D. A. Biesecker

PHOTOMETRIC STUDY OF THE KREUTZ COMETS OBSERVED BY SOHO FROM 1996 TO 2005

We present analysis of the photometry of more than 900 Kreutz comets observed by SOHO from 1996 to 2005. The Kreutz comets have sungrazing orbits with q ≈ 1-2 R� , high inclinations (i ≈ 143 ◦ ), and periods of 500-1000 years. We find that they do not have a bimodal distance of peak brightness as previously reported, but instead peak from 10.5 Rto 14 R� (prior to perihelion), suggesting there is a continuum of compositions rather than two distinct subpopulations. The light curves have two rates of brightening, typically ∝ r −7.3±2.0 when first observed by SOHO (at distances of 30-35 R� ) then rapidly transitioning to ∝ r −3.8±0.7 between 20 Rand 30 R� . It is unclear at what distance the steeper slope begins, but it likely does not extend much beyond the SOHO field of view. We derive nuclear sizes up to ∼50 m in radius for the SOHO-observed comets, with a cumulative size distribution of N(>R) ∝ R −2.2 for comets larger than 5 m in radius. This size distribution cannot explain the largest members of the family seen from the ground, suggesting that either the size distribution does not extend to the largest sizes or that the distribution is not uniform around the orbit. The total mass of the distribution up to the largest expected size (∼500 m) is ∼4 × 10 14 g, much less than the estimated masses of the largest ground-observed members. After correcting for the changing discovery circumstances, the flux of comets reaching perihelion has increased since 1996, and the increase is seen in comets of all sizes. Comparison of the SOHO comets with the Solwind and Solar Maximum Mission discoveries suggests there may have been an overabundance of bright comets arriving from 1979 to 1989, possibly indicative of a changing distribution around the Kreutz orbit.

Coronal Mass Ejection-Associated Coronal Dimmings

We report on a statistical analysis of 96 CME-associated EUV coronal dimmings between 1998 and 2000. We investigate the size and location of the events and characterize how these events evolve with time. The durations typically range from 3 to 12 hr. The dimmings appear most frequently within the belt of active regions (20°-50° latitude). Dimming events are generally symmetric in latitude and longitude with some tendency to be broader in latitude. The temporal profiles of most events are characterized by a sharp rise and a gradual recovery. Although the majority of cases are well fit by a single recovery slope, a large minority of events have a two-part decay with an initial decaying slope that is similar in magnitude to the rising slope and a secondary, flatter, decay lasting several hours.

A comparison of space weather analysis techniques used to predict the arrival of the Earth-directed CME and its shockwave launched on 8 April 2010

[1]xa0The Earth-directed coronal mass ejection (CME) of 8 April 2010 provided an opportunity for space weather predictions from both established and developmental techniques to be made from near–real time data received from the SOHO and STEREO spacecraft; the STEREO spacecraft provide a unique view of Earth-directed events from outside the Sun-Earth line. Although the near–real time data transmitted by the STEREO Space Weather Beacon are significantly poorer in quality than the subsequently downlinked science data, the use of these data has the advantage that near–real time analysis is possible, allowing actual forecasts to be made. The fact that such forecasts cannot be biased by any prior knowledge of the actual arrival time at Earth provides an opportunity for an unbiased comparison between several established and developmental forecasting techniques. We conclude that for forecasts based on the STEREO coronagraph data, it is important to take account of the subsequent acceleration/deceleration of each CME through interaction with the solar wind, while predictions based on measurements of CMEs made by the STEREO Heliospheric Imagers would benefit from higher temporal and spatial resolution. Space weather forecasting tools must work with near–real time data; such data, when provided by science missions, is usually highly compressed and/or reduced in temporal/spatial resolution and may also have significant gaps in coverage, making such forecasts more challenging.

THE RELATIONSHIP BETWEEN CORONAL DIMMING AND CORONAL MASS EJECTION PROPERTIES

Coronal dimmings are closely related to the footpoints of coronal mass ejections (CMEs) and, as such, offer information about CME origins and evolution. In this paper, we investigate the relationship between CME and dimming properties. In particular, we compare CME quantities for events with and without associated dimmings. We find that dimming-associated CMEs, on average, have much higher speeds than non-dimming-associated events. In fact, CMEs without an associated dimming do not appear to travel faster than 800 km s–1, i.e., the fast solar wind speed. Dimming-associated events are also more likely to be associated with flares, and those flares tend to have the highest magnitudes. We propose that each of these phenomena is affected by the energy available in the source region. Highly energetic source regions produce fast CMEs that are accompanied by larger flares and visible dimmings, while less energetic source regions produce slow CMEs that are accompanied by smaller flares and may or may not have dimmings. The production of dimmings in the latter case may depend on a number of factors including initiation height of the CME, source region magnetic configuration, and observational effects. These results have important implications for understanding and predicting CME initiations.

Relationship between Ulysses plasma observations and solar observations during the Whole Sun Month campaign

In this report, we summarize measurements made by the plasma experiment on the Ulysses spacecraft during the period designated as “Whole Sun Month” (WSM, August 10 to September 8, 1996). This interval coincided with the return of solar wind variability at Ulysses. Ulysses was located at ∼ 28°N heliographic latitude, at a heliocentric distance of 4.25 AU, and on the opposite side of the Sun from Earth. In particular, we explore the evolution of the solar wind between the Sun and Ulysses for several rotations surrounding WSM. Specifically, we map Ulysses measurements back toward the Sun by applying a two-dimensional inverse MHD algorithm. This approach is compared with the commonly used constant speed (or ballistic) approximation. We find that the MHD mapping technique produces substantially better results when compared with solar observations. Both the Ulysses MHD-mapped results and the solar observations are consistent with a picture of a modestly tilted streamer belt (< 10°) that was deformed northward by an active region at 240° –; 270° longitude.

Space weather conditions during the Galaxy 15 spacecraft anomaly

On 5 April 2010, the Galaxy 15 spacecraft, orbiting at geosynchronous altitudes, experienced an anomaly near local midnight when it stopped responding to any ground commands. The anomaly has been reported as due to a lockup of the field-programmable gate array within the spacecraft baseband communications unit during an onboard electrostatic discharge (ESD). This study evaluates the space weather conditions at the time of the Galaxy 15 anomaly. The study also compares the plasma and geomagnetic environments around the anomaly to space weather observations over the operational lifetime of Galaxy 15 up to the anomaly time. On 5 April, the Galaxy 15 spacecraft encountered severe plasma conditions while it was in eclipse and during the subsequent anomaly interval. These conditions included a massive magnetic field dipolarization that injected energetic particles from the magnetotail during a substorm observed by GOES and Time History of Events and Macroscale Interactions during Substorms satellites. Galaxy 15 was located at a near-optimum position and local time to experience the full impact of the injected energetic particles. During the largest previous storm experienced by Galaxy 15 in December 2006, evidence suggests that it would not have been exposed to the same level of space weather as on 5 April 2010. Hence, while Galaxy 15 was traversing the nightside on 5 April, it likely experienced, for a short period, the most severe local plasma conditions it had encountered since launch. The most likely contributions to the ESD were interactions of the spacecraft with substorm-injected energetic particles facilitating spacecraft surface charging and deep dielectric charging.

Theoretical basis for operational ensemble forecasting of coronal mass ejections

We lay out the theoretical underpinnings for the application of the Wang-Sheeley-Arge-Enlil modeling system to ensemble forecasting of coronal mass ejections (CMEs) in an operational environment. In such models, there is no magnetic cloud component, so our results pertain only to CME front properties, such as transit time to Earth. Within this framework, we find no evidence that the propagation is chaotic, and therefore, CME forecasting calls for different tactics than employed for terrestrial weather or hurricane forecasting. We explore a broad range of CME cone inputs and ambient states to flesh out differing CME evolutionary behavior in the various dynamical domains (e.g., large, fast CMEs launched into a slow ambient, and the converse; plus numerous permutations in between). CME propagation in both uniform and highly structured ambient flows is considered to assess how much the solar wind background affects the CME front properties at 1u2009AU. Graphical and analytic tools pertinent to an ensemble approach are developed to enable uncertainties in forecasting CME impact at Earth to be realistically estimated. We discuss how uncertainties in CME pointing relative to the Sun-Earth line affects the reliability of a forecast and how glancing blows become an issue for CME off-points greater than about the half width of the estimated input CME. While the basic results appear consistent with established impressions of CME behavior, the next step is to use existing records of well-observed CMEs at both Sun and Earth to verify that real events appear to follow the systematic tendencies presented in this study.

Correction to “Major geomagnetic storms (Dst ≤ −100 nT) generated by corotating interaction regions”

[1] In the paper ‘‘Major geomagnetic storms (Dst 100 nT) generated by corotating interaction regions’’ by I. G. Richardson et al. (Journal of Geophysical Research, 111, A07S09, doi:10.1029/2005JA011476, 2006), there are several typographical errors. In Figures 1, 2, 3, 4, and 7, the y component of the solar wind electric field (Ey) is plotted with the incorrect sign. Signed values of Ey referred to in the text and given in Table 1 also have the incorrect sign. As stated in the second paragraph of section 2, the ‘‘Ey’’ panel shows the value of VxBz. However, this is equal to Ey, not Ey (assuming that VxBz VzBx in the solar wind). JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, A12105, doi:10.1029/2007JA012332, 2007 Click Here for Full Article

Validation of an Operational Product to Determine L1 to Earth Propagation Time Delays

We describe the development and validation of an operational space weather tool to forecast propagation delay times between L1 and Earth using the Weimer and King (2008) tilted phase front technique. A simple flat plane convection delay method is currently used by the NOAA Space Weather Prediction Center (SWPC) to propagate the solar wind from a monitoring satellite located at L1 to a point upstream of the magnetosphere. This technique assumes that all observed solar wind discontinuities, such as interplanetary shocks and interplanetary coronal mass ejection boundaries, are in a flat plane perpendicular to the Sun-Earth line traveling in the GSE X direction at the observed solar wind velocity. In reality, these phase plane fronts can have significantly tilted orientations, and by relying on a ballistic propagation method, delay time errors of ±15u2009min are common. In principle, the propagation time delay product presented here should more accurately predict L1 to Earth transit times by taking these tilted phase plane fronts into account. This algorithm, which is based on the work of Weimer and King (2008), is currently running in real time in test mode at SWPC as part of the SWPC test bed. We discuss the current algorithm performance, and via our detailed validation study, show that there is no significant difference between the two propagation methods when run in a real-time operational environment.

From Predicting Solar Activity to Forecasting Space Weather: Practical Examples of Research-to-Operations and Operations-to-Research

The successful transition of research to operations (R2O) and operations to research (O2R) requires, above all, interaction between the two communities. We explore the role that close interaction and ongoing communication played in the successful fielding of three separate developments: an observation platform, a numerical model, and a visualization and specification tool. Additionally, we will examine how these three pieces came together to revolutionize interplanetary coronal mass ejection (ICME) arrival forecasts. Axa0discussion of the importance of education and training in ensuring a positive outcome from R2O activity follows. We describe efforts by the meteorological community to make research results more accessible to forecasters and the applicability of these efforts to the transfer of space-weather research. We end with a forecaster “wish list” for R2O transitions. Ongoing, two-way communication between the research and operations communities is the thread connecting it all.