Investigation of a potential correlation between OH nightglow variability and GNSS/EGNOS Integrity

The ionosphere plays an important role for the propagation of radio signals. The majority of ionospheric disturbances is caused by magnetospheric and solar processes. However, a significant number of disturbances cannot be explained by these external forcing mechanisms. It is suspected that internal atmospheric dynamics, including small- and large-scale waves propagating from the lower atmosphere into the ionosphere, are the cause of much of the remaining variability (e.g., the formation of sporadic E-layers).

These ionospheric disturbances are a significant and highly variable source of positioning errors of global navigation satellite system (GNSS) signals. The relation between middle atmospheric dynamics and GNSS signal integrity is studied by utilizing several years of OH airglow observations in the vicinity of European Geostationary Navigation Overlay Service (EGNOS) grid points.

OH airglow observations provide neutral atmospheric temperatures at the upper mesosphere lower thermosphere (UMLT), i.e. at approximately 80 to 100 kilometers height, so in the ionospheric D region. Ground-based airglow observations with high temporal resolution are performed at the reference site of the Network for the Detection of Mesospheric Change (NDMC) at the Environmental Research Station Schneefernerhaus (UFS, 11.0° N, 47.0° E) since 2009. These data allow precise observations of acoustic, gravity, tidal and planetary wave disturbances in the UMLT; at least some of these atmospheric waves can propagate from the D region higher up into the E region or maybe F region.

While the EGNOS provides integrated information on the ionospheric state at a given time, the OH airglow at the lower edge of the ionosphere is influenced amongst others by upward propagating phenomena. Therefore, we investigate the relationship between EGNOS-broadcasted ionospheric delays and observed UMLT-variability addressing the question whether airglow observations can be used to perform short-term predictions of GNSS signal deterioration by atmospheric variability. Emphasize is placed on the role of semi-diurnal tides and a potential connection to a semi-annual oscillation observed in EGNOS-delay information.