Airborne measurements of aerosol, ozone, and solar ultraviolet irradiance in the troposphere

Abstract

Measurements of the distributions of the aerosol characteristics and solar ultraviolet irradiance were conducted by using instrumentation flown on a Falcon aircraft over the entire Greek area from the sea up to the middle troposphere. To study the impact of the aerosol abundance to the solar ultraviolet irradiance at various altitudes, complementary observations of ozone concentration, relative humidity, and temperature have been also performed using instrumentation flown on free balloons. In addition to a detailed description of the observed aerosol characteristics we attempt an improvement of the earlier proposed theoretical algorithms regarding the absolute values of the solar ultraviolet irradiance at various tropospheric altitudes. This is achieved by taking into account the measured accumulation aerosol particle and cloud droplet size distributions. The measurements showed that a double-layer structure in the vertical distribution of the number density of the cloud droplets and particle size aerosol was prevalent. In particular, over the area west of Crete the aerosol particles possessed a bimodal size distribution with mean diameters of 0.11 and 0.225 μm. Moreover, upon using the obtained aerosol distribution data in the radiative transfer calculations, we find that the calculated values of the solar ultraviolet irradiance correlate well with the observed ones, showing an 4.3 ± 0.1% km-1 increase for altitudes ranging from the ground to 6.2 km. Copyright 2005 by the American Geophysical Union.