the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Jul 2023
Comparison of meteor radar and TIDI winds in the Brazilian equatorial region
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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RC1: 'Comment on angeo-2023-23', Anonymous Referee #1, 18 Aug 2023
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 -
AC1: 'Reply on RC1', Ana Roberta Paulino, 20 Dec 2023
Referee: 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
Authors: We appreciate the time which was dedicated to revise our
manuscripts and the important contributions pointed out by the Referee
#1.
Referee: 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.
Authors: The referee is right! We are revising this part of the
manuscript. We are analysing other periods comparing the
measurements, which will allow us to improve our interpretations. In
the revised version of the manuscript we will revise carefully this
point considering the contribution of the Referee.
Referee: 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.
Authors: The referee is correct! It is a composite day plot of the
hourly mean winds. We have revised this part of the manuscript. The
main discrepancies between Figures 2 and 3 is that: for the satellite
measurement we have, on average four passages of the satellite during
a day, which is not sun synchronous and along the two months can cover
a day, while the meteor radar presents data every hour. We can not
directly determine gravity waves from the measurements in Figures 3
and 5. What we meant was that, the meteor radar averages out the
effect of the gravity waves while the satellite measurements present
more variability. We have revised the statements on these statements.
Thank you for these contributions.
Referee: 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.
Authors: It is a good suggestion from the Referee and we can implement
it for the revised version. However, it is important to have in mind
that there are only a few soundings of the satellites during the day.
In the revised version, we will consider this suggestion and improve
the Discussion based on it. Additionally, we can provide a spectral
analysis to show the AO and SAO and test them statistically, as
suggested.
Referee: 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.
Authors: We hope that the previous suggestions of the Referee #1 can
help us to improve our discussion. Unfortunately, there are few
publications on this topic to support our interpretations.
Referee: 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.
Authors: We agree with the main concerns from Referee #1 and
certainly, after the revision, the referee will be more comfortable to
recommend our paper for publication.
Referee: 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:
Authors: Thank you for the contribution reading carefully the
statements and suggestion improvements. We have revised all statements
according to the recommendations.Citation: https://doi.org/10.5194/angeo-2023-23-AC1
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RC2: 'Comment on angeo-2023-23', Anonymous Referee #2, 06 Nov 2023
This manuscript presents a comparison between mesospheric winds obtained by a meteor radar located in north east Brazil (Sao Joao do Cariri), and the TIDI instrument onboard the TIMED satellite. The authors looked at almost coincident measurements, but also longer term observations. While the coincident measurements show a large variability and significant differences (even between 2 consecutive TIDI values), monthly averages and large-scale oscillations such as SAO, are in some kind of agreement.
This paper is correctly written and but there is nothing really new at this stage. Similar comparisons have been done between radar wind measurements and satellite observations, as mentioned in the text (Xu et al., 2009, John et al., 2011, Su et al., 2014).Main comments:
- Is it possible to have a map showing the coverage of both instruments (and at two times for TIDI), especially for Figure 1? There is a large discrepancy between two consecutive TIDI measurements, so it would be interesting to see if these measurements were made over mostly different regions.
- According to what you wrote (l. 72-74), because of the ways the two instruments work and what regions of the atmosphere they measure, it seems unlikely coincident measurements will be similar, so I'm not sure this part of the investigation is meaningful.
- l. 107: how many satellite soundings were used to plot the monthly mean winds? Did you use a threshold to limit the small sampling effect? Maybe you should.
- For Figure 6, you could have used the meteor data closest to the TIDI measurements instead of at 12 UT every day, especially considering the short-term variability in TIDI values, and the effects of tides on the winds.
- l. 135: why should you consider that the measurements follow a Gaussian distribution? Instead, could you fit AO and SAO oscillations to both curves. It would be easier to compare them.
- l. 150: not sure TIDI is reliable to study short scale GW if there is so much variability in 3 min (Figure 1).
Minor edits:
l. 5-6: ...which have a vertical resolution of 2.5 km, starting...
l. 9-10: While TIDI...
l. 13: for both techniques
l. 18: remove "of the atmosphere"
l. 26: others
l. 29: oscillations
l. 32: hand, satellite measurements
l. 40: a meteor radar
l. 47: to the ground
l. 54: wind components
l. 59: TIDI...using airglow emissions as...
l. 60: airglow emissions. It has a...
l. 62: there are vertical...
l. 73: ... hand, TIDI...
l. 83-84: remove "in the MLT"
l. 85: their interaction with...
l. 87: ratio
l. 88: TIDI
l. 89-90: can you clarify this sentence?
l. 98: upper levels
l. 101-102: TIDI
l. 102: within 60 days
l. 105: presented well-defined oscillations
l. 106-107: oscillations during the day could modulate the observed diurnal tide phase.
l. 111: smaller
l. 113: as Figure 3.
l. 114: zonal winds are larger than the meteor radar ones...period
l. 115: favorably
l. 119: remove "in the wind"
l. 120: origined
l. 127: during 2006
l. 131: Even though... presented
l. 134: oscillations
l. 135: Figures 6 and 7 obey...
l. 137: close to each other
l. 138: the values of the two measurements... close, could obey...
l. 148: TIDI
l. 155: smoother
l. 159: studies long term dynamics in the MLT.Figure 1: switch the times (14:13 and 14:17) so they are chronological. Caption: ... winds measured...
Figure 4: usingCitation: https://doi.org/10.5194/angeo-2023-23-RC2 -
AC2: 'Reply on RC2', Ana Roberta Paulino, 20 Dec 2023
Referee: This manuscript presents a comparison between mesospheric
winds obtained by a meteor radar located in north east Brazil (Sao
Joao do Cariri), and the TIDI instrument onboard the TIMED satellite.
The authors looked at almost coincident measurements, but also longer
term observations. While the coincident measurements show a large
variability and significant differences (even between 2 consecutive
TIDI values), monthly averages and large-scale oscillations such as
SAO, are in some kind of agreement. This paper is correctly written
and but there is nothing really new at this stage. Similar comparisons
have been done between radar wind measurements and satellite
observations, as mentioned in the text (Xu et al., 2009, John et al.,
2011, Su et al., 2014).
Authors: Thank you for your time revising our manuscript and for the
important contributions suggested for our manuscripts. Even
considering the previous studies on this topic comparing these kinds
of observations, we have pointed out unique aspects and our
conclusions are important to understanding the variability of the
horizontal wind in the equatorial region. We are going to implement
all suggestions from Referee #2 in order to improve the quality of the
presentation of the manuscript and the interpretations.
Referee: Is it possible to have a map showing the coverage of both
instruments (and at two times for TIDI), especially for Figure 1?
There is a large discrepancy between two consecutive TIDI
measurements, so it would be interesting to see if these measurements
were made over mostly different regions.
Authors: Yes, it is. We are going to add an extra Figure in the
revised version showing the coverage of both instruments. Regarding
the comparisons of Figure 1, we are going to improve it including
further analysis and improving the interpretation as suggested by the
Referee #1 as well.
Referee: According to what you wrote (l. 72-74), because of the ways
the two instruments work and what regions of the atmosphere they
measure, it seems unlikely coincident measurements will be similar, so
I'm not sure this part of the investigation is meaningful.
Authors: Yes, we agree, however, the importance of this comparison is
to show that the horizontal wind has a large short time variability.
Referee: l. 107: how many satellite soundings were used to plot the
monthly mean winds? Did you use a threshold to limit the small
sampling effect? Maybe you should.
Authors: At least two measurements within an hour interval. There was
no threshold, blank spaces represent intervals without measurements.
We need to have in mind that the satellite crosses the São João do
Cariri area only one or two times in a day and the measurements are
not sun synchronous.
Referee: For Figure 6, you could have used the meteor data closest to
the TIDI measurements instead of at 12 UT every day, especially
considering the short-term variability in TIDI values, and the effects
of tides on the winds.
Authors: Thank you for the suggestion! Yes, we can do that or use a
daily average as suggested by the Referee #1. We are performing some
tests and in the final version, we are going to present this Figure
improved.
Referee: l. 135: why should you consider that the measurements follow
a Gaussian distribution? Instead, could you fit AO and SAO
oscillations to both curves. It would be easier to compare them.
Authors: Thank you for the suggestion, which is in agreement with the
suggestion of Referee #1 as well. We are going to do that in the
revised version of the manuscript.
Referee: l. 150: not sure TIDI is reliable to study short scale GW if
there is so much variability in 3 min (Figure 1).
Authors: We think the statement was not clear enough. We meant that it
is important to support studies involving gravity waves, for example
to evaluate refraction, reflection and absorption of gravity waves. We
are going to revise this statement.
Referee: Minor edits...
Authors: We appreciate all minor suggestions and in the revised
version, all of them will be fixed.Citation: https://doi.org/10.5194/angeo-2023-23-AC2
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AC2: 'Reply on RC2', Ana Roberta Paulino, 20 Dec 2023
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