The mesospheric sodium layer as a remotely, optically pumped magnetometer for investigation of Birkeland currents (MOM)
This web page is dedicated geomagnetism and northern lights in general and specially to the Norwegian Research Council funded project “The mesospheric sodium layer as a remotely, optically pumped magnetometer for investigation of Birkeland currents“.
In this project, we want to study the aurora by making the first long-term in situ measurements of the geomagnetic field in the actual auroral region. Geomagnetic measurements are made to study Earth’s core and crust, but also to investigate processes related to aurora and their connection to the sun through the solar wind and Earth’s magnetic field. These magnetic measurements are typically performed from the ground or from satellites. Thus, apart from very short-lived rocket experiments, we hardly have any magnetic data between the ground and 300 km. The mesosphere at around 90 km height is a region of great interest, due to its proximity to the aurora and its associated processes. By coincidence, there exist a sodium layer at this height. By illuminating this layer with laser light at a specific wavelength, it will scatter light back to the ground. The sodium lidar at the ALOMAR observatory in northern Norway uses this mechanism to measure temperatures and wind velocities between 80 and 100 km. We plan to adapt the sodium lidar and, for the first time, make continuous mesospheric magnetic field measurements in the auroral region. By pulsing the laser light and varying the frequency of the pulses, it is possible to influence the intensity of the backscattered light. The pulse frequency causing the strongest backscatter is then related directly to the strength of the magnetic field in the sodium layer. Hence it is possible to remotely measure the magnetic field in the mesosphere from ground. We will apply this technique, which has been proposed earlier for low or mid latitudes, and open for a completely new domain of measurements of magnetic fields generated by currents in the magnetosphere-ionosphere system. It is, furthermore, anticipated that small, horizontal current structures, whose signature is not resolvable by other means, will be discernible when measurements are performed in the mesosphere.