The radio waves reflecting back from the ionosphere to the Earth can offer valuable information about climate change as well, researchers claim.
Their research shows that the strength of radio signals on the ground is a reliable indicator of temperature change above.
Prof. Colin Price of Tel Aviv University's Department of Geophysical, Atmospheric and Planetary Sciences and his team used simple radio antennae on the ground to measure radio waves broadcast by navigational transmitters around the globe, then compared information on the strength of these radio signals with data on temperature fluctuations in the upper atmosphere.
They discovered that climate change in the upper atmosphere - caused by an abundance of greenhouse gases - may lead to a greater absorption of radio waves.
Weaker signals could therefore be indicative of greater climate change.
This simple, cost-effective measurement can be a valuable contribution to the ongoing effort to track climate change, Prof. Price said, adding to measurements of ground and lower atmospheric temperatures to create a more holistic picture.
On the Earth's surface and in the lower atmosphere, an increase of greenhouse gases has a warming effect, the gases acting as a "blanket" and keeping heat from escaping from the Earth into space. But these gases, including carbon dioxide, are increasing in the upper atmosphere as well, where they have a cooling effect.
When cooled, the ionosphere contracts and descends into the atmosphere to where air is denser - leading to a higher absorption of radio waves, Prof. Price said.
By examining satellite-gathered data on the temperature in the upper atmosphere and comparing results to measurements of radio wave amplitudes collected on the ground, the researchers were able to uncover a clear correlation, consistent over time.
As the upper atmosphere gets colder, radio signals lose their strength.
According to Prof. Price, this new technique will be a valuable addition to current methods of monitoring climate change, such as the measurement of ground temperatures.
The research is published in the Journal of Geophysical Research.