Profiles in Science

HAO 2012 Profiles In Science: I-Te Lee

Contact:

I-Te Lee is a Graduate Research Assistant at the High Altitude Observatory (HAO), National Center for Atmospheric Research (NCAR). He is currently studying the data assimilation by using NCAR TIE-GCM and FORMOSAT-3/COSMIC radio occultation data. His research interests include the ionospheric density structure of mid- and low- latitude.

Publications

Figure 1: High resolution

(1) Lee, I. T., T. Matsuo, A. D. Richmond, J. Y. Liu, W. Wang, J. L. Anderson, C. H. Lin, and M. Q. Chen, 2012: Assimilation of FORMOSAT-3/COSMIC electron density profiles into a coupled Thermosphere/Ionosphere model using ensemble Kalman filtering. J. Geophys. Res., 117, A10318, doi:10.1029/2012JA017700.

Abstract: This paper presents our effort to assimilate FORMOSAT-3/COSMIC (F3/C) GPS Occultation Experiment 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 EDP are combined with the TIE-GCM simulations by EnKF algorithms implemented in the NCAR Data Assimilation Research Testbed 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. he comparison shows the improvement of the primary ionospheric parameters, such as NmF2 and hmF2. 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.

Figure 1 caption: Global NmF2 maps from 2008/04/12 06:00UT to 2008/04/13 04:00UT before and after assimilating the FORMOSAT-3/COSMIC electron density profiles. The upper and lower row of each panel displays the posterior and control, respectively. The black dots indicate the observation locations.

Figure 2: High resolution

(2) Lee, I. T., J. Y. Liu, C. H. Lin, K. I. Oyama, C. Y. Chen, 2012: Ionospheric plasma caves under the equatorial ionization anomaly. J. Geophys. Res., doi:10.1029/2012JA017868, in press.

Abstract:This paper reports the existence of plasma caves, minima in the electron density located at 5–10° to the magnetic equator, in the bottomside ionosphere based on electron densities simulations from the International Reference Ionosphere (IRI-2007) and clear evidences given by plasma density and drift measurements of the Dynamic Explorer-2 (DE-2) satellite during 1981-1983. The IRI simulations suggest plasma caves as daytime features (08:00–19:00LT; length of 18158 km in the longitudinal direction), that range from the E-region up to about 300 km altitude with 10° (or 1100 km) width in the latitudinal direction. In-situ measurements of the ion and electron densities probed by the DE-2 confirm the existence of the plasma caves at low altitudes of the EIA ionosphere. The unexpected downward and upward (or weakly and strongly upward) ion drifts respectively at the magnetic equator and the two off-equators seem to play an important role responsible for the plasma cave formation.

Figure 2 caption:The IRI simulation and the DE-2 observations at 11:30 LT on day 63 (4 March), 1982. The upper panel shows the IRI result (log10 (Ne), cm^−3) along the DE-2 longitude and the bold solid line indicates the DE-2 orbit with the ion drift velocity. The contour lines begin at 5.0 and are incremented linearly in steps of 0.1 to 6.0. The bottom panel illustrates the IRI electron density, LANG electron density, and RPA ion density by dotted, dashed, and solid line, respectively. Noted that the right scale is applied for the IRI results and left scale is used for the DE-2 observations. In addition, the vertical dashed lines are used to locate the magnetic equator.