Orbiter Cloud Photopolarimeter Investigation

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Abstract
The first polarization measurements of the orbiter cloud photopolarimeter have detected a planet-wide layer of submicrometer aerosols of substantial visible optical thickness, of the order of 0.05 to 0.1, in the lower stratosphere well above the main visible sulfuric acid cloud layer. Early images show a number of features observed by Mariner 10 in 1974, including planetary scale markings that propagate around the planet in the retrograde sense at roughly 100 meters per second and bright- and dark-rimmed cells suggesting convective activity at low latitudes. The polar regions are covered by bright clouds down to latitudes aproximately 50 degrees, with both caps significantly brighter (relative to low latitudes) than the south polar cloud observed by Mariner 10. The cellular features, often organized into clusters with large horizontal scale, exist also at mid-latitudes, and include at least one case in which a cell cuts across the edge of the bright polar cloud of the northern hemisphere.