Multi-year measurements of cloud base heights at South Pole by lidar

The Micropulse Lidar Network has operated a full-time lidar measurement program at South Pole Station since 2000. Observations from this instrument are an important multi-year record of clouds over the Antarctic plateau. Earlier South Pole observations relied mostly on passive measurements to characterize clouds; the lidar's active profiles present an opportunity to validate current understanding of Antarctic clouds, as well as study properties that are not adequately captured in passive measurements. Lidar observations show clouds to be present roughly 40 percent of the time, and often appearing in wind-swept layers immediately above ground-based scattering layers such as blowing snow and suspended ice particles. There is very little indication of seasonal variability in cloud base heights; this contradicts earlier observations from an interferometer made in 1992 when it was determined that the distribution of cloud base heights in the summer months was different from that seen at other times. Those observations had also indicated that cloud base heights over the high plateau are distributed bimodally, with many near-surface clouds, and a second mode of other clouds well above the surface - based inversion. The lidar observations, however, suggest that this may be true only of the optically thicker clouds and even then only in the spring.