The Mid-latitude Thermospheric Dynamics from An Inter-hemispheric Prospective

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Monday, January 28, 2019

Using Fabry-Perot interferometers (FPI) at five mid-latitude stations (Boulder, Palmer, Millstone Hill, Mt. John, and Kelan) in both hemispheres, we examine the inter-hemispheric and seasonal variations of mid-latitude thermospheric dynamics.

Graph depicting Meridional and Zonal Winds
Observations and Simulations for May 13, 2013, Day of Year (DOY) 133. The meridional winds (upper) and zonal winds (lower) from MJ (maroon), BD (pink), and KL (darkblue) FPIs (symbols) and TIEGCM with SAPS (dashed lines) and without SAPS (dotted lines) for the respective stations in the same color coding as observations. The data are plotted in local times of each station for an easy comparison. Note that the data from different longitudes are sampled at different UTs. The positive meridional winds are equatorward, so the nighttime meridional winds have the same sign in both the northern and southern hemispheres. Zonal winds are positive eastward.

We also use the NCAR Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) to simulate the seasonal changes of winds and the effects from SAPS (Sub-Auroral Polarization Streams). The observations and TIEGCM simulations show a clear seasonal variation with more westward and equatorward summer winds. The TIEGCM runs overestimate the westward zonal winds and underestimate the electron densities in the northern summer. We believe that the underestimated TIEGCM electron density leads to a weak ion drag effect in the model, and strong westward zonal winds. TIEGCM overestimates the SAPS effects on neutral winds in most cases, probably because the empirical SAPS model used by the TIEGCM applies an unrealistic persistent electric field for a long period of time (over 3 hours) due to the low temporal resolution of the Kp index.

Publication Name: JGR Space
First HAO Author's Name: Qian Wu

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