Solar Wind Acceleration Research Articles

Solar-wind predictions for the Parker Solar Probe orbit

Context. The Parker Solar Probe (PSP; formerly Solar Probe Plus) mission will be humanitys first in situ exploration of the solar corona with closest perihelia at 9.86 solar radii (R⊙) distance to the Sun. It will help answer hitherto unresolved questions on the heating of the solar corona and the source and acceleration of the solar wind and solar energetic particles. The scope of this study is to model the solar-wind environment for PSPs unprecedented distances in its prime mission phase during the years 2018 to 2025. The study is performed within the Coronagraphic German And US SolarProbePlus Survey (CGAUSS) which is the German contribution to the PSP mission as part of the Wide-field Imager for Solar PRobe.Aim. We present an empirical solar-wind model for the inner heliosphere which is derived from OMNI and Helios data. The German-US space probes Helios 1 and Helios 2 flew in the 1970s and observed solar wind in the ecliptic within heliocentric distances of 0.29 au to 0.98 au. The OMNI database consists of multi-spacecraft intercalibrated in situ data obtained near 1 au over more than five solar cycles. The international sunspot number (SSN) and its predictions are used to derive dependencies of the major solar-wind parameters on solar activity and to forecast their properties for the PSP mission.Methods. The frequency distributions for the solar-wind key parameters, magnetic field strength, proton velocity, density, and temperature, are represented by lognormal functions. In addition, we consider the velocity distributions bi-componental shape, consisting of a slower and a faster part. Functional relations to solar activity are compiled with use of the OMNI data by correlating and fitting the frequency distributions with the SSN. Further, based on the combined data set from both Helios probes, the parameters frequency distributions are fitted with respect to solar distance to obtain power law dependencies. Thus an empirical solar-wind model for the inner heliosphere confined to the ecliptic region is derived, accounting for solar activity and for solar distance through adequate shifts of the lognormal distributions. Finally, the inclusion of SSN predictions and the extrapolation down to PSPs perihelion region enables us to estimate the solar-wind environment for PSPs planned trajectory during its mission duration.Results. The CGAUSS empirical solar-wind model for PSP yields dependencies on solar activity and solar distance for the solar-wind parameters’ frequency distributions. The estimated solar-wind median values for PSPs first perihelion in 2018 at a solar distance of 0.16 au are 87 nT, 340 km s−1, 214 cm−3, and 503 000 K. The estimates for PSPs first closest perihelion, occurring in 2024 at 0.046 au (9.86 R⊙), are 943 nT, 290 km s−1, 2951 cm−3, and 1 930 000 K. Since the modeled velocity and temperature values below approximately 20 R⊙appear overestimated in comparison with existing observations, this suggests that PSP will directly measure solar-wind acceleration and heating processes below 20 R⊙ as planned.

A Self-consistent Model of the Coronal Heating and Solar Wind Acceleration Including Compressible and Incompressible Heating Processes

Abstract We propose a novel one-dimensional model that includes both shock and turbulence heating and qualify how these processes contribute to heating the corona and driving the solar wind. Compressible MHD simulations allow us to automatically consider shock formation and dissipation, while turbulent dissipation is modeled via a one-point closure based on Alfvén wave turbulence. Numerical simulations were conducted with different photospheric perpendicular correlation lengths λ 0 , which is a critical parameter of Alfvén wave turbulence, and different root-mean-square photospheric transverse-wave amplitudes δ v 0 . For the various λ 0 , we obtain a low-temperature chromosphere, high-temperature corona, and supersonic solar wind. Our analysis shows that turbulence heating is always dominant when λ 0 ≲ 1 Mm . This result does not mean that we can ignore the compressibility because the analysis indicates that the compressible waves and their associated density fluctuations enhance the Alfvén wave reflection and therefore the turbulence heating. The density fluctuation and the cross-helicity are strongly affected by λ 0 , while the coronal temperature and mass-loss rate depend weakly on λ 0 .

Research progress and future prospect of radiative magnetohydrodynamics numerical simulations in astrophysics and space physics

Over 99% of the baryonic matter in the universe is in the state of plasmas, where matter interacts strongly with the magnetic field. Radiation is generally involved in such interactions, hence affecting the dynamics of the plasmas. All these interactions are described by radiation magnetohydrodynamics (MHD) equations. Because of the strong non- linearity and the multi-scale coupling, only a very limited number of analytical solutions to the MHD equations have been obtained with various approximations and simplifications. To fully understand the physical processes involved in the violent astrophysical eruptions, we have to resort to numerical simulations, which are becoming more and more important in solving the equations and helping us understand the mechanisms hidden in the universe. Owing to the development of the computation hard wares and numerical algorithms, numerical simulations, together with theoretical analyses and experiments (or observations), become three major methods in nowadays research. In particular, numerical simulations have made tremendous progress in the past decades. This paper reviews the research progress of radiation MHD numerical simulations made in astrophysics (including solar physics) and space science during the past 10 years. Their future prospect is also envisioned. Limited by space, only the following topics are included in this review paper. (1) Radiation MHD numerical simulation has become more and more important in various aspects of astrophysical research. In this review, we take black hole accretion as an example. This is mainly because radiation MHD simulation is best developed and applied in this field. In fact, almost all the important progresses in the past 20 years in this field were achieved by radiation MHD numerical simulations. In this review, we introduce three examples. One is the magneto-rotational instability, which is widely believed to be the mechanism of angular momentum transport in accretion flows. The second one is the wind launched from black hole accretion flows, including why we believe the existence of strong winds and what the mechanisms of wind production are. The third topic is the super-Eddington accretion. We introduce how radiation MHD numerical simulations have completely changed our traditional paradigm that was reached by analytical studies. (2) In respect of solar physics, after briefly mentioning the necessity of radiation MHD numerical simulations in the solar atmosphere research, we introduce four different approaches in dealing with the radiation process based on different parameter regimes of various atmospheric layers, such as the photosphere, chromosphere, transition region, and the corona. We further describe the numerical results related to several crucial topics in solar physics, including the formation of several key spectral lines, the structure of the lower solar atmosphere, magnetic reconnection in the lower solar atmosphere, chromospheric and coronal heating, formation of coronal loops, filament formation, and so on. (3) As an illustrative example of typical applications of RMHD in space physics, we offer an overview as to how RMHD is incorporated into the numerical simulations of the solar wind in the inner heliosphere. For this purpose, we first offer a brief introduction to the consensus on the origins of the solar wind, thereby showing that the acceleration of the nascent solar wind is very likely to be a direct result of coronal heating in magnetically open regions. We go on to show that radiation needs to be carefully addressed to self-consistently account for the wind thermodynamics. With some illustrative examples we show how radiation is handled in current multi-dimensional solar wind models.

Radio sounding of the solar wind acceleration region with spacecraft signals

Data from coronal radio-sounding experiments carried out on various interplanetary spacecraft are used to derive the empirical radial dependence of solar wind velocity and density at heliocentric distances from 3 to 60 solar radii for heliolatitudes below 60° and for low solar activity. The radial dependencies of solar wind power and acceleration are derived from these results. Summaries of the radial behavior of characteristic parameters of the solar wind turbulence (e.g., the spectral index and the inner and outer turbulence scales), as well as the fractional density fluctuation, are also presented. These radio-sounding results provide a benchmark for models of the solar wind in its acceleration region.

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.

Interfacing MHD Single Fluid and Kinetic Exospheric Solar Wind Models and Comparing Their Energetics

An exospheric kinetic solar wind model is interfaced with an observation-driven single fluid magnetohydrodynamic (MHD) model. Initially, a photospheric magnetogram serves as observational input in the fluid approach to extrapolate the heliospheric magnetic field. Then semi-empirical coronal models are used for estimating the plasma characteristics up to a heliocentric distance of 0.1AU. From there on a full MHD model which computes the three-dimensional time-dependent evolution of the solar wind macroscopic variables up to the orbit of the Earth is used. After interfacing the density and velocity at the inner MHD boundary, we compare with the results of a kinetic exospheric solar wind model based on the assumption of Maxwell and Kappa velocity distribution functions for protons and electrons respectively, as well as with \textit{in situ} observations at 1AU. This provides insight on more physically detailed processes, such as coronal heating and solar wind acceleration, that naturally arise by inclusion of suprathermal electrons in the model. We are interested in the profile of the solar wind speed and density at 1AU, in characterizing the slow and fast source regions of the wind and in comparing MHD with exospheric models in similar conditions. We calculate the energetics of both models from low to high heliocentric distances.

Magnetic Nulls and Super-radial Expansion in the Solar Corona.

Magnetic fields in the Sun's outer atmosphere-the corona-control both solar-wind acceleration and the dynamics of solar eruptions. We present the first clear observational evidence of coronal magnetic nulls in off-limb linearly polarized observations of pseudostreamers, taken by the Coronal Multichannel Polarimeter (CoMP) telescope. These nulls represent regions where magnetic reconnection is likely to act as a catalyst for solar activity. CoMP linear-polarization observations also provide an independent, coronal proxy for magnetic expansion into the solar wind, a quantity often used to parameterize and predict the solar wind speed at Earth. We introduce a new method for explicitly calculating expansion factors from CoMP coronal linear-polarization observations, which does not require photospheric extrapolations. We conclude that linearly polarized light is a powerful new diagnostic of critical coronal magnetic topologies and the expanding magnetic flux tubes that channel the solar wind.

High-frequency torsional Alfv\xe9n waves as an energy source for coronal heating

The existence of the Sun’s hot atmosphere and the solar wind acceleration continues to be an outstanding problem in solar-astrophysics. Although magnetohydrodynamic (MHD) modes and dissipation of magnetic energy contribute to heating and the mass cycle of the solar atmosphere, yet direct evidence of such processes often generates debate. Ground-based 1-m Swedish Solar Telescope (SST)/CRISP, Hα 6562.8 Å observations reveal, for the first time, the ubiquitous presence of high frequency (~12–42 mHz) torsional motions in thin spicular-type structures in the chromosphere. We detect numerous oscillating flux tubes on 10 June 2014 between 07:17 UT to 08:08 UT in a quiet-Sun field-of-view of 60” × 60” (1” = 725 km). Stringent numerical model shows that these observations resemble torsional Alfvén waves associated with high frequency drivers which contain a huge amount of energy (~105 W m−2) in the chromosphere. Even after partial reflection from the transition region, a significant amount of energy (~103 W m−2) is transferred onto the overlying corona. We find that oscillating tubes serve as substantial sources of Alfvén wave generation that provide sufficient Poynting flux not only to heat the corona but also to originate the supersonic solar wind.

DIRECT AND INVERSE CASCADES IN THE ACCELERATION REGION OF THE FAST SOLAR WIND

ABSTRACT Alfvén waves are believed to play an important role in the heating and acceleration of the fast solar wind emanating from coronal holes. Nonlinear interactions between the dominant waves and minority waves have the potential to transfer wave energy either to smaller perpendicular scales (“direct cascade”) or to larger scales (“inverse cascade”). In this paper we use reduced magnetohydrodynamic (RMHD) simulations to investigate how the cascade rates depend on perpendicular wavenumber and radial distance from the Sun center. For models with a smooth background atmosphere, we find that an inverse cascade ( ) occurs for the dominant waves at radii between 1.4 and and dimensionless wavenumbers in the inertial range ( ), and a direct cascade ( ) occurs elsewhere. For a model with density fluctuations, there are multiple regions with an inverse cascade. In both cases, the cascade rate varies significantly with perpendicular wavenumber, indicating that the cacsade is a highly nonlocal process. As a result of the inverse cascades, the energy dissipation rates are much lower than expected from a phenomenological model and are insufficient to maintain the temperature of the background atmosphere. We conclude that RMHD models are unable to reproduce the observed properties of the fast solar wind.

A 17 June 2011 polar jet and its presence in the background solar wind

AbstractHigh‐speed jet responses in the polar solar wind are enigmatic. Here we measure a jet response that emanates from the southern polar coronal hole on 17 June 2011 at the extreme speed of over 1200 km/s. This response was recorded from the Sun‐Earth line in Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) and Large Angle and Spectrometric Coronagraph/C2 and both Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager and COR2 coronagraphs when the three spacecraft were situated ~90° from one another. These certify the coronal 3‐D location of the response that is associated with an existing solar plume structure and show its high speed to distances of over 14 RS. This jetting is associated with magnetic flux changes in the polar region as measured by the SDO/Helioseismic and Magnetic Imager instrumentation over a period of several hours. The fastest coronal response observed can be tracked to a time near the period of greatest flux changes and to the onset of the brightest flaring in AIA. This high‐speed response can be tracked directly as a small patch of outward moving brightness in coronal images as in Yu et al. (2014) where three slower events were followed from the perspective of Earth. This accumulated jet response has the largest mass and energy we have yet seen in 3‐D reconstructions from Solar Mass Ejection Imager observations, and its outward motion is certified for the first time using interplanetary scintillation observations. This jet response is surrounded by similar high‐speed patches, but these are smoothed out in Ulysses polar measurements, we speculate about how these dynamic activities relate to solar wind acceleration.

Observations of corotating solar wind structures at radio sounding by signals of the Rosetta and Mars Express spacecraft

In the implementation of the space projects Rosetta and Mars Express, a large-scale series of experiments has been carried out on radio sounding circumsolar plasma by decimeter (S-band) and centimeter (X-band) signals of the Rosetta comet probe (from October 3 to October 31, 2010) and the Mars Express satellite of Mars (from December 25, 2010 to March 27, 2011). It was found that in the phase of ingress the spacecraft behind the Sun, the intensity of the frequency fluctuations increases in accordance with a power function whose argument is the solar offset distance of radio ray path, and when the spacecraft is removed from the Sun (the egress phase), frequency fluctuations are reduced. Periodic strong increases in the fluctuation level, exceeding by a factor of 3–12 the background values of this value determined by the regular radial dependences, are imposed on the regular dependences. It was found that increasing the fluctuations of radio waves alternates with the periodicity m × T or n × T, where m = 1/2, n = 1, аnd T is the synodic period of the Sun’s rotation (T ≈ 27 days). It was shown that the corotating structures associated with the interaction regions of different speed fluxes are formed in the area of solar wind acceleration and at distances of 6–20 solar radii already have a quasi-stationary character.

EVOLUTION OF THE PROTON VELOCITY DISTRIBUTION DUE TO STOCHASTIC HEATING IN THE NEAR-SUN SOLAR WIND

ABSTRACT We investigate how the proton distribution function evolves when the protons undergo stochastic heating by strong, low-frequency, Alfvén-wave turbulence under the assumption that β is small. We apply our analysis to protons undergoing stochastic heating in the supersonic fast solar wind and obtain proton distributions at heliocentric distances ranging from 4 to 30 solar radii. We find that the proton distribution develops non-Gaussian structure with a flat core and steep tail. For r > 5 R S ?> , the proton distribution is well approximated by a modified Moyal distribution. Comparisons with future measurements from Solar Probe Plus could be used to test whether stochastic heating is occurring in the solar-wind acceleration region.

Alfvén waves as a solar-interplanetary driver of the thermospheric disturbances.

Alfvén waves have been proposed as an important mechanism for the heating of the Sun’s outer atmosphere and the acceleration of solar wind, but they are generally believed to have no significant impact on the Earth’s upper atmosphere under quiet geomagnetic conditions due to their highly fluctuating nature of interplanetary magnetic field (i.e., intermittent southward magnetic field component). Here we report that a long-duration outward propagating Alfvén wave train carried by a high-speed stream produced continuous (~2 days) and strong (up to ±40%) density disturbances in the Earth’s thermosphere in a way by exciting multiple large-scale gravity waves in auroral regions. The observed ability of Alfvén waves to excite large-scale gravity waves, together with their proved ubiquity in the solar atmosphere and solar wind, suggests that Alfvén waves could be an important solar-interplanetary driver of the global thermospheric disturbances.

OBSERVATIONS OF ALFVÉN AND SLOW WAVES IN THE SOLAR WIND NEAR 1 AU

Magnetohydrodynamic (MHD) waves play a significant role in the processes of the solar wind acceleration and the coronal heating. Based on the in situ measurements of the WIND spacecraft, some MHD waves in the quiet solar wind are identified with two criteria: (1) the correlation coefficients between velocity and magnetic field perturbations ( and ) and between thermal pressure and magnetic pressure perturbations (δpt and δpb), and (2) the dispersion relations of MHD waves. A preliminary statistics of those MHD modes is also achieved by selecting and analyzing the WIND data of 42,279 samples (45050.4 hr) in the 23rd solar cycle. It is found that the time fraction of Alfven waves is 8% in this period, while the existence time of slow waves is 3.4%, and the fast wave is rare. The statistical result also shows that the Alfven waves have a higher time fraction in fast solar wind, while the occurrence of slow waves is higher in moderate-speed solar wind. This work will provide more clues to understanding MHD activities in the solar wind, as well as the studies of solar wind acceleration and heating.

Solar Coronal Plumes

Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL) images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV) and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features.

Nonlinear interaction between wave and convective disturbances in the solar corona

During more than two decades, many non-stationary events have been observed in the solar corona by different ground and space instruments, namely: oscillations and flows. These events play a crucial role in a solving two important problems of the solar physics: coronal heating and solar wind acceleration. Numerous observational data and theoretical works demonstrate the nonlinear interaction between waves and flows in the solar atmosphere. On other hand, nonlinear effects can also be used in coronal seismology, where a significant success leaded to many original works on linear disturbances in the coronal plasma. The nonlinear approach should make it possible to achieve more precise results.

Solar Wind Electrons Alphas and Protons (SWEAP) Investigation: Design of the Solar Wind and Coronal Plasma Instrument Suite for Solar Probe Plus

The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Solar Probe Plus is a four sensor instrument suite that provides complete measurements of the electrons and ionized helium and hydrogen that constitute the bulk of solar wind and coronal plasma. SWEAP consists of the Solar Probe Cup (SPC) and the Solar Probe Analyzers (SPAN). SPC is a Faraday Cup that looks directly at the Sun and measures ion and electron fluxes and flow angles as a function of energy. SPAN consists of an ion and electron electrostatic analyzer (ESA) on the ram side of SPP (SPAN-A) and an electron ESA on the anti-ram side (SPAN-B). The SPAN-A ion ESA has a time of flight section that enables it to sort particles by their mass/charge ratio, permitting differentiation of ion species. SPAN-A and -B are rotated relative to one another so their broad fields of view combine like the seams on a baseball to view the entire sky except for the region obscured by the heat shield and covered by SPC. Observations by SPC and SPAN produce the combined field of view and measurement capabilities required to fulfill the science objectives of SWEAP and Solar Probe Plus. SWEAP measurements, in concert with magnetic and electric fields, energetic particles, and white light contextual imaging will enable discovery and understanding of solar wind acceleration and formation, coronal and solar wind heating, and particle acceleration in the inner heliosphere of the solar system. SPC and SPAN are managed by the SWEAP Electronics Module (SWEM), which distributes power, formats onboard data products, and serves as a single electrical interface to the spacecraft. SWEAP data products include ion and electron velocity distribution functions with high energy and angular resolution. Full resolution data are stored within the SWEM, enabling high resolution observations of structures such as shocks, reconnection events, and other transient structures to be selected for download after the fact. This paper describes the implementation of the SWEAP Investigation, the driving requirements for the suite, expected performance of the instruments, and planned data products, as of mission preliminary design review.

Cut-off period for slow magnetoacoustic waves in coronal plasma structures

Context. There is abundant observational evidence of longitudinal compressive waves in plasma structures of the solar corona, which are confidently interpreted in terms of slow magnetoacoustic waves. The uses of coronal slow waves in plasma diagnostics, as well as analysis of their possible contribution to coronal heating and the solar wind acceleration, require detailed theoretical modelling. Aims. We investigate the effects of obliqueness, magnetic field, and non-uniformity of the medium on the evolution of long-wavelength slow magnetoacoustic waves guided by field-aligned plasma non-uniformities, also called tube waves. Special attention is paid to the cut-off effect due to the gravity stratification of the coronal plasma. Methods. We study the behaviour of linear tube waves in a vertical untwisted straight field-aligned isothermal plasma cylinder. We apply the thin flux tube approximation, taking into account effects of stratification caused by gravity. The dispersion due to the finite radius of the flux tube is neglected. We analyse the behaviour of the cut-off period for an exponentially divergent magnetic flux tube filled in with a stratified plasma. The results obtained are compared with the known cases of the constant Alfven speed and the pure acoustic wave. Results. We derive the wave equation for tube waves and reduce it to the form of the Klein–Gordon equation with varying coefficients, which explicitly contains the cut-off frequency. The cut-off period is found to vary with height, decreasing significantly in the low-beta plasma and in the plasma with the beta of the order of unity. The depressions in the cut-off period profiles can affect the propagation of longitudinal waves along coronal plasma structures towards the higher corona and can form coronal resonators.

THE ANGULAR DISTRIBUTION OF SOLAR WIND SUPERHALO ELECTRONS AT QUIET TIMES

The angular distribution of superhalo electrons provides important information on the generation of superhalo electrons in the solar wind. Here we present a comprehensive study of the angular distribution of ~20–200 keV superhalo electrons measured at 1 AU by the WIND 3DP instrument during quiet times from 1995 January through 2005 December. For a given energy, we define the anisotropy of superhalo electrons (with respect to the interplanetary magnetic field) as where Jout (Jin) is the observed differential flux of electrons traveling outward from (inward toward) the Sun. We found that for ~96% of the selected quiet-time samples, superhalo electrons have isotropic angular distributions, while for ~3% (~1%) of quiet-time samples, superhalo electrons have outward-anisotropic (inward-anisotropic) angular distributions. All three groups of superhalo electrons show no correlation with the local solar wind plasma, interplanetary magnetic field, turbulence, and energetic electrons accelerated/reflected at the terrestrial bow shock. For the generation of quiet-time superhalo electrons, one possibility is that they are accelerated by nonthermal processes related to the solar wind source, followed by strong scattering/reflection in the interplanetary medium. Another possibility is that these superhalo electrons are formed due to the acceleration of solar wind halo/strahl electrons, e.g., by turbulence, throughout the interplanetary medium.

Coronal Heating & Solar Wind Acceleration by Drift Waves

An alternative approach to the coronal heating problem, based on the theory of drift waves, has been proposed. The drift mode is the only mode that is able to survive the drastically different (collisional/collisionless) extremes in the different layers of the solar atmosphere. As a matter of fact, this mode is over stable, i.e. able to grow, in both of these extreme situations, and has been called the universally growing mode in the literature. In collisional plasma of the lower layers of the solar atmosphere, the drift mode grows due to the electron collisions and this can be described within the two-fluid model. In the collisionless coronal plasma, however, the mode grows due to a pure kinetic effect, viz. the electron resonance effect in the presence of a density gradient.It has been shown, with qualitative and quantitative arguments, that the drift waves have the potential to satisfy all coronal heating requirements. The basic ingredient required for the heating is the presence of density gradients in the direction perpendicular to the magnetic flux surfaces. The drift wave theory is well-established and has been explicitly verified experimentally in laboratory (fusion) plasmas, similar (hot, low-beta, highly conductive) to those in the solar atmosphere. In these circumstances, two mechanisms of the energy exchange and heating take place simultaneously: Landau damping in the direction parallel to the magnetic field, and stochastic heating in the perpendicular direction. The latter, in fact, is more effective on ions than on electrons, acts predominantly in the perpendicular direction, and heats heavy ions more efficiently than lighter ions. Moreover, for plasmas at a temperature of 1MK and beyond, the parallel wave field resulting from the drift waves exceeds the Dreicer field so that the bulk plasma species (primarily electrons) can be accelerated/decelerated by the wave in the parallel direction. In addition, this acceleration is more effective on the particles that are already more energetic, resulting in a distribution function considerably different from a Maxwellian, similar to the observed kappa-distribution in the outer solar atmosphere and in the solar wind.