Influence of Polar Vortex on Short-term O/N2 Variability in the Ionosphere-Thermosphere from GOLD and WACCM-X

We quantify the contribution of the Northern Annular Mode (NAM), to the short-term variability of O/N2 in the Ionosphere-Thermosphere (IT) using observations from the GOLD instrument for all winters from December 2018 to February 2022. We find strong positive correlations between the NAM index and O/N2 perturbations within the GOLD FOV, with a largest value of +0.55 at ~20.0°N. Good qualitative agreement for O/N2 variability and O/N2/NAM correlations is found between GOLD observations and WACCM-X output, which is then used to delineate the global distribution of O/N2 and NAM correlations. In addition to the positive correlations comparable to GOLD observations at middle and low latitudes, we find negative correlations between WACCM-X O/N2 and NAM at high northern latitudes (as large as -0.40 at ~65.0°N). Positive correlations are found between GOLD O/N2 and several tidal components extracted from WACCM-X, including DW1 with a correlation of +0.61 and SW2 with a correlation of +0.45. These correlations suggest the following physical process: 1) enhanced tides during periods of weakened polar vortex induce westward circulation, which in turn induces poleward residual circulation; 2) this poleward circulation causes upwelling/downwelling at northern high/low latitudes, which increases/decreases IT O/N2, respectively; 3) such that negative/positive NAM corresponds to decreases/increases in O/N2 at high/low latitudes.