|Session:||Poster session: CMEs and ICMEs (14)|
|Date:||Monday, June 13, 2005|
|Time:||00:00 - 00:00|
Current Sheet Evolution in the Aftermath of a CME
Bemporad, A.1; Poletto, G.2; Suess, S.3; Ko, Y. K.4; Schwadron, N. A.5; Elliott, H. A.5; Raymond, J. C.4
1Dept. of Astronomy and Space Science, Florence University, ITALY; 2INAF - Arcetri Astrophysical Observatory, ITALY; 3NASA Marshall Space Flight Center, UNITED STATES; 4Harvard-Smithsonian Center for Astrophysics, UNITED STATES; 5Southwest Research Institute, UNITED STATES
We report on SOHO-UVCS observations of coronal restructuring following a Coronal Mass Ejection (CME) on November 26, 2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after the CME, which was directed towards Ulysses, UVCS began taking spectra at 1.7 solar radii, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6x10(6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by SWICS throughout the magnetic cloud associated with the CME, although the rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. Both the remote and in situ observations are compared with predictions of theoretical CME models.
Early Evolution of a CME from White Light and UV observations
Bemporad, A.1; Poletto, G.2; Raymond, J. C.3
1University of Firenze, ITALY; 2INAF - Arcetri Astrophysical Observatory, ITALY; 3Harvard-Smithsonian Center for Astrophysics, UNITED STATES
At least one third of Coronal Mass Ejections (CMEs) have, in the interplanetary medium, a magnetic flux rope structure, usually referred to as ``magnetic cloud''. The solar origin of the topology of in situ flux ropes is still debated: according to a recent study (Leamon et al., 2004) only models invoking magnetic reconnection between active regions (ARs) and the large-scale overlying structures can adequately account for the characteristics of the Ars and magnetic cloud fields. In this work we study the evolution of the coronal mass ejection, associated with AR 8851, which occurred in the solar NE quadrant on January 31, 2000, with the aim of inferring the structure of the CME in the early stage of its lifetime. To this end, Mauna Loa MARK IV K-Coronameter images and SOHO/UVCS spectral data taken at 1.6 and 1.9 solar radii have been analyzed: these data cover a time interval wide enough to include the CME initiation and its early development. The coronal source of the CME has been identified with the help of SOHO/EIT and Yohkoh/SXT images, while the earliest identification of the expanding loops in front of the CME and of the CME core occurred at ~ 1.2 solar radii in Mauna Loa images. These structures eventually reached the UVCS slit and their passage left a clear signature in UV H Lyman-alpha and OVI 1032 and 1037 A doublet lines. Mauna Loa white light and UVCS UV data allowed us to reconstruct the CME configuration: a comparison of the observed structure with that predicted by the Lin & Forbes (2000) CME model shows the two to be quite similar. To our knowledge, this is the first time that this structure has been identified at such low altitudes. The upward speed and densities of the expanding loops and CME core are also given, together with a tentative estimate of the dimension of the CME bubble.
Survey of Interplanetary Coronal Mass Ejections in the Near Earth Solar Wind During 1996 - 2005
Cane, H V; Richardson, I G
Goddard Space Flight Center, UNITED STATES
We extend and update our survey of ICMEs in the near-earth solar wind (Cane and Richardson, JGR, 2003) to include the declining phase of cycle 23. We also take into account compositional data to help refine the event identifications. We discuss the variation in properties such as the occurence rate (including evidence for a ~150 day periodicity), speed, magnetic field intensity, fraction of ICMEs that are magnetic clouds, the relationship between geomagnetic storms and ICME properties, and the association between halo CMEs and near-Earth ICMEs.
Evolution of interplanetary magnetic clouds from 0.3 AU to 1 AU: A joint Helios-Wind investigation
Farrugia, C. J.1; Leitner, M.2; Helfried, H. K.2; Matsui, H.1; Schwenn, R.3; Kucharek, H.1; Ogilvie, K. W.4; Lepping, R. P.4
1Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, UNITED STATES; 2Space Research Institute, Austrian Academy of Sciences, Graz, AUSTRIA; 3Max-Planck-Institut für Aeronomie, Katlenburg Lindau, GERMANY; 4Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, UNITED STATES
A class of interplanetary configurations which interact strongly with the Earth's magnetosphere are interplanetary magnetic clouds. A desideratum of space weather predictions is that they be made from data acquired by distant probes so as to guarantee as long a lead time as possible. For this to be viable, one must have accurate knowledge of how ejecta parameters evolve (scaling factors). To this end, we use observations of magnetic clouds made by the spacecraft Wind at 1 AU, and by Helios 1 & 2 between 0.3 and 1 AU. A model is constructed, considering magnetic clouds as a cylindrically symmetric, force-free constant-alpha magnetic field configurations. We least-squares fit the data to the model and obtain model parameters, e.g. the axial magnetic field strength, the helicity, the axis orientation, the diameter. We adopt two approaches: In the first we obtain the way these parameters scale with distance from the Sun statistically. In the second approach we focus on line-ups of the spacecraft and determine directly how parameters scale with distance. The two approaches are then intercompared. The results are also discussed in the context of the analysis of Bothmer and Schwenn (1998).
Cross-Correlation of interplanetary parameters for large X (~500 Re) and Y (~300 Re) separation: Dependence on interplanetary structure.
Farrugia, C. J.1; Kucharek, H.1; Matsui, H.1; Leitner, M.2; Ogilvie, K. W.3; Torbert, R. B.1; Lepping, R. P.3; Terasawa, T.4; Mukai, T.5; Saito, Y.5
1Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, UNITED STATES; 2Space Research Institute, Austrian Academy of Sciences, Graz, AUSTRIA; 3Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, UNITED STATES; 4Department of Earth and Planetary Physics, University of Tokyo, Tokyo, JAPAN; 5Institut of Space and Astronautical Sciences, Kanagawa, JAPAN
During several years of overlapping operations in interplanetary (IP) space, the WIND-ACE-GEOTAIL separations varied greatly. This permits a multi-spacecraft study of cross-correlations of IP parameters over larger distances in X and Y than hitherto undertaken. We examine here two intervals. In the first, the spacecraft were at their maximum separation in X (~500 Re); in the second, the largest separation was in Y (~300 Re). A 1-month stretch of data is selected in each case, the solar wind structures therein are identified, and the cross-correlation is obtained as a function of structure. Particular attention will be given to correlation length scales of the interplanetary electric field since this is a crucial quantity in determining the non-linear behavior of the magnetosphere under extreme forcing.
Application of a new technique for deriving prominence mass from SOHO/EIT Fe XII (19.5 nm) absorption features
Gilbert, Holly; Gilbert, H. R.
HAO/NCAR, UNITED STATES
It is presently unclear what role prominences play in the initiation and dynamics of coronal mass ejections (CMEs), although erupting prominences are strongly correlated with CMEs. The masses of prominences involved in CMEs are not generally measured, but the accurate determination of such masses may help in assessing the dynamical importance of prominences in CME events. We apply a new technique for deriving prominence mass to a sample of different types of prominences in which we use observations of coronal radiation in the Fe XII (19.5 nm) spectral line, which is absorbed by prominence material. This new method allows us to consider the effects of both foreground and background radiation in our calculations.
MHD Numerical Simulations of CMEs Propagating in the Interplanetary Medium
Gonzalez-Esparza, Americo1; Jeyakumar, S.2; Lara, A.2; Santillan, A.2; Casillas, G.2
1UNAM, Mexico, MEXICO; 2UNAM, MEXICO
We present 3-D MHD numerical simulations of the propagation of CMEs in the solar wind. The model is based on the ZEUS 3D code (version 3.4). This work is a continuation of the numerical studies of interacting ejecta that we perfomed in a previous study using a 2-D HD model. We discuss the similarities and differences of the results given by two models.
Modeling of CME Visibility for the STEREO Mission
Howard, Russell1; Thernisien, A.2; Marque, C.2; Vourlidas, A.3; Cook, J. W.3; Socker, D. G.3
1Naval Research Lab, UNITED STATES; 2University Space Research Association, UNITED STATES; 3NRL, UNITED STATES
One of the objectives of the STEREO mission is to determine the three-dimensional configuration of CMEs. The STEREO mission consists of two identical spacecraft, one leading Earth and the other trailing Earth, which will separate from each other at the rate of about 45 degrees per year. The SECCHI experiment consists of 5 telescopes (on each telescope) that will be able to track CMEs from their launch at the Sun through the inner heliosphere to 1 A.U. To understand the visibility of CMEs and the ability to discern the 3D structure, we have been developing a “forward modeling” capability. We are able to compute synthetic total and polarized brightness images using the Thomson scattering formulae from an assumed electron density model. Several (geometric) models of a CME have been defined – loop, spherical shell, cylindrical shell and a graduated cylindrical shell (GCS). Since the GCS model is a reasonable simulation of a flux-rope CME, we have used it to investigate the appearance of a CME as a function of STEREO separation angle. In this model the angular size in the two directions, the height of the leading edge, the orientation of the structure in the corona and the radial electron density distribution can be specified. We present the results of this study and compare the simulations with observed CMEs from LASCO.
Total Pressure Signature as a Qualitative Indicator of the Impact Parameter during ICME Encounters
Jian, Lan1; Russell, C.T.1; Gosling, J.T.2; Luhmann, J.G.3
1Institute of Geophysics and Planetary Physics, UCLA, UNITED STATES; 2LANL, Los Alamos, NM, UNITED STATES; 3Space Sciences Laboratory, UC Berkeley, UNITED STATES
Methods exist to estimate the direction of Coronal Mass Ejections (CMEs) but complementary methods for evaluating where an in situ observation lies within its interplanetary counterpart have been lacking. It is conventional wisdom that only about one-third of Interplanetary Coronal Mass Ejections (ICMEs) are found to contain a magnetic cloud. This suggests that two thirds of ICME encounters occur sufficiently far from the center of the ICME that the magnetic structure is not identifiable. In order to determine how many ICME observations do or do not include entry into a cloud, we must have a reliable method of defining an ICME encounter that does not depend on the presence of a rotating magnetic field. Total perpendicular pressure can be used to distinguish ICMEs from other solar wind disturbances such as stream interactions without examining the direction of the magnetic field or its temporal behavior. We have compared our identifications with those of other groups and conclude that this identifier is quite effective. We find that many of the ICMEs that do not exhibit rotating magnetic fields are encountered away from the center of the ICME, thus missing the cloud. By using such signatures we can improve our ability to match ICMEs with the causative CMEs back at the Sun.
3D Numerical MHD Modeling of CME Expansions
Kleimann, Jens; Kopp, A; Fichtner, H
Ruhr-Universitaet Bochum, GERMANY
During the last decade, vast advances in computing power have helped much to overcome the tight resolution limits previously imposed on numerical MHD studies. This allows us to carry out self-consistent MHD simulations of solar wind expansion in all three space dimensions. Our code operates on a 3D Cartesian grid and uses an implementation of a recent 3rd order CWENO scheme to advance the set of single-fluid MHD equations in time. We present selected results from standard and non-standard test cases and perform studies of the solar wind expansion during phases of minimum solar activity, serving mainly as a first "real world" test case. We can demonstrate convergence of the system into a stable Parker-like steady state for both HD and MHD winds. The model is subsequently applied to expansion studies of CME-like disturbances, and their evolution is monitored until the initial undisturbed state is eventually restored. Since the assumption of axial symmetry is avoided, the initial propagation direction of a disturbance can be chosen independently of the orientation of the unperturbed magnetic field. Also, different strategies to ensure the solenoidality condition for the magnetic field are discussed and evaluated.
On the Stand-Off Distance of the Shock Ahead of Fast Magnetic Clouds
Leitner, Martin1; Farrugia, C. J.2; Biernat, H. K.1; Erkaev, N. V.3
1Space Research Institute, Austrian Academy of Sciences, Graz, AUSTRIA; 2Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, UNITED STATES; 3Institute of Computational Modelling, Russian Academy of Sciences, Krasnoyarsk, RUSSIAN FEDERATION
Magnetic clouds (MCs) form a type of interplanetary coronal mass ejection identified by simple properties. In a simple model, MCs are pictured as locally straight cylindrical objects with a force-free magnetic field of constant alpha. Least-squares fitting of the data to this model yields several MC parameters, such as the orientation of the cloud's axis, the axial field strength, and a closest distance of the spacecraft to the axis. Focussing on MCs which drive a shock, a procedure to determine the influence of the magnetic field strength on the size of the sheath (stand-off distance of the shock) is outlined. This is done by comparing with the case of a cylindrical object moving in an supersonic flow in the hydrodynamic limit. From the analysis we give a prediction on the size of the sheath of MCs, and how the size of the sheath evolves with heliospheric distance. Observations from Helios 1 and 2 (0.3 to 1 AU) and Wind (1 AU) are used.
The relative distribution of the magnetic and plasma kinetic energy densities as a function of heliospheric distance
Leitner, Martin1; Farrugia, C. J.2; Osherovich, V. A.3; Fainberg, J.3; Biernat, H. K.1; Ogilvie, K. W.3; Schwenn, R.4
1Space Research Institute, Austrian Academy of Sciences, Graz, AUSTRIA; 2Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, UNITED STATES; 3Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, UNITED STATES; 4Max-Planck-Institut für Aeronomie, Katlenburg Lindau, GERMANY
The quasi-invariant parameter (QI) is defined as the ratio of the magnetic energy density to the plasma kinetic energy density, i.e., the inverse square of the Alfven Mach number, (Osherovich, Fainberg and Stone, 1999). Quantity QI was found to be a very good proxy for solar activity, correlating strongly with sunspot number (correlation coefficient > 0.9). This high correlation holds not only at 1 AU but also at the position of Venus at 0.72 AU (Fainberg, Osherovich and Stone, 2001). Finally, Voyager 2 observations in the range 1-20 AU confirm QI as a good measure of solar activity (Fainberg and Osherovich, 2001).
Characteristics of ICMEs with and without high charge states: Implications for their eruption and expansion into interplanetary space
Lepri, Susan; Lawitzke, A.; Zurbuchen, T. H.
University of Michigan, UNITED STATES
It has been suggested that magnetic connectivity of a coronal mass ejection (CME) to a flaring region during eruption will dictate the presence of the high charge states observed in-situ in ICMEs (Lepri and Zurbuchen, 2004). The presence of this hot material in the solar wind has proven to be an effective identifier of hot ICMEs at 1 AU and beyond (Lepri et al., 2001). We present analysis of the plasma properties observed in hot ICMEs at 1 AU using the Advanced Composition Explorer (ACE) Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Electron Proton Alpha Monitor (SWEPAM). We examine the energy partition as a function of event-averaged charge states in order to characterize the nature of the eruption and its subsequent expansion as it propagates through interplanetary space. We compare these results with those from ICMEs which do not exhibit elevated charge states in order to highlight similarities and differences in their properties, giving insight into the eruption mechanisms that play a key role in the release of CMEs from the Sun. We examine the results of our study of the properties of hot ICMEs to determine whether remote observations of coronal temperatures during a CME can be used to provide boundaries for ICME speed, magnetic field strength, density, and event duration at 1 AU.
Stereo/Waves : New perspective on the stereoscopy of solar radio sources in the interplanetary medium
Maksimovic, Milan1; Bougeret, J.-L.2; Cecconi, B.3
1Observatoire de Paris & CNRS, FRANCE; 2Observatoire de Paris, LESIA & CNRS, FRANCE; 3University of Iowa, UNITED STATES
We describe and review the capabilities of the WAVES (SWAVES) investigation on the two STEREO spacecraft. The WAVES instrument is composed of a set of 3 monopole antennas connected to a radio receiver. The receiver measures spectral and cross-spectral power densities on one, two or three antennas in the frequency range between 10 kHZ and 16 MHz. This package will therefore have direction finding (DF) capabilities, allowing to determine the direction of arrival of an incoming wave, its flux and polarization properties. A DF analytical model has been recently developed and applied to the CASSINI/RPWS data in order to perform DF on localized Jovian radio-emission (Cecconi et al., 2005). We present an extension of this latter model for extended solar radio emission such as type III and type II bursts, produced respectively by subrelativistic electrons travelling outward along open magnetic field lines to lower densities in the interplanetary medium (IPM) and by solar wind electrons accelerated by transient shocks moving outward from the Sun to the IPM. We discuss also the scientific objectives of SWAVES associated to the previous observations: to probe the density and IMF structure of the heliosphere before and after CMEs; to understand the radio emission process and the beam pattern of radio bursts; to measure the electron density and temperature of filament material in magnetic clouds.
INTERACTION OF INTERPLANETARY SHOCKS WITH THE BOW SHOCK
Nemecek, Zdenek1; Prech, L1; Safrankova, J1; Koval, A1; Samsonov, A2
1Charles University, CZECH REPUBLIC; 2St. Petersburg University, RUSSIAN FEDERATION
Forward and reverse fast shocks as well as slow shocks have been often reported in the interplanetary space. As an incident interplanetary (IP) shock transmits through the bow shock, a train of different discontinuity modes would be generated downstream of the bow shock. At the same time, the bow shock can be modified and moves earthward. This interaction of the bow shock and IP shocks has been studied by gasdynamic as well as MHD theories. We present observations of such interaction and its comparison with 3-D MHD modeling. Based on several examples, we can conclude that the subsolar bow shock moves inward due to different magnetosonic speed downstream of the IP shock. This inward motion creates a ring-like trough on the bow shock surface. The trough proceeds along the bow shock with a speed that is slightly lower than that of the original IP shock. The trough motion would result in multiple bow shock crossings observed by the spacecraft in an appropriate location. All these features are consistent with our MHD modeling. However, we should point out that we did not find any train of discontinuities resulting from a IP shock-bow shock interaction in experimental or model data. Our results reveal one discontinuity propagating downstream and the other reflected from the magnetopause.
Automatic detection of EIT waves and dimmings
Podladchikova, Olena1; Berghmans, D.2
1Royal Observatory of Belgium, BELGIUM; 2Royal Observatopry of Belgium, BELGIUM
Studies of earth-directed CME are based on solar disk observations where CME structures are extremely difficult to resolve because of the diversity and transient character of these objects. Essential reorganisation of magnetic fields in connection with such CME are most brightly shown as dimmings and coronal waves. Among them, the mechanism for EIT waves is still unclear. Such waves are considered as MHD perturbations or as a consequence of plasma compression on the extending border of dimming. We develop numerical algorithms based on the combination of several filtering techniques. Our goal is to detect automatically EIT waves and dimmings in the STEREO/SECCHI mission. The EIT/SOHO data catalogs are used for testing. At the current stage of work, the method can unambiguously detect dimmings and shorter life time EIT waves on a typical case event. Moreover, we propose a way to extract these events from the data, and determine such parameters as life time, depth, area and volume of dimmings for future catalogs. For EIT waves we unumbigously define, in near solar minimum conditions, the eruption center, the front of EIT wave and its propagation velocity. Some of new observed features are: a) geometrical form of dimmings in the connection with the EIT wave front properties, their development and duration of space structure b) angular rotation of EIT waves, together with the radial expansion of front forming spiral-like motion.
A Survey of Interplanetary Coronal Mass Ejections in the Near-Earth Solar Wind in 1996-2005
Richardson, I. G.; Cane, H. V.
Goddard Space Flight Center, UNITED STATES
We extend and update our comprehensive survey of ICMEs in the near-Earth solar wind (Cane and Richardson, JGR, 2003) to include the declining phase of solar cycle 23. In particular, we include additional information on plasma compositional signatures to help refine the event identifications. We discuss the variation in properties such as the occurence rate (including evidence for a ~150 day periodicity), speed, magnetic field intensity, fraction of ICMEs that are magnetic clouds, the relationship between geomagnetic storms and ICME properties, and the association between LASCO halo CMEs and near-Earth ICMEs.
Solar wind ions and energetic particles within magnetic clouds
Rodriguez, Luciano1; Woch, J.1; Krupp, N.1; Fraenz, M.1; von Steiger, R.2; Cid, C.3; Forsyth, R.4; Glassmeier, K.-H.5
1Max Planck Institut fuer Sonnensystemforschung, GERMANY; 2International Space Science Institute, SWITZERLAND; 3Universidad de Alcala, SPAIN; 4Imperial College, UNITED KINGDOM; 5Technische Universitaet Braunschweig, GERMANY
Magnetic clouds represent a special kind of interplanetary coronal mass ejections in which the magnetic field exhibits a characteristic configuration. They represent nearly one third of all the coronal mass ejections seen by Ulysses. Among the many open questions regarding their origin and evolution, one of the most challenging scientific problems is to gain insights into their internal structure. Using in-situ data provided by instruments onboard Ulysses, 40 magnetic clouds have been identified in the time period between 1992 and 2002.
Modelling of Fast Iinterplanetary Magnetic Clouds, with Forward and
Romashets, Eugene1; Vandas, Marek2
1Institute of Terrestrial Magnetis, Ionosphere, and Radio Wave Propagation of Academy of Sciences, RUSSIAN FEDERATION; 2Astronomical Institute, Academy of Sciences, CZECH REPUBLIC
There have been many model field structures inside magnetic clouds developed and applied recently: symmetric and non-symmetric, force-free with constant and variable alpha, non-force-free ones. In this paper we solve a more extended problem and construct also the field in forward and rare regions around a cloud. We assume that bow shocks and an internal boundary are parts of parabolic cylinders. Conditions for the magnetic field are the following: co-planarity and continuity of Bn at the shocks and tangential or contact discontinuity relations at the boundary. A force-free field plus an induced part (which is negligible at the center) are assumed inside the cloud. As it has been shown earlier, more correct self-consistent plasma flows can be found only in case of contact discontinuity on the cloud's boundary. We expect to apply the model to some of prominent events with very fast clouds.
SOLAR WIND DISCONTINUITIES AND THEIR EVOLUTION FROM L1 TO THE EARTH
Safrankova, Jana1; Koval, A1; Nemecek, Z1; Prech, L1; Richardson, J D2
1Charles University, CZECH REPUBLIC; 2MIT, UNITED STATES
The study of gradual evolution of interplanetary shocks and similar discontinuities in the solar wind from L1 to the Earth is an important topic of the Sun-Earth's system investigation. Based on multiple spacecraft observations, we have identified about 30 events with various plasma and interplanetary magnetic field signatures and traced their gradual evolution along the Sun-Earth line. We used different techniques based on single or multiple spacecraft data in order to analyze their topological properties, namely the propagation velocity and the shape of their leading edges. We present several examples showing that (1) strong IP shocks are usually planar on the magnetospheric scale length and their evolution is negligible, but (2) weaker discontinuities can change their properties along their path toward the Earth. Using determined normals and speeds as well as jumps of the parameters across the discontinuity, we are trying to find typical orientations and dimensions of discontinuities as well as a probability that a particular discontinuity will approach the Earth as a function of aforementioned quantities.
The association of coronal mass ejections with their effects near the Earth
Schwenn, Rainer1; Dal Lago, A.2; Huttunen, E.3; Gonzalez, W.D.2; Muñoz Martínez, G.4
1Max-Planck-Institut für Sonnensystemforschung, GERMANY; 2Instituto Nacional de Pesquisas Espaciais, Sao Jose dos Campos, SP, BRAZIL; 3Department of Physical Sciences, University of Helsinki, FINLAND; 4Instituto de Geofísica, UNAM, MEXICO
The association of coronal mass ejections (CMEs) with their interplanetary counterparts (ICMEs) near the Earth has been addressed by many authors, with often rather controversial conclusions. We performed a new comprehensive, study of this connection by searching a representative and complete data set from both ends: solar and coronal images and interplanetary data obtained near the Earth, for the period from January 1997 to April 15, 2001. The data were primarily provided by the LASCO coronagraphs, plus additional information from the EIT instrument on SOHO. Solar wind data from the plasma instruments on the SOHO, ACE and Wind spacecraft were used to identify ICME effects near the Earth. On correlating 181 CMEs on the one side and 187 ICMEs on the other side we found that in about 85% of front side full or partial halo CMEs an ICME effect at the Earth can be expected. That also means that in 15% of comparable cases a full or partial halo CME does NOT cause any ICME signature at Earth; every forth partial halo CME and every sixth limb halo CME does not hit the Earth (false alarms). On the other hand, every fifth transient shock or ICME or isolated geomagnetic storm is not caused by an identifiable partial or full halo CME on the front side (missing alarms). At times of high solar activity, CMEs often occur shortly one after the other such that they interact and merge with each other. Their effects at the Earth become highly unpredictable.
Improved space weather forecasting using the halo expansion speed .
Schwenn, Rainer1; Dal Lago, A.2; Huttunen, E.3; Gonzalez, W.D.2; Muñoz Martínez, G.4
1Max-Planck-Institut für Sonnensystemforschung, GERMANY; 2Instituto Nacional de Pesquisas Espaciais, Sao Jose dos Campos, SP, BRAZIL; 3Department of Physical Sciences, University of Helsinki, FINLAND; 4Instituto de Geofísica, UNAM, MEXICO
Forecasting space weather suffers from a fundamental problem: The radial propagation speed of “halo” CMEs (i.e. CMEs pointed along the Sun-Earth-line that are known to be the main drivers of space weather disturbances) towards the Earth cannot be measured directly because of the unfavorable geometry. For limb CMEs where the radial speed can readily be determined, we found that that it is usually well correlated with the speed of the halo's lateral expansion. This latter quantity can also be determined for earthward-pointed halo CMEs. Thus, it may serve as a proxy for the otherwise inaccessible radial speed of halo CMEs. We studied this connection for all events in the period from January 1997 to April 15, 2001. The data were primarily provided by the LASCO coronagraphs, plus additional information from the EIT instrument on SOHO. Solar wind data from the plasma instruments on the SOHO, ACE and Wind spacecraft were used to identify the arrivals of ICME signatures. We found 91 cases where CMEs were uniquely associated with ICME signatures in front of the Earth. 80 ICMEs were associated with a shock, and for 75 of them the halo expansion speed and the travel time of the shock could both be determined. We derived an empirical function that fits the data best, the 95% error margin being about one day. This empirical formula has since been used successfully for forecasting many ICME arrivals, .
CMEs Observed By SMEI Which Are Not Seen By LASCO
Simnett, George; Simnett, G.M.
University of Birmingham, UNITED KINGDOM
The Solar Mass Ejection Imager (SMEI) has been observing CMEs in the interplanetary medium since its launch on the Coriolis spacecraft on 6 January 2003. Approximately 1/8th of the events which are readily detected in the all-sky images produced once/orbit (102 minutes) are not accompanied by an event visible in LASCO running difference images within 12 hours of the nominal time the event left the Sun. The latter is based on a back-extrapolation of the elongation-time plot of the SMEI event. A further constraint is that the search of the LASCO data was restricted to a position angle within +/- 60 degrees of the position angle of the SMEI event. A further 1/8th of the SMEI events were accompanied by extremely faint LASCO events, which would not have been detected by a casual observer, but which otherwise matched well with the SMEI elongation-time plot at the same position angle. The conclusion form this work is that erupting magnetic structures from the Sun must frequently accumulate mass as they travel through the interplanetary medium.
Determining Shock Velocity Inputs for Sun-to-Earth Models.
Smith, Zdenka1; Detman, T. R.1; Dryer, M.2; Fry, C. D.3
1NOAA/Space Environment Center, UNITED STATES; 2NOAA/Space Environment Center, Boulder, CO, UNITED STATES; 3Exploration Physics International, Inc., UNITED STATES
One of the key parameters used for input by many numerical modeling codes that predict the arrival of interplanetary shocks at Earth on the basis of solar data is the estimated speed of shocks that precede ejecta from solar energetic eruptions. Forecasting these shocks is of interest because they are likely to be followed by significant geomagnetic activity. We have previously investigated the use of halo/partial halo CME and metric type II radio burst measurements for inputs into numerical models presently used to make forecasts of shock arrival times at the L1. These “fearless forecasts”* are distributed in near-real-time by e-mail to interested subscribers. The period of high solar activity in Oct.-Nov. 2003 was used for the study because the data required for input into the models was often available in near real time from a number of observing stations. Both CME and metric type II radio burst measurements were shown to be useful and complimentary, thereby demonstrating the desirability of having coronagraph data available for operational use. Guidelines for the selection of the speed for use as input to shock propagation models were presented, based on the kinematic 3D solar wind model HAFv.2 results. We here investigate how well these inputs perform when used by the Hybrid Heliospheric Modeling System (HHMS) 3D MHD code. This work was partially funded by the NASA Living With a Star (LWS) Targeted Research and Technology program, through Grant NAG5-12527 to Exploration Physics International, Inc (MD and CDF) and through NOAA Work Order No.W-10,118 (ZS and TD). *http://gse.gi.Alaska.edu/recent/vdp.html and http://gse.gi.Alaska.edu/recent/vdbs.html.
Plasma flows inside magnetic clouds
Vandas, Marek1; Romashets, E. P.2; Watari, S.3
1Astronomical Institute, Academy of Sciences, CZECH REPUBLIC; 2IZMIRAN, Troitsk, RUSSIAN FEDERATION; 3NICT, Tokyo, JAPAN
Recently we have developed a model of a magnetic cloud describing it as an oblate expanding cylinder with a constant-alpha force-free magnetic field configuration inside. Spacecraft in-situ magnetic cloud observations will be fitted by this model and magnetic field vectors and solar wind velocity vectors from the measurements and the model will be compared. A special emphasis will be laid to behaviour of velocity inside clouds and how it fit with the idea of cloud's expansion.
Growing mushroom clouds in the solar atmosphere and the heliosphere associated with fast coronal mass ejections
Veselovsky, I.S.; Panassenco, O.A.
Institute of Nuclear Physics, RUSSIAN FEDERATION
Formation, growth and decay of mushroom clouds will be described using LASCO/SOHO movies. Mushroom shapes appear in a natural way in the case of ejecta moving faster than the background plasma. One-leg and two-leg structures as well as more complicated geometry cases are documented. The phenomenon is similar to well known hydrodynamic analogues and explosions. Attributes include flattened tops, laminar and turbulent substructures of smaller size, shocks, secondary flows and others. Stereoscopic observations are promising for the 3D shape reconstruction of this phenomenon.
Interplanetary mass ejections between 0.3 and 30 AU:
Multi-spacecraft observations and model comparison
Wang, Chi1; Du, D.1; Richardson, J. D.2; Liu, Y.2
1Center for Space Science and Applied Research, Chinese Academy of Sciences, CHINA; 2MIT Center for Space Research, UNITED STATES
Using observations from multiple spacecraft such as Helios, PVO, ACE, Ulysses and Voyager 2 which are distributed throughout the heliosphere, we identify and characterize interplanetary mass ejections (ICMEs) between 0.3 and 30 AU. An abnormally low proton temperature is used as the primary identification signature of ICMEs. The occurrence rate of ICMEs approximately follows the solar activity cycle. Statistically, the average radial width of ICMEs increases with distance up to about 10 AU, with a radial expansion speed of the order of the Alfven speed. The expansion features of the average temperature, density, and magnetic field magnitude of ICMEs are also studied. We employ a one-dimensional, MHD numerical code to model the propagation of ICMEs to try to understand the observations. The model results reproduce the basic expansion characteristics of ICMEs.
Magnetohydrodynamic Tracking of CME from Its Birth to ICME
Wang, Aihua; Wu, S. T.; Zhang, T. X.
University of Alabama in Huntsville, UNITED STATES
We use a 2.5D streamer MHD model with a typical background solar wind to investigate the evolution of the CME from its birth to its maturity becoming an “ICME”. Two types of CMEs are studied: (i) a CME with flux-rope structure and (ii) a CME without flux-rope structure. To initiate a CME with flux-rope, we input an opposite polarity magnetic flux at the foot points of the streamer. Through the magnetic reconnection, a flux-rope formed and escaped from the streamer to launch a CME. This CME propagates outward to 1AU and beyond. On the other hand, we input an opposite polarity flux at the edge of the streamer, it launches a CME without flux-rope. This CME also propagates to 1AU and beyond. We will compare computed plasma and magnetic field parameters with those from the observations to examine the differences between ICME with and without flux-rope.
CMEs Observed in the Heliosphere by SMEI
Webb, David1; Mizuno, D.1; Simnett, G.2; Howard, T.2; Jackson, B.3; Johnston, J.4; Tappin, J.2
1Boston College, UNITED STATES; 2Univ. of Birmingham, UNITED KINGDOM; 3Univ. of California- San Diego, UNITED STATES; 4Air Force Research Lab, UNITED STATES
The Solar Mass Ejection Imager (SMEI) experiment on the Coriolis spacecraft has been obtaining all-sky, white light images on each 101-minute orbit for over 2 years. SMEI is fixed to the spacecraft and views the sky above Earth using sunlight-rejecting baffles and CCD camera technology. When fully calibrated, sky maps of structures having enhanced electron density in the inner heliosphere can be produced. We present results of examples and statistical analysis of SMEI observations of coronal mass ejections (CMEs) traveling through the heliosphere. These include observations of about 140 CMEs during the first 1.5 years of operations. Some of these, observed as frontside halo events by LASCO, were observed by SMEI propagating toward Earth and beyond and associated with major geomagnetic storms. We show examples of the CMEs and present a summary of their characteristics. We also show some 3D reconstructions of CMEs in the interplanetary medium using techniques being developed to analyze the evolution of heliospheric plasma, including transient CMEs and corotating dense regions (see related paper by Jackson et al.).
On methods of ICME identification on the basis of measurements
in the interplanetary space.
Yermolaev, Yuri; Yermolaev, M.Yu.; Nikolaeva, N.S.
Space Reserach Institute (IKI) RAN, RUSSIAN FEDERATION
Various parameters and techniques are used to identify ICME, but any parameter does not give absolutely reliable identification. Recently several researchers began to use parameters T/Texp (where T is measured proton temperature and Texp is proton temperature calculated on the basis of average T dependence on velocity V ) to select ICME (T/Texp < 0.5) and compressed streams (T/Texp > 2). Low T/Texp is also observed in the heliospheric current sheet (HCS). So usage of only this parameter does not allow one to select ICME. On the other hand, T/Texp is combination of measured parameters T and V (T/V**2), and if another well-known average dependence (nV**2=const, where n is density) is used we can calculate that T/Texp is proportional to nT, i.e. thermal pressure. In contrast to T/Texp, nkT is high in HCS and allows one to select ICME. We also discuss that in ICME the dependences of proton temperature, total ion density, minor ion abundance on the solar wind velocity differ from ones in another types of solar wind. Paper is support in part by Physical Department of Russian Academy of Sciences, Program N 18, and RFBR, grant 04-02-16131.
Determination of Geometrical and Kinematical Properties of Halo CMEs using the
Ice Cream Cone Model
Stanford University, UNITED STATES
Many limb coronal mass ejections (CMEs) show the shape of the ice cream cone. To determine the geometrical and kinematical properties of halo CMEs formed by scattering of Sun's white light at the plasma shell of such ice cream cone, we develop an ice cream cone model. The cone part of the model is determined by the straight legs (sides) of the CMEs with its apex coinciding with the center of the Sun, and the ice cream part of the model is expressed by a part of a spheroid that caps the cone part at a heliocentric distance. It is found that when the angle between the central axis of the ice cream cone and the line of sight is greater than 45 degrees the elliptical halo is not symmetric about the major axis of the halo, and when the angle is less than 45 degrees the halo is symmetric. In both cases, the geometric and kinematic properties can be uniquely determined.