Field-Aligned Neutral Wind Bias Correction Scheme for Global Ionospheric Modeling at Midlatitudes by Assimilating FORMOSAT-3/COSMIC hmF2 data under Geomagnetically Quiet Conditions
Yang-Yi Sun1,2, 3, Tomoko Matsuo2, 3, Naomi Maruyama2, 3, and Jann-Yenq Liu1
1Institute of Space Science, National Central University, Chung-Li, Taiwan.
2Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Colorado, USA.
3Space Weather Prediction Center, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA.
This study demonstrates the usage of a data assimilation procedure, which ingests the FORMOSAT-3/COSMIC (F3/C) hmF2 observations to correct the model wind biases to enhance the capability of the new global Ionosphere Plasmasphere Electrodynamics (IPE) model under geomagnetically quiet conditions. The IPE model is built upon the Field Line Interhemispheric Plasma (FLIP) model with a realistic geomagnetic ﬁeld model and empirical model drivers. The hmF2 observed by the F3/C radio occultation (RO) technique is utilized to adjust global thermospheric field-aligned neutral winds (i.e., a component of the thermospheric neutral wind parallel to the magnetic field) at midlatitudes according to a linear relationship between time differentials of the field-aligned wind and hmF2. The adjusted winds are further applied to drive the IPE model. The comparison of the modeled electron density with the observations of F3/C and ground-based GPS receivers at the 2012 March Equinox suggests that the modeled electron density can be significantly improved in the midlatitude regions of the Southern Hemisphere, if the wind correction scheme is applied. Moreover, the F3/C observation, the IPE model, and the wind bias correction scheme are applied to study the 2012 Southern Hemisphere Midlatitude Summer Nighttime Anomaly (southern MSNA) / Weddell Sea Anomaly (WSA) event at December Solstice for examining the role of the neutral winds in controlling the longitudinal variation of the southern MSNA/WSA behavior. With the help of the wind bias correction scheme, the IPE model better tracks the F3/C-observed eastward movement of the southern MSNA/WSA feature. The apparent eastward movement of the southern MSNA/WSA features in the local time coordinate is primarily caused by the longitudinal variation in the declination angle of the geomagnetic field that controls the field-aligned projection of both geographic meridional and zonal components of the neutral wind. Both the IPE simulations and the F3/C observations show the significant longitudinal variation in the speed of the eastward movement of the southern MSNA/WSA.