SPA-Solar and Heliospheric Physics General Contributions V
Presiding: A F Viñas, NASA Goddard Space Flight Center; P C Liewer, Jet Propulsion Laboratory, California Institute of Technology
SH41A-01 08:30h
Thickness of Heliospheric Current and Plasma Sheets: Dependence on Distance
Heliospheric current sheets (HCS) are well defined structures that separate the interplanetary magnetic fields with inverse polarities. Surrounded by heliospheric plasma sheets (HPS), the current sheets stretch throughout the heliosphere. Interesting questions that still remain unanswered include how the thickness of these structures will change along the distance? And what determines the thickness of these structures? To answer these fundamental questions, we have carried out a study of the HCS and HPS using recent Ulysses data near 5 AU. When the results were compared with earlier studies at 1 AU using ISEE-3 data, they were surprising and unexplained. Although the plasma sheet grew thicker, the embedded current sheet grew thinner! Using data under the same (or very similar) circumstances, we have extended the analysis in two ways. First, the same current-plasma sheets studied at 5 AU have been identified at 1 AU using ACE data. Second, data obtained while Ulysses was en-route to Jupiter near 3 AU have been analyzed. This three-point investigation reveals the thickness variation along the distance and enables the examination of the controller of this variation.
SH41A-02 08:45h
Validating solar wind prediction models: A large speed enhancement index
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. We compare 8 years of L1 in-situ spacecraft data with predictions of the solar wind speed made by the Wang-Sheeley-Arge (WSA) empirical model. Using the standard method of measuring prediction accuracy (i.e. by calculating the mean-square error (MSE) between the data and model) we test the 8 years of WSA predictions, and find the optimal lead-time for 1 AU solar wind speed predictions. However, we also highlight some potential problems with the interpretation of MSE, and put forward an additional, complementary, index based upon large speed enhancements (LSEs). A method for systematically selecting and associating LSEs from spacecraft and model data is outlined, and a "score" calculated based upon the model's hit to miss and false ratio, along with the timing and speed magnitude errors between the forecasted and observed LSEs. Furthermore, by defining discrete events it is also possible to use model predictions from above and below the ecliptic plane to predict timing errors in addition to the usual speed errors. Morphological differences between hit, miss and false LSEs are investigated to aid improvements to the model.
SH41A-03 09:00h
Validating the Proton Prediction System
The Proton Prediction System (PPS) is an empirical model developed at the Air Force Research Laboratory to generate solar energetic proton (SEP) time-intensity profiles at 1 AU following solar flares. PPS was designed to match statistical Earth-observed average intensity-time profiles, peak intensities, and event durations. The input parameters are solar flare peak or time-integrated X-ray or radio fluxes and their times of onsets or maxima, and solar flare locations. We have validated the PPS using 101 solar X-ray flares of peak intensity > M5 from Ha disk flares during the period 1997 through 2001. We looked for correlations between predicted and observed GOES E > 10 MeV peak intensities, rise times, and event durations. There was little correlation between the predicted and observed times from flare peak to either SEP onsets or SEP peak times. When a SEP event was both predicted and observed, the logs of the SEP peaks were correlated at about the 0.5 level. However, the numbers of correctly predicted events were similar to those of the false alarms and to those of unpredicted events. We do a further comparison between the SEP events and those solar flares with observed coronal shocks to look for a predictive capability improvement in the PPS.
SH41A-04 09:15h
Solar and heliospheric physics at US universities
We summarize the results of a one year assessment of university-based solar and heliospheric communities at US universities. The data represents results of a three-step process. First, all relevant funding agencies were contacted and provided information about university based funding during the last decades. Second, we analyzed university participation in space missions in leadership roles, and its evolution over time. Third, we contacted all key US universities active in solar and heliospheric physics and quantified their impact in teaching and research. We discuss these data in context and determine overall trends and challenges of university based research.
SH41A-05 09:30h
Solar Probe's Inside-Out UV Spectrography of the Solar Wind
The Solar Probe will fly through the corona, as close as 3 solar radii from the photosphere at perihelion. This will provide the unique and first-ever possibility of remote-sensing observations of ultraviolet (UV) coronal line-emission from inside-out, that is, along the radial direction of the solar wind outflow, and away from the Sun. Past UV spectrographic observations of the corona have been possible only from a sideways perspective (e.g., UVCS/SOHO). The expected UV spectra of the OVI doublet, 103.2/103.4 nm, Lyman-alpha HI, 121.6 nm, and HeII, 304 nm, lines from the Probe's new radial perspective will be presented. The collisional and resonantly scattered components of the line-emission when observed radially are spectroscopically separated. This allows a direct measure of the solar wind outflow speed from the Doppler shift of the collisional component. The line profiles and intensities of both components yield information on the unresolved velocity distribution of ions along the radial direction. This is the predominant direction of the coronal magnetic field. In the past, sideways, UV spectroscopic observations of line-emission have yielded information on the unresolved ion velocity distribution perpendicular to the magnetic field. Therefore, radial UV spectroscopic observations from Solar Probe will offer a unique opportunity of investigating the anisotropy of the unresolved coronal ion velocity distribution for the first time.
SH41A-06 09:45h
The Living With a Star (LWS) Sentinels Mission
The Sentinels Mission, the heliospheric element of the NASA Living With a Star (LWS) program, is still rapidly evolving, especially as the Sentinels Science and Technology Definition Team is progressing with its work. With the Solar Dynamics Observatory, the solar component, and the Geospace elements taking a more finalized form, it becomes clearer what scientific and measurement objectives will be necessary to establish the solar-geospace connection in order to achieve the goals of the LWS program. Possible, early formulation designs of the Sentinels mission will be presented that includes the Inner Heliospheric Mappers, a four spacecraft mission to observe the inner heliosphere between 0.25 and 1.0 AUs along with a Far Side Sentinel that will perform remote solar observations from nearly the opposite side of the Sun. Moreover, the complementarity of the various planned international missions (e.g., ESA Solar Orbiter, and Beppi Colombo) along with NASA planetary projects (e.g., Mars program and MESSENGER) will be discussed and how they can form a coherent system. Finally, the importance of already available heliospheric data will be emphasized.