Measurements of the J(O¹D) actinic flux within and above stratiform clouds and above snow surfaces

Photochemical reactions in the troposphere are strongly dependent on the amount of radiation available for radical production. Albedo changes affect significantly the vertical distribution of the actinic radiation fluxes in the planetary boundary layer. Actinic fluxes over and within cloud layers or snow surfaces with very high albedo are of special interest. Flight experiments were performed in an altitude range of up to 1000 m above ground with and without stratiform cloud layer, and above fresh snow surfaces. The photolysis rate J(O¹D) was measured from a hangglider with two 2π sensitive photoelectric detectors separately providing the upward and downward radiation components with a high vertical resolution. The actinic flux shows a very strong contribution of reflected or backscattered radiation within the planetary boundary layer. The albedo contributions seem to be more dependent on atmospheric optical thickness than are assumed in current model calculations.