3D FDTD Modeling of the effects of electromagnetic phenomena in the ionosphere and Earth’s magnetic field over the Sumatera-Malaysia region.

PhD proposal

Siti Harwani bt Md Yusoff

Universiti Sains Malaysia

April 2011

Abstract

Over a decades, a few techniques have been proposed to study, monitoring, observing and investigating the Earth’s ionosphere and geomagnetic field. Still, numerical and computer modeling is also notable to perform rigorous and more realistic analysis of the electrodynamics of Earth’s ionosphere and geomagnetic field. Here, I propose to use 3D FDTD method by solving full vector of Maxwell’s equations in order to model details global Earth-ionosphere waveguide. The model will be apply to investigate ionospheric anomalies over the Malaysia region that near to Sumatera earthquake epicenter and analyze the ULF band geomagnetic change associated with the earthquake. The comparative study with the experimental data will be done to verify and validate the results from numerical study.

1. INTRODUCTION

The Earth’s ionosphere and magnetosphere consists of partially ionized plasma extracted in the ionosphere regions and immersed into Earth’s magnetic field. The low frequency electrodynamics waves in ULF band that are generated by the interaction between solar wind and geomagnetic field propagate across the ambient magnetic field and spread wave energy all over the magnetosphere (Alperovich LS et.al 2007).

The ionosphere is divided into 4 region, depends on their electron density, which are

1. D region (60-90 km)

2. E region (90-140 km)

3. F1 region (140-200 km)

4. F2 region (200-500 km)

D region filled with a mixture of electron and negative and positive ions. In E region, concentration of electron is much higher by about 2 orders of magnitude than in the D region. F1 and F2 region are located with maximal electron concentration in F1 of _ during minimum solar activity and _ during maximum solar activity.

Fig 1.1 Electrodynamics properties of the system Earth’s atmosphere-ionosphere-magnetosphere (Alperovich LS et.al 2007)

Figure 1.1 shows the interaction happened in Earth’s atmosphere-ionosphere-magnetosphere system that generated regions system divided by its own properties. Electrodynamics between these regions are depend on the electrons density and frequency of collisions between the region.

2. RESEARCH BACKGROUND

2.1 Electromagnetic wave propagation.

Electromagnetic wave in ULF band is stipulated by a non-homogeneous and anisotropic geomagnetic field. The wave propagates in the range of 0.01-10Hz in different region of ionosphere parallel to the east and west. The movement of conductive medium in the Earth’s magnetic field, displacement of boundaries between high and low conductive crust of Earth as well as piezo-electric and piezo-magnetic may cause ionospheric disturbance associated with oscillations of the electrons and resulted ULF wave perturbation.

In recent years, there were studies to observe and investigate ULF wave perturbation that caused by ionopsheric anomalies. One of the discovery is the ULF wave propagation will change due to the electrical structure changes in the underground (Katsumi H, 2004). For a few reason that will be elaborated through this paper, the study of the anomalous in ULF wave may become one of the potential candidate for the earthquake precursor. In addition, Park SK et.al (1993) and Pulinet SA (2004) have published reports about anomalous in electromagnetic wave occurred prior to major earthquake as well. While Hasbi AM et.al (2009) investigated the presence of anomalous in ionospheric and geomagnetic field disturbance during Sumatera earthquake in 2005 by calculating the total electron content (TEC) using GPS and magnetometer.

2.2 3D FDTD method

Advance in computational technologies recently have provided the solution to simulate complex electromagnetic phenomena. The complex behavior and its electrodynamics of electromagnetic wave can be predict by solving full vector of Maxwell’s equations. Numerical method such as Finite-Difference Time-Domain (FDTD) method is capable to conduct advanced, high resolution 3D full vector Maxwell’s equations for its simplicity and versatility. The FDTD method can easily describe as details as Earth’s topography and bathymetry, non-homogeneous and anisotropic media such as geomagnetic field. (Taflove and Hagness 2005).

The FDTD method is first introduced by KS Yee in 1966, implemented cubic-unit-cell space lattice by solving Maxwell’s equations calculation but later named by Taflove (1980). This method can ambitiously model the Earth-ionosphere system, 2D model to 3D global Earth-ionosphere model and applicable for simulating wave propagation below 300kHz in very long range propagation model to fully 3D global propagation. To date, 3D FDTD method is applied to model long-range 2D propagation, lightning sources and radiation, global propagation, Schumann resonances, hypothesized pre-seismic lithosphere sources, detection of deep underground resource formations and remote sensing of localized ionospheric anomalies (Simpson JJ et.al 2007).

2.3 3D FDTD modeling for ionospheric anomalies over the Malaysia-Sumatera region.

Common techniques used in ground-based and space-borne observations only provide short term and discontinuous monitoring of the lower ionosphere and almost impossible to implement in many regions of the world. Model of localized ionospheric anomalies using 3D FDTD method can be proposed for a radar system to provide useful information prior to earthquake in Malaysia-Sumatera region.

3. PROBLEM STATEMENT

3.1 Numerical and computational study using 3D FDTD model of ionospheric anomalies only have been done in some regions of epicenter of earthquake of the world and not include Malaysia-Sumatera region. Since this region is in active seismic activity known as ‘Pacific ring of Fire’, such an active study, observation, investigation and monitoring should be conducted because the impact from the earthquake and tsunami as well can turn around the socio-economic of the country affected.

3.2 The techniques for ionosphere monitoring: vertical sounding (HF sounding), topside vertical sounding (rocket-borne sounder) and GPS TEC, still require details study of Earth’s atmosphere-ionosphere-magnetosphere system and modeling is capable to verify the experimental data for these techniques.

4. RESEACRH OBJECTIVES

The first objective of this project is to apply 3D FDTD method for modeling global Earth-ionosphere waveguide a fully 3D grid, extending an altitude from 100 km of Earth’s surface with nominal resolution on the order of 1-10 km in all direction by solving full vector time domain Maxwell’s equations of electromagnetic wave propagation.

The second objectives is to use the model to develop advance remote sensing system to locate and characterize ionospheric anomalies and geomagnetic perturbation over the Malaysia-Sumatera region within about 100 km of the Earth’s surface by assuming USM PP (5.36°N, 100.30°S) which located 543 km from the epicenter of Sumatera earthquake as a pulse sinusoidal source and passive detection of vertical electric field time waveform at the Earth’s surface in the vicinity of the ionospheric anomaly.

The third objective is to conduct comparative study with the experimental data to verify and validate the results.

5. LITERATURE REVIEW

The review will in two parts. First, a study related to electromagnetic wave propagation for potential earthquake precursor and second about the previous of the FDTD modeling in radio wave propagation.

5.1 Electromagnetic wave propagation for potential earthquake precursor

For almost 20 years, the scientific community all over the world monitored electromagnetic wave phenomena, aiming to trace earthquake precursor. Park SK et.al (1993) have presented mechanisms and observations in ULF band in the laboratory for precursor phenomena. They reported that in terms of stress and strain changes, anomalous in the electric field have been detected and measured prior to earthquake. Pulinet SA(2004) focused on three research areas, i) the physical mechanism, ii)main phenomenological features of ionospheric variations associated with earthquake and iii) their statistical properties permitting use of them in practical applications in orde to understand the physical mechanism of seismo-ionospheric coupling. The study was developed based on two hypotheses which are the influence of acoustic gravity waves generated in the earthquake zone on the ionosphere and the anomalous vertical electric field penetrating from the earthquake zone into the ionosphere.

Figure 5.1 shows all the processes involved in the physical mechanism of seismo-ionospheric coupling as proposed by Pullinet SA (2004).

Fig 5.1 Block diagram of seismo-ionospheric coupling model (Pulinet SA 2004)

In the same year, Hattori (2004) reported of ULF geomagnetic change as a potential short-term earthquake precursor by covering very wide frequency range all over the world to accumulate earthquake related electromagnetic observation reports and presented a very good deal and convincing evidence of ULF magnetic responses before large earthquakes.

Hasbi AM et.al (2009), Kon S et.al (2010), Dabas RS et.al (2007) and Hasbi AM et.al (2011) have investigated the ionospheric and geomagnetic disturbances before and after some major earthquake in Asia region, in specific, Sumatera, Japan and India, by measuring TEC near the epicenter of the earthquake and observed that the ionospheric anomalies existence due to the geomagnetic disturbances caused by seismic activities under quiet space weather.

5.2 The previous of the FDTD modeling in radio wave propagation.

First, in Yee (1966), he introduced a modified form of Transmission Line Matrix (TLM) method by implementing cubic-unit-space lattice by solving Maxwell’s curl equations and later Taflove (1980) named it Finite-Difference Time-Domain (FDTD) method. This method provides a direct solution to Maxwell’s equations without much complexity and take into account both of the electric and magnetic fields in a 3D model. Berenger (1994) used FDTD model to compare previous domain mode theory calculations and create new model with capability to accommodate continuous varying parameters over the propagation path and noted as the first to use FDTD method to model VLF-LF waves propagation.

In recent years, Thevenot et.al (1999), Cummer SA (2000) and Water CL et.al (2010) have developed 2D FDTD models in spherical or cylindrical coordinate system to solve the problems of ELF/VLF propagation within several 1000 km around the lightning source. Simpson and Taflove (2004) used periodic boundary conditions in conjunction with a spherical-coordinate 3D FDTD space lattice. This technique merged adjacent grid cells in the east-west direction as approaching the poles to maintain Courant stability for relatively large time steps.

Subsequently, Simpson and Taflove(2006) proposed a novel radar system at 76 Hz for locating and characterizing ionospheric depressions within ≈100 km of the Earth’s surface. By assuming Wisconsin Transmitting Facility (WTF) at 90.9°W, 46.5°N, as a distant well-characterized pulsed sinusoidal source and passive detection of the resulting vertical electric field time-waveform at the Earth’s surface in the vicinity of the ionospheric anomaly. The depressions were assumed to have depth of 20 km, within 100 km, 200 km and 380 km radius. The results from the modeling work show that FDTD can support simple measurement of the vertical E-field signal below a localized ionospheric depression and provide its location, size, shape and depth. The proposed radar therefore provide useful information as an earthquake precursor.

5.3 Remarks of literature review.

There have been a few decades of studying, monitoring, observing and investigating ionospheric anomalies through a few techniques of ground-based, air-borne and space-borne all over the world. However, numerical and computational approach of the earthquake precursor have been lacking performed the ionospheric anomalies phenomena prior to earthquake over the south-east Asia region. The study and monitoring of the earthquake in south-east Asia region as important as any study conduct all over the world because the earthquake and tsunami will give effect to Indonesia, Malaysia, Thailand and Singapore and leave impacts to socio-economic to the country respectively. The result from this study hopefully should lead to an improvement and advancement of remote sensing technology for earthquake precursor over the south-east Asia region, specifically.

6. EXPECTED OUTCOMES AND BENEFIT.

The expected outcomes and benefits from this project included:

1. The 3D geodesic-grid whole Earth FDTD wave propagation model as have been developed by Simpson and Taflove (2006) will illustrate local ionospheric anomalies over the Malaysia-Sumatera region within 100km of the Earth’s surface and could lead into an advance design for radar technology in remote sensing system.

2. The result from the model will verify and validate experimental data from GPS receiver and magnetometer.

3. The knowledge in 3D FDTD entire Earth modeling will eventually brings to more exploration in computer modeling technology of geomagnetic field and can be extended into realistic analysis of space weather and its relation to global temperature change, navigation communication technology and deep underground resources formation to accumulate data for Asia region, specifically.

4. The output from this project will be disseminated in local and international journals.

7. METHODOLOGY

This study will develop a model to study electromagnetic phenomena such as ionospheric anomalies in specific region which is Sumatera-Malaysia region.

At first, the model will be developed using latitude-longitude grid cell arrangement in 2D model generation – complete spherical surface of the Earth on Cartesian 2D, transverse magnetic FDTD grid and then 3D model generation – expanded version of 2D model in fully 3D FDTD model of entire Earth-ionosphere cavity. Similar by the model introduced by Simpson JJ (2006), this model will be extending into 2D and 3D geodesic grid cell arrangement to study its geophysical phenomena between ±100km of sea level.

The model then will be apply to locate and characterize ionospheric anomalies within 100 km and less of the Earth’s surface by assuming USM PP(5.36°N, 100.30°E) which located 543km from the epicenter of Sumatera earthquake 2005 as a passive detection of vertical electric field time-waveform at the Earth’s surface in the vicinity of the ionospheric anomalies and source for sinusoidal pulse.

7.1 Flow chart of research activities

8. MILESTONE AND DATES

* refer appendix A for Gantt Chart of research activities.

9. REFERENCES

Alperovich LS, Fedorov EN (2007) Hydromagnetic Waves in the Magnetosphere and the Ionosphere, Springer

Berenger JP (1994) Finite-difference computation of VLF-LF propagation in the Earth-ionosphere waveguide. EUROEM Symposium

Cummer SA (2000) Modeling electromagnetic propagation in the Earth-ionosphere waveguide. IEEE Trans Antenna Propag, 48(9):1420. Doi:10.1109/8.898776

Dabas RS, Das RM, Sharma K, Pillai KGM (2007) Ionospheric Precursors observed over low latitudes during some of the recent major earthquakes. Journal of Atmospheric and Solar-Terrestrial Physics,vol 69, 15:1813-1824. Doi:10.1016/j.jastp.2007.09.005

Hasbi AM, Momani MA, Mohd Ali MA, Misran N, Shiokawa K, Otsuka Y, Yumoto K (2009) ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes. Journal of Atmospheric and Solar-Terrestrial Physics 71. Doi:10.1016/j.jastp.2009.09.004

Hasbi AM, Mohd Ali MA, Misran N (2011) Ionospheric variations before some large earthquakes over Sumatra. Nat hazards Earth Syst Sci, 597-611

Hattori K (2004) ULF Geomagnetic Changes associated with Large Earthquake. Terrestrial, Atmospheric and Oceanic Science, vol 15, 3:329-360

Kon S, Nishihashi M, Hattori K (2010) Ionospheric anomalies possibly associated with M≥6 Earthquakes in the Japan area during 1998-2010: Case studies and statistical study. Journal of Asian Earth Science. Doi:10.1016/j.jseaes.2010.10.005

Park SK, Johnston MKS, Madden TR, Morgan FD, Morrison HF (1993) Electromagnetic Precursors to Earthquakes in the ULF band: a review of observations and mechanisms. Rev Geophys 31:117-132. Doi:10.1029/93RG00820

Pulinets SA (2004) Ionospheric Precursors of Earthquakes: recent advances in Theory and Practical applications. Terrestrial, Atmospheric and Oceanic Sci, vol 15, 3:413-435

Simpson JJ, Taflove A (2004) Three-dimensional FDTD modeling of impulsive ELF propagation about the Earth sphere. IEEE Trans Antenna Propag, 52:443-451. Doi:10.1109/TAP.2004.823953

Simpson JJ, Taflove A (2006) ELF radar system proposed for localized D-region ionospheric anomalies. IEEE GeoSci Remote Sens Lett 3(4):400-403. Doi:10.1109/LGRS.2006.878443

Simpson JJ, Taflove A (2007) A review progress in FDTD Maxwell’s equations Modeling of Impulsive Subionospheric Propagation below 300 kHz. IEEE Trans Antenna Propag, vol55, 6. Doi:10.1109/TAP.2007.897138

Simpson JJ (2009), Current and Future applications of 3D Global Earth-Ionosphere Model Based on the Full-vector Maxwell’s equations FDTD Method, Surv Geophys. Doi:10.1007/s10712.009.9063.5

Taflove A (1980) Application of the Finite-difference Time-domain method to sinusoidal steady state electromagnetic penetration problems. IEEE Trans Electromagn Compat 22:191-202. Doi:10.1109/TEMC.1980.303879

Taflove A, Hagness SC (2005) Computational Electrodynamics: The finite-difference time-domain method 3^rd edition. Artech House, Massachusetts.

Thevenot M, Berenger JP, Monediere T, Jecko F (1999) A FDTD scheme for the computation of VLF-LF propagation in the anisotropic Earth-ionosphere waveguide. Ann Telecommunications 54(5-6):297-310

Water CL, Sciffer MD, Lysak RL (2010) FDTD Modeling of ULF waves in the magnetosphere and ionosphere. International Conference on ICEAA, pp477-480

Yee K (1966) Numerical Solution of initial boundary value problems involving Maxwell’s equations in isotropic media. IEEE Trans Antenna Propag 14:302-307