On clear days and nights, we may think all is calm in the sky, but there is movement and energy in the atmosphere unseen to the human eye. When solar radiation wallops the upper layer of Earth’s atmosphere, called the ionosphere, large concentrations of ions and free electrons are left colliding.
Changes in the ionosphere result from both the space weather above and Earth’s weather below, and can disrupt communications and GPS signals. While we may not be able to view this phenomenon directly, scientists can measure it using incoherent scatter (IS) radar, a “powerful tool” to investigate the ionosphere at 80 to 1,000 kilometers (50 to 620 miles) above Earth’s surface. Although IS radars can track electron density, ion velocity, ion and electron temperatures, and more, their number is limited due to their high power demand and size.
Now, researchers have used IS radar in Antarctica to produce what they say are the first measurements from the region. The observations provide scientists with crucial data for models and improve our understanding of the most subtle features of our planet's atmospheric layers. In particular, the findings could help us understand the differences between the lower layers of the atmosphere in the northern and southern halves of the globe.
"Observations in the southern hemisphere are crucial to revealing global features of both the atmosphere and the ionosphere," said co-author Taishi Hashimoto, assistant professor at the National Institute of Polar Research, in a statement.
The team analyzed observations from the Program of the Antarctic Syowa Mesosphere-Stratosphere-Troposphere/Incoherent Scatter (PANSY) radar – first used in 2015 and then again in 2017 with a 24-hour observation – that consists of an active phased array of 1,045 Yagi antennas. The preliminary findings are published in the Journal of Atmospheric and Oceanic Technology.
The purpose was to measure incoherent scattering in the ionosphere. A useful analogy is a pebble skipped on the surface of a pond. The scattering is comparable to the small vertical changes in the water, but the most visually striking effect of the pebble is the concentric ripples it creates. When it comes to the ionosphere, these are called field-aligned irregularities (FAI), and the team had to come up with an inventive solution to filter them out. A specific computer algorithm was designed to suppress the FAI signal, which increased the number of usable power profiles by 23.85 percent.
"From these results, we conclude that using a subarray dedicated to FAI observation, together with adaptive signal processing, is valuable for ionosphere observations in the Antarctic region," wrote the team. "Furthermore, the [new] algorithm is acknowledged as a satisfactory workable solution for the PANSY radar."
"Our next step will be the simultaneous observation of ionosphere incoherent scatter and field-aligned irregularities, since the suppression and extraction are using the same principle from different aspects," Hashimoto said. "We are also planning to apply the same technique to obtain other types of plasma parameters, such as the drive velocity and ion temperature, leading to a better understanding of auroras.”