Ionosonde and GPS Total Electron Content Observations during the 26 December 2019 Annular Solar Eclipse over Indonesia
Abstract. We report our investigation of ionospheric effects due to the passage of an annular solar eclipse over Southeast Asia on 26 December 2019, using multiple set of observations. Two ionosondes (one at Kototabang and another at Pontianak) were used to measure dynamical changes in the ionospheric layer during the event. A network of ground-based GPS receiver stations in Indonesia were used to derive the distribution of total electron content (TEC) over the region. In addition, extreme ultraviolet (EUV) images of the Sun from the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO) satellite were also analyzed to determine possible impacts of solar active regions on the changes that occurred in the ionosphere during the eclipse. We found −1.67 MHz and −1.58 MHz reduction (23.2 % and 22.4 % relative reduction) in foF2 during the solar eclipse over Kototabang and Pontianak, respectively. The respective TEC reduction over Kototabang and Pontianak during the eclipse was −4.34 TECU and −5.45 TECU (24.9 % and 27.9 % relative reduction). Overall, there was 34–36 minutes delay from maximum eclipse until minimum foF2 was reached at these two locations. The corresponding time delays for eclipse-related TEC reduction at these two locations were 40 minutes and 16 minutes, respectively. The ionospheric F-layer was found to descend with a speed of 9–19 m/s during the first half of the eclipse period. We also found an apparent rise of the ionospheric F-layer height near the end of the solar eclipse period, equivalent to vertical drift velocity of 44–47 m/s. The GPS TEC data mapping along a set of cross-sectional cut lines indicate that the greatest TEC reduction actually occurred to the north of the solar eclipse path, opposite of the direction from which the lunar shadow fell. As the central path of the solar eclipse was located just to the north of the southern equatorial ionization anomaly (EIA) crest, it is suspected that such a peculiar TEC reduction pattern was caused by plasma flow associated with the equatorial fountain effect. Net perturbations of TEC were also computed and analyzed, which revealed the presence some wavelike fluctuations associated with the solar eclipse event. Some of the observed TEC perturbation patterns that propagated with a velocity matching the lunar shadow may be explained in terms of non-uniform EUV illumination that arose as various active regions on the Sun went obstructed and unobstructed during the eclipse. The remaining wavelike features are likely to be traveling ionospheric disturbances (TIDs) driven by acoustic-gravity waves (AGWs), generated by the passage of the solar eclipse on top of other diurnal factors.
Jiyo Harjosuwito et al.
Jiyo Harjosuwito et al.
Scaled Ionogram Parameters and Processed GPS TEC Data https://doi.org/10.7910/DVN/ZUXCCK
Masked Solar Images and 2-D Regional GPS TEC Maps https://doi.org/10.7910/DVN/ZUXCCK
Jiyo Harjosuwito et al.
Viewed (geographical distribution)
The authors present evidence of the effect of the 26 December 2019 solar eclipse on the ionosphere. They showed this using Total Electron Content (TEC) data from Global Navigation Satellite System (GNSS) receivers over the Indonesian region. Also, ionosonde data from Canadian Advanced Digital Ionosonde (CADI) in two locations were used to complement the TEC observation. Using the Solar Dynamics Observatory (SDO), they tracked the umbra of the eclipse spatiotemporally. Their investigation methods are clear. The authors gave much emphasis to the effect of the eclipse on the ionosphere particularly the reduction in the TEC and Ionosonde observations as well as the time delay. This current work contributes to literature by showing how this type of eclipse affects the ionosphere in the Indonesian region. However, the structure of the paper needs to be improved, especially the methodology and the results. Also, there are quite a number of repetitions of some sentences (please kindly rephrase). I, therefore, recommend the work be published after the implementation of the comments and corrections.
Kindly mention clearly what is the new findings of this work.
The resolution of some of the labels of some Figures needs to increase, they appear blurred.
Methodology and Results:
Please improve the methodology. I suggest you give more details on how the TEC was estimated with some equations and references. Similarly, the methodology of the keogram should be elaborated in detail. I would like to encourage the authors not to assume, the readers are already familiar with the techniques.
Figure 2, if it is possible I will suggest the authors improve the resolution.
For the Figures with subpanels, please label them for easy identification. E.g., Figure 14(a(i)).
Minor comments and technical corrections
#1. Line 10: Kindly rewrite this sentence for clarity.
#2. Line 18: Put "of" before “some”.
#1. Line 36: Change “solar local time” to “local solar time”.
#2. Lines 45-48: Please kindly rewrite “For many decades ... ; ...Hairston et al., 2018)
Instrumentation and Methodology:
#1. Line 73: Please remove “Relatively”.
#2. Lines 92 - 93: Change (x.xx°S yyy.yy°E) and anywhere in the text to (x.xx°S, yyy.yy°E).
#3. Line 128: Kindly rephrase the sentence “Further in the analysis, TEC data detrending was also performed”.
#4. Lines 128 - 130: Change “Two types of data detrending were performed: one to derive âTEC (general deviations from the normal condition) and another to derive TECP (wavelike perturbations with much smaller 130 amplitudes and finer structures)” to “Two types of data detrending were performed: (1) to derive âTEC (general deviations from the normal condition) and (2) to derive TECP (wavelike perturbations with much smaller 130 amplitudes and finer structures)”.
#5. Lines 133 - 134: Kindly rephrase the sentence “Only after completing the detrending process on the IPPs did we spatially map the TECP values onto fixed grid point(s) for data display.”
#1. Lines 144 - 145: Rewrite as ……….: one in the southeast of the solar disk and the other in the northwest of the solar disk.
#2. Lines 188 - 190: Please rephrase as: The recovery phase occurred over a duration of 155 minutes, starting at 06:20 UTC (13:20 LT) until 08:55 UTC (15:55 LT) with an increase in foF2 by 1.23 MHz (from 5.44 MHz to 6.67 MHz).
#3. Lines 195 - 196: change “……. while that over Pontianak was 83 minutes” to “……. whereas that over Pontianak was 83 minutes”.
#4. Line 235: …… climb …… to ……. ascent…. .
#5. Line 242: …… climb …… to ……. ascent…. .
GPS TEC Observations
#1. I will suggest the authors “change keogram” plot to “keogram”.
#2. Line 293: Kindly change “…… since at this time of day, …….. maximum level.” to “…… since at this time of the day, …….. maximum level.”
#3. Line 303 - 304: Please rephrase this sentence - “Not until nearing the maximum eclipse did âTEC started to drop, which eventually reached approximately -6 TECU at its lowest”.
#4. Line 342 -343: Change to: “The further away the striped patterns were from the alignment with the C1/max/C4 epoch lines, the more likely they are to be associated with AGW/TID.”
Solar EUV Illumination Variability
#1. Line 370: Please change “Further,……” to “Furthermore, …”
#1. Line 404: I suggest you change “…… 97 minutes and 83 minutes.” to “…… 97 and 83 minutes.”
#2. Line 408-409: Please insert “e.g.,” in the citation as (e.g., Farges et al., 2001; Adeniyi et al., 2007; Goncharenko et al., 2018), …. .
#3. Line 417: Same as comment #1, line 404.
#4. Line 438 - 440: This overshoot might have been caused by an inward shift of the EIA crest position during the post-eclipse period, after an outward shift that happened earlier during the eclipse (Aa et al., 2020). Please have done any analysis to prove this point in this study?
#5. Line 469: Please put a colon after “includes” as … includes: (1) ….