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1.
We propose a model three-dimensional current system for the magnetospheric substorm, which can account for the new findings of the field-aligned and ionospheric currents obtained during the last few years by using new techniques. They include (1) the ionospheric currents at the auroral latitude deduced from the Chatanika incoherent scatter radar data, (2) the field-aligned currents inferred from the vector magnetic field observations by the TRIAD satellite and (3) the global distribution of auroras with respect to the auroral electrojets appearing in DMSP satellite photographs. The model current system is also tested by a computer model calculation of the ionospheric current pattern. It is shown that the auroral electrojets have a strong asymmetry with respect to the midnight meridian. The westward electrojet flows along the discrete aurora in the evening sector, as well as along the diffuse aurora in the morning sector. The eastward electrojet flows equatorward of the westward electrojet in the evening sector. It has a northward component and joins the westward electrojet by turning westward across the Harang discontinuity. Thus, the latitudinal width of the westward electrojet in the morning sector is much larger than that in the evening sector. The field-aligned currents, consisting of two pairs of upward and inward currents (one is located in the morning sector and the other in the evening sector), are closed neither simply by the east-west ionospheric currents nor by the north-south currents, but by a complicated combination of the north-south and east-west paths in the ionosphere. The magnetospheric extension of the current system is also briefly discussed.  相似文献   

2.
The process of measuring granular velocity fields with an instrument having finite spectral and spatial resolution is investigated for the case that (1) a weak Fraunhofer line is used, (2) the velocity is constant with height in the solar atmosphere, (3) the original Doppler shifts are of the same order of magnitude as the intrinsic width of the line (width observed with infinitely high spectral and spatial resolution), (4) continuum brightness and line strength fluctuations are superimposed onto the velocity field.It is shown that using a spectral instrumental profile which is large compared to both the intrinsic line width and the rms Doppler shifts (as in the case of filtergrammes), the shift-induced brightness signal is always a linear function of the shift and corrections for finite spatial resolution can be applied to the measured shifts in the usual straightforward way.If the spectral instrumental profile is not large (as in the case of slit-spectrogrammes), the observed line profile is shown to depend upon the spatial resolution as well. It is altered (broadened, made asymmetric) by (1) spatially unresolved Doppler shifts and higher moments of the Doppler shift amplitude distribution, (2) by local correlation between continuum brightness, line strength, and velocity fluctuation. A value of the Doppler shift which is unaffected by nonlinearities, can be measured at a certain position in the line wing. Knowledge of the intrinsic line width is necessary, however, to determine this position, as well as the order of magnitude of the nonlinearity effects producing asymmetries in the observed line profile. Finally, the conditions are discussed under which a complete deconvolution of a spectrum could be accomplished.On leave from Fraunhofer Institut, Freiburg.  相似文献   

3.
An empirical model has been developed to reproduce the drift of the spectrum recorded by the EIS on Hinode using instrumental temperatures and relative motion of the spacecraft. The EIS spectrum shows an artificial drift in wavelength dimension in sync with the revolution of the spacecraft, which is caused by temperature variations inside the spectrometer. The drift amounts to 70 km s−1 in Doppler velocity and introduces difficulties in velocity measurements. An artificial neural network is incorporated to establish a relationship between the instrumental temperatures and the spectral drift. This empirical model reproduces observed spectrum shift with an rms error of 4.4 km s−1. This procedure is robust and applicable to any spectrum obtained with EIS, regardless of the observing field. In addition, spectral curvatures and spatial offset in the north – south direction are determined to compensate for instrumental effects.  相似文献   

4.
Atmospheric expansion through Joule heating by horizontal electric fields   总被引：1，自引：0，他引：1  
Incoherent scatter measurements made along a magnetic field line into aurora during a period of high electric field in the recovery phase of a substorm show (1) considerably increased electron densities well above the normal F-region maximum, and (2) field-aligned plasma drifts that increase with altitude. A model invoking atmospheric expansion through Joule heating by the horizontal electric field driving the auroral electrojet is used to explain the observations. From this study it is concluded that during magnetically disturbed periods (1) Joule heating by the auroral electrojet raises the neutral temperature and density in the auroral zone ionosphere at F-region heights, (2) ionization formed by the aurora is transported upward by the expanding atmosphere, at times producing an appreciable increase in lower exospheric plasma densities on the field lines containing the aurora, and (3) combined satellite, radar, and optical observations during periods of aurora and high electric field could provide measured F-region collision frequencies.  相似文献   

5.
The adiabatic motion of charged particles in the magnetosphere has been investigated using Mead-Fairfield magnetospheric field model (Mead and Fairfield, 1975). Since the motion of charged particles in a dipolar field geometry is well understood, we bring out in this paper some important features in characteristic motion due to non-dipolar distortions in the field geometry. We look at the tilt averaged picture of the field configuration and estimate theoretically the parameters like bounce period, longitudinal invariant and the bounce averaged drift velocities of the charged particle in the Mead-Fairfield field geometry. These parameters are evaluated as a function of pitch angle and azimuthal position in the region of ring current (5 to 7 Earth radii from the centre of the Earth) for four ranges of magnetic activity. At different longitudes the non-dipolar contribution as a percentage of dipole value in bounce period and longitudinal invariant show maximum variation for particles close to 90° pitch angles. For any low pitch angle, these effects maximize at the midnight meridian. The radial component of the bounce averaged drift velocity is found to be greatest at the dawn-dusk meridians and the contribution vanishes at the day and midnight meridians for all pitch angles. In the absence of tilt-dependent terms in the model, the latitudinal component of the drift velocity vanishes. On the other hand, the relative non-dipolar contribution to bounce averaged azimuthal drift velocity is very high as compared to similar contribution in other characteristic parameters of particle motion. It is also shown that non-dipolar contribution in bounce period, longitudinal invariant and bounce averaged drift velocities increases in magnitude with increase in distance and magnetic activity.  相似文献   

6.
Precise measurements of Doppler shifts of lines in stellar spectra allowing the radial velocity to be measured are an important field of astrophysical studies. A remarkable feature of the Doppler spectroscopy is the possibility to reliably measure quite small variations of the radial velocities (its acceleration, in fact) during long periods of time. Influence of a planet on a star is an example of such a variation. Under the influence of a planet rotating around a star, the latter demonstrates periodic motion manifested in the Doppler shift of the stellar spectrum. Precise measurements of this shift made it possible to indirectly discover planets outside the Solar system (exoplanets). Along with this, searching for Earth-type exoplanets within the habitable zone is an important challenge. For this purpose, accuracy of spectral measurements has to allow one to determine radial velocity variations at the level of centimeters per second during the timespans of about a year. Suchmeasurements on the periods of 10–15 years also would serve as a directmethod for determination of assumed acceleration of the Universe expansion. However, the required accuracy of spectroscopic measurements for this exceeds the possibilities of the traditional spectroscopy (an iodine cell, spectral lamps). Methods of radical improvement of possibilities of astronomical Doppler spectroscopy allowing one to attain the required measurement accuracy of Doppler shifts are considered. The issue of precise calibration can be solved through creating a system of a laser optical frequency generator of an exceptionally high accuracy and stability.  相似文献   

7.
Analyses of the widths and shifts of optically thin emission lines in the ultraviolet spectrum of the active dwarf ε Eri (K2 V) are presented. The spectra were obtained using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer . The linewidths are used to find the non-thermal energy density and its variation with temperature from the chromosphere to the upper transition region. The energy fluxes that could be carried by Alfvén and acoustic waves are investigated, to test their possible roles in coronal heating. Acoustic waves do not appear to be a viable means of coronal heating. There is, in principle, ample flux in Alfvén waves, but detailed calculations of wave propagation are required before definite conclusions can be drawn concerning their viability. The high sensitivity and spectral resolution of the above instruments have allowed two-component Gaussian fits to be made to the profiles of the stronger transition region lines. The broad and narrow components that result share some similarities with those observed in the Sun, but in ε Eri the broad component is redshifted relative to the narrow component and contributes more to the total line flux. The possible origins of the two components and the energy fluxes implied are discussed. On balance our results support the conclusion of Wood, Linsky & Ayres, that the narrow component is related to Alfvén waves reaching to the corona, but the origin of the broad component is not clear.  相似文献   

8.
The relative radar reflectiveness of Saturn's classical ring sections were estimated from delay-Doppler observations made at 12.6-cm wavelength. The A and B rings are responsible for most, if not all, of the radar echo. The average radar reflectivity per unit projected area of the A ring is nearly (～90%) as large as that of the B ring. The outer half of the B ring contains the most reflective part of the ring system. There is no firm evidence for detection of radar backscattering from particles interior to the B ring, exterior to the A ring, or from the planet itself. The radar reflectivity of the C ring is certainly no more than one-half that of the B ring, and probably is much less. Unexpectedly large amounts of power at Doppler shifts near the center of the echo spectrum, previously reported at both λ3.5 and λ12.6 cm for ring-plane tilt angles δ ≥ 24.4°, are not apparent in λ3.5- or 12.6-cm spectra obtained at δ ≤ 21.4°.  相似文献   

9.
The simulated Doppler shifts of the solar Mg I Fraunhofer line produced by scattering on the solar light by asteroidal, cometary, and trans-neptunian dust particles are compared with the shifts obtained by Wisconsin H-Alpha Mapper (WHAM) spectrometer. The simulated spectra are based on the results of integrations of the orbital evolution of particles under the gravitational influence of planets, the Poynting-Robertson drag, radiation pressure, and solar wind drag. Our results demonstrate that the differences in the line centroid position in the solar elongation and in the line width averaged over the elongations for different sizes of particles are usually less than those for different sources of dust. The deviation of the derived spectral parameters for various sources of dust used in the model reached maximum at the elongation (measured eastward from the Sun) between 90° and 120°. For the future zodiacal light Doppler shifts measurements, it is important to pay a particular attention to observing at this elongation range. At the elongations of the fields observed by WHAM, the model-predicted Doppler shifts were close to each other for several scattering functions considered. Therefore the main conclusions of our paper do not depend on a scattering function and mass distribution of particles if they are reasonable. A comparison of the dependencies of the Doppler shifts on solar elongation and the mean width of the Mg I line modeled for different sources of dust with those obtained from the WHAM observations shows that the fraction of cometary particles in zodiacal dust is significant and can be dominant. Cometary particles originating inside Jupiter's orbit and particles originating beyond Jupiter's orbit (including trans-neptunian dust particles) can contribute to zodiacal dust about 1/3 each, with a possible deviation from 1/3 up to 0.1-0.2. The fraction of asteroidal dust is estimated to be ∼0.3-0.5. The mean eccentricities of zodiacal particles located at 1-2 AU from the Sun that better fit the WHAM observations are between 0.2 and 0.5, with a more probable value of about 0.3.  相似文献   

10.
In movies of H spectra taken with the slit tangential to the solar limb we can observe motion of spicules both parallel to the slit and along the line of sight. We find strong evidence that, although most motion is along the axis of the spicule, some features move at right angles to their axes. Several cases were observed of features separating into two widely-split components. A power spectrum of the changes of Doppler shifts with time shows the 1/frequency characteristics of random motion.  相似文献   

11.
We study properties of Fe K lines of a large sample of Seyfert 1s observed by ASCA . Fits with power laws and Gaussian lines yield the average linewidth and equivalent width of 0.22±0.03 keV and 0.13±0.01 keV, respectively. Thus, the typical lines are weak and narrow. We then obtain the average line profile of all our spectra, and find it to consist of a narrow core and blue and red wings, with the red wing being much weaker than that of e.g. MCG −6-30-15. We obtain three average spectra of Seyferts grouped according to the hardness, and find the equivalent width of the core (originating in a remote medium) to be ≃50 eV in all three cases. The wings are well fitted by a broad line from a disc with strong relativistic effects. Its equivalent width correlates with the slope, increasing from ∼70 eV for the hardest spectrum to ∼120 eV for the softest one. The inner disc radius decreases correspondingly from ∼40 to ∼10 gravitational radii, and the fitted disc inclination is ∼45°. The obtained correlation between the slope and the strength of the broad Fe K line is found to be consistent with the previously found correlation of the slope and Compton reflection.  相似文献   

12.
The Extreme ultraviolet Imaging Spectrometer (EIS) onboard Hinode is the first solar telescope to obtain wide-slit spectral images that can be used for detecting Doppler flows in transition region and coronal lines on the Sun and to relate them to their surrounding small-scale dynamics. We select EIS lines covering the temperature range 6×104 to 2×106 K that give spectrally pure images of the Sun with the 40-arcsec slit. In these images Doppler shifts are seen as horizontal brightenings. Inside the image it is difficult to distinguish shifts from horizontal structures but emission beyond the image edge can be unambiguously identified as a line shift in several lines separated from others on their blue or red side by more than the width of the spectrometer slit (40 pixels). In the blue wing of He ii, we find a large number of events with properties (size and lifetime) similar to the well-studied explosive events seen in the ultraviolet spectral range. Comparison with X-Ray Telescope (XRT) images shows many Doppler shift events at the footpoints of small X-ray loops. The most spectacular event observed showed a strong blue shift in the transition region and lower corona lines from a small X-ray spot that lasted less than 7 min. The emission appears to be near a cool coronal loop connecting an X-ray bright point to an adjacent region of quiet Sun. The width of the emission implies a line-of-sight velocity of 220 km s−1. In addition, we show an example of an Fe xv shift with a velocity of about 120 km s−1, coming from what looks like a narrow loop leg connecting a small X-ray brightening to a larger region of X-ray emission.  相似文献   

13.
Slope probability densities were derived from the power spectra of radar echoes from Mars using integral inversion. The inverse problem is ill-posed; that is, small changes in the data can lead to large changes in the solution. We describe a method of stabilizing the inversion, which was necessary for echoes with signal-to-noise power spectral densities on the order of unity, and for those with broad spectral distributions. The resulting slope probabilities usually consisted of a component due to quasi-specular reflection which decreased rapidly with tilt, plus a broad, slowly decreasing, “diffuse” component due to scattering from (1) surface scales small compared with a radar wavelength, or (2) larger features with high slopes. In the absence of more complete polarization measurements, we are unable to In the absence of more complete polarization measurements, we are unable to distinguish between these possibilities. Root mean square tilts have been determined separately for the two cases. For case (1), values of rms tilt associated with surface features responsible for the quasi-specular echo are normally less than 3°; for case (2), values greater than 8° are common. Knowledge of the depolarization of radar returns would help distinguish between these possibilities.  相似文献   

14.
To infer velocities and longitudinal magnetic fields from Dopplergram and magnetogram signals obtained by the Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission, one must know the width of the observed emission line. Although the instrument control system provided for a line-width calibration feature which utilized periodically commanded shifts of the line, it was not always used. However, it is possible to use the time-varying line-of-sight component of the orbital velocity of the spacecraft as a means of calibrating the line width for each pixel in a raster. Such a method based on a least-squares fit of the observed Doppler signal to the line-of-sight component of the spacecraft velocity is described here; it then applied to magnetogram observations. As background, the theoretical expressions for the interpretation of the observed Dopplergram and magnetogram signals for both wide and narrow exit slits are also summarized.  相似文献   

15.
Electron spectra measured on a rocket flight AMD-VB-34 through and over a series of auroral forms at Fort Churchill, Canada on 23 January 1974 show what can be described as inverted V events. Comparison with all-sky photographs identify clearly three of the events with three periods when the aurora was successively to the south of, underneath and to the north of the field line on which the rocket was located. In each of these events the electron spectrum changed from one resembling a Maxwellian of characteristic energy 3–4 keV on either side of the form to a nearly flat one out to 18 keV while the rocket was over the form. There was no indication of any spectral peaks in these spectra, which were confined to pitch angles of 70–90°. During descent the rocket moved slowly from over a quiet, fading arc to the equatorward side. Detailed electron observations show the spectrum returning to a Maxwellian distribution with steadily decreasing characteristic energy to 2 keV.  相似文献   

16.
The observations of the prompt emission of gamma ray bursts (GRB) by GLAST Burst Monitor (GBM), on board Fermi Gamma-ray Space Telescope, suggest the presence of a significant thermal spectral component, whose origin is not well understood. Recently, it has been shown that for long duration GRBs, the spectral width as defined as the logarithm of the ratio of the energies at which the spectrum falls to half its peak value, lie in the range of 0.84–1.3 with a median value of 1.07. Thus, while most of the GRB spectra are found to be too narrow to be explained by synchrotron emission from an electron distribution, they are also significantly broader than a blackbody spectrum whose width should be 0.54. Here, we consider the possibility that an intrinsic thermal spectrum from a fire-ball like model, may be observed to be broadened if the system undergoes a rapid temperature evolution. We construct a toy-model to show that for bursts with durations in the range 5–70 s, the widths of their 1 second time-averaged spectra can be at the most ≲ 0.557. Thus, while rapid temperature variation can broaden the detected spectral shape, the observed median value of ∼ 1.07 requires that there must be significant sub-photospheric emission and/or an anisotropic explosion to explain the broadening for most GRB spectra.  相似文献   

17.
Optical spectra taken in 1997–2008 are used to analyze the spectral peculiarities and velocity field in the atmosphere of the peculiar supergiant 3 Pup. The profiles of strong Fe II lines and of the lines of other iron-group ions have a specific shape: the wings are raised by emissions, whereas the core is sharpened by a depression. The latter feature becomes more pronounced with the increasing line strength, and the increasing wavelength. Line profiles are variable: the magnitude and sign of the absorption asymmetry, and the blue-to-red emission intensity ratios vary from one spectrum to another. The temporal Vr variations are minimal for the forbidden emissions and sharp shell cores of the absorption features of FeII(42), and other strong lines of iron-group ions. The average velocity for the above lines can be adopted as the systemic velocity: Vsys = 28.5 ± 0.5 km/s. The weakest photospheric absorptions and photospheric MgII, Si II absorptions exhibit well-defined day-to-day velocity variations of up to 7 km/s. Quantitative spectral classification yields the spectral type of A2.7±0.3 Ib. The equivalent widths and profiles of Hδ and Hγ, and the equivalent width of the OI 7774 Å triplet yield an absolute magnitude estimate of Mv=?5.5m ± 0.3m, implying the heliocentric distance of 0.7 kpc.  相似文献   

18.
Mkn 841 has been observed during 3 different periods (January 2001, January 2005 and July 2005) by XMM‐Newton for a total cumulated exposure time of ∼108 ks. We present in this paper a broad band spectral analysis of the complete EPIC‐pn data sets. These observations confirm the presence of the strong soft excess and complex iron line profile known to be present in this source since a long time. They also reveal their extreme and puzzling spectral and temporal behaviors. Indeed, the 0.5–2 keV soft X‐ray flux decreases by a factor 3 between 2001 and 2005 and the line shape appears to be a mixed of broad and narrow components, both variable but on different timescales. The broad‐band 0.5–10 keV spectra are well described by a model including a primary power law continuum, a blurred photoionized reflection and a narrow iron line, the blurred reflection fitting self‐consistently the soft excess and the broad line component. The origin and nature of the narrow component is unclear. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
Measurements of the properties of Pi 2 pulsations along a magnetic meridian at high latitudes during a number of substorms have been analyzed for their relationship to the auroral electrojet. It is found that the maximum Pi 2 pulsation amplitudes are closely associated with the instantaneous position of the electrojet. That is, the average pulsation amplitude in the Pi 2 band as well as the amplitudes of pulsations at specific frequencies in the band have maximum amplitudes at latitudes close to the instantaneous electrojet location. Stations equatorward of the electrojet tend to observe a classical Pi 2 waveform concurrent with the onset of the substorm electrojet. Stations near the electrojet observe a broad spectrum of pulsations indicating a multiplicity of sources. Stations poleward of the initial electrojet position see little pulsation activity until the electrojet moves overhead. The appearance of large amplitude Pi 2 pulsations at a station which was poleward of the electrojet at the onset of a substorm appears to be coincident with the arrival of the poleward border of the electrojet.  相似文献   

20.
Ground based high resolution (R ～ 120,000) spectra of the zenith day sky near 6300 Å were obtained with a PEPSIOS. When compared with the solar spectrum taken with the same spectrometer, the 6300.3 Å line of atomic oxygen was clearly present in emission. The apparent emission rate averaged 6 to 8 kR for solar zenith angles of 50 to 60 deg and decreased smoothly to about 1 kR as the solar zenith angle increased to 95 deg. The average emission line is somewhat different in width than the thermal line width expected with the Jacchia (1971) model for a 250 km altitude.  相似文献   

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