Using the GRAIT Detrender to Study Ionospheric Bubbles / Irregularities over South America and the Caribbean

Transcription

1 Using the GRAIT Detrender to Study Ionospheric 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

2 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 America might expand/extend northward, reaching the Caribbean region. However, sometimes we found ionospheric irregularities that are unique to the Caribbean region (independent of EPB occurrence). Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 2/34

3 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 GPS receiver stations, but the region is still largely understudied. What could be accomplished with much of the observation data from these receiver stations? What are the potential challenges? Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 3/34

4 Main Outline GRAIT Detrender technique (gradual roll above implicit terrain) basic principles of the technique test & validation against ionosondes side products from the validation runs Bubbles and irregularities over South America and the Caribbean expansion of equatorial plasma bubbles reaching the Caribbean midlatitude ionospheric irregularities unique to the Caribbean Prospects for the Southeast Asia-Pacific region data coverage by GPS receiver network prospect for scientific & tech. initiatives Summary and conclusions Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 4/34

5 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. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 5/34

6 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. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 6/34

7 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. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 7/34

8 Mechanical Analogy of Rolling Barrel for TEC Detrending Finding the next contact point: minimize the angular distance δ = β θ where β = sin 1 ( x)2 +( y) 2 [ ] θ = tan 1 y x and x x x 0 y y y 0 2R 0 ] The terrain is set in an xy-space where x time/τ 0 and y TEC/ζ 0. Common settings: R 0 = 1, τ 0 = 2 hr, and ζ 0 = 40 TECU. The completed set of contact points barrel-roll curve (BRC) Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 8/34

9 An Illustrative Example of the TEC Detrending Procedure After BRC has been computed, back into TEC-vs-time domain. Real GPS data from station 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 filter was used in the final step to obtain the overall TEC trend. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 9/34

10 Mapping Equatorial Plasma Bubbles in 2-D with TEC Data from 240 GPS stations; use lat/lon grid with resolution. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 10/34

11 Basic Comparison with the Ionosonde Observations Peruvian sector (west coast): light spread echoes, clear near F-peak Brazilian sector (east coast): stronger range + freq spread echoes Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 11/34

12 Extended Comparison: GRAIT Detrender & Ionosondes We compared GRAIT Detrender results with spread-f observations at 4 ionosonde stations: Jicamarca, Cach. Paulista, Fortaleza, and Ascension. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 12/34

13 Using Ionosonde to Detect Turbulence in the Ionosphere Spread-F echoes characteristic signatures of ionospheric turbulence. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 13/34

14 FTI/RTI Summary Plots for the Ionosonde Data FTI (freq-time-intensity) plot integrate the signals across virt. heights RTI (range-time-intensity) plot integrate the signals across frequencies Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 14/34

15 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) Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 15/34

16 A Sample of GRAIT Detrender vs Ionosonde Comparison Top: RTI plot of the ionosonde data from Fortaleza station on 4-5 Dec 2011 UTC. Bottom: the TEC time series plot at the Fortaleza cordinate on 4-5 Dec 2011 UTC. Agreement betwen the appearance of spread-f echoes and TEC depletions from GRAIT Detrender. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 16/34

17 Specifics of GRAIT Detrender vs Ionosonde Comparison Binary classification: here we have either occurrence / no occurrence of spread-f and TEC depletions. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 17/34

18 Statistics from the GRAIT-Ionosonde Comparison some spread-f echoes & TEC depletions/bubbles good agreement no spread-f echoes & no TEC depletions/bubbles good agreement some spread-f echoes & no TEC depletions/bubbles OK no spread-f echoes & some TEC depletions/bubbles failure Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 18/34

19 Statistics: Spatial Pattern of TEC Depletion Occurrence Certain spatial combination patterns of TEC depletion occurrence are more dominant than others, but none has absolute majority. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 19/34

20 Statistics: Spatial Pattern of Spread-F Occurrence Certain spatial combination patterns of spread-f occurrence are more dominant than others, but none has absolute majority. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 20/34

21 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 also examined the ionogram records for spread-f echoes. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 21/34

22 Expansion of EPBs over the Caribbean 2-D TEC data map on 25 Oct 2011 (doy 298) over South America and nearby 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. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 22/34

23 Expansion of EPBs over the Caribbean (continued) Top panels: ionograms from Ramey AFB, Puerto Rico 25 Oct Bottom panels: ionograms from Jicamarca JRO, Peru 25 Oct Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 23/34

24 Expansion of EPBs over the Caribbean (continued) Top: RTI plot of the ionosonde data from Ramey, Puerto Rico on 25 Oct Bottom: RTI plot of ionosonde data from Jicamarca JRO, Peru on 25 Oct The turbulence over the Caribbean had started 1 hr later than the turbulence over South America. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 24/34

25 Local Midlatitude Irregularities over the Caribbean 2-D TECP data map on 20 Jun 2011 (doy 171) over South America and nearby areas. No equatorial plasma bubbles is expected over South America 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. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 25/34

26 Local Midlatitude Irregularities over the Caribbean (cont.) Top panels: ionograms from Arecibo Obs., Puerto Rico 20 Jun Bottom panels: ionograms from Jicamarca JRO, Peru 20 Jun Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 26/34

27 Local Midlatitude Irregularities over the Caribbean (cont.) Top: RTI plot of the ionosonde data from Arecibo, Puerto Rico on 20 Jun Bottom: RTI plot of ionosonde data from Jicamarca JRO, Peru on 20 Jun There was significant degree of turbulence over the Caribbean. However, there was essentially little/no iono turbulence over South America. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 27/34

28 Some Lessons from the Tests & Experimental Findings Combination of GPS TEC and ionosonde measurements (with adequate detrending/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 the equatorial bubbles stronger. Under special circumstances such as geomagnetic storms, equatorial plasma bubbles over South America can extend further northward to reach the Caribbean area. Yet, ionospheric plasma density irregularities can also appear/develop locally over the Caribbean as a midlatitude region. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 28/34

29 Prospects for the Southeast Asia-Pacific Region Encouragement for science collaboration within ASEAN and/or other regional frameworks could play an important role. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 29/34

30 Some Promising Development in Recent Years Acceleration of infrastructure development across much of the region by the current government/administration in Indonesia (potentially lowering logistical costs and reducing other forms of barriers). Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 30/34

31 Some Promising Development in Recent Years (continued) LAPAN is currently preparing a new National Observatory near Kupang in eastern part of Indonesia. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 31/34

32 Some Promising Development in Recent Years (continued) Check Point A Check Point B Check Point C path of totality path of totality Studies of ionospheric phenomena related to the 9 March 2016 solar eclipse, demonstrating the potential utility of the GPS TEC data for advancing space science in the region. Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 32/34

33 Another Potential Initiative for the Asia-Pacific Region Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 33/34

34 Conclusions We have developed and tested the GRAIT Detrender technique with an inherent capacity to distinguish depletions from wave fluctuations. We implemented this TEC data detrending technique to study TEC depletions 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 are unique to the Caribbean region (independent of EPB occurrence). With the growing network of GPS receiver stations, we hope to accomplish 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: /2015ja Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 34/34

35 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 Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 35/34

36 Sample Sequential Snapshots of TEC Maps Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 36/34

37 Sample Sequential Snapshots of dtec/dt Maps Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 37/34

38 Sample Sequential Snapshots of ROTI Maps Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 38/34

39 Comparison: GRAIT Detrender vs C/NOFS (part 1) Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 39/34

40 Comparison: GRAIT Detrender vs C/NOFS (part 2) Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 40/34

41 EPB Zonal Drift Velocity from the 2-D TEC Maps Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 41/34

42 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 Rezy P., BC ISR Seminar GPS TEC Data Detrending & Ionospheric Bubbles/Irregularities 42/34