ON THE EFFICIENCY OF SOLAR HEATING IN THE MIDDLE ATMOSPHERE

We calculate the efficiency at which solar ultraviolet radiation absorbed in the Hartley band of ozone is directly converted to heat in the terrestrial mesosphere and lower thermosphere (50-110 km). The ozone molecule undergoes photolysis to yield the excited species O(1D) and O2(1-DELTA) with a quantum yield of about 0.9. Spontaneous emission from O2(1-DELTA) and from O2(1-SIGMA) (excited by energy transfer from O(1D)) significantly decreases the amount of energy available for heat. Similarly, we calculate the efficiency at which solar ultraviolet radiation absorbed by O2 in the Schumann-Runge continuum is directly converted to heat in the lower thermosphere (95-110 km). The O2 undergoes photolysis and the excited product O(1D) is generated. Spontaneous emission from O2(1-SIGMA) (excited by energy transfer from O(1D)) reduces the amount of energy available for heat in the lower thermosphere. The consideration of these energy transfer and loss processes results in significantly reduced heating rates as compared to those conventionally calculated in models of the middle atmosphere.