At sunrise or sunset, while it is still dark on the ground, sounding rockets can release small clouds of barium into the upper reaches of the atmosphere. There, once they are out of Earth’s shadow, these clouds are exposed to the sunlight peeking around the edge of Earth. Sunlight ionizes barium, causing the clouds to feel the forces from Earth’s electric fields.
The barium ions move in response to these fields, tracing out the electric currents in the ionosphere. Geomagnetic storms, which increase currents in the ionosphere, transfer energy from space into our atmosphere. Much of this energy comes in the form of Joule heating. Like a current running through a resistor, the currents generated during storms create heat as they run through Earth’s atmosphere.
Using cameras on the dark ground below, scientists can record the movements of the glowing barium clouds to study the heating of our atmosphere during times of geomagnetic activity.
By using the drift velocities of the barium ions released by three separate sounding rockets, launched in 1967 and 1987, scientists were able to observe the small- and large-scale oscillations of the electric field. Researchers then calculated, in two ways, the amount of heating these fields produced. First, they calculated the heating profile using both the large- and small-scale oscillations, and second, they repeated the calculation using only the average values as a proxy for the electric field that radar measurements would have recorded.
Here Hurd and Larsen showed that the first method, with the more detailed measurements, detected much more heat than the second method. This means that the small oscillations around the mean electric field are actually responsible for 50% or more of the total heat created. This result was true for all three rocket flights, even though they took place at differing levels of geomagnetic storm activity. Sounding rocket flights are limited to small patches of sky and can only yield short bursts of data, but these results are important for global atmospheric and ionospheric simulations as scientists continue to develop advanced space weather models. (Journal of Geophysical Research: Space Physics, doi:10.1002/2015JA021868, 2016)
—Aleida K. Higginson, Freelance Writer
Citation: Higginson, A. K. (2016), Half of atmospheric joule heating is due to small oscillations, Eos, 97, doi:10.1029/2016EO047017. Published on 29 February 2016.