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Mesoscale eddies in the global ocean are thought to be powered primarily through transfer from available potential energy stored in mean flows to eddy available potential energy (EAPE). Part of the EAPE is further converted to eddy kinetic energy (EKE) with the residue dissipated through diabatic processes. Currently, the effect of frictional processes on the EAPE budget has not been thoroughly analyzed. Using an eddy‐resolving (1/10°) global climate simulation, we demonstrate that frictionally driven mesoscale eddy flow plays an important role in the EAPE budget, accounting for more than 30% of the EAPE‐to‐EKE conversion in the global ocean and dominating its seasonal cycle. This role can be understood based on the turbulent thermal wind balance under which the frictional force induces an ageostrophic secondary circulation producing a prominent EAPE‐to‐EKE conversion in the winter surface boundary layer. Plain Language Summary: The swirling mesoscale (100–1,000 km) eddies are a prominent feature in the upper ocean. Their vigorous currents are powered primarily by releasing the potential energy stored in the tilting isopycnals (surface of constant density). To date, this release is prevailingly attributed to baroclinic instability, a process lowering the center of gravity by slumping isopycnals in a frictionless manner. However, based on a state‐of‐the‐art global climate simulation resolving mesoscale eddies, we demonstrate that frictional forces play an important role in converting the potential energy to kinetic energy of mesoscale eddies. It generates an overturning flow that is directed upwards on the buoyant side and downwards on the dense side, lowering the center of gravity. This frictionally driven overturning flow is stronger in winter than in summer as a result of active turbulent mixing induced by intense sea surface cooling and wind stirring in winter. Accordingly, the conversion of potential energy to kinetic energy of mesoscale eddies exhibits a distinct seasonal cycle in the global ocean. Key Points: Frictional processes make an important contribution to the conversion of eddy potential energy to kinetic energy and its seasonal changesThe effects of frictional processes on the eddy potential energy budget can be understood based on the turbulent thermal wind balance [ABSTRACT FROM AUTHOR]

We present 14 simultaneous Chandra X‐ray Observatory (CXO)‐Hubble Space Telescope (HST) observations of Jupiter's Northern X‐ray and ultraviolet (UV) aurorae from 2016 to 2019. Despite the variety of dynamic UV and X‐ray auroral structures, one region is conspicuous by its persistent absence of emission: the dark polar region (DPR). Previous HST observations have shown that very little UV emission is produced by the DPR. We find that the DPR also produces very few X‐ray photons. For all 14 observations, the low level of X‐ray emission from the DPR is consistent (within 2‐standard deviations) with scattered solar emission and/or photons spread by Chandra's Point Spread Function from known X‐ray‐bright regions. We therefore conclude that for these 14 observations the DPR produced no statistically significant detectable X‐ray signature. Plain Language Summary: Jupiter produces the most powerful ultraviolet (UV) and X‐ray aurorae in the solar system. While the UV and X‐ray aurora of the planet have each been explored independently, previous work exploring the spatial connection between Jupiter's X‐ray and UV aurorae was limited to a single simultaneous Chandra X‐ray Observatory (CXO) and Hubble Space Telescope (HST) observation from 2003. Since 2016, the arrival of the Juno spacecraft at Jupiter has led to extensive observing campaigns with CXO and HST, resulting in many new simultaneous X‐ray‐UV observations. Here, we present the analysis of 14 simultaneous CXO and HST observations of Jupiter's Northern aurorae from 2016 to 2019. While much of the emission from these bright aurorae is dynamic, there is one region that is dim for all 14 observations: Jupiter's dark polar region. Previous observations of this region have shown that it produces very little UV light. However, the extent to which X‐ray light is produced by the region remained unexplored and could provide the key to identifying why the region is so dark and what this tells us about the Jovian system. Across these 14 observations, we find that the region produces no significant X‐ray emission. Key Points: We compare 14 simultaneous Chandra X‐ray Observatory and Hubble Space Telescope UV observations of Jupiter's Northern AuroraeWe detect no statistically significant X‐ray emission from the UV dark polar region (DPR)The DPR expands and the X‐ray and UV emission on the swirl region boundary shifts when the aurora show solar wind compression morphology [ABSTRACT FROM AUTHOR]

The scattering of light off the bright regions of lunar swirls suggests a relatively higher fraction of fine‐grained dust compared to dust with similar optical maturity values found elsewhere on the lunar surface when assuming an isotropically oriented dust distribution, without preferred grain orientation. Here we propose a mechanism by which the ferromagnetic lunar fines, lofted by electrostatic effects or by meteoroid impacts, may rotate in a lunar magnetic anomaly and, upon landing, produce patches of organized alignments, generating anisotropic surface structures. We simulate these rotations for Reiner Gamma and provide a proof of concept for such a dust rotation model. While the magnetic forces remain negligibly small to influence the trajectories of the lofted particles, the magnetic torques have a significant effect on the rotation of magnetized dust, and can generate an organized landing pattern for elongated lunar fines, which offers a possible explanation for the lunar albedo patterns. Plain Language Summary: Lunar swirls are one of the most striking albedo features on the surface of the Moon. Light scattering of the bright regions of swirls suggest the presence of a relatively higher fraction of fine‐grained dust compared to dust with similar optical properties found elsewhere on the lunar surface when assuming an isotropically oriented dust distribution without preferred grain orientation. Here, we investigate a mechanism by which magnetized lofted dust may generate anisotropic surface structures. We simulate these rotations for the Reiner Gamma region and provide a proof of concept for such a dust rotation model. While the magnetic forces remain negligibly small to influence the trajectories of the lofted particles, the magnetic torque can influence the landing pattern, offering a possible explanation for the lunar albedo patterns. Key Points: We propose a rotation model in which the orientation of elongated dust particles becomes organized by magnetic fields in the lunar regolithThe rotation dynamics of lofted magnetized dust can produce surface structures by capturing an imprint of the magnetic field directionality [ABSTRACT FROM AUTHOR]

Taylor's frozen turbulence hypothesis (FTH) is investigated in the roughness sublayer of a sloped vineyard canopy using a spatial array of fine‐wire thermocouples and ultrasonic anemometers. The Ellipse Approximation (EA) method is applied to the measured space‐time temperature correlation function to delineate sweeping effects from advection velocity. Sweeping effects are explained primarily by the turbulence kinetic energy. Upon the removal of sweeping effects, the advection velocity is found to be commensurate with the mean velocity. Plain Language Summary: Turbulent flows are presumed to be a superposition of swirling motions of different sizes and activities labelled as 'eddies'. Eddies constitute a form of 'ordered' motion, and describing their characteristics (e.g., the distribution of sizes and associated energy content for each size) is a lacunarity in theory and practical applications such as weather forecasting. A major advance in experimentally studying the characteristics of eddies is Taylor's frozen turbulence hypothesis (FTH). This hypothesis suggests that eddies are transported by the average velocity without any alterations in their aforementioned characteristics. The implication of this hypothesis to shaping theories and models of turbulence eddies has been enormous as it enabled temporal measurements of temperature and velocity at a single point to provide information about eddy sizes and their associated energy for the first time. What are the limits of applicability of the FTH and can distortions to it be quantified and modeled? Here, we employ a method called the Ellipse Approximation (EA) method to investigate the behavior of turbulent eddies in the airspace within and above a sloped vineyard. The EA method separates two different turbulence velocities from one another, one is associated with the velocity at which the eddies travel and the other is associated with the timescale at which the eddies break apart. We find that the largest eddies travel at a velocity comparable to the mean velocity, and that the kinetic energy of the eddies dictates the timescale of their destruction. Key Points: Elliptic Approximation (EA) for space‐time correlations explored for scalar turbulence within the roughness sublayer of canopiesAdvection velocity of eddies is commensurate with the mean streamwise velocitySquared sweeping velocity obtained via EA scales linearly with measured turbulent kinetic energy [ABSTRACT FROM AUTHOR]

Temperature and salinity measurements of a warm‐core eddy at the northern flank of the Ross Gyre are analyzed for dominant mixing mechanisms. The eddy is centered at the depths of the Circumpolar Deep Water and carries heat towards the gyre. Vertical and horizontal heat fluxes out of the eddy associated with internal wave turbulent mixing and thermohaline intrusions are estimated. Upward internal wave turbulent heat flux is O(100) W/m2, whereas, the lateral intrusive heat flux is of the order of O(1000) W/m2. The horizontal flux due to intrusions is suggested to be the dominant mechanism for eddy decay and yields an eddy lifetime of about 6 months. The thermohaline intrusion‐eddy suppression mechanism is proposed and shown to be effective in suppressing the eddy field at the northern flank of the Ross Gyre. This effect has important implications for setting the basin‐wide heat budget and regulating sea‐ice cover. Plain Language Summary: The Southern Ocean Ross gyre separates the Antarctic Circumpolar Current (ACC) from the Antarctic continental margin. It carries warm water toward the continent at its eastern limit and brings cold freshwater from the continental margin into proximity with the ACC at its western boundaries. In this study, we examine a warm‐core eddy that carries anomalous warm water towards the gyre center from the ACC. Estimates of vertical and horizontal heat fluxes indicate a short lifetime of such eddies (roughly 6 months). We propose that such eddies can be suppressed by thermohaline intrusions. Thus, the thermohaline intrusion‐eddy suppression mechanism may regulate the overall heat budget within the Ross Gyre and influence sea‐ice properties. Key Points: Mesoscale warm‐core eddy sampled by rapid float profilingSpin‐down by thermohaline intrusions dominates turbulent mixingEddy transport across the northern Ross Gyre is limited by this thermohaline intrusion‐eddy suppression mechanism [ABSTRACT FROM AUTHOR]