Abstract
Continuous observations play an important role in the studies of solar variability. While such observations can be achieved from space with an almost 100% duty cycle, it is difficult to accomplish a very high duty cycle from the ground. In this context, we assess the duty cycle that has been achieved from the ground by analyzing the observations of a six station network of identical instruments, the Global Oscillation Network Group (GONG). We provide a detailed analysis of the duty cycle using GONG observations spanning over 18 yr. We also discuss the duty cycle of individual sites and point out various factors that may impact individual site or network duty cycles. The mean duty cycle of the network is 93%, however it reduces by about 5% after all images pass through the stringent quality-control checks. The standard deviations in monthly and yearly duty cycle values are found to be 1.9% and 2.2%, respectively. These results provide a baseline that can be used in the planning of future ground-based networks.
Highlights
Solar observations are available for a few centuries, most of the records prior to the 20th century are sparse
While observations from space are almost continuous with small disruptions, the ground-based observations are adversely affected by the diurnal cycle
There were two possibilities for continuous observations from ground: either from the South Pole but for a limited time during the Austral Summer (Grec et al 1980) or build a network of identical instruments at geographically separated locations around the Earth. This led to the inception of several networks for helioseismic observations; some are still operational even after more than 25 years and other ceased operations after a few years. Observations from these networks allowed the measurement of solar oscillations from low to high degrees where degree is the number of waves around the solar circumference
Summary
Solar observations are available for a few centuries, most of the records prior to the 20th century are sparse. There were two possibilities for continuous observations from ground: either from the South Pole but for a limited time during the Austral Summer (Grec et al 1980) or build a network of identical instruments at geographically separated locations around the Earth. This led to the inception of several networks for helioseismic observations; some are still operational even after more than 25 years and other ceased operations after a few years.
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