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Nudging Earth's ionosphere with radio waves helps us learn more about it, study shows

Between 50 and 1,000 kilometers above our heads is the ionosphere, a layer of Earth's upper atmosphere consisting of charged particles: ions (atoms that have gained or lost a negatively charged electron) and loose electrons. The ionosphere alters the path of electromagnetic waves that reach it, including radio and GPS signals, so studying it is helpful for understanding communication and navigation systems.

One way to study the ionosphere is to "nudge" it with powerful radio waves sent from the ground to see how it reacts. Where the waves hit the ionosphere, they temporarily heat it, changing the density of charged particles into irregular patterns that can be detected from the way they scatter radio signals. By studying these irregularities, known as artificial periodic inhomogeneities (APIs), scientists can learn more about the ionosphere's composition and behavior.

However, factors such as space weather and solar activity can inhibit both the formation and detection of APIs. in Radio Science, La Rosa and Hysell sought to enhance the reliability and utility of the API research technique by examining API formation in all three main regions of the ionosphere, the D, E, and F regions. Past techniques focused only on API formation in the E region.

To do so, the researchers revisited data from research conducted in April 2014 at the High-frequency Active Auroral Research Program (HAARP) facility in Alaska. HAARP's radio transmitters created small perturbations in the ionosphere, and the facility's receivers captured the resulting scattered radio signals.

Initial analysis of the 2014 data revealed some APIs in the E region, but this team of researchers reprocessed the data at higher resolution. This reanalysis allowed them to document, for the first time, simultaneous APIs across all three regions, all triggered by a single radio nudge.

API formation in each of the three regions is dictated by a different set of mechanisms, including chemical interactions, heating effects, and forces that change the density of charged particles; this variability has made it difficult to develop a stand-alone model of API formation across the ionosphere.

To address that challenge, the researchers extended a model previously created to capture API formation in the E region by incorporating the relevant mechanisms for the D and F regions. In simulation tests, the model successfully reproduced the behavior observed in all three regions. This model could help deepen understanding of the physics at play in the ionosphere.