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Magnetic field measurements delivered by spacecraft are often contaminated by artificial magnetic fields generated by other instruments or spacecraft subsystems. In this work we propose an advanced multi-sensor data cleaning method able to remove 3 ( N - 1 ) independent disturbances from N sensors data. The BepiColombo composite spacecraft is a good test-bed to illustrate the application of the proposed method. We identify five disturbance sources in the magnetic field data measured by the Mercury Planetary Orbiter magnetometer during the cruise phase, and apply the novel method to a 7 h interval to remove the disturbances. We show that all five disturbances are most probably produced by the solar panels of the Mercury Transfer Module. Graphical abstract

The brain has a remarkable capacity to adapt to changes in sensory inputs and to learn from experience. However, the neural circuits responsible for this flexible processing remain poorly understood. Using optogenetic silencing of ArchT-expressing neurons in adult ferrets, we show that within-trial activity in primary auditory cortex (A1) is required for training-dependent recovery in sound-localization accuracy following monaural deprivation. Because localization accuracy under normal-hearing conditions was unaffected, this highlights a specific role for cortical activity in learning. A1-dependent plasticity appears to leave a memory trace that can be retrieved, facilitating adaptation during a second period of monaural deprivation. However, in ferrets in which learning was initially disrupted by perturbing A1 activity, subsequent optogenetic suppression during training no longer affected localization accuracy when one ear was occluded. After the initial learning phase, the reweighting of spatial cues that primarily underpins this plasticity may therefore occur in A1 target neurons. Sensory circuits can adapt flexibly to changes in inputs yet the neural mechanisms related to experience dependent plasticity are not well understood. Here, the authors use optogenetic approaches in ferrets to show that suppression of auditory cortex during sound localization training can affect learning.

There has been considerable confusion in the literature about what mirror mode (MM), magnetic decrease (MD), and linear magnetic decrease (LMD) structures are and are not. We will reexamine past spacecraft observations to demonstrate the observational similarities and differences between these magnetic and plasma structures. MM structures in planetary magnetosheaths, cometary sheaths, and the heliosheath have the following characteristics: (1) the structures have little or no changes in the magnetic field direction across the magnetic dips; (2) the structures have quasiperiodic spacings, varying from ∼20 proton gyroradii (rp) in the Earth's magnetosheath to ∼57 rp in the heliosheath; and (3) the magnetic dips have smooth edges. Magnetosheath MM structures are generated by the mirror instability where β⊥/β∥ > 1 + 1/β⊥ (β is the plasma thermal pressure divided by the magnetic pressure). In general, the sources of free energy for the mirror instability are reasonably well understood: shock compression, field line draping, and, in the cases of comets and the heliosheath, also ion pickup. The observational properties of interplanetary MDs are as follows: (1) there is a broad range of magnetic field angular changes across them; (2) their thicknesses can range from as little as 2–3 rp to thousands of rp, with no “characteristic” size; and (3) they typically are bounded by discontinuities. The mechanism(s) for interplanetary MD generation is (are) currently unresolved, although at least five different mechanisms have been proposed in the literature. Tsurutani et al. (2009a) have argued against mirror instability for those MDs generated within interplanetary corotating interaction regions. Interplanetary LMDs are by definition a subset of MDs with small angular changes across them (θ < 10°). Are LMDs generated by the mirror instability or by another mechanism? Is it possible that there are several different types of LMDs involving different generation mechanisms? At the present time, no one knows the answers to these latter questions.

Magnetic flux transfer events (FTEs) are signatures of unsteady magnetic reconnection, often observed at planetary magnetopauses. Their generation mechanism, a key ingredient determining how they regulate the transfer of solar wind energy into magnetospheres, is still largely unknown. We report THEMIS spacecraft observations on 2007‐06‐14 of an FTE generated by multiple X‐line reconnection at the dayside magnetopause. The evidence consists of (1) two oppositely‐directed ion jets converging toward the FTE that was slowly moving southward, (2) the cross‐section of the FTE core being elongated along the magnetopause normal, probably squeezed by the oppositely‐directed jets, and (3) bidirectional field‐aligned fluxes of energetic electrons in the magnetosheath, indicating reconnection on both sides of the FTE. The observations agree well with a global magnetohydrodynamic model of the FTE generation under large geomagnetic dipole tilt, which implies the efficiency of magnetic flux transport into the magnetotail being lower for larger dipole tilt.

An examination of the magnetic field and plasma observed by the inner THEMIS‐D spacecraft (P3) close to the equatorial plane at ∼11RE at local midnight reveals the occurrence of mirror‐mode structures. These structures have the same characteristic waveform seen in other regions. The examination of the mirror‐mode instability shows that inside these structures the threshold of mirror instability is marginally reached, while the surrounding plasma is mirror stable. The observed mirror structures occur in the dipolarized magnetic field following a substorm‐related dipolarization. It is found that after the dipolarization front, the local ions become more anisotropic and initial magnetic holes form inside this anisotropic plasma before the fully‐fledged mirror structures are observed. The ions become less anisotropic afterward, but the strong field depression in the magnetic holes enhances the effective plasma beta so that the mirror instability threshold is marginally reached. Thus, the dipolarization process provides the large‐amplitude magnetic field fluctuations and the anisotropic plasma environment for mirror structures to grow. The isolated large‐amplitude mirror‐mode structures survive in the mirror‐stable plasma even through the plasma becomes less anisotropic. It is also found that the width of magnetotail mirror‐structures is smaller than one gyroradius of a plasma sheet proton, which is different from the width of mirror structures in other regions. These mirror structures appear to have a strong correlation with electron anisotropy changes. These observations suggest that electron kinetics may also play a role during the growth and saturation of mirror instability in the near‐Earth tail.

It has been hypothesized that the brain organizes concepts into a mental map, allowing conceptual relationships to be navigated in a manner similar to that of space. Grid cells use a hexagonally symmetric code to organize spatial representations and are the likely source of a precise hexagonal symmetry in the functional magnetic resonance imaging signal. Humans navigating conceptual two-dimensional knowledge showed the same hexagonal signal in a set of brain regions markedly similar to those activated during spatial navigation. This gridlike signal is consistent across sessions acquired within an hour and more than a week apart. Our findings suggest that global relational codes may be used to organize nonspatial conceptual representations and that these codes may have a hexagonal gridlike pattern when conceptual knowledge is laid out in two continuous dimensions.

The Kelvin-Helmholtz Instability (KHI) can drive waves at the magnetopause. These waves can grow to form rolled-up vortices and facilitate transfer of plasma into the magnetosphere. To investigate the persistence and frequency of such waves at the magnetopause we have carried out a survey of all Double Star 1 magnetopause crossings, using a combination of ion and magnetic field measurements. Using criteria originally used in a Geotail study made by Hasegawa et al. (2006) (forthwith referred to as H2006), 17 candidate events were identified from the entire TC-1 mission (covering 623 orbits where the magnetopause was sampled), a majority of which were on the dayside of the terminator. The relationship between density and shear velocity was then investigated, to identify the predicted signature of a rolled up vortex from H2006 and all 17 events exhibited some level of rolled up behavior. The location of the events had a clear dawn-dusk asymmetry, with 12 (71 %) on the post noon, dusk flank suggesting preferential growth in this region.

We present results from a statistical analysis of the oscillatory motion of the magnetopause based on THEMIS spacecraft observations, yielding the first experimental evidence for the existence of standing Alfvénic surface or Kruskal‐Schwarzschild modes at the magnetopause. The magnetopause boundary represents a membrane under tension, which may resonantly interact with magnetospheric cavity or waveguide modes. Ultra‐low “magic” geomagnetic pulsation frequencies, often observed in ground‐based and ionospheric measurements and attributed to these cavity or waveguide modes, agree with the detected magnetopause oscillation frequencies and are reinterpreted in terms of surface mode eigenfrequencies.

The five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft offer new possibilities to analyze ULF waves in the magnetosphere by means of multipoint measurements. During the coast phase, THEMIS observed many compressional oscillations with periods in the Pc5 range and longer. The observed events occur inside a well‐defined spatial domain in the outer equatorial duskside magnetosphere. We analyze these waves using the unique string‐of‐pearls configuration of the THEMIS constellation to evaluate their phase speed and propagation direction. We find that the waves are propagating sunward (westward) and radially outward, orthogonal to the mean magnetic field, with phase speeds around 30 km/s and higher in the spacecraft frame. In the plasma frame the propagation direction is still sunward, with lower speeds (up to 30 km/s for most events). The oscillations exhibit a strong anticorrelation between the magnetic field and the plasma density. On the basis of this, as well as their low propagation speed, orthogonal to the mean magnetic field propagation direction and almost parallel to the magnetic field maximum variance direction, we conclude that the most likely source of these waves is the drift mirror instability.

During its early coast phase the configuration of the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft resembled pearls on a string. Between April and September 2007 they traversed the magnetopause boundary layer far more than 6000 times. The radial extension of the spacecraft configuration as well as the resolution due to the high number of simultaneous observation points along the orbit provided us with the unique opportunity to study the spatiotemporal evolution of the magnetopause location. In this study we present single and multiple spacecraft analyses with a special emphasis on a statistical analysis of the magnetopause motion reconstructed from crossing locations and times by spline interpolation. Our observations allow us to infer a higher stability of the magnetopause surface against deformation in field‐aligned direction. Its overall stability increases with decreasing distance to the Earth as well. Additionally, we were able to determine amplitude, velocity and period distributions of the boundary oscillations.