摘要:

We outline the recent in situ radio observations obtained by Ulysses during its second fast latitude scan near the 2001 solar maximum. From ∼ 72° N, Ulysses was embedded in a continuous fast wind associated with a northern polar coronal hole. During that period, we enlight the variation of the electron density and thermal temperature with the heliocentric distance and latitude, obtained with the quasi‐thermal noise spectroscopy method. Since the scaled mass flux is observed roughly constant, we derive the profile of the electron thermal temperature, assuming a simple power‐law model. Indeed, we find that the electron density varies asR−2.0±0.1while the thermal temperature varies asR−0.7±0.1, in good agreement with the results obtained in polar coronal holes in 1995 near solar minimum. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618541

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A self‐consistent model of the solar wind interaction with the two‐component (plasma and H atoms) interstellar medium is employed to calculate heliospheric Lyman‐alpha absorption spectra. It is shown that the heliospheric absorption consists of absorption in the hydrogen wall region and in the heliosheath. Both absorption components are computed in different directions. We perform a parametric study by varying the proton and H atom number densities of the interstellar gas. The theoretical absorption spectra are compared with Hubble Space Telescope observations toward six nearby stars. Results of the comparison and possible constraints on the structure of the heliospheric interface are presented and discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618542

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Recent Ulysses observations of the heliospheric magnetic field (HMF) reveal that the sun’s open magnetic flux in the solar wind, as measured by r2Br, is independent of heliographic latitude at solar maximum and at solar minimum. It follows that 4&pgr; r2Br at any latitude provides an accurate estimate of the total open flux from the sun. An additional Ulysses result is that long term averages of r2Br are very nearly the same at the recent solar maximum as at the preceding minimum. The model of the HMF developed by L. Fisk and his colleagues, which includes several features absent from the well‐ known Parker model, leads to the prediction that the open flux is relatively constant or perhaps invariant. Motivated by these considerations, Br has been analyzed over the longer interval of four sunspot cycles (20–23) using the archived OMNI field measurements obtained in the ecliptic at 1 AU. Averages of Br, after separation into inward and outward sectors as with Ulysses data, agree within a few percent with previous results based on |Br|, the modulus of the radial component. Averages of Br increase by a factor of about 2 from solar minimum to maximum in cycles 21 and 22 but change only slightly in cycles 20 and 23. The variations in open flux are better correlated with total unsigned flux in the photosphere than with sunspot number, both reaching peak values after sunspot maximum. The open flux decreases at solar minima and secondary decreases occur when the polar cap fields vanish. It appears that the near equality of the open flux at minimum and maximum observed by Ulysses was, in fact, caused by a time variation with the measurements near maximum being obtained while a secondary decrease was occurring. Thus, the open flux is generally variable and only constant during shorter intervals when the solar field is stable. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618543

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This paper reviews solar wind observations in the outer heliosphere, concentrating on the recent data near solar maximum. The speed and temperature tend to be lower at solar maximum, due to the lack of coronal holes. The near‐absence of a latitudinal speed gradient at solar maximum allows us to measure the speed decrease of the solar wind and find a value for the H density in the local interstellar medium (LISM) at the termination shock of 0.09 cm−3. The temperature profile is well‐matched by a model using pickup ion heating and a speed dependence of the temperature. The density profile at solar maximum is dominated by MIRs; we show one case where converging CME ejecta form a MIR. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618544

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We have developed a Computer Assisted Tomography (CAT) program that modifies a time‐dependent three‐dimensional kinematic heliospheric model to fit interplanetary scintillation (IPS) observations. The tomography program iteratively changes this global model to least‐squares fit IPS data. The short time intervals of the kinematic modeling (∼1 day) force the heliospheric reconstructions to depend on outward solar wind motion to give perspective views of each point in space accessible to the observations, allowing reconstruction of interplanetary Coronal Mass Ejections (CMEs) as well as corotating structures. We show these models as velocity or density Carrington maps and remote views. We have studied several events, including the July 14, 2000 Bastille‐day halo CME. We check our results by comparison with additional remote‐sensing observations, and observations from near‐Earth spacecraft. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618545

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The solar wind can, to a good approximation be described as a two‐component flow with fast, tenuous, quiescent flow emanating from coronal holes, and slow, dense and variable flow associated with the boundary between open and closed magnetic fields. In spite of its simplicity, this picture naturally produces a range of complex heliospheric phenomena, including the presence, location, and orientation of corotating interaction regions and their associated shocks. In this study, we apply a two‐step mapping technique, incorporating a magnetohydrodynamic model of the solar corona, to bring in situ observations from Ulysses, WIND, and ACE back to the solar surface in an effort to determine some intrinsic properties of the quasi‐steady solar wind. In particular, we find that a “layer” of ∼35,000 km exists between the Coronal Hole Boundary (CHB) and the fast solar wind, where the wind is slow and variable. We also derive a velocity gradient within large polar coronal holes (that were present during Ulysses’ rapid latitude scan) as a function of distance from the CHB. We find thatv= 713 km/s + 3.2d, wheredis the angular distance from the CHB boundary in degrees. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618546

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Recent outer‐heliosphere observations are reviewed from a space weather point of view by comparing the nature of solar wind, solar particle, and cosmic ray variations at the Voyagers and 1 AU. While the Sun still controls the interplanetary medium at 75 AU, the nearby boundaries of the heliosphere exert a strong influence on the environment. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618547

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Most investigations addressing the global structure of the heliosphere, including explicitly the interaction between the solar wind and the partially ionized local interstellar medium (LISM), have focused on hydrogen since it is the most abundant particle species. We use kinetic models that include heavy elements such as He, C, N, O, and others, to study the heliospheric distribution of neutrals and the singly charged ions of these species, besides H. Our model describes the evolution of interstellar heavy neutral atom distributions throughout the heliosphere, and we include the interaction of heavy particles with neutral hydrogen and protons through charge exchange (i.e., the creation of pickup ions), while the heavy particles are subject to photoionization and gravity. We use improved, recently published charge exchange cross‐sections as well as recently identified LISM boundary conditions. A realistic description of the basic heavy element distribution and filtration at heliospheric boundaries will provide an important theoretical basis for interpreting observations of pickup ions made by Ulysses and ACE. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618548

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Recent analyses using suprathermal electrons as sensors of true magnetic polarity indicate that the steady‐state concepts of the heliospheric current sheet and its encasing plasma sheet often break down at solar wind time scales of less than a day owing to transient and turbulent effects. These create magnetic configurations with localized current and plasma sheets and sometimes cause the current to split off from the surface separating fields of true opposite polarity. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618549

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

It has been shown recently [1] that the average solar wind speed at 1 AU is faster (slower) in Spring than in Fall around positive (negative, respectively) helicity minima. This implies a related 22‐year variation in the solar hemisphere from which a faster solar wind stream is received at 1 AU during each season. We have earlier studied [2] the effective latitudinal gradients of the solar wind speed in the two magnetic hemispheres around the heliographic equator by comparing observations at the Earth’s orbit in Spring and Fall. We found that there is a large effective gradient of about 10 km/s/deg in the southern magnetic hemisphere around each solar minimum. However, no statistically significant effective gradient was found in the northern magnetic hemisphere. Here we discuss the related properties of the solar wind proton temperature and show that the temperature and speed behave very similarly in the two hemispheres. In particular, there is a large effective gradient of about 2700–5400 K/deg in the southern magnetic hemisphere while no significant gradient exists in the northern hemisphere. This supports the earlier result [2] that the streamer belt is systematically displaced toward the northern magnetic hemisphere. The displacement of the streamer belt implies a new, persistent north‐south asymmetry related to the solar magnetic cycle which needs to be explained by realistic solar dynamo models. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1618550

出版商:AIP    

年代:1903

数据来源: AIP