Time Distance Products
Time-distance helioseismology pipeline generates subsurface maps of
horizontal flow velocities and wave-speed perturbation for the full-disk
Sun, and also for selected active regions. The maps are obtained for
8-hour intervals, and cover horizontal areas of 30° x 30° and 0 -- 20 Mm
in depth.
Data Analysis Procedure:
The basic procedure for the time-dis
tance data-analysis pipeline is the following:
- Track the HMI Dopplergrams with the differential rotation rate
(Snodgrass and Ulrich, 1990), and map the tracked areas into heliographic
coordinates using the Postel's projection. The tracked datacubes represent
3D arrays with dimensions of 512x512x640, with a 0.06° sampling horizontal
scale, and 45-second time cadence, covering 30° x 30° areas for continuous
8 hour intervals.
- Phase-speed filtering procedure is then applied to the datacubes,
and acoustic travel times are calculated from the cross-correlation functions.
Two types of travel times are obtained using two different fitting
algorithms:
- Gabor wavelet fitting (Duvall & Kosovichev, 1997)
- Gizon-Birch (2002) fitting method.
- Inversions of the travel-times are performed using the Multi-Channel
Deconvolution method, with two different sensitivity kernels employed:
- ray-path approximation kernel
- Born-approximation kernel.
Thus, our products include two sets of acoustic
travel times and four sets of inversion results in both the flow-velocity
and wave-speed perturbation fields.
Available Data products
- Full-disk Data Products
The travel times and inverted flow and wave-speed
perturbation maps are provided for 25 areas of 30x30 degrees covering
the full disk and processed independently. Each day is divided into
three 8-hr intervals: 00:00 -- 07:59UT, 08:00 -- 15:59UT, and 16:00
-- 23:59UT. The JSOC series of these data products are:
-
hmi.tdVtimes_synopHC contains fitted travel times, with data segments 'gabor' from Gabor wavelet fitting and 'GB' from Gizon-Birch defined travel times. Users can download either one or both.
- hmi.tdVinvrt_synopHC contains inversion results, with 'vx' for subsurface east-west direction velocity, 'vy' for subsurface north-south direction velocity, and 'cs' for subsurface wave-speed perturbations. Keywords 'Gabor' and 'GizonBirch' define which fitted travel times are used, and 'Born' and 'Raypath' define which sensitivity kernels are used.
The full-disk flow and wave-perturbation maps are then obtained by merging these 25 areas.
- Data sequence will soon be available.
- Active Region Data
details will soon be available.
References
Detailed procedure and description of results can be found in the paper :
Time-Distance Helioseismology Data-Analysis Pipeline
for Helioseismic and Magnetic Imager Onboard Solar Dynamics Observatory (SDO/HMI) and Its Initial Results
For details of the travel-time fittings and comparion of different fitting methods, please refer to the paper:
Implementation and Comparison of Acoustic
Travel-Time Measurement Procedures for the Solar Dynamics
Observatory/Helioseismic and Magnetic Imager Time-Distance
Helioseismology Pipeline
Joint Science Operations Center (JSOC)
