Solar Wind Properties Research Articles

Mirror mode waves in Venus's magnetosheath: solar minimum vs. solar maximum

Abstract. The observational rate of mirror mode waves in Venus's magnetosheath for solar maximum conditions is studied and compared with previous results for solar minimum conditions. It is found that the number of mirror mode events is approximately 14 % higher for solar maximum than for solar minimum. A possible cause is the increase in solar UV radiation, ionizing more neutrals from Venus's exosphere and the outward displacement of the bow shock during solar maximum. Also, the solar wind properties (speed, density) differ for solar minimum and maximum. The maximum observational rate, however, over Venus's magnetosheath remains almost the same, with only differences in the distribution along the flow line. This may be caused by the interplay of a decreasing solar wind density and a slightly higher solar wind velocity for this solar maximum. The distribution of strengths of the mirror mode waves is shown to be exponentially falling off, with (almost) the same coefficient for solar maximum and minimum. The plasma conditions in Venus's magnetosheath are different for solar minimum as compared to solar maximum. For solar minimum, mirror mode waves are created directly behind where the bow shock will decay, whereas for solar maximum all created mirror modes can grow.

Penetration of external plasma into a rotation‐driven magnetosphere

AbstractThomsen et al. (2016) provide a new statistical analysis of nearly 8 years of Cassini Plasma Spectrometer data, revealing that hot electrons injected from Saturn's outer magnetosphere penetrate into the inner magnetosphere but only to a distinct inner edge whose location is independent of external solar wind properties. This result is fully consistent with the hypothesis that centrifugally driven interchange motion is responsible for plasma transport between inner and outer magnetosphere.

Observations of high and low Fe charge states in individual solar wind streams with coronal-hole origin

The solar wind originating from coronal holes is comparatively well-understood and is characterized by lower densities and average charge states compared to the so-called slow solar wind. Except for wave perturbations, the average properties of the coronal-hole solar wind are passably constant. In this case study, we {ocus on observations of the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE) of individual streams of coronal-hole solar wind that illustrate that although the O and C charge states are low in coronal-hole wind, the Fe charge distribution is more variable. In particular, \markmeold{we illustrate that the Fe charge states in coronal-hole solar wind are frequently as high as in slow solar wind. We selected individual coronal-hole solar wind} streams based on their collisional age as well as their respective O and C charge states and analyzed their Fe charge-state distributions. Additionally, with a combination of simple ballistic back-mapping and the potential field source surface model, transitions between streams with high and low Fe charge states were mapped back to the photosphere. The relative frequency of high and low Fe charge-state streams is compared for the years 2004 and 2006. We found several otherwise typical coronal-hole streams that include Fe charge states either as high as or lower than in slow solar wind. Eight such transitions in 2006 were mapped back to equatorial coronal holes that were either isolated or connected to the northern coronal-hole. Attempts to identify coronal structures associated with the transitions were so far inconclusive.

MHD‐IPS analysis of relationship among solar wind density, temperature, and flow speed

AbstractThe solar wind properties near the Sun are a decisive factor of properties in the rest of heliosphere. As such, determining realistic plasma density and temperature near the Sun is very important in models for solar wind, specifically magnetohydrodynamics (MHD) models. We had developed a tomographic analysis to reconstruct three‐dimensional solar wind structures that satisfy line‐of‐sight‐integrated solar wind speed derived from the interplanetary scintillation (IPS) observation data and nonlinear MHD equations simultaneously. In this study, we report a new type of our IPS‐MHD tomography that seeks three‐dimensional MHD solution of solar wind, matching additionally near‐Earth and/or Ulysses in situ measurement data for each Carrington rotation period. In this new method, parameterized relation functions of plasma density and temperature at 50 Rs are optimized through an iterative forward model minimizing discrepancy with the in situ measurements. Satisfying three constraints, the derived 50 Rs maps of plasma quantities provide realistic observation‐based information on the state of solar wind near the Sun that cannot be well determined otherwise. The optimized plasma quantities exhibit long‐term variations over the solar cycles 21 to 24. The differences in plasma quantities derived from the optimized and original IPS‐MHD tomography exhibit correlations with the source‐surface magnetic field strength, which can in future give new quantitative constrains and requirements to models of coronal heating and acceleration.

GALACTIC COSMIC-RAY INTENSITY MODULATION BY COROTATING INTERACTION REGION STREAM INTERFACES AT 1 au

ABSTRACT We present a new model that couples galactic cosmic-ray (GCR) propagation with magnetic turbulence transport and the MHD background evolution in the heliosphere. The model is applied to the problem of the formation of corotating interaction regions (CIRs) during the last solar minimum from the period between 2007 and 2009. The numerical model simultaneously calculates the large-scale supersonic solar wind properties and its small-scale turbulent content from 0.3 au to the termination shock. Cosmic rays are then transported through the background, and thus computed, with diffusion coefficients derived from the solar wind turbulent properties, using a stochastic Parker approach. Our results demonstrate that GCR variations depend on the ratio of diffusion coefficients in the fast and slow solar winds. Stream interfaces inside the CIRs always lead to depressions of the GCR intensity. On the other hand, heliospheric current sheet (HCS) crossings do not appreciably affect GCR intensities in the model, which is consistent with the two observations under quiet solar wind conditions. Therefore, variations in diffusion coefficients associated with CIR stream interfaces are more important for GCR propagation than the drift effects of the HCS during a negative solar minimum.

Characteristics of solar wind control on Jovian UV auroral activity deciphered by long‐term Hisaki EXCEED observations: Evidence of preconditioning of the magnetosphere?

AbstractWhile the Jovian magnetosphere is known to have the internal source for its activity, it is reported to be under the influence of the solar wind as well. Here we report the statistical relationship between the total power of the Jovian ultraviolet aurora and the solar wind properties found from long‐term monitoring by the spectrometer EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) on board the Hisaki satellite. Superposed epoch analysis indicates that auroral total power increases when an enhanced solar wind dynamic pressure hits the magnetosphere. Furthermore, the auroral total power shows a positive correlation with the duration of a quiescent interval of the solar wind that is present before a rise in the dynamic pressure, more than with the amplitude of dynamic pressure increase. These statistical characteristics define the next step to unveil the physical mechanism of the solar wind control on the Jovian magnetospheric dynamics.

Verification of high‐speed solar wind stream forecasts using operational solar wind models

AbstractHigh‐speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium‐level geomagnetic storm activity. Modeling high‐speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high‐speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang‐Sheeley‐Arge (WSA) model based on the in situ plasma measurements from the Advanced Composition Explorer (ACE) spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near‐Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona and the background solar wind conditions. We found that both solar wind models are capable of predicting the large‐scale features of the observed solar wind speed (root‐mean‐square error, RMSE ≈100 km/s) but tend to either overestimate (ESWF) or underestimate (WSA) the number of high‐speed solar wind streams (threat score, TS ≈ 0.37). The predicted high‐speed streams show typical uncertainties in the arrival time of about 1 day and uncertainties in the speed of about 100 km/s. General advantages and disadvantages of the investigated solar wind models are diagnosed and outlined.

Suprathermal electron penetration into the inner magnetosphere of Saturn

AbstractFor most Cassini passes through the inner magnetosphere of Saturn, the hot electron population (> few hundred eVs) largely disappears inside of some cutoff L shell. Anode‐and‐actuation‐angle averages of hot electron fluxes observed by the Cassini Electron Spectrometer are binned into 0.1 Rs bins in dipole L to explore the properties of this cutoff distance. The cutoff L shell is quite variable from pass to pass (on timescales as short as 10–20 h). At energies of 5797 eV, 2054 eV, and 728 eV, 90% of the inner boundary values lie between L ~ 4.7 and 8.4, with a median near L = 6.2, consistent with the range of L values over which discrete interchange injections have been observed, thus strengthening the case that the interchange process is responsible for delivering the bulk of the hot electrons seen in the inner magnetosphere. The occurrence distribution of the inner boundary is more sharply peaked on the nightside than at other local times. There is no apparent dependence of the depth of penetration on large‐scale solar wind properties. It appears likely that internal processes (magnetic stress on mass‐loaded flux tubes) are dominating the injection of hot electrons into the inner magnetosphere.

Voyager 2 solar plasma and magnetic field spectral analysis for intermediate data sparsity

AbstractThe Voyager probes are the furthest, still active, spacecraft ever launched from Earth. During their 38 year trip, they have collected data regarding solar wind properties (such as the plasma velocity and magnetic field intensity). Unfortunately, a complete time evolution of the measured physical quantities is not available. The time series contains many gaps which increase in frequency and duration at larger distances. The aim of this work is to perform a spectral and statistical analysis of the solar wind plasma velocity and magnetic field using Voyager 2 data measured in 1979, when the gap density is between the 30% and 50%. For these gap densities, we show the spectra of gapped signals inherit the characteristics of the data gaps. In particular, the algebraic decay of the intermediate frequency range is underestimated and discrete peaks result not from the underlaying data but from the gap sequence. This analysis is achieved using five different data treatment techniques coming from the multidisciplinary context: averages on linearly interpolated subsets, correlation without data interpolation, correlation of linearly interpolated data, maximum likelihood data reconstruction, and compressed sensing spectral estimation. With five frequency decades, the spectra we obtained have the largest frequency range ever computed at five astronomical units from the Sun; spectral exponents have been determined for all the components of the velocity and magnetic field fluctuations. Void analysis is also useful in recovering other spectral properties such as micro and integral scales.

Effects of solar wind speed on the secondary energetic neutral source of the Interstellar Boundary Explorer ribbon

The Interstellar Boundary EXplorer (IBEX) ribbon is an intense energetic neutral atom (ENA) emission feature encircling the sky, spanning energies ≤0.5–6 keV. The ribbon may be produced by the “secondary ENA” mechanism, where ENAs emitted from a source plasma population inside the heliosphere propagate outside the heliopause, undergo two charge-exchange events, and become secondary ENAs that may be directed back toward Earth and detected by IBEX. In this scenario, the source plasma population is governed by the interaction of the solar wind (SW) with the interstellar medium and is thus sensitive to the global SW properties. Moreover, this scenario predicts that the distance to the source of secondary ENAs depends on the ENA energy and SW speed, which in turn may affect the shape of the ribbon. In this paper, we use a computational model of the heliosphere with simplified SW boundary conditions to analyze the influence of ENA energy and SW speed, independent of time and latitude, on the global spatial and geometric properties of the ribbon. We find a strong dependence of the simulated ribbon energy spectrum and spatial symmetry on SW speed and ENA energy, and only a slight dependence on ribbon geometry. Our results suggest a significant number of primary ENAs from the inner heliosheath may contribute to the pickup ion source population outside the heliopause, depending on the ENA energy and SW speed. The lack of variation in the simulated ribbon center as a function of ENA energy and SW speed, in contrast to the observations, implies that the asymmetry of the SW plays an important role in determining the position of the ribbon. Comparisons to the IBEX data also signify the ribbon’s dependence on the properties of the local interstellar medium, particularly the interstellar magnetic field.

Coronal Sources and In Situ Properties of the Solar Winds Sampled by ACE During 1999 – 2008

We identify the coronal sources of the solar winds sampled by the ACE spacecraft during 1999-2008, and examine the in situ solar wind properties as a function of wind sources. The standard two-step mapping technique is adopted to establish the photospheric footpoints of the magnetic flux tubes along which the ACE winds flow. The footpoints are then placed in the context of EIT 284~\AA\ images and photospheric magnetograms, allowing us to categorize the sources into four groups: coronal holes (CHs), active regions (ARs), the quiet Sun (QS), and "Undefined". This practice also enables us to establish the response to solar activity of the fractions occupied by each kind of solar winds, and of their speeds and O$^{7+}$/O$^{6+}$ ratios measured in situ. We find that during the maximum phase, the majority of ACE winds originate from ARs. During the declining phase, CHs and ARs are equally important contributors to the ACE solar winds. The QS contribution increases with decreasing solar activity, and maximizes in the minimum phase when QS appear to be the primary supplier of the ACE winds. With decreasing activity, the winds from all sources tend to become cooler, as represented by the increasingly low O$^{7+}$/O$^{6+}$ ratios. On the other hand, during each activity phase, the AR winds tend to be the slowest and associated with the highest O$^{7+}$/O$^{6+}$ ratios, and the CH winds correspond to the other extreme, with the QS winds lying in between. Applying the same analysis method to the slow winds only, here defined as the winds with speeds lower than 500 km s$^{-1}$, we find basically the same overall behavior, as far as the contributions of individual groups of sources are concerned. This statistical study indicates that QS regions are an important source of the solar wind during the minimum phase.

Three-dimensional multi-fluid model of a coronal streamer belt with a tilted magnetic dipole

Abstract. Observations of streamers in extreme ultraviolet (EUV) emission with SOHO/UVCS show dramatic differences in line profiles and latitudinal variations in heavy ion emission compared to hydrogen Ly-α emission. In order to use ion emission observations of streamers as the diagnostics of the slow solar wind properties, an adequate model of a streamer including heavy ions is required. We extended a previous 2.5-D multi-species magnetohydrodynamics (MHD) model of a coronal streamer to 3-D spherical geometry, and in the first approach we consider a tilted dipole configuration of the solar magnetic field. The aim of the present study is to test the 3-D results by comparing to previous 2.5-D model result for a 3-D case with moderate departure from azimuthal symmetry. The model includes O5+ ions with preferential empirical heating and allows for calculation of their density, velocity and temperature in coronal streamers. We present the first results of our 3-D multi-fluid model showing the parameters of protons, electrons and heavy ions (O5+) at the steady-state solar corona with a tilted steamer belt. We find that the 3-D results are in qualitative agreement with our previous 2.5-D model, and show longitudinal variation in the variables in accordance with the tilted streamer belt structure. Properties of heavy coronal ions obtained from the 3-D model together with EUV spectroscopic observations of streamers will help understanding the 3-D structures of streamers reducing line-of-sight integration ambiguities and identifying the sources of the slow solar wind in the lower corona. This leads to improved understanding of the physics of the slow solar wind.

The dipole tilt angle dependence of the bow shock for southward IMF: MHD results

The location and shape of the Earth׳s bow shock depend on the properties of the upstream solar wind, as well as the size and shape of the downstream magnetopause. Many studies have suggested that the influence of the dipole tilt angle on the magnetopause is significant, especially at the high-latitude region, however, to date there is no bow shock model which depends on the dipole tilt angle. Using a physics-based global magnetohydrodynamic (MHD) model, the Space Weather Modeling Framework (SWMF), we investigate the effect of the dipole tilt angle on the location and shape of the bow shock, and our results show that (1) the subsolar standoff distance and the north-south asymmetry of bow shock increase with the increasing dipole tilt angle; (2) with the dipole tilt angle positively increasing, the flaring angle of the bow shock increases in the northern hemisphere but keeps almost unchanged in the southern hemisphere, and the rotational asymmetry slightly decreases in the northern hemisphere and rapidly decreases in the southern hemisphere; and (3) the influence of dipole tilt angle on the shape of the bow shock is north-south symmetric.

Plasma and Magnetic-Field Characteristics of Magnetic Decreases in the Solar Wind at 1 AU: Cluster-C1 Observations

Magnetic decreases (MDs) are structures observed in interplanetary space with significant decreases in magnetic-field magnitude. Events with little or no change in the field direction are called linear magnetic decreases (LMDs), the others are called nonlinear MDs (NMDs). In this article we focus on LMD and NMD trains, where LMD trains are defined as at least three LMDs in a row and NMD trains as trains (≥ three MDs in a row) that are not all linear. If the temporal separation between two MDs was shorter than five minutes, they were considered as one train event. A total of 16 273 MD trains (including 897 LMD trains and 15 376 NMD trains) were identified and studied. The details of the background magnetic-field and plasma (e.g. ion-density and velocity) features were examined and compared with the average solar-wind properties. LMD trains are found to occur in regions with relatively low magnetic-field strengths, high ion-number densities, and large plasma βs (ratio of the plasma thermal pressure to the magnetic pressure). In sharp contrast, NMD trains have plasma properties similar to the average solar wind. Forty-three LMD trains are related to interplanetary coronal mass ejections (ICMEs) (including 19 events that occurred in ICME sheaths and 24 in the ICME proper), while 222 LMD trains occurred in corotating interaction regions (CIRs), and the remaining 632 events in the normal solar wind. The LMD trains that occurred in ICME sheaths are thought to be associated with the generation mechanism of the mirror-mode instability. Only 552 of the NMD trains are related to ICMEs (including 236 events in ICME sheaths and 316 in ICMEs proper), while 3889 (25 %) NMD trains occurred in CIRs, and the remaining 71 % occurred in the normal solar wind. Because the NMD trains have various plasma properties that differ from the LMD trains, we suggest that NMD trains may be generated by different mechanisms, for instance by a steepening of Alfven waves.

POLAR AND EQUATORIAL CORONAL HOLE WINDS AT SOLAR MINIMA: FROM THE HELIOSPHERE TO THE INNER CORONA

Fast solar wind can be accelerated from at least two different sources: polar coronal holes and equatorial coronal holes. Little is known about the relationship between the wind coming from these two different latitudes and whether these two subcategories of fast wind evolve in the same way during the solar cycle. Nineteen years of Ulysses observations, from 1990 to 2009, combined with ACE observations from 1998 to the present provide us with in situ measurements of solar wind properties that span two entire solar cycles. These missions provide an ideal data set to study the properties and evolution of the fast solar wind originating from equatorial and polar holes. In this work, we focus on these two types of fast solar wind during the minima between solar cycles 22 and 23 and 23 and 24. We use data from SWICS, SWOOPS, and VHM/FGM on board Ulysses and SWICS, SWEPAM, and MAG on board ACE to analyze the proton kinetic, thermal, and dynamic characteristics, heavy ion composition, and magnetic field properties of these two fast winds. The comparison shows that: (1) their kinetic, thermal, compositional, and magnetic properties are significantly different at any time during the two minima and (2) they respond differently to the changes in solar activity from cycle 23 to 24. These results indicate that equatorial and polar fast solar wind are two separate subcategories of fast wind. We discuss the implications of these results and relate them to remote-sensing measurements of the properties of polar and equatorial coronal holes carried out in the inner corona during these two solar minima.

A Study of Coronal Holes Observed by SOHO/EIT and the Nobeyama Radioheliograph

Abstract Coronal holes (CHs) are areas of reduced emission in EUV and X-ray images that show bright patches of microwave enhancements (MEs) related to magnetic network junctions inside the CHs. A clear correlation between the CH size and the solar wind (SW) speed is well known, but we have less information about the relationship between MEs and other CH and SW properties. We studied the characteristics of 21 equatorial CHs associated with corotating interaction regions (CIRs) during 1996 to 2005. Our CHs were divided into two groups according to the intensity of the associated geomagnetic storms: Dst≤-100 nT (10 events) and > -100 nT (11 events). Using EUV 284 Å images obtained by SOHO/EIT and 17 GHz microwave images obtained by the Nobeyama Radioheliograph (NoRH), we found a linear correlation not only between the maximum SW speed and the area of EUV CH (r = 0.62), but also between the maximum SW speed and the area of the ME (r = 0.79). We also compared the EUVCH areas with and without an overlapping ME. The area of the CHs with an ME is better correlated with the SW speed (r = 0.71) than the area of those without an ME (r = 0.36). Therefore, the radio ME may play an important role in understanding the origin of SW.

Revisiting cometary bow shock positions

The Rosetta spacecraft will arrive at comet 67P/Churyumov–Gerasimenko in 2014 and will escort the comet along its journey around the Sun. The predicted outgassing rate of the comet and the solar wind properties close to its perihelion at 1.24AU lead to the expectation that a cometary bow shock will form during the escort phase. Since the forecasts of the subsolar stand off distances differ, this study revisits selected models and presents hybrid simulations of the comet–solar wind interaction region performed with the A.I.K.E.F. code. It is shown that small variations of the solar wind parameters will shift the bow shock position considerably. In addition, a model is presented that reproduces the bow shock distances observed in the hybrid simulations.

Energetic-particle-flux decreases related to magnetic cloud passages as observed by the Helios 1 and 2 spacecraft

It has been observed that a magnetic cloud (MC) can affect the propagation conditions of solar energetic particles and low-energy cosmic rays. This effect is commonly observed as a decrease in the energetic-particle fluxes, which are partially excluded from the interior of the cloud. The twin spacecraft Helios 1 and Helios 2 explored the inner heliosphere between 0.29 AU and 1 AU from the mid 1970s to early 1980s. The E6 Experiment onboard Helios is the energetic-particle detector able to measure electrons, protons and alphas in the range of 300 keV/n to >50 MeV/n. It has been shown previously that, in absence of strong solar-particle events, the single detector rates of the E6 anti-coincidence and saphire Cherenkov detectors are sensitive to cosmic rays with rigidities above GV. Because their statistical precision is in the order of hundreds of counts per second, both detectors are very well suited for studying the short-term decreases observed in their count rates during magnetic cloud passages. A total of 35 magnetic clouds have been identified at the Helios locations. Nineteen of them were free of solar energetic-particle contamination. This subset led us to investigate the effect of magnetic clouds on the galactic cosmic ray (GCR) flux. The depth of the decreases are studied in terms of the solar wind and magnetic field properties of the magnetic cloud. We found dependences with the MC magnetic field strength, magnetic rigidity and with the MC time of flight, with the latter supporting the idea of magnetically closed MCs, i.e. with the two legs rooted in the Sun. We also studied MC properties and found evidence of MC expansion during its journey through the inner heliosphere.

On the electron temperature downstream of the solar wind termination shock

Abstract. In this paper we study the temperatures of electrons convected with the solar wind to large solar distances and finally transported over the solar wind termination shock. Nearly nothing, unless at high energies in the cosmic ray regime, is known about the thermodynamical behaviour of these distant electrons from in~situ plasma observations. Hence it is tacitly assumed these electrons, due to their adiabatic behaviour and vanishing heat conduction or energization processes, have rapidly cooled off to very low temperatures once they eventually arrive at the solar wind termination shock (at about 100 AU). In this paper we show that such electrons, however, at their passage over the termination shock due to the shock–electric field action undergo an over-adiabatic heating and therefore appear on the downstream side as a substantially heated plasma species. Looking quantitatively into this heating process we find that solar wind electrons achieve temperatures of the order of 2–4 × 106 K downstream of the termination shock, depending on the upstream solar wind bulk velocity and the shock compression ratio. Hence these electrons therewith play an important dynamical role in structuring this shock and determining the downstream plasma flow properties. Furthermore, they present an additional ionization source for incoming neutral interstellar hydrogen and excite X-ray emission. They also behave similar to cosmic ray electrons and extend to some limited region upstream of the shock of the order of 0.1 AU by spatial diffusion and thereby also modify the upstream solar wind properties.

Turbulent heating and acceleration of He++ ions by spectra of Alfvén‐cyclotron waves in the expanding solar wind: 1.5‐D hybrid simulations

Both remote sensing and in situ measurements show that the fast solar wind plasma significantly deviates from thermal equilibrium and is strongly permeated by turbulent electromagnetic waves, which regulate the ion temperature anisotropies and relative drifts. Thus, the ion kinetics is governed by heating and cooling related to absorption and emission of ion‐acoustic and ion‐cyclotron waves, as well as nonresonant pitch angle scattering and diffusion in phase space. Additionally, the solar wind properties are affected by its nonadiabatic expansion as the wind travels away from the Sun. In this study we present results from 1.5‐D hybrid simulations to investigate the effects of a nonlinear turbulent spectrum of Alfvén‐cyclotron waves and the solar wind expansion on the anisotropic heating and differential acceleration of protons and He++ ions. We compare the different heating and acceleration by turbulent Alfvén‐cyclotron wave spectra and by pure monochromatic waves. For the waves and the wave spectra used in our model, we find that the He++ ions are preferentially heated and by the end of the simulations acquire much more than mass‐proportional temperature ratios, Tα/Tp>mα/mp. The differential acceleration between the two species strongly depends on the initial wave amplitude and the related spectral index and is often suppressed by the solar wind expansion. We also find that the expansion leads to perpendicular cooling for both species, and depending on the initial wave spectra, it can either heat or cool the ions in parallel direction. Despite the cooling effect of the expansion in perpendicular direction, the wave‐particle interactions provide an additional heating source, and the perpendicular temperature components remain higher than the adiabatic predictions.