Initial results from radio occultation measurements with Mars Global Surveyor

Abstract

Abstract.A series of radio occultation experiments conducted with Mars Global Surveyor in early 1998 has yielded 88 vertical profiles of the neutral atmosphere. The measurements cover latitudes of 29øN to 64øS and local times from 0600 through midnight to 1800 during early summer in the southern hemisphere (Ls -264 ø-308 ø). Retrieved profiles of pressure and temperature versus radius and geopotential extend from the surface to the 10-Pa pressure level. Near-surface uncertainties in temperature and pressure are about i K and 2 Pa, respectively, far smaller than in previous radio occultation measurements at Mars. The profiles resolve the radiativeconvective boundary layer adjacent to the surface and also reveal gravity waves, particularly at northern and equatorial latitudes, which appear to be breaking in some cases. Distinctive meridional gradients of pressure and temperature indicate the presence of a low-altitude westerly jet at latitudes of 15ø-30øS at southern summer solstice. This jet appears in predictions of general circulation models in connection with the strong, seasonal, cross-equatorial Hadley circulation. The pressure gradient at •02 km altitude implies a wind speed of 33 m s -t, stronger than predicted, which may help explain the occurrence of numerous local dust storms within this latitude band in late southern spring. These measurements also characterize the response of the atmosphere to stationary thermal forcing at midsouthern latitudes, where high terrain south of Tharsis and low terrain in Hellas Planitia produce large, zonal temperature variations in the lowest scale height above the surface. Pressure measured at constant geopotential decreases at an average rate of 0.13% per degree Ls, due primarily to condensation of CO2 at the North Pole.

Structure and dynamics of the convective boundary layer on Mars as inferred from large‐eddy simulations and remote‐sensing measurements

“…The numerous Thermal Emission Spectrometer (TES) temperature vertical profiles were of insufficient vertical resolution in the BL (Smith et al, 2001). Radio-occultation (RO) profiles with less than 1 km vertical resolution in the lower atmosphere were available (Hinson et al, 1999), but the latitude and time coverage were not suitable for BL convection studies. The TES instrument, however, enabled high-resolution retrievals of soil thermal properties (albedo, thermal inertia).…”

Caracterización climática de la región de Nili Fossae, Marte

“…Sin embargo, los cambios estacionales en esta corriente, hacen que estos vientos se produzcan en latitudes medias durante el invierno (Barlow, 2008). En las regiones subtropicales (entre los 15º y los 30º N y S), durante el solsticio, se produce una corriente en chorro (jet-stream) procedente del oeste con velocidades de hasta 33 ms -1 a 2 km de altitud (Hinson et al, 1999), mientras que los vientos en superficie suelen encontrarse entre los 5 y los 10 ms -1 (Joshi et al, 1995). En los polos se produce el equivalente a los vientos catabáticos terrestres, que salen desde los polos (a causa de las diferencias de presión y temperatura) y divergen latitudinalmente a causa de la rotación planetaria.…”

Current understanding of the aeronomy of Mars

“…The other in-situ plasma composition data, comes from the ASPERA instrument [6] on Mars Express (MEX), which has been providing information on the density, composition and energy of ions and electrons of energies between about 10 eV to~36 keV at altitudes beyond about 300 km. Much electron density data exists from the MARSIS instrument on MEX [7] from in situ and remote wave sounding -spottily from radio occultation observations obtained on early missions (e. g. Mariners, Viking, Russian "Mars" missions) and more comprehensively from the radio science limb occultation experiments on the more recent Mars Express [8] and Mars Global Surveyor [9] missions. The same Mars missions also provided some remote and inferred atmosphere information from UV occultation, from low altitude aerobreaking-phase satellite drag data (MRO, MGS, Odyssey) and more extensively from Mars Global Surveyor (MGS), reflectometer measurements of atmospherescattered electron pitch angle distributions (e.g., [10]).…”