Altitude Extension of the NCAR‐TIEGCM (TIEGCM‐X) and Evaluation. Issue 11 (3rd November 2022) - Cai, Yihui
Abstract: The upper boundary height of the traditional community general circulation model of the ionosphere‐thermosphere system is too low to be applied to the topside ionosphere/thermosphere study. In this study, the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (NCAR‐TIEGCM) was successfully extended upward by four scale heights from 400–600 km to 700–1, 200 km depending on solar activity, named TIEGCM‐X. The topside ionosphere and thermosphere simulated by TIEGCM‐X agree well with the observations derived from a topside sounder and satellite drag data. In addition, the neutral density, temperature, and electron density simulated by TIEGCM‐X are morphologically consistent with the NCAR‐TIEGCM simulations before extension. The latitude‐altitude distribution of the equatorial ionization anomaly derived from TIEGCM‐X is more reasonable. During geomagnetic storm events, the thermospheric responses of TIEGCM‐X are similar to NCAR‐TIEGCM. However, the ionospheric storm effects in TIEGCM‐X are stronger than those in NCAR‐TIEGCM and are even opposites at some middle and low latitudes due to the presence of more closed magnetic field lines. Defense Meteorological Satellite Program observations prove that the ionospheric storm effect of TIEGCM‐X is more reasonable. The well‐validated TIEGCM‐X has significant potential applications in ionospheric/thermospheric studies, such as the responses to storms, low‐latitude dynamics, and data assimilation. Plain Language Summary: Conventional GCMs based on pressure or altitude coordinate systems typically have a lower upper boundary, from 400 to 600 km depending on solar activity, which greatly limits their ability to reconstruct certain climatological phenomena, such as equatorial ionization anomaly (EIA). This study successfully extends NCAR‐TIEGCM upward to 700–1, 200 km depending on solar activity, named TIEGCM‐X. The low altitude thermosphere density and temperature simulated by TIEGCM‐X deviate from NCAR‐TIEGCM within 10%, while it can better reproduce the observed characteristics of the high altitude thermosphere. In addition, TIEGCM‐X can also more reasonably simulate the topside ionosphere and the complete EIA structure without height truncation. Furthermore, TIEGCM‐X can better simulate the response of the ionosphere to storms. The well‐validated TIEGCM‐X has significant potential applications in ionospheric/thermospheric studies, such as the responses to storms, low‐latitude dynamics, and data assimilation. Key Points: The NCAR‐TIEGCM was extended upward with four scale heights, extending the upper boundary height from 400–600 km to 700–1, 200 km The TIEGCM‐X can simulate the topside ionosphere/thermosphere well, as well as the complete equatorial ionization anomaly structure and the ionospheric storm effect The topside neutral density and electron density simulated by TIEGCM‐X are in good agreement with observations