Computer Science – Sound
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.4005b&link_type=abstract
American Astronomical Society, DPS meeting #40, #40.05; Bulletin of the American Astronomical Society, Vol. 40, p.468
Computer Science
Sound
Scientific paper
Radio sounding measurements at Venus were performed as part of the ESA Venus Express (VEX) radio science investigation (VeRa) during the first three occultation seasons. A total of 118 vertical scans of the Venus ionosphere and neutral atmosphere were obtained during the nominal VEX mission from June 2006 to October 2007. Radial profiles of neutral number density, which cover the height range from 40-90 km, are used to derive vertical profiles of temperature and pressure. The observations reveal distinct cold collar regions in both hemispheres. The tropopause altitude and temperature reach relative extrema at the cold collar latitude (near 65 deg), which are about 7 km higher and 60 K colder than the respective values at low latitude. The VeRa temperatures at any given pressure level are typically within 5 K of those obtained on Pioneer Venus. Calculated profiles of static stability are latitude dependent. A nearly adiabatic region extends from 50-60 km (middle cloud), above which the static stability increases sharply to a maximum typically between 60-70 km. The Venus dayside ionosphere displays a sharp bottomside cutoff in electron density at 115 km altitude and pronounced peaks at 125 km and 140 km. The maximum density of these peaks decreases with solar zenith angle (SZA) in a roughly Chapman-like behavior; the peak density near the terminator being about 30% of that for SZA < 45 deg. The topside ionosphere is highly variable, often displaying a bulge at altitudes in the range 155-175 km. Even more variable are the nighttime profiles, which occasionally reveal no measurable ionization above the noise level ( 2000 el/cc) at all heights. The altitude of the ionopause at low to moderate SZA has been observed to vary by more than 100 km within a few days, presumably an effect of the varying solar wind ram pressure.
Bird Michael K.
Häußler Boris
Pätzold Martin
Tellmann Silvia
Tyler Leonard G.
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