11:30 〜 11:45
[PCG21-09] Dust and cloud transport by traveling waves in the Martian atmosphere studied with Mars Climate Sounder
キーワード：火星、大気、波動
Baroclinic waves in the Martian atmospheres are considered to play a crucial role in determining the climate at mid-to high latitudes, as is the case with Earth. Observations from landers have discovered that baroclinic waves exist in the Martian atmosphere, and they become dominant from early autumn to late winter in the northern hemisphere. Their behavior near the surface and in the middle atmosphere had been revealed by analyzing atmospheric data sets measured by infrared sounders on several spacecraft. Their influences on the dust cycle were also revealed through images of Mars. However, the influences had not been studied quantitatively. Since the atmosphere of Mars is thin, dust and water ice clouds are thought to play an important role in determining the Martian climate. Understanding the interaction between traveling (zonally propagating) waves and the transport of substances in the atmosphere leads to a deeper understanding of the climatology of Mars.
Measurements taken by Mars Climate Sounder (MCS) onboard Mars Reconnaissance Orbiter (MRO) of NASA in MY30 and MY31 are used in this study. MCS is an infrared radiometer which provides vertical profiles of temperature, dust opacity, and water ice opacity. Its vertical resolution is ∼5 km, which provides a better vertical information than other infrared sounders of Mars. Hovmoller diagrams were made and the wave components for each zonal wavenumber were extracted by discrete Fourier transform.
This study identified the traveling waves in the middle atmosphere above 18 Pa, where previous studies had not surveyed. Eastward propagations with different phase speeds were observed during the northern autumn and winter seasons. They were considered to be atmospheric disturbances caused by baroclinic instabilities. We discovered that waves with zonal wavenumber of 1 dominate the atmosphere in the altitude regions at 10-55 km above the surface.
Furthermore, this study provides a quantitative analysis of how traveling waves affect the distributions of dust and water ice clouds. The results indicated that traveling waves have possible connections with dust and water ice transport. Distributions of dust and water ice propagated eastward at the same season when the eastward propagations of temperature were seen. The temperature and dust disturbances are in-phases, whereas the temperature and water ice are anti-phases. Assuming that the substances are transported by the meridional advection of traveling waves, the amplitudes of migration distances in the meridional direction were of the same order, but their relative ratios varied widely from 1. It is argued that not only traveling waves, but also other atmospheric conditions have impacts on dust and water ice cycle.
Measurements taken by Mars Climate Sounder (MCS) onboard Mars Reconnaissance Orbiter (MRO) of NASA in MY30 and MY31 are used in this study. MCS is an infrared radiometer which provides vertical profiles of temperature, dust opacity, and water ice opacity. Its vertical resolution is ∼5 km, which provides a better vertical information than other infrared sounders of Mars. Hovmoller diagrams were made and the wave components for each zonal wavenumber were extracted by discrete Fourier transform.
This study identified the traveling waves in the middle atmosphere above 18 Pa, where previous studies had not surveyed. Eastward propagations with different phase speeds were observed during the northern autumn and winter seasons. They were considered to be atmospheric disturbances caused by baroclinic instabilities. We discovered that waves with zonal wavenumber of 1 dominate the atmosphere in the altitude regions at 10-55 km above the surface.
Furthermore, this study provides a quantitative analysis of how traveling waves affect the distributions of dust and water ice clouds. The results indicated that traveling waves have possible connections with dust and water ice transport. Distributions of dust and water ice propagated eastward at the same season when the eastward propagations of temperature were seen. The temperature and dust disturbances are in-phases, whereas the temperature and water ice are anti-phases. Assuming that the substances are transported by the meridional advection of traveling waves, the amplitudes of migration distances in the meridional direction were of the same order, but their relative ratios varied widely from 1. It is argued that not only traveling waves, but also other atmospheric conditions have impacts on dust and water ice cycle.