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Träfflista för sökning "WFRF:(Vasavada Ashwin) ;pers:(Wong Michael H.)"

Sökning: WFRF:(Vasavada Ashwin) > Wong Michael H.

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1.
  • Moores, John E., et al. (författare)
  • Observational evidence of a suppressed planetary boundary layer in northern Gale Crater, Mars as seen by the Navcam instrument onboard the Mars Science Laboratory rover
  • 2015
  • Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 249, s. 129-142
  • Tidskriftsartikel (refereegranskat)abstract
    • The Navigation Cameras (Navcam) of the Mars Science Laboratory rover, Curiosity, have been used to examine two aspects of the planetary boundary layer: vertical dust distribution and dust devil frequency. The vertical distribution of dust may be obtained by using observations of the distant crater rim to derive a line-of-sight optical depth within Gale Crater and comparing this optical depth to column optical depths obtained using Mastcam observations of the solar disc. The line of sight method consistently produces lower extinctions within the crater compared to the bulk atmosphere. This suggests a relatively stable atmosphere in which dust may settle out leaving the air within the crater clearer than air above and explains the correlation in observed column opacity between the floor of Gale Crater and the higher elevation Meridiani Planum. In the case of dust devils, despite an extensive campaign only one optically thick vortex (τ=1.5±0.5×10-3) was observed compared to 149 pressure events > 0.5Pa observed in REMS pressure data. Correcting for temporal coverage by REMS and geographic coverage by Navcam still suggests 104 vortices should have been viewable, suggesting that most vortices are dustless. Additionally, the most intense pressure excursions observed on other landing sites (pressure drop >2.5Pa) are lacking from the observations by the REMS instrument. Taken together, these observations are consistent with pre-landing circulation modeling of the crater showing a suppressed, shallow boundary layer. They are further consistent with geological observations of dust that suggests the northern portion of the crater is a sink for dust in the current era.
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2.
  • Webster, Christopher R., et al. (författare)
  • Background levels of methane in Mars' atmosphere show strong seasonal variations
  • 2018
  • Ingår i: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 360:6393, s. 1093-1096
  • Tidskriftsartikel (refereegranskat)abstract
    • Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.
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