This paper presents our effort to assimilate FORMOSAT‐3/COSMIC (F3/C) GPS Occultation Experiment (GOX) observations into the National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) by means of ensemble Kalman filtering (EnKF). The F3/C electron density profiles (EDPs) uniformly distributed around the globe which provide an excellent opportunity to monitor the ionospheric electron density structure. The NCAR TIE‐GCM simulates the Earth's thermosphere and ionosphere by using self‐consistent solutions for the coupled nonlinear equations of hydrodynamics, neutral and ion chemistry, and electrodynamics. The F3/C EDP are combined with the TIE‐GCM simulations by EnKF algorithms implemented in the NCAR Data Assimilation Research Testbed (DART) open‐source community facility to compute the expected value of electron density, which is ‘the best’ estimate of the current ionospheric state. Assimilation analyses obtained with real F3/C electron density profiles are compared with independent ground‐based observations as well as the F3/C profiles themselves. The comparison shows the improvement of the primary ionospheric parameters, such as NmF2 and hmF2. Nevertheless, some unrealistic signatures appearing in the results and high rejection rates of observations due to the applied outlier threshold and quality control are found in the assimilation experiments. This paper further discusses the limitations of the model and the impact of ensemble member creation approaches on the assimilation results, and proposes possible methods to avoid these problems for future work.

[1] The effect of a disturbance dynamo during geomagnetic activity on the equatorial ionospheric electric fields is investigated, using model results from the NACR/TIEGCM (National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model). Model runs are made for different time-lengths of geomagnetic activity, for different seasons, and for different solar activities to investigate how and where the maximum electric potential forms. Model results show that the maximum electric potential is located at around 300 km altitude and at local time after the pre-reversal enhancement at equinox for high solar activity. For the case at solstice, without pre-reversal enhancement, the location moves to around 110 km altitude and to the local time close to midnight. Giving various parameters in the model runs to simulate different background conditions, many important output quantities are used to study the distributions of perturbed electric potential at the geomagnetic equator. Model investigation indicates that normal quiet time electrodynamics, at different seasons with different solar activities, significantly affect the distribution of perturbed current density associated with geomagnetic activity. Furthermore, model results also reveal that significant perturbed zonal electric fields tend to build up six hours after the onset of geomagnetic activity, except at regions close to sunset and sunrise, and the perturbed vertical electric fields increase with the time length of geomagnetic activity.Citation: Huang, C. M., and M. Q. Chen (2008), Formation of maximum electric potential at the geomagnetic equator by the disturbance dynamo,

[1] In this paper, the total electron content (TEC) of the global ionosphere map (GIM) is used to detect seismoionospheric anomalies associated with the 12 January 2010 M7 Haiti earthquake, and an ionospheric model is applied to simulate the detected anomalies. The GIM temporal variation shows that the TEC over the epicenter significantly enhances on 11 January 2010, 1 day before the earthquake. The latitude-time-TEC (LTT) plots reveal three anomalies: (1) the northern crest of equatorial ionization anomaly (EIA) moves poleward, (2) the TECs at the epicenter and its conjugate increase, and (3) the TECs at two dense bands in the midlatitude ionosphere of 35°N and 60°S further enhance. The spatial analysis demonstrates that the TEC enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area. The simulation well reproduces the three GIM TEC anomalies, which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period.

[1] In this paper, temporal and spatial analyses are employed to detect seismo-ionospheric precursors (SIPs) in the ionospheric total electron content (TEC) during the 16 October 1999 M w 7.1 Hector Mine earthquake. To discriminate anomalies caused by global effects, such as solar radiations, magnetic storms, etc., and local effects, such as earthquake, we crossexamine the GPS TECs and their gradients in the eastward and northward directions at epicenter/centers of the Hector Mine area and the other two reference areas at similar magnetic latitudes in Europe and Japan. Temporal variations of the northward TEC gradient suggest SIPs most likely appearing on days 6-5 before the earthquake. A global search by using the TEC of the global ionosphere map shows that the TEC increase and decrease anomalies continuously and specifically appear around the epicenter on day 5 before the earthquake.

[1] During geomagnetic activities, perturbed electric fields at middle and low latitudes of the ionosphere may result from the effect of prompt penetration from high latitudes and the disturbance dynamo mechanism, respectively. The polarity of penetration electric fields depends on the orientation of the interplanetary magnetic field (IMF) Bz, and that of electric fields associated with the disturbance dynamo is almost opposite to that in the quiet time condition. Although a few hours are required to build up the perturbed electric fields through the disturbance dynamo mechanism, the dynamo electric fields can persist for several hours after geomagnetic activities cease. It turns out that the low-latitude electric field disturbances associated with the disturbance dynamo mechanism should be more persistent than that associated with the direct penetration from the polar cap, especially for the period in the recovery phase. Model results show a significant, westward disturbance dynamo electric field at period close to sunset, but it seems not important in the empirical model. This perturbed electric field at sunset will weaken the intensity of the prereversal enhancement and of the following fountain effect in the storm time.Relative to the quiet time condition, it produces an enhancement in the total electron content. This phenomenon is seasonal. It only occurs at period close to equinox, when the hemispheric wind (summer to winter) is minimal. These theoretical results have been substantiated by model results of the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model and by the global integration and modeling in this study. Both results show that the positive phase of the ionospheric storm at the magnetic equator close to sunset is produced by the westward disturbance dynamo electric field.