Impact of Sudden Stratospheric Warming and Elevated Stratopause Events
on the Very Low Frequency Radio Signal
Abstract
Sudden Stratospheric Warmings (SSW) and Elevated Stratopause (ES) events
are mid-to-high latitudinal, atmospheric wave-driven phenomena leading
to significant changes in wind, temperatures, and vertical mass
transport, especially in stratospheric and mesospheric altitudes.
Presumably, SSW and ES-induced changes also cause modifications in the
highly variable D-region ionization. This bottom side of the ionosphere
behaves with the Earth’s surface as a reflection boundary for Very Low
Frequency (VLF) radio signal transmission used for long-distance
communication. Since perturbations of the D-region ionization are also
notable in the VLF signal, it is a valuable tool for continuous
investigations of the D-region. Here, we study the impact of four SSW/ES
events on the VLF signal amplitude between the high latitude
transmitter-receiver link Keflavik, Iceland, to NyÅlesund, Svalbard, to
gain further knowledge about interactions between the D-region and the
atmosphere during these atmospheric phenomena. For three of four SSW/ES
events, a very similar VLF signal amplitude signature is observed,
characterized by a significant increase during the SSW period in the
signal amplitude followed by a decrease during the ES period. This study
aims to reveal a possible mechanism driving these similar VLF signal
amplitude variations, involving modified electron neutral collision
frequencies and electron densities due to changed temperatures and minor
constituent concentrations according to the SSW/ES events. However, the
VLF signal amplitude for one event increased two weeks later than during
the other three events and did not show a decrease during the ES period.
Possible causes for the different VLF signal amplitude variations are
discussed.