the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Characteristic Analysis of the Differences between TEC Values in GIM Grids
Jiaru Zhu
Abstract. Using total electron content (TEC) from global ionosphere map (GIM) for ionospheric delay correction is a common method of eliminating ionospheric errors in satellite navigation and positioning. On this basis, the TEC of puncture point can be obtained by GIM grid TEC interpolation. However, in terms of grid, only few studies have analyzed the TEC value size characteristics of its four grid points, that is, the TEC difference characteristics among them. In view of this, by utilizing the GIM data from high solar activity years (2014) and low solar activity years (2021) provided by CODE, this paper proposes the grid TEC difference to analyze TEC variation characteristics within the grid, which is conducive to exploring and analyzing the variation characteristics of the ionosphere TEC in the single-station area. The results show that the TEC difference size within GIM grid is mainly related to the activity of ionosphere. The value is larger in high solar activity years and generally small in low solar activity years, and the value of high latitude area is always smaller than that of low latitude area. Specifically, in high solar activity years, most of the GIM grid TEC internal differences are within 4TECu in high and mid latitude regions, while only 78.17 % in low latitude regions; the grid TEC differences at 2-hour intervals are more scattered, and larger values occur in low latitude regions. In low solar activity years, the TEC difference values within GIM grid are mostly less than 2TECu, and most of them in the high and middle latitudes are within 1TECu. The GIM grid TEC difference values within 1-hour intervals are mostly less than 4TECu, and most of them in the high and middle latitudes are within 2TECu. The main finding of this analysis is that the grid TEC differences are small for most GIM grids, especially in the mid-high latitudes of low solar years. This means that relevant extraction methods and processes can be simplified when TEC within these GIM grids is needed.
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Qisheng Wang and Jiaru Zhu
Status: final response (author comments only)
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RC1: 'Comment on angeo-2023-25', Anonymous Referee #1, 13 Aug 2023
This work is very interesting and deals with something that many of us do not take into account when estimating variables which are obtained from an interpolation of nearby points. So, I consider it can be accepted for publication in this journal, but after additional analysis.
In my understanding, the authors aim to quantify the interpolation error when estimating the value of TEC at a point on the map based on the four nearest values from the GIM grid, and also when we analyze variation in time. The topic is interesting, but the conclusions they reach, which I think should be expected based on the well known spatial and time TEC variation, are not well interpreted. This could be done using the TEC data itself. I would expect, for example, a comparison of the variability of differences between the values of the grid points, with the actual TEC values themselves.
In the case of the time variability analysis, in general, it can be expected that a parameter of a variable would be larger if the variable itself is larger. Therefore, given that TEC values are higher during high solar activity, I would logically expect that the temporal variation between consecutive times would also be greater, for example.
When analyzing the latitude variation of the difference between grid points in a gird, the peaks in Figure 4 are similar to the peaks of the Equatorial Ionization Anomaly of the F2 region, which are also the region of greatest TEC spatial gradient. This could be checked by doing a plot of TEC in terms of latitude and longitude. That is a map. So, if this is the case this would be an explanation for greater difference in consecutive grid points.
The peaks shown in Figure 6 occur in equinox, which may be due to equinoctial maximum in TEC annual variation. This can be checked from the TEC values from where this figure was obtained also.
The paragraph explaining Table 1 I consider it is obvious, and can be deduced from just seeing a TEC map in terms of longitude and latitude (a map, again). The high values are logical at equatorial and low latitudes, since in this region foF2 and TEC present the larger latitudinal gradients due to the Equatorial Ionization Anomaly. Also it is the region with most ionization disturbances. (I mention this same argument in a previous paragraph regarding Figure 4). May be I am wrong with this reasoning, but the authors can perfectly check this, and probably argue another reason for the behavior observed.
High latitudes, close to the auroral zones, can also be regions with large ionization disturbances, but for a different reason. Here we have energetic particle fluxes that cause ionization perturbations.
The paragraph explaining Table 2 results (line 175-180), in my opinion is quite expected also. Low solar activity level implies low TEC value, and probably lower differences in absolute values (assuming the same pattern of variation along the solar cycle).
In summary, I think that the behavior you observe in the variation of grid points (in space and time) are marked by the TEC variation in space and time. Greater TEC values implies greater time variation in grid points. And greater TEC values' spatial gradient (as it occurs in low and equatorial latitudes) implies greater differences between grid points in a given grid.
I suggest the authors to verify if this is the case.
Minor comments.
Line 79: "It can be seen that It can be seen that the puncture points ..." delete one "It can be seen. That is should be "It can be seen that the puncture points ..."
Line 141: I think that "Like Figure 5, ..." should be "Like Figure 4, ..."
In line 142, you mention "... which is different from Figure 3." I think you wanted to say Figure 4. Since Figure 3 shows F10.7 variability.
In line 152: " This trend is the same as the trend of F10.7 in 2014 in Figure 1.". You probably mean " This trend is the same as the trend of F10.7 in 2014 in Figure 3." Please check.
Line 165: I think that "... depicted in Figure 5." should be "... depicted in Figure 7." Please check.
Citation: https://doi.org/10.5194/angeo-2023-25-RC1 -
AC1: 'Reply on RC1', Qisheng Wang, 01 Sep 2023
The comment was uploaded in the form of a supplement: https://angeo.copernicus.org/preprints/angeo-2023-25/angeo-2023-25-AC1-supplement.pdf
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AC1: 'Reply on RC1', Qisheng Wang, 01 Sep 2023
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RC2: 'Comment on angeo-2023-25', Anonymous Referee #2, 31 Aug 2023
This paper proposes the grid TEC difference to analyze TEC variation characteristics within the grid. This work is very interesting in my option. It can be accepted after appropriate revisions
Minor comments.
1. Â Â Some tables in the manuscript have obvious mistakes, such as Chinese words should be replaced with English words
2. Â Â There are errors in the reference of the figure in the analysis section., as like line 141-165. Please carefully check.
3. Â Â The format of the table needs to be adjusted to better display relevant data.
4. Â Â Some Figures is not clear, it is difficult to distinguish what each picture represents. Please check the manuscript carefully.
5.   In line 152, you mention" ……F10.7 in 2014 in Figure 1.". You probably mean " This trend is the same as the trend of F10.7 in 2014 in Figure 3." Please check.Citation: https://doi.org/10.5194/angeo-2023-25-RC2 -
AC2: 'Reply on RC2', Qisheng Wang, 01 Sep 2023
The comment was uploaded in the form of a supplement: https://angeo.copernicus.org/preprints/angeo-2023-25/angeo-2023-25-AC2-supplement.pdf
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AC2: 'Reply on RC2', Qisheng Wang, 01 Sep 2023
Qisheng Wang and Jiaru Zhu
Qisheng Wang and Jiaru Zhu
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