共查询到20条相似文献，搜索用时 234 毫秒
1.
Correlation analysis of solar wind parameters, namely solar wind velocity, pro- ton density, proton temperature and mean interplanetary magnetic field (IMF) from the ACE spacecraft data near Earth, was done. To our best knowledge, this study is a novel one since we consider here only the parameters inside the solar wind, including the mean IMF and, hence, the solar wind is a self consistent system. We have proposed a Multiple Linear Regression (MLR) model for the prediction of the response variable (solar wind velocity) using the parameters proton density, proton temperature and mean IMF mea- sured as dally averages. About 60% of the observed value can be predicted using this model. It is shown that, in general, the correlation between solar wind parameters is sig- nificant. A deviation from the prediction at the solar maximum is interpreted. These results are verified by a graphical method. 相似文献
2.
Opitz A. Karrer R. Wurz P. Galvin A. B. Bochsler P. Blush L. M. Daoudi H. Ellis L. Farrugia C. J. Giammanco C. Kistler L. M. Klecker B. Kucharek H. Lee M. A. Möbius E. Popecki M. Sigrist M. Simunac K. Singer K. Thompson B. Wimmer-Schweingruber R. F. 《Solar physics》2009,256(1-2):365-377
The two STEREO spacecraft with nearly identical instrumentation were launched near solar activity minimum and they separate by about 45° per year, providing a unique tool to study the temporal evolution of the solar wind. We analyze the solar wind bulk velocity measured by the two PLASTIC plasma instruments onboard the two STEREO spacecraft. During the first half year of our measurements (March?–?August 2007) we find the typical alternating slow and fast solar wind stream pattern expected at solar minimum. To evaluate the temporal evolution of the solar wind bulk velocity we exclude the spatial variations and calculate the correlation between the solar wind bulk velocity measured by the two spacecraft. We account for the different spacecraft positions in radial distance and longitude by calculating the corresponding time lag. After adjusting for this time lag we compare the solar wind bulk velocity measurements at the two spacecraft and calculate the correlation between the two time-shifted datasets. We show how this correlation decreases as the time difference between two corresponding measurements increases. As a result, the characteristic temporal changes in the solar wind bulk velocity can be inferred. The obtained correlation is 0.95 for a time lag of 0.5 days and 0.85 for 2 days.
相似文献3.
The solar wind velocity near Earth shows systematic structure in and around the heliospheric current sheet. The solar wind velocity measurements at IMF sector boundary crossings at 1 AU during 1972–1977 have been used to infer the azimuthal structure of the solar wind velocity in the current sheet. We found that the solar wind velocity in the in-ecliptic portion of the current sheet varies from longitude to longitude, where it originates from the corona. Also, the yearly average value of solar wind velocity in the HCS is found to vary with the phase of the solar cycle; with a maximum value around 1974. TheK-corona brightness on the source surface corresponding to the IMF sector boundary crossings during the period of study also shows a similar but opposite pattern of variation when the data are averaged over a long period. However, this relation is not observed when we considered them individually. So, we conclude that there exists a longitudinal variation of solar wind velocity in the heliospheric current sheet. 相似文献
4.
Wen-Rui Hu 《Astrophysics and Space Science》1984,98(1):171-189
The influence of the momentum addition, which may be associated with the average or fluctuation transverse component of the magnetic field or others, on the acceleration the solar wind or stellar wind is studied in a local streamtube. The results show that the larger the momentum addition the stronger the acceleration of the wind. For example, if the typical transverse magnetic field is about 0.1 of the longitudinal field, the velocity of the solar wind at 1 AU may be increased by 40%. The coronal hole may be considered as a streamtube, the presence of a high stream from the coronal hole may be explained by the existence of an average or fluctuation transverse magnetic field in the streamtube. A similar conclusion may be applied to the polar region, where the velocity of the solar wind will be larger than elsewhere as if there is a transverse component of magnetic field, as well as to the stellar wind. The influence of other parameters on the acceleration of the solar wind is also discussed. From the viewpoint of the solar wind mechanism, the present paper shows that the momentum addition in the subsonic flow region can increase the velocity of the solar wind at 1 AU. 相似文献
5.
Cross-correlation functions have been computed between green-line intensity (Kislovodsk) and Vela solar wind velocity January–June 1967. They are calculated separately for east and west limb observations in 5° latitude increments, and the solar wind velocites are correlated at their estimated emission times by correcting for the plasma Earth-Sun transit time using the observed velocities. The cross-correlation patterns appear to be dominated by two competing effects: a tendency of quasi-stationary green-line emission and solar wind velocity to anti-correlate; and a tendency of transient green-line emission and solar wind velocity enhancements to correlate positively. We also find evidence for simultaneous (same-day) emission brightenings over 2 to 4 limb quadrants. It is therefore recommended that, following a well-known practice in solar terrestrial studies, recurrent and transient events in both solar wind and green-line emissions should be studied separately. 相似文献
6.
借助于弱散射理论和模式拟合方法，单站行星际闪烁观测可以诊断太阳风速度，本文讨论了太阳风参数和射电源角尺度对闪烁谱的影响，以及太阳风速度的积分效应，结果表明，闪烁谱的特征是与视线上距太阳最近处的太阳风速度直接相关的。 相似文献
7.
We analyze in situ measurements of the solar wind velocity obtained by the Advanced Composition Explorer (ACE) and the Helios spacecraft during the years 1998?–?2012 and 1975?–?1983, respectively. The data mainly belong to solar cycles 23 (1996?–?2008) and 21 (1976?–?1986). We used the directed horizontal-visibility-graph (DHVg) algorithm and estimated a graph functional, namely, the degree distance (D), which is defined using the Kullback–Leibler divergence (KLD) to understand the time irreversibility of solar wind time-series. We estimated this degree-distance irreversibility parameter for these time-series at different phases of the solar activity cycle. The irreversibility parameter was first established for known dynamical data and was then applied to solar wind velocity time-series. It is observed that irreversibility in solar wind velocity fluctuations show a similar behavior at 0.3 AU (Helios data) and 1 AU (ACE data). Moreover, the fluctuations change over the phases of the activity cycle. 相似文献
8.
The influence of latitudinally dependent boundary conditions on the large radius values of meridional flow in the distant solar wind is examined through a double perturbation expansion of the magnetohydrodynamic equations. A general result is derived for the meridional velocity which allows arbitrary specification of radial velocity, radial magnetic field, and mass flux, as a function of colatitude at some coronal reference surface. Three specific examples are treated, including the model of Pneuman and Kopp (1971). The latter example indicates that there may be flow toward the equator at large radii, as opposed to the pure equatorial divergence of internally generated motion due to a flow which is latitudinally uniform at the reference radius. A solar cycle effect most probably averages the boundary conditions so that only the equatorial divergence from an average spherically symmetric corona is seen in comet-tail observations. This may also explain the off-and-on-again nature of the meridional gradient in the radial velocity of the solar wind as seen in radio scintillation observations. 相似文献
9.
W. Köhnlein 《Astrophysics and Space Science》1996,245(1):81-88
Long-term variations of solar wind parameters at 1 AU are correlated with sunspots for the time interval 1973 to 1993 (solar cycles 21, 22). Using theNear-Earth Heliosphere Data OMNI the plasma density, the magnitude of the interplanetary magnetic field, the solar wind velocity and the solar wind temperature show consistent long-term variations in each cycle (21 and 22) — pointing to specifictime-lags in the coupling between sunspots (and the underlying convection zone), the solar corona and the solar wind parameters at 1 AU (ecliptic). 相似文献
10.
《天文和天体物理学研究(英文版)》2017,(10)
The primary goal of pulsar timing array projects is to detect ultra-low-frequency gravitational waves. Pulsar data sets are affected by numerous noise processes including varying dispersive delays in the interstellar medium and from the solar wind. The solar wind can lead to rapidly changing variations that, with existing telescopes, can be hard to measure and then remove. In this paper we study the possibility of using a low frequency telescope to aid in such correction for the Parkes Pulsar Timing Array(PPTA) and also discuss whether the ultra-wide-bandwidth receiver for the FAST telescope is sufficient to model solar wind variations. Our key result is that a single wide-bandwidth receiver can be used to model and remove the effect of the solar wind. However, for pulsars that pass close to the Sun such as PSR J1022+1022, the solar wind is so variable that observations at two telescopes separated by a day are insufficient to correct the solar wind effect. 相似文献
11.
The initially supersonic flow of the solar wind passes through a magnetic shock front where its velocity is supposed to be reduced to subsonic values. The location of this shock front is primarily determined by the energy density of the external interstellar magnetic field and the momentum density of the solar wind plasma. Interstellar hydrogen penetrating into the heliosphere undergoes charge exchange processes with the solar wind protons and ionization processes by the solar EUV radiation. This results in an extraction of momentum from the solar wind plasma. Changes of the geometry and the location of the shock front due to this interaction are studied in detail and it is shown that the distance of the magnetic shock front from the Sun decreases from 200 to 80 AU for an increase of the interstellar hydrogen density from 0.1 to 1.0 cm−3. The geometry of the shock front is essentially spherical with a pronounced embayment in the direction opposite to the approach of interstellar matter which depends very much on the temperature of the interstellar gas. Due to the energy loss by the interaction with neutral matter the solar wind plasma reduces its velocity with increasing distance from the Sun. This modifies Parker's solution of a constant solar wind velocity. 相似文献
12.
《Planetary and Space Science》2007,55(12):1793-1803
In this paper, the solar wind flow around Venus is modeled as a nondissipative fluid which obeys the ideal magnetohydrodynamic equations extended for mass loading processes. The mass loading parameter is calculated for four different cases, corresponding to solar minimum and maximum XUV flux and to nominal and low solar wind velocity. We get smooth profiles of the field and plasma parameters in the magnetosheath. Based on the results of this flow model, we investigate the occurrence of the Kelvin–Helmholtz (K–H) instability at the equatorial flanks of the ionopause of Venus. By comparing the instability growth time with the propagation time of the K–H wave, we find that the K–H instability can evolve at the ionopause for all four solar wind conditions. 相似文献
13.
M.S. Bobrov 《Planetary and Space Science》1979,27(12):1461-1467
It is found that from the viewpoint of the magnetic field configuration there are only two types of solar wind: streams with closed field lines (flare-induced streams) and streams with open field lines (M-streams of various velocity and lifetime, and quiet solar wind). We emphasize that in the absence of flare-induced streams the Earth's magnetosphere is, as a rule, circum-flown not by a quiet but by a variably disturbed solar wind—M-streams. An important feature of M-streams is that within a given interplanetary magnetic field sector the sign (+ or −) of the stream magnetic field almost always coincides with that of the sector. These facts lead to the conclusion that M-streams are mainly responsible for the sector structure. 相似文献
14.
Stephen Pintér 《Solar physics》1974,35(1):225-232
The annual average values of the solar wind velocity over the period 1962–1972 were investigated on the basis of data obtained from different space probes. The comparison of the pattern of the annual average solar wind velocities observed by the Vela and Pioneer 6 satellites indicates that the pattern presented by Gosling et al. (1971) is realistic. The long-range trend in the solar wind velocity during the 11-year cycle is governed by the number and intensity of irregularities occurring in the corona. These irregularities may represent motions of mass or some types of MHD shock waves and they are responsible for the increased heating of the corona which then in turn causes an increase in the values of the solar radar cross-section and of the solar wind velocity. A close relation is demonstrated between the monthly and annual average values of the solar wind velocity and of the cross-section. 相似文献
15.
A study is made of electron concentration altitude profiles within the F1-layer. By using a mathematical model with a variety of atmospheric conditions and neutral air wind patterns we demonstrate the appearance of a daytime valley. Such valleys have been observed at St. Santin during summer for low-to-moderate levels of solar activity by Taieb et al. (1975,1978). Our calculations show that a valley occurs when there is a vertical shear in the meridional component of the neutral air wind velocity. This wind component must be directed poleward below the shear and equatorward above the shear. A valley will also occur when the meridional component of the neutral air wind velocity is directed poleward at all altitudes within the F1-region provided there is a rapid change in the velocity. We conclude from our results that the non-appearance of a valley at St. Santin during the winter and solar maximum observation periods of Taieb et al. (1975) is due to the neutral air wind pattern having an inappropriate form. Thus, it appears from observational evidence of the F1-layer that the pressure gradients existing in the neutral air during winter and at a solar maximum are unable to produce a wind pattern capable of producing a valley in the electron concentration profile. 相似文献
16.
Coronal holes as sources of solar wind 总被引：3，自引：0，他引：3
J. T. Nolte A. S. Krieger A. F. Timothy R. E. Gold E. C. Roelof G. Vaiana A. J. Lazarus J. D. Sullivan P. S. McIntosh 《Solar physics》1976,46(2):303-322
We investigate the association of high-speed solar wind with coronal holes during the Skylab mission by: (1) direct comparison of solar wind and coronal X-ray data; (2) comparison of near-equatorial coronal hole area with maximum solar wind velocity in the associated streams; and (3) examination of the correlation between solar and interplanetary magnetic polarities. We find that all large near-equatorial coronal holes seen during the Skylab period were associated with high-velocity solar wind streams observed at 1 AU.Harvard College Observatory-Smithsonian Astrophysical Observatory.A substantial portion of this work was done while a visiting scientist at American Science and Engineering. 相似文献
17.
MACS for Multi-Aperture Coronal Spectrometer is a fiber-optic-based spectrograph designed and used to perform global measurement of the solar wind velocity and the thermal electron temperature of the solar corona during the total solar eclipse on 11 August 1999. The motivation for the construction of MACS was provided by the theory formulated by Cram (1976) for the formation of the K-coronal spectrum and a method for determining the radial profile of the thermal electron temperature of the solar corona. Based on this theory a subsequent application was carried out by Ichimoto et al. (1996) using a slit-based spectroscopic study during the total solar eclipse on 3 November 1994. We have modified Cram's theory to incorporate the role of the solar wind velocity in the formation of the K-corona and have identified wind and temperature sensitive intensity ratios. Instead of a slit-based spectrograph MACS consists of twenty fiber optic tips placed at the focal plane of the telescope and positioned to see different radii and latitudes of the solar corona. Another fiber is placed at the center of the frame and uses the lunar shadow for a measure of the background signal. The other ends of the fibers are vertically aligned and placed at the primary focus of the collimating lens of the spectrograph thus providing simultaneous spectra from all of the fibers. In this first paper (Paper I) we describe our instrument and the obtained coronal spectra. The final and complete results will be presented in Paper II (Reginald and Davila, 2000). 相似文献
18.
《Chinese Astronomy and Astrophysics》1982,6(3):192-198
We investigate the possibility of an additional acceleration of the high speed solar wind by whistler waves propagating outward from a coronal hole. We consider a stationary, spherically symmetric model and assume a radial wind flow as well as a radial magnetic field. The energy equation consists of (a) energy transfer of the electron beam which excites the whistler waves, and (b) energy transfer of the whistler waves described by conservation of wave action density. The momentum conservation equation includes the momentum transfer of two gases (a thermal gas and an electron beam). The variation of the temperature is described by a polytropic law. The variation of solar wind velocity with the radial distance is calculated for different values of energy density of the whistler waves. It is shown that the acceleration of high speed solar wind in the coronal hole due to the whistler waves is very important. We have calculated that the solar wind velocity at the earth's orbit is about equal to 670 km/sec (for wave energy density about 10?4 erg cm?3 at 1.1R⊙). It is in approximate agreement with the observed values. 相似文献
19.
Recent advances in wide-angle imaging by the Solar Mass Ejection Imager (SMEI) on board the Coriolis spacecraft and more recently by the Heliospheric Imagers (HI) aboard NASA’s Solar TErrestrial RElations Observatory (STEREO), have enabled solar wind transients to be imaged and tracked from the Sun to 1 AU and beyond. In this paper we consider two of the techniques that have been used to determine the propagation characteristics of solar wind transients based on single-spacecraft observations, in particular propagation direction and radial speed. These techniques usually assume that the observing spacecraft remains stationary for the duration of observation of the solar wind transient. We determine the inaccuracy introduced by this assumption for the two STEREO spacecraft and find that it can be significant, and it can lead to an overestimation of the transient velocity as seen from STEREO-A and an underestimation as seen by STEREO-B. This has implications for the prediction or solar wind transients at 1 AU and hence is important for the study of space weather. 相似文献
20.
S. V. Chalov 《Astrophysics and Space Science》2018,363(6):124
The process of deceleration of the solar wind downstream of the termination shock is studied on the basis of a one-dimensional multi-component model. It is assumed that the solar wind consists of thermal protons, electrons and interstellar pickup protons. The protons interact with interstellar hydrogen atoms by charge-exchange. Two cases are considered. In the first one, the charge-exchange cross-section for thermal protons and hydrogen atoms is the same as for pickup protons and atoms. Under this condition, there is a strong dependence of the solar wind velocity on the downstream temperature of pickup protons. When the proton temperature is close to 10 keV, the change in the velocity with the distance from the termination shock is similar to that measured on the Voyager 1 spacecraft: linear velocity decrease is accompanied by an extended transition region with near-zero velocity. However, with a more careful approach to the choice of the charge-exchange cross-section, the situation changes dramatically. The strong dependence of the solar wind speed on the pickup proton temperature disappears and the transition region in the heliosheath disappears as well, at least at reasonable distances from the TS. 相似文献