Total Electron Content32N 115W, 2007-2009

Rachel Thessin, CSI 763, April 15, 2010

Data Overview US TEC data from the

National Geophysical Data Center

Two data types: Ground GPS: CORS, RTIGS Sat GPS: GPS/Met

Vertical TEC grids 1 deg x 1 deg 15 min resolution Oct 2004 – present Each day: 26 MB

compressed; 64 MB uncompressed

http://www.ngdc.noaa.gov/stp/IONO/USTEC/

TEC: total electron content (integral of electron density)

Time Series Extracted TEC 2007-2009 at 32N 115W

Overlaps with 12/2009 5.8 mag earthquake

Data Expectations TEC is a function of

Solar / geomagnetic activity

Time of day Day of year (season) Lat / Lon / Alt

2007 – 2009: Solar minimum Relatively flat solar

activity across three years

http://solarscience.msfc.nasa.gov/images/ssn_predict_l.gif

Literature Review, 1 of 2 Dautermann et al ("Investigation

of ionospheric electron content variations before earthquakes in southern California, 2003 – 2004," Journal of Geophysical Research, VOL. 112, 2007)

11 year, 1 year, 27 day, 1 day, 12 hr

Literature Review, 2 of 2 Bilitza (2001)

“International Reference Ionosphere 2000,” Radio Science, v. 36, n. 2, pp 261-275, March-April 2001

E region Solar influenced 24-hr periodicity related to SZA

F region plasma is transported along magnetic field lines 24-hr dependence related to LT

External drivers solar irradiance (11-year cycle) (and hence the use of F10.7 and

twelve-month running mean of SSN as inputs) Conclusion: IRI will miss the 27-day periodicity in the data

These periodicities are ephemeral and caused by “random” events.

Time Series 2007-2009 at 32N 115W

Flat with daily varaitions

Data Gaps 120 gaps among

103,000 data points 18 1-minute gaps and

112 gaps longer than 16 minutes

Linear Interpolation

Data Distribution TEC varies daily

Sinuosoidal appearance

Most data values at peak or trough bimodal data distribution

Bounded on lower end, unbounded on upper end broader upper peak

Autocorrelation Long correlation lag

Values correlated with counterparts one year later

Yearly cycle + flat solar activity

Short correlation lag Large variance in

correlation small lags apart

Daily variation in TEC

Raw Periodogram Signal at period of 1 day; no other signals

Aliasing of this signal Data set is too short and flat to see 1-year, 11-year signals 12-hour – 1/(1/2 day) = 2 day-1; 27-day – 1/(27 days) = 0.037

day-1

1-year – 1/(365 days) = 0.0027 day-1

Welchs Periodogram 8 equal-sized, overlapping windows with a

Hamming function shape leads to less high-freq noise

1-day and 12-hr signals visible

Welch’s Periodogram, 60-day window Smaller window less high-freq noise 12 hr

signal becomes more visible

Welch’s Periodogram, 10-day window Smaller window less high-freq noise 12 hr

signal becomes more visible No longer physically feasible to see 1 year or 27

day signals

Error on Periodogram Bootstrap, n = 1000, l = 45

days Peak at 1 day is statistically

significant, as is peak at 12 hours

Aliasing peaks seem almost significant – meaning of 3 hour period?

Error on Welch’s Bootstrap, n=1000, l =

45 days 1 day and 12 hour

signals statistically significant