On pressure measurement and seasonal pressure variations during the Phoenix mission

Abstract

[1] In situ surface pressures measured at 2 s intervals during the 150 sol Phoenix mission are presented and seasonal variations discussed. The lightweight Barocap®/Thermocap® pressure sensor system performed moderately well. However, the original data processing routine had problems because the thermal environment of the sensor was subject to more rapid variations than had been expected. Hence, the data processing routine was updated after Phoenix landed. Further evaluation and the development of a correction are needed since the temperature dependences of the Barocap sensor heads have drifted after the calibration of the sensor. The inaccuracy caused by this appears when the temperature of the unit rises above 0°C. This frequently affects data in the afternoons and precludes a full study of diurnal pressure variations at this time. Short-term fluctuations, on time scales of order 20 s are unaffected and are reported in a separate paper in this issue. Seasonal variations are not significantly affected by this problem and show general agreement with previous measurements from Mars. During the 151 sol mission the surface pressure dropped from around 860 Pa to a minimum (daily average) of 724 Pa on sol 140 (Ls 143). This local minimum occurred several sols earlier than expected based on GCM studies and Viking data. Since battery power was lost on sol 151 we are not sure if the timing of the minimum that we saw could have been advanced by a low-pressure meteorological event. On sol 95 (Ls 122), we also saw a relatively lowpressure feature. This was accompanied by a large number of vertical vortex events, characterized by short, localized (in time), low-pressure perturbations.Citation: Taylor, P. A., et al. (2010), On pressure measurement and seasonal pressure variations during the Phoenix mission,

Convective vortices and dust devils at the Phoenix Mars mission landing site

“…In this work, the near‐continuous measurements of pressure and temperature by the MET instrumentation on the Phoenix Mars Lander [ Taylor et al , 2009] are investigated to identify the passage of vertically oriented vortex structures such as convective vortices and dust devils at the Phoenix landing site. Similar work was done on Mars Pathfinder pressure data in the work of Murphy and Nelli [2002].…”

“…During the Phoenix mission air temperatures were measured at the three levels on the 1 m mast and pressure was measured with a Vaisala Barocap®/Thermocap® system on the deck of the lander, being about 1 m above ground level [ Taylor et al , 2008, 2009]. Measurements were made at 0.5 Hz with a sensor noise level of 0.1 Pa and ran almost continuously through the landed mission from sols 0–151 apart from short daily breaks due to data transfers [ Taylor et al , 2009].…”

“…During the Phoenix mission air temperatures were measured at the three levels on the 1 m mast and pressure was measured with a Vaisala Barocap®/Thermocap® system on the deck of the lander, being about 1 m above ground level [ Taylor et al , 2008, 2009]. Measurements were made at 0.5 Hz with a sensor noise level of 0.1 Pa and ran almost continuously through the landed mission from sols 0–151 apart from short daily breaks due to data transfers [ Taylor et al , 2009]. The atmospheric pressure data shows regular diurnal cycles and during this period of time, the pressure can be seen falling steadily from about 860 Pa to near 720 Pa, due to the deposition of CO 2 ice in the south polar region [ Taylor et al , 2009].…”

Laboratory investigation of perchlorate deliquescence at the surface of Mars with a Raman scattering lidar

“…The total pressure required in the chamber was 726 Pa, and this coincidentally matched the surface pressure measured during the second half of the Phoenix mission [Taylor et al, 2010]. The liquid nitrogen plumbing was carefully insulated with polyethylene material to ensure that any water condensation occurring in the chamber was restricted to the sample plate.…”

New analysis software for Viking Lander meteorological data

“…This is especially the case for all the landed Mars missions with atmospheric observations, e.g. Mars Pathfinder, Phoenix, Mars Science Laboratory Harri et al, 1998;Golombek et al, 1999;Savijärvi et al, 2004Savijärvi et al, , 2005Shotwell, 2005;Taylor et al, 2008Taylor et al, , 2010.…”