The Global Oscillation Network Group (GONG) Project is a community-based activity to operate a six-site helioseismic observing network, to do the basic data reduction, provide data and software tools to the community, and to coordinate analysis of the rich data set that is resulting. GONG data is available to any qualified investigator whose proposal has been accepted. Information on the status of the Project, the scientific investigations, as well as access to the data is available on our Web page at: www.gong.noao.edu.
While operations, data reduction and scientific analysis proceed very well,
much of our attention is being devoted to the development, production,
and -- yes -- deployment of the 10242 GONG+ camera system within the next year.
We are delighted with the l- diagrams from our first time series with the
new script system (see figure), which show excellent response out to the
optical cut off at around l of 950. We are looking forward to the first
deployment of the GONG+ system this Winter with a fully operational network
by the Summer.
A workshop on Helioseismic Diagnostics of Solar Convection and Activity was held at Stanford University, Palo Alto, California, 12-15 July, with many new results on internal dynamics, horizontal inhomogeneities, and time variations being presented by 100 participants representing the international community.
The GONG network of telescopes continued to perform well during the second quarter of 1999. Two preventive maintenance (PM) visits occurred, one to El Teide, 4-13 April, and the other to CTIO, 26 May to 3 June.
One of the major difficulties affecting network operation during this period was a damaged Uninterruptable Power Supply at CTIO, which was most likely caused by a lightning strike. During the troubleshooting process, 36.3 hours of images were lost. Although the on-site staff did much of the initial work, the unit was inoperative until the PM team was on-site and repaired the unit.
Additional network down time resulted from generator problems at Udaipur. The generator failed to start when needed, and because no one was available to monitor the circumstances, the instrument was intentionally shutdown. A lapse of 83.6 hours, primarily at night, resulted. The on-site staff at Udaipur deserves recognition not only for keen attention to the instrument, but also for repairing the generator.
Problems related to the Exabyte tape drives occurred at most of the sites again this quarter, resulting in nearly 36 hours of lost data. We are really looking forward to the DLT drives, which should be replacing them within the year. More than the usual amount of lost images (about 20 hours) attributable to system "glitches" such as resyncs, reboots and hung operations, occurred this quarter as well. Although no obvious patterns have appeared, the Operations Team will continue to investigate.
The campaign to identify the mode frequencies in the initial three years of nearly continuous images (35, 36-day, months from 950507 to 981017) has been completed. These sets of mode frequencies were extracted from power spectra generated from 108-day time series, centered every 36 days. There are 33 sets of mode frequencies, one for each GONG month, less the first and last months.
In addition, magnetogram images from the time interval between the beginning of GONG's three-site network operations (950507) and beginning of the original magnetogram reduction campaign in early 1996 (Carrington Rotation 1906), were inspected and processed. As a result, the beginning of the sequence of GONG synoptic maps and other magnetogram products has been extended backward from Rotation 1906 to Rotation 1896 (950516).
The DMAC has upgraded two components of its reduction software in preparation for GONG+. The project's calibration software has been revised to improve the quality and efficiency of the calibration process and to remove (using temporal smoothing) a low-temporal-frequency artifact in the time series of calibrated images. The latter artifact did not affect Classic GONG p-mode data, but will affect the higher resolution images from GONG+. In addition, a package of improvements, including a revision of the algorithm for registering images into heliographic coordinates, has been incorporated in the p-mode data reduction software.
Brian Pohl has left the GONG Project after working in the DMAC as a Data Reduction Specialist for over four years. Brian has taken a position with the US Naval Observatories, Astronomy Department, in Washington, DC. We wish him well.
As mentioned in the Data Management and Analysis section, the frequencies of the solar oscillations have now been determined for all 33 108-day blocks from 7 May 1995 to 29 September 1998. During this time, solar activity has progressed from the minimum in early 1996 and is now in the rapidly ascending phase of cycle 23. The GONG measurements continue to show the expected increase in the basic frequencies of the oscillations, as well as more subtle variations (the so-called even splittings), which are well-correlated with the activity level and appear to be linked to the latitudinal distribution of magnetic field. Thanks to the efforts of Rachel Howe and Rudi Komm, we have recently pushed the expansion of these subtle variations up to 14th order, and find that the high correlation with the corresponding higher-order latitudinal components of the magnetic field still holds.
We have also detected changes in the odd coefficients up to 15th order. These variations are not correlated with the latitudinal magnetic field distribution; evidence that Zeeman-induced distortions of the observed spectral line profile are not contaminating the frequencies. Inversions of the odd splitting coefficients show the torsional oscillation pattern also observed in surface measurements and indicate that this pattern penetrates to depths of at least 35 to 70 Mm in the convection zone. There are also suggestions of a polar spin-down that changes substantially with depth as the cycle begins to rise. With these exciting signs of activity-related changes in the convection zone dynamics, we are now beginning to reap one of the major benefits of long-term helioseismic observations.
The remapping from sky coordinates to heliographic coordinates has been
improved to correctly treat the rectangular pixels of the camera. This
change has been installed at GONG month 36. The major effect is to
substantially alter the relative amplitudes of the spatial leaks in the m-
diagram. Visual inspection of the spectra suggests that the target ridge is
not systematically affected, and a test is underway to assess the impact of
the revision on the fitted frequencies. When this test is completed, we will
resume routine peak finding going forward in time from GM36.
Stuart Jefferies has left the GONG Project and NSO to take a position at Big Bear Solar Observatory. Stuart has made several fundamentally important contributions to helioseismology, and his scientific presence will be sorely missed.
A project milestone was successfully passed on 11 June when an NOAO panel of internal experts reviewed and approved the Camera and Video Data Acquisition Systems. All ten cameras have been received and we are now awaiting delivery and acceptance testing of the Data Acquisition Systems.
While we are continuing to evaluate the performance of the camera and Video Data Acquisition System at the Tucson observing facility, the development team is turning their attention to the data caching subsystem. This system consists of hard disk drives, which will temporarily store the real-time accumulated data during the daytime, and DLT 7000 tape drives, which will permanently store the data be returned to Tucson for processing.
John Leibacher