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 at 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 Ny‐Ålesund, 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 2 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.