Peter M. Woiceshyn

The atmosphere of Io from Pioneer 10 radio occultation measurements

Abstract The occultation of the Pioneer 10 spacecraft by Io (JI) provided an opportunity to obtain two S -band radio occultation measurements of its atmosphere. The dayside entry measurements revealed an ionosphere having a peak density of about 6 × 10 4 elcm −3 at an altitude of about 100 km. The topside scale height indicates a plasma temperature of about 406 K if it is composed of Na + and 495 K if N 2 + is principal ion. A thinner and less dense ionosphere was observed on the exit (night side), having a peak density of 9 × 10 3 elcm −3 at an altitude of 50 km. The topside plasma temperature is 160 K for N 2 − and 131 K for Na + . If the ionosphere is produced by photoionization in a manner analogous to the ionospheres of the terrestrial planets, the density of neutral particles at the surface of Io is less than 10 11 −10 12 cm 3 , corresponding to a surface pressure of less than 10 −8 to 10 −9 bars. Two measurements of its radius were also obtained yielding a value of 1830 km for the entry and 192 km for the exit. The discrepancy between these values may indicate an ephemeris uncertainty of about 45 km. The two measurements yield an average radius of 1875 km, which is not in agreement with the results of the Beta Scorpii stellar occultation.

Global seasonal atmospheric fluctuations on Mars

Abstract The Mariner 9 S-band radio occultation measurements, which were taken over half a Martian year, were examined for seasonal variations in atmospheric pressures and temperatures. Seasonally related atmospheric pressure oscillations on a global scale were discovered when the pressures were compared on equi-potential levels. There was a global increase in pressure of about 13% between northern winter and spring seasons, and a global decrease in pressure of nearly 14% between northern spring and summer seasons. The maximum global pressure occurred during the northern spring season approximately one Martian month prior to aphelion. These pressure oscillations were correlated with the seasonal growth and decay, and the total area of the polar caps. Temperatures in the mid-latitude regions near the subsolar points were highest during the northern winter season when Mars was closest to the sun. In addition, high latitudinal temperature gradients (up to 2°K per degree latitude) were found. This has important atmospheric dynamical implications, especially for the growth of baroclinic waves. Occultation observations also indicated that the average elevation of the southern hemisphere was nearly 4km higher than the northern hemisphere when referenced to an equipotential level. The occultation measurements showed that the atmospheric pressures near the surface in the southern hemisphere were 33 to 43% lower than the atmospheric pressures near the surface in the northern hemisphere. In addition to other parameters, the asymmetry in the density of the Martian atmosphere and the hemispheric altitude differences are important in understanding the seasonal dynamic processes that exist in the polar cap regions and in the Martian atmosphere generally.

Atmosphere of Jupiter from the Pioneer 11 S-Band Occultation Experiment: Preliminary Results

Two additional radio occultation measurements of the atmosphere of Jupiter were obtained with Pioneer 11. The entry measurement leads to a temperature profile that is substantially in agreement with those obtained with Pioneer 10, showing temperatures much higher than those derived from other observations. The exit measurement is not usable because of the discontinuous drift of the spacecraft auxiliary oscillator, presumably due to the trapped radiation belts of Jupiter. The combination of two Pioneer 10 measurements and one Pioneer 11 measurement yields an oblateness of 0.06496 at 1 millibar and 0.06547 at 160 millibars. Measurements in the Jovian ionosphere indicate a number of layers distributed over about 3000 kilometers, with a topside temperature of about 750 K.

Preliminary and novel estimates of CO2 gas transfer using a satellite scatterometer during the 2001GasEx experiment

The ocean takes up approximately 30% of the annual anthropogenic emissions of CO2. However, the air–sea exchange of carbon dioxide varies by a factor of 2 depending on the formulation of the exchange process. This considerable uncertainty is due in part to the difficulty in parameterizing the gas transfer velocity, k 660, usually given as a function of wind speed. Recent field data showed that parametrization using the mean square slope of small scale surface waves provides a more robust strategy to estimate gas transfer (Frew et al. 2004). Here we present a preliminary estimation of the gas transfer velocity as a function of upwind Normalized Radar Cross-Section (NRCS) as measured by the scatterometer QuikSCAT. The gas transfer velocity calculated from upwind NRCS exhibits a quadratic-like dependence at low and intermediate wind speeds (≃6 ms–1 ). This approach represents a promising new tool to obtain global quasi-synoptic estimates of oceanic uptake of CO2.