Wave signatures in the midlatitude ionosphere during a sudden stratospheric warming of January 2010

This paper presents a case study of the day-to-day variability in the midlatitude upper atmospheric ion temperature (∼200-400 km) with a focus on variability resulting from meteorological forcing. The data are obtained by the Millstone Hill incoherent scatter radar (42.6°N, 288.5°E) on 18-31 January 2010, in coincidence with a major sudden stratospheric warming. We elucidate oscillations in ion temperature with both tidal periods (∼8 h and ∼12 h) and non-tidal periods (>24 h) by analyzing residuals between the observed temperatures and those expected from an empirical model. We present the spatial-temporal development of periodicities in ion temperature and discuss to what degree these periodicities might be related to the sudden stratospheric warming event. The spectral location and temporal evolution of periodicities with ∼9.9-12.9 h and ∼6.2-7.9 h suggest that they are related to the semidiurnal (12 h) and terdiurnal (8 h) tides that are enhanced during the sudden stratospheric warming. Periodicities with ∼3-4 d and ∼10-13 d are likely related to Rossby waves with 4 d and 10 d periods, while the strong periodicity observed at 16-17 h could result from the nonlinear interaction of the quasi 2 d wave with the semidiurnal tide. As planetary waves are not expected to propagate to altitudes of ∼200-250 km, these experimental results raise questions about the potential mechanisms of coupling between the lower and upper atmosphere.