Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe 2018 Martian Global Dust Storm over the South Polar Region studied with MEx/VMC
97
0
0.0
(
0
)
Added by
Jorge Hernandez Bernal
Publication date
2021
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We study the 2018 Martian Global DustStorm (GDS 2018) over the Southern Polar Region using images obtained by the Visual Monitoring Camera (VMC) on board Mars Express during June and July 2018. Dust penetrated into the polar cap region but never covered the cap completely, and its spatial distribution was nonhomogeneous and rapidly changing. However, we detected long but narrow aerosol curved arcs with a length of 2,000-3,000 km traversing part of the cap and crossing the terminator into the night side. Tracking discrete dust clouds allowed measurements of their motions that were towards the terminator with velocities up to 100 m/s. The images of the dust projected into the Martian limb show maximum altitudes of around 70 km but with large spatial and temporal variations. We discuss these results in the context of the predictions of a numerical model for dust storm scenario.
rate research
Read More
Northern line-of-sight extinction within Gale Crater during the 2018 global dust storm was monitored daily using MSLs Navcam. Additional observations with Mastcam (north) and Navcam (all directions) were obtained at a lower cadence. Using feature identification and geo-referencing, extinction was estimated in all possible directions. Peak extinction of $>1.1$ km$^{-1}$ was measured between sols 2086 and 2090, an order of magnitude higher than previous maxima. Northern and western directions show an initial decrease, followed by a secondary peak in extinction, not seen in column opacity measurements. Due to foreground topography, eastern direction results are provided only as limits, and southern results were indeterminable. Mastcam red and green filter results agree well, but blue filter results show higher extinctions, likely due to low signal-to-noise. Morning results are systematically higher than afternoon results, potentially indicative of atmospheric mixing.
The winter polar vortices on Mars are annular in terms of their potential vorticity (PV) structure, a phenomenon identified in observations, reanalysis and some numerical simulations. Some recent modeling studies have proposed that condensation of atmospheric carbon dioxide at the winter pole is a contributing factor to maintaining the annulus through the release of latent heat. Dust and topographic forcing are also known to be causes of internal and interannual variability in the polar vortices. However, coupling between these factors remains uncertain, and previous studies of their impact on vortex structure and variability have been largely limited to a single Martian global climate model (MGCM). Here, by further developing a novel MGCM, we decompose the relative roles of latent heat and dust as drivers for the variability and structure of the northern Martian polar vortex. We also consider how Martian topography modifies the driving response. By also analyzing a reanalysis dataset we show that there is significant dependence in the polar vortex structure and variability on the observations assimilated. In both model and reanalysis, high atmospheric dust loading (such as that seen during a global dust storm) can disrupt the vortex, cause the destruction of PV in the low-mid altitudes (> 0.1 hPa), and significantly reduce spatial and temporal vortex variability. Through our simulations, we find that the combination of dust and topography primarily drives the eddy activity throughout the Martian year, and that although latent heat release can produce an annular vortex, it has a relatively minor effect on vortex variability.
Mars polar layered deposits (PLD) are comprised of layers of varying dust-to-water ice volume mixing ratios (VMR) that may record astronomically-forced climatic variation over Mars recent orbital history. Retracing the formation of these layers by quantifying the sensitivity of deposition rates of polar material to astronomical forcing is critical for the interpretation of this record. Using a Mars global climate model (GCM), we investigate the sensitivity of annual polar water ice and dust surface deposition to various obliquities and surface water ice distributions at zero eccentricity, providing a reasonable characterization of the evolution of the PLD during recent low-eccentricity epochs. For obliquities between 15{deg} - 35{deg}, predicted net annual accumulation rates range from -1 to +14 mm/yr for water ice and from +0.003 to +0.3 mm/yr for dust. GCM-derived rates are ingested into an integration model that simulates polar accumulation of water ice and dust over 5 consecutive obliquity cycles (~700 kyrs) during a low eccentricity epoch. A subset of integration simulations predict combined accumulation of water ice and dust in the north at time averaged rates that are near the observationally-inferred value of 0.5 mm/yr. Three types of layers are produced per obliquity cycle: a ~30 m-thick dust-rich (~25% dust VMR) layer forms at high obliquity, a ~0.5 m-thick dust lag forms at low obliquity, and two ~10 m-thick dust-poor (~3%) layers form when obliquity is increasing/decreasing. The ~30 m-thick dust-rich layer is reminiscent of a ~30 m feature derived from visible imagery analysis the north PLD, while the ~0.5 m-thick dust lag is a factor of ~2 smaller than observed thin layers. Overall, this investigation provides further evidence for obliquity forcing in the PLD climate record, and demonstrates the importance of ice-on-dust nucleation in polar depositional processes.
The importance of the investigation of magnetic superstorms is not limited to academic interest, because these superstorms can cause catastrophic impact on the modern civilisation due to our increasing dependency on technological infrastructure. In this context, the Carrington storm in September 1859 is considered as a benchmark of observational history owing to its magnetic disturbance and equatorial extent of the auroral oval. So far, several recent auroral reports at that time have been published but those reports are mainly derived from the Northern Hemisphere. In this study, we analyse datable auroral reports from South America and its vicinity, assess the auroral extent using philological and astrometric approaches, identify the auroral visibility at - 17.3{deg} magnetic latitude and further poleward and reconstruct the equatorial boundary of the auroral oval to be 25.1{deg} +/- 0.5{deg} in invariant latitude. Interestingly, brighter and more colourful auroral displays were reported in the South American sector than in the Northern Hemisphere. This north-south asymmetry is presumably associated with variations of their magnetic longitude and the weaker magnetic field over South America compared to the magnetic conjugate point and the increased amount of magnetospheric electron precipitation into the upper atmosphere. These results attest that the magnitude of the Carrington storm indicates that its extent falls within the range of other superstorms, such as those that occurred in May 1921 and February 1872, in terms of the equatorial boundary of the auroral oval.
We present spatial and temporal distributions of dust on Mars from Ls = 331 in MY26 until Ls = 80 in MY33 retrieved from the measurements taken by the Planetary Fourier Spectrometer (PFS) aboard Mars Express. In agreement with previous observations, large dust opacity is observed mostly in the southern hemisphere spring/summer and particularly over regions of higher terrain and large topographic variation. We present a comparison with dust opacities obtained from Thermal Emission Spectrometer (TES) - Mars Global Surveyor (MGS) measurements. We found good consistency between observations of two instruments during overlapping interval (Ls = 331 in MY26 until Ls = 77 in MY27). We found a different behavior of the dust opacity with latitude in the various Martian years (inter-annual variations). A global dust storm occurred in MY28. We observe a different spatial distribution, a later occurrence and dissipation of the dust maximum activity in MY28 than in other Martian years. A possible precursor signal to the global dust storm in MY 28 is observed at Ls = 200 - 235 especially over west Hellas. Heavy dust loads alter atmospheric temperatures. Due to the absorption of solar radiation and emission of infrared radiation to space by dust vertically non-uniformly distributed, a strong heating of high atmospheric levels (40 - 50 km) and cooling below around 30 km are observed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
