International Journal of Current Research and Review
Research Article
DOI: 10.7324/IJCRR.2018.1011
IJCRR
Section: General
Science
Sci. Journal
Impact Factor
4.016
ICV: 71.54
Stratosphere-mesosphere Coupling
Through Vertically Propagating
Gravity Waves During Mesospheric
Temperature Inversion (MTI): An
Evidence
G. Venkata Chalapathi1, S. Eswaraiah2*, M. Venkat Ratnam3,
K. Niranjan Kumar4, P. Vishnu Prasanth5, Jaewook Lee1,
Yong Ha Kim1, S.V.B. Rao6
Department of Physics, Govt. Degree college, Anantapur-515001, India; 2Department of Astronomy and Space Science, Chungnam National
University, Daejeon-305-764, Korea; 3National Atmospheric Research Laboratory (NARL), Gadanki, Tirupati-517501, India; 4Atmosphere and
Ocean Research Institute (AORI), The University of Tokyo, Chiba, 277-8568, Japan; 5Department of Physics, Sree Vidyanikethan Engineering
College, Tirupati-517102, India; 6Department of Physics, Sri Venkateswara University, Tirupati-517501, India.
1
ABSTRACT
Objective: It is theoretically observed that atmospheric gravity waves play a key role in vertical coupling during the Mesosphere
Temperature Inversion (MTI). Therefore, the present paper describes the observational evidence for vertical coupling between
the stratosphere and mesosphere through the short-period gravity waves (GWs), during the Mesosphere Temperature Inversion
(MTI) over a tropical region, Gadanki (13.5oN, 79.2oE), India.
Method: The combined observations of Mesosphere-Stratosphere-Troposphere (MST) Radar and Rayleigh LIDAR located at
Gadanki is utilized to study the vertical coupling. We used a unique experimental design from the two ground-based instruments
that scan the lower and middle atmosphere simultaneously during the observational campaign. This kind of combined instruments are very sparsely located on the same site to make the observations unique to understand the vertical coupling processes
of GWs.
Result: The vertical flux of the horizontal momentum of GWs of periods in the range 20 min. to 2h is investigated in the mesosphere using the MST Radar winds. The emphasis is made on the variability of zonal and meridional momentum fluxes in the
mesosphere and possible reasons for the variability of fluxes during MTI. It is observed that raise in momentum fluxes of ~7 m2/
s2 in the eastward flux and ~10 m2/s2 in southward flux at mesospheric altitudes during the MTI.
Conclusion: The gravity wave (GW) analysis using the LIDAR temperature profiles indicate the connection between GW breaking at mesosphere altitudes and temperature inversion and thus the turbulence caused mesospheric echoes. The study suggests the prospect of coupling between stratosphere and mesosphere during the MTI.
Key Words: Gravity wave coupling, Mesospheric Temperature Inversion (MTI), MST Radar, Rayleigh LIDAR
INTRODUCTION
The role of atmospheric gravity waves (GWs) in modulating
the energy budget of the Mesosphere-Lower thermosphere
(MLT) has been well recognized (Fritts and Alexander,
2003). The short-period GWs are playing a key role in vertical coupling of the different regions of the atmosphere (Sato,
1993;Fritts and Alexander, 2003). The tropical region is
found to be a fountain of generating short-period GWs (Fritts
and Alexander, 2003), and their generation and propagation
Corresponding Author:
Dr. Sunkara Eswaraiah, Department of Astronomy and Space Science, Chungnam National University, Daejeon, Korea;
Ph:+82-10-30690508; E-mail:eswar.mst@gmail.com.
ISSN: 2231-2196 (Print)
ISSN: 0975-5241 (Online)
Received: 27.11.2017
Revised: 12.12.2017
Int J Cur Res Rev | Vol 10 • Issue 1 • January 2018
Accepted: 26.12.2017
1
Chalapathi et.al.: Atmosphere coupling during MTI
studies are well established in the lower atmosphere over the
Indian tropical region (Dhaka et al., 2002; Debashis Nath et
al.,2009 and references therein). However, its effects on the
MLT is sparsely studied over this region.
Earlier studies highlighted the importance of GWs in changing the MLT thermal structure (Fritts and Alexander, 2003).
It was understood that vertically propagating GWs begins
to break at the level where there is a sudden change in the
temperature lapse rate or at the critical level(Meriwetherand
Gerrard, 2004), and deposit large amount of energy and momentum (Fritts and Nastrom, 1992; Gardner and Yang, 1998;
Ramesh and Sridharan, 2012). The studies on GW effects on
the mesosphere temperature and the Mesosphere Temperature Inversion (MTI) are well existed (Garcia and Solomon,
1985; Hauchecorne et al., 1987; Venkat Ratnam et al., 2003;
Ramesh and Sridharan, 2012). The occurrence mechanism
of MTI or “mesospheric inversion layer” (MIL) is clearly
discussed by Meriwether and Gerrard (2004). The occurrence of MIL and its characteristics are well studied using
LIDAR’s, Radars, Rocket Sonde, and Satellites over different geographic locations (Ramesh et al., 2014 and references
therein). Thus the earlier studies described the relation between MTI and GW breaking, however, the relation between
the mesospheric radar echoes and MTI and GWs breaking
studies sparsely exist over the tropical region. Further, the
simultaneous ground-based observations both in the stratosphere and mesosphere and the quantification of GW breaking at mesosphere altitudes is still incomplete. In the present
study, we made an attempt to unclear this issue and presented
the vertical coupling using the unique data set over a tropical
region Gadanki.
To this end, up to our knowledge concerned, this is the first
report on the mesospheric echo phenomenon and their relation to GW breaking and thus the MTI. The details of the
data used and methodology followed for the current study is
briefly given in section 2, the results and discussions are provided in section 3, comprehensive summary, and key findingsare emphasized in section 4.
DATA
In the present study, the unique data set of Mesosphere-Stratosphere-Troposphere (MST) Radar and Rayleigh LIDAR located in a tropical region, Gadanki(13.5oN, 79.2oE), India is
utilized. Short-period (20 min.-2 h) GW momentum fluxes
are estimated in the mesosphere using the MST Radar wind
data, and LIDAR temperature profiles are used to represent
the MTI and GW characteristics both at the stratosphere and
mesosphere altitudes.
METHODOLOGY
Int J Cur Res Rev | Vol 10 • Issue 1 • January 2018
MST radar
The Gadanki MST Radar is high power VHF radar with a
peak transmitter power of2.5 MW and operates at 53 MHz.
The MST Radar provides winds from surface to 22 km and
65-85 km. More details of MST Radar can be found in Rao
et al. (1995). As mesospheric echoes from the MST Radar
are mainly due to fluctuations in electron density gradients
and irregularities, they are confined to day-time and hence
the availability of data is restricted to ∼10:00 to 17:00h Indian Standard Time (IST) (IST=UT+05:30 h).The structure
and characteristics of MST Radar mesospheric echoes and
mesospheric wind estimation are discussed in Kumar et al.
(2007) and Eswaraiah et al. (2011). For the present study, a
clear analysis of radar radial velocity profiles of individual
days and defined percentage occurrence (PO) of echoes are
performed for reliable wind estimation; the detailed procedure is given in Eswaraiah et al (2013). The reliable estimates
of GW momentum flux can be obtained using a threshold of
20% of PO. Thus, the echoes in the range bins with PO less
than 20% are omitted. For the flux estimation, the symmetric
beam radar method of Vincent and Reid (1983) is utilized
and the procedure has been discussed in Eswaraiah et al.
(2013).
The momentum fluxes of horizontal winds have been estimated using the following equations
Momentum flux for the E-W beam:
2
u 'w' =
2
(v E v W )
(1)
2 sin 2
moreover, for the N-S beam:
2
v 'w' =
2
(v N v S )
(2)
2 sin 2
Where v ' w ' is zonal momentum flux, v ' w ' is meridional momentum flux and v v , v , v are square of radial wind perturbation in east, west, north and south directions, respectively,
and θ is the anglebetween the radar beam to the zenith. Two
consecutive radar beams make an angle θ, each beam being
at zenith. In the present case, it is 10o.
2
2
2
2
E
W
N
S
Rayleigh Lidar
The Gadanki Rayleigh LIDAR data is used to observe the
MTI and GWs in the stratosphere and mesosphere, but not
for GW momentum flux estimation. The LIDAR employs
the second harmonic of Nd: YAG pulsed laser at 532 nm with
a pulse energy of ~ 550 mJ and Rayleigh receiver is used,
which employs a Newtonian telescope. The LIDAR provides
photon count profiles with an altitude resolution of 300m and
time resolution of 250s (5000 laser shots were integrated for
one profile). Although the temperature can be derived up to
85 km, due to low SNR at higher altitudes, the altitude range
2
Chalapathi et.al.: Atmosphere coupling during MTI
considered for the present study is from 35 to 75 km. The
basic method of deriving the temperature profile from the
measured photon count is similar to the procedure given by
Hauchecorne and Chanin (1980). Usually, the random errors
occur while deriving the temperature and they vary from 2 K
at 30 km to 4 K at 75 km (Parameswaran et al., 2000). The
total vertical flux of horizontal momentum using LIDAR
temperature profiles is discussed in Eswaraiah et al., (2013).
More details of this instrument and method of analysis can
be found from Bhavani Kumar et al. (2001), Siva Kumar et
al. (2001) and Ratnam et al. (2002).
For the present study, MST Radar data on 18 November
1998 and 11 January 1999 has been used. Similarly, the Rayleigh LIDAR night time temperature measurements on 18
November 1998 and 11 January 1999 have been used. For
18/19 November 1998, the temperature measurements were
made from 03:20 h IST to 05:40 h IST and for 11/12 January
1999 the observations were made between 21:29 h IST to
04:10 h IST on the next day. The simultaneous MST radar
observations in the mesosphere and Lidar observations are
very rarely will match, since the radar mesospheric echoes
are highly sporadic and they will not every day. Though the
observational data is old, the scope of the present study is
sparse and it is new.
DISCUSSIONS
Figures 1(a) and 1(b) depicts the radar reflectivity in terms
of SNR (Signal to Noise Ratio) observed on 18 November
1998 and 11 January 1999, respectively. Corresponding late
night time mean temperature profiles observed by Rayleigh
LIDAR are shown in Figure 1(c) and 1(d). Temperature inversion in the mesosphere (Fig.1(c)) is seen on 18 November
1998 but not on 11 January 1999. On the temperature inversion day active radar (MST) echoes at mesospheric altitudes
just below the temperature inversion layer (below 75 km)
are observed, whereas on non-inversion day no radar echoes
are seen in the mesosphere, indicating a close association
between mesospheric radar echo occurrence and temperature inversion. Past studies on mesosphere thermal structure
(Ratnam et al., 2002; Kishore Kumar et al., 2008) explained
the reasons behind this phenomenon. It is observed that
whenever the strong mesospheric radar echoes are noticed
in the day-time, then mesospheric temperature inversion is
evident in the associated night-time LIDAR temperature profiles. It is also seen that whenever there is no temperature
inversion, there are no strong echoes observed in the MST
Radar observations (Ratnam et al., 2002).The temperature
inversion at mesospheric altitudes and turbulence generated
to form mesospheric echoes can be understood by verifying
the short-period GW features in both the stratosphere and
mesosphere and their breaking at mesosphere altitudes. To
find the existence of short-period GWs and their propaga3
tion from the lower atmosphere to mesosphere, the periodicities and propagation of GW shave been tested. The GW
features and their propagation has been verified using the
simultaneous observations of MST Radar and LIDAR from
the troposphere to mesosphere altitudes by performing spectral analysis. Wavelet analysis has been applied for the detrended radial velocities of radar, both at the troposphere (18
km) and mesosphere (70.8 km) altitudes and for the temperature perturbations of LIDAR at the stratosphere (45.1
km) and mesosphere (77.2 km) altitudes on 18 November
1998 and are shown in Figure 2.The magnitude of wavelet
power is shown in logarithmic values. From the figure, it
can be noticed that in the mesosphere at 70.8 km (Figs.2(a)
and 2(b)),30 min. to 1 h and 1-2 h period waves are present
between 11:30 h-12:30 h IST in east beam and again between
14:30 h-15:30 h IST in the north beam of MST Radar observations. Since the MST Radar will not give background
wind information in the gap region (20-60 km), the LIDAR
temperature perturbations for the wave information is taken
into consideration. At 45 km (Fig.2(c)) in the stratosphere,
30 min. to 1 h period and at 77.2 km (Fig.2(d)) 30 min. to 2
h period, waves are evidenced. The similar analysis has been
performed at 18 km (Figs. (2e) and (2f)) i.e., in the troposphere, and it shows that the waves with periodicities up to 1
h are significant both in east and north beams of radar radial
velocities. The analysis resembles that at the troposphere altitudes waves with a wide spectrum of periodicities exist and
with altitude the waves with low periods propagate to the
mesosphere altitude and break when there exists temperature
inversion in the background, resulting in turbulence at the
mesosphere altitudes below the inversion layer (Fig.1(a)).
Further, to show the difference in wave propagation on inversion and non-inversion days, the 30 min. to 1 h and 1-2 h
periodicities are filtered from LIDAR temperature perturbations and shown along with daily mean temperature profiles
in Figure 3. Figs.3(a), and 3(b) shows the upward propagation of 30 min. to 1h and 1-2 h period waves respectively, on
18/19 November 1998. Fig.3(c) shows the mean temperature
profile on 18/19 November 1998. Figs.3(d) and 3(e) and 3(f)
are same as (a,b,c), but on 11/12 January 1999. Usually, the
waves with low periods (or high frequency) can propagate to
the mesosphere (above 60 km) and others get filtered as their
phase speed match with the background wind speeds. On 11
January 1999 (Lower panel), the 30 min. to 1h and 1-2 h
period waves (Figs.3(d) and 3(e)) continuously existed in the
mesosphere altitudes without breaking and hence no inversions in resulting mean temperature. In contrast, on 18 November 1998 (Upper panel), 30 min. to 1h and 1-2 h period
waves (Figs.3(a) and 3(b)) are continuously observed above
75 km altitude and below that they are not frequent, which
tells that the waves are breaking at ~ 75 km throughout the
day and hence at 75 km large inversion appeared in the mean
temperature (Fig.3(c)). So far it is unresolved that whether
due to inversion waves will break or due to the breaking of
Int J Cur Res Rev | Vol 10 • Issue 1 • January 2018
Chalapathi et.al.: Atmosphere coupling during MTI
the waves inversion occurs. Further, to elucidate the GW
breaking at mesosphere altitudes, the characteristics of shortperiod GWs have been estimated and displayed in Figure 4.
Fig.4(a) shows the vertical wavelength of short-period GWs
during the observational period, Fig.4(b) depicts the GW
amplitude with height, Fig.4(c) presents the momentum flux
deposition by short-period GWs, and Fig.4(d) exhibits the
variation of Brunt Väisala Frequency (BVF) of short-period
GWs. From the figure, it is evident that the significant 10-20
km vertical wavelength GWs exist during the span of observational period, and the amplitude is increasing with height
and peak amplitude is reaching ~ 75 km and results in the
wave breaking by producing the large zonal momentum flux
at 75 km (Fig.4(c)). Sudden variation in BVF can be seen
when the wave breaking and depositing large flux into the
background. The analysis further supports the vertical propagation of short-period GWs and their breaking at ~ 75 km.
Using the procedure given in section 2, the time variation of
zonal and meridional momentum flux of 20 min. to 2 h GWs
during the inversion day(18 Nov.1998) are estimated and
presented in Figure 5.The fluxes are evaluated using the procedure shown above and averaged over about 15 min. Even
though a high degree of temporal variability in zonal momentum fluxes are seen from Figure 5, a significant momentum flux determination can only be obtained by averaging
it over reasonably long periods (Kudeki and Franke, 1998).
In the mesosphere, at times of (Figure 2) dominant wave
presence, sudden enhancement in flux is observed (Figs.5(a)
and 5(b)). The zonal flux is quite low after ~ 14:00 h IST
(Fig.5(a)) whereas the meridional flux (Fig.(5b)) continues
to be strong and fluctuating. As shown in Figure 5 at 70.8
km in the forenoon hours the dominant flux is eastward, and
later it is southward. Momentum fluxes are mainly eastward
(~7 m2/s2) between 11:30-12:30 h IST and later observed in
southward (~ 10 m2/s2) direction between 14:30-15:30 h IST.
In the troposphere, no significant changes are noticed in the
fluxes which could be attributed to small wave amplitudes
due to high density.
1. The relation between MST Radar mesospheric echoes and mesospheric temperature inversion (MTI)
obtained with LIDAR daily mean temperatures have
been noticed and it is consistent with earlier reports.
2. Using LIDAR temperature profiles, the propagation of
short-period GWs during the MTI and non-MTI cases
and their breaking at 75 km leads to mesospheric turbulence and the formation of MTI has been observed.
3. Upward propagation of GWs and their breaking has
been tested by studying the characteristics of the shortperiod GWs using the LIDAR temperature profiles.
4. The present case study during MTI showed the rise
in momentum fluxes with ~7 m2/s2 in the eastward
flux and ~10 m2/s2 in southward flux at mesospheric
altitudes with no significant variation in the lower atmosphere. This could be due to large wave breaking at
mesosphere altitudes.
The present study suggests that during MTI, the Stratosphere
and the mesosphere are coupled through the propagation of
short-period GWs, and hence the waves are transporting energy and momentum from lower atmosphere to the mesosphere. The role of GWs in causing the turbulence to form
the mesospheric radar echoes is highly substantial.
ACKNOWLEDGEMENTS
We deeply appreciate the National Atmospheric Research
Laboratory (NARL) for providing the data used in the present
study. SE acknowledges for financial support by the Korea
Polar Research Institute (PE17020), Korea and Chungnam
National University, Daejeon, Korea. We alsoacknowledge
the technical staff who helped to retrieve the data from the
MST radar and Rayleigh Lidar.
Authors acknowledge the immense help received from the
scholars whose articles are cited and included in references
of this manuscript. The authors are also grateful to authors /
editors / publishers of all those articles, journals and books
from where the literature for this article has been reviewed
and discussed.
CONCLUSIONS
By Utilizing the combined observations of MST Radar, and
Rayleigh LIDAR, at a tropical station, Gadanki (13.5oN,
79.2oE), India, the existence and propagation of the shortperiod (~of periods 20 min. to 2 h) gravity waves during the
mesospheric temperature inversion (MTI) has presented.
Further, the coupling between the Stratosphere and mesosphere has been investigated during MTI through LIDAR
temperature measurements and estimating the momentum
fluxes in the mesosphere.
The main outcomes or conclusions of the present study are
summarized below:
Int J Cur Res Rev | Vol 10 • Issue 1 • January 2018
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Figure 2: Wavelet analysis applied to the radial velocities obtained using MST radar on 18 November 1998 at 70.8 km and
18 km (a,b,e,f) and for Lidar temperature at 45.1 km and 77.2
km (c,d). The black line represents the cone of influence.
Int J Cur Res Rev | Vol 10 • Issue 1 • January 2018
Chalapathi et.al.: Atmosphere coupling during MTI
Figure 3: (a) and (b) show 30 min. to 1 h and 1 to 2 h period
oscillations along with mean temperature (c) on the Inversion
day (18 November 1998) (top panel). (d), (e) and (f) are same
as Figs.3(a), (b) and (c) but during Non-Inversion day (11 January 1999) (bottom panel).
Figure 5: Zonal (left panels) and meridional (right panels) momentum fluxes at different altitudes observed on 18 November
1998 in the troposphere (bottom panels) and mesosphere (top
panels).
Figure 4: (a)Vertical wavelength of 20 min.-2 h GWs and
vertical profiles of (b) Amplitude, (c) Zonal momentum, and
(d) Brunt-Vaisala frequency on Inversion day (18 November
1998).
Int J Cur Res Rev | Vol 10 • Issue 1 • January 2018
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