SH53B-0306 1340h
Numerical MHD Simulation of Key Parameters for CME Initiation
Recently, Falconer et al. (2002) have developed a set of physical parameters to correlate the coronal mass ejection productivity of solar active regions with measures of their non-potentiality from vector magnetograms. In this presentation, we will use a newly developed three-dimensional, time-dependent, magnetic field transport model with magnetohydrodynamic (MHD) effects, which is named the Photospheric Surface Dynamo (PSD) model. This model is based on MHD theory with additional physics of the photosphere including differential rotation and meridional flow. Thus, the inertial centrifugal force and the coriolis force which are usually not taken into account in the MHD equations are included. In addition, the effect of diffusion due to random motion of the granules or super-granules and cyclonic turbulence are also included. This model is used to simulate those CME production parameters: (i) the magnetic flux content ($\Phi)$ of the active region, (ii) the length of strong-shear, strong-field main neutral line ($L_{ss}$), (iii) the net electric current ($I_n$) and (iv) a flux-normalized measure of the field twist ($\alpha = \mu I_n / \Phi$), suggested by Falconer et al. (2002). An example is given by using SOHO/MDI magnetic field measurements of AR8100, recorded from October 31, - November 3, 1997. These simulated parameters show good agreement with the observations.
SH53B-0307 1340h
A statistical comparison of solar wind sources of intense and moderate geomagnetic storms at solar maximum and minimum
Superposed epoch analyses of 153 storms are performed to make a comparison of solar wind typical features of geomagnetic storm events at solar minimum (January, 1995 - June, 1997) and solar maximum (July, 1999 - June, 2002). In this study, geomagnetic storms are defined by the pressure corrected Dst (Dst$^{*}$) and classified into intense storms and moderate storms. After the seasonal distribution of storms in each category is shown,the average values of interplanetary magnetic fields (IMF), solar wind plasma, NOAA/POES Hemispheric Power, Kp and Dst$^{*}$ are analyzed and compared among different storm categories. Occurrence peak shiftings between intense storms and moderate storms are found in the storm seasonal distributions. It is shown that the peak of solar wind density leads minimum Dst* by 5.2-7.3 hours, which is longer than the peak time difference (0.5-1.0 hour) between IMF B$_{z}$ and Dst$^{*}$$_{min}$. During intense storms, it is found that much higher solar wind density and lower solar wind bulk flow speed at solar minimum than at solar maximum. The results obtained also show that the average interplanetary cause of intense storms is IMF B$_{s}$ -Y 10 nT lasting for over 3 hours with longer duration and less fluctuations at solar maximum than at solar minimum. As for moderate storms, the primary cause is IMF B$_{s}$ -Y 5 nT lasting for over 2 hours with almost no average value difference among solar wind parameters at solar maximum and minimum, except for higher solar wind temperature during moderate storms at solar minimum than at solar maximum. The interplanetary and solar origins of storms in different categories are also discussed.
SH53B-0308 1340h
Predictions of solar wind properties at 1 AU: A comparison of empirical and physics-based models to spacecraft data.
One of the primary goals of the Center for Integrated Space-weather Modelling (CISM) effort is to assess and improve prediction of the solar wind conditions in near-Earth space, arising from both quasi-steady and transient structures. Empirical models play a key role in the CISM approach, as they act as a baseline by which to track the changes in the prediction accuracy of the physics-based models during their development. We compare spacecraft measurements of the 1 AU solar wind with predictions made by coupled MHD models of the corona (MAS) and heliosphere (ENLIL), and with empirical predictions made by the Wang-Sheeley-Arge (WSA) model. The results are interpreted in terms of both the current predictive capability and validity of the models.
SH53B-0309 1340h
Solar UV Irradiance Measurements from SUSIM UARS
The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) aboard the Upper Atmosphere Research Satellite (UARS) has measured the solar UV irradiance since October 1991. This 13 year time period includes a secondary maximum of solar cycle 22, the ensuing solar minimum, the maximum of solar cycle 23, and its declining phase. SUSIM maintains the calibration of its changing responsivity through a combination of measurements of four stable onboard deuterium calibration lamps and measurements of infrequently exposed reference channels. The wavelength-dependent UV irradiance time series exhibit two dominant periodicities, that of solar rotation (27~days) and solar cycle (11~years). The solar cycle variation of the UV irradiance was similar for solar cycles~22 and 23: about 55% at Ly-$\alpha$, about 7% at 205~nm, and less than 1% above 300~nm. The SUSIM measurements are compared with other coincident measurements including those of SOLSTICE over a similar time period and with the Mg~II core-to-wing ratio index. Prospects and requirements for continued and possibly improved monitoring of the solar UV irradiance are discussed.
http://solarwww.nrl.navy.mil/susim_uars.html
SH53B-0310 1340h
Does the aa Index Really Imply a Rich Doubling of the Heliospheric Magnetic Field during the Last 100 Years?
It is known since long that the long-term geomagnetic activity presented by the aa index increases considerably during the last 100 years. This increase, together with the more recent in situ measurements of the heliospheric parameters, has been used to claim that the heliospheric magnetic field has more than doubled during the last centennium. Here we reanalyze the implications of the centennial increase of the aa index by studying the relation between the various heliospheric parameters and geomagnetic activity. We show that, while the heliospheric magnetic field does increase during the last 100 years, the earlier estimate on this increase is grossly exaggerated. Moreover, since serious concern has recently been raised on the long-term consistency of the aa index, we have reanalyzed geomagnetic activity during the last 100 years using data from several stations and extracted a new centennial index C of global geomagnetic activity. We compare the implications of this new index and the aa index for the last 100 years.
SH53B-0311 1340h
Short-term changes in solar spectral irradiance - synthesis calculations
We present the latest results from the SunRISE spectral synthesis in specific spectral bands in the UV, visible, and near-IR in response to short-term (days-months) solar activity in the latter stage of solar cycle 23 and compare to observations from SORCE/SIM and other datasets. We will comment on the degree of redundancy in parts of the solar spectrum and how this could affect what wavelengths and bandpasses in the spectrum are important for observing programs.
SH53B-0312 1340h
Solar Torsional Oscillations and the Extended Solar Cycle
Torsional Oscillations were first observed on the surface of the sun as waves of small deviations from differential rotation, which propagate from the pole to the equator over solar-cycle time scales. More recently they have been inferred from observations of solar global oscillations to occur in the convection zone. Other solar phenomena, such as ephemeral regions and brightenings in the corona, have also been observed to propagate from near the poles to the equator over similar time scales. These other phenomena have been collectively referred to as the "Extended Solar Cycle". This paper will discuss the relationship between torsional oscillations as observed in the convection zone and the "Extended Solar Cycle" as observed in the corona.
http://nsosp.nso.edu/data/corona.html
SH53B-0313 1340h
Comparison of Solar Energetic Particle Events and Impulsive Nitrate Increases in Greenland Ice Cores
Using nitrate measurements from Greenland ice cores we examine the correlation of nitrate spikes and solar proton events. We choose a few large space-age events for analysis, focusing particular attention on the amplitude and timing of the nitrate increase in relation to the onset and characteristics of the SEP event. A time delay between nitrate spikes and SEP onset has previously been observed to be a few weeks, which is much faster than current atmospheric downward transport theory allows. Independent confirmation or invalidation of the previous analysis of this short delay has not been attempted before.
SH53B-0314 1340h
Solar Radius Measurements at Mount Wilson
Variations of the solar radius are not only important for solar physics but they also play a fundamental role in the research of terrestrial climate. In fact, changes in the apparent size of the Sun could account for a significant fraction of the total irradiance variations, and solar irradiance is known to be a primary force in driving atmospheric circulation. While the MDI instrument aboard SOHO is likely to provide the most accurate constraint on possible solar radius variations, the radius measurements obtained from ground base observations represent a unique resource due to their long temporal coverage. Since 1970, the Mount Wilson synoptic programme of solar magnetic observations carried out at the 150-foot tower scans the solar disk using the radiation in the neutral iron line at 525.0 nm. For these images, the radius has been determined and results are presented on this paper. We show first the temporal behavior of these measurements. Secondly, if data are gathered by heliolatitude, the shape of the Sun differs from a perfect ellipsoid and shows solar distortions. We compare these results with others obtained with the heliometer at the Pic du Midi observatory in France. The comparison show a similitude in the shape with a bulge near the equator extending on 20-30 degrees followed by a depression at higher latitude near 60-70 degrees. These solar distortions needs to be confirmed by future space measurements (PICARD microsatellite) but it already raises the problem of a better understanding of the physics in the sub-surface layers.
SH53B-0315 1340h
The asymmetry in sunspot area and magnetic flux variations in 1996-2004 extracted from the Solar Feature Catalogues
This research utilizes a searchable Solar Feature Catalogue (SFC) for sunspots created from the SOHO/MDI full disk whitelight images and magnetograms in 1996-2004 using the automated pattern recognition techniques {\bf $http://www.cyber.brad.ac.uk/egso/$}. A comparison of sunspot areas from the SFC with the averaged sunspot numbers published in the Sunspot Index Data Centre (SIDC) verified the detected sunspots with their correlation with sunspots areas on agiven day that revealed a very good detection accuracy of $86%$ for the whole period 1996-2003. The latitudinal (N-S) and longitudinal variations of sunspot areas, a total and resulting, or excess, magnetic flux are presented for the whole period of observations. The total sunspot areas measured from a single solar image have shown to have a strong Northern-Southern asymmetry that reveals the similar trend in the cumulative sunspot areas. At the start of the cycle from 1996 until 1999 the Northern hemisphere area trails the Southern one then followed by a bigger increase of the areas in the Northern hemisphere. The excess magnetic flux confined in sunspots also shows a significant N-S asymmetry being mostly negative in the Southern hemisphere and positive in the Northern one. However, towards the solar minimum in 1996 and in 2003-4 the excess flux becomes positive in the Southern and negative in the Northern hemispheres. These variations of total and excess magnetic fluxes during the solar cycle are compared with a few solar dynamo models.
SH53B-0316 1340h
Brightness Characteristics of Halo CMEs
It is generally accepted that halo Coronal Mass Ejections (CMEs) are regular, low latitude, CMEs traveling towards (or away FROM) the observer. The association between halo CMEs and solar energetic particles events (SEPs) and Type II bursts is higher compared to regular CMEs. Halo CMEs are observed up to large heliocentric distances as compared to the regular CMEs. This is somewhat contradictory to the theory of Thomson scattering because the visibility conditions for halo CMEs are rather poor, assuming that the longitudinal widths of halo CMEs are the similar to those of regular CMEs. In this paper, we present some observational characteristics of halo CMEs, such as high brightness at large distances and symmetry in the velocity space. The CMEs were observed by the Solar and Heliospheric Observatory (SOHO) mission's Large Angle and Spectrometric Coronagraph (LASCO). We also present a possible model that explains the apparent contradiction
SH53B-0317 1340h
Predicting Intensity of Major Geomagnetic Storms from Solar and Interplanetary Properties of CMEs: A Statistical Model
This paper describes a statistical model based on logistic regression for predicting the occurrence of intense geomagnetic storms. Previous studies show that the strength of the resulting geomagnetic storms depend upon various solar and interplanetary properties. During 1996-2002, 64 geo-effective events were recorded which were used for determining the parameters influencing the strength or the magnitude of the resulting geomagnetic storms. 60% of the events recorded were used for determining the model parameters while the rest 40% were used for validating the model. Independent variables which include a number of solar and interplanetary factors were provided as input to the model and regressed against a binary dependent variable viz. occurrence of the intense geomagnetic storms. The present model predicts 90% of the training events correctly and 90% of the validation events correctly. The results indicate that the logistic regression model can be effectively used for space weather prediction i.e. the strength of the geomagnetic storms.
SH53B-0318 1340h
The effect of adiabatic energy loss on the parallel mean free path of solar energetic particles
The focused transport equation without adiabatic energy loss is widely used to model solar energetic particles'(SEP) interplanetary propagation. However, SEPs experience the effect of adiabatic energy loss because of the divergence of the solar wind flows. Our particle simulations show that adiabatic energy loss is significant even in a short period, e.g., less than one day. In this paper we will show the comparison between solutions of focused transport equations with and without energy loss. It will be shown that without energy loss, for gradual events, we can only fit the initial phase of SEP events. However, with energy loss, we can fit the entire (initial and decaying) phases. In addition, the values of the mean free path obtained by fitting the SEP events with or without energy loss are different. The results indicate that adiabatic energy loss cannot be neglected in the modeling of SEP events.
SH53B-0319 1340h
Solar Wind Modeling and Data Assimilation: Concept and First Results
Up to five simultaneously operating spacecraft monitored the solar wind in 1998-2000 between the L1 point and Earth (ACE, WIND, IMP 8, Geotail, and Interball-1). However, the current space weather prediction methods do not take advantage of these observations made at multiple points. Rather, a single upstream monitor is selected out of the available spacecraft, effectively assuming a completely uniform solar wind flow. We have initiated a project with an aim to assimilate all solar wind observations into the numerical 3D MHD model ENLIL in order to reconstruct the solar wind profile perpendicular to the Sun-Earth line. We present preliminary results of simplified model runs and discuss the benefits and difficulties of data assimilation in the solar wind.
SH53B-0320 1340h
A new source of the slow solar wind
Slow solar wind has been found to exhibit a high level of variability and the source of its origin is still unclear. Helmet streamers underneath the base of the heliospheric current sheet has been suggested to be the source of slow solar wind, though low latitude coronal holes could be another source. It has been shown recently that the helmet streamers occur between coronal holes of opposite polarity as well as between coronal holes of like polarity. The former is called the bipolar closed field regions and the latter unipolar closed field regions [Zhao and Webb, 2003]. We investigate the association of slow solar wind observed by WIND, ACE and IPS with unipolar closed field regions.
SH53B-0321 1340h
SOLAR AND HELIOSPHERIC MODELS AT THE CCMC.
The Community Coordinated Modeling Center(CCMC) is a multi-agency effort to aid in the development of operational space weather forecasting tools. The centers principal roles are to help transition community research models from research to operational status, and on behalf of the model developers, to provide access to these models to the greater community for research purposes. The CCMC currently hosts five solar and heliospheric models. In this presentation we will outline the various functions and services provided to the solar and heliospheric community in association with these five models and will also discuss future plans to extend the CCMC support to this community.
SH53B-0322 1340h
A Loss-Cone Precursor of an Approaching Shock Observed by a Cosmic-Ray Muon Hodoscope at Mt. Norikura
We analyze a loss-cone anisotropy observed by a ground-based muon hodoscope at Mt. Norikura in Japan for 7 hours preceding the arrival of interplanetary shock at Earth on October 28, 2003. The observed anisotropy can be well reproduced with a model taking account of the directional distribution of cosmic ray intensity in space, the average rigidity dependence of Forbush decrease region formed behind the shock and the rigidity dependence of the lead-time of the precursory anisotropy. Best-fitting a model to the observed anisotropy suggests that the loss-cone in this event has rather broad pitch-angle distribution from the IMF. According to numerical simulations of high-energy particle transport across the shock, this implies that the shock is _gquasi-parallel_h shock in which the angle between the magnetic field and the shock normal is small. It is also suggested that the lead-time of this precursor rapidly decreases with decreasing rigidity. It is 10 hours at 30 GV for muon detectors, while it is only 1.4 hours at 10 GV for neutron monitors. We also estimate the parallel mean free path of pitch angle scattering to shorter than that predicted from the representative power spectrum of IMF turbulence. This implies that the IMF is much more turbulent in this event than that characterized by the representative power spectrum.
SH53B-0323 1340h
Space Weather Drivers in the ACE Era
The Advanced Composition Explorer (ACE) spacecraft was launched Aug.~25, 1997 [{\it Stone et al.}, 1998]. Beginning shortly after launch and continuing to the present day ACE has provided real-time data telemetry of solar wind conditions upstream of the Earth. The real-time data includes solar wind speed and density, magnetic field direction and magnitude, and a range of energetic particle intensities [{\it Zwickl et al.}, 1999]. The real-time data product is provided within 5 minutes of observation and many partners from both industry and science use these data for a variety of purposes. The most common purpose of practical industrial application involves mitigation of lost services arising from magnetospheric storm activity. Many space weather efforts are directed at providing improved predictions of magnetospheric response that can be applied to real-time data in the hope of better predicting the vulnerability and required action of industry to approaching disturbances. It therefore seems prudent that following 6 years of activity including one solar maximum period we should evaluate the nature and strength of the largest disturbances observed with the hope of better assessing the industrial response. Simply put: ``Did ACE observe disturbances that were as large as those seen previously during the space age?'' If not, it may be the case that industry must evaluate its response to the real-time warnings and not become complacent by the simple act of survival. We compare the most intense space weather events of the ACE era with those recorded on the Omnitape data set spanning 40+ years of spacecraft measurements in the near-Earth environment. We compare both magnetospheric response parameters and solar wind drivers. In addition, we compare the large energetic particle events over the same time frame. Stone, E.~C., et al., Space Science Rev., 86(1-4), 357-408, 1998. Zwickl, R.~D., et al., Space Science Rev., 86(1-4), 633-648, 1998.
SH53B-0324 1340h
Improved Empirical CME Arrival Time Prediction Model
We have successfully developed an innovative analytical method to determine the angular width and propagation orientation of Halo Coronal Mass Ejections (Xie et al. 2003). We will apply this new method to improve the existing empirical space weather forecasting models (e.g., Gopalswamy et al., 2001). Gopalswamy et al. (2001) presented an empirical model to provide the predication of CME transit time from the Sun to the Earth. The model is in good agreement with the observations for high-speed CMEs. However, the agreement is not good for low-speed events. One of possible reasons may be due to errors caused by the significant scatter of CME prjection speeds used in the model. Using our new method can determine the actual speed of CMEs and thus reduce the errors and improve the model.
SH53B-0325 1340h
Space Weather Modeling Framework: Modeling the Sun-Earth System Faster Than Real Time
The Space Weather Modeling Framework (SWMF) aims at providing a flexible plug-and-play type framework for physics based space weather simulations, as well as for various space physics applications. The SWMF combines numerical models of the Solar Corona (including an Eruptive Event Generator), the Inner Heliosphere, Solar Energetic Particles, Global Magnetosphere, Inner Magnetosphere, Radiation Belt, Ionosphere Electrodynamics and Upper Atmosphere into a high performance coupled model. All the components can be replaced with alternatives, and one can use only a subset of the components. The configuration, compilation and execution of the framework can be done with a user friendly Graphical User Interface. The components are coupled to the control module via standardized interfaces, and an efficient parallel coupling toolkit is used for the pairwise coupling of the components. The execution and parallel layout of the components is controlled by the SWMF. Both sequential and concurrent execution models are supported. The SWMF enables us to do simulations that were not possible with the individual components. Using reasonably high spatial and temporal resolutions in all the coupled components, the SWMF can still run significantly faster than real time on massively parallel super computers. We highlight some numerical simulations obtained with the SWMF.
http://csem.engin.umich.edu
SH53B-0326 1340h
Global distributions of auroral emissions derived from POLAR UVI observations and parameterized by the IMF strength and direction
In this study, we show our recent results in parameterizing POLAR UVI observations (in LBH short and long wavelength bands of auroral emissions) by the IMF strength/direction and Earth's dipole tilt (seasons). A mathematical representation for this parameterization is similar to our flexible, IMF-dependent models of the high-latitude ionospheric convection and field-aligned currents, derived from the DMSP and \O rsted satellites, respectively. In many respects, we confirm results obtained earlier by Baker et al. (2003) in Michigan and by Newell, Liou, Shue et al. (2001) of JHU/APL; however, none of the previous studies has yet addressed the full parameterization of auroral emissions by the IMF strength and direction during the solar activity cycle. These global distributions of auroral emissions can be utilized for construction of the IMF-dependent models of ionospheric conductivity for the quiet and disturbed conditions.
http://mist.engin.umich.edu/limie.html
SH53B-0327 1340h
Space Climate and Space Weather: Exploration and Forecasts
A new approach of exploring and forecasting solar activity was recently introduced. The Lund Solar Activity Model (LSAM) uses as input solar activity indicators: For exploration of the long-term space climate C14 proxy. For short-term (space weather) flare forecasts solar magnetic field and helioseismic data. The Lund Group also operates the Region Warning Center (RWC) Sweden of ISES. Real-time forecasts of the space weather and effects are offered. New real-time forecasts of the local geomagnetic activity have been developed, as part of the ESA GIC pilot project. A third workshop on Artificial Intelligence Applications in Solar-Terrestrial Physics is planned to be held in Lund, September 21-23, 2005.
http://www.lund.irf.se
SH53B-0328 1340h
Transient Coronal Holes: EUV and IR HeI 1083nm Observations
We present cases of transient coronal holes following a CME observed simultaneously by SOHO/EIT and the instruments at Mauna Loa Solar Observatory (MLSO). We describe the formation of the transient coronal holes and their relationship to the flare evolution, filament eruption, and CME taking advantage of the high 3-minute temporal cadence of the MLSO observations. We find that transient coronal holes in HeI 1083nm correspond well to the EUV ones, both spatially and temporally
SH53B-0329 1340h
Coronal Transequatorial Loops and Coronal Mass Ejections
Several papers have addressed many interesting aspects of coronal Trasequatorial Loop Systems (TLSs) in terms of their formation between different regions on the Sun, the evolution and the morphology. A few papers also studied the association between TLSs and Coronal Mass Ejections (CMEs). For those CME association studies, the largest data set cover only two years with most of the events from 1998, although consistent results were shown. In this work, we study the solar cycle dependence of the TLSs using PFSS models and MWO synoptic maps. In PFSS models here TLSs are represented with field lines that rooted in active regions at one or both ends. Comparisons between the selected PFSS field lines and YOHKOH coronal loops have shown good agreement. Our results show that TLSs take on the butterfly diagram trend. We also study TLS and CME association using an extended data set (including some published event lists) covering 1996 to 2000 when YOHKOH and SOHO were both in operation.
SH53B-0330 1340h
A Reanalysis of Geomagnetic Activity during the Last 100 Years
Long-term geomagnetic activity presented by the aa index has recently been used to show that the heliospheric magnetic field has more than doubled during the last 100 years. However, serious concern has recently been raised on the long-term consistency of the aa index and, thereby, on the centennial rise of solar magnetic activity. Here we reanalyze geomagnetic activity during the last 100 years by calculating the recently suggested IHV index for seven stations. We find that local geomagnetic activity in all stations follows the same qualitative long-term pattern as depicted by the aa index, and has a higher average level during the last two decennia of the 20th century than in the first two decennia. This verifies the result based on the aa index that global geomagnetic activity, and thereby, the open solar magnetic field has indeed increased during the last 100 years. However, quantitatively, the estimated centennial increase varies greatly from one station to another. We find that the relative increase is higher at the high-latitude stations and lower at the low and mid-latitude stations. Moreover, we find a considerably smaller (about 24-35%) centennial increase for global geomagnetic activity than given by the aa index (about 65%). We also show that the IHV index needs to be corrected for the long-term change of the daily curve, and calculate the corrected IHV values. We find that in four out of seven stations this correction further reduces the estimated centennial increase of local geomagnetic activity.
SH53B-0331 1340h
Geometry of Interplanetary CME Deduced from Cosmic Rays
A coronal mass ejection (CME) associated with an X17 solar flare reached Earth on October 29, 2003, causing an $\sim$ 11 % decrease in the intensity of high-energy Galactic cosmic rays recorded by muon detectors. The CME also produced a strong enhancement of the cosmic ray directional anisotropy. Based upon a simple inclined cylinder model, we use the anisotropy data to derive for the first time the three-dimensional geometry of the cosmic ray depleted region formed behind the shock in this event. We also compare the geometry derived from cosmic rays with that derived from in situ interplanetary magnetic field (IMF) observations using a Magnetic Flux Rope model. We also will analyze other events with the same model and discuss the geometry of the depleted region in each event.