Time-Dependent Tomography Using Helios 2 Photometer Data

The above images depicting the heliosphere northern heliosphere on May 10, 1979 at 12 UT and on May 29, 1979 at 00 UT and a 2.9 Mbyte *.avi video presentation that includes the above images are reconstructions of heliospheric plasma density (extrapolated to heights as great as 3.0 times the distance of the Earth from the Sun) derived from a combination of Helios 2 photometer observations and UCSD interplanetary scintillation (IPS) velocity observations. This "time-dependent" tomographic modeling technique maps day to day changes in the solar wind density content in three dimensions over the heliosphere. The Helios photometer Thomson-scattering brightness observations map density and are least squares fit to a time-dependent kinematic model using time steps of one day. These short time steps restrict the data fits so that outward plasma motion alone is used to deconvolve the 3-D structures. The data for the video were obtained from the time period from 18 UT 26 April to 00 UT 6 June 1979, and includes all of Carrington Rotation 1681. The spatial resolution is approximately 10 by 10 degrees in heliographic latitude and longitude and 0.25 AU (Earth to Sun) in solar distance. Higher density features are more yellow and more opaque. The Sun is depicted as a dot in the center of the image, and the Earth, a blue dot on its orbit around the Sun. The view is from 30 degrees above the ecliptic plane from a position about 45 degrees west of the Sun-Earth line at the beginning of the video at a distance of 3 AU. The video sequence presents each day's tomographic model result with a cadence of one-quarter day between frames over the time interval.

During the time interval Helios 2 moved from 0.37 AU 11 degrees west of the Sun-Earth line to 0.63 AU 162 degrees west. The tomographic model fit to brightness has a far more simple relationship with density than does IPS g-level with density (see "Time-Dependent" Cambridge/STELab Tomography) accessed in current Space Weather Forecasts. The time period shown in 1979 is during the maximum of solar activity cycle 21; only the northern hemisphere is shown. This time interval includes several Coronal Mass Ejections (CMEs) that were well-studied by the Solwind Coronagraph and the Helios spacecraft photometers. The first image above shows a CME seen from Earth labeled "3-pronged" by the Solwind coronagraph group (Poland, et al., 1981) that arose from the Sun to the solar northwest seen from Earth at about 12 UT 7 May 1979. This CME had a mass of approximately 10^16 g. A far more massive event sequence beginning with a loop-like CME that arose from the Sun 1554 UT 24 May, 1979 (second image) was studied in detail by Jackson and Hick (1994) and others (see references). A Helios 2 image of this event and a video of this CME sequence can be found at: HELIOS Photometer CME Video Sequence.

More details about the tomography using the Helios Photometer data can be found in Jackson, B.V. and Hick, P. (2000)


7 May 1979 CME:

Jackson, B.V. and Leinert, C.,
"Helios Images of Solar Mass Ejections",
J. Geophys. Res., 90, 10,759, 1985.

Jackson, B.V.,
"Imaging of Coronal Mass Ejections by the Helios Spacecraft",
Invited review paper in the 100th 'Jubilee' issue of Solar Phys.,
100, 563, 1985.

Jackson, B.V., Rompolt, B., and Svestka, Z.,
"Solar and Interplanetary Observations of the Mass Ejection on 7 May 1979",
Solar Phys., 115, 327, 1988.

Jackson, B.V. and Froehling, H.R.,
"Three-Dimensional Reconstruction of Coronal Mass Ejections",
Astron. Astrophys., 299, 885, 1995.

Poland, A.I., Howard, R.A., Koomen, M.J.,Michels, D.J., Sheeley, N.R., Jr.,
"Coronal Transients near Sunspot Maximum",
Solar Phys., 69, 169, 1981.

24 May 1979 CME sequence:

Jackson, B.V., Howard, R.A., Sheeley, N.R., Jr., Michels, D.J.,
Koomen, M.J. and Illing, R.M.E.,
"Helios Spacecraft and Earth Perspective Observations of Three Loop-Like Solar Mass Ejection Transients",
J. Geophys. Res., bf 90, 5075, 1985.

Jackson, B.V. and Hick, P.L.,
"Three Dimensional Reconstruction of Coronal Mass Ejections",
in the proceedings of the Third SOHO Workshop on Solar Dynamic
Phenomena & Solar Wind Consequences, ESA SP-373, 199, 1994.

Jackson, B.V., Hick, P.L., Kojima, M. and Yokobe, A.,
"Heliospheric Tomography Using Interplanetary Scintillation Observations 1. Combined Nagoya and Cambridge Data",
J. Geophys. Res., 103, 12,049, 1998.

Jackson, B.V. and Hick, P.,
"Three Dimensional Tomography of Heliospheric Features Using Global Thomson Scattering Data",
Adv. Space Res., 25, No. 9, 1875, 2000.

Leinert, C., Link, H., Pitz, E., Salm, N. and Kluppelberg, D.,
"Helios Zodiacal Light Experiment,
Raumfahrtforschung, 19, 264, 1975.

Richter, I., Leinert, C. and Planck, B.,
"Search for Short Term Variations of Zodiacal Light and Optical Detection of Interplanetary Plasma Clouds",
Astron. and Astrophys., 110, 115, 1982.