the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Comparison of meteor radar and TIDI winds in the Brazilian equatorial region
Delis Otildes Rodrigues
Igo Paulino
Lourivaldo Mota Lima
Ricardo Arlen Buriti
Paulo Prado Batista
Aaron Ridley
Abstract. Using data collected from a meteor radar deployed at São João do Cariri (7.4°, 36.5° S) and the TIMED Doppler Interferometer (TIDI) on board the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite for 2006, comparisons of the horizontal winds (meridional and zonal components) were made in order to evaluate these techniques for scientific investigation and pointed out advantages of each instrument. A grid of ± 5 degrees of latitude and longitude centered at São João do Cariri was used to calculate the mean winds from the TIDI, which have a resolution of 2.5 km altitude starting from 82.5 km up to 102 km altitude. Otherwise, the meteor radar computes the winds for 7 layers of 4 km thickness overlapping 0.5 km above and below, which produces layers spaced by 3 km from 81 to 99 km altitude. When almost simultaneous measurements were compared, substantial discrepancies were observed in the vertical wind profiles. It happened because the meteor radar uses one hour bin size to estimate the wind from the echoes detected in the whole sky. While the TIDI measures instantaneous winds from the airglow emissions. In contrast, when the longer period of observation was taken into account, the meteor radar daily winds, averaged within a time interval of one month, were smoothed and showed more clearly the characteristics of the propagation of tides. The responses of the horizontal wind to the intraseasonal, semiannual and annual oscillations were satisfactory for the both techniques.
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Ana Roberta Paulino et al.
Status: open (until 03 Nov 2023)
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RC1: 'Comment on angeo-2023-23', Anonymous Referee #1, 18 Aug 2023
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This paper aims at investigating the horizontal (zonal and meridional) wind velocity at about 80-100 km altitude observed with the meteor radar at Sao Joao dos Cariri, Brazil and TIDI on board the TIMED satellite. I appreciate the devoted efforts by the authors to investigate characteristics of both ground-based radar and satellite measurements of the wind velocity in the mesosphere and lower thermosphere (MLT) region, where not so many effective wind velocity observations are available. However, I have major concerns regarding the statistical treatments on the comparison of the wind velocity data between the two techniques, as well as description and interpretation of the analyzed results.
The authors carried out three types of comparisons, which are (a) snap-shot profiles on a specific day (15 March 2006), (b) monthly mean of hourly wind velocity, and (c) day-to-day variations of wind velocity at 12 UT for one full year in 2006.
- Regarding (a), discrepancies between the meteor radar and TIDI are discussed, attributing to the difference in the field of view, the integration time of each measurement and the effects of gravity waves. However, I particularly do not agree that gravity waves significantly change the wave structure within four minutes, which are as short as the buoyancy period, but spatial separation between the two TIDI profiles may explain the discrepancy. Please show the horizontal extent of the meteor radar illuminating area and the locations of the TIDI measurements. In any case, single snap-shot is not enough to draw a conclusive remark. As the authors stated on Line 78, comparisons should be repeated for more cases.
- For the comparison (b), it is explained as the “daily mean wind”, but the figures seem to show the (local) time variations of the hourly wind velocity averaged over one month. Figure 2 with the meteor radar clearly shows the behavior of the diurnal and semidiurnal tides. On the other hand, Fig. 3 with TIDI includes irregular variations. Are the number of data comparable between the two determinations? I suspect Fig. 3 does not sufficiently smear out the waves other than tides, such as gravity waves, equatorial waves and so on, which are not synchronous to the local time. The same comments apply to Figs. 4 and 5.
- The day-to-day variations of the wind velocity at 12 UT are shown in Figs. 6 and 7 at 90 km in year 2006. Because the one hour data at 12 UT is crucially affected by tides as recognized in Figs. 2 and 4, it does not represent the daily mean wind velocity. Instead, the wind velocity averaged throughout one full day should be used. Although the variations are explained in term of AO (annual oscillation), SAO (semiannual oscillation) and intra-seasonal oscillations, I do not clearly recognize signals of AO, SAO and others. At least, a harmonic analysis should be applied to identify AO and SAO. Statistical comparison over one full year, assuming the Gaussian distribution, may not be enough to show consistency between the two techniques. Day-to-day variations of the wind velocity and the decomposed AO and SAO signals should be statistically tested.
Overall, description and interpretation of the results are not fully convincing. Although the authors referred to earlier studies on related subjects, little discussions are given on agreement, discrepancy and progress compared to these published results.
I hope this study will be considerably improved, provided the authors revise the data analysis procedures and investigation of the results. However, I am sorry for not becoming positive to recommend publication of this manuscript in Annales Geophysicae.
I am afraid I do not clearly understand some statements. I would like to recommend the manuscript be fully refined considering the specific comments listed below:
L 9: “vertical wind profiles” is misleading.
L 16: Are “the acoustic waves” recognized evident in the MLT region?
L 25-26: “satellite measurement of wind” and “using wind measurements” are redundant. In addition, “wind” should be reworded as “wind velocity” everywhere.
L 44: Is “transceiver” commonly used to explain configuration of a radar?
L 48: Why is the meteor echo rate so variable between 1,000 and 3,000? I am also interested in the local time dependence of the meteor echo rate.
L 49-: Description of a meteor radar system could be refined.
L 53: Does “mean wind” indicate the determination of the horizontal wind velocity in 4 km x 1 hour? How many meteor echoes in each bin?
L 62: Does “vertical measurement” mean “measurement of a vertical (height) profile”? Please refine the sentence.
Figure 1 and L 76-77, L79-80: Comparison of snap-shot profiles is not enough to derive the conclusive statements. If comparisons for more cases are expected to show a better agreement, please extend the analysis, and show the results.
L 80-84: I am curious why the ducting of gravity waves is explained in detail. Are their effects important in discussing the comparisons?
L 88: Why is TIDI advantageous to estimate Ri?
L 89-90: I simply do not understand this statement.
L 92: “climatological” is not an appropriate wording, as just one year data is analyzed.
Figure 2 and L 94: Fig. 2 does not seem to show “daily mean winds”, but the local time (diurnal) variations of hourly wind velocity averaged over one month.
Figure 2 and L 99: Because large amount of the meteor radar data is averaged, short period waves are smeared out, which do not synchronize with local time. Such averaging is not completely achieved for TIDI, so that irregular patterns appear in Fig. 3. Thus, the discrepancy is simply attributed to the amount of available data for TIDI, right? Please show the number of TIDI data used for comparisons.
L 105-106: How does “mask the vertical propagation of tides” mean? Are the small ooscillations (gravity waves) interacting with tides? Or, do they just visually overwrite the regular progression pattern of tides? Why can the “short period structures” be captured after averaging over 60 days, which do not seem to synchronize with local time?
L 108-109: I do not understand this statement. Is the accuracy of TIDI dependent of latitudes?
Figures 4 and 5: The same concerns as in Figs. 2 and 3.
L 119-120: What is the “noise” of TIDI?
Figures 6 and 7: If the long-term variations, such as AO and SAO, are the target, daily mean wind is appropriate, rather than one hour data at 12 UT.
Figure 6 and L 130: I do not clearly see AO with maximum in summer. How are the intra-seasonal oscillations detected?
L 131: “even the zonal wind” Is the zonal wind shown in Fig. 6? Am I missing anything?
Table 1: The Gaussian distribution over one full year is not very useful. Day-to-day variations of the wind velocity and the AO and SAO signals should be statistically tested.
Section 4: Reviewing descriptions and explanations in Section 3, I am afraid I am not convinced with the concluding statements in this section.
More appropriate references could be cited on earlier studies about the atmosphere dynamics and the measurement techniques. Some of self-citations to the author’s group do not seem inevitable.
Citation: https://doi.org/10.5194/angeo-2023-23-RC1
Ana Roberta Paulino et al.
Ana Roberta Paulino et al.
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