Magnetic field draping occurs when the magnetic field lines frozen in a plasma flow wrap around a body or plasma environment. The draping of the interplanetary magnetic field (IMF) around the Earth’s magnetosphere has been confirmed in the early days of space exploration. However, its global and three‐dimensional structure is known from modeling only, mostly numerical. Here, this structure in the dayside of the Earth’s magnetosheath is determined as a function of the upstream IMF orientation purely from in‐situ spacecraft observations. We show the draping structure can be organized in three regimes depending on how radial the upstream IMF is. Quantitative analysis demonstrates how the draping pattern results from the magnetic field being frozen in the magnetosheath flow, deflected around the magnetopause. The role of the flow is emphasized by a comparison of the draping structure to that predicted to a magnetostatic draping.

Global Three‐Dimensional Draping of Magnetic Field Lines in Earth’s Magnetosheath From In‐Situ Spacecraft Measurements

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has been orbiting Mars since 2014 and now has over 10,000 orbits which we use to characterize Mars' dynamic space environment. Through global field line tracing with MAVEN magnetic field data we find an altitude dependent draping morphology that differs from expectations of induced magnetospheres in the vertical ($\hat Z$ Mars Sun-state, MSO) direction. We quantify this difference from the classical picture of induced magnetospheres with a Bayesian multiple linear regression model to predict the draped field as a function of the upstream interplanetary magnetic field (IMF), remanent crustal fields, and a previously underestimated induced effect. From our model we conclude that unexpected twists in high altitude dayside draping ($>$800 km) are a result of the IMF component in the $\pm \hat X$ MSO direction. We propose that this is a natural outcome of current theories of induced magnetospheres but has been underestimated due to approximations of the IMF as solely $\pm \hat Y$ directed. We additionally estimate that distortions in low altitude ($<$800 km) dayside draping along $\hat Z$ are directly related to remanent crustal fields. We show dayside draping traces down tail and previously reported inner magnetotail twists are likely caused by the crustal field of Mars, while the outer tail morphology is governed by an induced response to the IMF direction. We conclude with an updated understanding of induced magnetospheres which details dayside draping for multiple directions of the incoming IMF and discuss the repercussions of this draping for magnetotail morphology.

pdf/magnetic-field-draping-in-induced-magnetospheres-evidence-44k5bq6wcs.pdf

Magnetic Field Draping in Induced Magnetospheres: Evidence from the MAVEN Mission to Mars

With the increasing demand for underwater detection, interest in the acoustic field of range-dependent ocean waveguides is also growing. For weakly range-dependent ocean waveguides, adiabatic modes represent a compromise between accuracy and computational cost and occupy an important place in the simulation of numerical sound fields. However, either existing adiabatic-mode programs consider too few layers of media or the root-finder tends to miss roots. In addition, none of the programs can solve the acoustic field excited by a line sound source located anywhere in the plane. In this paper, we first derive an expression for the acoustic field excited by a line source by adiabatic modes and then introduce a high-precision spectral method to solve the local eigenmodes. For the lower boundary condition of the acoustic half-space, we use the eigenvalue transformation technique to transform the transcendental algebra system formed by spectral discretization into a generalized eigenvalue problem. Several representative numerical experiments are designed to verify the accuracy of the algorithm. After analyzing the parallelism, the multiprocess and multithread hybrid strategy is adopted to further accelerate the algorithm in parallel, and parallel numerical simulation is carried out on the Tianhe–2 multicore supercomputer; favorable acceleration is achieved.

Parallel numerical simulation of weakly range-dependent ocean acoustic waveguides by adiabatic modes based on a spectral method

In this paper, we study the variations of holograms of a moving source in an inhomogeneous ocean waveguide. It is assumed that intense internal waves (internal solitons) are the reason for the inhomogeneities of the shallow water waveguide. The results of 3D modeling of the sound field considering horizontal refraction by internal waves are presented. In the context of 3D modeling, the interferogram (sound intensity distributions in frequency–time coordinates) and hologram (2D Fourier transform of the interferogram) of moving sources are analyzed. The hologram consists of two disjoint regions corresponding to the unperturbed field and the field perturbed by internal waves. This structure of the hologram allows for the reconstruction of the interferogram of the unperturbed field in a waveguide in the absence of intense internal waves. The error in the reconstruction of the unperturbed interferogram is estimated.

Three-Dimensional Modeling of Sound Field Holograms of a Moving Source in the Presence of Internal Waves Causing Horizontal Refraction

Using the 8.5‐year Venus Express measurements, we demonstrate the asymmetric plasma distributions in the Venusian magnetosheath. An escaping plume is formed by pickup oxygen ions in the hemisphere where the motional electric field points outward from Venus, while the velocity of solar wind protons is faster in the opposite hemisphere. The pickup O+ escape rate is estimated to be (3.6 ± 1.4) × 1024 s−1 at solar maximum, which is comparable to the ion loss rate through the magnetotail, and (1.3 ± 0.4) × 1024 s−1 at solar minimum. The increase of O+ fluxes with extreme ultraviolet (EUV) intensity is significant upstream of the bow shock, partially attributed to the increase of exospheric neutral oxygen density. However, the solar wind velocity just has a slight effect on the pickup O+ escape rate in the magnetosheath, while the effect of solar wind density is not observed. Our results suggest the pickup O+ escape rate is mainly controlled by EUV radiation.

Solar Control of the Pickup Ion Plume in the Dayside Magnetosheath of Venus

Using over 6 years of magnetic field data (October 2014–December 2020) collected by the Mars Atmosphere and Volatile EvolutioN, we conduct a statistical study on the three‐dimensional average magnetic field structure around Mars. We find that this magnetic field structure conforms to the pattern typical of an induced magnetosphere, that is, the interplanetary magnetic field (IMF) which is carried by the solar wind and which drapes, piles up, slips around the planet, and eventually forms a tail in the wake. The draped field lines from both hemispheres along the direction of the solar wind electric field (E) are directed toward the nightside magnetic equatorial plane, indicating that they are “sinking” toward the wake. These “sinking” field lines from the +E‐hemisphere (E pointing away from the plane) are more flared and dominant in the tail, while the field lines from the –E‐hemisphere (E pointing toward) are more stretched and “pinched” toward the plasma sheet. Such highly “pinched” field lines even form a loop over the pole of the –E‐hemisphere. The tail current sheet also shows an E‐asymmetry: the sheet is thicker with a stronger tailward J→×B→ $\overrightarrow{J}\times \overrightarrow{B}$ force at +E‐flank, but much thinner and with a weaker J→×B→ $\overrightarrow{J}\times \overrightarrow{B}$ (even turns sunward) at –E‐flank. Additionally, we find that IMF Bx can induce a kink‐like field structure at the boundary layer; the field strength is globally enhanced and the field lines flare less during high dynamic pressure.

Three‐Dimensional Configuration of Induced Magnetic Fields Around Mars

/pdf/application-of-a-spectral-method-to-simulate-quasi-three-4ep4e2q6.pdf

Application of a Spectral Method to Simulate Quasi-Three-Dimensional Underwater Acoustic Fields

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Three‐Dimensional Configuration of Induced Magnetic Fields Around Mars

Application of a Spectral Method to Simulate Quasi-Three-Dimensional Underwater Acoustic Fields