[Previous] | [Session 4] | [Next]
J.A. Magalhaes, A. Seiff (NASA Ames/ SJSUF), R.E. Young (NASA Ames)
The Galileo Probe Atmospheric Structure Investigation (ASI) directly sensed temperature, pressure, and probe acceleration during the parachute descent phase which started at p~0.4 bars and ended at p~22 bars. Pressure sensor measurements were compromised by an anomaly in the internal probe temperatures and thus far the accurate determination of any deviations from the adiabatic lapse rate has not been possible. Here we present two independent determinations of the thermal stratification during the parachute descent phase using only T sensor measurements, which were unaffacted by the thermal anomaly. The first determination uses the temperatures in combination with the well justified assumptions of hydrostatic balance and of equilibrium descent of the probe. A static stability of ~0.15 degrees K/km is found during most of the parachute descent phase. Our second technique searches for wave-like oscillations at vertical scales consistent with atmospheric gravity waves, which require a statically stable atmosphere. High pass spatial filtering of the data shows oscillatory structures with amplitude ~0.1-0.2 degrees K throughout the parachute descent phase. Spectral analysis shows these oscillations can be well represented by the sum of two waves with statistically significant amplitudes of ~0.05 degrees K and vertical wavelengths of ~19 km and ~24 km. The waves show behavior consistent with that expected for vertically propagating gravity waves. We will report on efforts to further constrain the wave properties. If the gravity wave interpretation is correct, a lower bound on the static stability can be set and is consistent with the thermal static stability found using our first method. Static stability due to the molecular weight gradients deduced from other Galileo Probe observations is insufficient to account for the observed oscillations except near p~10 bars.
This work was supported by NASA’s Planetary Atmospheres Program under RTOP 344-33-20-03.