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in the mesosphere-lower thermosphere (MLT) and Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM) simulations are employed for investigating the diurnal tide variability at quasi-biennial scales. The model simulations are evaluated using the meteor radar observations at three tropical locations. WACCM simulations could reproduce the seasonal evolution of diurnal tides very well over Thumba and Tirupati but there are small discrepancies over Kototabang. In order to investigate the modulation of the diurnal tide amplitudes in the MLT region by the stratospheric quasi-biennial oscillation (SQBO), deseasonalized perturbations of diurnal tides and stratospheric winds are analyzed. A very good correspondence is found between meridional diurnal tide perturbation amplitudes and the SQBO with positive tidal perturbations during the eastward phase of SQBO and negative perturbations during the westward phase over Thumba and Tirupati. SQBO modulations of diurnal tides at global scales exhibits a positive correlation between the meridional diurnal tide perturbation with SQBO winds at 20 hPa and a negative correlation with SQBO winds at 70 hPa within ±40° latitude, except over the equator. It is also noted that the equatorial electrojet strength, is modulated by the SQBO over the Thumba, which is a dip equatorial location. The significance of present study lies in evaluating WACCM simulations at tropical locations using meteor radar measurements and in investigating the SQBO modulations of diurnal tides at global scales.Plain Language Summary Atmospheric tides are global scale oscillations having periods that are harmonics of solar day (24-, 12-, 8-h, etc.) and play a significant role in coupling lower and middle/upper atmosphere. Tides are generated in the troposphere/stratosphere and propagate upwards. In order to conserve the momentum, the amplitude of tides increases with altitude in response to decreasing density with altitude. Among many atmospheric waves present in the mesosphere-lower thermosphere (MLT), diurnal tides (24-h period) have the largest amplitudes over the low-latitudes and thus play a key role in shaping the structure and dynamics of this region. Even though tides are well represented in numerical models, time-to-time evaluation of these models against observations from several groundbased measurements is needed to employ them in day-to-day research applications. In the present study, SD-WACCM model simulations of mean winds and diurnal tides in the MLT region are evaluated using meteor radar observations over three tropical locations [Thumba (8.5°N, 77°) Kototabang (0.2°S, 100.3°E) and Tirupati (13.63°N, 79.4°E)]. There exists a long-period oscillation in the stratosphere known as stratospheric quasi-biennial oscillation (SQBO), which is believed to modulate the amplitude of diurnal tides at interannual scales. The present study also investigates the relationship between SQBO and the tidal variability in the MLT region. The results show significant correlation between the SQBO phase an...

Meteor radar observations of gravity wave momentum fluxes (GWMFs) in the 82-94 km altitude region, which is a part of mesosphere lower thermosphere (MLT), are employed to identify the best fit gravity wave source spectrum using Gravity wave Regional or Global Ray Tracer (GROGRAT) model simulations over a low-latitude location, Tirupati (13.63°N, 79.4°E). GROGRAT model is used to propagate a spectrum of gravity waves from the troposphere to the lower thermosphere. A total number of five gravity wave source spectra with various permutations and combinations are considered for the model simulations and by comparing the model simulated and radar observed gravity wave fields in the 82-94 km region, a best fit source spectrum is identified. The significance of the present study lies in appropriating the gravity wave source spectrum using meteor radar observations for the first time, which will have implications in improving gravity parameterization schemes in global models. Plain Language Summary Gravity waves are ubiquitous in the Earth's atmosphere and play a pivotal role in coupling lower and upper atmosphere. Once generated in the lower atmosphere, these waves carry momentum and energy and deposit somewhere in the middle and upper atmosphere. One of the important areas of research in the realms of middle atmospheric dynamics is to identify the source spectra of these waves so that they can be represented reasonably well in the numerical models. In the present communication, five different forms of source spectra with several combinations of parameters are employed to estimate the gravity wave momentum fluxes using a ray tracing model. The simulated gravity wave momentum fluxes in the 82-94 km region are then compared with those estimated from meteor radar located at a low-latitude station, Tirupati [13.63°N, 79.4°E]. The source spectrum, which simulates the meteor radar observed gravity wave momentum fluxes reasonably well, is identified to be the best fit spectrum. The present results are first of their kind and have implications in representing gravity wave source spectra in numerical models.

The equatorial stratosphere is characterized by a long-period oscillation known as the quasi-biennial oscillation (QBO), which is responsible for the observed interannual variability of many geophysical parameters in the global middle atmosphere. The QBO has an average time period of ∼28 months and is driven by equatorial waves as well as gravity waves through wave-mean flow interactions (Baldwin et al., 2001;Lindzen & Holton, 1968;Plumb & McEwan, 1978). The QBO modulates many atmospheric processes across the globe such as ozone transport from tropics to high-latitudes, the strength of the polar vortex and the propagations of atmospheric tides, planetary and gravity waves (

The programmed water system frameworks are received as of late to provide support to the agriculturists in turn reducing the manpower and improving cost effective techniques. In this paper, a detailed survey is done analysing the crop detection techniques which are in existence. This paper provides an insight study on pH level monitoring in the soil, water and soil nutrients management techniques, temperature and humidity measurement, surveillance of crop field and other smart irrigation techniques utilized for monitoring the farmland. This paper discusses about the effective methodology with enhanced technique that could be implemented in future to attain better performance and user-friendly for the farmers.