Development Institution: University of California, Los Angeles (UCLA)
GMAG Lead: C. T. Russell
Purpose: Measure changes in Earth's magnetic field near Earth's surface due to substorm onset to help determine the timing of substorm events.
At onset, currents within the Earth's magnetotail are diverted to the ionosphere, 100 km above the Earth's surface. The ground-based magnetometers measure the magnetic field perturbations that these currents generate on the surface of the Earth to detect substorm onset signatures. They also measure waves associated with the magnetospheric substorm onset out in Earth's magnetosphere. Measurements of these magnetometer signatures will allow scientists to determine when the aurora reacts to the onset trigger in the magnetosphere even when the ground-based all-sky cameras cannot detect the aurora because of clouds.
THEMIS engineers have installed over 21 GMAG stations, providing overlapping coverage for the THEMIS project in the Northern United States (AK, OR, NV, ND, SD, MT, WI, MI, PA, and VT) and in Canada. Ten of these systems are installed with the Ground-Based Observatory (GBO) systems for THEMIS. Eleven are installed in schools and are part of the THEMIS Education and Public Outreach (E/PO) program. These magnetometers, known as the E/PO magnetometers, are the exact same type of magnetometer as those built for the GBOs.
The GMAGs are ground-based Flux Gate Magnetometers (FGM) and operate in the same way that the space-based FGMs work. The GMAGs measure the magnetic field, a Global Positioning System (GPS) system provides accurate position and an inexpensive personal computer collects data, provides data storage and distributes the data. The GMAGs are the next generation of the low-cost ground-based magnetometers developed at UCLA. The magnetic field at Earth is 60,000 nanotesla (nT) maximum with typical space-related changes on the order of 10-100 nT and superimposed waves on the order of 0.1-1nT. These magnetometers measure the magnetic field with 0.01 nT resolution at 2 samples/second.
These GMAG systems are new in several ways. They can be operated in a stand-alone mode, requiring only AC power. When there is connectivity, they are configured to provide near-real time data over the internet. Internet connectivity is also used for remote data collection and remote reconfiguration/reprogramming of the magnetometer setup.