Mesospheric airglow measurements of two or three layers were used
to characterize both vertical and horizontal parameters of gravity waves. The
data set was acquired coincidentally from a multi-channel filter (Multi-3)
photometer and an all-sky imager located at São João do Cariri
(7.4∘ S, 36.5∘ W) in the equatorial region from 2001 to
2007. Using a least-square fitting and wavelet analysis technique, the phase
and amplitude of each observed wave were determined, as well as the amplitude
growth. Using the dispersion relation of gravity waves, the vertical and
horizontal wavelengths were estimated and compared to the horizontal
wavelength obtained from the keogram analysis of the images observed by an
all-sky imager. The results show that both horizontal and vertical
wavelengths, obtained from the dispersion relation and keogram analysis,
agree very well for the waves observed on the nights of 14 October and
18 December 2006. The determined parameters showed that the observed wave on
the night of 18 December 2006 had a period of ∼43.8±2.19 min,
with the horizontal wavelength of 235.66±11.78 km having a downward
phase propagation, whereas that of 14 October 2006 propagated with a period
of ∼36.00±1.80 min with a horizontal wavelength of
∼195±9.80 km, and with an upward phase propagation. The
observation of a wave taken by a photometer and an all-sky imager allowed us
to conclude that the same wave could be observed by both instruments,
permitting the investigation of the two-dimensional wave parameter.
Atmospheric composition and structure (airglow and aurora) – electromagnetics (wave propagation) – history of geophysics (atmospheric sciences)Introduction
Propagation of atmospheric gravity waves in the upper atmosphere is extremely
unstable. The vertical component of the propagating gravity wave is a very
vital aspect in investigating the coupling dynamics between different regions
of the atmosphere . Due to the exponential decay
of density with altitude and conservation of energy, gravity wave amplitudes
increase exponentially with altitude, whereas dissipation processes like wave
saturation and wave interaction with other waves and background wind limit
the growth of the amplitude of the wave . Some
studies on gravity wave saturations revealed that the momentum is transferred
into the background wind, thereby depositing the wave energy into the
background atmosphere (e.g. ).
Measurements of gravity waves with periodicity in the mesosphere and lower
thermosphere (MLT) region require passive airglow observation of the sky in a
two-dimensional form with relatively high temporal resolution (in a few
minutes). Among several gravity wave observational techniques, such as radio
frequency and optical measurements, airglow observations using a photometer
and all-sky imagers have been effectively used
(). Airglow emissions are prominent physical
phenomena used to further study the vertical and horizontal parameters of
gravity waves. According to , the airglow
emission layers that have been extensively used to monitor wave activity in
the MLT region are OI5577 (hereafter OI), O2(0–1) band (hereafter O2),
NaD-line (hereafter NaD) and OH(6–2) band (hereafter OH) at their respective
peak emission altitudes of 97, 94, 90 and 87 km. Simultaneous
observation of multiple airglow emissions is one of the techniques used to
investigate the vertical propagation of gravity waves. For this technique to
be feasible, the vertical wavelengths of the wave must be larger than the
thickness of the airglow emission layer .
According to and , such
observational data can be used to compute the amplitude growth and the
propagation characteristics of gravity waves.
In the present study, we investigated gravity wave parameters propagating
vertically through OI, O2, NaD and OH emissions, their phase difference
and variability of the amplitudes of the oscillations. Using the dispersion
relation of gravity waves, the horizontal and vertical wavelengths are
estimated for the observed short period oscillations
. The discussion will be focused on the similar
periodicity observed within the three emission layers; the amplitude growth
and the propagation direction.
Multi-channel airglow photometer (Multi-3) wavelength resolution and
sensitivity.
The instruments used for the present study are the multi-channel filter
photometer (Multi-3), the all-sky imager and the meteor radar at São João
do Cariri, located geographically at 7.4 ∘ S and
36.5∘ W. Among the listed instruments, the photometer is the main
instrument used in observing the vertical parameters of the waves of
interest, whereas the all-sky imager and the meteor radar were co-located
instruments used to observe the horizontal parameters and the wind velocity
respectively.
Photometer
A multi-channel tilting filter photometer (Multi-3) with five interference
filters was used to measure the OI, O2, NaD and OH mesospheric airglow
emissions. The observations were made between January 2001 and December 2007,
resulting in 1051 nights of clear sky. Out of 1051 nights, only 389 nights
present similar periods in at least two emission layers, of which 24 nights
present similar periods in three emission layers.
The background continuum intensity (R nm-1) and the line intensity (R) were measured in obtaining the zenith
sky spectrum by tilting the filters relative to their optical axes in which a
scan of about 8 nm wavelength was made. The mesospheric component of the
OI557.7 nm was estimated by subtracting the ionospheric F region component
computed as 20 % of the simultaneously observed OI630.0 nm intensity
. The time interval between the observation cycle
was approximately 2 min, thereby making the temporal resolution 2 min. The
photometer characteristics, spectral resolution and sensitivity, are
summarised in Table 1.
A MgO white screen illuminated by a laboratory standard lamp (Eppley 8315,
100 W Tungsten filament lamp) was used to calibrate the absolute sensitivity
(counts/Rayleigh) of the photometer. The estimated error in the absolute
intensity for OI was approximately 5 and 10 % for OH(6–2) and O2 due
to the increased systematic error in calibration. For rotational temperature
(TOH), the instrumental error determined was ±3 K
.
The usual observation scheme was undertaken with a period of 13 nights per
month focused around the time of new moon with more than 6 h of
uninterrupted observation time per night. In this work, a database of OI,
O2, NaD and OH was analysed to find the similar periodicities in the
propagating gravity waves in each emission altitude. More details on the
multi-channel filter photometer can be found in
, ,
and .
All-sky imager
An all-sky imager in São João do Cariri was used. Images of OH (Meinel),
OI5577, OI6300 and OI7774 airglow emission layers were taken by this
equipment. With regards to the present work, only the OH Meinel airglow image
corresponding to the selected coincident photometer observation was used.
The airglow all-sky imager is an optical instrument made of a fast fish-eye
(f/4) lens and a telecentric lens system, a filter wheel, a charged coupled
device (CCD) camera, and a set of lenses for reconstruction of the images on
the CCD. The entire system is microcomputer-based controlled. The CCD camera
has an area of 6.04 cm2, with a 1024 × 1024 back-illuminated
pixel array of 14 bits per pixel. In order to enhance the signal-to-noise
ratio, the images were binned on-chip down to a resolution of
512 × 512. The high quantum efficiency, low dark noise
(0.5 electrons pixel-1 s-1), low readout noise (15 electron rms) and high linearity
(0.05 %) of this device enable it to measure airglow emissions
(Medeiros et al., 2001). More details about the São João do Cariri
imager have been reported by .
Meteor radar
A SKiYMET all-sky interferometric meteor radar using an antenna array
composed of two-element reception yagi antennas and three-element
transmitting yagi antenna (five antennas) was used to observe winds in the
mesosphere. This radar operates at a frequency of 35.24 MHz with a maximum
output power of 12 kW. The radar measures the radial velocity by transmitted
radiation scattered from meteor trails and the differences in the phase of
the signal received by each possible pairing of antennas determines the
position of the trail. This radar also measures the temperature at the height
of the meteor peak count rates, but this parameter was not used in this work.
The range is obtained by the delay between the transmitted and received
signal. The least-square fitting technique applied to all the radial
velocities measured in a given time/height bin was used to determine the
zonal, meridional and vertical velocity components. Vertical velocities are
normally very small and are therefore ignored. The respective temporal and
vertical resolutions of this radar are typically 60 min and 2–3 km. More
details on the radar have been published elsewhere
().
(a) Lomb–Scargle periodogram and (b) wavelet
spectrogram for the airglow intensity on 14 October 2006. The blue line is
for the OH emission, the red line is for NaD emission and the black line is
for O2.
Methodology and data analysisPhotometer time series
The first step considered before processing the photometer time series data
was the background intensity variation. This variation gives the degree of
contaminants composed of artificial light sources, clouds or astronomical
lights. The time range with high contaminants is eliminated, which leads to
the reduction of the time duration of the observation period.
Secondly, high-frequency oscillations are removed by taking three-point
running means. Since gravity waves are modulated by tidal waves
(), the effects of
tides are eliminated by constructing a harmonics for ter-diurnal and
semi-diurnal tides. The harmonics (H) used is expressed mathematically by
H=A+Bcos(2π(x-ϕ)T)+Ccos(2π(x-ϕ)T),
where A, B and C are the unknown amplitude, x is the time of
observation, ϕ is the phase and T is the period. Subtracting the
harmonics from the average (smoothed) intensity, the residual (only gravity
waves) time series is obtained. The residual is then subjected to a
Lomb–Scargle periodogram and wavelet spectrogram to obtain the observed
gravity wave period. Using the least-square fitting method and the wavelet
spectrogram, the amplitude and the phase were estimated. The vertical phase
velocity (Vz) was then estimated from the quotient of the difference
between the higher and lower emission layers observed and their corresponding
phase, expressed by Eq. (2):
Vz=ΔdΔϕ.
Multiplying the period obtained by the vertical phase speed, the vertical
wavelength was obtained using Eq. (3).
λz=Vz×T
Using the intrinsic period, the horizontal wavelength was calculated by using
the dispersion relation for gravity waves ,
kH=[(m2+14H2)ωI2×(N2-ωI2)-1]12,
where m is the vertical wavenumber, H is the scale height, N is the
buoyancy frequency and ωI is the intrinsic frequency. By scale
analysis, the effect of the Coriolis parameter is ignored due to the period
of observation and the location of the observation site. From the horizontal
wavenumber, kH, the horizontal wavelength is estimated using Eq. (5),
λH=2πkH.
The intrinsic frequency, ωI, was estimated by finding the difference
between the vertical observed period obtained from Lomb–Scargle and the
estimated background wind frequency using Eq. (6).
ωI=ω0-UH⋅kH
where ωI is the intrinsic frequency, ω0 is the observed
frequency, UH is the velocity of the background wind and kH is the
horizontal wavenumber estimated from the horizontal wavelength obtained from
the keogram analysis.
(a) Same as Fig. 1a but for 18 December 2006.
The superposition of the 14 October 2006 residual wave and the
reconstructed wave with two harmonics.
The superposition of the 18 December 2006 residual wave and the
reconstructed wave with two harmonics.
All-sky image
The co-located all-sky images were analysed using the keogram analysis from
which the horizontal parameters of the same wave are obtained. The keogram
simply separates the image of the oscillation under study into meridional and
zonal components. The wave parameters are then obtained from the geometrical
relationship between the components. For this study we used the keogram
analysis to obtain the horizontal wave parameters such as the horizontal
wavelength, the period and the direction of propagation of the wave observed
by the photometer. Details on the methodology of the keogram analysis can be
found in , with more details in
. The co-located meteor radar is operated in a
routine base providing information on zonal and meridional wind velocities
which aided in the estimation of the intrinsic wave frequency.
Results and discussionAirglow photometer
Out of the 7 years of data used, we found two nights which present similar
periods of oscillations in the airglow emission layers in the photometer data
and images from the all-sky imager. Due to cloud contaminations, only 3 h of
observed data were used for the selected nights. On 14 October, observations
made between 21:00 and 23:00 local time (LT) were used in the present study,
whereas on 18 December, observations between 20:00 and 22:00 LT were used.
Similar periodic oscillations were found in the co-located airglow images and
the spectral characteristics of these oscillations were estimated and
studied.
The gravity wave period estimated using Lomb–Scargle on the night of
14 October 2006 in the O2, NaD and OH airglow emission layers presented
two major peaks with confidence levels greater than 95 %; Fig. 1a shows
the Lomb–Scargle periodogram; the first peak presented a period of
∼0.60±0.03 h (36±2.00 min) and
∼1.33±0.07 h (79.80±4.00 min) for the second peak.
To confirm the true presence of the second peak, we subjected this period to
the Horne and Baliunas test . According to the
Horne and Baliunas test, spectral leaked frequencies may have significant
height, which might appear as a true signal. The Horne and Baliunas test is
used to test the originality of the frequencies with lower power spectral
density (PSD). This was done by subtracting a sinusoid with frequency
corresponding to the most significant peak from the data
and recomputing the periodogram. If the second
peak (the so-called ghost frequency) still exists, it implies the second peak
is a true signal. The Horne and Baliunas test was done to verify the true
existence of the periodicities obtained in the Lomb–Scargle periodograms
(Fig. 1a) for the cases presented, but the test plots are not shown here.
Since the photometer data is almost evenly distributed, wavelet analysis
(as shown in Fig. 1b) of the same residual data
was applied to confirm the periods observed in the Lomb–Scargle analysis.
Comparing these two techniques, we affirm that the periods are true.
The estimated amplitude and phase of 14 October and 18 December 2006
observed waves.
14 Oct 2006 18 Dec 2006 Properties0.60 h period 1.33 h period Properties0.73 h period 1.33 h period EmissionAmp (R)Phase (h)Amp (R)Phase (h)EmissionAmp (R)Phase (h)Amp (R)Phase (h)layerslayersO29.37±0.480.79±0.046.98±0.350.29±0.10OI3.87±0.190.05±0.002.84±0.140.14±0.00NaD2.07±0.100.69±0.031.58±0.030.20±0.01O217.52±0.880.16±0.009.67±0.480.59±0.09OH29.78±1.490.63±0.0321.47±1.070.09±0.00OH21.11±1.060.37±0.0224.65±1.231.15±0.06
Similarly, Fig. 2a and b show the same analysis for the waves observed on
18 December 2006. It is noted that, for the OI and O2 emission layers, the
oscillation periods of ∼ 0.73 ± 0.04 (43.80 ± 2.20 min)
and ∼ 1.33 ± 0.10 h (79.80 ± 4.00 min) were obtained in
which the highest peak was ∼ 0.73 ± 0.04 h
(43.80 ± 2.20 min). On the other hand, the OH emission layer had the
highest peak at ∼ 1.33 ± 0.10 h (79.80 ± 4.00 min) and
the lowest at 0.73 ± 0.10 h. Due to this inversion, the
1.33 ± 0.10 h (79.80 ± 4.00 min) period dominated in the
wavelet spectrogram, as shown in Fig. 2b, whereas the 0.73 ± 0.10 h
period was not seen.
Upward phase propagation of the two harmonics of the 14 October 2006
observed wave.
In order to confirm the result estimated from the residual time, an
artificial wave was reconstructed using the amplitude, phase and observed
period as presented in Table 3 to evaluate the obtained result. To achieve
that, the reconstructed waves of two harmonics were overplotted on the
residual photometer data as shown in Figs. 3 and 4.
Downward phase propagation of the two harmonics of the
18 December 2006 observed wave.
Keogram of 14 October 2006.
Keogram 18 December 2006.
Results from keogram analysis for 14 October 2006.
Results from keogram analysis for 18 December 2006.
Vector diagram of the wave with respect to the background wind for
(a) 14 October 2006 and (b) 18 December 2006 observation.
The amplitude (Rayleigh), phase (hour) and observed period (hour) obtained
from the least-square fitting approach and Lomb–Scargle are shown in Table 2
for 14 October and 18 December 2006 observation, respectively.
Vertical propagation
From Table 2, we observed on the night of 14 October that O2 lags NaD by
∼0.10±0.00 h (6.20±0.00 min) with a vertical phase
velocity (Vz) of 38.71±,1.16 km h-1 (10.75±0.32 m s-1) and vertical wavelength (λz) of
23.22±0.67 km, whilst NaD also lags behind OH by ±0.05±0.00 h (3.05±0.09 min) with a vertical phase velocity
(Vz) of 59.04±1.77 km h-1 (16.40±0.49 m s-1)
and vertical wavelength (λz) of 35.42±1.06 km. Considering
the three emission layers, O2 lags behind OH by 0.15±0.01 h
(9.25±0.46 min) with a vertical phase velocity (Vz) of
45.41±1.36 km h-1 (12.60±0.38 m s-1) and
vertical wavelength (λz) of 27.24±0.82 km. Based on the
wave parameters obtained we plot the harmonic analysis of 14 October, which
is shown in Fig. 5. From Fig. 5, one can see that there is a tendency of
phase delay from OH to O2, indicating an upward phase propagation.
According to the gravity wave propagation theory, upward phase propagation
means downward energy propagation .
Summary of the 14 October and 18 December 2006 observed gravity wave
parameters.
Properties/date14 October 2006 18 December 2006 InstrumentPropertiesValuePropertiesValueMeteorZonal wind velocity-8.0 m s-1Zonal wind velocity-3.0 m s-1RadarMeridional wind velocity16.0 m s-1Meridional wind velocity50.0 m s-1Period (τ)36.00±2.00 minPeriod (τ)44.00±2.20 minPhotometerVertical phase velocity (Vz)12.60±0.38m s-1Vertical phase velocity (Vz)8.50±0.38 m s-1Vertical wavelength (λz)27.24±0.82 kmVertical wavelength (λz)22.31±1.00 kmEstimated usingIntrinsic period (τI)38±1.90 minIntrinsic period (τI)54.00±2.70 mintheVertical wavelength (λz)27.32±0.82 kmVertical wavelength (λz)22.13±,1.05 kmdispersion relationHorizontal wavelength (λH)195.93±9.80 kmHorizontal wavelength (λH)235.66±11.78 kmObserved period (τ)33.30±1.67 minObserved period (τ)43.90±2.20 minAll-sky imagerHorizontal phase speed (CH)93.00±4.65 m s-1Horizontal phase speed (CH)88.94.45 m s-1Horizontal wavelength (λH)185.80±9.30 kmHorizontal wavelength (λH)233.90±11.70 km
Considering only two emission layers, i.e. O2 and NaD, and NaD and OH, we
found the average of their sum for the phase velocities and vertical
wavelengths to be 48.88±1.47 km h-1
(13.57±0.41 m s-1) and 31.33±0.94 km respectively.
Comparing these with the values obtained from the direct three emission layer
estimation, it is noted that there is a slight difference between the
computed values. These differences can be attributed to the difference in the
assumed emission altitudes of the two layers and the background wind at that
layer. Statistically, the linear fitting of the altitude of the three
emission layers against their respective phase has a coefficient of
determination of 0.96.
Referring to Table 2 for 18 December 2006, it was revealed that, OI leads
O2 by ∼0.11±0.01 h (6.82±0.34 min) with a vertical
phase velocity (Vz) of 26.40±0.79 km h-1
(7.31±0.22 m s-1) and vertical wavelength (λz) of
19.36±0.77 km while O2 leads OH by ∼0.21±0.01 h
(4.27±0.21 min) with vertical phase velocity (Vz) of
32.78±1.31 km h-1 (9.10±0.36 m s-1) and
vertical wavelength (λz) of 23.93±1.00 km. Considering the
three emission layers; OI leads OH by ∼0.33±0.02 h
(19.63±0.98 min) with a vertical phase velocity (Vz) of
30.56±1.38 km h-1 (8.49±0.38 m s-1) and
vertical wavelength (λz) of 23.21±1.05 km. This shows that,
the wave is having an upward energy propagation (a downward phase
propagation). Thus, taking the average of the two emission layers, OI versus
O2, and O2 versus OH, we found that the phase velocity and vertical
wavelength were 29.59±1.33 km h-1
(8.22±0.37 m s-1) and 21.64±0.97 km respectively.
Comparing these with the values obtained from the three emission layers
direct estimation, slight variations between the values were noted. These
variations can be due to the assumed altitudes between the emission layers
and the background wind at that layer. Statistically, the linear fit of the
three emission layers (altitude against their corresponding phase) have a
coefficient of determination of 0.97. Figure 6 shows the downward phase
propagation of the 18 December 2006 observed wave.
Keogram analysis
Figures 7 and 8 are the OH NIR co-located keogram developed from the unwarped
images obtained from the all-sky imager of the same waves observed in the
photometer data on 14 October and 18 December 2006. The results of the
spectral analysis obtained are shown in Figs. 9 and 10.
For the case of 14 October 2006 (Fig. 9), the period of the horizontal
component of the wave is 0.55±0.03 h (33.30±1.70 min)
propagating at 334.80±16.74 km h-1
(93.00±7.30 m s-1) and having a horizontal wavelength of
185.80±10.09 km with an azimuthal angle of 64∘ suggesting
that, the horizontal component of the wave is northeastward.
Similarly, Fig. 10 shows the result from the all-sky image of
18 December 2006. The intrinsic period of the horizontal component of the
wave is 0.73±0.04 h (43.90±2.20 min) propagating at
88.90±6.90 m s-1 with a horizontal wavelength of
233.90±14.00 km moving at 65.8∘ from the azimuth and
showing that the wave on this day is propagating northeastward. To estimate
the influence of the background wind, coincident meridional and zonal wind
velocities were taken from the Meteor radar.
The coincident measurement of the horizontal component of the wave using the
all-sky imager and the background wind velocity from the Meteor radar jointly
gave the general insight about the interaction of the wave with the
background wind. The background wind velocity was smoothed by a 3 h running
average. Using the zonal and meridional wind velocities, the magnitude and
the direction of the winds were also estimated. With these two parameters,
the angle (β) that the wind made with the wave was found to be
89.6∘, indicating that the wind was moving northwestward. By using
the projection method of the dot product , the
intrinsic frequency obtained using Eq. (6) was found to be 2.74×10-3 s-1 (38.19 min) and the observed frequency to be 2.91×10-3 s-1 (33.30 min) for the case of 14 October 2006.
This value was confirmed using the inner product method, where the angle
(α=46.1∘), their respective wind velocity and wave numbers
were used in this estimation. The inner product method also yielded the same
result for the intrinsic frequency. From the dispersion relation for gravity
waves (Eq. 4), the estimated value for the horizontal wavelength
(λH) is 195.93±9.80 km.
For 18 December 2006, the angle (β) that the wind made with the wave
was found to be 69.2∘. By using the projection method of the dot
product, the intrinsic frequency was found to be 1.91×10-3 s-1 (54.00 min), whereas the observed frequency was 2.39×10-3 s-1 (43.90 min). Applying the same inner product
approach used earlier, we found that the angle (α) the wave made with
the azimuth was 24.2∘. This agreed with the estimated value
obtained using the projection method. Their respective wind and wave numbers
were used in this estimation. The inner product method also yielded the same
result for the intrinsic frequency. From the dispersion relation for gravity
waves, the estimated value for the horizontal wavelength is
235.66±11.78 km. The estimated values from our analysis for the two
cases are shown in Table 3.
Conclusions
The simultaneous observation of similar gravity wave periods within the three
airglow emission layers in the photometer data suggests a vertical
propagation of the same gravity wave. The observed waves propagated through
the emission altitudes OH (87 km), NaD (90 km) to O2 (94 km) for
the case of 14 October 2006, whereas that of 18 December 2006 propagated
through OH (87 km), O2 (94 km) to OI (97 km). From our
observation, the amplitude growth reflects theory and agrees reasonably with
previous observational works done (e.g. ).
Using the wind data from the meteor radar, the intrinsic frequency of the
vertical (either upward or downward) phase propagation was estimated using
Eq. (6). With the estimated intrinsic frequency, the horizontal wavelength
was estimated using the dispersion relation of gravity waves
and compared to the horizontal wavelength
obtained from the keogram analysis of the simultaneously observed OH images.
Both the analytical and numerical results of the horizontal wavelength agree
reasonably, hence suggesting that the same wave was observed by the
photometer and the all-sky imager. The observations of the same wave in both
instruments allow the investigation of the two-dimensional properties of the
waves.
From the case study on the night of 14 October and 18 December 2006, we
observed two different wave propagation modes, one had an upward phase
propagation while the other had a downward phase propagation. The latter is
well known as upward propagation of gravity wave .
However, the former can not be explained by the upward propagating gravity
waves. In order to further investigate the present case we have to know more
about the background atmosphere (wind and temperature, for example).
The data used to produce the results of this manuscript were obtained from the
Observatório de Luminescência Atmosférica da Paraíba at São João do Cariri, which is
supported by the Universidade Federal de Campina Grande and Instituto Nacional de
Pesquisas Espaciais. If someone would like to access these data, please contact either
Amauri F. Medeiros (afragoso@df.ufcg.edu.br) or Cristiano M. Wrasse
(cristiano.wrasse@inpe.br).
The authors declare that they have no conflict of
interest.
This article is part of the special issue “Space weather
connections to near-Earth space and the atmosphere”. It is a result of the
6∘ Simpósio Brasileiro de Geofísica Espacial e Aeronomia
(SBGEA), Jataí, Brazil, 26–30 September 2016.
Acknowledgements
This work has been supported by Coordeção de Aperfeiçoamento de
Pessoal de Nível Superior (CAPES) and Conselho Nacional de
Desenvolvimento Cinetífico e Tecnóligo (CNPq). Also we
acknowledge, Christopher Torrence of the National Snow and Ice Data Center,
CIRES, CU Boulder and Gilbert P. Compo of CIRES, University of Colorado &
Physical Sciences Division, NOAA ESRL Boulder, Colorado for their significant
contribution in their guidance to the Wavelet Analysis used in this work. Igo
Paulino thanks the CNPq for the grant with number 303511/2017-6. Finally, a
special thanks goes to both the reviewers and editor, who have tremendously
helped to improve this paper through their comments and constructive
criticism.
The topical editor, Christoph
Jacobi, thanks M. Sivakandan and one anonymous referee for help in evaluating
this paper.
ReferencesBuriti, R., Takahashi, H., and Gobbi, D.: First results from mesospheric
airglow observations at 7.5∘ S, Revista Brasileira de
Geofísica, 19, 169–176, 2001.Buriti, R., Takahashi, H., Gobbi, D., de Medeiros, A., Nepomuceno, A., and
Lima, L.: Semiannual oscillation of the mesospheric airglow at 7.4∘ S during the PSMOS observation period of 1998–2001,
J. Atmos. Sol.-Terr. Phy., 66, 567–572, 2004.Buriti, R. A., Hocking, W. K., Batista, P. P., Medeiros, A. F., and Clemesha,
B. R.: Observations of equatorial mesospheric winds over Cariri
(7.4∘ S) by a meteor radar and comparison with existing models, Ann.
Geophys., 26, 485–497, 10.5194/angeo-26-485-2008, 2008.
Dewan, E. and Good, R.: Saturation and the “universal” spectrum for
vertical
profiles of horizontal scalar winds in the atmosphere, J. Geophys.
Res.-Atmos., 91, 2742–2748, 1986.
Dray, T. and Manogue, C. A.: Journal of Online Mathematics and Its Applications
The Geometry of the Dot and Cross Products, 6, 1–13, 2006.
Ferraz-Mello, S.: Estimation of periods from unequally spaced observations,
Astron. J., 86, 619–624, 1981.
Figueiredo, C., Takahashi, H., Wrasse, C., Otsuka, Y., Shiokawa, K., and
Barros, D.: Medium scale traveling ionospheric disturbances observed by
detrended total electron content maps over BrazilMedium scale traveling
ionospheric disturbances observed by detrended total electron content maps
over Brazil, J. Geophys. Res.-Space, 123, 2215–2227, 2018.
Fritts, D. C.: Gravity wave saturation in the middle atmosphere: A review of
theory and observations, Rev. Geophys., 22, 275–308, 1984.
Fritts, D. C. and Alexander, M. J.: Gravity wave dynamics and effects in the
middle atmosphere, Rev. Geophys., 41, 1–64, 2003.Ghodpage, R., Taori, A., Patil, P., Gurubaran, S., Sharma, A., Nikte, S., and
Nade, D.: Airglow measurements of gravity wave propagation and damping over
Kolhapur (16.5∘ N, 74.2∘ E),
Int. J. Geophys., 2014, 1–9, 2014.
Gossard, E. and Hooke, W.: Waves in the Atmosphere, 456 pp., 1975.
Hecht, J., Walterscheid, R., Sivjee, G., Christensen, A., and Pranke, J.:
Observations of wave-driven fluctuations of OH nightglow emission from Sondre
Stromfjord, Greenland, J. Geophys. Res.-Space, 92,
6091–6099, 1987.
Hocking, W.: Dynamical coupling processes between the middle atmosphere and
lower ionosphere, J. Atmos. Terr. Phys., 58,
735–752, 1996.
Hocking, W.: Middle atmosphere dynamical studies at Resolute Bay over a full
representative year: Mean winds, tides, and special oscillations, Radio
Sci., 36, 1795–1822, 2001.
Horne, J. H. and Baliunas, S. L.: A prescription for period analysis of
unevenly sampled time series, Astrophys. J., 302, 757–763, 1986.
Kirchhoff, V.: Elementos básicos sobre fotômetros de filtro inclinável,
1984.Medeiros, A. F., Taylor M. J., Takahashi, H., Batista, P. P., and Gobbi, D.: An unusual airglow wave
event observed at Cachoeira Paulista 23∘ S, Adv. Space Res., 27, 1749–1754, 10.1016/S0273-1177(01)00317-9,
2001.Medeiros, A., Fechine, J., Buriti, R., Takahashi, H., Wrasse, C., and Gobbi,
D.: Response of OH, O2 and OI5577 airglow emissions to the mesospheric
bore in the equatorial region of Brazil, Adv. Space Res., 35,
1971–1975, 2005.
Nappo, C. J.: An introduction to atmospheric gravity waves, Academic Press,
2013.
Noxon, J.: Effect of internal gravity waves upon night airglow temperatures,
Geophys. Res. Lett., 5, 25–27, 1978.
Paulino, I., Takahashi, H., Medeiros, A., Wrasse, C., Buriti, R., Sobral, J.,
and Gobbi, D.: Mesospheric gravity waves and ionospheric plasma bubbles
observed during the COPEX campaign, J. Atmos.
Sol.-Terr. Phys., 73, 1575–1580, 2011.
Preusse, P., Eckermann, S. D., and Ern, M.: Transparency of the atmosphere to
short horizontal wavelength gravity waves, J. Geophys. Res.-Atmos., 113, 1–16, 2008.Silverman, S.: Night airglow phenomenology, Space Sci. Rev., 11,
341–379, 1970.
Smith, S. A., Fritts, D. C., and Vanzandt, T. E.: Evidence for a saturated
spectrum of atmospheric gravity waves, J. Atmos. Sci.,
44, 1404–1410, 1987.Takahashi, H., Sahai, Y., Batista, P. P., and Clemesha, B. R.: Atmospheric
gravity wave effect on the airglow O2 (0, 1) and OH (9, 4) band intensity
and temperature variations observed from a low latitude station, Adv.
Space Res., 12, 131–134, 1992.
Takahashi, H., Batista, P., Buriti, R., Gobbi, D., Nakamura, T., Tsuda, T., and
Fukao, S.: Simultaneous measurements of airglow oh emissionand meteor wind by
a scanning photometer and the muradar, J. Atmos.
Sol.-Terr. Phys., 60, 1649–1668, 1998.
Takahashi, H., Batista, P., Buriti, R., Gobbi, D., Nakamura, T., Tsuda, T., and
Fukao, S.: Response of the airglow OH emission, temperature and mesopause
wind to the atmospheric wave propagation over Shigaraki, Japan, Earth
Planet. Space, 51, 863–875, 1999.Takahashi, H., Onohara, A., Shiokawa, K., Vargas, F., and Gobbi, D.:
Atmospheric wave induced O2 and OH airglow intensity variations: effect of
vertical wavelength and damping, Ann. Geophys., 29, 631–637,
10.5194/angeo-29-631-2011, 2011.
Taori, A. and Kamalakar, V.: Airglow measurements of wave damping at upper
mesospheric altitudes over a low latitude station in India, Indian Journal of Radio and Space Physics (IJRSP), 42, 371–379, 2013.Taori, A. and Taylor, M.: Characteristics of wave induced oscillations in
mesospheric O2 emission intensity and temperatures, Geophys. Res.
Lett., 33, 1–5, 2006.Taori, A., Taylor, M. J., and Franke, S.: Terdiurnal wave signatures in the
upper mesospheric temperature and their association with the wind fields at
low latitudes (20∘ N), J. Geophys. Res.-Atmos., 110, 1–12,
2005.Taori, A., Guharay, A., and Taylor, M. J.: On the use of simultaneous
measurements of OH and O2 emissions to investigate wave growth and
dissipation, Ann. Geophys., 25, 639–643,
10.5194/angeo-25-639-2007, 2007.
Taylor, M. J., Espy, P., Baker, D., Sica, R., Neal, P., and Pendleton Jr, W.:
Simultaneous intensity, temperature and imaging measurements of short period
wave structure in the OH nightglow emission, Planet. Space Sci., 39,
1171–1188, 1991.Taylor, M. J., Pautet, P.-D., Medeiros, A. F., Buriti, R., Fechine, J.,
Fritts, D. C., Vadas, S. L., Takahashi, H., and São Sabbas, F. T.:
Characteristics of mesospheric gravity waves near the magnetic equator,
Brazil, during the SpreadFEx campaign, Ann. Geophys., 27, 461–472,
10.5194/angeo-27-461-2009, 2009.
Torrence, C. and Compo, G. P.: A practical guide to wavelet analysis, B. Am.
Meteorol. Soc., 79, 61–78, 1998.
Vadas, S. L. and Liu, H.: Generation of
large-scale gravity waves and
neutral winds in the thermosphere from the dissipation of convectively
generated gravity waves, J. Geophys. Res.-Space, 114, 1–25,
2009.
Wrasse, C. M., Takahashi, H., and Gobbi, D.: Comparison of the OH(8–3) and
(6–2) band rotational temperature of the mesospheric airglow emissions,
Revista Brasileira de Geofísica, 22, 223–231, 2004.