A Record of Water-ice Clouds at the Phoenix Landing Site Derived from Modeling MET Temperature Data

Water-ice clouds were frequently detected throughout the 151-sol Phoenix mission by the Phoenix lidar, providing insight into the Martian water cycle. However, the lidar could not be used continuously, and as such, the cloud data were temporally constrained to when observations were acquired. Here we reconstruct a record of water-ice clouds at the Phoenix landing site by examining the radiative contribution made by the clouds to the surface energy balance. This is accomplished by modeling the data from the 2 m MET air temperature sensor on board the lander. Clouds radiating from 0 and 30 W m(-2) of energy toward the surface are consistent with the MET record over the course of the mission. The additional longwave flux at the surface induced a warming of the surface and near-surface temperatures, usually between 1-3 K; however, the clouds showed a high degree of sol-to-sol variability. This radiative analysis indicates that clouds were present much earlier in the mission than previously known, and cloud emission reached a maximum near sol 90, consistent with analyses of the annular cloud at the Phoenix landing site. The modeled flux from clouds was compared to the water-ice optical depth retrieved from the Phoenix lidar, showing that optically thicker clouds emitted more radiation toward the surface.