Bernard V. Jackson

Heliospheric tomography using interplanetary scintillation observations: 1. Combined Nagoya and Cambridge data

We have produced a computer assisted tomography program that optimizes a three-dimensional model to fit observational data. We have used this program with interplanetary scintillation data from Nagoya, Japan, and Cambridge, England. The program iterates to a least squares solution fit of observed data using solar rotation and solar wind motion to provide perspective views of each point in space accessible to the observations. We plot the optimized model as Carrington maps in velocity V and density N e for the two data sets with resolutions of 10° in heliographic longitude and latitude. We map the model to 1 AU and compare this to in situ observations from the IMP spacecraft. From this comparison we find ΔN e N e 0.3 . We plot Carrington maps extrapolated to the solar surface to compare with Yohkoh Soft X ray Telescope (SXT), Sacramento Peak green line, and Mark III K-coronameter observations. High velocities modeled at the solar surface for individual rotations trace coronal holes (including polar ones) observed in SXT data. Regions of high density modeled from the Cambridge scintillation level data generally show a high correlation with regions of high solar activity observed as bright in Yohkoh SXT and green line observations. There is also a general correspondence of the regions of high density and the areas which are bright in K-coronameter observations.

Evidence for space weather at Mercury

Mercurys sodium atmosphere is known to be highly variable both temporally and spatially. During a week-long period from November 13 to 20, 1997, the total sodium content of the Hermean atmosphere increased by a factor of 3, and the distribution varied daily. We demonstrate a mechanism whereby these rapid variations could be due to solar wind-magnetosphere interactions. We assume that photon-stimulated desorption and meteoritic vaporization are the active source processes on the first (quietest) day of our observations. Increased ion sputtering results whenever the magnetosphere opens in response to a southward interplanetary magnetic field (IMF) or unusually large solar wind dynamic pressure. The solar wind dynamic pressure at Mercury as inferred by heliospheric radial tomography increased by a factor of 20 during this week, while the solar EUV flux measured by the Solar EUV Monitor (SEM) instrument on board the Solar and Heliospheric Observatory (SOHO) increased by 20%. While impact vaporization provides roughly 25% of the source, it is uniformly distributed and varies very little during the week. The variations seen in our data are not related to Caloris basin, which remained in the field of view during the entire week of observations. We conclude that increased ion sputtering resulting from ions entering the cusp regions is the probable mechanism leading to large rapid increases in the sodium content of the exosphere. While both the magnitude and distribution of the observed sodium can be reproduced by our model, in situ measurements of the solar wind density and velocity, the magnitude and direction of the interplanetary magnetic field, and Mercurys magnetic moments are required to confirm the results.

Heliospheric tomography using interplanetary scintillation observations: 2. Latitude and heliocentric distance dependence of solar wind structure at 0.1–1 AU

Interplanetary scintillation is a useful means to measure the solar wind in regions inaccessible to in situ observation. However, interplanetary scintillation measurements involve a line-of-sight integration, which relates contributions from all locations along the line of sight to the actual observation. We have developed a computer assisted tomography (CAT) program to reduce the adverse effects of the line-of-sight integration. The program uses solar rotation and solar wind motion to provide three-dimensional perspective views of each point in space accessible to the interplanetary scintillation observations and optimizes a three-dimensional solar wind speed distribution to fit the observations. We analyzed IPS speeds observed at the Solar-Terrestrial Environment Laboratory and confirmed that (1) the solar wind during the solar minimum phase has a dominant polar high-speed solar wind region with speeds of about 800 km s−1 and within 30° of the solar equator speeds decrease to 400 km s−1 as observed by Ulysses, and (2) high-speed winds get their final speed of 750–900 km s−1 within 0.1 AU, and consequently, that acceleration of the solar wind is small above 0.1 AU.

Heliospheric tomography using interplanetary scintillation observations: 3. Correlation between speed and electron density fluctuations in the solar wind

We have examined the relationship between solar wind speed and electron density fluctuations on scale sizes around 100 km in the heliocentric distance range of 0.3 to 0.8 AU using interplanetary scintillation (IPS) data obtained at the Solar-Terrestrial Environment Laboratory. The solar wind properties derived from the IPS data are biased by line of sight integration through a three-dimensional structured solar wind. Therefore we have applied a computer-assisted tomography (CAT) method to deconvolve the line of sight integration and reconstruct the solar wind structure. The analysis was made for the solar wind speed V and electron density fluctuations δNe in the solar activity minimum phase when high-speed regions are separated from an equatorial low-speed region by a sharp velocity gradient. From results of the CAT analysis we derived the best fit power law relation of δNe ∝ V−γ with γ = 0.5 ± 0.15, indicating that fractional density fluctuations δNe/Ne in the high-speed wind are larger than those in the low-speed wind. Combining this relation with results of previous workers [Coles et al., 1995; Manoharan, 1993; Celnikier et al., 1987; Jackson et al., this issue], we suggest that the fractional density fluctuation level of the high-speed wind evolves with heliocentric distance.

Tracking a major interplanetary disturbance with SMEI

[1] We present the first clear observations of an Earth-directed interplanetary disturbance tracked by the Solar Mass Ejection Imager (SMEI). We find that this event can be related to two halo CMEs seen at the Sun about 2 days earlier, and which merged in transit to 1 AU. The disturbance was seen about 16 hours before it reached Earth, and caused a severe geomagnetic storm at the time which would have been predicted had SMEI been operating as a real-time monitor. It is concluded that SMEI is capable of giving many hours advance warning of the possible arrival of interplanetary disturbances.

Exquisite Nova Light Curves from the Solar Mass Ejection Imager (SMEI)

We present light curves of three classical novae (KT Eridani, V598 Puppis, V1280 Scorpii) and one recurrent nova (RS Ophiuchi) derived from data obtained by the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite. SMEI provides near complete sky-map coverage with precision visible-light photometry at 102-minute cadence. The light curves derived from these sky maps offer unprecedented temporal resolution around, and especially before, maximum light, a phase of the nova eruption normally not covered by ground-based observations. They allow us to explore fundamental parameters of individual objects including the epoch of the initial explosion, the reality and duration of any pre-maximum halt (found in all three fast novae in our sample), the presence of secondary maxima, speed of decline of the initial light curve, plus precise timing of the onset of dust formation (in V1280 Sco) leading to estimation of the bolometric luminosity, white dwarf mass and object distance. For KT Eri, Liverpool Telescope SkyCamT data confirm important features of the SMEI light curve and overall our results add weight to the proposed similarities of this object to recurrent rather than to classical novae. In RS Oph, comparison with hard X-ray data from the 2006 outburst implies that the onset of the outburst coincides with extensive high velocity mass-loss. It is also noted that two of the four novae we have detected (V598 Pup and KT Eri) were only discovered by ground-based observers weeks or months after maximum light, yet these novae reached peak magnitudes of 3.46 and 5.42 respectively. This emphasizes the fact that many bright novae per year are still overlooked, particularly those of the very fast speed class. Coupled with its ability to observe novae in detail even when relatively close to the Sun in the sky, we estimate that as many as 5 novae per year may be detectable by SMEI.

Analysis of Plasma-Tail Motions for Comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) Using Observations from SMEI

Comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) passed within � 0.3 AU of Earth in April and May of 2004. Their tails were observed by the Earth-orbiting Solar Mass Ejection Imager (SMEI) during this period. A time series of photometric SMEI sky maps displays the motions and frequent disruptions of the comet plasma tails. Ephemerides are used to unfold the observing geometry; the tails are often seen to extend � 0.5 AU from the comet nuclei. Having selected 12 of the more prominent motions as ‘‘events’’ for further study, we introduce a new method for determining solar wind radial velocities from these SMEI observations. We find little correlation between these and the changing solar wind parameters as measured close to Earth, or with coarse three-dimensional reconstructions using interplanetary scintillation data. A likely explanation is that the transverse sizes of the solar wind perturbations responsible for these disruptions are small, P0.05 AU. We determine the radial velocities of these events during the disruptions,usingatechniqueonlypossiblewhentheobservedcomettailsextendoverasignificantfractionof anAU. We find typical radial velocities during these events of 50Y100 km s � 1 lower than before or afterward. Time durations of such events vary, typically from 3 to 8 hr, and correspond to comet traversal distances � 10 6 km (0.007 AU). We conclude that these large disturbances are primarily due to ubiquitous solar wind flow variations, of which these measured events are a subset. Subject headingg comets: individual (C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), C/2004 F4 (Bradfield)) — solar wind — Sun: coronal mass ejections (CMEs)

Three-Dimensional Tomography of Interplanetary Disturbances

We have developed a Computer Assisted Tomography (CAT) program that modifies a three-dimensional kinematic heliospheric model to fit interplanetary scintillation (IPS) or Thomson scattering observations. The tomography program iteratively changes this global model to least-squares fit the data. Both a corotating and time-dependent model can be reconstructed. The short time intervals of the time-dependent modeling (to shorter than 1 day) force the heliospheric reconstructions to depend on outward solar wind motion to give perspective views of each point in space accessible to the observations, allowing reconstruction of interplanetary Coronal Mass Ejections (CMEs) as well as corotating structures. We show these models as velocity or density Carrington maps and remote views. We have studied several events, including the 2000 July 14 Bastille-Day halo CME and several intervals using archival Cambridge IPS data, and we have also used archival Helios photometer data to reproduce the heliosphere. We check our results by comparison with additional remote-sensing observations, and in-situ observations from near-Earth spacecraft. A comparison of these observations and the Earth forecasts possible using them is available in real time on the World Wide Web using IPS data from the Solar Terrestrial Environment Laboratory, Japan.

Helios observations of the earthward-directed mass ejection of 27 November, 1979

The Helios spacecraft zodiacal light photometers are used to observe the earthward-directed solar mass ejection transient of 27 November, 1979 described by Howard et al. (1982) that completely circles the Sun in coronagraph observations. At this time, Helios B was situated 30° east of the Sun-Earth line at 0.5 AU. The brightness increase moved outward directly along the Sun-Earth line over a period of approximately 24 hr, indicating a strong collimation of the ejection. The outward motion and mass estimates of the ejected material from the photometers compared with near-Earth observations from IMP spacecraft show that at least a portion of the density increase observed at Earth on 29 and 30 November was associated with this ejection.

A CME mass distribution derived from SOLWIND coronagraph observations

Using estimates of the masses of nearly 1000 CMEs observed by SOLWIND from Howardet al. (1985), we re-plot the numbers of CMEs as a function of CME mass on a log-linear plot. The plot is significant in that it shows a linear trend over more than a decade of CME masses. The plot indicates a simple form for the distribution of the CME masses and allows an easy determination of the total mass ejected into the solar wind in the form of CMEs. We find that approximately 16% of the solar wind at solar maximum can be comprised of CME mass. There is no indication that the numbers of low-mass CMEs increase in number above the trend set by the more massive ones. Specifically, there is no increase in the numbers of small CMEs such that the whole of the solar wind can be comprised of them.