[1] Without a global intrinsic magnetic field, oxygen ions in the Martian atmospheric corona can be picked up by the solar wind directly. The majority of the pickup ions escape, while some can precipitate into the atmosphere, producing sputtering of atmospheric constituents, which may play a significant role in the loss of neutral atmosphere. With its widely distributed crustal magnetic fields, Mars is unique. While it has been shown that Mars's crustal fields can alter the global distribution of escaping ions, little is known about the influence of the crustal fields on the spatial distribution and energy deposition of precipitating pickup ions. In this paper, the global distribution and energy spectrum of the precipitating pickup oxygen ions are calculated using the test particle method in the electric and magnetic fields set up by MHD simulation. Cases of different crustal field conditions are compared to show the influence of the crustal fields on the oxygen ion precipitation. We find, using a test particle code, that the crustal fields likely change the spatial distribution of the precipitation, resulting in irregularly distributed low-energy ion precipitation parches and wide high-energy ion precipitation belts on both the dayside and nightside. The crustal fields increase O + ion precipitation substantially, enhancing energy deposition especially on the nightside. Our results imply that atmospheric sputtering, and accompanying neutral escape, might happen globally and may be enhanced by a factor of almost 2 with the presence of the crustal magnetic fields.
A B S T R A C TCenozoic rifted lacustrine basins in east China display three main basin types: (1) basins with steeply dipping boundary fault, whose hanging walls tilt along pivot points; (2) basins with listric boundary faults, whose hanging walls bend along flexural bending points; and (3) basins formed by earlier extensional rifting with later strike-slip movement superimposed.The sequence development is intimately linked to the tectonic movements in the area, where second-order sequences are regionally correlatable from basin to basin and relate to the largescale tectonic movements in the region. Third-order sequences are related to local tectonic activity and are correlatable within basins, between subbasins, and sometimes, between neighboring basins. Detailed sequence-stratigraphic analysis and mapping of depositional systems demonstrate that sand-body distribution patterns are related to sequence-stratigraphic frameworks. For the three kinds of basins, the positions of pivot point zones, flexural bend zones, and strike-slip faults plus the syndepositional faults all control the distribution of depositional systems, systems tract, and sand bodies. These controlling factors can be attributed to different structural and stratigraphic features that change the accommodation. Structural elements include boundary faults, syndepositional faults, and abrupt changes in dip. Stratigraphic controls include preexisting surfaces with local channelization, paleobathymetric lows, and onlap onto clinoform slopes. The lowstand sand bodies deposited at the downdip
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Lunar horizon glows observed by the Apollo missions suggested a dense dust exosphere near the lunar terminator. But later missions failed to see such a high-density dust exosphere. Why the Apollo missions could observe so large number of dust grains remains a mystery. For the first time, we report five dust enhancement events observed by the Lunar Dust Experiment on board Lunar Atmosphere and Dust Environment Explorer mission, which happen near a twilight crater with dust densities comparable to the Apollo measurements. Moreover, the dust densities are larger on the downstream side of the crater and favor a higher solar wind temperature, consistent with an electrostatic dust lofting from the negatively charged crater floor. We also check the Apollo observations and find similar twilight craters, suggesting that the so-called dust exosphere is not a global phenomenon but just a local electrified dust fountain near twilight craters. Plain Language Summary With in situ dust measurements, we find that a shadowed crater near the terminator can dramatically change the surface electrical environment and bring a dense dust cloud surrounding the crater, which should be carefully assessed by engineers for future lunar explorations. Moreover, our findings have the general implications in studying the dust environment near large topographic features (mountains and deep craters) of all kinds of airless bodies. On the other hand, the electrostatic mechanism has been improved in recent years. Stubbs et al. (2006) proposed a dynamic fountain model, in which the like-charged dust grains with radii of 0.01-0.1 μm could be RESEARCH LETTER
The measurements from the Mars Atmosphere and Volatile EvolutioN spacecraft, in orbit around Mars, are utilized to investigate interplanetary coronal mass ejections (ICMEs) near 1.52 au. We identify 24 ICMEs from 2014 December 6 to 2019 February 21. The ICME list is used to examine the statistical properties of ICMEs. On average, the magnetic field strength of 5.99 nT in ICMEs is higher than that of 5.38 nT for stream interaction regions (SIRs). The density of 5.27 cm−3 for ICMEs is quite comparable to that of 5.17 cm−3 for SIRs, the velocity of 394.7 km s−1 for ICMEs is slightly lower than that of 432.8 km s−1 for SIRs, and the corresponding dynamic pressure of 1.34 nPa for ICMEs is smaller than that of 1.50 nPa for SIRs. Using existing databases of ICMEs at 1 au for the same time period, we compare ICME average properties at 1.52 au with those at 1 au. The averages of the characteristic quantities decrease by a factor of 1.1–1.7 from 1 to 1.52 au. In addition, we analyze an unusual space weather event associated with the ICME on 2015 March 9–10, and propose that the extremely strong dynamic pressure with a maximum of ∼18 nPa on March 8 is caused by the combined effects of the enhanced density inside a heliospheric plasma sheet (HPS), the compression of the HPS by the forward shock, and the high velocity of the sheath ahead of the ICME.
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