摘要:

The flare-CME-shock relationship has been controversial for more than two decades. This issue was traditionally addressed using white light coronagraphic data on CMEs, H-alpha or GOES data on flares and radio spectrographic data on shocks (inferred from metric type II radio bursts). A wealth of new information has become available after the advent of Yohkoh, SOHO and WIND missions that can be used to address the dynamical phenomena associated with CMEs. We present multiwavelength observations of the 1998 April 27 CME associated with coronal dimming, an X-class flare and type II radio bursts. We find that the coronal dimming observed in X-rays and EUV is indeed a CME signature and that the CME clearly precedes the accompanying flare. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58816

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Because coronal mass ejections (CMEs) are viewed in projection, it is difficult to determine their three-dimensional nature. We use an analytic model of CMEs as an example of a fully three-dimensional magnetic field structure in MHD force balance with an emerging CME. We present the CME magnetic field and its associated density structure, seen projected at the limb from two viewing angles perpendicular to the plane of the sky, and emerging from disk center representing “earth-directed” CME events. The range of CME structures thus produced compares well to existing CME white-light coronagraph and full disk EUV and X-ray observations. In particular, we find that both 3-part “front-cavity-core” and “U-shaped” white light CMEs, as well as the twin dimmings (also referred to as transient coronal holes) observed in X-ray and EUV, can successfully be reproduced by the CME model. All of these structures are a direct consequence of a single three-dimensional magnetic field topology, viewed from different directions. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58817

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

This study presents joint observations of an ‘halo’ coronal mass ejection from the EIT telescope and LASCO coronagraphs on SOHO, from the Nanc¸ay Radioheliograph (NRH) and the Zurich ETH radiospectrograph (Phoenix-2). This event includes different manifestations: a coronal wave and a dimming region detected by EIT, a CME showing bright discrete portions above east and west limbs. Radio signatures of all these manifestations are found and the interpretation is briefly discussed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58818

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We use dynamic spectra that display the observed radio intensity as a function of inverse frequency and time for tracking CME associated radio emissions through the interplanetary medium. The analyses of these radio emissions directly reveal the dynamics of the CME-driven shock as well as the nature of the radiation mechanism. For the two examples illustrated, we deduce that the type II radio emissions were generated primarily at the harmonic of the plasma frequency and in the upstream region of the CME-driven shock. For the two events, which have very different speeds, we found no evidence for significant deceleration of the CME-driven shock as it propagated through the interplanetary medium. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58709

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

It is generally believed that type II bursts are caused by electrons accelerated at a shock front. Holman and Pesses (1) suggested that type II bursts can be caused by electrons accelerated by the shock drift mechanism. In order to explain a fine structure of type II bursts (herringbones), Zlobec et al. (2) presented a qualitative model where electrons are accelerated by a nearly perpendicular wavy shock front. We discuss this possibility quantitatively, namely we present an analytical solution of electron motion in a wavy shock front. Then we perform a parametric study in order to determine which parameters of the model are necessary for an appropriate electron energy gain. The calculations show that electrons are rarely reflected more than once at the wavy shock front and their final energy is mostly 1–3 times the initial one. This is similar to the theoretical acceleration gain of reflected electrons at the Earth’s bow shock. In the present case all electrons are eventually transmitted downstream where they form two downstream beams. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58819

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A 3-D numerical magnetohydrodynamic model is used to investigate the temporal and spatial evolution of large-scale solar wind (SW) disturbances. A tilted-dipole outflow configuration is specified at the inner boundary near the Sun, and a structured, corotating SW flow is established by dynamic relaxation between 0.14 and 1.04 AU. Time-dependent variation of the pressure and velocity at the inner boundary is applied to simulate injection of a coronal mass ejection (CME) near the streamer belt with a monopolar interplanetary magnetic field (IMF). Numerical results show that the motion and appearance of a CME are affected by its interaction with the velocity and density structure of the background SW. This 3-D dynamic interaction also affects the orientation and magnitude of the IMF. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58710

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A 3-D hydrodynamic numerical model is used to investigate the essential physics of the large-scale interaction between CMEs and the structured background solar wind. A tilted-dipole steady outflow configuration is established by numerical relaxation between 0.14 and 5.04 AU. Time-dependent velocity and pressure pulses are introduced at the inner boundary at differing locations with respect to the corotating streamer belt flow. Results show that CMEs may be significantly distorted due mainly to local variations in the background flow speed geometry. Thus an individual CME can present radically different appearances at various locations in the heliosphere. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58711

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The possibility of exciting electromagnetic ion cyclotron waves in solar ejecta was proposed in earlier work (Farrugia et al.,JGR103, 6543–6550 (1998)). Here we focus on the twofold aspect of the effect of the protons on this instability, specifically, the proton thermal anisotropy,Ap=T⊥,p/T∥,p−1,and the non-Maxwellian tail representing bidirectionally streaming energetic protons (BPs), which are often observed in solar ejecta. Parameters expected to represent a number of solar ejecta are chosen and kept fixed. We solve the kinetic dispersion relation for a population of protons, electrons, and alpha particles. WhileApdoes not affect the phase speed of the waves, increasing|Ap|leads to a substantial enhancement of growth rates and a widening of the unstable frequency range. Maximum growth rates increase exponentially with|Ap|.The BPs are modeled by a &kgr;appa distribution along the field in addition to the bi-Maxwellian describing the rest of the population. A linear relation exists between maximum growth rates and the density ratio of &kgr;appa proton to Maxwellian protons(&eegr;&kgr;).Saturation of the width of the unstable frequency range occurs around&eegr;&kgr;∼10&percent;.©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58820

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The occurrence and properties of plasma waves associated with coronal mass ejections (CMEs) are investigated using the plasma wave instruments of the Unified Radio and Plasma Wave (URAP) experiment of the Ulysses spacecraft. Several CMEs observed by Ulysses at heliographic latitudes from the ecliptic plane to S60° are examined. Four wave modes are observed within the CMEs. 1) Electric waves at a few kHz, which are interpreted as Doppler shifted ion acoustic waves. They tend to occur in the region where the proton temperature is low. In all the cases that we studied, the electron temperature for the periods of enhanced ion acoustic like waves is greater than the proton temperature, although sometimes they are comparable(1<Te/Ti<10).2) Electromagnetic whistler waves are observed in regions where the solar wind plasma is turbulent (near interplanetary shocks or during the period of increasing solar wind velocity). 3) Electric waves near the electron plasma frequency, which are probably generated by streaming electrons within the CME structure. 4) Electric fluctuations below local electron cyclotron frequencies are observed during periods of decreasing solar wind velocity. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58821

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In recent studies, we have pointed out that the characteristic energetic particle signatures of interplanetary shocks, ejecta and corotating streams can be used to infer the presence of these structures even when in-situ solar wind observations are not available. The detailed solar observations currently available provide a test of this method. Using observations in 1996–97, we find that most (∼80&percent;) of the earthward-directed CMEs observed by the SOHO/LASCO coronagraph produced signatures in the energetic particle data. We also note that, considering all the CMEs observed by LASCO, those associated with energetic (>20 MeV) particle events were accompanied by the “traditional” signatures of energetic solar events such as type II and IV radio emissions, and H&agr;, and X-ray flares. They also had higher than average speeds and angular widths in the coronagraph observations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58712

出版商:AIP    

年代:1999

数据来源: AIP