Images from the Solar Oscillations Investigation - Michelson Doppler Imager
Presented at the Joint Users Resource Allocation Planning Meeting
20 June 1996
Figure 1: MDI Single Dopplergram
The MDI instrument is designed to observe the line-of-sight
motion of the Sun's photosphere, and to produce a velocity image or
dopplergram once per minute. This figure illustrates a typical MDI
dopplergram, with the dominant feature being the solar rotation, which
appears as a shift from dark to light across the Sun's disk. The dark
colors indicate motion toward the observer and lighter colors indicate
motion away from the observer.
Figure 2: MDI Single
Dopplergram Minus 45 Image Average Subtracting an average solar
velocity image observed over 45 minutes from a single velocity image
reveals the surface motions associated with sound waves traveling
through the Sun's interior. The small-scale light and dark regions
represent the up and down motions of the hot gas near the Sun's
surface. The pattern falls off towards the limb because the acoustic
waves are primarily radial.
Figure 3: MDI 45 Image
Average Dopplergram Minus Polynomial Fit Subtracting the average
solar rotation signal from a 45 image average of full disk
dopplergrams enhances the surface motions associated with solar
convection. Convective flow transports material and energy from the
Sun's interior along narrow plumes. At the surface, the upwelling
material then spreads out horizontally in the granulation pattern seen
in this image. Little of this pattern is seen at the center of the
solar disk because the motion is perpendicular to the line of sight.
Figure 4: Interior Solar Cutaway and Mode
Diagram This sketch illustrates how sound waves propagate
through the Sun's interior. These sound waves last long enough to set
up standing waves that have well defined periods and wavelengths. The
diagram at the right shows the relationship between period and
wavelength for sound waves in the Sun.
Figure 5: MDI Observed Oscillations This
figure is the l-nu (period versus wavelength) diagram determined from
observations made by the MDI instrument during a continuous 83-hour
observing run in April 1996. The x axis is the inverse spatial
wavelength, with the right end representing waves on the order of
10,000 km (l=400). The y axis represents the wave frequency up to the
instrument Nyquist cutoff (1 minute or 0.016 Hz).
Figure 6: MDI
Partial High Resolution Dopplergram This image is a portion of a
MDI high-resolution dopplergram and shows about 4% of the solar
disk. The large-scale rotation signature has been removed to clarify
the smaller-scale surface motions.
Figure 7: Acoustic Wave Paths for
Time-Distance Studies Sound waves propagate into the solar
interior along ray paths illustrated in this diagram. The waves are
refracted because of changes in the sound speed due to varying density
and temperature. The propagation path depends on the initial direction
the sound waves travel.
Figure 8: MDI Observed Solar
Surface Flows Variations in the solar surface velocity will show
up at other locations depending on the propagation path taken by the
sound waves. Correlating the time delay as a function of distance
provides information on the subsurface temperature and flows. This
diagram illustrates the flow at the Sun's surface deduced from a
time-distance analysis. The dark regions are magnetic fields
simultaneously measured by the MDI instrument.
Figure 9: Solar Subsurface Flows
Deduced from MDI Observations By combining the time-distance
analysis with inversion models, the subsurface flows can be
calculated. This picture indicates the inferred convective flow in the
solar interior near the Sun's surface.
Figure 10: MDI 160 kbps Telemetry
Coverage during April 1996 This diagram indicates the coverage
of the 160 kbps MDI telemetry from the SOHO spacecraft for the month
of April 1996. The light gray indicates data that has been received
and processed at Stanford, the medium gray indicates data that is
missing, and the dark gray is data that has been received but needs to
be reprocessed. The 83-hour continuous contact from April 24th to 28th
resulted in 97% recovery of all MDI 160 kbps packets and 94.5%
recovery of complete dopplergrams.
Figure 11: MDI 160 kbps
Telemetry Coverage during May 1996 The MDI 60-day continuous
coverage started on May 23rd. This diagram illustrates data recovery
and processing of the May 1996 data through the last week in June
Please address comments and questions to the
SOHO SOI/MDI Results.
The SOI Main Page.
Last Modified by Amara Graps,
SOI, on 15 November 1996.