Tidal harmonics obtained from Dynasonde measurements in the bottom F-Layer
Friday, 19 December 2014
It is now well accepted that atmospheric tidal waves have a dramatic influence on thermospheric and ionospheric structure and variability. Considerable effort goes into understanding the characteristics of tidal modes, their interactions with planetary and gravity waves and other tidal modes, as well as their influence on the background state of the thermosphere-ionosphere system. For the altitude interval between roughly 120 and 400 km, this effort is somewhat hindered by the lack of global observations. We propose a new method of determining tidal variability by making use of Dynasonde measurements. The NeXtYZ inversion procedure (a part of the Dynasonde software package) produces altitude profiles of the ionospheric parameters with a vertical resolution typically below 1 km. This, together with the 2 minute cadence of the instrument results in extensive datasets with wide temporal and altitude coverage. Because of the natural ionospheric variability, at any given altitude we have non-uniform sampling over extended time intervals. A Lomb-Scargle implementation is used to mitigate this issue, allowing us to obtain both amplitude and phase information in an equivalent manner at all altitudes and locations. In this poster, we provide altitude profiles of the first 3 diurnal harmonics derived from dynasonde measurements. The data analyzed include the truly vertical electron density profiles, the ionospheric X (East-West) "tilt" measurement and the derived zonal plasma density gradient. Both the tilt and the gradient can be shown to be sensitive tracers of atmospheric waves, in some cases more so than the raw electron density. We use data from Wallops Island, VA and San Juan, PR for May and September 2013, thus capturing seasonal, latitudinal and altitude variations of tidal amplitude and phase. This can be used for comparisons with existing theoretical work and also to test propagation of tidal waves in coupled ionosphere-thermosphere models.