Inter-annual variations of 6.5-day planetary waves and their relations with QBO

This paper studies inter-annual variations of 6.5-Day Waves(6.5 DWs) observed at altitudes 20-110 km between 52°S-52°N latitudes during March 2002-January 2021, and how these variations were related to the equatorial stratospheric Quasi-Biennial Oscillation(QBO). Temperature amplitudes of the 6.5 DWs are calculated based on SABER/TIMED observations. QBO zonal winds are obtained from an ERA5 reanalysis dataset. QBO phases are derived using an Empirical Orthogonal Functions(EOF) method. Wavelet analysis of the observed 6.5 DW variations demonstrates obvious spectral maximums around 28-38 months at 32°N-52°N, and around 26-30 months at 32°S-52°S. In the Northern Hemisphere, peak periods lengthened poleward;in the Southern Hemisphere, however,they were unchanged with latitude. Residual 6.5 DWs amplitudes have been determined by removing composite amplitudes from 6.5 DWs amplitudes. Comparisons between QBO and monthly maximum residual 6.5 DWs amplitudes(AMmax) show clear correlations between the QBO and 6.5 DWs in both hemispheres, but the observed relationship is stronger in the NH. When AMmax NH, the mean QBO profile was easterly at all levels from 70 to 5 hPa;when the AMmax below 30 hPa. Linear Pearson correlation coefficients between QBO phases and AMmax 20°N-52°N in April and around 64 km at 24°S in February, and large negative values from 80 to 110 km between 20°N-50°N in August and at 96-106 km between 20°S-44°S in February. These results indicate quantitative correlations between QBO and 6.5 DWs and provide credible evidences for further studies of QBO modulations on long-term variations of 6.5 DWs.

Paleomagnetism of late Cretaceous dykes in the Gangdese belt: New constraints on the position and structure of the southern margin of Asia prior to the India-Asia collision

This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constraints on pre-collisional structure of the southern margin of Asia and the onset of the India-Asia collision.Magnetite is identified as the main magnetic carrier in our study.The magnetite shows no evidence of metamorphism or alteration as determined from optical and scanning electron microscope observations.A strong mineral orientation is revealed by anisotropy of magnetic susceptibility analysis both for the intruded dykes and the country rocks.The authors interpret this AMS fabric to have formed during intrusion rather than deformation.Fifteen of 23 sites yield acceptable site mean characteristic remanences with dual polarities.A scatter analysis of the virtual geomagnetic poles suggests that the mean result adequately averaged paleosecular variation.The paleomagnetic pole from the Gangdese dykes yields a paleolatitude of 14.3°N±5.8°N for the southern margin of Asia near Lhasa.The paleolatitude corresponds to an in-between position of the Lhasa terrane during about 130‒60 Ma.Furthermore,the mean declination of the characteristic remanent magnetization reveals a significant counterclockwise rotation of 18°±9°for the sampling location since about 83 Ma.In the light of tectonic setting of the dykes,the strike of the southern margin of Asia near Lhasa is restored to trend approximately about 310°,which is compatible with the hypothesis that the southern margin of Eurasia had a quasi-linear structure prior to its collision with India.

The anisotropy of suprathermal electrons in the Martian ionosphere

Suprathermal electrons are an important population of the Martian ionosphere, either produced by photoionization of atmospheric neutrals or supplied from the Solar Wind (SW). This study is dedicated to an in-depth investigation of the pitch angle distribution of suprathermal electrons at two representative energies, 19−55 eV and 124−356 eV, using the extensive measurements made by the Solar Wind Electron Analyzer on board the Mars Atmosphere and Volatile Evolution. Throughout the study, we focus on the overall degree of anisotropy, defined as the standard deviation of suprathermal electron intensity among different directions which is normalized by the mean omni-directional intensity. The available data reveal the following characteristics: (1) In general, low energy electrons are more isotropic than high energy electrons, and dayside electrons are more isotropic than nightside electrons;(2) On the dayside, the anisotropy increases with increasing altitude at low energies but remains roughly constant at high energies, whereas on the nightside, the anisotropy decreases with increasing altitude at all energies;(3) Electrons tend to be more isotropic in strongly magnetized regions than in weakly magnetized regions, especially on the nightside. These observations indicate that the anisotropy is a useful diagnostic of suprathermal electron transport, for which the conversion between the parallel and perpendicular momenta as required by the conservation of the first adiabatic invariant, along with the atmospheric absorption at low altitudes, are two crucial factors modulating the observed variation of the anisotropy. Our analysis also highlights the different roles on the observed anisotropy exerted by suprathermal electrons of different origins.

Wavelike perturbations in Titan’s ionosphere and their compositional variation:A preliminary survey of Cassini Ion Neutral Mass Spectrometer measurements

Wavelike perturbations in the ionosphere of Titan,the largest satellite of Saturn,are explored based on the Cassini Ion Neutral Mass Spectrometer(INMS)measurements.Strong wavelike perturbations are identified for more than twenty ion species,from simple ones such as N^(+)and CH_(4)^(+)to complex ones such as C_(2)H_(3)CNH^(+)and C_(4)H_(7)^(+).Simultaneous wavelike perturbations in background N_(2),indicative of atmospheric gravity waves,are also observed,motivating us to speculate that the INMS-derived ion perturbations are wave-driven.The amplitudes of the ion perturbations are found to be larger than that of the N_(2)perturbations.Clear compositional variation is revealed by the data:heavier ion species exhibit greater amplitudes.Such observations might be understood based on considerations either of force balance or chemical loss in Titan’s ionosphere.

An updated constraint on the local stratigraphy at the Chang'E-4 landing site

The Chang’E-4 mission has been exploring the lunar farside.Two scientific targets of the rover onboard are(1)resolving the possible mineralogy related to the South Pole-Aitken basin and(2)understanding the subsurface processes at the lunar farside.Publications to date that are based on the reflectance spectra and radar data obtained by the rover have shown a persistent inconsistency about the local stratigraphy.To explain both the abnormal surface topography at the landing site and the unexpected radargram observed by the rover,the Alder crater has been frequently reported to be older than the mare basalts at that landing site.However,this argument is not supported by earlier geological mapping nor recent crater statistics.Resolving this controversy is critical for a full understanding of the geological history of the landing area and for correct interpretations of the scientific data returned.Employing detailed crater statistics,rigorous statistical analyses,and an updated crater chronology function,this study is determined to resolve the relative ages of the Alder crater,Finsen crater,and the mare basalts on the floor of Von Kármán.Our results reveal that while background secondaries and local resurfacing have widely occurred in the study area,affecting age determinations,the statistics are significant enough to conclude that the Alder crater is the oldest among the three targets.This independent constraint is consistent with both the crosscutting relationships of different terrains in this area and global stratigraphic mapping.Our results exclude Alder as a possible contributor of the post-mare deposits at the landing site,appealing for a more systematic stratigraphy study to resolve the provenances of these deposits.

Martian Thermosphere Response to Solar Flares:MAVEN NGIMS Observations

The solar flare is a sudden eruptive solar phenomenon with significant enhancements in solar X-ray and Extreme Ultraviolet radiations,resulting in large amounts of energy being injected into the planetary atmosphere.Case studies have been extensively presented to analyze the effect of extremely large flares on the Martian upper atmosphere,but the general features of the Martian thermospheric response to flares are still poorly understood.In this work,we select 12 intense solar flares that occurred between 2015 and 2017 and investigate the densities and compositional variations of the dayside Martian thermosphere to these flares with the aid of the measurements made by the Mars Atmosphere and Volatile EvolutioN.The statistical studies indicate that the responses of the Martian thermosphere to flares are complicated that both the class of the flare and the wavelength of the enhanced radiation may have prominent influences on the thermal expansion of the atmosphere and the atmospheric photochemical reactions.

Geological Context of the SLIM Landing Site

INTRODUCTION Japan’s first successful lunar landing mission,Smart Lander for Investigating Moon(SLIM),was landed on the Moon on January 19th,2024.SLIM made a precise landing within 100 m of the targeted landing zone(central coordinates 13.316°S,25.251°E),which is located around the Shioli crater(D=270 m,central coordinates as 13.33°S,25.23°E)in the southwestern ejecta of the Theophilus crater(D=98.6 km,central coordinates as 11.45°S,26.28°E).

Response of photoelectron peaks in the Martian ionosphere to solar EUV/X-ray irradiance

An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals.A typical photoelectron energy spectrum is characterized by a distinctive peak near 27 eV related to the strong solar HeⅡ emission line at 30.4 nm,and an additional peak near 500 eV related to O Auger ionization.In this study,the extensive measurements made by the Solar Wind Electron Analyzer on board the recent Mars Atmosphere and Volatile Evolution spacecraft are analyzed and found to verify the scenario that Martian ionosphere photoelectrons are driven by solar radiation.We report that the photoelectron intensities at the centers of both peaks increase steadily with increasing solar ionizing flux below 90 nm and that the observed solar cycle variation is substantially more prominent near the O Auger peak than near the HeⅡ peak.The latter observation is clearly driven by a larger variability in solar irradiance at shorter wavelengths.When the solar ionizing flux increases from 1 mW·m^-2 to 2.5 mW·m^-2,the photoelectron intensity increases by a factor of 3.2 at the HeⅡ peak and by a much larger factor of 10.5 at the O Auger peak,both within the optically thin regions of the Martian atmosphere.

The diurnal transport of atmospheric water vapor during major dust storms on Mars based on the Mars Climate Database,version 5.3

In recent studies of the Martian atmosphere,strong diurnal variation in the dust was discovered in the southern hemisphere during major dust storms,which provides strong evidence that the commonly recognized meridional transport process is driven by thermal tides.This process,when coupled with deep convection,could be an important part of the short-term atmospheric dynamics of water escape.However,the potential of this process to alter the horizontal distribution of moist air has not been systematically investigated.In this work,we conducted pre-research on the horizontal transport of water vapor associated with the migrating diurnal tide(DW1)at 50 Pa in the upper troposphere during major dust storms based on the Mars Climate Database(MCD)5.3,a state-of-the-art database for Martian atmospheric research that has been validated as simulating the relevant short-period atmospheric dynamics well.We found westward-propagating diurnal patterns in the global water vapor front during nearly all the major dust storms from Martian years(MYs)24 to 32.Statistical and correlation analyses showed that the diurnal transport of water vapor during global and A-season regional dust storms is dominated by the DW1.The effect of the tidal transport of water vapor varies with the types of dust storms in different seasons.During regional dust storms,the tidal transport induces only limited diurnal motion of the water vapor.However,the horizontal tidal wind tends to increase the abundance of daytime water vapor at mid-to low latitudes during the MY 28 southern summer global dust storm while decreasing it during the MY 25 southern spring global dust storm.The tidal transport process during these two global dust storms can induce opposite effects on water escape.

Is Solar Wind electron precipitation a source of neutral heating in the nightside Martian upper atmosphere?

Solar Wind(SW)electron precipitation is able to deposit a substantial amount of energy in the nightside Martian upper atmosphere,potentially exerting an influence on its thermal structure.This study serves as the first investigation of such an issue,with the aid of the simultaneous measurements of both neutral density and energetic electron intensity made on board the recent Mars Atmosphere and Volatile Evolution(MAVEN)spacecraft.We report that,from a statistical point of view,the existing measurements do not support a scenario of noticeable neutral heating via SW electron precipitation.However,during 3%−4%of the MAVEN orbits for which data are available,strong correlation between nightside temperature and electron intensity is observed,manifested as collocated enhancements in both parameters,as compared to the surrounding regions.In addition,our analysis also indicates that neutral heating via SW electron precipitation tends to be more effective at altitudes below 160 km for integrated electron intensities above 0.01 ergs·cm^−2·s^−1 over the energy range of 3−450 eV.The results reported here highlight the necessity of incorporating SW electron precipitation as a heat source in the nightside Martian upper atmosphere under extreme circumstances such as during interplanetary coronal mass ejections.

Solar control of CO2^+ultraviolet doublet emission on Mars

The CO2^+;ultraviolet doublet(UVD)emission near 289 nm is an important feature of dayside airglow emission from planetaryupper atmospheres.In this study,we analyzed the brightness profiles of CO2^+;UVDemission on Mars by using the extensive observationsmade by the lmaging Ultraviolet Spectrograph on board the recent Mars Atmosphere and Volatle Evolution spacecraft.Strong solar cycleand solar zenith angle variations in peak emission intensity and altitude were revealed by the data:(1)Both the peak intensity and altitude increase with increasing solar activity,and(2)the peak intensity decreases,whereas the peak altitude increases,with increasingsolar zenith angle.These observations can be favorably interpreted by the solar-driven scenario combined with the fact that photoionization and photoelectron impact ionization are the two most important processes responsible for the production of excited-state cotand consequently the intensity of CO2^+;UVDemission.Despite this,we propose that an extra driver,presumably related to thecomplicated variation in the background atmosphere,such as the occurrence of globaldust storms is required to fuly interpret theobservations.In general,our analysis suggests that the CO2^+;UVD emission is a useful diagnostic of the variability of the dayside Martianatmosphere under the influences of both internal and external drivers.

The nighttime ionospheric response and occurrence of equatorial plasma irregularities during geomagnetic storms:a case study

Recent studies revealed that the long-lasting daytime ionospheric enhancements of Total Electron Content(TEC)were sometimes observed in the Asian sector during the recovery phase of geomagnetic storms e.g.,Lei(J Geophys Res Space Phys 123:3217-3232,2018),Li(J Geophys Res Space Phys 125:e2020JA028238,2020).However,they focused only on the dayside ionosphere,and no dedicated studies have been performed to investigate the nighttime ionospheric behavior during such kinds of storm recovery phases.In this study,we focused on two geomagnetic storms that happened on 7-8 September 2017 and 25-26 August 2018,which showed the prominent daytime TEC enhancements in the Asian sector during their recovery phases,to explore the nighttime large-scale ionospheric responses as well as the small-scale Equatorial Plasma Irregularities(EPIs).It is found that during the September 2017 storm recovery phase,the nighttime ionosphere in the American sector is largely depressed,which is similar to the daytime ionospheric response in the same longitude sector;while in the Asian sector,only a small TEC increase is observed at nighttime,which is much weaker than the prominent daytime TEC enhancement in this longitude sector.During the recovery phase of the August 2018 storm,a slight TEC increase is observed on the night side at all longitudes,which is also weaker than the prominent daytime TEC enhancement.For the small-scale EPIs,they are enhanced and extended to higher latitudes during the main phase of both storms.However,during the recovery phases of the first storm,the EPIs are largely enhanced and suppressed in the Asian and American sectors,respectively,while no prominent nighttime EPIs are observed during the second storm recovery phase.The clear north-south asymmetry of equatorial ionization anomaly crests during the second storm should be responsible for the suppression of EPIs during this storm.In addition,our results also suggest that the dusk side ionospheric response could be affected by the daytime ionospheric plasma density/TEC variations during the recovery phase of geomagnetic storms,which further modulates the vertical plasma drift and plasma gradient.As a result,the growth rate of post-sunset EPIs will be enhanced or inhibited.

月球上发现半透明玻璃球

利用嫦娥四号月球探测任务玉兔二号月球车获取的全景相机数据,在巡视路线上附近发现了数粒直径达2.5 cm的半透明玻璃球.这是首次在月球上发现手标本尺度大小的透明玻璃球.区域地质研究和撞击破碎模型对比表明这些玻璃球不是火山玻璃或降落至月面的陨石,而是形成在月球上的撞击玻璃.对比典型的月球岩石的化学成分及其熔体在冷凝时成核结晶的临界降温速率,发现月球玄武岩和其他富铁的岩石不是形成这些撞击玻璃的原岩.斜长岩熔体的临界降温速率极低,在月球环境下冷凝时足以形成直径高达5 cm的透明/半透明玻璃球.基于高能远撞击玻璃的成因机理,结合嫦娥四号着陆点附近1 km/s的上限弹道溅射距离中的矿物和元素含量数据,发现很多撞击事件足以形成此类撞击玻璃.这些撞击玻璃记录了重要的撞击过程和早期撞击历史的信息,是未来月球探测的重要采样目标.

Correlated observations linking loss of energetic protons to EMIC waves

Electromagnetic ion cyclotron(EMIC)emission is an efficient mechanism for scattering loss of energetic protons.Here,we report an event that provides both in-situ observation of energetic proton differential fluxes in the inner magnetosphere and precipitation of protons at ionospheric altitudes.During the 7-8 September 2015 geomagnetic storm the Van Allen Probes observed strong EMIC waves around L=5 and a distinct decrement in fluxes of tens of keV protons around pitch angles 0°-45°.Meanwhile,precipitating protons at ionospheric altitudes were found to significantly enhanced(by several orders of magnitude),measured by NOAA 18 and 19 when they magnetically linked to the Van Allen Probe-A.By solving the Fokker-Planck diffusion equation,we show that EMIC waves can efficiently produce loss of energetic protons within about 2 h in the pitch angle range of~0°-45°,comparable to the satellite observations.