Hold a compass at different spots on Earth, and the needle will dip up or down to indicate the direction of our planet’s magnetic field. Midway between the two poles, the needle should orient itself at a perpendicular angle; this is the horizontal magnetic equator. The closer one gets to the poles, the more the compass needle will tilt one way or the other, forming an angle called magnetic dip or inclination.
A study now reveals that radio waves can be affected during daytime near Earth’s magnetic equator by abnormal activity in a layer of the electrically charged upper atmosphere called the ionosphere.
When radio waves pass through the ionosphere, they sometimes experience rapid fluctuations in the received signals. During nighttime, these fluctuations are associated with ionospheric irregularities in the F region, a layer between roughly 200 and 600 kilometers in altitude. However, during daytime, radio fluctuations are produced by irregularities that are embedded in the lower-altitude E region (between 85 and 200 kilometers high).
These E region irregularities, which scientists call “sporadic E,” are thin layers distributed sporadically in time and space. The degradation in radio waves that they cause, known as scintillation, can interfere with radio communications.
Sporadic E irregularities have long been thought to be negligible near the magnetic equator. But the new findings from Seif et al. show otherwise, linking scintillation to sporadic E layer irregularities over the magnetic equator using combined ground- and space-based measurements.
The team found radio scintillation during daytime periods along the magnetic equator, which is associated with the sporadic E layer, and detected no aberrations in the F layer. Finding evidence of these layers at the magnetic equator is a new scientific discovery. The team also observed far more scintillation events over the magnetic equator in Asia than in America, which fits with previous observations that sporadic E layers are 10 times higher in Asia than in other regions.
By revealing peaks and dips in this activity throughout the day, the study could help us to explain and avoid disruptions to radio signals such as those used in global navigation satellite systems and GPS. (Radio Science, https://doi.org/10.1002/2017RS006393, 2017)
—Emily Underwood, Freelance Writer