Wind Interaction Research Articles

Acceleration of Pick‐Up Ions in the Martian Magnetosheath: A Tianwen‐1 Case Study

AbstractThis study delves into a Pick‐Up Ion (PUI) event captured by the Mars Ion and Neutral Particle Analyzer aboard Tianwen‐1, revealing a faster acceleration than expected within the Martian magnetosheath. This event suggests the presence of a convection electric field considerably stronger than that typically observed in the solar wind. Through Magnetohydrodynamic simulation, we identified two regions of intensified convection electric fields within the inner magnetosheath, prominently manifested at mid to high solar zenith angles (SZA = 40°–70°) in the X‐Z plane of the Mars Solar Electric field coordinates. Tianwen‐1 observed that the peak of the electric field strength, up to five times of that in the solar wind, is located at the upper edge or within the Magnetic Pileup Boundary. Further study by test particle simulations showed acceleration by the electric field effectively doubles the energy gain of PUIs, in comparison to scenarios absent of this extra acceleration. It is revealed that the presence of such electric field regions within the Martian magnetosheath is a prevailing feature, shaped by the solar wind's interaction with Mars and modulated by the planet's rotating crustal magnetic fields.

TEC disturbances caused by CME-triggered geomagnetic storm of September 6–9, 2017

This study investigates the ionospheric response to a geomagnetic storm triggered by a Coronal Mass Ejection (CME) during 6–9 September 2017, across GPS stations located in diverse geographical regions. We analyze the changes in the magnetic field component (ΔH), the Prompt Penetration Electric Fields (PPEF), and the Total Electron Content (TEC). We find that ΔH exhibits latitude-dependent responses during the storm, with high-latitude stations experiencing more significant reductions compared to low-latitude stations. The PPEF behavior is found to be directly correlated with solar wind disturbances. Particularly during the main phase of the storm, fluctuations in PPEF were clearly associated with negative values in the Dst index. The KIRU station, located at a high latitude, shows the most pronounced PPEF effects, indicating the increased susceptibility of high-latitude regions to solar wind interactions. The time series plot of TEC, covering a full month at different stations, shows a distinct diurnal pattern driven by solar ionization. Equatorial stations such as HYDE, BOU, HON (HNLC), and DODM exhibit the highest daily TEC values. During the geomagnetic storm, TEC disturbances are evident across all stations, with significant disturbances and varying trends in TEC depletion rate observed at different locations. The TEC values differ by 5–25 TECU during the storm period, suggesting intricate ionospheric responses to geomagnetic storms at different stations. This highlights the importance of considering different geographical regions to fully understand the ionospheric dynamics related to solar activities.

Taming the TuRMoiL: The Temperature Dependence of Turbulence in Cloud–Wind Interactions

Turbulent radiative mixing layers play an important role in many astrophysical contexts where cool (≲104 K) clouds interact with hot flows (e.g., galactic winds, high-velocity clouds, infalling satellites in halos and clusters). The fate of these clouds (as well as many of their observable properties) is dictated by the competition between turbulence and radiative cooling; however, turbulence in these multiphase flows remains poorly understood. We have investigated the emergent turbulence arising in the interaction between clouds and supersonic winds in hydrodynamic enzo-e simulations. In order to obtain robust results, we employed multiple metrics to characterize the turbulent velocity, v turb. We find four primary results when cooling is sufficient for cloud survival. First, v turb manifests clear temperature dependence. Initially, v turb roughly matches the scaling of sound speed on temperature. In gas hotter than the temperature where cooling peaks, this dependence weakens with time until v turb is constant. Second, the relative velocity between the cloud and wind initially drives rapid growth of v turb. As it drops (from entrainment), v turb starts to decay before it stabilizes at roughly half its maximum. At late times, cooling flows appear to support turbulence. Third, the magnitude of v turb scales with the ratio between the hot phase sound-crossing time and the minimum cooling time. Finally, we find tentative evidence for a length scale associated with resolving turbulence. Underresolving this scale may cause violent shattering and affect the cloud’s large-scale morphological properties.

Hydraulic Analysis and Cold-Air Pool Interaction of the Raco Gap Wind

Abstract Raco is a local wind occurring in central Chile where the Maipo River Canyon exits into the Santiago valley. The intensification of the easterly down-canyon flow starts at any time during some cold season nights, accompanied by increases in temperature and drops in humidity. The hypothesis of the raco being a gap wind controlled by the narrowest section in the 12-km canyon exit corridor is tested with data from two events in July 2018 and July 2019. The data are analyzed in the framework of hydraulic theory, and a subcritical-to-supercritical transition is documented to occur at the narrows of the gap where the Froude number is close to unity, confirmed by radiosondes launched in the narrows in 2019. For the raco flow, the sum of potential and kinetic energy is conserved upstream of the narrows, while the acceleration occurring farther downstream loses a large fraction of energy to frictional dissipation. The raco events occur under the influence of regional subsidence, but a differential nocturnal warming of the in-canyon air mass is responsible for a pressure gradient driving the raco. In the 2019 case, a ceilometer mounted on an instrumented pickup truck documented the structure and movement of the interface between the raco air and the cold-air pool (CAP) existing over the valley to the west. Together with a radiosonde launched near the CAP–raco surface front, the observations reveal the intense shear-driven mixing taking place at the interface and the factors supporting the establishment of a stationary front.

Three-dimensional Modeling of the Solar Wind and Local Interstellar Medium Interaction with Pickup Ions in the Presence of Heliospheric Current Sheet

Our three-dimensional, time-dependent, multi-fluid model has been used to investigate the solar wind (SW)–local interstellar medium (LISM) interaction with pickup ions (PUIs) treated as a separate fluid. A non-zero, but fixed, angle between the Sun’s magnetic and rotation axis is adopted. The flow of the plasma mixture (thermal SW protons, PUIs, and electrons), is described by the system of ideal magnetohydrodynamic equations with the source terms responsible for charge exchange between ions and neutral atoms. Different populations of neutral atoms are governed by the individual sets of the Euler equations. As the standard Rankine–Hugoniot relations are not appropriate to describe the anisotropic behavior of PUIs at the termination shock, we use a kinetically-derived set of boundary conditions at it. We extend our previous work [1] and perform these new simulations on a Cartesian grid. This approach allows us to maintain a uniform grid resolution in all directions, without compromising resolution, at large distances from the Sun. The possibility of transition of the SW flow to a stochastic regime in the region between the termination shock and heliopause is further investigated.

Enhancing wildfire propagation model predictions using aerial swarm-based real-time wind measurements: A conceptual framework

The dynamic behaviour of wildfires is mainly influenced by weather, fuel, and topography. Based on fundamental conservation laws involving numerous physical processes and large scales, atmospheric models require substantial computational resources. Therefore, coupling wildfire and atmospheric models is impractical for high resolutions. Instead, a static atmospheric wind field is typically input into the wildfire model, either as boundary conditions on the control surface or distributed over the control volume. Wildfire propagation models may be (i) data-driven; (ii)theoretical; or (iii)mechanistic surrogates. Data-driven models are beyond the scope of this paper. Theoretical models are based on conservation laws (species, energy, mass, momentum) and are, therefore, computationally intensive; e.g. the Fire Dynamics Simulator (FDS). Mechanistic surrogate models do not closely follow fire dynamics laws, but related laws observed to make predictions more efficiently with sufficient accuracy; e.g. FARSITE, and FDS with the Level Set model (FDS-LS). Whether theoretical or mechanistic surrogate, these wildfire models may be coupled with or decoupled from wind models (e.g. Navier-Stokes equations). Only coupled models account for the effect of the fire on the wind field. In this paper, a series of simulations of wildfire propagation on grassland are performed using FDS-LS to study the impact of the fire-induced wind on the fire propagation dynamics. Results show that coupling leads to higher Rates of Spread (RoS), closer to those reported from field experiments, with increasing wind speeds and higher terrain slopes strengthening this trend. Aiming to capture the fire–wind interaction without the hefty cost of solving Navier-Stokes equations, a conceptual framework is proposed: 1) a swarm of unmanned aerial vehicles measure wind velocities at flight height; 2) the wind field is constructed with the acquired data; 3) the high-altitude wind field is mapped to near-surface, and 4) the near-surface wind field is fed into the wildfire model periodically. A series of simulations are performed using an in-house decoupled physics-based reduced-order fire propagation model (FireProM-F) enhanced by wind field “measurements”. In this proof of concept, wind velocities are not measured but extracted from physics-based Large Eddy Simulations taken as ground truth. Unsurprisingly, higher measurement frequencies lead to more accurate and realistic predictions of the propagating fire front. An initial attempt is made to study the effect of wind measurement uncertainty on the model predictions by adding Gaussian noise. Preliminary results show that higher noise leads to the fire front displaying more irregular shapes and slower propagation.

High-energy particle observations from the Moon.

The Moon is a unique natural laboratory for the study of the deep space plasma and energetic particles environment. During more than 3/4 of its orbit around the Earth it is exposed to the solar wind. Being an unmagnetized body and lacking a substantial atmosphere, solar wind and solar energetic particles bombardthe Moon's surface, interacting with the lunar regolith and the tenuous lunar exosphere. Energetic particles arriving at the Moon's surface can be absorbed, or scattered, or can remove another particle from the lunar regolith by sputtering or desorption. A similar phenomenon occurs also with the galactic cosmic rays, which have fluxes and energy spectra representative of interplanetary space. During the remaining part of its orbit the Moon crosses the tail of the terrestrial magnetosphere. It then provides the opportunity to study in-situ the terrestrial magnetotail plasma environment as well as atmospheric escape from the Earth's ionosphere, in the form of heavy ions accelerated and streaming downtail. The lunar environment is thus a unique natural laboratory for analysing the interaction of the solar wind, the cosmic rays and the Earth's magnetosphere with the surface, the immediate subsurface, and the surface-bounded exosphere of an unmagnetized planetary body. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'.

Transitions in surface thermal signatures during the evolution of long-lived eddies in the global ocean

Mesoscale eddies are quasi-circular ocean currents accompanied by dynamic and thermodynamic variations, and are classified as anticyclonic (AEs) and cyclonic eddies (CEs) according to their rotation direction. Eddies transition between surface cold CEs/surface warm AEs (“conventional” eddies) and surface warm CEs/surface cold AEs (“unconventional” eddies) during their lifetimes. However, the characteristics and mechanisms of these transitions remain unclear. In this study, satellite and in-situ data were used to explore the spatiotemporal variation and vertical structures of “conventional” and “unconventional” eddies during the evolution of long-lived eddies (>1 year) in the global ocean from 1993 to 2015. On average, long-lived eddies are “unconventional” for about 40% of their lifetimes, and these “unconventional” eddies are concentrated in the South Atlantic Ocean and off the western and southern coasts of Australia. “Unconventional” eddies show distinct temporal variation and subsurface temperature structures. Generally, cold AEs and warm CEs last <3 months and are more active in summer than in winter. They have cold or warm cores within the mixed layer depth of the water column, which is affected by eddy–wind interactions via eddy-induced Ekman pumping. However, some cold AEs in the South Atlantic and warm CEs in the South Indian Ocean can last for >3 months and display weak seasonal variation. In addition, their cold and warm cores can extend to ∼200 and ∼300 m, respectively, and are related to subduction and the Leeuwin Current System.

The Energetic Oxygen Ion Beams in the Martian Magnetotail Current Sheets: Hints From the Comparisons Between Two Types of Current Sheets

AbstractUsing data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we explore the plasma properties of Martian magnetotail current sheets (CS), to further understand the solar wind interaction with Mars and ion escape. There are some CS exhibit energetic oxygen ions that show narrow beam structures in the energy spectrum, which primarily occurs in the hemisphere where the solar wind electric field (Esw) is directed away from the planet. On average, these CS have a higher escaping flux than that of the CS without energetic oxygen ion beams, suggesting different roles in ion escape. The CS with energetic oxygen ion beams exhibits different proton and electron properties to the CS without energetic oxygen ion beams, indicating their different origins. Our analysis suggests that the CS with energetic oxygen ion beams may result from the interaction between the penetrated solar wind and localized oxygen ion plumes.

Determining the Influence of the IMF and Planetary Magnetic Field Models on Mercury's Magnetosphere Along Spacecraft Trajectories of MESSENGER, BepiColombo and MPO

AbstractMercury's planetary magnetic field models (PMFMs) agree on a majorly dipolar field structure with a northward shift of the magnetic equator. However, due to the northerly biased orbit coverage of past spacecraft missions and different data analyzing methods, the available PMFMs differ in the determined multipole magnitudes for the dipole, quadrupole and octupole moments. While the PMFMs agree well with northern observations, we find that the predicted magnetic field values differ in the unexplored equatorial and southern regions. In the forward modeling approach of this study, we apply three different PMFM representatives, differing in their values of the dipole, quadrupole and octupole moments, and model the resulting solar wind interaction via a global hybrid model with sets of the 4 most common interplanetary magnetic field (IMF) directions under otherwise average solar wind conditions. Extracting our modeled fields along the flybys of MESSENGER and BepiColombo, as well as along four representative orbits of the Mercury Planetary Orbiter (MPO), allows us to estimate local field variations due to IMF and PMFM influence. Our modeled magnetic field components separate significantly by up to 60 nT between the PMFMs in low‐altitude southern regions, leading to displacements of magnetopause, cusps and current sheet locations. We find that MESSENGER flyby observations agree best with modeled field ranges resulting from a quadrupolar PMFM and that certain nightside regions are useful to estimate upstream IMF polarity. We also demonstrate how comparing BepiColombo swingby and MPO orbit phase observations with modeled results can help determine the correct PMFM for Mercury.

The analysis of variants of the main frame of the two-nave steel hall for sports purposes

The objective of the analysis was the choice of the cross sections of the Steel hall’s main frame. The minimisation of weight of the construction elements was assumed as a criterion of optimisation. Initially, the forces which load the main frame, caused by constant interactions, snów interactions and wind interactions, were calculated. In the first phase of the analysis, the choice of cross sections for the elements of the lattice girder was madę. Ninę variants of the lattice girder were considered and the lightest truss was chosen. In the second phase, the analysis of the cross sections of the spandrel beam and the columns was performed. Four variants of these elements were considered. Similarly to the first phase, the variant considered best in terms of weight of the elements was chosen. The results of the calculations from both phases were shown in the bar graphs

Ecological indicators to monitor offshore wind interactions with fisheries resources

Abstract Offshore wind development (OWD) will generate much needed renewable energy, but it will also introduce several stressors to the marine ecosystem. Therefore, there is a need to develop information-rich monitoring programs to assess ecological impacts and inform solutions to mitigate adverse effects. This paper evaluates potential indicators of OWD impacts on fisheries resources that could be considered for monitoring programs, including indices of aggregate biomass, sensitive species, fish size, and trophic dynamics. Short-term (year-to-year) variability and the direction and strength of long-term trends were explored at both the scale of the US Southern New England wind energy area (WEA) and at the scale of the Southern New England region. The majority of candidate OWD indicators exhibited substantial temporal variability at either the WEA scale, the region scale, or both, highlighting the importance of addressing temporal variability in the design and duration of monitoring programs. Recommendations are provided to advance informative monitoring approaches both in the USA and elsewhere where such approaches are urgently needed. Among these is a recommendation for a minimum of 3–5 years of baseline data collection and continued monitoring for the lifetime of the wind project. This will enable an understanding of the temporal structure inherent to the time series of ecological indicators measured so that OWD impacts can be disentangled from those caused by other ecosystem pressures.

Properties of Mars' Dayside Low‐Altitude Induced Magnetic Field and Comparisons With Venus

AbstractMars and Venus have atmospheres but lack intrinsic dipole magnetic fields. Consequently, the solar wind interaction at each planet results in the formation of an induced magnetosphere. Our work aims to compare the low‐altitude (&lt; 250 km) component of the induced magnetic field at Venus and Mars using observations from Pioneer Venus Orbiter and Mars Atmosphere and Volatile EvolutioN. We restrict the in‐situ data from Mars to regions of weak crustal magnetism. At Venus, it has long been known the vertical structure of the induced magnetic field profiles have recurring features that enable them to be classified as either magnetized or unmagnetized. We find the induced field profiles at Mars are more varied, lack recurring features, and are unable to be classified in the same way. The solar zenith angle dependence of the low‐altitude field strength at both planets is controlled by the shape of the magnetic pileup boundary. Also, because the ionospheric thermal pressure at Venus is often comparable to the solar wind dynamic pressure, the induced fields are weaker than required to balance the solar wind by themselves. By contrast, induced fields at Mars are stronger than required to achieve pressure balance. Lastly, we find the induced fields in the magnetized ionosphere of Venus have a weaker dependence on solar wind dynamic pressure than the induced fields at Mars. Our results point to planetary properties, such as planet‐Sun distance, having a major effect on the properties of induced fields at nonmagentized planets.

Examining Wind Flow's Impact on Multi-Storey Buildings: A Quest for Quality Improvement

Abstract This scientific article delves into the intricacies of wind flow's impact on multi-storey buildings, presenting results from a series of experimental investigations. The research encompasses an examination of wind interactions with buildings of varying heights and geometric profiles. Furthermore, it unveils the effects of tall structures on the natural ventilation and smoke evacuation systems of shorter edifices, considering different wind flow directions. The study leverages specialized wind tunnel and measurement techniques for a comprehensive analysis of wind-induced loads on buildings. The acquired insights furnish crucial input for the design of single-story temporary modular constructions within densely populated urban areas, subject to wind-induced stresses. Additionally, they hold potential applicability in the advancement of energy-efficient technologies and strategies within the realm of construction. The acquired dataset underscores the criticality of scrutinizing wind flow's impact on structures of varied typologies and dimensions and will allow to significantly improve the quality and efficiency of modern buildings in the future.

The interaction of a large-scale nuclear wind with the high velocity HII region G0.17+0.15

Abstract We investigate the nature of a Galactic center source, G0.17+0.15, lying along the northern extension of the Radio Arc near l ∼ 0.2○. G0.17+0.15 is an HII region located toward the eastern edge of the radio bubble, embedded within the highly polarized Galactic center eastern Lobe where a number of radio filaments appear to cross through the HII region. We report the detection of hydrogen and helium recombination lines with a radial velocity exceeding 140 km s−1 based on GBT and VLA observations. The morphology of G0.17+0.15, aided by kinematics, and spectral index characteristics, suggests the presence of an external pressure dragging and shredding the ionized gas. We argue that this ionized cloud is interacting with a bundle of radio filaments and is entrained by the ram pressure of the radio bubble, which itself is thought to be produced by cosmic-ray driven outflows at the Galactic center. In this interpretation, the gas streamers on the western side of G0.17+0.15 are stripped, accelerated from 0 to δv ∼ 35 km s−1 over a time scale roughly 8 × 104 years, implying that ablating ram pressure is ∼700 eV cm−3, comparable to the ∼103 eVcm−3 cosmic-ray driven wind pressure in the Galactic center region.

Exploration of the methods and rules of syndrome/pattern differentiation and treatment of headache from the acupuncture-moxibustion prescriptions of ancient literature based on the data mining technology.

The study aims to identifying and exploring the methods and rules of the syndrome/pattern differentiation and treatment of headache through collating acupuncture-moxibustion prescriptions recorded earliest in ancient literature. Using Excel2016 software, the structural data table was prepared with "name of disease", "location of disease", "etiology and pathogenesis", "complicated symptoms", "sites for acupuncture and moxibustion" and "techniques of acupuncture and moxibustion" included. The normative approach was conduced on "name of disease", "etiology and pathogenesis", "complicated symptoms" and "nomenclature of acupoint". Using conventional literature statistical method, combined with Apriori algorithm of association rule, the implicit multi-dimensional correlation rules were explored among various elements of syndrome/pattern differentiation of headache and corresponding therapeutic methods. Based on the findings of the study, the regularity was distinct regarding the treatment at "distal acupoints along the affected meridian and the local acupoints at the affected area" after identifying the location of headache; the strong association was presented between "etiology and pathogenesis" and "acupoint selection", and between "etiology and pathogenesis" and "therapeutic methods", including 9 and 12 rules, respectively. Guanyuan (CV 4) selected in treatment of headache was associated with kidney deficiency, the combination of Zhongwan (CV 12) and Zusanli (ST 36) was with phlegm, Fengfu (GV 16), Fengchi (GB 20), Xinghui (GV 22) and Baihui (GV 20) was with wind, and Hegu (LI 4) was with cold. Moxibustion was dominant in treatment if headache was caused by pathogenic cold or related to deficiency syndrome; acupuncture was used specially for the case caused by phlegm, or interaction of wind and phlegm or wind and heat. For heat syndrome, either acupuncture or moxibustion was applicable, in general, acupuncture was more commonly used in comparison with moxibustion for headache. There were 6 association rules regarding the acupoint selection and the techniques of acupuncture and moxibustion. Moxibustion was generally applied to Xinghui (GV 22), Shangxing (GV 23) and Baihui (GV 20) ; and acupuncture was to Fengfu (GV 16), Hegu (LI 4) and Zusanli (ST 36). There were few association rules between the complicated symptoms and acupoint selection. Among nearly 100 complications, there were only 3 feature associations. Zhongwan (CV 12) was selected for the case with poor appetite, Chengjiang (CV 24) was with neck stiffness, and Fengchic (GB 20) combined with Fenglong (ST 40) or Jiexi (ST 41) was used if vertigo was present. In the ancient time, regarding the treatment of headache, acupuncture and moxibustion are delivered based on the three aspects, i.e. the location of illness, the etiology and pathogenesis, and the complicated symptoms. For acupoint selection, in line with the courses of affected meridians, the adjacent and distal acupoints are combined according to the location of headache. The acupoint prescription is composed in terms of the etiology and pathogenesis. The techniques of acupuncture and moxibustion are optimized in consideration of the sites where acupuncture and moxibustion are operated.

The effect of relativistic precession on light curves of tidal disruption events

ABSTRACT The disruption of a star by the tidal forces of a spinning black hole causes the stellar stream to precess, affecting the conditions for triggering the tidal disruption event (TDE). In this work, we study the effect that precession imprints on TDE light curves due to the interaction of the TDE wind and luminosity with the stream wrapped around the black hole. We perform two-dimensional radiation-hydrodynamic simulations using the moving-mesh hydrodynamic code jet with its radiation treatment module. We study the impact of black hole mass, accretion efficiency, and inclination between the orbital and spin planes. From our results, we identified two behaviours: (i) models with low-mass black holes (Mh ∼ 106 M⊙), low inclination (i ∼ 0), and low accretion efficiency (η ∼ 0.01) show light curves with a short early peak caused by the interaction of the wind with the inner edge of the stream. The line of sight has little effect on the light curve, since the stream covers a small fraction of the solid angle due to the precession occurring in the orbital plane; and (ii) models with high-mass black holes (Mh ≳ 107 M⊙), high inclination (i ∼ 90°), and high accretion efficiency (η ∼ 0.1) produce light curves with luminosity peaks that can be delayed by up to 50–100 d depending on the line of sight due to presence of the precessed stream blocking the radiation in the early phase of the event. Our results show that black hole spin and misalignment do not imprint recognizable features on the light curves but rather can add complications to their analysis.

Effects of charge exchange on plasma flow in the heliosheath and astrosheathes

ABSTRACT Shock boundary layers are regions bounded by a shock wave on the one side and tangential discontinuity on the other side. These boundary layers are commonly observed in astrophysics. For example, they exist in the regions of the interaction of the stellar winds with the surrounding interstellar medium. Additionally, the shock layers (SLs) are often penetrated by the flows of interstellar atoms, as, for instance, in the astrospheres of the stars embedded by the partially ionized interstellar clouds. This paper presents a simple toy model of an SL that aims to qualitatively describe the influence of charge exchange with interstellar hydrogen atoms on the plasma flow in astrospheric SLs. To clearly explore this effect, magnetic fields are neglected, and the geometry is kept as simple as possible. The model explains why the cooling of plasma due to charge exchange in the inner heliosheath leads to an increase in plasma density in front of the heliopause. It also demonstrates that the source of momentum causes changes in the pressure profile within the SL. The paper also discusses the decrease in plasma density near the astropause in the outer SL in the case of layer heating, which is particularly relevant in light of the Voyager measurements in the heliospheric SL.

Snowfall deposition in mountainous terrain: a statistical downscaling scheme from high-resolution model data on simulated topographies

One of the primary causes of non-uniform snowfall deposition on the ground in mountainous regions is the preferential deposition of snow, which results from the interaction of near-surface winds with topography and snow particles. However, producing high-resolution snowfall deposition patterns can be computationally expensive due to the need to run full atmospheric models. To address this, we developed two statistical downscaling schemes that can efficiently downscale near-surface, low-resolution snowfall data to fine-scale snow deposition accounting for the effect of preferential deposition in mountainous regions. Our approach relies on a comprehensive, model database generated using 3D wind fields from an atmospheric model and a preferential deposition model on several thousand simulated topographies covering a broad range in terrain characteristics. Both snowfall downscaling schemes rely on fine-scale topographic scaling parameters and low-resolution wind speed as input. While one scheme, referred to as the “wind scheme”, further necessitates fine-scale vertical wind components, a second scheme, referred to as the “aspect scheme”, does not require fine-scale temporal input. We achieve this by additionally downscaling near-surface vertical wind speed solely using topographic scaling parameters and low-resolution wind direction. We assess the performance of our downscaling schemes using an independent subset of the model database on simulated topographies, model data on actual terrain, and spatially measured new snow depth obtained through a photogrammetric drone survey following a snowfall event on previously snow-free ground. While the assessments show that our downscaling schemes perform well (relative errors ≤ ±3% with modeled and ≤ ±6% with measured snowfall deposition), they also demonstrate comparable results to benchmark downscaling models. However, our schemes notably outperform the benchmark models in representing fine-scale patterns. Our downscaling schemes possess several key features, including high computational efficiency, versatility enabled by the comprehensive model database, and independence from fine-scale temporal input data (aspect scheme), indicating their potential for widespread applicability. Therefore, our downscaling schemes for near-surface snowfall and vertical wind speed can be beneficial for various applications at fine grid resolutions such as in atmospheric and climate sciences, snow hydrology, glaciology, remote sensing, and avalanche sciences.

Disappearing Solar Wind at Mars: Changes in the Mars‐Solar Wind Interaction

AbstractOn 26 December 2022 the solar wind density dropped by over an order of magnitude and remained low for about a day. We have utilized in‐situ plasma measurements made by the Mars Atmosphere and Volatile EvolutioN mission to determine how this change affected the Mars‐solar wind interaction. During this time period, on inbound orbit segments, MAVEN sampled the terminator ionosphere, which switched from a magnetized to unmagnetized state immediately following the minimum in solar wind density. The magnetic field amplitude was typically 5–10 nT within the upper ionosphere prior to the event and consistently &lt;1 nT after. During the event the magnetic pressure dominated immediately above the ionosphere while within the ionosphere the ionospheric plasma pressure dominated. The high altitude terminator ionosphere remained in this unmagnetized state throughout the event, suggesting that it was the new equilibrium state of the system. The terminator upper ionosphere returned to its original magnetized state once the solar wind density had recovered. The outbound orbit segments sampled the dayside subsolar region which remained magnetized throughout the event: the magnetization state of the ionosphere varied locally, dependent upon the solar zenith angle and corresponding incident solar wind dynamic pressure. Such conditions are different to the commonly reported unmagnetized ionospheric state at Venus during solar maximum conditions, where the interplanetary magnetic field is repelled from the entire dayside ionosphere. Drastic changes in the upstream solar wind are able to change the Mars‐solar wind interaction state on timescales less than one MAVEN orbit (∼3.5 hr).