摘要:

We investigate time‐dependent siphon flows in coronal loops driven by Alfve´n waves. We consider a 1.5 D isothermal, MHD model in which the coordinate is the abscissa along the loop, with an external gravity field reversing sign in the middle, and a uniform magnetic field parallel to the x‐axis. We use transparent boundary conditions, meant to describe the upper part of the loop. The reaction of the loop to Alfve´n waves depends entirely on whether we allow or not incoming parallel velocity fluctuations: only in the latter case do transonic flows arise, but the flow is in that case generated by a nonlinear coupling of the waves with the boundaries. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618701

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We studied the propagation of interplanetary counterpart of coronal mass ejections (ICMEs) by using interplanetary scintillation (IPS) measurements of the Solar‐Terrestrial Environment Laboratory at 327MHz. In this study, we analyzed data of the solar wind disturbance factor, so‐called g‐value, derived from our IPS measurements. We analyzed two ICME events observed in 1997 and 2000. We assumed a shell‐shape ICME model, defined by six parameters (location, propagation directions, radial thickness, angular width, and enhancement factor). We determined the most suitable set of those parameters by matching the model calculations of g‐value to IPS observations. Then, we determined the radial variation of the propagation speed of CME or ICME by comparing our IPS data with coronagraph data and in‐situ data. As result, it is found that the propagation speed of ICME decelerated asV∝r−1.05for the 2000 event andV∝r−0.55the 1997 event. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618702

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We discuss the similarities and differences of two intervals of extreme interplanetary solar wind conditions, separated almost precisely by two solar cycles, in April 1979 and March–April 2001. The similarities extend to various data‐sets: Energetic particles, solar wind plasma and interplanetary magnetic field. In April 1979 observations were made by three spacecraft covering a wide longitudinal range (∼ 70°) in the heliosphere. Data are presented from Helios 2, located 28° East of the Sun‐Earth line at ∼ 2/3 AU, and from near the Earth. Observations of the 2001 interval are from Wind. We examine the geomagnetic activity during each interval. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618703

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The solar cycle leads to important changes in the solar wind, which can have an important effect on the structure of the global heliosphere. In the ecliptic, the ram pressure can vary from one cycle to the other, being greater during periods of minimum activity. We investigate the response of the heliosphere to a temporally varying solar wind. Since neutral hydrogen is a key component in determining the global structure of the heliosphere, we employ a multi‐fluid model in which the self‐consistent charge‐exchange interaction between neutral hydrogen and protons is included self‐consistently. The variability of the termination shock location is described and the response of the hydrogen wall to the temporal solar wind is discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618704

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

It is increasingly being realized that by affecting geoeffective scale lengths the interplanetary electric field (IEF) is a key quantity in space weather discussions. In this work we derive and analyze statistically IEF coherence lengths in year 2000, i.e., near maximum of solar cycle 23, working in a much used formulation for the IEF. We focus on the frequency domain. We use magnetic field and plasma data sets acquired by Wind and ACE. During year 2000, ACE‐Wind separations were very variable and, in particular, Wind’s first dayside distant prograde orbit resulted in a Y‐separation comparable to the X‐separation (∼220RE). We find IEF coherence lengths of 200–250RE(X) and 50–100RE(Y). The coherence is mainly carried by the low frequency components (f< 0.01 min−1). © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618705

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In recent work, promising agreement has been obtained between measured indices of geomagnetic activity (Dst, and cross‐polar cap potential) and their predicted values using interplanetary input from probes in the inner heliosphere (∼0.7 AU) when the probe was close to, (5), and even substantially displaced from, (4), the Earth‐Sun line. Implicit in this agreement is a good correlation of, at least, the basic temporal profiles of the major interplanetary parameters at the two observing sites. In this work we discuss a case study using Helios 1 and 2 data when the spacecraft are lined ‐ up and separated by an almost constant radial distance of 0.2 AU. In the period studied, the interplanetary medium consists of a fast stream being trailed by a magnetic cloud in a slower flow. Good correlation is found between the plasma and field observations at the two sites. Two lag times, reflecting the two types of major structures in the interval chosen, are determined. Evidence of evolutionary processes are briefly discussed. Spectral analysis confirms the results obtained from time series analysis. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618706

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We investigate some statistical properties of soft X‐ray bursts produced by solar flares. The Probability Density Functions (PDFS) of soft X‐ray intensity fluctuations are shown to display wide, non‐gaussian tails. The shape of the PDFs is nearly unchanged as the timelag, used to calculate fluctuations, varies. A very similar behavior is found for PDFs of energy dissipation fluctuations in a shell model of Magnetohydrodynamic (MHD) turbulence. Recalling also that both flare soft X‐ray bursts and dissipative bursts in the MHD shell model are characterized by a power law distribution for waiting times between successive bursts, we suggest that the results shown in this paper support the idea that solar flares could represent bursty dissipative events of MHD turbulence. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618707

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We present a recent analysis with 1996 SOHO CELIAS CTOF data, which reveals correlations of He+pickup ion fluxes and spectra with the magnetic field strength and solar wind density. The motivation is to better understand the ubiquitous large variations in both pickup ion fluxes and their velocity distributions found in interstellar pickup ion datasets. We concentrate on time periods of that can be associated with compression regions in the solar wind. Along with enhancements of the overall pickup ion fluxes, adiabatic heating and acceleration of the pickup ions are also observed in these regions. Transport processes that lead to the observed compressions and related heating or acceleration are discussed. A shift in velocity space associated with traveling interplanetary compression regions is observed, and a simple model presented to explain this phenomenon based on the conserved magnetic adiabatic moment. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618708

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

WIND, ACE, IMP 8 and Geotail data shows that the magnetosheath signature of IP shocks is primarily a fast‐mode shock or pressure pulse with a wide ramp. No model predicted secondary discontinuities could be identified above the magnetosheath background fluctuation level. Even though the interplanetary surface geometry of IP shocks could be significantly corrugated, this study suggests that there is no significant deceleration of the pressure front in the magnetosheath. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618709

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In the last years, interest in the study of the relationship between the magnetic helicity of solar active regions and the one contained in the interplanetary structures has grown. This has lead us to compute the helicity content of an interplanetary hot tube observed by Wind on October 24–25, 1995, applying three different approaches in cylindrical geometry: a linear force‐free field, a constant twist angle, and a non force‐free model with constant current. We have fitted the set of free parameters for each of the three models, finding that the determined magnetic helicity values are very similar when using the same orientation for the flux tube. From our point of view, these results imply that, whatever be the model used, magnetic helicity is a well‐determined quantity and, thus, it is worth using it to understand the link between solar and interplanetary phenomena. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618710

出版商:AIP    

年代:1903

数据来源: AIP