研究目的
To study the spatial and temporal variations of thermal structure and minor species (CO, SO, HDO, SO2) in the Venus mesosphere using ALMA submillimeter observations.
研究成果
ALMA observations provided 3D maps of mesospheric temperatures and minor species abundances on Venus, revealing complex variations with altitude, latitude, local time, and day-to-day changes. Temperatures are colder than VIRA model below 90 km, with inversions at 80-100 km. SO, SO2, and H2O show negligible abundance below ~85 km and increase above, with significant temporal and spatial variability. The SO2/SO ratio is consistent with previous studies. Future simultaneous observations are planned to further investigate correlations and dynamics.
研究不足
Low signal-to-noise ratio (S/N) for some species (e.g., SO2 only detectable on first day, HDO not mappable on all days), radiative transfer model does not include limb-sounding geometries, retrievals near limb are less reliable, altitude boundary between depleted and enriched layers cannot be precisely determined due to low S/N, temporal and spatial coverage limited to four days in November 2011, assumptions in CO profile and D/H ratio may introduce errors.
1：Experimental Design and Method Selection:
Used ALMA interferometer to observe CO, SO, HDO, and SO2 transitions at specific frequencies. Employed a line-by-line non-scattering radiative transfer model adapted from previous work, with spectroscopic parameters from JPL Molecular Spectroscopy catalog. Assumed a nominal CO abundance profile for temperature retrieval and used HDO as a tracer for water with a D/H enrichment of 200 times terrestrial value.
2：Sample Selection and Data Sources:
Observations of Venus were conducted on four dates in November 2011 (14th, 15th, 26th, 27th) with Venus angular diameter about 11'' and illumination factor 92%, focusing on the day side. Data reduction performed using ALMA Common Astronomy Software Applications (CASA) and GILDAS software.
3：List of Experimental Equipment and Materials:
ALMA interferometer (Atacama Large Millimeter Array), CASA software, GILDAS software, quasar J1924-292 for bandpass calibration, quasar NRAO530 for amplitude and phase calibration.
4：Experimental Procedures and Operational Workflow:
Calibrated raw visibilities using quasars, corrected for planet topocentric velocity, applied self-calibration to improve phase, scaled fluxes to Venus continuum model, oriented maps with North Pole on top, performed baseline tapering for consistent beam size, used CLEAN algorithm for deconvolution. Temperature and minor species retrievals used constrained and regularized algorithm with a priori profiles and iterative fitting.
5：Data Analysis Methods:
Retrieved temperature profiles from CO line assuming fixed CO abundance, then used these to retrieve SO, SO2, and H2O abundances. Error analysis included uncertainties from measurement noise, a priori choices, and calibration. Functional derivatives used to determine sensitivity altitudes.
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