The image depicting the heliosphere on July 14, 2000 at 2 UT, the
model correlation with Advanced Composition Explorer (ACE) in-situ density near Earth and a
1.9 Mbyte *.avi video presentation that includes the image as one of the
time sequence steps is a reconstruction 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 interplanetary scintillation (IPS) intensity-level
and velocity observations. This "time-dependent" tomographic modeling technique operates on each day's data and
maps day to day changes in the solar wind density content in three dimensions near Earth.
The IPS observations
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 Carrington Rotation 1965 (July 10 to August 4, 2000.
The spatial resolution
is approximately 20 by 20 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 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. Densities during the time interval from July 12 to July 22 correlate
to in-situ densities from ACE near Earth with a CCF of ~0.9 (see figure). The major density structures
directed toward Earth are associated with the halo CMEs that occurred on
July 11 and
July 14 observed by
EIT and the
LASCO coronagraphs on the
SOHO spacecraft.
The image and video sequence shows that the primary mass of the July 11 halo CME was well past 1 AU to the
northeast of Earth when the high density associated with this event sequence arrived in Earth's vicinity early July 15.
An alternate 3.0 Mbyte mpeg video sequence of this event sequence is also
available. This video sequence spans the time from midday 10 July until 29 July in quarter-day steps. Both this
and the above video sequence removes a 1/r squared density gradient up to 1 AU, and outward from that distance,
yet another 1/r density gradient which allows more structure (lower densities) to be observed in the inner heliosphere
unobscured by the foreground. In both videos, the July 14 CME is well-observed moving outward past Earth.
The tomographic sequence temporal and spatial filters are also adjusted to fit the in-situ density time and
velocity sequence, and this gives a correlation of 0.77 over the whole Carrington time interval shown above.
More information about the IPS data from STELab (and the data present here) can be found on the Web at:
http://stesun5.stelab.nagoya-u.ac.jp/index-e.html.
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