HR: 14:16h
AN: AE53A-04    [Abstracts]
TI: FDTD Studies of Eigenfrequencies and Q-factors of the Earth-ionosphere Cavity
AU: * Yang, H
EM: hxy149@psu.edu
AF: Pennsylvania State University, 204 EE East, University Park, PA 16802 United States
AU: Pasko, V
EM: vpasko@psu.edu
AF: Pennsylvania State University, 204 EE East, University Park, PA 16802 United States
AB: Resonance properties of the Earth-ionosphere cavity were predicted by W. O. Schumann in 1952 [Schumann, Z. Naturforsch., 7a, 149, 1952]. Since then observations of electromagnetic signals in the frequency range 1-500 Hz have become a powerful tool for variety of remote sensing applications [e.g., Williams, Science, 256, 1184, 1992; Cummer, IEEE Trans. Antennas Propagat., 48, 1420, 2000; Roldugin et al., JGR, 109, A01216, 2004], which in recent years included studies of thunderstorm related transient luminous events in the middle atmosphere and related lightning discharges [e.g., Sato and Fukunishi, GRL, 30, 1859, 2003; Su et al., Nature, 423, 974, 2003]. In this talk we will provide a comparison of a limited set of results from a simplified version of a 3-D FDTD model of the Earth-ionosphere cavity originally introduced in [Yang and Pasko, EOS Trans. AGU, 84, Fall Meet. Suppl., AE42A-0796, 2003] with a set of classical eigenfrequency (fn) and quality factor (Qn) solutions for laterally uniform spherically symmetric Earth-ionosphere cavity and with recent observations of Schumann resonances (SR) during solar proton events (SPEs) and X-ray bursts in order to demonstrate the potential and applicability of the FDTD technique for studies of realistic SR problems. The specific uniform cavities, which will be discussed in our talk, incorporate the following conductivity models: (1) a single-exponential profile with a perturbation [Sentman, JATP, 45, 55, 1983]; (2) a "knee" profile [e.g., Mushtak and Williams, JASTP, 64, 1989, 2002]; and (3) a two-exponential profile [Greifinger and Greifinger, Radio Sci., 13, 831, 1978; Sentman, JATP, 52, 35, 1990; JGR, 101, 9479, 1996; Mushtak and Williams, 2002]. The FDTD fn and Qn solutions for uniform cavity appear to be in excellent agreement (within several %) with well-known results documented in the literature [e.g., Sentman, 1983; Mushtak and Williams, 2002], including such particular details as a very flat frequency dependence of Q factor for the two-exponential conductivity model (see discussion in [Mushtak and Williams, 2002]). A potential of the FDTD model to treat 3-D systems will be demonstrated in our talk by introduction of non-uniformities in the model, which correspond to perturbations of the cavity associated with SPEs and X-ray bursts. The related analysis generally indicates the first mode SR frequency decrease during SPEs and increase during X-ray bursts by a fraction of a Hz, in agreement with physical arguments presented in [Sentman, 1983] and with recent time resolved observations reported by Roldugin et al. [JGR, 106, 18555, 2001; JGR, 108, 1103, 2003; 2004]. The validated FDTD model opens new perspectives for attacking problems in a realistic non-uniform cavity, including those related to diurnal, seasonal and inter-annual variations in SR parameters [e.g., Price and Melnikov, JASTP, 66, 1179, 2004].
DE: 3324 Lightning
DE: 2427 Ionosphere/atmosphere interactions (0335)
DE: 2435 Ionospheric disturbances
DE: 3304 Atmospheric electricity
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting