Although many electrical engineers work with the ionosphere for communications, there is still much that's unknown about the ionosphere's physical behavior in different situations. Sometimes a signal passing through the ionosphere behaves as expected, and sometimes it doesn't. Space weather researchers are figuring out why.
While most electrical engineers are familiar with bouncing radio waves off the ionosphere for communications purposes, space weather researchers are using the practice to study and diagnose the ionosphere itself.
Last summer, Professor Wayne Scales and four Ph.D. students traveled to remote Gakone, Alaska to study the electromagnetic energy that is reradiated when a powerful, high-frequency transmitter aims at the ionosphere. The High Frequency Active Auroral Research Program (HAARP) facility can transmit powerful radio waves at frequencies between 2.8 and 10 MHz hundreds of miles into the ionosphere (see page 18).
"HAARP is the most powerful research facility of its kind," Scales says. "The facility can send up a very powerful radio wave, which heats a small section of the ionosphere," he explains. A small amount of the energy is reradiated back to the earth's surface. Researchers use this stimulated electromagnetic emission (SEE) to study the ionosphere.
From left: Ph.D. students Hai Yang Fu and Alireza Samimi, with Wayne Scales, Steve Floyd ('80), and Ph.D. student Maitrayee Bordikar.
To complicate matters, the reradiated energy returns at frequencies different from what HAARP transmits. "The HAARP transmission is strong enough that some nonlinear processes are stimulated," he explains.
By measuring and analyzing the reradiated energy, researchers hope to determine the types of ions at the time, what type of nonlinear processes are happening, what type of turbulence is there, and how electron temperatures can change, according to Scales. "However, you need theoretical models to develop that understanding. That's what my students are doing; they are developing some of the first theoretical models based on the frequency spectrum of the SEE data."
Maitrayee Bourdikar, Alireza Mahmoudian, Alireza Samimi, and Haiyang Fu all wrote short proposals to participate in the HAARP Summer Student Research Campaign. The program enables graduate students to do state-of-the art experiments while learning how to design experiments and how to use a premier scientific research facility. "The students get to work with premier scientists in the field. The program helps to train tomorrow's leaders in space science," Scale explains.
The Virginia Tech team collaborated with the Naval Research Laboratory and researchers at the University of Alaska. The team was using new receivers, positioned 5 miles away from the HAARP transmission facility. "We were fortunate, we got a great dataset," Scales says in spite of being pestered by Alaska's infamous mosquitos.
The students even made some discoveries of frequencies that had not been observed in such experiments before. The phenomenon could be related to a geomagnetic substorm that dumped protons that normally would not be in the heated region, Scales says.
The team is taking the experimental measurements and developing theoretical models to understand what kind of diagnostic information they can get out of the space environment. "It was an extraordinarily successful experiment."