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
An Executive Summary
SS-TECP appears right after the shock, if IMF Bz oscillates north/south
Rezy P., BC ISR Seminar
Continent-size TEC Pulsations
2/26
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
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
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
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
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
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Interpolation from Individual IPPs into a Fixed Grid
inverse distance-weighted (IDW) interpolation; grid resolution: 0.5◦×0.5◦
Rezy P., BC ISR Seminar
Continent-size TEC Pulsations
8/26
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
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
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
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
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
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
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
Continent-size (or “super-size”) TEC Pulsations
Play two animations of 2-D TEC data:
24-25 October 2011 storm
26 September 2011 storm
Rezy P., BC ISR Seminar
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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
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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
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
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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
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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
The Overall Timeline / Sequence (26 Sep 2011 Storm)
IMF Bz was oscillating when SS-TECP appeared; not visib. by ionosondes
Rezy P., BC ISR Seminar
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The Overall Timeline / Sequence (24 -25 Oct 2011 Storm)
IMF Bz was oscillating when SS-TECP appeared; not visib. by ionosondes
Rezy P., BC ISR Seminar
Continent-size TEC Pulsations
23/26
Physical Mechanism behind the SS-TECP
oscillating IMF Bz 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
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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
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 Bz 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 (0.1 - 0.2 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
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