共查询到20条相似文献，搜索用时 31 毫秒
1.
M. I. Stodilka 《Kinematics and Physics of Celestial Bodies》2012,28(4):162-168
Observations of the Fe I line are used to simulate spatial and temporal pressure variations in the solar photosphere. The local internal gravity waves, which are essentially structures that are quasi-periodic in space (on granular and mesogranular scales) and time and propagate along inclined paths at subsonic velocities, are isolated by appropriate filtering. The phase and group velocities of the wave trains are orthogonal; their z-projections are of the opposite sign. 相似文献
2.
Ultraviolet albedo contrasts in the Venus atmosphere are probably large-scale atmospheric waves propagating slowly with respect to the rapid cloud-top zonal winds. Using a simple theoretical model and profiles of mean wind and thermal structure based on Pioneer Venus data, we find planetary-scale gravity waves with phase velocities matching the speeds of the uv markings. We propose an upward-propagating wave and waves trapped at cloud levels as candidates to explain the observed uv features. 相似文献
3.
B. Schmieder 《Solar physics》1978,57(2):245-253
In a previous paper (Schmieder, 1977), we solved simultaneously the hydrodynamical and radiative transfer equations, so we do not have to assume any relaxation time of the atmosphere. In this paper, we use that theory to interpret photospheric observations of the Mg i line at 5172 Å.For periods between 400 and 140 s, the phase-shifts observed between velocities and the phase shifts between intensity and velocity fluctuations are explained by the existence of radiative dissipation coupled with evanescent waves or upward propagating waves, according to the frequency.For smaller periods partial or total reflections must be considered.The results relative to radiative dissipation are expressed in terms of the variation of a relaxation time with frequency through the atmosphere (10–3<5000<1). 相似文献
4.
Temperature and wind measurements extending up to 95 km have been made with rocket-grenade experiments at Natal, Brasil. On many occasions the temperature and wind speed above 60 km show uniformly spaced maxima and minima. In one series of these experiments four rockets were launched during a period of 18 hr. A comparison of these spaced observations gives an indication of the propagating character of the maxima and minima and also suggests a downward phase propagation. The perturbations in the temperature and the wind speed are similar in form but they appear to differ in phase. The wavelike appearance of the temperature profiles is believed to be caused by the adiabatic heating and cooling associated with propagating gravity waves. The wavelength obtained from these observations is 10–12 km which coincides with the expected vertical wavelength of 12 km for the dominant gravity wave in this altitude range. The observed temperature variations are also in agreement with the computed values for the prevailing conditions. 相似文献
5.
The various modes of hydrodynamic waves are considered for a model of the solar atmosphere which is based on the Bilderberg model and includes the effects of ionization. The atmosphere forms a potential well for internal gravity waves, since the stability is low at the base (near the convection) and low again in the region of partial ionization in the chromosphere. Calculations show that there are two resonant (trapped) modes of internal gravity waves for horizontal wavelengths based on the scale of the granulation. The properties of these modes are in close agreement with the two modes of oscillation observed by Frazier (1968). Trapped acoustic modes are found to have periods too short to account for the observations.Presently Visiting Fellow, Joint Institute for Laboratory Astrophysics, University of Colorado, Boulder, Colo. 相似文献
6.
Alfvénic waves are thought to play an important role in coronal heating and solar wind acceleration. Recent observations by
Hinode/SOT showed that the spicules mostly exhibit upward propagating high frequency waves. Here we investigate the dissipation
of such waves due to phase mixing in stratified environment of solar spicules. Since they are highly dynamic structures with
speeds at about significant fractions of the Alfvén phase speed, we take into account the effects of steady flows. Our numerical
simulations show that in the presence of stratification due to gravity, damping takes place in space than in time. The exponential
damping low,
\operatornameexp(-\operatornameAt3)\operatorname{exp}(-\operatorname{At}^{3}), is valid under spicule conditions, however the calculated damping time is much longer than the reported spicule lifetimes
from observations. 相似文献
7.
The difficulties of the primary interpretation of wave processes observed in the sunspot chromosphere are discussed. Frequency filtering is shown to be helpful in revealing traveling waves more clearly, which eventually affects the objectivity of estimating their parameters. The measured horizontal phase velocities are 40–70 km s?1 for umbrae and 30–70 km s?1 for penumbrae. Analysis of high-cadence observations has revealed an altitude inversion of the spatial localization of the three-minute oscillation power. It is pointed out that the pattern of umbral traveling waves is not constant and periodically gives way to the pattern of standing waves. 相似文献
8.
This study results from a coordinated experiment involving ionospheric observations of Faraday rotation between a geostationary satellite and three ground based receivers at Aberystwyth and Bournemouth in the U.K. and Lannion, France, together with incoherent scatter observations at St. Santin-Nancay, France.Quasi-periodic variations of electron content observed simultaneously at the three stations are interpreted in terms of medium scale gravity waves travelling in the ionospheric F-region. Characteristics of these waves are derived by means of a cross-correlation technique.A reverse ray tracing computation, using data on the neutral atmosphere and neutral wind stratification from the incoherent scatter observations, has been used in an attempt to locate the sources of these waves.The results show that some of the waves are almost certainly generated above 100 km altitude, probably by auroral phenomena, while the others could be produced near ground level by meteorological sources. The reverse ray tracing indicates that the latter sources are in general located in a geographic area in the vicinity of a weather disturbance. A production mechanism for these waves is proposed involving ageostrophic perturbations of the neutral wind in a jet stream. 相似文献
9.
We study the propagation of gravity waves in the martian atmosphere using a linearized one-dimensional full-wave model. Calculations are carried out for atmospheric parameters characteristic of Mars Orbiter Laser Altimeter (on Mars Global Surveyor MGS) observations of apparent gravity waves in high latitude clouds and MGS radio occultation measurements of temperature variations with height suggestive of gravity wave activity. Waves that reach the thermosphere produce fluctuations in density comparable in amplitude with the density variations detected in Mars Odyssey aerobraking data. Gravity waves of modest amplitude are found to deposit momentum and generate significant heating and cooling in the martian atmosphere. The largest heating and cooling effects occur in the thermosphere, at altitudes between about 130 and 150 km, with heating occurring at the lower altitudes and cooling taking place above. 相似文献
10.
I. K. Csada 《Solar physics》1976,47(2):555-561
The physical meaning of the photospheric short-period magnetic variation is interpreted. The motion of progressive waves along the equator with a 4.12 year circulation period may explain the basic feature of the variation. These waves have only one wavelength along the equator. The field distribution of one constituent of these waves is similar to that of a rotating dipole. The subharmonics of this dipole-wave are multipole terms circulating with periods of multiples of 4.12 years and the wave-lengths along the equator contain the same multiplying factor. The interference of the dipole and the multipole waves with a background rotation and with the 27-day Bartels rotation time results in a series of periods recorded by the earlier published analysis. The relevant linear relationship for the angular velocities has also been proved based on the magnetic observation. 相似文献
11.
Alfvénic waves are thought to play an important role in coronal heating and solar wind acceleration. Here we investigate the dissipation of such waves due to phase mixing at the presence of shear flow and field in the stratified atmosphere of solar spicules. The initial flow is assumed to be directed along spicule axis and to vary linearly in the x direction and the equilibrium magnetic field is taken 2-dimensional and divergence-free. It is determined that the shear flow and field can fasten the damping of standing Alfvén waves. In spite of propagating Alfvén waves, standing Alfvén waves in Solar spicules dissipate in a few periods. As height increases, the perturbed velocity amplitude does increase in contrast to the behavior of perturbed magnetic field. Moreover, it should be emphasized that the stratification due to gravity, shear flow and field are the facts that should be considered in MHD models in spicules. 相似文献
12.
M. I. Stodilka 《Kinematics and Physics of Celestial Bodies》2012,28(3):149-154
Using the data of observations in the Fe I line, the spatial-time variations of pressure in solar photosphere are reproduced, and local internal gravity waves are identified through the filtration. Based on the power spectra of gravity waves, some integral features of excitation and propagation of g-modes in real solar photosphere are studied which are excited by the dynamical processes near the boundary region of penetrative convection. 相似文献
13.
We study the effects of both the solar granulation and short-period oscillations on the solar profile of the Ki 7699 resonance line and its center-to-limb variations.The granular model we used is that of Nelson (1978). The wave field is obtained by adding two 30 s acoustic waves with opposite horizontal wavenumbers to allow for the center-to-limb calculations.We find that the broadening and strengthening produced by our dynamical models do not fill the gap existing between the observations and the values computed in a static atmosphere. Then, either the granular model has to be revised (in particular its r.m.s. velocities are too low) or other types of motions, like gravity waves, have to be accounted for.The upper part of the mean bisectors is affected by granulation and the lower part by waves. With some qualification concerning the data used for comparison, a satisfactory fit of the observed center-to-limb variations of the mean bisectors is obtained when both dynamical models are included and the granular velocities are increased by a factor 1.5.Currently NAS/NRC Research Associate, on leave from the Universita' di Napoli.Operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation. Partial support for the NSO is provided by the USAF under a Memorandum of understanding with the NSF. 相似文献
14.
Surface gravity waves have been used to probe flows in the two megameters beneath the photosphere using the techniques of
timedistance helioseismology. The results suggest that supergranule velocities are smaller than at the surface. The outward
flow outside a sunspot penumbra (the moat) is observed, as is an inward flow in the region beyond the moat. 相似文献
15.
O. Røyrvik 《Planetary and Space Science》1983,31(2):253-264
An investigation of the relationship between the occurrence of midlatitude sporadic-E layers and convergent points in the ion drift profiles has been made using the 430 MHz incoherent scatter radar at the Arecibo Observatory. Electron concentration profiles were obtained using a 13 baud Barker coded pulse yielding 600 m range resolution, while a 5-pulse sequence with 2.4 km range resolution was used to obtain line-of-sight ion drift velocities. With some exceptions, observed sporadic-E layers occur near convergent points in the vertical metallic ion drift profile, and vertical motions of these layers follow the vertical motions of the convergent point.Vertical motions and intensity variations of observed sporadic-E layers are due to interaction between the mean wind, tidal waves, and gravity waves of different periods producing a predominantly downward motion of the layer. However, a sudden increase in the altitude of a sporadic-E layer has been observed. This is attributed to the disappearance of the convergent point—releasing the layer—followed by an ascent of the layer to the closest overlying convergent point. 相似文献
16.
Toshiki Aikawa 《Astrophysics and Space Science》1984,104(2):405-408
It is shown that the coincidence between the pulsation periods and the critical frequencies found by Fadeyev (1982) results from strong effects of non-adiabaticity on the linear pulsation periods in low surface gravity models. If we apply the boundary condition of running waves for super-critical pulsations, it is found that the linear growth-rates are considerably affected by the boundary condition. 相似文献
17.
We examine the excitation of oscillations in the magnetic network of the Sun through the footpoint motion of photospheric magnetic flux tubes located in intergranular lanes. The motion is derived from a time series of high-resolution G-band and continuum filtergrams using an object-tracking technique. We model the response of the flux tube to the footpoint motion in terms of the Klein-Gordon equation, which is solved analytically as an initial value problem for transverse (kink) waves. We compute the wave energy flux in upward-propagating transverse waves. In general we find that the injection of energy into the chromosphere occurs in short-duration pulses, which would lead to a time variability in chromospheric emission that is incompatible with observations. Therefore, we consider the effects of turbulent convective flows on flux tubes in intergranular lanes. The turbulent flows are simulated by adding high-frequency motions (periods 5-50 s) with an amplitude of 1 km s(-1). The latter are simulated by adding random velocity fluctuations to the observationally determined velocities. In this case, we find that the energy flux is much less intermittent and can in principle carry adequate energy for chromospheric heating. 相似文献
18.
This paper provides an analysis of magneto-sonic eigenwaves travelling in magnetic plasma structures based on the Chew-Goldberger-Low approximation, for which the plasma kinetic pressure is different along and across the magnetic field. The anisotropy does not lead to the emergence of new modes. The dependence of phase velocities of the waves, trapped by a single magnetic surface, on the pressure anisotropy is investigated. For a magnetic slab with field-free surroundings, the dispersion relations for the eigenwaves are obtained. The pressure anisotropy may change dispersion relations of such modes significantly. In particular, backward waves are possible in the case of strong anisotropy. The dependences of the thresholds for the mirror and hose instabilities on the system parameters are obtained. In particular, hose and mirror instabilities of such waves are absent for some wave number regions. The results are used to obtain the eigenwave characteristics in coronal loops and chromospheric flux tubes. 相似文献
19.
Arbitrary amplitude electron acoustic (EA) solitary waves in a magnetized nonextensive plasma comprising of cool fluid electrons, hot nonextensive electrons, and immobile ions are investigated. The linear dispersion properties of EA waves are discussed. We find that the electron nonextensivity reduces the phase velocities of both modes in the linear regime: similarly the nonextensive electron population leads to decrease of the EA wave frequency. The Sagdeev pseudopotential analysis shows that an energy-like equation describes the nonlinear evolution of EA solitary waves in the present model. The effects of the obliqueness, electron nonextensivity, hot electron temperature, and electron population are incorporated in the study of the existence domain of solitary waves and the soliton characteristics. It is shown that the boundary values of the permitted Mach number decreases with the nonextensive electron population, as well as with the electron nonextensivity index, q. It is also found that an increase in the electron nonextensivity index results in an increase of the soliton amplitude. A comparison with the Vikong Satellite observations in the dayside auroral zone is also taken into account. 相似文献
20.
Properties of acoustic-gravity waves in the upper atmosphere of Venus are studied using a two-fluid model which includes the effects of wave-induced diffusion in a diffusively separated atmosphere. In conjunction with neutral mass spectrometer data from the Pioneer Venus orbiter, the theory should provide information on the distribution of wave sources in the Venus upper atmosphere. Observed wave structure in species density measurements should generally have periods ?30–35 min, small N2, CO, and O amplitudes, and highly variable phase shifts relative to CO2. A near resonance may exist between downward phase-propagating internal gravity and diffusion waves near the 165-km level at periods near 29 min. As a result, if very large He wave amplitudes are observed near this level, it will indicate that the wave source is below the 150- to 175-km level and that the exospheric temperature is close to 350°K. Wave energy dissipation may be an important mechanism for heating of the nightside Venus thermosphere. Large-density oscillations in stratospheric cloud layer constituents are also possible and may be detectable by the Pioneer Venus large probe neutral mass spectrometer. 相似文献