Deceleration Of Wind Research Articles

Effect of adiabatic deceleration on the focused transport of solar cosmic rays

view Abstract Citations (188) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effect of Adiabatic Deceleration on the Focused Transport of Solar Cosmic Rays Ruffolo, D. Abstract In the framework of focused transport theory, adiabatic deceleration arises from adiabatic focusing in the solar wind frame and from differential solar wind convection. An explicit formula is given for the deceleration of individual particles as a function of the pitch angle. Deceleration and other first-order effects of the solar wind, including convection, are incorporated into a numerical code for simulating the transport of energetic particles along the interplanetary magnetic field. We use this code to model the transport of solar flare protons. We find that including deceleration can increase the decay rate of the near-Earth intensity by 75\% more than would be expected based on advection from higher momenta, due to an interplay with diffusive processes. Improved response functions are derived for the impulsive injection of particles near the Sun, and it is found that neglecting deceleration leads to incorrect estimates of the scattering mean free path based on the intensity decay alone, especially for lower-energy particles. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175489 arXiv: arXiv:astro-ph/9408056 Bibcode: 1995ApJ...442..861R Keywords: Deceleration; Interplanetary Magnetic Fields; Particle Acceleration; Radiation Transport; Solar Cosmic Rays; Solar Protons; Solar Wind; Transport Theory; Adiabatic Flow; Astronomical Models; Convection; Particle Flux Density; Particle Trajectories; Solar Flares; Solar Physics; ACCELERATION OF PARTICLES; ISM: COSMIC RAYS; SUN: PARTICLE EMISSION; SUN: SOLAR WIND; Astrophysics E-Print: accepted for publication in Astrophys. J., 17 pp. plain TEX + 7 uuencoded-compressed-tarred PostScript figures, 1 non-PostScript figure available from david@chulkn.chula.ac.th full text sources arXiv | ADS |

Interaction of upstream diffuse ions with the solar wind

We review observations, theory, and simulations concerning the interaction of diffuse upstream ions with the solar wind. Spacecraft observations in the quasi-parallel region of the Earth's bow shock have demonstrated the deceleration and deflection of the solar wind in the region of diffuse upstream ions and ULF waves. This can, in principle, be explained by the pressure gradient force exerted by the diffuse ions on the solar wind. On the micro-scale this coupling is due to electromagnetic ion/ion beam instabilities between the diffuse ions and the solar wind. Since the time scale for the coupling is of the same order as the convection time of the solar wind through the foreshock region, the deceleration can only be studied by a collisionless, self-consistent approach. We report on recent hybrid simulations of collisionless shocks, which demonstrate the close connection between diffuse ions, upstream waves and pulsations, and their effect on the solar wind.

A study of the solar wind deceleration in the Earth's foreshock region

Previous observations have shown that the solar wind is decelerated and deflected in the earth's upstream region populated by long-period waves /1–3/. This deceleration is correlated with the ‘diffuse’ but not with the ‘reflected’ ion population. The speed of the solar wind may decrease tens of km/s in the foreshock region. The solar wind dynamic pressure exerted on the magnetopause may vary due to the fluctuation of the solar wind speed and density in the foreshock region. In this study, we examine this solar wind deceleration and determine how the solar wind deceleration varies in the foreshock region.

On the problem of the Martian atmosphere dissipation: Phobos: 2 TAUS Spectrometer results

The measurements of proton spectra obtained by the TAUS spectrometer on board the Phobos 2 spacecraft in elliptical orbits near Mars are presented. A strong deceleration of the solar wind upstream of the Martian bow shock was revealed. It can be caused by the mass loading of the plasma flow by ions originating from the hot oxygen/hydrogen corona of Mars and/or by protons specularly reflected from the bow shock. In the first case the deceleration of the solar wind by about 100 km/s implies that the hot oxygen corona of Mars could be several times denser than it was anticipated to be (at least during the observation period that was close to solar cycle maximum). Furthermore, the loss of planetary oxygen through the corona appears to be the main process of oxygen loss from Mars. The upper limit of loss rate for such a process is determined to be 1026 oxygen atoms or 2.5 kg of oxygen per second.

Eolian Event Stratigraphy--A Conceptual Framework

A basis for eolian event stratigraphy is to distill the impact of events into fundamental processes and products. For accumulation (net deposit through time) to occur, the sediment budget must be positive. If the sediment budget becomes neutral or negative, accumulation ceases and a bypass or erosional super bounding surface, respectively, forms capping the genetic unit. Within the three types of eolian systems (dry, wet, stabilized), the mechanisms of accumulation and super-surface formation differ. In the dry system, accumulation occurs because of areal deceleration of sand-carrying winds. Because of dune-interdune flow conditions, accumulation begins when interdune flats are closed, requiring sand supply, time, and conditions for dune growth at the expense of interdune flats. In the wet system, accumulation of dune and interdune deposits occurs by trapping with a rising water table. Accumulations vary with the nature of the water table rise, proportion of dunes and interdune flats, and interdune topography. In the stabilized system, accumulation occurs with rapid stabilization of elements of active eolian systems; super surfaces form when the causes of stabilization cease. The eolian rock record consists of preserved accumulations and super surfaces. Accumulation space is distinct from preservation space. Preservation space is made by subsidence andmore » water table rise. Without preservation space, an unconformity results. The dominance of subsidence versus water table rise is reflected in dry and wet accumulations respectively, such as the Jurassic Navajo and Entrada sandstones.« less

Steepening of kinetic magnetosonic waves into shocklets: Simulations and consequences for planetary shocks and comets

Numerical simulations are used to investigate the nonlinear evolution of oblique low‐frequency electromagnetic (kinetic magnetosonic) waves, which have been observed upstream of planetary bow shocks and at comet Giacobini‐Zinner. The observations show that the waves are elliptically polarized and have a sinusoidal form when their amplitude is small, but they become steepened and linearly polarized as they grow in amplitude. These waves have been referred to as shocklets. A high‐frequency whistler wave packet is commonly seen at the steepened edge of the shocklets. To investigate the generation and the nonlinear evolution of kinetic magnetosonic waves in a self‐consistent manner, an electromagnetic hybrid code (particle ions, fluid electrons) is used in two stages. In the first stage, a large nonperiodic box is utilized to generate a series of small‐amplitude waves, one of which is then isolated for the second stage of the simulations, in which much higher resolution is employed to investigate further growth and the nonlinear evolution of the isolated wave. The results show that the original small‐amplitude elliptically polarized wave grows and steepens, such that its polarization changes and becomes somewhat linear. The steepening process is associated with the coherent generation of a broad spectrum of waves on the magnetosonic whistler branch, which propagate at various phase and group velocities. As a result, the waveform spreads in space, causing the change in polarization. Because the phase and group velocities of the whistler waves increase with frequency, the high end of the spectrum generated during the steepening propagates ahead of the steepened front and forms a high‐frequency wave packet, whose amplitude decreases with distance from the steepened edge of the magnetosonic wave. This drop in amplitude is due to the transitory nature of the wave packet. By investigating the behavior of the solar wind upstream and within the steepened wave it is shown that these waves are very similar to subcritical dispersive shock waves and can result in local heating and deceleration of the solar wind. This interpretation of the steepened waves has a number of implications for planetary bow shocks and the nature of the transition region at comet Giacobini‐Zinner. The presence of shocklets upstream of a planetary bow shock can modify its local structure by changing the solar wind Mach number and temperature, or by colliding with the shock. Further, it is suggested that the transition region at comet Giacobini‐Zinner consists of solar wind plasma which has been heated and decelerated by a series of steepened waves, until it becomes subsonic in the comet's rest frame.

Illuminating a red supergiant wind around SN 1987A

A recently discovered light echo at a radius of about 9" from SN 1987A is interpreted as the result of a circumstellar shell at a radius of 4.5 pc from the supernova. The shell may have its origin in the deceleration of the presupernova red supergiant wind by the pressure of the surrounding medium. The required pressure is p/k ~ 10^3^ cm^-3^ K. The echo is predicted to expand and contract over the next 30 yr with a declining surface brightness and a broadening of its width. Colors of the echo compared to those of the larger echoes may show differences in the wavelength dependence of scattering of the circumstellar grains compared to interstellar grains. The evolution of the flux from the echo will give information on the average scattering phase function of the grains. A significant linear polarization of the echo light is expected, and the evolution of the polarization will give information on the dependence of polarization on scattering angle. The model predicts the presence of an undisturbed red supergiant wind inside of the echo shell. Supernova light scattered in the wind is expected to have half-intensity radius of 2" at present and may have been detected. The wind echo should expand as (t - t_e_), where t_e_ is the time of maximum light, and its flux should decline as (t - t_e_)^-2^.

Constrains on gravity wave induced diffusion in the middle atmosphere

A review of the important constraints on gravity wave induced diffusion of chemical tracers, heat, and momentum is given. Ground-based microwave spectroscopy measurements of H2O and CO and rocket-based mass spectrometer measurements of Ar constrain the eddy diffusion coefficient for constituent transport (K zz ) to be (1 – 3) × 105 cm2s-1 in the upper mesosphere. Atomic oxygen data also limits K zz to a comparable value at the mesopause. From the energy balance of the upper mesosphere the eddy diffusion coefficient for heat transport (D H ) is, at most 6 × 105 cm2s-1 at the mesopause and decreasing substantially with decreasing altitude. The available evidence for mean wind deceleration and the corresponding eddy diffusion coefficient for momentum stresses (D M ) suggests that it is at least 1 × 106 cm2s-1, in the upper mesosphere. Consequently the eddy Prandtl number for macroscopic scale lengths is > 3.

Magnetospheric convection during quiet or moderately disturbed times

We review the main processes which contribute to the large‐scale plasma circulation in the environment of the Earth during quiet times or during reasonably stable magnetic conditions (when the concept of average pattern of plasma convection can make sense). Since field‐aligned currents are the way by which plasma motion perpendicular to the magnetic field is transmitted between the remote regions (solar wind, magnetosphere) and the ionosphere, we describe the processes driving plasma convection as processes generating field‐aligned currents. The electric field distribution will then result as a consequence of the coupling between the regions generating field‐aligned current and the circuit constituted by the ionospheric conducting layer. We discuss the effects of horizontal gradients of ionospheric conductivities on the resulting electric field distribution. As concerns the mechanisms which drive field‐aligned currents, the convective derivative of plasma flow vorticity, produced by the flow deceleration of the solar wind, is believed to be the main generator for region 1 currents, whereas the azimuthal pressure gradients within the region of closed field lines are believed, in the classical view, to be the main generators for region 2 currents. In turn, we recognize two kinds of sources for producing azimuthal pressure gradients in the region of closed field lines, and we illustrate them in the framework of linear theory. These are (1) the adiabatic distortion of the distribution of energetic trapped plasma from azimuthally symmetric distribution in the presence of an electric field and (2) particle losses undergone by the plasma while it is azimuthally convected.

A kinetic study of solar wind mass loading and cometary bow shocks

A detailed numerical study is conducted to understand the kinetic processes associated with solar wind mass loading due to pickup of cometary ions and the formation of cometary bow shocks. Because in this study we are most interested in phenomena which take place over time and spatial scales associated with ion dynamics, electrons are treated as a massless fluid. On the other hand, solar wind protons and heavy cometary ions are treated kinetically. It is found that solar wind deceleration and pickup of cometary ions take place through both the macroscopic electromagnetic fields embedded in the solar wind, as well as the microscopic fields associated with low‐frequency electromagnetic waves that are generated by the unstable velocity distribution function of the cometary ions. These electromagnetic waves can grow to very large amplitudes and their nonlinear evolution is controlled by their wave normal angle. At parallel propagation where the waves are noncompressional, parametric instabilities seem to be operative, while the oblique, compressional waves are found to steepen and form shocklets. As for the nature of cometary bow shocks, three different regimes are found, based on the shock normal angle. For shock normal angles at or near 90° (quasi‐perpendicular), a typically thin transition region (shock) is formed through steepening of fast magnetosonic pulses. This shock is a pure proton shock in that no sharp change in density or velocity of the cometary ions is observed across the shock. At intermediate shock normal angles (oblique), a much wider transition region is seen where the solar wind is gradually heated and decelerated. This region, whose width is much larger than the gyroradius of cometary ions, is associated with a high level of turbulence due to ion pickup instabilities and is unlike a typical fast magnetosonic shock. Finally, at small shock normal angles (quasi‐parallel), a narrow transition region is found which is similar to a parallel terrestrial shock. The formation of this shock is not due to wave steepening but rather is the result of scattering and heating of the solar wind protons by the large‐amplitude electromagnetic waves that are generated through the relative drift between the protons and the cometary ions. These results are compared and shown to be in qualitative agreement with the recent observations at comets.

Alfv�n wave plasma turbulence during solar wind-comet interaction

The large differences in drift velocities between the solar wind protons and the picked-up ions of cometary origin cause the Alfven waves (among others) to become unstable and generate turbulence. A self-consistent treatment of such instabilities has to take into account that these cometary ions affect the solar wind plasma in a decisive way. With the help of a previously developed formalism one finds the correct Alfven instability criterion, which is here nondispersive, in contrast to recent calculations where the cometary ions are treated as a low-density, high-speed, and non-neutral beam through an otherwise undisturbed solar wind. The true bulk speed of the combined solar wind plus cometary ion plasma clearly shows the mass-loading and deceleration of the solar wind near the cometary nucleus, indicating a bow shock. The instability criterion is also used to determine the region upstream where the Alfven waves can be unstable, based upon recent observations near comet Halley.

Energization of positive ions in the cometary foreshock region

The energization of positive ions in front of a cometary bow shock is investigated. Ions produced by ionization of the cometary neutrals interact with the solar wind protons to produce, among other waves, large amplitude oscillations of the ambient magnetic field. Such oscillations are convected towards the comet at the unperturbed solar wind speed far from the shock and at a lower speed closer to the shock (due to the solar wind mass loading) ; hence, they can energize the suprathermal ions by Fermi acceleration. The spatial extension of the acceleration region is of the order of 10 6 km and the resulting ion energy spectrum is harder than in the Earth's bow shock case. The energization of cometary ions produces an additional deceleration of the solar wind, such that the cometary bow shock of Halley-type comet may be regarded as a “cosmic ray shock”.

A sudden warming in the middle atmosphere of the southern hemisphere

AbstractThis paper presents a case study of a wave‐mean flow interaction, or minor warming, near the southern hemisphere stratopause for 15‐30 July 1974. the analysis is based mainly on data from the selective chopper radiometer carried by Nimbus 5.A deceleration of the zonal mean wind of 70 m s‐1 from 20 to 25 July is observed in middle latitudes at 0.5 mb, with an acceleration further south. the polar vortex is, however, not disrupted.Eliassen‐Palm cross‐sections are presented for the event and a good correlation found between the E‐P flux convergence and the deceleration. the channelling of the E‐P fluxes from the tropopause to the convergent region is in broad agreement with the distribution of refractive index but there is a region of E‐P flux divergence at high levels in polar latitudes suggesting a source of wave activity there.The residual circulation is calculated both from the momentum budget and from an omega equation, both methods diagnosing a region of modest equatorward flow near the region of E‐P flux divergence embedded in the stronger poleward flow elsewhere.Maps of potential vorticity on the isentropic surface of 0 = 1640 K are presented and the evolving pattern related to zonal mean and isobaric descriptions. the event is shown to be associated with an incursion of low latitude air into middle latitudes with a corresponding irreversible mixing of potential vorticity reminiscent of the ‘wave breaking’ in northern hemisphere events reported by McIntyre and Palmer (J. At. Ter. Ph., 46, 825), but of much smaller amplitude.

Wave Transience and Wave-Mean Flow Interaction Caused by the Interference of Stationary and Traveling Waves

Abstract Madden and Labitzke reported an exceptionally large 18-day traveling wave 1 in the troposphere and lower stratosphere during January 1979. Observations from the LIMS instrument on Nimbus 7 indicate that during this period the regular westward phase regression extended upward as far as the lower. mesosphere. Alternate destructive and constructive interference between the transient wave and the time mean wave 1 resulted in large variations in wave amplitude with time. Analysis of the zonal wind deceleration during the minor sudden warming of that month indicates that this wave 1 transience was the primary cause of the warming. Prior to the large wave 1 amplitude growth immediately preceding the sudden warming (18-22 January), there were two other pulses of exceptionally large wave 1 amplitude (>2000 m peak amplitude) separated by about ten days. Thew earlier pulses were not associated with the traveling wave, which first appeared around 10 January. The change in the zonal wind associated with these...

Energetic positive ions in the cometary “foreshock” region

Ions produced by ionization of the cometary neutrals interact with the solar wind protons to produce large amplitude oscillations of the ambient magnetic field. Such oscillations are convected towards the comet at the unperturbed solar wind speed far from the shock and at a lower speed closer to the shock (due to the solar wind mass loading); hence, they can energize the incoming ions by Fermi acceleration. The spatial extension of the acceleration region is of the order of 10 6 km and the resulting energy spectrum is harder than in the Earth's bow shock case. The energization of cometary ions produces an additional deceleration of the solar wind. It is suggested that Comet Halley may be the most efficient “cosmic ray shock” in the solar system.

An Observational Study of the Upper-Tropospheric Vorticity Fields in GATE Cloud Clusters

Abstract A large-amplitude asymmetric vorticity couplet has been observed in the upper troposphere near a lame cloud cluster in GATE (GARP Atlantic Tropical Experiment) on 5 September 1974. The couplet consists of a cyclonic center to the north of the cluster and an anticyclonic center to the south. The couplet is a result of the deceleration of the upper-tropospheric easterly winds in a region near the center of the cluster. These features also appear on a composite of large slow-moving clusters occurring during Phase 3 of GATE. Vorticity budget analysis shows that the couplets are produced by subcluster-scale process and, to a lesser degree, by cluster-scale twisting. On the basis of this finding and on the basis of the three-dimensional structure of horizontal momentum fields, it is suggested that a part of the deceleration producing the couplet is a result of momentum redistribution by subcluster-scale circulations (such as cumulonimbi or mesoscale cloud lines). The composite wind fields of the large ...

Solar wind deceleration and MHD turbulence in the Earth's foreshock region: ISEE 1 and 2 and IMP 8 observations

The interaction of the solar wind with ions backstreaming from the earth's bow shock is investigated using plasma and magnetic field measurements on ISEE 1 and 2 and IMP 8 at widely separated positions in the earth's foreshock. This technique separates temporal and spatial variations within the foreshock. It is found that the solar wind acceleration associated with backstreaming ions is correlated with the amplitude of the MHD turbulence and that the largest decelerations are seen close to the bow shock. The density of the backstreaming ion beam is strongly correlated with distance from the shock and decreases by about a factor of 3 in a distance of about 3 RE.

Parameterization of IR cooling in a middle atmosphere dynamics model: 1. Effects on the zonally averaged circulation

A computationally efficient two‐stream parameterization of IR cooling is developed for a middle atmosphere dynamics model. The parameterization combines the monochromatic feature of an emissivity formulation with the computational simplicity of a single spatial integral to evaluate the monochromatic transfer equation. Our calculations show strong radiative control of the mesopause region (radiative relaxation rate > [5 days]−1) and the need for substantial deceleration of the mean zonal winds (∼40 m s−1 day−1) Calculated temperatures show good agreement in the summer hemisphere where planetary wave activity is negligible, but in the polar night of the winter hemisphere they are ∼30°K too cold which suggests planetary wave heating must make up the deficit. With observed ozone densities our globally averaged radiative equilibrium temperatures in the 65–75 km region are too cold and an additional heat source ∼1°K day−1 is required.

成層圏突然昇温時のEliassen-Palmフラックスによるプラネタリー波の記述および波に対する平均流の影響

Eliassen-Palm (E-P) flux whose direction is interpreted as that of planetary wave propagation in the meridional plane, is used for diagnosing planetary waves for the 1973 sudden stratospheric warming. E-P flux by zonal wavenumber 1 component was focused into the polar stratosphere prior to the circulation reversal. By the focusing there occurred the intense convergence of E-P flux which embodies the forcing of waves on mean flow. The convergence brought about the intense deceleration of mean zonal wind and the poleward residual mean meridional flow in the stratosphere.A discussion is made of the "refractive index" Q defined as mean quasi-geostrophic potential vorticity gradient divided by mean zonal wind. It is the maximum of Q which was situated in the polar stratosphere prior to the warming that is interpreted as a main factor which determines the switching of E-P flux from equatorward to poleward. After the easterly winds appeared in the polar stratosphere the convergence of E-P flux concentrated around the zero wind line, suggesting that the mechanism of critical layer absorption was driven.

Deceleration of the solar wind in the Earth's foreshock region: Isee 2 and Imp 8 observations

The deceleration of the solar wind, in the region of the interplanetary space filled by ions backstreaming from the earth's bow shock and associated waves, is studied using a two‐spacecraft technique. This deceleration, which is correlated with the ‘diffuse’ but not with the ‘reflected’ ion population, depends on the solar wind bulk velocity: at low velocities (below 300 km/s) the velocity decrease is ∼5 km/s, while at higher velocities (above 400 km/s) the decrease may be as large as 30 km/s. Along with this deceleration the solar wind undergoes a deflection by ∼1° away from the direction of the earth's bow shock. The energy balance shows that the kinetic energy loss far exceeds the thermal energy which is possibly gained by the solar wind; therefore at least part of this energy must go into waves and/or into the backstreaming ions.