VARIATIONS IN VENUS CLOUD PARTICLE PROPERTIES - A NEW VIEW OF VENUSS CLOUD MORPHOLOGY AS OBSERVED BY THE GALILEO NEAR-INFRARED MAPPING SPECTROMETER

Using Venus nightside data obtained by the Galileo Near-Infrared Mappi ng Spectrometer, we have studied the correlation of 1.74 and 2.30 mu m radiation which is transmitted through the clouds. Since the scatteri ng and absorption properties of the cloud particles are different at t hese two wavelengths, one can distinguish between abundance variations and variations in the properties of the cloud particles themselves. T he correlation of intensities shows a clustering of data into five dis tinct branches. Using radiative transfer calculations, we interpret th ese branches as regions of distinct but different mixes of Mode 2' and 3 particles. The data and calculations indicate large differences in these modal ratios, the active cloud regions varying in content from n early pure Mode 2' particles to almost wholly Mode 3. The spatial dist ribution of these branches shows large scale sizes and both hemispheri c symmetries and asymmetries. High-latitude concentrations of large pa rticles are seen in both hemispheres and there is banded structure of small particles seen in both the North and South which may be related. The mean particle size in the Northern Hemisphere is greater than fou nd in the South. If these different branch regions are due to mixing o f vertically stratified source regions (e.g. photochemical and condens ation source mechanisms), then the mixing must be coherent over very l arge spatial scales.