Three-dimensional and numerical ray tracing on a phenomenological ionospheric model

Transcription

1 Three-dimensional and numerical ray tracing on a phenomenological ionospheric model Lung-Chih Tsai 1, 2, C. H. Liu 3, T. Y. Hsiao 4, and J. Y. Huang 1 (1) Center for Space and Remote Sensing research, National Central Univ. (NCU), Chung-Li, Taiwan (lctsai@csrsr.ncu.edu.tw) (2) Institute of Space Science, NCU, Chung-Li, Taiwan (3) Academia Sinica, Taiwan (4) Department of Information Technology, Hsing Wu College,Taiwan FS3/COSMIC Data User Workshop, Boulder, CO, Oct , 2009

2 FormoSat-3 3(FS3) /COSMIC: ~ 2500 radio occultation (RO) measurements worldwide daily Numbers of daily RO observations on board FS3 / COSMIC and retrieved N e profiles

3 Top level view of FormoSat-3/COSMIC ionospheric i data processing UCAR LEVEL 1 PROCESSING NCU LEVEL 2/3 PROCESSING Compensated IGS fiducial and orbital data TEC Vertical Ne Profiles 2D/3D COSMIC Science Data TEC Excess Precise Orbit Abel Level 1 Phase files Determination Inversion Processing Processing Processin 2D/3D Red-Black Smoothing Initial Guess MART Algorithm 2D/3D Tomography High Rate fiducial data Spherical Harmonics Processing fof2, hmf2 foe, and hme numerical maps 3D/4D Modelling 3D/4D Ne images

4 Modelling of 3D Ionospheric Electron Density: The TaiWan Ionospheric Model (TWIM) 1st approach : 2D surface spherical harmonics + vertical Chapman layers fitting N e n,, h Nemax, i1 e hhm, 1 e 2 H, 1 h hm H, where n=6 for F3, F2, F1.5, F1, E, and D-layers, and the peak density (N emax ), peak height (h m ), and scale height (H) are combinations of surface spherical harmonics. Advantage: equivalent layers for physical layers; peak height and peak density for each physical layer are explicit parameters. Drawback: inaccuracy of fitting profiles. Radio Science, 44, doi: /2009rs004154, 2009.,

5 Comparisons between Chapman-layer fitting profiles (in blue) and RO N e profiles (in red)

6 Numerical mapping of ionospheric parameters (e.g. fof2 and hmf2) by the least squares method - The spherical surface Laplace equation is 1 sin sin 1 sin The resulting real and orthogonal functions are defined by U V nm nm 2n 1 ( n m)!, n and 2 ( n m)! m P cos cos m, 2n 1 ( n m)! 2 ( n m)! fof2 maps in UT m, P cos sin m, where n 0,1, 2,, m 0,1, 2,, n. n - Includes universal time (UT) and local l time (LT) modes.

7 Local time variation (every hour) of global fof2 numerical maps from TWIM Mixed latitude and longitude trend mapping (after the 3rd order) using the FS3/COSMIC data (day numbers 181 to 210 in 2007)

8 Validation of TWIM fof2 and foe by ionosonde Evaluated by ionosonde data (58 stations) from July 2006 to Oct The mean dfof2s are 0.5 MHz at <70 dip-latitude region. The rms dfof2s are less at 30 ~60 diplatitudes than those at the other regions. The TWIM foe values are underestimated ~0.5 MHz and typically worse at the southern hemisphere.

9 March, June, September, and December noontime fof2 maps (from top to bottom) N 磁赤道線 S 1. The June noontime fof2 map shows that the north-pole area has higher values (~5 MHz) than the south-pole area (~2 MHz), which is in continuous night during the winter. 2. All the noontime fof2 maps show one equatorial N e trough along the dip equator and two N e crest traces at ~18 magnetic dip latitudes for equatorial anomaly (EA). 3. For seasonal variations of EA at noon, the fof2 values along the two crests are highest at the March equinox and lowest at the June solstice.

10 March, June, September, and December noontime hmf2 maps (from top to bottom) 1. From the June noontime hmf2 map the mid- and high-latitude hmf2s in the northern hemisphere generally have relatively higher values (by km) than the southern hemisphere. 2. Summer-to-winter wind effects can transport plasma up the field line and produce higher hmf2s in the northern hemisphere and low dip latitude regions, as shown in the June hmf2 maps; there are lower hmf2s in the southern hemisphere h and low dip latitude regions vice versa.

11 March, June, September, and December noontime HF2 maps (from top to bottom) 1. The June noontime HF2 map shows that the mid- and high-latitude HF2s in the northern hemisphere h generally have relatively thicker values (by km) than the southern hemisphere. 2. Summer-to-winter wind effects can also transport plasma up the field line and produce thicker HF2s in the northern hemisphere and low dip latitude regions, as shown in the June HF2 maps; there are lower HF2s in the southern hemisphere and low dip latitude regions vice versa. 3. The noontime HF2 values display peaks along the dip equator and are largest in March and lowest in June. 4. For seasonal variations of EA at noon, the HF2 values along the dip equator are highest at the March equinox and lowest at the June solstice.

12 March, June, September, and December noontime VTEC maps (from top to bottom) 1. The June and December noontime VTEC maps show that the summer hemispheres generally have higher VTEC values than the winter hemispheres. 2. For seasonal variations of low-latitude VTEC, the noontime VTEC values are highest at the March equinox and lowest at the June solstice. 3. The equatorial anomaly (EA) feature is NOT typical from the VTEC maps except for the March noontime map, which show two crest traces at <18 magnetic dip latitudes.

13 Basic Equations of 3D Ray Tracing : - The Fermat s principle n r ds cos ds 0, where n r is the ray refractive index, μ is the phase refractive index of the ionosphere, α is the angle between the wave vector and the ray direction. - The generalized differential form of Snell s law d dp 1 u uˆ, where p is the phase path, and u are the wave-normal vector number.

14 TWIM Application I : MUF estimation for HF communication MUF sec( min( fof2)

15 TWIM Application II : 3D ray tracing Ordinary rays in white and extraordinary rays in black Showing the spitze Including N e Including the magnetic field and N e Excluding the magnetic field and N e Including the magnetic field

16 TWIM Application II : 3D ray tracing One central ray (in white) and four side rays (in red and blue) Global top view on fof2 map Latitudinal side view in f n map Regional top view on fof2 map Longitudinal side view in f n map

17 Comparison between actual ionograms and synthetic ionograms at Chung-Li, Taiwan Red and blue dots show the ordinary and extraordinary echoes of actual ionograms respectively. Green and black dots show the ordinary and extraordinary echoes of synthetic ionograms using TWIM.

18 Final remarks FormoSat-3/COSMIC has become a promising program for monitoring the large-scale global ionosphere. A 3D approach using vertical Chapman layers and surface spherical harmonics for modeling variations of ionospheric Ne have been proposed and implemented to be the TaiWan Ionospheric Model (TWIM). A numerical and stepped ray-tracing method on the TaiWan Ionospheric Model (TWIM) has been implemented including the Earth s magnetic field and N e gradient effects. Future works The predictions of TWIM.