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[PPS09-13] Conditions for the occurrences of dust storms in the Acidalia Planitia on Mars using EMARS reanalysis data
Keywords:Mars, Dust storms, Baroclinic waves, Thermal tides
Martian dust storms, from local to global scales, are observed in the Northern Hemisphere (NH) during late summer and spring (Ls=150° ~360° , 0° ~30° ). The Acidalia Planitia, located in the mid-to-high latitudes of the NH, has the highest dust storm frequency [Battalio and Wang 2021]. The baroclinic waves dominate the dynamics of the lower atmosphere during fall and spring at mid-to-high latitudes and have been suggested to be related to dust storm occurrences. Hinson [2006] suggested a relationship between the dominance of zonal wavenumber s=3 at 50° ~65° N and flushing dust storms in Mars Year (MY) 24. Hinson et al. [2012] showed that meridional wind in the lower atmosphere was strengthened during the s=2 and s=3 predominance at 55° ~80° N. However, the characteristics of the meteorological field during occurrence have not been clarified, and accurate model reproduction has not yet been achieved. As dust storms strongly reduces solar radiation on the surface, it is important to predict the occurrences for future explorations. This study investigates meteorological conditions during the occurrences in the Acidalia Planitia (40° ~70° N, 0° ~80° W).
We used the Mars Dust Activity Database (MDAD) [Battalio and Wang., 2021] and the Ensemble Mars Atmosphere Reanalysis (EMARS) dataset [Greybush et al., 2019] for MY24-32. EMARS is a reanalysis data of temperature profiles observed by the Thermal Emission Spectrometer and the Mars Climate Sounder. These observations were assimilated into the MGCM using the Local Ensemble Transform Kalman Filter method. The dataset has a horizontal resolution of 5° latitude × 6° longitude. We classified storms into members, which lasted for more than 1-sol, and sequences, where members organized and persisted for at least 3-sols. We then compared meteorological fields between the ‘occurrence’ and ‘non-occurrence’ periods of dust members/sequences.
Seasonal distributions of the occurrences showed that the most members (108) occurred in the NH spring (Ls=0° ~30° ), while the most sequences (10) occurred in fall (Ls=180° ~210° ) within the analysis area. As for the fall sequences, 1-sol mean winds from between north and west in ‘occurrence’ periods were more prominent than ‘non-occurrence’ periods. As for the spring sequences, local time (LT) variations showed the peak of wind speeds at LT=14 in ‘occurrence’ periods. Spectral analyses of 5~7 hPa mean zonal and meridional winds showed that the winds from between north and west during fall sequences were driven by the baroclinic waves. The area of occurred dust storms in fall was larger than in other seasons, which suggests that dust storm sequences are developed by several-sol fluctuations such as the baroclinic waves.
To investigate the effects of topography and seasonality, we analyzed wind speeds for the six pseudo-seasons [Wang et al., 2023] for a local area (46° ∼60° N, 36° ~54° W) where the most dust storms occurred in Acidalia. Our results showed that wind speeds during the occurrences of dust storm members were stronger than during the non-occurrences, but only in the 6th season (Ls=295° ~360° ). Next, we analyzed zonal and meridional winds during the occurrences caused by the baroclinic and tidal wave components for spring, fall, and winter (Ls=330° ~360° ). The tidal components accelerated southerly winds up to 40 m s-1 in spring. We consider that the dust storm occurrences in spring are often driven by components varying within the diurnal period, suggesting that storms remain as members without forming organized sequences. In winter, the baroclinic and tidal components contributed up to 10 m s-1 to westerly wind acceleration, though their effects were weaker than in spring. In fall, the tidal components contributed up to 20 m s-1 to westerly wind acceleration, while the baroclinic ones contributed up to 5 m s-1 in various directions. This suggests that the tidal waves enhance the winds from between north and west during fall sequences.
Acknowledgment: This work is supported by JST FOREST program (JPMJFR212U).
We used the Mars Dust Activity Database (MDAD) [Battalio and Wang., 2021] and the Ensemble Mars Atmosphere Reanalysis (EMARS) dataset [Greybush et al., 2019] for MY24-32. EMARS is a reanalysis data of temperature profiles observed by the Thermal Emission Spectrometer and the Mars Climate Sounder. These observations were assimilated into the MGCM using the Local Ensemble Transform Kalman Filter method. The dataset has a horizontal resolution of 5° latitude × 6° longitude. We classified storms into members, which lasted for more than 1-sol, and sequences, where members organized and persisted for at least 3-sols. We then compared meteorological fields between the ‘occurrence’ and ‘non-occurrence’ periods of dust members/sequences.
Seasonal distributions of the occurrences showed that the most members (108) occurred in the NH spring (Ls=0° ~30° ), while the most sequences (10) occurred in fall (Ls=180° ~210° ) within the analysis area. As for the fall sequences, 1-sol mean winds from between north and west in ‘occurrence’ periods were more prominent than ‘non-occurrence’ periods. As for the spring sequences, local time (LT) variations showed the peak of wind speeds at LT=14 in ‘occurrence’ periods. Spectral analyses of 5~7 hPa mean zonal and meridional winds showed that the winds from between north and west during fall sequences were driven by the baroclinic waves. The area of occurred dust storms in fall was larger than in other seasons, which suggests that dust storm sequences are developed by several-sol fluctuations such as the baroclinic waves.
To investigate the effects of topography and seasonality, we analyzed wind speeds for the six pseudo-seasons [Wang et al., 2023] for a local area (46° ∼60° N, 36° ~54° W) where the most dust storms occurred in Acidalia. Our results showed that wind speeds during the occurrences of dust storm members were stronger than during the non-occurrences, but only in the 6th season (Ls=295° ~360° ). Next, we analyzed zonal and meridional winds during the occurrences caused by the baroclinic and tidal wave components for spring, fall, and winter (Ls=330° ~360° ). The tidal components accelerated southerly winds up to 40 m s-1 in spring. We consider that the dust storm occurrences in spring are often driven by components varying within the diurnal period, suggesting that storms remain as members without forming organized sequences. In winter, the baroclinic and tidal components contributed up to 10 m s-1 to westerly wind acceleration, though their effects were weaker than in spring. In fall, the tidal components contributed up to 20 m s-1 to westerly wind acceleration, while the baroclinic ones contributed up to 5 m s-1 in various directions. This suggests that the tidal waves enhance the winds from between north and west during fall sequences.
Acknowledgment: This work is supported by JST FOREST program (JPMJFR212U).