摘要:

The concept of space and the ponderable dynamical activity in space have a long history of development, going back centuries and millenia, and what is commonplace today should not be considered apriori obvious, however “obvious” it may seem now that it has been discovered and studied. The development of space physics over the centuries has followed close on the heels of the development of physics. With the fundamental laws of classical physics well in hand today, present space physics research aims at direct discovery of the diverse phenomena occurring in space, followed by sufficiently detailed quantitative study to understand how the effects follow from the basic principles of Newton, Maxwell, Boltzmann, et al. The pursuit of space physics often turns up new twists to the “old” physics of the terrestrial laboratory, made possible by the vastly greater dimensions of space. The present review traces the development of physics and its application to space physics from classical times to the early years of the space age, when direct in situ studies of space became possible. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58782

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The outflow of coronal plasma into interplanetary space is a consequence of the coronal heating process. Therefore the formation of the corona and the acceleration of the solar wind should be treated as a single problem. The deposition of energy into the corona through some mechanical or electromagnetic energy flux is balanced by the various sinks available to the corona, and the sum of these processes determines the coronal structure, i.e. its temperature and density. Heating of the extended solar corona leads to high proton and ion temperatures and relatively low electron temperatures. This is due to the low heat conductivity in the proton (ion) gas as compared to the electrons. To a fairly good approximation we can say that most of the energy flux deposited in the protons and ions is lost as kinetic and gravitational energy flux in the solar wind flow, whereas a large fraction of the energy flux added to the electrons is conducted back into the transition region and lost as radiation. In order to drive high speed wind most of the energy must be deposited in the ions. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58783

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Basic physical considerations, observations and numerical simulations show that the solar chromosphere is very dynamic. The enhanced chromospheric emission, which corresponds to an outwardly increasing semiempirical temperature structure, can even be produced by wave motion without any increase in the mean gas temperature. Hence, the sun may not have a classical chromosphere in magnetic field free internetwork regions. This dynamic picture of the solar internetwork chromosphere is consistent with ground based observations of the Call resonance lines and with observations from the SOHO satellite. The simulations also show that a static picture and a dynamic picture of the chromosphere are fundamentally different and that time variations are crucial for our understanding of the chromosphere itself and the spectral features formed there. Whether the dynamic nature of the chromosphere is important for solar wind models depends on their sensitivity to chromospheric conditions. Contrary to some claims in the literature, the ionization of hydrogen in the upper chromosphere is dominated by collisional excitation in the Lyman line followed by photo-ionization by Balmer continuum photons—the Lyman continuum does not play any significant role. In the transition region, collisional ionization takes over as the major process. Ionization/recombination time-scales can be on the order of hundreds of seconds causing the ionization balance in the chromosphere to be significantly out of equilibrium with higher ionization than the equilibrium value. The hydrogen ionization zone is also considerably thicker than is claimed from dimension analyses; the ionization fraction goes from 1&percent; to 40&percent; over a height range of 600 km. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58753

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Spacecraft observations of the solar wind have been confined to regions near the ecliptic plane until the Ulysses spacecraft has recently made a pass over both solar poles at a heliocentric distance of 2 to 4 AU (1) and encountered continuous fast wind at high latitudes, generally in a range of 700 to 800 km/s (2). On the other hand, there has been no direct measurement at solar distances inside70&hthinsp;R⊙where the solar wind is significantly accelerated. The interplanetary scintillation (IPS) method is a unique and useful means to measure global structure of the solar wind in regions near the Sun and at high latitudes wherein situmeasurements are difficult. Since the IPS measurements, however, are biased by line-of-sight integration effects, a computer assisted tomography method has been developed to deconvolve the line-of-sight integration. We introduce several results from the IPS tomography analysis on latitudinal velocity structure up to 90°, radial distance dependence of fast wind speed, origin of very slow wind, and density fluctuations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58781

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Using empirical ion velocity distributions derived from UVCS and SUMER ultraviolet spectroscopy, we construct theoretical models of the nonequilibrium plasma state of the polar solar corona. The primary energy deposition mechanism we investigate is the dissipation of high frequency (10-10000 Hz) ion-cyclotron resonant Alfve´n waves which can heat and accelerate ions differently depending on their charge and mass. We find that it is possible to explain many of the kinetic properties of the plasma with relatively small amplitudes for the resonant waves. There is evidence for steepening of the Alfve´n wave spectrum between the coronal base and the largest heights observed spectroscopically, and it is important to take Coulomb collisions into account to understand observations at the lowest heights. Because the ion-cyclotron wave dissipation is rapid, the extended heating seems to demand a constantly replenished population of waves over several solar radii. This indicates that the waves are probably generated throughout the wind rather than propagated up from the base of the corona. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58772

出版商:AIP    

年代:1999

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.58784

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We have investigated a magnetohydrodynamic mechanism which accounts self-consistently for the variability, latitudinal extent, and bulk acceleration of the slow solar wind. Our model represents a streamer beyond the underlying coronal helmet as a neutral sheet embedded in a plane fluid wake, characterized by two parameters which vary with distance from the Sun: the ratio of the cross-stream velocity scale to the neutral sheet width (&dgr;), and the ratio of the typical Alfve´n velocity to the typical flow speed far from the neutral sheet (A). Depending on the values of these parameters, our linear theory predicts that this system responds to perturbations with three kinds of instability: a streaming tearing instability, and two ideal fluid instabilities with different cross-stream symmetries (varicose and sinuous). In the magnetically-dominated region near the helmet cusp, the steamer is resistively and ideally unstable, evolving from tearing-type reconnection in the linear regime to a nonlinear varicose fluid instability. Travelling magnetic islands are formed which are similar to “blobs” recently revealed by the Large-Angle Spectroscopic COronagraph (LASCO) on the joint ESA/NASA Solar and Heliospheric Observatory (SOHO). Past the Alfve´n point, the tearing mode is suppressed but an ideal sinuous fluid mode can develop, producing additional acceleration up to typical slow-wind speeds and substantial broadening of the wake. Farther from the Sun, the streamer becomes highly turbulent, thus slowing the acceleration and producing strong filamentation throughout the core of the wake. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58678

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The highly irregular nature of most photospheric magnetic fields is analyzed here, trying to emphasize the connection between photospheric fluctuations and those existing in the solar wind. It is discussed how the magnetic flux conservation in sunspots demands penumbrae pervaded by kilometer-wide irregularities. The diagnosis of this type of tiny scales requires special tools having degrees of freedom for optically-thin magnetic irregularities. One of such tools is introduced here, to be subsequently applied to the quiet Sun. It turns out to reproduce the observed Zeeman induced polarization, despite the fact that the polarization is frequently very abnormal. The kind of irregular atmosphere that the inversion technique favors seems to provide a consistent picture of the quiet Sun magnetism. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58695

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We review our magnetic reconnection model of the solar coronal X-ray jets. The plasma of an X-ray jet is accelerated and heated by reconnection between the emerging flux and a pre-existing coronal field. Many observed characteristics of the X-ray jets could be successfully reproduced through the two-dimensional MHD numerical simulations based on this model. We also discuss the Alfve´n wave generated by the reconnection process. The simulation results show that the amount of Alfve´n wave energy is ≈3&percent; of the total energy released by the magnetic reconnection. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58705

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The emission measure of the quiet corona, defined by the plasma hotter than one million degrees, is fluctuating in nearly every1900&hthinsp;km×1900&hthinsp;kmpixel observed by EIT on SoHO. In the average, the larger the emission measure in a pixel, the more it fluctuates. Increases in emission measure constitute a major energy input into the corona, suggesting that the lower corona is not just heated, but continuously replenished by chromospheric material heated to coronal temperatures. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58785

出版商:AIP    

年代:1999

数据来源: AIP