Astronomy and Astrophysics – Astronomy
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...p32a05k&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #P32A-05
Astronomy and Astrophysics
Astronomy
5405 Atmospheres--Composition And Chemistry, 5409 Atmospheres--Structure And Dynamics, 5410 Composition, 6225 Mars
Scientific paper
Water vapor is strongly depleted above the condensation level which is very sensitive to atmospheric temperature. High variability of H2O above 10-20 km results in strong variations of high-altitude ozone. Photolysis of O3 excites the O2(1Δ ) dayglow at 1.27 μ m which is quenched by CO2 below 20 km. Therefore, the O2 1.27 μ m dayglow reflects high-altitude ozone on Mars and is the best tracer of photochemistry at low and middle latitudes. The dayglow can be observed and mapped on Mars using the CSHELL long-slit high-resolution spectrograph at the IRTF [Krasnopolsky and Bjoraker, JGR 105, 20,179, 2000]. We have made mapping observations of the 1.27 μ m dayglow at five seasonal points between aphelion and perihelion on Mars (LS = 71 and 251° , respectively). The extracted dayglow intensities were corrected for air mass and surface reflection. The observed dayglow maps demonstrate a complex combination of seasonal, latitudinal, diurnal, and local (place to place) variations. Mean intensities near local noon decrease from 6 MR at LS = 68° to 2.5 MR at 112° and then to 1 MR at 247° . The latitudinal variations are even more complicated and reflect a composite effect of water abundance, hygropause, local solar irradiance, and atmospheric dynamics. Some strong dayglow features remain unexplained, for example, a broad maximum of 5 MR at LS = 177° , 30° N, 1330 LT. The seasonal and latitudinal variations of the dayglow intensities near local noon form a map which reminds a similar map of the H2O abundance based on the Viking MAWD observations [Jakosky and Farmer, JGR 87, 2999, 1982]. The dayglow behavior with local time is different for various seasons and latitudes. Typically the dayglow peaks between 1100 and 1400 LT. These peaks are the most prominent at 20-50° S for LS = 112° and 20-50° N for LS = 177 and 247° . The morningside (0600-0930 LT) intensities are very low (<=0.5 MR) at all latitudes for LS = 177° and at 20-50° N for LS = 247° . The dayglow is almost constant at ~=1 MR southward of 20° N for LS = 247° . The observed maps may be used to study photochemistry and dynamics of the martian atmosphere. This work was supported by NASA Planetary Astronomy Program via grants NAG5-9400 and NAG5-10492.
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