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NOAO Newsletter - Global Oscillation Network Group - September 1998 - Number 55


Global Oscillation Network Group

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 and provide the data and software tools to the community, and to coordinate analysis of the rich data set that is resulting. GONG data are available to any qualified investigator whose proposal has been accepted; however, active membership in a GONG Scientific Team encourages early access to the data and the collaborative scientific analysis that the Teams are undertaking. Information on the status of the Project and the scientific investigations, as well as access to the data, is available on our WWW server whose URL is www.gong.noao.edu.

The GONG 1998 Meeting, and the 6th SOHO Workshop, hosted by the CFA and organized by Sylvain Korzennik, were held jointly in Boston, 1-4 June. The workshop focused on the results from the continued GONG operations and the helioseismic experiments aboard SOHO (GOLF, MDI/SOI, and VIRGO). Results from other ground-based multi-site projects, TON, MWO-CRAO, BISON, and IRIS, were also included. All of the helioseismic projects have produced a wealth of data of unprecedented quality from which new insights on the structure and dynamics of the solar interior are being inferred. The Meeting provided the perfect venue for assessing the needs and expectations of future activities.

image

Caption: The first magnetogram from the GONG+ camera and polarization modulator [right] and a roughly co-temporal magnetogram from the KPVT [left]. We hope to be able to provide continuous magnetograms when the existing, low-resolution, network camera systems have been replaced.Our plans are for them to be summed for 5 minutes to increase sensitivity and reduce data volume.

Representatives from five of the sites attended, providing a rare opportunity for us all to discuss site issues together. The DMAC Users Committee and the Project's Scientific Advisory Committee also met and had extremely productive discussions. The "proof of concept" high-resolution breadboard instrument dominated the discussions, which resulted in several ideas for helping to move the effort forward.

Operations

The GONG network of telescopes continues to achieve a high level of operational success. Most of the network down-time is due to the scheduled preventative maintenance visits which, in the second quarter of 1998, occurred during eight days of May at Udaipur, and the final seven days of June at El Teide.

The Learmonth station suffered a loss of power due to a failure of the Uninterruptible Power Supply (UPS). The unit was bypassed, and the system was brought up using the unconditioned line power. Although operating again, the station was vulnerable to any power outages at the site. As fortune would have it, the site power was lost when an electrical line was accidentally cut during construction. The total downtime incurred was about 8.5 hours.

The Big Bear Station was down for about an hour due to weather related causes. The morning after a day of rain and a cold night in May, some ice formed on the turret, causing a circuit breaker to trip when the turret tried to unstow. Resetting the breaker got things operating again. Some early morning images are still being lost on occasions when condensation forms on the turret mirrors after a cold night.

Then there are the ongoing difficulties with Exabyte tape drives. Only one site did not experience tape drive failures during the time period in question. The total downtime, as measured by the number of images lost while the equipment was inoperative or being replaced or repaired, was about 77 hours. (These hours could include periods of poor weather and nighttime when other stations could be acquiring good images. This number is a worst case value indicating downtime caused by equipment failure only.) The efforts of the on-site personnel who contributed considerable time to remedying these problems deserve heartfelt recognition.

Data Management and Analysis

During the past quarter, month-long (36-day) velocity, time series, and power spectra were produced for GONG months 25, 26, 27, and 28 (ending 980207) with fill factors of 0.85, 0.75, 0.83, and 0.82.

The p-mode reprocessing campaign (data that have been reprocessed or initially processed with the improved p-mode pipeline) added GONG months 8 and 9, boosting the available data set to months 8-28 (960114-980207). The project is also producing time series and power spectra from the intensity images. These products were generated for GONG month 20.

Data Algorithm Developments

A set of mode parameters has been estimated from the average of six 108-day long time series. These parameters are now being used to create a new first guess table for producing GONG frequencies.

A test of an image merging algorithm is underway. Cliff Toner is producing a time series of four days of merged images, using a weighted average of restored, remapped images. The dates of these images have been chosen to be during the first SOI dynamics run in 1996. Irene Gonzalez will then perform a coarse ring diagram analysis and compare with her previous results from the SOI/MDI data.

The multi-taper method is moving towards installation in the GONG production pipeline. Final tests are underway to finalize the number of tapers, and to verify the method with a random-restart test.

The leakage matrix code has been run for all degrees up to 100, with 25 leaks on either side, and for months 21-23. The code is now being upgraded to include MTFs and horizontal components, and to improve the speed of the calculation.

New Camera Development

Development is proceeding on the installation of a higher-resolution (1024 1024), square-pixel camera and data acquisition system at the Tucson observing station. A fully developed prototype is expected to be in operation by mid-fall.

A Silicon Mountain Designs 1M60_20 camera has been obtained and subjected to a number of tests to verify its suitability. Although limited by our present video data acquisition electronics, the camera has been successfully used to acquire helioseismic time series, and we are very pleased with the results.

A request-for-bid has been issued for the high-speed data acquisition electronics, and a vendor will be selected by the end of the summer.

Visitors

This summer we have had the pleasure of extended visits from Rafael Garcia, Irene Gonzalez, and J. Javaraiah.

Rafael Garcia (DAPNIA/Service d'Astrophysique, CEA/Saclay, France) is working with Stuart Jefferies continuing their effort on the High-frequency Interference Peaks (HIPs) which they detected for the first time for low-degree solar modes. They are pursuing two different strategies for their work: 1) the analysis of new techniques to increase the signal-to-noise ratio of the detected peaks, and 2) continue the study of the HIPs from a theoretical point of view.

Irene Gonzalez Hernandez (Instituto de Astrofisica de Canarias, Tenerife, Spain) is testing the new image merging method, currently being developed by Cliff Toner, using "ring diagram analysis". Currently, the spherical harmonic coefficients are merged. However, for high-resolution applications of local helioseismology, it is necessary to use the images themselves. She will compare the results of applying this method to a set of GONG data with the results obtained in previous work using MDI data.

J. Javaraiah (Indian Institute of Astrophysics, Bangalore, India) is working with Rudi Komm to determine solar surface meridional motion from small magnetic features observed on high-resolution SOI/MDI magnetograms. Latitudinal motions of small magnetic features will be determined by two-dimensional cross-correlation analysis of consecutive (96 minute interval) observations from which active regions are excluded. They have determined the short-term periodicities in solar differential rotation on time scales shorter than the 11-year solar cycle through power spectrum analysis of the differential rotation parameters derived from Mt. Wilson velocity data (1969-1994) and Greenwich sunspot group data (1879-1976). They found considerable differences in the periodicities in solar differential rotation determined from the velocity data and the spot group data. They are currently revising a paper on these results which will be published in Solar Physics.

John Leibacher


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