Measurements Of ULWIR and DLWIR

A couple of plots from :
http://www.nrel.gov/midc/srrl_bms/

It is interesting to note:

•  that Upward LWIR is increasing faster than Downward LWIR over the very short period of available data.
• That often the downward LWIR is close to the upward LWIR during the night and presumably cloudy conditions

Final Plot but with cloud cover added