the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Aug 2024
Tracking Traveling Ionospheric Disturbances through Doppler-shifted AM radio transmissions
Abstract. Six specialized radio receivers were developed to measure the Doppler shift of amplitude modulation (AM) broadcast radio carrier signals due to ionospheric effects. Five were deployed approximately on a circle at a one-hop distance from an 810-kHz clear-channel AM transmitter in Schenectady, New York, and the sixth was located close to the transmitter, providing a reference recording. Clear-channel AM signals from New York City and Connecticut were also received. The experiment confirmed detection of travelling ionospheric disturbances (TIDs) and measurement of their horizontal phase velocities through monitoring variations of the Doppler shift of reflected AM signals imparted by vertical motions of the ionosphere. Comparison of thirteen events with simultaneous global navigation satellite system (GNSS) based TID measurements showed generally good agreement between the two techniques, with differences attributable to differing sensitivities of the techniques to wave altitude and characteristics within a complex wave environment. Detected TIDs had mostly southward phase velocities, and in 4 cases they were associated with auroral disturbances that could plausibly be their sources. A purely automated software technique for event detection and phase velocity measurement was developed and applied to one year of data, revealing that AM Doppler sounding is much more effective when using transmitter signals in the upper part of the AM band (above 1 MHz) and demonstrating that the AM Doppler technique has promise to scale to large numbers of receivers covering continent-wide spatial scales.
- Preprint
(2043 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
-
RC1: 'Comment on egusphere-2024-2383', Anonymous Referee #1, 28 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2383/egusphere-2024-2383-RC1-supplement.pdf
-
AC1: 'Reply on RC1', James LaBelle, 03 Dec 2024
The authors thank both referees for their careful reading of the manuscript and their helpful suggestions which have resulted in significant improvements of the paper, which they believe is now suitable for publication. Below find a detailed response to each point raised by each of the referees. One of the principal changes is modification of the conclusions somewhat regarding the comparison of horizontal phase velocities measured at the same times by the AM Doppler technique and the GNSS-TEC technique. The responses have also entailed adding many citations to the reference list.Â
Responses to the five enumerated comments of Referee 1:
1. We examined vertical ionograms at 7.5 minute cadence from mid-latitude observations at Westford, MA (42.6 N latitude / 288.5 E longitude). Â The ionosonde data, comprising station MHJ45 within the Global Ionospheric Radio Observatory (GIRO), originated from the University of Massachusetts Lowell's ionosonde station operated on the MIT Haystack observatory grounds. Â MHJ45 was located on the eastern edge of the study region. Â No sporadic E was recorded during any of the TID events in Tables 2-3 of our paper. Â Around event times, Sporadic E was detected about an hour before one of the events (on Sept 26, 2020) and an extremely weak Sporadic E layer was detected at 2 MHz frequency for 90 minutes after one of the events (December 30, 2020). Based on this survey, we conclude that our study was not significantly impacted by sporadic E propagation. This information and conclusion is described in text added at lines 311-318.
2. We have done as the referee suggests, but this comment is closely linked to comment 3 of referee 1; see below.3. We have re-run the analysis of the GNSS-TEC data using a 60-minute detrending window to complement the former analysis using a 30-minute window. A column has been added to Table 3 which now shows both results. In seven cases the change in detrending window makes a significant difference in the inferred horizontal phase velocity. This is discussed in the paper at lines 350-onward.
Based on these results, we have replaced and added significant discussion of the comparison between the two techniques at lines 359-375. The significant change is that we have altered the conclusions of the paper somewhat: a slight majority of the events studied show pretty good agreement by our criteria between horizontal phase velocities measured with GNSS-TEC versus those measured with AM Doppler sounding, and a slight minority of events show significant differences in either direction, magnitude, or both. We believe that the reason for these differences lies in the complexity of the wave environment a fair fraction of the time, which includes presence of multiple waves that can be detected with different efficiencies by the different methods.
Accordingly, we have changed wording in the conclusions at lines 611-617 and in the abstract at lines 18-19.
4. We have significantly re-worked Figure 8, changing the labels (and improving the font size in the process). We have also added a sentence to the figure caption.
5. We have done a more thorough literature search, finding more papers than we previously cited which address the seasonal dependence of mid-latitude nighttime MSTIDs using a range of techniques, including GNSS-TEC, in-situ satellite, and optical imaging as suggested by the referee. These papers, reviewed in text added at lines 539-555, establish a consistent and robust pattern of seasonal dependence which differs significantly with that discovered with the fully automated version of the AM Doppler technique. Discussion of this discrepancy follows in a paragraph added at lines 557-567.
Responses to the minor comments of Referee 1:
We have addressed all of the minor comments raised by Referee 1. Providing more information about the semi-automated tracking entails significantly enhanced longer text inserted at lines 179-187. Verifying geomagnetic conditions entails adding a column to Table 3 with the Kp index associated with each event, and added discussion at lines 449-455. We replaced reference to Fritts and Alexander (2003) with reference to a different review paper.
Citation: https://doi.org/10.5194/egusphere-2024-2383-AC1
-
AC1: 'Reply on RC1', James LaBelle, 03 Dec 2024
-
RC2: 'Comment on egusphere-2024-2383', Anonymous Referee #2, 29 Oct 2024
First off, I wish to apologize to the authors for a very late response.
This investigation presents a study using AM Doppler measurements from 5 stations in the northeast USA and extends the previous work done by Chilote et al., 2015. The methodology that is more general than the more standard 3-station configuration for the velocity and direction of propagation estimates of TIDs. Three methods are applied, but methods following from a previous investigation by Chum et al., 2014 are shown in the tables, along with uncertainty estimates. The events are further compared with GNSS keograms to compare the direction of propagation from GNSS vs. this method using AM Doppler. While there is generally good agreement, there are two events which show significant differences. Some examination of the events versus auroral activity is also presented.
This techniques paper is fundamentally publishable, however after some significant clarifications and revisions. Since the purpose is to discuss some of the methods of estimation used, more work needs to be done in a few areas in particular before the paper will be acceptable for publication. The generalization of TID direction and speed using multiple midpoints is indeed an advancement in terms of the usual 3-point methods describe in many other TID publications. This paper also makes comparisons between HF methods and GNSS, which is a type of comparison that needs to happen more frequently, and to understand the limitations of either method.
Major issues:
1. Three methods are used to estimate the TID velocity and direction. However, I had a very hard time understanding the sine method. I think a figure of some sort could go a long way towards describing what is written out in lines 205. It wasn't clear to me what you were doing here.
2. Why didn't you compare between the methods for TID estimation and present that in table 2? You sort of mention the methods, but only present findings from the Chum et al., 2014 method.Â
3. How were your uncertainties calculated as presented in Table 2? I didn't see anything in the paper regarding this point. The uncertainty estimates are also fairly sizable too. Why is that? In some cases it looks like the uncertainty is makes it really hard to know how fast the TID is actually propagating since the range is significant It is difficult to draw a conclusions from that.
4. I think a limitation of your investigation is that the baselines are fairly short. This should be discussed a little bit more in the text.Â
5. It wasn't clear to me but were there always days of large AE that corresponded to the LSTIDs? Or were there intervals when it was geomagnetically quiet, but you still saw LSTIDs?
Citation: https://doi.org/10.5194/egusphere-2024-2383-RC2 -
AC2: 'Reply on RC2', James LaBelle, 03 Dec 2024
The authors thank both referees for careful reading of the manuscript and helpful suggestions which have resulted in significant improvements of the paper, which we believe is now suitable for publication. Below find a detailed response to each point raised by each of the referees. One of the principal changes is modification of the conclusions somewhat regarding the comparison of horizontal phase velocities measured at the same times by the AM Doppler technique and the GNSS-TEC technique. The responses have also entailed adding many citations to the reference list.Â
Responses to the five enumerated comments of Referee 2:
1. We replaced the paragraph describing the "sine method" with a lengthier more more precise mathematical description at lines 224-240, along with an alteration to Figure 2.
2. We have added columns to Table 2 which give horizontal phase velocity direcions and magnitudes inferred from the triad and sine methods, to complement the values given previously for the slowness method. We have altered and added discussion of these results at lines 279-287.
3. We have modified the description of the uncertainty calculation at lines 260-264. As noted, the relative uncertainty values in the table are useful for comparing one phase velocity to another calculated with the slowness method, but they do not convey the absolute uncertainty of the measurement.
4. We added sentences at lines 134-137 justifying the choice of baselines in this experiment.
5. We have altered and added discussion of the auroral activity associated with the events at lines 449-455, including specifying which events were not associated with auroral activity indicated by AE index connected to the events via appropriate timing. We have added a column to Table 3 with the Kp index associated with each event.
Citation: https://doi.org/10.5194/egusphere-2024-2383-AC2
-
AC2: 'Reply on RC2', James LaBelle, 03 Dec 2024
Data sets
Replication data for: "Tracking Traveling Ionospheric Disturbances through Doppler-shifted AM Radio Signals" James LaBelle https://doi.org/10.7910/DVN/L3JXIH
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 145 | 96 | 14 | 255 | 2 | 3 |
- HTML: 145
- PDF: 96
- XML: 14
- Total: 255
- BibTeX: 2
- EndNote: 3
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1