudy (#) $ F " (#) clear

Heuristic Model of Cloud Radiative Effect (CRE) Longwave bit a.k.a. Cloud Forcing!F " (#) = F " cloudy (#) $ F " (#) clear Expand using grey absorption integral equations T {z ct,#} & T {z s,#}!f " (#) = $T 4 zct T {z ct,#}% $T 4 s T {z s,#}% $ T ( z ') 4 dt { z ',#} Assume cloud top is above most of water vapor, then OLR is emission from top of cloud T {z ct,!}" 1.0!F " (#) = $T 4 zct % $T 4 s T {z s,#}% $ T ( z ') 4 dt { z ',#}!F " (#) = $T zct & 1 T {z s,#} 4 % F " clear (#)

Heuristic Model of Cloud Radiative Effect (CRE) a.k.a. Cloud Forcing Putting the pieces together, becomes!r TOA = R cloudy " R clear =!Q abs "!F # ($)!R = " S 0 TOA 4!# p + F $ (%) " &T 4 clear zct The solar and longwave parts tend to be of opposite sign and we can calculate the cloud top temperature at which they will exactly cancel. ') T zct =!(S / 4)"# + F $ (%) 0 p clear ( *) & + ), -) 1/4

50 ISCCP CLOUD CLASSIFICATION 180 CLOUD TOP PRESSURE (MB) 310 440 560 680 CIRRUS ALTOCUMULUS CIRROSTRATUS ALTOSTRATUS DEEP CONVECTION NIMBOSTRATUS HIGH MIDDLE 800 CUMULUS STRATOCUMULUS STRATUS LOW 1000 0 1.3 3.6 9.4 23 60 379 CLOUD OPTICAL THICKNESS

Cloud Radiative Forcing A_i = cloud amount for cloud type i A = total cloud amount A = A_i I OvcCRF_i = ovc CRF for cloud type i CRF_i = avg CRF for cloud type i CRF = total avg CRF CRF_i = A_i * OvcCRF_i CRF = A_i CRF_i = OvcCRF_i I

A_i * OvcCRF_i = CRF_i from Hartmann, Moy, and Fu 2001

There is good agreement between modeled radiative fluxes (using observed cloud type frequencices) and observed (ERBE) radiative fluxes. TABLE 1. ERBE and modeled radiation balance components for the west Pacific convective region 0 15N, 120 150E (Wm 2 ). Longwave Shortwave Net radiation ERBE Model ERBE Model ERBE Model Average sky Clear sky Cloud forcing 211 280 70 213 278 65 117 40 77 119 42 77 96 103 7 92 103 11 from Hartmann, Moy, and Fu 2001

Observed Cloud Fractions! High Clouds (p<440mb) Max High Cloud in tropical rain areas

Observed Cloud Fractions! Low Clouds (p > 680mb) Max low cloud subtropical stratus

Net Radiation Annual Mean

Observed Cloud Radiative Effects in Wm -2 from CERES Jun-Aug

Observed Cloud Radiative Effects in Wm -2 from CERES Jun-Aug

Observed Cloud Radiative Effects in Wm -2 from CERES July-Aug