Of the total solar radiation received at the ground, some is reflected, some goes to heat the earth's surface, some is sent back as long-wave radiation, some is used in evaporation, and the remainder is effective in heating the lower layers of the atmosphere. Estimates are made of the amounts used in the first four ways. These amounts subtracted from the average insolation received on clear days leave the effective insolation for changing the lapse rate near the ground.
The effective insolation at Chicago is arrived at in this way. Using these values, the maximum temperature was computed for several days when advective change was expected to be slight. The agreement with observation was found to be excellent.
*On leave from U. S. Weather Bureau. This paper was presented at a staff meeting, U. S. Weather Bureau, Washington, D.C., April, 1940 and at the Cambridge Seminar, Feb., 1941.