GPS Observation of Continent-size (or super-size ) Traveling TEC Pulsations at the Start of Geomagnetic Storms

Transcription

1 GPS Observation of Continent-size (or super-size ) Traveling TEC Pulsations at the Start of Geomagnetic Storms Rezy Pradipta Boston College Institute for Scientific Research Tuesday, 18 November 2014

2 An Executive Summary SS-TECP appears right after the shock, if IMF B z oscillates north/south Rezy P., BC ISR Seminar Continent-size TEC Pulsations 2/26

3 Outline of Presentation Automated GPS TEC data processing at BC ISR overview of relevant GPS receiver networks TEC calculations & 2-D TEC data mapping additional TEC data detrending process Main usage of the detrended TEC data (TECP) study of AGW/TID study of equatorial plasma bubbles Observation of super-size TEC pulsations (SS-TECP) overview of the phenomena estimating the speed of SS-TECP discussion on physical mechanism Summary and conclusions Rezy P., BC ISR Seminar Continent-size TEC Pulsations 3/26

4 The GPS Receiver Networks / Data Source a total of more than 1900 stations; but actually only need 200 stations (automated daily processing), or 500 stations (manual data processing) Rezy P., BC ISR Seminar Continent-size TEC Pulsations 4/26

5 The GPS Receiver Networks / Data Source (cont.) The differential code bias solutions (satellite biases) are obtained from the University of Bern via ftp://ftp.unibe.ch/aiub/code/ Rezy P., BC ISR Seminar Continent-size TEC Pulsations 5/26

6 Routine Absolute TEC Calculation the receiver bias is estimated using the minimum scalloping method; if there are negative TEC values, we revert to a zero minimum TEC Rezy P., BC ISR Seminar Continent-size TEC Pulsations 6/26

7 Daily Plots of 2-D TEC Scatter Map Here, the ionospheric piercing point (IPP) is set at 350 km altitude. Rezy P., BC ISR Seminar Continent-size TEC Pulsations 7/26

8 Interpolation from Individual IPPs into a Fixed Grid inverse distance-weighted (IDW) interpolation; grid resolution: Rezy P., BC ISR Seminar Continent-size TEC Pulsations 8/26

9 Scatter & Interpolated 2-D TEC Maps Data from 25 October 2011, 05:45 UTC (integrated 05:35 05:55 UTC) scatter map: generally more truthful in terms of data representation interp map: could be more insightful to help discern the dynamics Rezy P., BC ISR Seminar Continent-size TEC Pulsations 9/26

10 TEC Data Detrending TECP Signal The TEC data is detrended using 12th order polynomial. If a given data segment is too long, then break into two separate segments. Rezy P., BC ISR Seminar Continent-size TEC Pulsations 10/26

11 2-D TECP Data Maps: Identifying Auroral LSTIDs Data from 26 Sept 2011 (integration time for each frame = 20min); (a) 20:45 UTC, (b) 21:00 UTC, (c) 21:30 UTC Train of auroral LSTIDs can be seen coming from both polar regions, and they meet around the equator producing wave interference patterns. Rezy P., BC ISR Seminar Continent-size TEC Pulsations 11/26

12 Capturing the Propagation of Auroral LSTIDs Temporal evolution of TECP signal along a specified magnetic meridian. Average propagation speed: 866 ± 120 m/s (N S) Rezy P., BC ISR Seminar Continent-size TEC Pulsations 12/26

13 Capturing the Propagation of Auroral LSTIDs (cont.) Temporal evolution of TECP signal along a specified magnetic meridian. Average prop. speed: 666 ± 34 m/s (N S), 686 ± 72 m/s (S N) Rezy P., BC ISR Seminar Continent-size TEC Pulsations 13/26

14 TEC Detrending Procedure for Eq. Bubble Study The aim: get both AGW/TID & depletion profile (still a work in progress) Rezy P., BC ISR Seminar Continent-size TEC Pulsations 14/26

15 TEC Detrending Procedure for Eq. Bubble Study (cont.) The aim: get both AGW/TID & depletion profile (still a work in progress) Rezy P., BC ISR Seminar Continent-size TEC Pulsations 15/26

16 Continent-size (or super-size ) TEC Pulsations Play two animations of 2-D TEC data: October 2011 storm 26 September 2011 storm Rezy P., BC ISR Seminar Continent-size TEC Pulsations 16/26

17 Characteristics of SS-TECP on Each Satellite Pass The oscillatory behavior can be visible in the absolute TEC data as well. Rezy P., BC ISR Seminar Continent-size TEC Pulsations 17/26

18 Characteristics of SS-TECP on Each Satellite Pass (cont.) Consistent pattern from several stations: SS-TECP periodicity is 1 hr. Rezy P., BC ISR Seminar Continent-size TEC Pulsations 18/26

19 Estimating the Propagation Speed of SS-TECP (a) to estimate the SS-TECP speed, (b) to examine the overall time seq. Rezy P., BC ISR Seminar Continent-size TEC Pulsations 19/26

20 Estimating the Propagation Speed of SS-TECP (cont.) inferred speed: v =1769 ± 336 m/s (left tr); v =2122 ± 488 m/s (right tr) Rezy P., BC ISR Seminar Continent-size TEC Pulsations 20/26

21 Estimating the Propagation Speed of SS-TECP (cont.) The inferred SS-TECP propagation speed: v =3391 ± 237 m/s Rezy P., BC ISR Seminar Continent-size TEC Pulsations 21/26

22 The Overall Timeline / Sequence (26 Sep 2011 Storm) IMF B z was oscillating when SS-TECP appeared; not visib. by ionosondes Rezy P., BC ISR Seminar Continent-size TEC Pulsations 22/26

23 The Overall Timeline / Sequence (24-25 Oct 2011 Storm) IMF B z was oscillating when SS-TECP appeared; not visib. by ionosondes Rezy P., BC ISR Seminar Continent-size TEC Pulsations 23/26

24 Physical Mechanism behind the SS-TECP oscillating IMF B z polarity a series of magnetic reconnection occurred magnetosphere: cycles of being halfway opened, closed, and reopened these repeated cycles could modulate the press. on the magnetosphere SS-TECP might be a type of MHD wave mode in the magnetosphere Rezy P., BC ISR Seminar Continent-size TEC Pulsations 24/26

25 Physical Mechanism behind the SS-TECP (cont.) possible candidate: ion drift waves propagate in the westward direction; ion drift waves in the magnetosphere: 5-50 km/s [Cheng and Lin, 1997] would scale down linearly to a few km/s if projected into 350 km shell Rezy P., BC ISR Seminar Continent-size TEC Pulsations 25/26

26 Summary and Conclusions Supersize TEC Pulsations (SS-TECP) were observed using GPS measurements over the N. American sector at the beginning of geomagnetic storms, immediately after the shock had arrived Several basic characteristics of the SS-TECP: appears when the IMF B z was oscillating north/south propagates zonally westward, with apparent speed of 2-3 km/s has wavelength at least as large as E/W span of North America does not seem to have significant ionospheric plasma signatures has amplitudes similar to auroral LSTIDs ( TECU) The SS-TECP appears to be a magnetospheric / plasmaspheric phenomenon rather than an ionospheric phenomenon. Possible candidate: ion drift waves in the magnetosphere Rezy P., BC ISR Seminar Continent-size TEC Pulsations 26/26