Title: An objective classification of Saturn cloud features from Cassini ISS images,
Abstract: A clustering algorithm is applied to Cassini Imaging Science Subsystem
continuum and methane band images of Saturns northern hemisphere to objectively
classify regional albedo features and aid in their dynamical interpretation.
The procedure is based on a technique applied previously to visible-infrared
images of Earth. It provides a new perspective on giant planet cloud morphology
and its relationship to the dynamics and a meteorological context for the
analysis of other types of simultaneous Saturn observations. The method
identifies six clusters that exhibit distinct morphology, vertical structure,
and preferred latitudes of occurrence. These correspond to areas dominated by
deep convective cells; low contrast areas, some including thinner and thicker
clouds possibly associated with baroclinic instability; regions with possible
isolated thin cirrus clouds; darker areas due to thinner low level clouds or
clearer skies due to downwelling, or due to absorbing particles; and fields of
relatively shallow cumulus clouds. The spatial associations among these cloud
types suggest that dynamically, there are three distinct types of latitude
bands on Saturn: deep convectively disturbed latitudes in cyclonic shear
regions poleward of the eastward jets; convectively suppressed regions near and
surrounding the westward jets; and baroclinically unstable latitudes near
eastward jet cores and in the anti-cyclonic regions equatorward of them. These
are roughly analogous to some of the features of Earths tropics, subtropics,
and midlatitudes, respectively. Temporal variations of feature contrast and
cluster occurrence suggest that the upper tropospheric haze in the northern
hemisphere may have thickened by 2014.