the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Calibrating estimates of ionospheric long-term change
Christopher John Scott
Matthew N. Wild
Luke Anthony Barnard
Bingkun Yu
Tatsuhiro Yokoyama
Michael Lockwood
Cathryn Mitchel
John Coxon
Andrew Kavanagh
Abstract. Long-term change in the height of the ionospheric F2 layer, hmF2, is predicted to result from increased levels of tropospheric greenhouse gases. Sufficiently long sequences of ionospheric data exist to investigate this long-term change, recorded by a global network of ionosondes. However, direct measurements of ionospheric layer height with these instruments is not possible. As a result, most estimates of hmF2 rely on empirical formulae based on parameters routinely scaled from ionograms. Estimates of trends in hmF2 using these formulae show no global consensus. We present an analysis in which data from the Japanese ionosonde station at Kokubunji were used to estimate monthly median values of hmF2 using an empirical formula. These were then compared with direct measurements of the F2 layer height determined from Incoherent Scatter measurements made at the Shigaraki MU observatory, Japan. Our results reveal that the formula introduces diurnal, seasonal and long-term biases in the estimates of hmF2 of ≈ ±10 % (±25 km an altitude of 250 km). These can be explained by the presence of underlying F1 layer ionisation not accounted for in the formula. We demonstrate, that for Kokobunji, the ratio of F2/F1 peak electron concentrations is strongly controlled by changes in geomagnetic activity represented by the am index. Changes in thermospheric composition in response to geomagnetic activity have been shown to be highly localised. We conclude that localised changes in thermospheric composition modulate the F2/F1 peak ratio, leading to differences in hmF2 trends. We further conclude that the influence of thermospheric composition on the underlying ionosphere needs to be accounted for in these empirical formulae if they are to be applied to studies of long-term ionospheric change.
- Preprint
(1190 KB) - Metadata XML
- BibTeX
- EndNote
Christopher John Scott et al.
Status: open (until 21 Dec 2023)
-
CC1: 'Comment on egusphere-2023-2599', Claudia Borries, 01 Dec 2023
reply
This manuscript written by C. Scott et al. addresses the limitations of using the height of the F2-layer maximum electron density (hmF2), which is a derived quantity from ionosonde data, for studying long-term changes in the ionosphere. This is an important topic because there have been already many publications using hmF2 for long-term studies and this work helps evaluating these results and using hmF2 more careful in future. From my point of view the manuscript is written excellently. It contains a very good overview of the state of the art at the beginning and the applied analysis and presentation of the results is adequate and well understandable. The authors detect a relation between the occurrence and strength of the F1 layer and the accuracy of the hmF2 layer (derived with one of the common approaches), which has not been described before. The results are discussed with respect to numerous related studies and the conclusions are logically derived from the results. The manuscript also contains some relevant results and discussions on the potential impact of climate change on the ionosphere. I evaluate the manuscript very good and I have some questions and remarks which may be considered before publication.
Questions and remarks:
- Section 3.5 provides corrections for the time delay in the ISR data. Why has this correction not been applied earlier in the study?
- line 482: Geomagnetic activity correlates to Joule heating driven by solar wind. How do the authors evaluate the potential that changes in thermosphere due to greenhouse effects may affect the magnitude of geomagnetic activity?
- The authors use the ratio of foF2 and F10.7 as a composition proxy and refer to Wright and Conkright (2001). Such a proxy sounds very favourable, but reading Wright and Conkright (2001) I cannot see a justification that the ration of foF2 and F10.7 is a proxy for thermosphere composition. Wright and Conkright (2001) worked with a sunrise extrapolation index SRCC, which is related indirectly to foF2. Wright and Conkright (2001) correlate the ratio log(SRCC/F10.7) with log(O/N2) and find a rather moderate correlation. The authors describe in their conclusion that they intended to provide a composition index, but the morphology of the proposed one differs from that of [O/N2]. If the ratio [foF2/10.7] is used by Scott et al. as a proxy for thermosphere composition, they need to provide better justification.
Minor issues
- line 75 “Data from a such …”
- lines 92 and 96 error in citing
- line 243 “… function of The Earth …”
- line 296 “In the ionosphere, While the …”
- line 371 “… in to the …”
- line 389 “… formulae tends introduces …”
- line 413 “(\pm 25 km at 250)”. Add “km altitude” after the 250
- line 416: Using am index is very reasonable. However, since it is not yet very popular to use, I recommend adding some justification, why this is used instead of the more frequently used kp/ ap indices.
- line 417: “… between the two, …” it is not immediately clear what are the two parameters that are correlated. Accordingly, it is not clear for the correlation values in lines 423 and 426, too.
- line 430: What is meant with “longitude sector near to the geomagnetic pole (\approx 48-50N)”? How can a longitude sector be close to the pole and why does it have latitude (north) coordinates?
- line 438: I get confused with the description. Chilton does not have a semiannual variation in foF2?
- line 438-439 “such as is seen”: Where is it seen? Is there a figure or paper?
- line 437: What means far enough away? Does it just need to be outside the auroral oval or even further away?
- line 440 “at these stations”: here the two station are addressed and in the second part of the sentence only Chilton. This is confusing.
Citation: https://doi.org/10.5194/egusphere-2023-2599-CC1
Christopher John Scott et al.
Christopher John Scott et al.
Viewed
HTML | XML | Total | BibTeX | EndNote | |
---|---|---|---|---|---|
50 | 17 | 5 | 72 | 1 | 3 |
- HTML: 50
- PDF: 17
- XML: 5
- Total: 72
- BibTeX: 1
- EndNote: 3
Viewed (geographical distribution)
Country | # | Views | % |
---|
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
- 1