GONG Newsletter #31, August - National Solar Observatory

What Data Can I Get from GONG
GONG provides data freely to its members. Becoming
a member is simple — go to the GONG web page
and select the “Scientic Enterprise” link and then the
“GONG Membership Application” link and then the
“GONG Research Program Application” link. You can ll
out the forms electronically, or by using a text le. After
the forms are submitted and processed, you will be able to
search and order our data.
Some of the currently available products for the helioseismologist
are:
Power spectra of solar oscillations covering the range of
0 ≤ l ≤ 200, -l ≤ m ≤ +l, and 0 ≤ ν ≤ 8.33 mHz.
Time series of complex spherical harmonic coefcients as
a function of l and m in the range 0 ≤ l ≤ 200 and 0 ≤ |m|
≤ l.
Estimated frequencies, amplitudes, and linewidths of solar
oscillation modes, as a function of l, m, and ν covering
the range 0 ≤ l ≤ 150, -l ≤ m ≤ +l, and 1.2 ≤ ν ≤ 4.0
mHz.
Both the time series and power spectra are available for temporal
intervals of GONG months (GM), with 1 GM ≡ 36
days. Note, however, that the mode parameters are computed
from overlapping three-GM (108 day) temporal
intervals, with a one-GM spacing. Time series and power
spectra are also available for 0 ≤ l ≤ 45 for intervals of 1
GONG Year (10 GM or 360 days) and 35 GM. All data
from 7 May 1995 to 6 October 2000 have been processed
to time series and power spectra, and the mode parameters
have been computed on all possible 53 intervals of 3 GM.
For the non-helioseismologist, we have:
• Minute-by-minute images of the solar surface Doppler
velocity eld from 7 May 1995 to the present.
• Magnetograms every 20 minutes, plus derived synoptic
maps for Carrington rotation cycles 1896 through
1942; and
• Low-pass, temporally ltered, and geometrically registered
images of the surface Doppler velocity with a
cadence of 4 minutes and a lter width of 17 minutes,
useful for studies of slowly evolving ows from 7 May
1995 to 17 October 1998.
Finally, we have implemented a new data service that provides
near-real-time magnetograms with rough calibration
and a cadence of about one every two hours around the
clock. They can now be obtained at:
ftp://www.gong.noao.edu/pub/gong/magnetograms
Sasha Kosovichev called attention to changes in GONG+ observations of the X20 are of April 2, 2001 in NOAA 9393, and
Jack Harvey prepared this gure to show the temporal evolution. The left panel is the line-of-sight component of the magnetic
eld near the northeast limb averaged over 30 minutes prior to the are (2100-2129 UT). The next six panels show the difference
between the absolute value of the signal averaged over subsequent ten minute periods and the 30 minute pre-are average. White
(black) represents increasing (decreasing) line-of-sight signal strength. The panels are averaged from left to right over 2130-39
(preare), 2140-49 (rising phase), 2150-59 (maximum), 2200-09 and 2210-2219 (declining phase), and 2250-59 (post are). The
changes shown are a combination of seeing effects, change in perspective as the Sun rotates, line prole changes associated with
the maximum phase of the are, normal evolution of the active region eld, and real eld changes associated with the are. The
later panels are coincident with a strongly sheared sunspot. It is not clear if the are eld changes are in strength, direction or
position or some combination.