2:15 PM - 2:30 PM
[PPS09-15] Study of local winds over large-scale slopes at low latitude on Mars
Keywords:dust storm, local wind
The Solis Planum, which is located around 20S, 260E, is famous for its unique and strong dust activities. They sometimes globally affect the Martian atmosphere (Battalio et al. (2019)).
We investigated the onset local time of dust storms in the region (Okuno et al., 2024). The result suggested that it was likely to occur frequently around LT1200 in the southern winter, and LT0900 in the southern spring. Since the region is characterized by the large topographic slopes, slope winds may contribute to the formation of the dust storms. However, not much attention has been given to slope winds over large, gentle slopes.
One of the famous models of steady slope flow was proposed by Prandtl (1942). The model describes the steady flow resulting from the balance between momentum advection and heat transport in the stably stratified atmosphere. It is useful to understand the nature of slope wind. However, it does not discuss the temporal variation of the flow. Zardi, et al. (2014) analytically solved the time variation of the model proposed by Prandtl (1942) to describe the flow generated by time-periodic changes in surface temperature. They obtained three flow regimes as solutions called SuperCritical, SubCritical, Critical. SuperCritical cases occur for strong stability and/or large slope angles and both wind velocity and temperature oscillate in phase. SubCritical occur for weak stability and/or small slope angles. Wind velocity oscillations lag ground temperature. In Critical cases, temperature oscillations and wind speed oscillations resonate. In comparison with the other two cases, strong winds may blow at higher altitudes. However, they set some parameters such as diffusion coefficients as constants.
In this study, we conducted numerical simulation to investigate the local time variation of slope winds in the low latitude region on Mars. We referred to the model established by Zardi et al., (2014), but applied temporal variation to some parameters. Initial results indicated that with a slope angle of 0.42 degree, the downslope wind speed reached 40m/s at LT0900 and the upslope wind showed 40m/s at LT1700 at altitudes between 200m and 400 m.
We investigated the onset local time of dust storms in the region (Okuno et al., 2024). The result suggested that it was likely to occur frequently around LT1200 in the southern winter, and LT0900 in the southern spring. Since the region is characterized by the large topographic slopes, slope winds may contribute to the formation of the dust storms. However, not much attention has been given to slope winds over large, gentle slopes.
One of the famous models of steady slope flow was proposed by Prandtl (1942). The model describes the steady flow resulting from the balance between momentum advection and heat transport in the stably stratified atmosphere. It is useful to understand the nature of slope wind. However, it does not discuss the temporal variation of the flow. Zardi, et al. (2014) analytically solved the time variation of the model proposed by Prandtl (1942) to describe the flow generated by time-periodic changes in surface temperature. They obtained three flow regimes as solutions called SuperCritical, SubCritical, Critical. SuperCritical cases occur for strong stability and/or large slope angles and both wind velocity and temperature oscillate in phase. SubCritical occur for weak stability and/or small slope angles. Wind velocity oscillations lag ground temperature. In Critical cases, temperature oscillations and wind speed oscillations resonate. In comparison with the other two cases, strong winds may blow at higher altitudes. However, they set some parameters such as diffusion coefficients as constants.
In this study, we conducted numerical simulation to investigate the local time variation of slope winds in the low latitude region on Mars. We referred to the model established by Zardi et al., (2014), but applied temporal variation to some parameters. Initial results indicated that with a slope angle of 0.42 degree, the downslope wind speed reached 40m/s at LT0900 and the upslope wind showed 40m/s at LT1700 at altitudes between 200m and 400 m.