A lot of people have asked about this. I haven’t been so interested in the subject, but because I came across it in a paper I thought I would post it.
What is the effective height of outgoing longwave radiation? I.e., the radiation from the climate system that leaves the planet.
What is the effective height of downward longwave radiation as measured at the surface?
By effective height we mean that there isn’t just one level that radiation comes from, so it is the average height.
For reference here is a typical pressure vs height comparison (this one is calculated, using the standard hydrostatic equations and ideal gas laws):
So in the tropics the typical emission height of DLR we receive at the surface (called DLB in the paper) is just under 2km and in the mid-latitudes and poles it is around 5km.
Likewise for the OLR, the typical height is around 5km in low latitudes and 4km near the poles.
How is this calculated?
Here the effective emission level is defined as the level at which the climatological annual mean tropospheric temperature is equal to the emission temperature: (OLR/σ)1/4, where σ is the Stefan–Boltzmann constant.
The effective emission level for the downward longwave radiation at the ground is analogously defined as the level at which the climatological annual mean tropospheric temperature is equal to (DLB/σ)1/4 , where DLB is the clear-sky downward longwave radiation at the bottom.
Tropospheric Water Vapor and Climate Sensitivity, by Schneider, Kirtman & Lindzen, Journal of the Atmospheric Sciences, 1999