Mars: Dissipating Behavior of the Cloud Belt

This is a brief report on the Martian climate, based on our observations in 2001 as well as those in 1997 and 1999. The focus is the dissipating behavior of the low-latitude cloud belt appearing around the aphelion, the behavior of which has never been explicitly examined. We derive the optical thickness of water ice clouds (WICs) as τWIC ≈0.1 (λ � 4400 u A) at the solar longitude Ls = 174 ◦ in 2001. The latitudinal coverage of the cloud belt is approximately Ls-independent just until its end. The cloud belt divides into a “semi-encircling” cloud band and discrete WICs before its dissipation (over Ls ∼ 100 ◦ –110 ◦ ) in many cases. We suggest that this cloud division should embody localization of the cross-equatorial Hadley circulation.