Presentation Information
[PPS07-P10]Study of Martian Atmospheric Gravity Wave Activity Using MGS Radio Occultation Data
*Satsuki Minoura1, Chikako Hashimoto1, Katsuyuki Noguchi1 (1.Nara Women's University)
Atmospheric gravity waves propagate as air parcels oscillate vertically under buoyancy as the restoring force. Their primary sources of excitation include topography, convective activity, and jet streams [Nappo, 2002]. In Earth’s atmosphere, previous theoretical studies have shown that atmospheric gravity waves attenuate and break during their upward propagation, transporting momentum to the background atmosphere [Lindzen, 1981]. Observational studies have also demonstrated their significant influence on the general circulation of the atmosphere [Fritts and Alexander, 2003].
Because the Martian atmosphere is also stably stratified, atmospheric gravity waves are expected to play a role similar to that in Earth’s atmosphere. One effective method for observational studies of Martian atmospheric gravity waves is radio occultation. In this technique, radio signals transmitted from a spacecraft orbiting a planet are received by ground stations on Earth. Frequency variations of the signals caused by refraction in the planetary atmosphere are used to derive vertical profiles of refractivity, from which temperature and pressure profiles are obtained. Creasey et al. [2006] estimated the activity of atmospheric gravity waves using temperature profiles derived from radio occultation measurements by the Mars Global Surveyor (MGS) and investigated their latitudinal and longitudinal distributions as well as seasonal variations. The authors suggested that the primary sources of gravity waves are large-scale topography in low-latitude regions and that wave activity remains low at high latitudes throughout the year. However, their analysis was limited to data from only the early phase of the MGS mission, restricting the coverage in latitude, longitude, and season. Consequently, the spatial distribution and seasonal variability of gravity wave activity were not fully characterized.
In this study, we extend the analysis of Creasey et al. [2006] by using data covering the entire MGS mission (Martian Years 24–28) to investigate the spatio-temporal variation of atmospheric gravity wave activity. Consistent with Creasey et al. [2006], we find that gravity wave activity remains high at low latitudes throughout the year, which is interpreted as a result of wave excitation by mountainous regions in these areas. In addition, we reveal clear seasonal variations at high latitudes that were not sufficiently evaluated in that study. In particular, enhanced activity is observed from autumn to winter in the northern hemisphere and from winter to spring in the southern hemisphere. Furthermore, the vertical distribution of gravity wave activity is found to vary with latitude, longitude, and season. These results suggest that the excitation of atmospheric gravity waves on Mars cannot be explained solely by topography and indicate the presence of additional sources with spatial and seasonal dependence.
Because the Martian atmosphere is also stably stratified, atmospheric gravity waves are expected to play a role similar to that in Earth’s atmosphere. One effective method for observational studies of Martian atmospheric gravity waves is radio occultation. In this technique, radio signals transmitted from a spacecraft orbiting a planet are received by ground stations on Earth. Frequency variations of the signals caused by refraction in the planetary atmosphere are used to derive vertical profiles of refractivity, from which temperature and pressure profiles are obtained. Creasey et al. [2006] estimated the activity of atmospheric gravity waves using temperature profiles derived from radio occultation measurements by the Mars Global Surveyor (MGS) and investigated their latitudinal and longitudinal distributions as well as seasonal variations. The authors suggested that the primary sources of gravity waves are large-scale topography in low-latitude regions and that wave activity remains low at high latitudes throughout the year. However, their analysis was limited to data from only the early phase of the MGS mission, restricting the coverage in latitude, longitude, and season. Consequently, the spatial distribution and seasonal variability of gravity wave activity were not fully characterized.
In this study, we extend the analysis of Creasey et al. [2006] by using data covering the entire MGS mission (Martian Years 24–28) to investigate the spatio-temporal variation of atmospheric gravity wave activity. Consistent with Creasey et al. [2006], we find that gravity wave activity remains high at low latitudes throughout the year, which is interpreted as a result of wave excitation by mountainous regions in these areas. In addition, we reveal clear seasonal variations at high latitudes that were not sufficiently evaluated in that study. In particular, enhanced activity is observed from autumn to winter in the northern hemisphere and from winter to spring in the southern hemisphere. Furthermore, the vertical distribution of gravity wave activity is found to vary with latitude, longitude, and season. These results suggest that the excitation of atmospheric gravity waves on Mars cannot be explained solely by topography and indicate the presence of additional sources with spatial and seasonal dependence.