Objectives: To investigate the electrochemical performance of TiO2 (Titanium dioxide) nanoparticles prepared from Ocimum tenuiflorum Plant (OTP) Leaves extract. Methods : cost-effective and eco-friendly green synthesis approach is used to synthesize the TiO2 nanoparticles. XRD (X-ray diffraction) and FESEM (Field Emission Scanning Electron Microscopy) techniques are used to analyse microstructural details. Raman and EDX (Energy Dispersive X-ray spectroscopy) are used to analyse the phase and the chemical composition of the synthesized TiO2 nanoparticles. The nature of chemical bonding as well as the functional groups that the sample contains is identified by using FITR (Fourier Transform Infrared spectroscopy) investigation. The optical band gap of the prepared nanoparticles is estimated by UV-Vis spectroscopic analysis. Finally, Cyclic Voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) are used to investigate the electrochemical performance of the produced TiO2 nanoparticles. Findings: The XRD data exhibited that the prepared TiO2 nanoparticles are in a tetragonal structure with an anatase phase and have a crystallite size of 18.6 nm. FESEM images of the TiO2 nanoparticles confirm the smooth surface morphology of spherical grains having an average grain size of 92 nm. The formation of the anatase phase is confirmed by the Raman spectroscopic analysis. The Ti-O-Ti bonds are identified in the sample through the FTIR absorption spectra. The optical band gap of green TiO2 nanoparticles is found to be 3.07 eV and indexed to the anatase phase. Moreover, the better electrochemical performance of the prepared TiO2 nanoparticles is identified from both CV and CP studies in Na2SO4 aqueous electrolyte. At last, the capacitive retention attains up to 65% even after 5000 cycles for the sample prepared from OTP. Novelty: A significant component of this study is the creation of the 3D nanostructured morphology of TiO2 nanoparticles using the green synthesis method which followsthe green chemistry principles. This type of research provides assurance for the protection of rights of the future generations and ecosystems. This type of 3D nanostructure demonstrates superior performance as a supercapacitor electrode, photocatalyst, antibacterial agent, UV-resistant material and solarpowered H2 fuel producer. Keywords: TiO 2 nanoparticles; Green synthesis; Ocimum tenuiflorum Plant (OTP); Optical band gap; Specific capacitance

Synthesis of three dimensional nanostructures with high specific surface area is very much essential to enhance the capacitance of supercapacitors. In this work, we have made an attempt to prepare 3D flower like TiO2 nanoparticles via green approach. The detailed microstructural, morphological and optical properties are examined thoroughly using various characterization techniques. More attention is paid to investigate the electrochemical performance of TiO2 nanoparticles by different methods such as cyclic voltammetry (CV), chronopotentiometry (CP) and impedance spectroscopy in aqueous electrolyte at different reaction times. The result establishes that the TiO2 nanoparticles prepared through 10 h reaction time in 1M Na2SO4 aqueous electrolyte demonstrated better electrochemical performance due to its delightful structural morphology.

Objectives: Green synthesis of Titanium dioxide (TiO2) nanoparticles using Calotropis gigantea (CG) plant leaf extract. Methods: Environmental ecofriendly green approach is used to synthesize nanostructured TiO2 nanoparticles by using TiCl4 as a precursor and C. gigantea plant leaf extract as a catalyst. The secondary metabolites in the CG plant leaf extract help to transform the Ti4+ ions to TiO2 nanoparticles. The detailed structural properties are studied using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The phase formation and chemical state of the prepared samples are examined by Raman and Energy Dispersive X-ray spectroscopy (EDX). The vibrational frequencies between the bonds of atoms are studied with Fourier Transform InfraRed spectroscopy (FTIR). The electrochemical properties of green synthesized nanoparticles using cyclic voltammetry (CV) technique in aqueous electrolyte. Findings: XRD data conform to the tetragonal structure of TiO2 in the rutile phase with P42/mnm space group and crystallite size is also found to be 9.84 nm. The SEM and TEM images show that the non-uniform spherical and flowerlike shape of grains with an average grains size of 100 nm. The specific capacitance of the sample is estimated to be 238 F g-1 at a scan rate of 1 mV s-1 with good reversibility. Novelty: The novelty of this research lies in the fabrication of the electrode material with TiO2 3D nanostructures for supercapacitor applications. This kind of morphology certainly enhances the surface area and leads to achieving better electrochemical performance. Keywords: Titanium tetra chloride; TiO 2 nanoparticles; Green synthesis; Calotropis gigantea (CG) Plant; 3D nanostructure; specific capacitance

The signature of the low-latitude mesosphere response to the February 2017 minor sudden stratosphere warming (SSW) was detected using the observations of a meteor radar at Fuke (19.5°N, 109.1°E) a low-latitude station in China and ERA-5 data. Radar detected the zonal wind reversal in the mesosphere three days before the SSW event, whereas the ERA-5 does not reproduce the mesospheric wind response at low-latitudes during the 2017 SSW and large discrepancies are found between the mesospheric zonal winds derived from the Fuke radar and ERA-5. The quasi oscillatory pattern was noted in the meridional winds before the SSW event, afterward, the northward winds are significant. We observed the existence of 20–28-day planetary waves (PWs) in the Fuke meteor radar measured mesospheric zonal winds before the SSW and the 2-12-days period PWs before and after the SSW in the meridional winds. The zonal structure and periodicity of the PWs have been verified with the other meteor radar at the Indian tropical station Tirupati (13.63°N, 79.4°E). However, ERA-5 does not capture the PW activity in the mesosphere as radar. The similarities and dissimilarities among the different techniques have been discussed. Therefore, the present study re-emphasizes the strong response of the low-latitude mesosphere to the 2017 minor SSW in a manner similar to the major SSW event.

The flower like TiO2 nanoparticles have been identified as potential electrode material for efficient next generation electrochemical energy storage devices. The present work reports, a novel green approach to synthesize high surface area TiO2 nanoparticles using medicinal plant leaf extracts namely Ocimum Tenuiflorum Plant and Calotropis Gigantea Plant. The TiO2 nanoparticles synthesized using Calotropis Gigantea plant confirmed rutile phase from X-ray powder diffraction and Raman spectra. The fourier transform infrared spectroscopy spectra of the sample indicate the presence of TiO2 vibrational bonds. The field emission scanning electron microscopy images revealed that the flower like shape of nano-granules with an average granule size of 200 nm. The presence of Ti and O elements qualitatively confirmed using energy dispersive spectroscopy spectra, which shows the good stoichiometry in the sample. The flower like shapes with nano petals were further disclosed with the help of high resolution transmission electron microscopy. The corresponding optical band gap was observed to be 3.0 eV. The electrochemical investigations of the sample exhibited a high specific capacitance of 224 F g(-1) at 0.5 A g(-1) with 71% of capacitive retention after 5000 cycles.

The observations of the advanced meteor radar at the Indian tropical station Tirupati (13.63 degrees N, 79.4 degrees E) have been used to investigate the effects of the 2017 minor Sudden Stratospheric Warming (SSW) on the tropical mesosphere and lower thermosphere (MLT). The episodic minor warmings were observed in February 2017 with the gain of similar to 40 K in the polar stratospheric temperature (PST), followed by a weakening of the eastward wind by 27 m/s. The observations show the large temporal variations in the zonal wind at 75-80 km during the SSW. We report the occurrence of 14-16 day waves in the MLT zonal wind during SSW and the secondary waves (2-7 days) in the meridional wind after SSW. A large enhancement (similar to 30 m/s) is observed in the amplitude of the semi-diurnal tide (SDT) during the SSW. The present results are similar to those observed during the major SSW. Therefore, the present results stress that the studies of minor SSW on the tropical MLT dynamics must be important. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

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.

Objective: Usually, the stratospheric ozone will show its significance in the variability of mesospheric tides in normal days over the low-latitude region.But during sudden stratosphere warmings, the water vapor and ozone over the polar region will change and shows some different effects on mesosphere tides.In the present study, we have provided the unusual changes in both water vapor and ozone over Antarctica and their role in altering the mesospheric tides.Method: Using MLS data in the stratosphere and Rothera (68oS, 68oW) MF radar observations in the mesosphere, the variability of Antarctica ozone and H2O during sudden stratospheric warming (SSW) winter 2010, and their influence on mesosphere dynamics has presented.The unusual increment of ozone reduction is noticed and consequent enhancement in H2O and HNO3 is also observed during the warming period.Mesospheric tidal components (diurnal, semi-diurnal and terr-diurnal) have been estimated using the hourly wind data from the MF radar. Result:The unusual changes in H2O and Ozone were observed during the warming period the similar behavior was observed in semi-diurnal tidal components during 2010 winter and their relation to ozone enhancement is discussed. Conclusion:The observations indicate that the enhancement of H2O and HNO3 leads to produce the ozone during warming period and hence the increment in ozone reduction is achieved over the polar region.Further, the enhancement of Brewer-Dobson mean circulation was clearly noticed through ozone transport during the warming period.The tidal enhancement after the SSW could be due to the non-linear interaction between planetary waves and tides.

We have utilized the Gadanki MST Radar and Rayleigh LIDAR to understand the vertical coupling between the lower atmosphere and mesosphere through the short-period gravity waves (GWs). The short-period GWs (20 min-2 h) are noticed both in the troposphere and in the mesosphere during the deep convection. During the convection, the large vertical velocities (>5 m/s) and significant variations in the momentum flux (similar to 3 m(2)/s(2)) are noticed in the troposphere and higher fluxes (similar to 45 m2=s2) are evidenced in the mesosphere. The observations suggest the vertical coupling between the lower and middle atmosphere during convection.

For the first time, climatology of the middle atmosphere thermal structure is presented, based on 14 years of LIDAR and satellite (HALOE, SABER, CHAMP and COSMIC) temperature measurements. The data is collected over a southern sub-tropical site, Reunion Island (20.8° S; 55.5° E), for the height range between 30 and 60 km. The overall monthly mean temperature shows a maximum of 265–270 K at the stratopause height region from ~44–52 km and peaks during the months of March and November. Furthermore, the temperature profiles are compared with different satellite datasets (HALOE, CHAMP, COSMIC and SABER) and the results are found to be in reasonable agreement with each other, although a relative difference in temperature of ± 5 to 6 K is noticed. In comparison, LIDAR shows higher/lower temperatures for the lower mesosphere/upper stratosphere height region. The differences in temperature measured by the LIDAR and satellite measurements are analogous with previous results available elsewhere. Long-term temperature measurements are used to further study seasonal oscillations, especially annual, semi-annual and quasi-biennial oscillations. In comparison with SAO, the measured spectral amplitudes of AO shows dominant amplitudes in both the upper stratosphere and lower mesosphere height regions. Using LIDAR and the other satellite measurements, the quasi-biennial oscillation was found to be approximately 26 months. The spectral amplitudes are comparable to the results reported earlier by other researchers.

In this paper, we present seasonal and nocturnal variations of mesospheric sodium (Na) layer parameters observed over Gadanki (13.5° N, 79.2° E), based on 166 nights during the period from January 2005 to December 2006, for the first time. The total Na content decreases during the evening and reaches a minimum value around midnight and maximum in the early morning. The year-to-year variations illustrate that Na layers reach the peak value close to 93.5 km for the year 2005 and ~93 km for the year 2006 and falls to near zero value around 110 km. Though, seasonal variation of sodium density illustrate maximum values in September, December and March, we require a larger data base for September months to conclude the statement. The column abundance shows maximum during autumn equinox and minimum during winter. The obtained seasonal and nocturnal variation of sodium layer parameters are compared with mid-latitude observations and further possible mechanisms are discussed.

Resonance lidar observations of sodium density in the upper mesosphere region over Gadanki (13.5°N, 79.2°E) rarely show complex structures with rapid enhancements of sodium density, completely different from normal sporadic sodium structures. The hourly averaged meteor radar zonal winds over Trivandrum (8.5°N, 76.5°E) show an eastward shear with altitude during the nights, when these events are formed. As suggested by Kane et al. [2001. Joint observations of sodium enhancements and field-aligned ionospheric irregularities. Geophysical Research Letters 28, 1375–1378], our observations show that the complex structures may be formed due to Kelvin–Helmholtz instability, which can occur in the region of strong wind shear.

The present study reports long-term variabilities and trends in the middle atmospheric temperature (March 1998–2008) derived from Rayleigh backscattered signals received by the Nd:YAG lidar system at Gadanki (13.5°N, 79.2°E). The monthly mean temperature compositely averaged for the years 1998–2008 shows maximum temperature of 270K in the months of March–April and September at altitudes between ∼45 and 55km. The altitude profile of trend coefficients estimated from the 10 years of temperature observations using regression analysis shows that there exists cooling at the rate with 1σ uncertainty of 0.12±0.1K/year in the lower stratospheric altitudes (35–42km) and 0.2±0.08K/year at altitudes near 55–60km. The trend is nearly zero (no significant cooling or warming) at altitudes 40–55km. The regression analysis reveals the significant ENSO response in the lower stratosphere (1K/SOI) and also in mesosphere (0.6K/SOI). The solar cycle response shows negative maxima of ∼1.5K/100F10.7 units at altitudes 36km, 41km and 1K/100F10.7 units at 57km. The response is positive at mesospheric altitude near 67km (1.3K/100F10.7 units). The amplitudes and phases of semiannual, annual and quasi-biennial oscillations are estimated using least squares method. The semiannual oscillation shows larger amplitudes at altitudes near 35, 45, 62 and 74km whereas the annual oscillation peaks at 70km. The quasi-biennial oscillations show larger amplitudes below 35km and above 70km. The phase profiles of semiannual and annual oscillations show downward propagation.

We studied the characteristics of sporadic sodium layers (SSLs) observed with the sodium (Na) resonance scattering lidar at Gadanki (13.5° N, 79.2° E). The SSLs were observed on a total of 63 occasions during 464 h of Na lidar observations from January 2005 to February 2006. The observations showed that one SSL event occurred, on average, every 7 h. The most prominent sporadic layer, which formed on 12 February 2005, exhibited a peak density of 60 722 Na atoms/cm³ around 92 km and it was nearly twice the peak density reported from elsewhere using ground-based observations. In general, the SSLs exhibited the following characteristics: (1) they developed at heights between 88 and 98 km with an average height around 94 km; (2) maximum density occurred during the early morning hours between 02:00 and 05:00 IST; (3) the ratio of the maximum peak Na density to the average density was normally around 3 to 5 and it exceeded even 10 in some cases; (4) the events lasted from a few minutes to several hours. The formation period of the SSLs was longer compared to the decay period of the SSLs. Most of the SSL events showed downward motions.

We report on the first lidar observations of the nighttime mesospheric sodium layer from Gadanki (13.5°N, 79.2°E) site in India. The lidar measurements of upper atmospheric sodium made on 6 nights between the 10 and 16 January 2005 are presented in this paper. The Gadanki lidar uses a Nd:YAG pumped dye laser, tuned to the sodium D2 line (589.0 nm), as a transmitter. Using the system, sodium number density profiles have been obtained with a vertical resolution of 300 m, a time sampling of 120 s. During the initial six nights of observation, the peak sodium concentration is found at a height of 95 km, and the top side scale height is usually about 2 km. On three occasions, a secondary peak was observed at heights between 87 and 92 km. Measurements at Gadanki site indicate that the mean sodium abundances appear to decrease after sunset and increase before sunrise. The average nocturnal columnar abundances were in the range 2–8.9 × 10 9 cm 2 . The nightly mean centroid heights range between 92.9 and 95.2 km and the rms widths vary between 4.3 and 4.9 km. On some nights, wave like structures in the sodium layer were observed with wavelength of about 3 km and downward phase velocities of about 1 km/hr. Four sporadic layers were observed during the initial 54 h of observation. The formation and decay of an intense sporadic sodium layer was observed on the night of 11 January 2005. The layer was found to develop between 93 and 90 km altitude and appear between 0230 and 0430 LT.

In the gravity wave spectrum, frequencies ranging from inertial frequency (low) of the geographical location to the Brunt-Vaisala (BV) frequency (high), it is the high frequency part that contributes to the significant vertical transport of momentum and energy flux up into the mesosphere and the low frequency part that plays a major role in the vertical transport of chemical constituents. Often the high frequency waves retard significantly or induce negative drag on the mesospheric flows and they can easily be incited by convective sources in the lower troposphere over equatorial regions. In the present work, we present the observational results on high frequency gravity waves that are generated in the lower troposphere and propagated deep into the mesosphere using very high frequency (VHF, 53 MHz) radar in the height region of 3.5-21 km and Nd-Yag lidar (532 nm) in the height region of∼25-75 km over the Indian tropical station, Gadanki (13.5 N, 79.2 E). For this purpose, we identified a few days during which both the radar and lidar operated simultaneously but for day times in the case of lidar. The frequency spectral analyses carried out for both the radar and lidar data indicates that the high frequency part of the spectrum (∼ 10-50 minutes) is present predominantly at almost all the heights from about 5 km. This would indicate that latent heating associated with low-level convective clouds is an important source of generation of the high frequency gravity waves that have the characteristics to propagate easily up to the mesosphere region. Apart from the frequency spectral analyses, vertical wavenumber spectra also calculated for all the heights. It is found that in the troposphere, the dominant vertical wavelength range is about 0.5 to 2 km and in the stratosphere it is about 2-5 km, indicating that short vertical wavelength gravity waves are filtered in the lower atmosphere and higher vertical wavelength gravity waves are propagated or otherwise the lower vertical wavelengths might have Doppler shifted to higher vertical wavelengths in the stratosphere. Another important observation is that the power spectral density (∼10-50 minutes periodicity) in zonal wind enhances strongly above the tropopause in the vertical wavelength region of 0.5 –2 km. In the case of vertical winds, the spectrum shows enhanced power above about 19 km instead