Spatial and temporal variability of the ionosphere as revealed by modal decomposition

We examine two approaches to capture the modes of spatial and temporal variability observed in the ionosphere: 1. decomposition into modes as functions of local time and zonal wavenumber and 2. analysis using empirical orthogonal function (EOF) decomposition and the corresponding principal component analysis (PCA) technique. The spectral analysis of the different time series of reveals how different mechanisms such as solar flux variation, change of the orbital declination, nonlinear mode coupling and geomagnetic activity are separated and expressed in different modes. We examine similar analysis performed on output from the Thermosphere- Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) to provide insight for the interpretation of the observed phenomena. In this talk we examine the relationship between the variability observed in mesospheric and lower thermospheric dynamical fields to variations observed in the low latitude ionosphere using these long-term global satellite observations and through simulations using the TIE-GCM.