Boundary-layer simulations for the Mars Phoenix lander site

Diurnal simulations and sensitivity studies were made with a moist column model at the Mars Phoenix lander site (68 degrees N) for the summer solstice (solar day 30) and for a later date (sol 99), when the LIDAR on board Phoenix detected fog, dust, ice clouds and even snowfall from cloud. The sol 30 simulation reproduces the observed repetitive diurnal 2 m temperature cycle quite well, displaying a well-mixed boundary layer up to 4 km in the afternoon and a strong surface inversion to 500 m each night. Weak frost formation peaks at midnight and a very thin radiation fog appears during the coldest hour. The near-surface water vapour pressure is underestimated during daytime but is close to the thermal and electrical conductivity probe observations during the night. The Prandtl slope wind mechanism produces veering winds in the model as observed by the 'telltale' device while coupled dust evolution implies well-mixed dust to 4 km throughout the sol as observed by the LIDAR. The colder diurnal conditions around sol 99 are also simulated rather well. In these, the morning fog grows up to 800 m height and a water ice cloud forms at 4 km height at about 0300 local time, as observed. The cloud marks the radiatively cooled top of the moist residual boundary layer. Strong ground frost formation peaks in the evening, having a visible impact on the temperatures. The fog and cloud display weak feedbacks to the modelled radiative fluxes. Copyright (C) 2010 Royal Meteorological Society