O. C. St. Cyr

A catalog of white light coronal mass ejections observed by the SOHO spacecraft

[1]xa0The Solar and Heliospheric Observatory (SOHO) missions white light coronagraphs have observed nearly 7000 coronal mass ejections (CMEs) between 1996 and 2002. We have documented the measured properties of all these CMEs in an online catalog. We describe this catalog and present a summary of the statistical properties of the CMEs. The primary measurements made on each CME are the apparent central position angle, the angular width in the sky plane, and the height (heliocentric distance) as a function of time. The height-time measurements are then fitted to first- and second-order polynomials to derive the average apparent speed and acceleration of the CMEs. The statistical properties of CMEs are (1) the average width of normal CMEs (20° 900 km s−1) show deceleration. Solar cycle variation and statistical properties of CMEs are revealed with greater clarity in this study as compared with previous studies. Implications of our findings for CME models are discussed.

Successive CMEs and complex ejecta

[1]xa0We identified three sets of successive halo CMEs directed toward Earth (two or more CMEs observed within 1–4 days in the corona) and the corresponding flows and magnetic fields at 1 AU. Each set of successive halo CMEs was associated with complex ejecta at 1 AU. Complex ejecta were defined by Burlaga et al. [2001] as fast (>600 km/s) flows that are neither corotating flows nor magnetic clouds, which move past Earth during a day or more. They correspond to the transient flows discussed in the literature prior to the discovery of magnetic clouds. We infer that in each case the successive CMEs merged en route from the Sun to the Earth to form complex ejecta. In general, the components of the complex ejecta corresponding to individual CMEs cannot be identified, suggesting that the merging process is nonlinear and irreversible, and memory of the conditions near the sun is lost in the process. The identity of the individual CMEs is gradually lost as the interaction proceeds within 1 AU. In some cases, the interaction can result in what appears to be a single stream in the speed profile at 1 AU. Nevertheless, given observations of successive halo CMEs, one can possibly predict the arrival of complex ejecta or more complicated transient flow systems at 1 AU. In some cases, complex ejecta related to multiple CMEs can be associated with a single source region, an active region.

Flux-Rope Coronal Mass Ejection Geometry and Its Relation to Observed Morphology

A simple parameterization of a three-dimensional flux rope is used to determine a typical flux-rope geometry that corresponds to observed flux-rope coronal mass ejection (CME) morphologies (average apparent angular widths) at a leading-edge height of about 5.5 R☉. The parameterized flux rope, the curved axis of which is assumed to trace out an ellipse, is described in terms of the eccentricity of the ellipse, the width (minor diameter d) of the flux rope at the apex, and the height of the apex above the solar surface 2R1. Assuming self-similar expansion, there are only two geometrical parameters to be determined: the eccentricity and the axial aspect ratio Λa ≡ 2R1/d. For each pair of geometrical parameters, an ensemble of 72 orientations is considered, with each being specified in terms of a latitude angle, a longitude angle, and a rotation about the direction of motion. The resulting ensemble of synthetic coronagraph images is used to produce statistical measures of the morphology for comparison to corresponding observational measures from St. Cyr et al. (2004). We find that a typical flux-rope CME has = 0.7 ± 0.2 and Λa = 1.1 ± 0.3.

Solar activity and economic fundamentals: Evidence from 12 geographically disparate power grids

[1]xa0This study uses local (ground-based) magnetometer data as a proxy for geomagnetically induced currents (GICs) to address whether there is a space weather/electricity market relationship in 12 geographically disparate power grids: Eirgrid, the power grid that serves the Republic of Ireland; Scottish and Southern Electricity, the power grid that served northern Scotland until April 2005; Scottish Power, the power grid that served southern Scotland until April 2005; the power grid that serves the Czech Republic; E.ON Netz, the transmission system operator in central Germany; the power grid in England and Wales; the power grid in New Zealand; the power grid that serves the vast proportion of the population in Australia; ISO New England, the power grid that serves New England; PJM, a power grid that over the sample period served all or parts of Delaware, Maryland, New Jersey, Ohio, Pennsylvania, Virginia, West Virginia, and the District of Columbia; NYISO, the power grid that serves New York State; and the power grid in the Netherlands. This study tests the hypothesis that GIC levels (proxied by the time variation of local magnetic field measurements (dH/dt)) and electricity grid conditions are related using Pearsons chi-squared statistic. The metrics of power grid conditions include measures of electricity market imbalances, energy losses, congestion costs, and actions by system operators to restore grid stability. The results of the analysis indicate that real-time market conditions in these power grids are statistically related with the GIC proxy.

Space weather and the electricity market: An initial assessment

[1]xa0The paper examines the economic impact of space weather by drawing on hourly data from the PJM power grid over the period 1 June 2000 through 31 December 2001. The PJM grid is one of the largest power pools in North America. As of 31 December 2001, its service area had a population of approximately 22 million and included all or part of Pennsylvania, New Jersey, Maryland, Delaware, Virginia, and the District of Columbia. Market prices are determined for every hour of the day. As of June 2000, there are actually two markets for energy: a real-time market in which market participants can buy and sell electricity in “real time” and a day ahead market that allows participants to enter into transactions one day ahead of time. The existence of these two markets allows us to disentangle the effect of space weather conditions from other factors (such as fuel prices and expected demand) that affect the baseline price (as established in the day ahead market) for wholesale electricity. Several econometric analyses are conducted. The first examines the contribution of space weather to transmission congestion within the power grid. Building on the first analysis, the second analysis constructs an econometric model that examines the impact of space weather on the real-time market. Factors considered in the model include the outcome in the day ahead market, the level of generation utilization, unexpected demand, generation outages, unexpected transmission outages that are believed to be terrestrial in origin, and space weather. The results indicate the presence of space weather effects on the real-time price even after controlling for the other factors. A third model examines whether these space weather impacts affect subsequent prices in the far larger day ahead market.

An anatomy of space weather's electricity market impact: Case of the PJM power grid and the performance of its 500 kV transformers

[1]xa0The PJM Interconnection is a regional electricity transmission organization which as of 30 April 2004 coordinated the dispatch of electricity over 320,000 km of transmission lines. The backbone of PJMs transmission system is a series of 500 kilovolt (kV) transmission lines and transformers. PJM operates both hourly real-time and day-ahead markets for energy. The differences between PJMs real-time and day-ahead prices reflect unexpected operating conditions. Using ground-based magnetometer data as a proxy for geomagnetically induced currents (GICs), we present evidence that the differences between PJMs real-time and day-ahead prices are statistically related with the GIC proxy. Extra high voltage energy losses and a measure of real-time congestion costs are also shown to be statistically related with the GIC proxy. The paper investigates these statistical linkages by examining the incidence of declared constraints in the 500 kV transformers. The relationship between the GIC proxy and the incidence of declared constraints in the transformers is examined using a multivariate regression model with a dependent variable that is binary. The model is estimated using hourly data over the period 1 April 2002 through 30 April 2004. The results indicate that GICs can contribute to conditions in which the system operator declares one or more of the 500 kV transformers to be constrained. This finding takes into account forecasted load, load forecasting errors, ambient temperature, a proxy for known transmission constraints, and scheduled flows with other power grids. The results are also consistent with published findings that GICs can contribute to overheating problems in transformers.

Did geomagnetic activity challenge electric power reliability during solar cycle 23? Evidence from the PJM regional transmission organization in North America

[1]xa0During solar cycle 22, a very intense geomagnetic storm on 13 March 1989 contributed to the collapse of the Hydro-Quebec power system in Canada. This event clearly demonstrated that geomagnetic storms have the potential to lead to blackouts. This paper addresses whether geomagnetic activity challenged power system reliability during solar cycle 23. Operations by PJM Interconnection, LLC (hereafter PJM), a regional transmission organization in North America, are examined over the period 1 April 2002 through 30 April 2004. During this time PJM coordinated the movement of wholesale electricity in all or parts of Delaware, Maryland, New Jersey, Ohio, Pennsylvania, Virginia, West Virginia, and the District of Columbia in the United States. We examine the relationship between a proxy of geomagnetically induced currents (GICs) and a metric of challenged reliability. In this study, GICs are proxied using magnetometer data from a geomagnetic observatory located just outside the PJM control area. The metric of challenged reliability is the incidence of out-of-economic-merit order dispatching due to adverse reactive power conditions. The statistical methods employed make it possible to disentangle the effects of GICs on power system operations from purely terrestrial factors. The results of the analysis indicate that geomagnetic activity can significantly increase the likelihood that the system operator will dispatch generating units based on system stability considerations rather than economic merit.

Three‐dimensional coronal density structure: 1. Model

[1]xa0The three-dimensional (3-D) density structure of the solar corona is a fundamental boundary condition on the solar wind. Most easily applied models of the global coronal density have been restricted to date to axisymmetric 2-D cases. We present here a 3-D model made up of a superposition of multiple streamers, having distinct gaussian widths in longitude and latitude and both longitudinal and latitudinal dependence of the neutral lines implicit beneath the streamer cores. Nonradiality of streamers and solar B-angle tilt are also explicitly treated. We show how this simple model can capture many of the general properties of coronal white light observations and demonstrate how such a model can assist in the interpretation of the multiple views on coronal structures such as will be provided by the upcoming STEREO mission.

X-ray Ejecta, White-Light CMEs and a Coronal Shock Wave

We report on a coronal shock wave inferred from the metric type II burst of 13 January 1996. To identify the shock driver, we examined mass motions in the form of X-ray ejecta and white-light coronal mass ejections (CMEs). None of the ejections could be considered fast (> 400 kmxa0s−1) events. In white light, two CMEs occurred in quick succession, with the first one associated with X-ray ejecta near the solar surface. The second CME started at an unusually large height in the corona and carried a dark void in it. The first CME decelerated and stalled while the second one accelerated, both in the coronagraph field of view. We identify the X-ray ejecta to be the driver of the coronal shock inferred from metric type II burst. The shock speed reported in the Solar Geophysical Data (1000–2000xa0kmxa0s−1) seems to be extremely large compared to the speeds inferred from X-ray and white-light observations. We suggest that the MHD fast-mode speed in the inner corona could be low enough that the X-ray ejecta is supermagnetosonic and hence can drive a shock to produce the type II burst.