THE ENERGY-BALANCE IN THE RAMDAS LAYER

On calm clear nights, air at a height of a few decimetres above bare s oil can be cooler than the surface by several degrees in what we shall call the Ramdas layer (Ramdas and Atmanathan, 1932). The authors have recently offered a logical explanation for such a lifted temperature minimum, together with a detailed numerical model. In this paper, we p rovide physical insight into the phenomenon by a detailed discussion o f the energy budget in four typical cases, including one with a lifted minimum. It is shown that the net cooling rate near ground is the sma ll difference between two dominant terms, representing respectively ra diative upflux from the ground and from the air layers just above grou nd. The delicate energy balance that leads to the lifted minimum is up set by turbulent transport, by surface emissivity approaching unity, o r by high ground cooling rates. The rapid variation of the flux emissi vity of humid air is shown to dominate radiative transport near the gr ound.