Locations for the best lidar view on mid-level and high clouds

Mid-level altocumuls clouds (Ac) and high cirrus clouds (Ci) can be considered as natural observatories for studying cloud glaciation in the atmosphere. While their altitude makes them difficult to access with in-situ instruments, they can be conveniently observed from ground with active remote-sensing instruments such as lidar and radar. However, active remote sensing of Ac and Ci at visible wavelengths with lidar requires a clear line of sight between the instrument and the target cloud. It is therefore advisable to carefully assess potential locations for deploying ground-based lidar instruments in field experiments or for long-term observations that are focussed on mid-level or high clouds. Here, observations of clouds with two spaceborne lidars are used to assess where ground-based lidar measurements of mid- and upper level clouds are least affected by the light-attenuating effect of low-level clouds. It is found that cirrus can be best observed in the tropics, the Tibetan plateau, the western part of North America, the Atacama region, the southern tip of South America, Greenland, Antarctica, and parts of Western Europe. For the observation of altocumuls clouds, a ground-based lidar is best placed on Greenland, Antarctica, the western flank of the Andes and Rocky Mountains, the Amazon, central Asia, Siberia, Western Australia, or the southern half of Africa.