P. P. Hick

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)

Synoptic IPS and Yohkoh soft X‐ray observations

Interplanetary scintillation measurements of the disturbance factor, g, from October 1991 to October 1992 are used to construct synoptic Carrington maps. These maps, which show the structure of the quiet solar wind, are compared with X-ray Carrington maps from the Yohkoh SXT instrument. For the period studied the global structure outlined by (weakly) enhanced g-values apparent in the IPS maps tends to match the active regions (as shown in the X-ray maps) significantly better than the heliospheric current sheet. Contrary to traditional opinion, which views active regions as magnetically closed structures that do not have any significant impact on the solar wind flow, our results suggest that density fluctuations in the solar wind are significantly enhanced over active regions. These results support the suggestion by Uchida et al. (1992), based on Yohkoh observations of expanding active regions, that active regions play a role in feeding mass into the quiet solar wind.

Time‐dependent tomography of hemispheric features using interplanetary scintillation (IPS) remote‐sensing observations

We have developed a Computer Assisted Tomography (CAT) program that modifies a time‐dependent three‐dimensional kinematic heliospheric model to fit interplanetary scintillation (IPS) observations. The tomography program iteratively changes this global model to least‐squares fit IPS data. The short time intervals of the kinematic modeling (∼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 July 14, 2000 Bastille‐day halo CME. We check our results by comparison with additional remote‐sensing observations, and observations from near‐Earth spacecraft.

A procedure for fitting point sources in SMEI white-light full-sky maps

The Solar Mass Ejection Imager (SMEI) instrument consists of three CCD cameras with individual fields of view of 60° × 3° degrees that combined sweep a 160° arc of sky. SMEI covers the entire sky in one spacecraft orbit of 102 minutes. Individual 4-s exposures from each orbit are assembled into full-sky maps. The primary objective in the SMEI data reduction is to isolate the Thomson-scattering signal across the sky from free electrons in the solar wind. One of the steps needed to achieve the required photometric precision is the individual fitting and removal of stars brighter than 6th magnitude from the full-sky maps. The point-spread function of the SMEI optics has several unusual properties. It has a full width of about one degree, is asymmetric, and varies in width depending on where in the field of view the image is formed. Moreover, the orientation of the PSF on the sidereal sky rotates over 360 degree over the course of a year. We describe the procedure used to fit and subtract individual stars from the SMEI full-sky maps. A by-product of this procedure are time series at the orbital time resolution for stars brighter than 6th magnitude. These results are used by Buffington et al. (2007) to calibrate the SMEI instrument against the LASCO C3 coronagraph.

The UCSD kinematic IPS solar wind boundary and its use in the ENLIL 3‐D MHD prediction model

The University of California, San Diego interplanetary scintillation (IPS) time-dependent kinematic 3-D reconstruction technique has been used and expanded upon for over a decade to provide predictions of heliospheric solar wind parameters. These parameters include global reconstructions of velocity, density, and (through potential field modeling and extrapolation upward from the solar surface) radial and tangential interplanetary magnetic fields. Time-dependent results can be extracted at any solar distance within the reconstructed volume and are now being exploited as inner boundary values to drive the ENLIL 3-D MHD model in near real time. The advantage of this coupled system is that it uses the more complete physics of 3-D MHD modeling to provide an automatic prediction of coronal mass ejections and solar wind stream structures several days prior to their arrival at Earth without employing coronagraph observations. Here we explore, with several examples, the current differences between the IPS real-time kinematic analyses and those from the ENLIL 3-D MHD modeling using IPS-derived real-time boundaries. Future possibilities for this system include incorporating many different worldwide IPS stations as input to the remote sensing analysis using ENLIL as a kernel in the iterative 3-D reconstructions.

Time-dependent tomography of heliospheric features using the three-dimensional reconstruction techniques developed for the solar mass ejection imager (SMEI)

Precise photometric images of the heliosphere are expected from the Air Force/NASA Solar Mass Ejection Imager (SMEI) now scheduled for launch in February 2003, and the all-sky cameras proposed for other NASA missions. To optimize the information available from these instruments, we are developing tomographic techniques for analyzing remote sensing observations of heliospheric density as observed in Thomson scattering (e.g. using the Helios photometer data) for eventual use with SMEI. We have refined the tomography program to enable us to analyze time-dependent phenomena, such as the evolution of corotating heliospheric structures and more discrete events such as coronal mass ejections. Both types of phenomena are discerned in our data, and are reconstructed in three dimensions. We use our tomography technique to study the interaction of these phenomena as they move outward from the Sun for several events that have been studied by multiple spacecraft in situ observations and other techniques.

THE THREE-DIMENSIONAL ANALYSIS OF HINODE POLAR JETS USING IMAGES FROM LASCO C2, THE STEREO COR2 CORONAGRAPHS, AND SMEI

Images recorded by the X-ray Telescope on board the Hinode spacecraft are used to provide high-cadence observations of solar jetting activity. A selection of the brightest of these polar jets shows a positive correlation with high-speed responses traced into the interplanetary medium. LASCO C2 and STEREO COR2 coronagraph images measure the coronal response to some of the largest jets, and also the nearby background solar wind velocity, thereby giving a determination of their speeds that we compare with Hinode observations. When using the full Solar Mass Ejection Imager (SMEI) data set, we track these same high-speed solar jet responses into the inner heliosphere and from these analyses determine their mass, flow energies, and the extent to which they retain their identity at large solar distances.

A DETERMINATION OF THE NORTH–SOUTH HELIOSPHERIC MAGNETIC FIELD COMPONENT FROM INNER CORONA CLOSED-LOOP PROPAGATION

A component of the magnetic field measured in situ near the Earth in the solar wind is present from north–south fields from the low solar corona. Using the Current-sheet Source Surface model, these fields can be extrapolated upward from near the solar surface to 1 AU. Global velocities inferred from a combination of interplanetary scintillation observations matched to in situ velocities and densities provide the extrapolation to 1 AU assuming mass and mass flux conservation. The north–south field component is compared with the same ACE in situ magnetic field component—the Normal (Radial Tangential Normal) Bn coordinate—for three years throughout the solar minimum of the current solar cycle. We find a significant positive correlation throughout this period between this method of determining the Bn field compared with in situ measurements. Given this result from a study during the latest solar minimum, this indicates that a small fraction of the low-coronal Bn component flux regularly escapes from closed field regions. The prospects for Space Weather, where the knowledge of a Bz field at Earth is important for its geomagnetic field effects, is also now enhanced. This is because the Bn field provides the major portion of the Geocentric Solar Magnetospheric Bz field coordinate that couples most closely to the Earths geomagnetic field.