Longwave derived cloud amounts compared with shortwave cloud amounts

Though it seems to be a simple quantity, cloud amount can be rather elusive. First of all, cloud amount is determined by the physical scale under consideration. The cloud amount over a 100km grid box can be quite different from that over a single pyranometer within that box. Measurements of cloud amount are dependent on the wavelength, sampling frequency, field of view, and other properties of the instruments. It would not be surprising if adjacent instruments yield different cloud amounts for the same cloud scene.

Here cloud amounts derived from longwave measurements will be compared to passive shortwave cloud amounts. This comparison provides a useful basis for determining the cloud types and conditions where longwave and shortwave cloud amounts differ and when they are similar. In addition, limited night-time sky imager cloud amounts can assess nighttime longwave cloud amounts.