North Polar Region Research Articles

An Endogenic Origin for Titan's Rampart Craters: Assessment of Explosion Mechanisms

AbstractRampart craters are a class of lakes or depressions in Titan's north polar region that have morphological attributes suggestive of an explosive origin. Two previous studies have proposed that rampart craters form via nitrogen or methane vapor explosions analogous to terrestrial maar explosions. We propose a new terrestrial analog for rampart craters: gas emission craters (GECs) found in permafrost zones. We evaluate the explosive origin of Titan's rampart craters by modeling the dispersal of material from an explosive vent. The dimensions of nine rampart craters with radar‐bright ramparts were used to model the explosion process. The model yields a range of explosion conditions (e.g., gas mass and reservoir depth) producing ejecta dispersal patterns matching the observed features. We find that gas masses of 1011–1014 kg are required to produce a rampart crater. We examine two explosion scenarios: (a) rapid, maar‐like vaporization and explosion of liquid nitrogen or methane, and (b) more gradual gas accumulation and explosion akin to a GEC driven by methane released from destabilizing clathrates. If Titan's crust is composed of pure water ice, the calculated gas pressures are consistent with a rapid, maar‐like explosion mechanism. If the subsurface is predominantly composed of organic materials or clathrate, either scenario may be plausible. Further research on the composition and tensile strength of Titan's subsurface are required to discriminate between hypotheses. Nevertheless, we conclude that explosive dispersal of ejecta from a vent can account for the morphologies of Titan's rampart craters and may contribute to atmospheric methane replenishment.

Long-term geomagnetic activities and stratospheric winter temperature

In this research, impact of long term solar forcing on stratospheric winter temperature is checked. The 11- year sunspot activity and geomagnetic indices (AE, Kp, Dst) are used as an indicator for solar forcing, as geomagnetic activity indices show good correlation with solar variability. To understand the impact of solar forcing through high latitude, stratospheric winter (November to March) time North Polar Region (60N–90N) temperature anomalies are considered. The findings showed that temperature changes in the stratosphere are significantly correlated with solar activity, as evidenced by a significant positive correlation between the 11-year moving mean of stratospheric (10 hPa) temperature anomalies and sunspot number. Approximately from 1970 to 2000, the North Polar Region saw positive anomalous stratospheric winter temperatures. During the same time, the geomagnetic activity also showed a substantial increase. The year-to-year correlation between stratospheric pole temperature and geomagnetic activity is significant (about 0.5). The Empirical Mode Decomposition analysis reveals a highly significant correlation (around 0.9) between the long-term component of stratospheric winter temperature (IMF-4) and the long-term component of geomagnetic activity (IMF-3 and IMF-4). One of the reasons for the increase in lower stratospheric temperature is an increase in ozone concentration during the same period when geomagnetic activity is higher. Empirical orthogonal function (EOF) and correlation analysis of stratospheric winter temperature with large-scale circulation patterns are also carried out. The spatial correlation is checked for stratospheric winter temperature at North Pole and lower atmospheric levels (250 hPa and 850 hPa) followed by pre-monsoon and monsoon season. This study includes statistical analysis, however, also highlights the necessity of in-depth dynamical analysis to improve our understanding of how solar activity impacts Earth's atmospheric layers, which may be helpful in predicting the weather and climate.

The puzzling north polar region of Uranus: Continued zero-shear winds and increasing brightness from 2015 through 2022 according to 7 years of Keck AO imaging

There may be a permanent north–south asymmetry in the zonal wind profile of Uranus. According to high signal-to-noise near-IR observations with the Keck telescope NIRC2 camera, through 2014 the winds north of 60∘N had a constant (zero shear) longitudinal drift rate of 4.1∘/h westward (Sromovsky et al., 2015). Yet the south polar winds in 1986 had strong latitudinal shear, reaching speeds of 8.5∘/h (Karkoschka, 2015). If that asymmetry were a result of extreme seasonal forcing, it might be expected to reverse before the 2030 solstice. However, continued high signal-to-noise near-IR observations from 2015 through 2022 provide little evidence that the north polar winds have changed at all, although there have been changes in the distribution of cloud features used to track those winds and an increase in the brightness of the background haze that makes it harder to detect these small low-contrast features. Between 2015 and 2017, a gap in easily trackable features developed in the 55∘N–60∘N latitude region, and at the northern edge of that gap there was a hint that a dramatic change to the inverted profile might be starting. To further investigate that possible change and to fill in the gap, we developed a new wind measurement technique that was more sensitive to low-contrast spatial structure. Our new method does not confirm any significant wind speed change in the gap, nor at its northern edge.The lifetimes of many of the small discrete polar features are surprisingly long. Many were tracked over time spans over 24 h, and some lasted for weeks. More prominent features seen at low latitudes seem to persist for multiple years and vary in latitude and drift rate in a cyclical fashion. While measurements so far favor a permanent asymmetry in the zonal wind profile of Uranus, the possibility remains that a dramatic circulation change might take place between 2022 and the next solstice in 2030. Using simplified radiation transfer modeling we infer a largely unchanging upper layer of small particles of very low optical depth vertically distributed above an active deeper mid-level layer, at an effective pressure of ∼2–2.5 bar. That middle layer increased in reflectivity at 1.6 μm by more than a factor of 2 from 2015 to 2022 and is the main source of the top-of-atmosphere brightness increase seen over that period, rather than any significant temporal change in polar methane abundance.

Lunar North Polar Cold Traps Based on Diurnally and Seasonally Varying Temperatures

Lunar cold traps are defined by extremely low sublimation rates, such that water ice could have accumulated in them. Here time-averaged sublimation rates are calculated for the north polar region of the Moon based on over 14 years of Diviner surface temperature measurements. Data for each spatial pixel are binned according to subsolar (diurnal) and ecliptic (seasonal) longitude. The cold trap area poleward of 80°N is about 32% larger when defined by a time-average sublimation rate instead of by peak temperature. Apparently sunlit cold traps are identified, e.g., in Lenard Crater, where modeling of direct illumination reveals that the Sun briefly rises above the horizon each Draconic year. The true cold trap area is smaller than what can be determined from Diviner data. Also presented are north polar maps for the potential sublimation rate of relic buried ice and for subsurface cold trapping.

Temperature Dependence of the Dielectric Constant on the Lunar Surface Based on Mini-RF and Diviner Observations

Radar observation is an effective way to understand subsurface structures in terms of the dielectric constant, whose controlling factors include chemical composition, packing density, and water/ice content. Recently, laboratory measurements have shown that the dielectric constant of lunar regolith simulants also depends on the temperature, which has never been evaluated from remote sensing data. In this study, we estimated the dielectric constant from the Miniature Radio Frequency (Mini-RF) data on a lunar crater floor in the north polar region at two different local times (i.e., different surface temperatures). We calculated the dielectric constant using the inversion method and obtained the bolometric surface temperature from the Diviner Lunar Radiometer Experiment (Diviner) data. The histograms of the estimated dielectric constant values are different between the two local times. This could be interpreted as a result of the temperature dependence of the dielectric constant, while further evaluation of the influence of topography on the incidence angle and small surface roughness is needed. Nevertheless, our result suggests that the temperature dependence of the dielectric constant should be considered when interpreting S-band radar observations of the Moon and other celestial bodies with large surface temperature differences.

Mineralogical Characterization of the Lunar South Polar Region: 1. The Artemis Exploration Zone

AbstractThe lunar south pole is a region of focused scientific and exploration interest, with several crewed and robotic missions to this region planned within the next decade. Understanding the mineralogy of the region is essential to inform landing site characterization and selection and provides the key context for interpreting samples and in situ observations. At high latitudes, extreme illumination conditions (high phase angles) can negatively impact the data quality of orbital instruments. This is especially true for passive near‐infrared spectrometers such as the Moon Mineralogy Mapper (M3) and the Kaguya Spectral Profiler, which measure the spectral properties of the surface using reflected sunlight. Using Moon Mineralogy Mapper data, we observed that the south polar region is associated with a detectable mafic signature consistent with the presence of pyroxenes. The strongest mafic signatures are associated with the South Pole—Aitken Basin, suggesting that impact melt and basin ejecta from the lower crust and upper mantle are present within this region. This observation is validated in several ways: (a) comparisons between M3 data acquired during different mission phases, (b) comparisons between multiple spectral parameters sensitive to the presence of mafic minerals, (c) comparisons between the north and south lunar polar regions, and (d) comparisons with publicly available Kaguya polar mineralogy maps and Lunar Prospector elemental abundances. We also investigate the nature of an anomalous high‐albedo region within 2–3° of the south pole observed in Lunar Orbiter Laser Altimeter reflectance data exhibiting a spatially conflicting apparent FeO abundance pattern between several data sets.

Thickness of the Seasonal Deposits at the Martian North Polar Region From Shadow Variations of Fallen Ice Blocks

AbstractThe seasonal deposition and sublimation of CO2 constitute a major element in the Martian volatile cycle. Here, we propose to use the shadow variations of the ice blocks at the foot of the steep scarps of the North Polar Layered Deposits (NPLD) to infer the vertical evolution of the seasonal deposits. We conduct an experiment at a steep scarp centered at (85.0°N, 151.5°E). We assume that no snowfall remains on top of the selected ice blocks, the frost ice layer is homogeneous around the ice blocks and their surroundings, and no significant moating is present. We show that the average thickness of the seasonal deposits due to snowfalls in Mars Year 31 is 0.97 ± 0.13 m at Ls = 350.7° in late winter. The large depth measured makes us wonder if snowfalls are more frequent and violent than previously thought. Meanwhile, we show that the average frost thickness in Mars Year 31 reaches 0.64 ± 0.18 m at Ls = 350.7° in late winter. Combined, the total thickness of the seasonal cover in Mars Year 31 reaches 1.63 ± 0.22 m at Ls = 350.7° in late winter, continuously decreases to 0.45 ± 0.06 m at Ls = 42.8° in middle spring and 0.06 ± 0.05 m at Ls = 69.6° in late spring. These estimates are up to 0.8 m lower than the existing Mars Orbiter Laser Altimeter results during the spring. Meanwhile, we observe that snow in the very early spring of Mars Year 36 can be 0.36 ± 0.13 m thicker than that in Mars Year 31. This study demonstrates the dynamics of the Martian climate and emphasizes the importance of its long‐term monitoring.

History of Ceres’s Cold Traps Based on Refined Shape Models

Permanently shadowed regions (PSRs) in the north polar region of Ceres have been previously mapped by the Dawn spacecraft. Putative ice deposits are found in some of these PSRs, whereas most PSRs host no bright deposits, which is thought to be due to oscillations of the axis tilt with a ∼25 ka period. We use stereophotoclinometry to construct refined topographic models of PSR-hosting craters. Ray-tracing calculations reveal that no PSRs remain at the maximum axis tilt, which implies that the ice deposits are remarkably young. The bright ice deposits do not extend beyond PSRs at an axis tilt of 10°, which last occurred about 6 ka ago. This suggests that water is delivered to the polar regions or exposed within the craters by frequent and short-lived events. Surface temperatures are calculated with a terrain irradiance model to delineate cold traps. Based on maximum equilibrium temperatures, Cerean PSRs are too warm to trap supervolatiles.

VOLUMETRIC CHARACTERISTICS OF PACIFIC WATERS IN THE ARCTIC OCEAN

Volumetric characteristics and renewal time of the Pacific waters (PW) in the Arctic Ocean were calculated based on the data of oceanographic expeditions during the 2007-2008 International Polar Year (617 stations). Isopycnal surfaces of their upper and lower boundaries (25,5 and 27,5 kg/m3, respectively), the thickness between these limits and the equivalent thickness (i. e. the specific thickness of untransformed “pure” water mass) have been determined, as well as the boundaries where the highest concentrations of silicates in the selected density interval disappears. The Pacific waters extend to the north up to the North Pole region (thickness up to 40-50 m), in the west they can be traced up to the northern part of the Laptev Sea (thickness 20-30 m), in the east they are preserved in a minimally transformed form (thickness of more than 100 m) up to the Canadian Arctic Archipelago. The characteristic depths are between 50 and 150 m. The thickest PW exceeding 150 m were found within the Beaufort Gyre. The total volume of “pure” (untransformed) Pacific waters in the Arctic Ocean was estimated at (197 ± 19) · 103 km3 or about 1,1% of the overall volume of the Arctic Ocean. If their mixing with the surrounding waters between selected isopycnic surfaces is taken into account, the volume of Pacific waters is (313 ± 16) · 103 km3, or about 1,7% of the volume of the Arctic Ocean. Taking into account the total inflow of the PW through the Bering Strait, their renewal time in the Arctic basin is estimated to be about 5-6 years.

Investigating the Presence of Biomass Burning Events at Ny-Ålesund: Optical and Chemical Insights from Summer-Fall 2019

Summer 2019 is remembered as one of the most intense biomass burning (BB) seasons on record for the Northern Hemisphere. During the MOSAiC expedition, a smoke-dominated layer was identified in the upper troposphere over the North Pole region. The origin of this layer remains unclear, and no evidence has been found to indicate the intrusion of such particles into the Arctic Boundary Layer. The main aim of this work was to evaluate if biomass burning events in the summer 2019 were detectable at Gruvebadet Atmospheric Laboratory, close to Ny-Å lesund (Svalbard Islands) during the second half of 2019. This paper proposes an innovative approach to discriminate biomass burning events based on optical measurements combined with chemical analysis and air mass back-trajectories. Monthly background values of optical coefficients were defined using multi-annual (2018–2021) statistics and twelve possible events were identified. Source apportionment through positive matrix factorization (PMF) identified that the biomass burning factor by PMF accounted for only 2% of the total investigated concentration. The specific biomass burning tracers such as levoglucosan and phenolic compounds were compared with optical measurements and with the PMF results. Air mass trajectory analysis revealed that the early summer fires detected at Ny-Å lesund originated mainly from North America, as also confirmed by the presence of BB factor of PMF, levoglucosan and also vanillic species (softwood combustion tracers). In contrast, the chemical composition and air masses analysis of the highest peak detected in early December suggested residential heating as plausible source, further amplified by the onset of the harsh winter season and the expansion of the polar vortex towards mid-latitudes.

One decade of temperature change at the North Pole and South Pole using ANN backpropagation algorithm

Global warming is an event in which the average temperature of the atmosphere, ocean and land rises. Changes in atmospheric temperature cause changes in the physical conditions of the atmosphere to become unstable, causing anomalies in weather parameters that cause climate change. In the last decade there have been temperature changes in the North Pole (Greenland) and the South Pole (Antarctica). The impacts caused by temperature changes are melting ice sheets, rising sea levels, extinction of species in large numbers, people living on the coast are threatened by tidal floods, while small islands can sink. To anticipate temperature changes, a model is needed that can forecast air or temperature conditions using Artificial Neural Network with Backpropagation method using Matlab software media. Data obtained from Data Access Viewer of NASA. After training and testing the data, the average value of the prediction results for the south polar region (Antarctica) is -47.910C with a Mean Square Error (MSE) value of 0.0015. Meanwhile, for the North Pole region (Greenland), the average value of the prediction results is -22.410C with an MSE value of 0.0069. By looking at the average value of the prediction results, it can be concluded that the temperature change for the South Pole region (Antarctica) is higher than the temperature change for the North Pole region (Greenland).

Revelations of interannual dune evolution from the swiftest aeolian system on Mars by MRO/HiRISE long-term monitoring

The north polar region of Mars, with its greater atmospheric pressure and vast inventory of ever-changing volatiles (e.g., CO2, H2O), hosts arguably the most active and diverse aeolian bedform systems on the planet. Here, we explore how these dune fields evolve spatiotemporally using up to 8 Mars years (16 Earth years) of MRO HiRISE observations to test the impact of various boundary conditions on annual mobility. A high degree of sand flux heterogeneity was observed for some dunes, whereas other sites displayed steady-state migration relative to long-term rates. These large changes in annual migration are attributed to the variable length of the frost-free seasons, sediment availability in relation to the timing of peak katabatic winds, and the influence of global dust storms on seasonal ice thickness. Consistent with our previous work, we continue to observe extremely high transport rates at Olympia Cavi. All stages of aeolian system evolution are observable (sand patch > protodune > dune), along with additional phenomena not previously observed outside of terrestrial settings (e.g., dune calving and collisions, remote transfer). Transitory protodunes may evolve from modest sand mounds to prominent barchans with slipfaces several meters tall within 3–5 Mars years, while adjacent duneforms may suffer slipfaces collapse as they lose sand supply. These Martian protodunes, which appear to be larger than terrestrial equivalents, and mature dunes found downwind are among the swiftest yet reported on Mars. These rapidly evolving cryo-aeolian systems provide a window into longer-term landscape evolution of non-polar dune fields.

New global topography of Enceladus: Hypsometry, basins, spherical harmonics, shell thickness, and true polar wander revisited

A new global high-resolution stereogrammetric and photogrammetric topographic map and updated 3-color global mosaic of Enceladus reveal that the shape of this active icy ocean world is distorted from a simple triaxial ellipsoid. Although the topographic range (high-to-low) of Enceladus, when referenced to its global triaxial figure, is the narrowest among icy bodies mapped globally thus far, the global DEM indicates a pronounced zonal latitudinal zoning of topography, with the north polar region and mid-southern latitudes being ∼300–400 m higher and south polar and mid-northern latitudes being ∼400 m lower on average than the triaxial figure. Dynamically, both north and south poles are low, but the south remarkably so, by >1 km. Spherical harmonic analysis also indicates the tidal axis of the body is located ∼4°W of the current IAU-defined prime meridian. Superposed on this global pattern are topographic features associated with geologic units within each terrain, as well as several prominent regional 100-km-scale basins, 1-to-1.8 km deep, previously reported. The shapes of these large basins depend on the terrains they formed in; those in older cratered terrains are relatively simple (i.e., ovate) in shape, but those in resurfaced terrains are more complex in shape, often correlating with geologic features and units within those terrains. Thus, while these basins exhibit no explicit local-scale geologic deformation or disruption of the icy shell in association with their elevations/formation, they are partially controlled by the physical characteristics of the terrains they formed in, suggesting that the icy shell can be heterogenous in character. Most of these basins occur on the trailing hemisphere and although a few of these are aligned, we find that they do not form a global great circle pattern, weakening previous arguments for true polar wander. Our preferred hypothesis is that these basins are due to isostatic adjustment of the ice shell in response to thermal anomalies from below and suggest that they may be surface manifestations of diffused hydrothermal plumes originating at the surface of Enceladus' rocky core. If so, similar patterns in core activity might be revealed once global topographic mapping is complete on Europa.

Local Ice Mass Balance Rates via Bayesian Analysis of Mars Polar Trough Migration

AbstractWith the aim of better understanding the past depositional environment of the north polar region of Mars, we infer local ice accumulation and retreat rates in the area between 86° and 87°N and 16°–20°E. We follow a novel approach utilizing a Bayesian framework with observations of bounding surfaces associated with the migration of two polar spiral troughs. Over time, spiral troughs have migrated toward the north pole due to ice accumulation, sublimation, and wind transport. We relate the record of trough migration with local ice accumulation and retreat rates using a phenomenological migration model and explore the climate parameters that affect these rates using a Markov chain Monte Carlo algorithm. Using this data‐driven approach, we find best fit mean accumulation rates of 0.11–0.18 mm/yr in the upper 500 m of the stratigraphy of our study region. These mean accumulation rates correspond to trough ages of over 4 Myr, which implies that the north polar cap is older than most current assumptions. We also find that the relationship between accumulation rates and the obliquity of Mars is complex, with periods of positive correlation occurring in the last several Myr. Future work extending this analysis to all troughs in the cap will further constrain these relationships and ages.

Producing 3D radargrams from orbital radar sounding data at Mars: History, results, methods, lessons and plans

The Shallow Radar (SHARAD) instrument aboard Mars Reconnaissance Orbiter (MRO) has been conducting sounding operations of Mars' near surface for more than 16 years. Results of the SHARAD investigation have been well documented in the literature, with relatively high coverage density in the polar regions leading to some of the earliest scientific discoveries there. Data collection and ensuing surprises of SHARAD's primary and first extended science phases were the impetus for choosing the north polar region for producing a first 3D radar image. This early attempt was successful, producing the first 3D radar image of Mars' north polar layered deposits in Planum Boreum, and shortly thereafter a companion 3D radar image of the south polar layered deposits in Planum Australe. Subsequent work refined the 3D methodology used to produce these images, leading to a significantly higher quality 3D image of the former as well as the first 3D radar image of the debris-covered glaciers in the east-central portion of Deuteronilus Mensae (DM) in the mid-latitudes. Prior experience in terrestrial seismic data processing and analysis methods forms the basis of the 3D methodology used with Martian radar data, and has been indispensable in ongoing efforts to improve this methodology to further clarify the 3D images of the targets. The purposes of this article are to review 1) the SHARAD 3D work history and results, 2) the methodology developed and challenges encountered thus far in producing the SHARAD 3D images, 3) the broader impact on the processing and analysis of SHARAD data, and 4) current efforts and plans for producing follow-on SHARAD 3D images. Similarities and differences between orbital radar and seismic sounding and data processing are sprinkled throughout the article as reminders that the outcomes in this case are very much the product of cross-disciplinary knowledge and experience.

Observations of North Polar Region of Mars from the Mars Colour Camera Onboard Indian Mars Orbiter Mission

Observations of North Polar Region of Mars from the Mars Colour Camera Onboard Indian Mars Orbiter Mission

The fully coupled regionally refined model of E3SM version 2: overview of the atmosphere, land, and river results

Abstract. This paper provides an overview of the United States (US) Department of Energy's (DOE's) Energy Exascale Earth System Model version 2 (E3SMv2) fully coupled regionally refined model (RRM) and documents the overall atmosphere, land, and river results from the Coupled Model Intercomparison Project 6 (CMIP6) DECK (Diagnosis, Evaluation, and Characterization of Klima) and historical simulations – a first-of-its-kind set of climate production simulations using RRM. The North American (NA) RRM (NARRM) is developed as the high-resolution configuration of E3SMv2 with the primary goal of more explicitly addressing DOE's mission needs regarding impacts to the US energy sector facing Earth system changes. The NARRM features finer horizontal resolution grids centered over NA, consisting of 25→100 km atmosphere and land, a 0.125∘ river-routing model, and 14→60 km ocean and sea ice. By design, the computational cost of NARRM is ∼3× of the uniform low-resolution (LR) model at 100 km but only ∼ 10 %–20 % of a globally uniform high-resolution model at 25 km. A novel hybrid time step strategy for the atmosphere is key for NARRM to achieve improved climate simulation fidelity within the high-resolution patch without sacrificing the overall global performance. The global climate, including climatology, time series, sensitivity, and feedback, is confirmed to be largely identical between NARRM and LR as quantified with typical climate metrics. Over the refined NA area, NARRM is generally superior to LR, including for precipitation and clouds over the contiguous US (CONUS), summertime marine stratocumulus clouds off the coast of California, liquid and ice phase clouds near the North Pole region, extratropical cyclones, and spatial variability in land hydrological processes. The improvements over land are related to the better-resolved topography in NARRM, whereas those over ocean are attributable to the improved air–sea interactions with finer grids for both atmosphere and ocean and sea ice. Some features appear insensitive to the resolution change analyzed here, for instance the diurnal propagation of organized mesoscale convective systems over CONUS and the warm-season land–atmosphere coupling at the southern Great Plains. In summary, our study presents a realistically efficient approach to leverage the fully coupled RRM framework for a standard Earth system model release and high-resolution climate production simulations.

Transient energetic particles as the origin of the mid-infrared north polar hotspot of Jupiter

Since it was detected in 1980, Jupiter's 8-μm CH4 north polar hot spot (8CNPHS), ∼20 K warmer than the surrounding polar stratosphere, has been observed for four decades. Unlike normal auroral ovals (i.e., the bright rings of auroral emissions), it is usually filled with bright emission. The causes of both its shape and longevity are not understood, although several mechanisms have been proposed to explain its existence. In order to investigate the deriving mechanism of the 8CNPHS, we have observed the north polar regions near 3 μm, where line emission from another CH4 band as well as a C2H6 fundamental band occur. Using Gemini North/GNIRS in 2013, 2020, 2021, and 2022, we have detected transient 3-μm CH4 and/or C2H6 bright spots within the 8CNPHS, and occasionally no apparent bright spots. By comparing the emission from CH4 with that from C2H6, we demonstrate that the origin of the 8CNPHS must be due to transient and energetic magnetospheric particles, which can penetrate down to the hydrocarbon layers, heating the homopause (∼1 μbar level) and the stratosphere (∼1 mbar level) and energize the 8CNPHS. Based on our observations and analysis, we propose the following three mechanisms for maintaining and containing the decades long warmth of the 8CNPHS: 1) energetic and transient auroral particle precipitations warming the stratosphere of the 8CNPHS, 2) a longer radiative cooling time in the 8CNPHS stratosphere (∼6 months) compared to less than or equal to one month at the homopause, and 3) recently detected polar stratospheric jets likely associated with polar fronts, which resist the free flow of warm gas in the 8CNPHS to the surrounding polar regions. We show that other heating mechanisms proposed so far in the literature, such as Joule heating, polar haze heated by sunlight, etc., are only the secondary mechanisms that follow atmospheric ionization caused by energetic particle bombardment. Our finding of the magnetospheric-ionospheric-stratospheric coupling in the Jovian polar regions open the possibility of quantitatively refining 3-D global circulation models for the atmospheres of giant planets and exoplanets.

Morphology and distribution of Martian wedge dunes and their terrestrial analogs

Wedge dunes are widespread on Mars and contain important information about Mars surface processes and environmental characteristics. These dunes are wedge-shaped in plan-view, similar in scale to a barchan dune, with two slip faces intersecting at an obtuse angle and extending outward toward the main ridge downwind. And, the length of its main ridge does not exceed its width. At present, our understanding of wedge dunes and their development in nature is limited. The type, morphology, distribution and spatial composition of wedge dunes on Mars and Earth were investigated using high-resolution satellite image data. The results reveal that wedge dunes are simple in type and similar in size to barchan dunes. Martian wedge dunes are similar in shape to terrestrial wedge dunes but larger in size. The average angles between the sub-ridges of Martian and terrestrial wedge dunes are similar, at about 116°. Martian wedge dunes are mainly located in Abalos Undae, Siton Undae, and Aspledon Undae in the North Polar region, accounting for about 5% of the total area covered by dune fields. Wedge dunes are rare on Earth and can only be found on the edge of a few contiguous dune fields. These dunes indicate acute bimodal or obtuse bimodal wind regimes. Wedge dunes have distinct transitional characteristics and may be the initial stage of the development of various dune patterns. The implications of these findings are discussed, in particular the periodic changes in the regional wind direction reflected by the wedge dunes, as well as the significance of the distinctive transitional features of the wedge dunes for improving our understanding of the genesis of complex dune patterns.

Modeling the thermal environment of Mercury’s north pole using MLA. Implications for locations of water ice

Radar observations made by the Arecibo Observatory have revealed radar-bright deposits in the north polar region of Mercury which are consistent with water ice. These deposits are generally associated with floors of deep craters in permanent shadow. In this paper, we revisit topographic data, illumination, and associated thermal conditions of the north polar region of Mercury to investigate these radar-bright deposits. We used Mercury Laser Altimeter (MLA) data from the MESSENGER mission to derive a dedicated, adjusted high-resolution Digital Terrain Model (DTM) of the north polar region at 250 m/pixel. Based on this DTM, illumination conditions and temperature were derived for the first time on the fully available MLA dataset. Generally, craters equatorward of 86 ∘N are found to be too hot to contain surface water ice due to effective self-heating. For those warm craters that do contain radar-bright deposits, temperatures within the upper 10–20 cm of regolith are cold enough for water ice to be stable. Using our improved DTM, we confirm previously MLA-modeled illumination conditions in Prokofiev crater and argue that radar-bright patches outside the PSR in the area may be explained by icy deposits in cold and shallow (within 5 cm) sub-surface layers. In the radar observations we find a strong, unphysical correlation between radar-bright pixels and the number of radar observations per pixel. Consequently, several PSRs which were classified as free of radar-bright material (mainly at longitudes 120–340 ∘E) are most likely subject to a bias in the averaging process in deriving the composite radar image and might contain water ice after all.