Solar winds transport more energy towards the Earth than expected

Polar lights over Greenland (photo: J. Matzka, GFZ).

30.11.2016: Solar winds are a permanent flow of charged particles from the sun – mainly consisting of ionized hydrogen. The Earth’s magnetic field stops these particles at the upper atmosphere, where a fraction of the kinetic energy of the particle flow is converted into electric energy. During strong solar winds this energy transition becomes visible by polar lights. In a new study, published in Annales Geophysicae, an international team of scientists under the participation of the GFZ section Earth's magnetic field now showed that solar winds transport way more energy towards the Earth than previously thought.

Since late 2013 the Swarm satellite mission of the European Space Agency ESA, supported by the GFZ, investigates the Earth’s magnetic field and the conditions of the upper atmosphere. Two of the overall three satellites fly side by side and thereby measure even the smallest changes in the strength of the geomagnetic field on short distance. Thereby they also track changes in the magnetic field that are caused by solar winds: the so called field-aligned currents. These electric currents flow alongside the field lines of the geomagnetic field, which causes the conduction of electric energy towards the Earth’s surface. The GFZ developed the software used in the Swarm mission that allows for a measurement of the field-aligned currents.

The electricity is formed because a portion of the kinetic energy from the solar particle flow is converted into electric energy. This electricity is then converted into heat. The stronger the solar winds, the more electricity flows: charged particles from the upper atmosphere are shot towards the Earth. Polar lights are the visible sign of this energy transition. And, the stronger the currents, the more colorful are the polar lights.

Field-aligned currents in polar regions

The scientists now evaluated how much energy is formed by solar winds. With unprecedented precision the Swarm data revealed even the weakest field-aligned currents. The researchers showed that a significant amount of the kinetic energy of the solar winds of about 30 percent is converted into energy and therewith into heat. This proves that the upper atmosphere is heated by solar winds way more than was known before. They thereby play an important role for the Earth’s energy balance.

The new study evaluates satellite data from the high latitudes of both hemispheres. The scientists verify the existence of field-aligned currents where no other mission has ever detected them. “An investigation of the field-aligned currents in the auroral zone suggests that significantly more energy is transported towards the polar regions than was known before”, explains Herman Lühr, main author of the study. This clearly shows that field-aligned currents in the auroral zones are an important coupling mechanisms between space and the Earth’s atmosphere. (ak)

Lühr, H., Huang, T., Wing, S., Kervalishvili, G., Rauberg, J., Korth, H., 2016. Filamentary field-aligned currents at polar cap region during northward interplanetary magnetic field derived with the Swarm constellation. Annales Geophysicae, 34, 901–915. DOI: 10.5194/angeo-34-901-2016