Reproducing Meteorological Observations at the Mars Phoenix Lander Site Using the Nasa Ames

The mission began in late Spring (L s ~77˚) and ended in midSummer (L s ~148˚), lasting for 151 sols [2]. In situ measurements by the lander characterized the local atmospheric conditions (i.e. temperature, pressure, wind speeds and direction, opacity of dust and water ice, and the detection of surface water ice frost) [3,4]. Phoenix measured a steady decline in near surface atmospheric pressures over the course of the mission. Atmospheric pressure fell from ~8.5 mbars at the beginning of the mission to ~7.4 mbars near the end of the lander's life. Atmospheric temperatures were measured with daytime highs ~245 K and nighttime lows ~190 K. Late in the mission, water ice clouds and surface frosts, along with dust devils were imaged with the Surface Stereo Imager [3,4] and opacities were measured with the weather station lidar [4,5]. Using the NASA Ames General Circulation Model (GCM) v2.1, we reproduce atmospheric conditions at the Mars Phoenix Lander site in an effort to explain the measured atmospheric phenomena (water ice clouds, ground frosts, dust devils, etc.). We attempt to answer why many of these features occur late in the mission, but not during the early sols after landing [4]. NASA Ames GCMv2.1: The NASA Ames Mars General Circulation Model (GCM version 2.1) is a finite difference numerical grid point model of Mars' atmosphere. Current model geophysical processes include the treatment of the radiative transfer equation using a correlated-k approach [6]. CO 2 condensa-tion/sublimation are accounted for, and MOLA topography [7] is smoothed to the required model resolution. Aerosol transport and the atmospheric thermodynamic equations are solved on a 5˚latitude by 6˚longitude Arakawa C grid by the model's dynamical core [8]. Dust opacity in the model is prescribed by ingesting the first year of MGS TES 9 µm dust opacity data into the model (a nominally dusty year) [9]. A surface water ice source [10] with approximate area to the measured North Polar cap is seasonally exposed at northerly model latitudes to produce a representative water cycle [9] (Figure 1a). Using a moment scheme based on work by Rodin [11] and Montmessin et al. [12], a simplified microphysical treatment for cloud formation is