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A. Seiff (San Jose State U. Foundation), J.T. Schofield (Jet Propulsion Lab., NASA), J.R. Murphy (New Mexico State U.), J.D. Mihalov (Ames Research Center, NASA)
Near-surface winds on Mars were measured by a hot-wire anemometer sensor atop the meteorology mast on the Pathfinder lander, ~1 m above the spacecraft solar panels. The sensor, designed and developed for Pathfinder, had 6 hot wire elements arrayed around the periphery of a 2.5 cm diameter cylinder. This arrangement permitted definition of both wind directions, published earlier, and magnitudes.
Data were acquired on all sols, normally in short (15 min) sessions, but on 5 sols, were taken around the clock over 24 Mars hours. The data showed sensitive response to wind magnitude and direction, but were initially difficult to interpret quantitatively because of dependence not only on the winds but also on atmospheric temperature. There was also some variation in sensitivity of individual elements. Detailed calibrations in Aug., 98, have allowed us to make the first quantitative interpretations.
Winds in the early part of the mission, sol 25, showed a systematic diurnal variation, increasing in magnitude from 0 to ~10 m/s during the daytime hours to a peak at 13:00, then subsiding toward sunset. Daytime winds were also very gusty, with gust magnitudes of a few m/s on a time scale of a few seconds. Some lander interference effects were noted. After the turbulence and wind magnitude quieted suddenly at sundown, they remained quiet, near zero, until 23:00, when a night flow began which peaked at 4 m/s near 2:30 AM. From this peak until dawn, winds were subsiding to near zero at dawn. There also appears to have been a seasonal change in wind patterns, with more vigorous winds appearing in the morning hours near mission's end, when the season was early fall.
We will present the status of the wind investigation as of the meeting date, and will also make interpretations of the significance of the data, where possible.