LOFAR observations of atmospheric gravity wave damping

Activity: Academic and Industrial eventsConference, workshop or symposium

Description

Travelling ionospheric disturbances (TID) are the well known ionospheric counterpart of atmospheric gravity waves (AGW). They can be driven by space weather events such as auroral sub-storms, or from a variety of terrestrial effects such as orographic deflection of lateral wind, sunrise, or tropospheric storm systems. AGWs are ubiquitous throughout Earth’s atmosphere and couple the different layers via vertical propagation. Upwards propagating AGWs transfer their energy to the surrounding atmosphere by way of viscous damping which can, in turn, spawn secondary AGW at thermospheric heights.

Observations of trans-ionospheric radio propagation is a long standing technique for studying ionospheric behaviour, typically with the use of GNSS satellites as the extra-atmospheric radio source. The LOw Frequency ARray (LOFAR) is a radio telescope consisting of many networked ground based observing stations spread throughout Europe. It can be used for broadband observations of ionospheric scintillation, with high frequency and time resolution, enabled by utilising natural cosmic radio sources which are inherently broadband emitters.

On 17 December 2018, LOFAR detected the ionospheric radio signatures of a fast moving TID with clearly resolved internal substructure. The TID moved approximately South West and consisted of an internal wavetrain exhibiting broadband ionospheric radio scattering features. On closer inspection it was revealed that the substructures showed evidence of damping, with each wave in the wavetrain consisting of an initial ‘beat’ followed by several fainter ‘beats’ before the signal returned to the noise floor. In most LOFAR stations at least 4-5 of these internal waves were detected, all presenting the same behaviour, but in some of the German LOFAR stations at least 14 of these internal waves were resolved. The behaviour was characteristic of an under-damped system in which >1 oscillatory period is required before the signal is fully damped. Periodograms of the LOFAR detail show the dominant modes of oscillation to be ~120-seconds. The absence of significant space weather effects in the hours prior to the observation suggest this TID was caused by terrestrial phenomena.
PeriodApr 2023
Event titleMagnetosphere Ionosphere and Solar-Terrestrial Physics (MIST) meeting
Event typeConference
LocationBirmingham, United KingdomShow on map
Degree of RecognitionNational