using the `grait detrender' to study ionospheric bubbles

Using the ‘GRAIT Detrender’ to StudyIonospheric Bubbles / Irregularities over

South America and the Caribbean(and the prospect for Southeast Asia-Pacific)

Rezy Pradipta

Boston College

Institute for Scientific Research

Thursday, 15 February 2018

An Executive Summary

We have implemented a special type of TEC data detrending technique[Pradipta et al., 2015] to study ionospheric bubbles and irregularities.

We found that equatorial plasma bubbles (EPBs) over South Americamight expand/extend northward, reaching the Caribbean region.

However, sometimes we found ionospheric irregularities that are uniqueto the Caribbean region (independent of EPB occurrence).

Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 2/34

An Executive Summary (continued)

We have implemented a special type of TEC data detrending technique[Pradipta et al., 2015] to study bubbles/irregularities over South America.

The Southeast Asia-Pacific region also has a growing network of GPSreceiver stations, but the region is still largely understudied.

What could be accomplished with much of the observation data fromthese receiver stations? What are the potential challenges?


Main Outline

GRAIT Detrender technique (gradual roll above implicit terrain)

basic principles of the techniquetest & validation against ionosondesside products from the validation runs

Bubbles and irregularities over South America and the Caribbean

expansion of equatorial plasma bubbles reaching the Caribbeanmidlatitude ionospheric irregularities unique to the Caribbean

Prospects for the Southeast Asia-Pacific region

data coverage by GPS receiver networkprospect for scientific & tech. initiatives

Summary and conclusions


Objectives and Challenges of TEC Data Detrending

Large depletions are often mistaken for part of the background variation.Or worse: they may be misinterpreted as large-amplitude wave oscillation.


Common Flaw in TEC Data Detrending (involving bubbles)

Large depletions are often mistaken for part of the background variation.Or worse: they may be misinterpreted as large-amplitude wave oscillation.


Mechanical Analogy of Rolling Barrel for TEC Detrending

Treat absolute TEC signal as a form of terrain (for a barrel to roll on it).Contact points of this rolling barrel = a template for the overall trend.

Depletions excluded → can continue with conventional TEC detrending.


Mechanical Analogy of Rolling Barrel for TEC Detrending

Finding the next contact point:minimize the angular distanceδ = β − θwhere

β = sin−1[

√(∆x)2+(∆y)2

2R0]

θ = tan−1[

∆y∆x

]and

∆x ≡ x − x0

∆y ≡ y − y0

The terrain is set in an xy-space where x ≡ time/τ0 and y ≡TEC/ζ0.Common settings: R0 = 1, τ0 = 2 hr, and ζ0 = 40 TECU.

The completed set of contact points ⇒ barrel-roll curve (BRC)


An Illustrative Example of the TEC Detrending Procedure

After BRC has beencomputed, back intoTEC-vs-time domain.

Real GPS data fromstation GVAL, PRN 21

(on 20 Dec 2011).

The BRC envelopes:BRC + 1 TECU, and

BRC − 3 TECU

Examine |dTEC/dt|also to cross-check.

Savitzky-Golay filterwas used in the finalstep to obtain theoverall TEC trend.


Mapping Equatorial Plasma Bubbles in 2-D with ∆TEC

Data from ∼240 GPS stations; use lat/lon grid with 0.2◦×0.2◦ resolution.


Basic Comparison with the Ionosonde Observations

Peruvian sector (west coast): light spread echoes, clear near F-peakBrazilian sector (east coast): stronger range + freq spread echoes


Extended Comparison: GRAIT Detrender & Ionosondes

We compared GRAIT Detrender results with spread-F observations at 4ionosonde stations: Jicamarca, Cach. Paulista, Fortaleza, and Ascension.


Using Ionosonde to Detect Turbulence in the Ionosphere

Spread-F echoes → characteristic signatures of ionospheric turbulence.


FTI/RTI Summary Plots for the Ionosonde Data

FTI (freq-time-intensity) plot ⇒ integrate the signals across virt. heightsRTI (range-time-intensity) plot ⇒ integrate the signals across frequencies


FTI/RTI Summary Plots for the Ionosonde Data (cont.)

Essential info from the FTI/RTI summary plots: foF2 critical frequency,ionospheric height variation, and spread echoes (indicator of turbulence)


A Sample of GRAIT Detrender vs Ionosonde Comparison

Top: RTI plot of theionosonde data fromFortaleza station on4-5 Dec 2011 UTC.

Bottom: the ∆TECtime series plot at theFortaleza cordinate on4-5 Dec 2011 UTC.

Agreement betwenthe appearance ofspread-F echoes andTEC depletions fromGRAIT Detrender.


Specifics of GRAIT Detrender vs Ionosonde Comparison

Binary classification: here we have either occurrence / no occurrence ofspread-F and TEC depletions.


Statistics from the GRAIT-Ionosonde Comparison

some spread-F echoes & TEC depletions/bubbles → good agreementno spread-F echoes & no TEC depletions/bubbles → good agreementsome spread-F echoes & no TEC depletions/bubbles → OKno spread-F echoes & some TEC depletions/bubbles → failure


Statistics: Spatial Pattern of TEC Depletion Occurrence

Certain spatial combination patterns of TEC depletion occurrence aremore dominant than others, but none has absolute majority.


Statistics: Spatial Pattern of Spread-F Occurrence

Certain spatial combination patterns of spread-F occurrence are moredominant than others, but none has absolute majority.


Bubbles/Irregularities over South America & the Caribbean

In this study, we rely on ionospheric observations from:

wide-area network of 200+ GPS receivers

ionosondes (HF vertical radio sounders)

GPS TEC data were detrended using the GRAIT Detrender, and we alsoexamined the ionogram records for spread-F echoes.


Expansion of EPBs over the Caribbean

2-D ∆TEC data map on 25 Oct 2011 (doy 298) over South America andnearby areas. A major geomagnetic storm had occurred on that day.

Left: a snapshot of the spatial distrib of ∆TEC at around 00:45 UTC.Right: aggregate max of the TEC depletions over a 6-hour duration.


Expansion of EPBs over the Caribbean (continued)

Top panels: ionograms from Ramey AFB, Puerto Rico – 25 Oct 2011.Bottom panels: ionograms from Jicamarca JRO, Peru – 25 Oct 2011.


Expansion of EPBs over the Caribbean (continued)

Top: RTI plot of theionosonde data fromRamey, Puerto Ricoon 25 Oct 2011.

Bottom: RTI plot ofionosonde data fromJicamarca JRO, Peruon 25 Oct 2011.

The turbulence overthe Caribbean hadstarted ∼1 hr laterthan the turbulenceover South America.


Local Midlatitude Irregularities over the Caribbean

2-D TECP data map on 20 Jun 2011 (doy 171) over South America andnearby areas. No equatorial plasma bubbles is expected over SouthAmerica during this season.

Left: a snapshot of the distribution of TECP values at around 04:15 UTC.Right: aggregate max of the TECP amplitudes over a 6-hour duration.


Local Midlatitude Irregularities over the Caribbean (cont.)

Top panels: ionograms from Arecibo Obs., Puerto Rico – 20 Jun 2011.Bottom panels: ionograms from Jicamarca JRO, Peru – 20 Jun 2011.


Local Midlatitude Irregularities over the Caribbean (cont.)

Top: RTI plot of theionosonde data fromArecibo, Puerto Ricoon 20 Jun 2011.

Bottom: RTI plot ofionosonde data fromJicamarca JRO, Peruon 20 Jun 2011.

There was significantdegree of turbulenceover the Caribbean.However, there wasessentially little/noiono turbulence overSouth America.


Some Lessons from the Tests & Experimental Findings

Combination of GPS TEC and ionosonde measurements (with adequatedetrending/mapping techniques and data representation/display format)can be very effective for monitoring irregularities in the ionosphere.

Geomagnetic storms usually supress equatorial plasma bubbles. However,depending on the exact start time of the storms, they can also make theequatorial bubbles stronger.

Under special circumstances such as geomagnetic storms, equatorialplasma bubbles over South America can extend further northward toreach the Caribbean area.

Yet, ionospheric plasma density irregularities can also appear/developlocally over the Caribbean as a midlatitude region.


Prospects for the Southeast Asia-Pacific Region

Encouragement for science collaboration within ASEAN and/or otherregional frameworks could play an important role.


Some Promising Development in Recent Years

Acceleration of infrastructure development across much of the region bythe current government/administration in Indonesia (potentially loweringlogistical costs and reducing other forms of barriers).


Some Promising Development in Recent Years (continued)

LAPAN is currently preparing a new National Observatory near Kupangin eastern part of Indonesia.


Some Promising Development in Recent Years (continued)

path of

totality

path of

totality

Check Point B

Check Point A

Check Point C

Studies of ionospheric phenomena related to the 9 March 2016 solareclipse, demonstrating the potential utility of the GPS TEC data foradvancing space science in the region.


Another Potential Initiative for the Asia-Pacific Region


Conclusions

We have developed and tested the GRAIT Detrender technique withan inherent capacity to distinguish depletions from wave fluctuations.

We implemented this TEC data detrending technique to study TECdepletions and ionospheric irregularities around South America.

Equatorial plasma bubbles (EPBs) over South America can expand/extend northward, reaching the Caribbean region.

However, sometimes we may have ionospheric irregularities that areunique to the Caribbean region (independent of EPB occurrence).

With the growing network of GPS receiver stations, we hope toaccomplish similar act in the Asia-Pacific region as well.

For further details on the GRAIT Detrender technique:Pradipta, R., C. E. Valladares, and P. H. Doherty (2015), An Effective TEC Data Detrending

Method for the Study of Equatorial Plasma Bubbles and Traveling Ionospheric Disturbances,

J. Geophys. Res. Space Physics, 120, doi:10.1002/2015JA021723.


Supplementary Slides

List of back-up / supplementary slides:

1. Sample sequential snapshots of ∆TEC maps

2. Sample sequential snapshots of |dTEC/dt| maps

3. Sample sequential snapshots of ROTI maps

4. GRAIT Detrender vs C/NOFS comparison (1)

5. GRAIT Detrender vs C/NOFS comparison (2)

6. Other applications of GRAIT Detrender

7. Perfecting the GRAIT Detrender technique


Sample Sequential Snapshots of ∆TEC Maps


Sample Sequential Snapshots of |dTEC/dt| Maps


Sample Sequential Snapshots of ROTI Maps


Comparison: GRAIT Detrender vs C/NOFS (part 1)


Comparison: GRAIT Detrender vs C/NOFS (part 2)


EPB Zonal Drift Velocity from the 2-D ∆TEC Maps


Moving Forward: Perfecting the TEC Data Detrender

Objectives of GPS TEC data detrending techniques — the triad:

wavelike TEC fluctuations [v ]

TEC depletions/bubbles [v ]

TEC salients/accretions [x ] ← GRAIT Detrender is not there yet


using the `grait detrender' to study ionospheric bubbles

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