Understanding Trends Associated with Clouds in Irradiated Exoplanets
  Unlike previously explored relationships between the properties of hot Jovian
atmospheres, the geometric albedo and the incident stellar flux do not exhibit
a clear correlation, as revealed by our re-analysis of Q0 to Q14 Kepler data.
If the albedo is primarily associated with the presence of clouds in these
irradiated atmospheres, a holistic modeling approach needs to relate the
following properties: the strength of stellar irradiation (and hence the
strength and depth of atmospheric circulation), the geometric albedo (which
controls both the fraction of starlight absorbed and the pressure level at
which it is predominantly absorbed) and the properties of the embedded cloud
particles (which determine the albedo). The anticipated diversity in cloud
properties renders any correlation between the geometric albedo and the stellar
flux to be weak and characterized by considerable scatter. In the limit of
vertically uniform populations of scatterers and absorbers, we use an
analytical model and scaling relations to relate the temperature-pressure
profile of an irradiated atmosphere and the photon deposition layer and to
estimate if a cloud particle will be lofted by atmospheric circulation. We
derive an analytical formula for computing the albedo spectrum in terms of the
cloud properties, which we compare to the measured albedo spectrum of HD
189733b by Evans et al. (2013). Furthermore, we show that whether an optical
phase curve is flat or sinusoidal depends on whether the particles are small or
large as defined by the Knudsen number. This may be an explanation for why
Kepler-7b exhibits evidence for the longitudinal variation in abundance of
condensates, while Kepler-12b shows no evidence for the presence of
condensates, despite the incident stellar flux being similar for both
exoplanets.
