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1.
The global distribution and temporal variations of thermospheric heating due to Joule dissipation of measured ionospheric electric fields are computed. It is shown that the volume Joule dissipation rate at high and middle latitude is similar in magnitude and altitudinal profile to the global solar EUV absorption rate discussed in the previous papers. Thus, Joule dissipation contributes significantly towards reconciling the quantitatively known sources of thermospheric heat input and that required to maintain the normal thermosphere. The combined heat source due to EUV absorption and Joule dissipation varies with the annual cycle in a manner closely resembling that of the thermospheric density. 相似文献
2.
The daily averages of the dawn and dusk observed exospheric temperatures (deduced from solar EUV attenuation measurements between 250 and 400 km) are presented for 280 days from day 227, 1969. They are compared with the empirical model of the US Standard Atmosphere Supplements 1966 and the Jacchia 35 H model. Although consistently lower temperatures than either model were found, a better fit to the latter rather than the former was observed. The exospheric response to solar and geomagnetic activity is investigated, and refinements to the models are suggested. 相似文献
3.
In this paper we compute the rate of solar EUV heating in the upper atmosphere by photo-dissociation and photo-ionization, taking care to include properly the effects of oblique incidence of solar flux, sphericity of the atmosphere and ellipticity of the Earth's orbit. The time and latitudinal variations of the computed heat function are revealed by numerical Fourier analysis of the heat function into harmonics of the yearly cycle. It is shown that EUV absorption contains a ‘latitude independent’ semi-annual component of heating with the ‘proper phase’ to account for the semi-annual density variations. Further, the annual component of the heat function predicts the existence of ‘summer polar’ density increases in the northern and southern hemispheres. 相似文献
4.
X-ray and EUV observations of the solar corona reveal a very complex and dynamic environment where there are many examples of structures that are believed to outline the Sun's magnetic field. In this present study, the authors investigate the temporal response of the temperature, density and pressure of a solar coronal plasma contained within a magnetic loop to an intermittent heating source generated by Ohmic dissipation. The energy input is produced by a one-dimensional MHD flare model. This model is able to reproduce some of the statistical properties derived from X-ray flare observations. In particular the heat deposition consists of both a sub-flaring background and much larger, singular dissipative events. Two different heating profiles are investigated: (a) the spatial average of the square of the current along the loop and (b) the maximum of the square of the current along the loop. For case (a), the plasma parameters appear to respond more to the global variations in the heat deposition about its average value rather than to each specific event. For case (b), the plasma quantities are more intermittent in their evolution. In both cases the density response is the least bursty signal. It is found that the time-dependent energy input can maintain the plasma at typical coronal temperatures. Implications of these results upon the latest coronal observations are discussed. 相似文献
5.
As an important measurement parameter, global total electron content (TEC) is appropriate for the study of the Sun–Earth connection.
In this paper, the wavelet technique is employed to investigate the periodicities in global mean TEC during 1995–2008. Analysis
results show several remarkable components (including 27-day, semiannual and annual cycles) existing in global mean TEC with
obvious time-variable characteristics, besides 11-year cycle. After analyzing sunspot numbers and solar extreme ultra-violet
(EUV) radiation variations during this time period, except for semiannual variations, close correlation between global mean
TEC and solar variations is found, especially, a strong resemblance of the 27-day fluctuation exists in global mean TEC, sunspot
and solar EUV radiation variations. 相似文献
6.
Atmospheric densities have been deduced from high resolution radar-determined orbital decay data and from data obtained from a uniaxial accelerometer flown onboard the low altitude satellite 1970-48A. Data were obtained during late June and early July, 1970. The orbital decay-deduced densities, having an effective 6 hr temporal resolution, were determined at an altitude of 143 km, essentially one-half scale height above perigee. The accelerometer deduced densities at the same altitude were obtained on both the approaching-perigee and leaving-perigee portions of each of fifty-nine orbits. A detailed comparison of the densities derived from both types of data is presented. In general, agreement is very good. A comparison of both types of data has also been made with the Jacchia 1970 and 1971 atmospheric models as well as the new OGO-6 atmospheric model. The Jacchia models display reasonable agreement with the data, but the OGO-6 model is unsuitable as a representation of atmospheric density at this altitude. 相似文献
7.
Using Hinode EUV Imaging Spectrometer (EIS) spectra recorded daily at Sun center from the end of 2006 to early 2011, we studied the long-term evolution of the quiet corona. The light curves of the higher temperature emission lines exhibit larger variations in sync with the solar activity cycle while the cooler lines show reduced modulation. Our study shows that the high temperature component of the corona changes in quiet regions, even though the coronal electron density remains almost constant there. The results suggest that heat input to the quiet corona varies with the solar activity cycle. 相似文献
8.
Gaël Cessateur Jean Lilensten Mathieu Barthélémy Thierry Dudok de Wit Cyril Simon Wedlund Guillaume Gronoff Hélène Ménager Matthieu Kretzschmar 《Icarus》2012,218(1):308-319
In the framework of future space missions to Ganymede, a pre-study of this satellite is a necessary step to constrain instrument performances according to the mission objectives. This work aims at characterizing the impact of the solar UV flux on Ganymede’s atmosphere and especially at deriving some key physical parameters that are measurable by an orbiter. Another objective is to test several models for reconstructing the solar flux in the Extreme-UV (EUV) in order to give recommendations for future space missions.Using a Beer–Lambert approach, we compute the primary production of excited and ionized states due to photoabsorption, neglecting the secondary production that is due to photoelectron impacts as well as to precipitated suprathermal electrons. Ions sputtered from the surface are also neglected. Computations are performed at the equator and close to the pole, in the same conditions as during the Galileo flyby. From the excitations, we compute the radiative relaxation leading to the atmospheric emissions. We also propose a simple chemical model to retrieve the stationary electron density. There are two main results: (i) the modelled electron density and the one measured by Galileo are in good agreement. The main atmospheric visible emission is the atomic oxygen red line at 630 nm, both in equatorial and in polar conditions, in spite of the different atmospheric compositions. This emission is measurable from space, especially for limb viewing conditions. The OH emission (continuum between 260 and 410 nm) is also probably measurable from space. (ii) The input EUV solar flux may be directly measured or reconstructed from only two passbands solar observing diodes with no degradation of the modelled response of the Ganymede’s atmosphere. With respect to these results, there are two main conclusions: (i) future missions to Ganymede should include the measurement of the red line as well as the measurement of OH emissions in order to constrain the atmospheric model. (ii) None of the common solar proxies satisfactorily describes the level of variability of the solar EUV irradiance. For future atmospheric planetary space missions, it would be more appropriate to derive the EUV flux from a small radiometer rather than from a full-fledged spectrometer. 相似文献
9.
A least-squares multiple linear regression is performed on orbital decay density data obtained from precise orbital analysis of 22 low-perigee (130–160 km) Air Force satellites. Variations related to solar activity, the semi-annual effect, geomagnetic activity, and the zenith angle of the Sun are in agreement with the model of Jacchia (1971). Density variations in longitude and latitude are also deduced and compared with recent results from other investigations within this altitude regime. 相似文献
10.
F.A. Marcos H.B. Garrett K.S.W. Champion J.M. Forbes 《Planetary and Space Science》1977,25(5):499-507
Density measurements at 140, 160, 180 and 200km from the AE-C accelerometer experiment during 1974 are analyzed by least-squares multiple linear regression. The resulting empirical model is compared to the widely-used Jacchia (1971) model which is primarily based on satellite orbital decay data above 200 km. The semiannual and geomagnetic (Kp) variations derived from the AE-C data set are in good agreement with Jacchia's predictions. However, individual magnetic storm responses often exceed such average representations of the geomagnetic effect by more than a factor of two. The density is more variable with respect to the daily 10.7cm solar flux than Jacchia's model predicts. The regression analysis reveals a positive correlation with the absolute value of the geographic latitude. The statistical weakness of this latter effect reflects the transient, aperiodic nature of high-latitude heating events related to magnetic activity, which can only be properly analyzed on an individual basis. Finally, the sub-solar bulge effect enters the regression equation with about half the amplitude predicted by the Jacchia model at these heights. 相似文献
11.
R. G. Giovanelli 《Solar physics》1975,44(2):315-329
Thermal transfer in closed magnetic tubes in the corona and transition region is described on the basis of a static model in which all heat generated is radiated away, though conduction transfers much of the heat to the transition region prior to emission. The rate of conductive transfer depends on the cross-section of the magnetic tube as it passes through the chromosphere and transition region. This is derived from the pressure in the normal chromosphere. There is then only one main parameter to establish conditions in the corona and transition region, viz. the heating per unit area of the Sun's surface, which must equal the observed radiation from corona and transition region. The density adjusts itself so as to radiate away all heat generated within the tube; conditions in the tube below the transition region have little influence other than to decide where the base of the transition region lies and the width of the region particularly in its lower parts. For the observed rate of heating, the computed densities (or pressures), the ratio of coronal to transition region emissions, and the distribution of radiation in the EUV spectrum agree closely with those observed. The optimum maximum temperatures are found with heating concentrated in the highest regions of the flux tubes. It is only in the lowest 20–40 km of the transition region, where T<105K, that any additional heating is needed to explain EUV line intensities. The equation of heat transfer also has solutions in which the temperature is oscillatory with disance. These do not apply to the normal corona, but may be relevant to prominences. 相似文献
12.
Measurements of the Lyman α airglow intensity were made between June 1969 and June 1970 by a u.v. photometer experiment on the OGO-6 satellite. The data for the zenith intensity at altitudes between 400 and 1100 km were fitted to theoretical airglow models to derive atomic hydrogen density nc at a reference altitude, taken to be 500 km. nc was determined for each of 286 orbits throughout the year. The mean exospheric temperature T∞(J) during this period varied from 900 to 1300 K according to the Jacchia model. The solar Lyman α flux at line center F0 was also determined over each 90-min orbit in the model-fitting procedure. F0 was found to be correlated with sunspot number, in agreement with previous results. A nearly-exact linear relationship was found for F0, when averaged over ‘bins’ which are 20 sunspot numbers in width. nc was found to be inversely correlated with T∞(J); however the dependence is not that predicted by steady-state models whose only escape mechanism is Jeans evaporative escape. Unless the total atmospheric loss rate depends upon 27-day changes in the solar EUV, which is unlikely, an additional upper atmospheric loss is required in order that the total loss remain constant with T∞(J). This extra loss may be largely due to charge-exchange reactions in the exosphere, wherein energetic protons are converted to fast hydrogen atoms, as suggested previously by a number of authors. An additional result is suggested by the apparent spherical symmetry of the inferred density, namely that the familiar diurnal variation of hydrogen is absent at the high latitudes preferentially sampled by the OGO-6 data. 相似文献
13.
利用色球Hα、TRACE／WL、SOHO／EITEuV单色像观测资料及SOHO／MDI光球磁场观测资料，对2003年10月22日太阳活动区AR0484内发生的日浪事件进行了研究．发现：(1)在Ha线心观测上，日浪包含有亮、暗2个分量，这2个分量先后出现而且并不共空间．日浪的亮分量与UV和EUV波段上观测到的喷发具有较好的同时性和共空间性．(2)日浪喷发物质沿着EUV环运动。(3)在光球层，日浪足根处的黑子和磁场有明显的变化．这些观测结果支持日浪的磁重联模型。 相似文献
14.
Using data from the Transition Region and Coronal Explorer (TRACE), Solar and Heliospheric Observatory (SOHO), Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and Hida Observatory (HO), we present a detailed study of an EUV jet and the associated Hα filament eruption in
a major flare in the active region NOAA 10044 on 29 July 2002. In the Hα line wings, a small filament was found to erupt out
from the magnetic neutral line of the active region during the flare. Two bright EUV loops were observed rising and expanding
with the filament eruption, and both hot and cool EUV plasma ejections were observed to form the EUV jet. The two thermal
components spatially separated from each other and lasted for about 25 minutes. In the white-light corona data, a narrow coronal
mass ejection (CME) was found to respond to this EUV jet. We cannot find obvious emerging flux in the photosphere accounting
for the filament eruption and the EUV jet. However, significant sunspot decay and magnetic-flux cancelation owing to collision
of opposite flux before the events were noticed. Based on the hard X-ray data from RHESSI, which showed evidence of magnetic
reconnection along the main magnetic neutral line, we think that all of the observed dynamical phenomena, including the EUV
jet, filament eruption, flare, and CME, should have a close relation to the flux cancelation in the low atmosphere. 相似文献
15.
Three-dimensional (3D) tomographic analysis of extreme ultraviolet (EUV) images is used to place empirical constraints on the corona’s temperature and density structure. The input data are images taken by the EUVI instrument on STEREO A and B spacecraft for Carrington Rotation 2069 (16 April to 13 May 2008). While the reconstructions are global, we demonstrate the capabilities of this method by examining specific structures in detail. Of particular importance are the results for coronal cavities and the surrounding helmet streamers, which our method allows to be analyzed without projection effects for the first time. During this rotation, both the northern and southern hemispheres exhibited stable polar crown filaments with overlying EUV cavities. These filaments and cavities were too low-lying to be well observed in white-light coronagraphs. Furthermore, due to projection effects, these cavities were not clearly discernible above the limb in EUV images, thus tomography offers the only option to study their plasma properties quantitatively. It is shown that, when compared to the surrounding helmet material, these cavities have lower densities (about 30%, on average) and broader local differential emission measures that are shifted to higher temperatures than the surrounding streamer plasma. 相似文献
16.
EUV97 is a solar EUV empirical model that incorporates revised soft X-ray fluxes from the SOLRAD-11 satellite (1976–1979) and uses Lα recently recalibrated to the UARS satellite (1991–present) SOLSTICE Lα. The soft X-ray data have been revised from the original flux values using Mewe's spectral fits to the data. The recalibrated AE-E and SME Lα datasets use UARS Lα for absolute flux values to provide two solar cycles of Lα irradiance extending back to 1977. Lα is used by EUV97 as a proxy for chromospheric EUV irradiances. The EUV97 empirical solar model takes its heritage from the EUV91 model based on a multiple linear regression technique that fits soft X-ray and EUV irradiances to 10.7 cm flux for transition region and coronal emissions or to Lα and Hei 10830 Ú EW for chromospheric emissions. 相似文献
17.
Chiuderi Drago F. Alissandrakis C.E. Bastian T. Bocchialini K. Harrison R.A. 《Solar physics》2001,199(1):115-132
In this paper we compare simultaneous extreme ultraviolet (EUV) line intensity and microwave observations of a filament on the disk. The EUV line intensities were observed by the CDS and SUMER instruments on board SOHO and the radio data by the Very Large Array and the Nobeyama radioheliograph. The main results of this study are the following: (1) The Lyman continuum absorption is responsible for the lower intensity observed above the filament in the EUV lines formed in the transition region (TR) at short wavelengths. In the TR lines at long wavelengths the filament is not visible. This indicates that the proper emission of the TR at the filament top is negligible. (2) The lower intensity of coronal lines and at radio wave lengths is due to the lack of coronal emission: the radio data supply the height of the prominence, while EUV coronal lines supply the missing hot matter emission measure (EM). (3) Our observations support a prominence model of cool threads embedded in the hot coronal plasma, with a sheath-like TR around them. From the missing EM we deduce the TR thickness and from the neutral hydrogen column density, derived from the Lyman continuum and Hei absorption, we estimate the hydrogen density in the cool threads. 相似文献
18.
We study the effect of projection and line-of-sight integration on the interpretation of the morphology and kinematics of EUV waves. We have performed a three-dimensional magnetohydrodynamic simulation of a coronal mass ejection (CME) erupting in an environment that mimics the low solar corona and calculated the resulting emission measure of the event from five different viewing angles. Our study provides more quantitative information about the impact of the viewing angle and projection effect on the properties of EUV waves than previous studies on the subject. Analyzing the emission measure of the lower corona reveals wave-like increases that move away from the eruption site, which we interpret as EUV waves. Behind the EUV wave front we can recognize coronal dimming regions. A comparison of the emission measure and calculated density supports the view that EUV waves are true waves. Our results show that the origin of the observed EUV wave is height-dependent, which means that the measured speed and the morphology depend on the viewing direction. Consequently, care should be taken when EUV observations are used to infer the true propagation speeds of EUV wave fronts. 相似文献
19.
V. V. Grechnev A. N. Afanasyev A. M. Uralov I. M. Chertok M. V. Eselevich V. G. Eselevich G. V. Rudenko Y. Kubo 《Solar physics》2011,273(2):461-477
On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white light a large-scale dome-shaped expanding coronal
transient with perfectly connected off-limb and on-disk signatures. Veronig et al. (Astrophys. J. Lett.
716, L57, 2010) concluded that the dome was formed by a weak shock wave. We have revealed two EUV components, one of which corresponded
to this transient. All of its properties found from EUV, white light, and a metric type II burst match expectations for a
freely expanding coronal shock wave, including correspondence with the fast-mode speed distribution, while the transient sweeping
over the solar surface had a speed typical of EUV waves. The shock wave was presumably excited by an abrupt filament eruption.
Both a weak shock approximation and a power-law fit match kinematics of the transient near the Sun. Moreover, the power-law
fit matches the expansion of the CME leading edge up to 24 solar radii. The second, quasi-stationary EUV component near the
dimming was presumably associated with a stretched CME structure; no indications of opening magnetic fields have been detected
far from the eruption region. 相似文献
20.
According to the theory of spectral line formation in the state of non-local thermodynamic equilibrium and by using the software package FAC for the relativistic multi-configuration atomic processes, the X-ray and EUV spectra of Be-like oxygen ions are simulated. The effects of indirect processes on the X-ray and EUV spectra of Be-like O ions are probed. In the situation of the typical cosmical plasma density (ne = 1010/cm3), three models are adopted. For different temperatures, the processes of formation of X-ray and EUV spectra are simulated, and the contributions of indirect processes to the formation of spectral lines are analyzed and compared. Besides, their rate coefficients are given. It is found that in the process of spectral line formation, the indirect processes have exceedingly important effects. 相似文献