Mountain waves in the stratosphere have been observed over elevated topographies using both nadir‐looking and limb‐viewing satellites. However, the characteristics of mountain waves generated over ...the Himalayan Mountain range and the adjacent Tibetan Plateau are relatively less explored. The present study reports on three‐dimensional (3‐D) properties of a mountain wave event that occurred over the western Himalayan region on 9 December 2008. Observations made by the Atmospheric Infrared Sounder on board the Aqua and Microwave Limb Sounder on board the Aura satellites are used to delineate the wave properties. The observed wave properties such as horizontal (λx, λy) and vertical (λz) wavelengths are 276 km (zonal), 289 km (meridional), and 25 km, respectively. A good agreement is found between the observed and modeled/analyzed vertical wavelength for a stationary gravity wave determined using the Modern Era Retrospective Analysis for Research and Applications (MERRA) reanalysis winds. The analysis of both the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis and MERRA winds shows that the waves are primarily forced by strong flow across the topography. Using the 3‐D properties of waves and the corrected temperature amplitudes, we estimated wave momentum fluxes of the order of ∼0.05 Pa, which is in agreement with large‐amplitude mountain wave events reported elsewhere. In this regard, the present study is considered to be very much informative to the gravity wave drag schemes employed in current general circulation models for this region.
Key Points
Gravity waves over western Himalayan Mountain region
Observations through the space‐borne instruments such as AIRS, MLS
Validation of mountain waves with the global model reanalysis data
The climate variability on Earth is strongly influenced by the changes in the Sea Surface Temperature (SST) anomalies in the tropical oceans. More specifically, the inter-annual climate variability ...in the tropics as well as extra-tropical areas has large impact due to the anomalous SSTs in the tropical Pacific coupled with the El Niño Southern Oscillation (ENSO) through atmospheric teleconnections. However, the effect of ENSO on Middle Eastern region, specifically the Arabian Peninsula (AP) is marginally explored in previous studies. Hence, this study explicitly focuses on the assessment of ENSO variability and its winter climate teleconnections to the AP using the Community Atmospheric Model Version 4.0 (CAM4) simulations and Reanalysis datasets. ENSO teleconnections are also evaluated based on two sensitivity experiments (ENSO-related and ENSO-unrelated) using the CAM4 model. It is observed that during El Niño years the peninsular region receives more rainfall through enhanced moisture transport associated with anomalous westerly winds from adjoining Seas. The Rossby wave energy propagation in the atmosphere underlies important teleconnections involving ENSO. It is also noticed that there exist a distinct change in the phase of the Rossby wave pattern during El Niño and La Niña years which further causes the shift in the position of the jet stream over the Middle East.
In the present research, the wear behaviour of magnesium alloy (MA) AZ91D is studied and optimized. MA AZ91D is casted using a die-casting method. The tribology experiments are tested using ...pin-on-disc tribometer. The input parameters are sliding velocity (1‒3 m/s), load (1‒5 kg), and distance (0.5‒1.5 km). The worn surfaces are characterized by a scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). The response surface method (RSM) is used for modelling and optimising wear parameters. This quadratic equation and RSM-optimized parameters are used in genetic algorithm (GA). The GA is used to search for the optimum values which give the minimum wear rate and lower coefficient of friction. The developed equations are compared with the experimental values to determine the accuracy of the prediction.
The purpose of this paper is to introduce a new chaotic oscillator. Although different chaotic systems have been formulated by earlier researchers, only a few chaotic systems exhibit chaotic ...behaviour. In this work, a new chaotic system with chaotic attractor is introduced for triangular wave non-linearity. It is worth noting that this striking phenomenon rarely occurs in respect of chaotic systems. The system proposed in this paper has been realized with numerical simulation. The results emanating from the numerical simulation indicate the feasibility of the proposed chaotic system. More over, chaos control, stability, diffusion and synchronization of such a system have been dealt with.
Ahmedabad is an urban site in western region of India. Dust loading and its variability are very high over this semi-arid location. A state-of-the-art ground-based Raman lidar has been used for the ...study of day-to-day variability in vertical distribution of aerosol loading over Ahmedabad (23.02° N, 72.57° E) from 8 to 11 May 2018. We have done a comprehensive study about vertical profiles of aerosols across two wavelengths recorded simultaneously, namely, 355 nm and 532 nm, over this location. An interesting hump feature has been noted on 9 May at around 18 h (Local Time), with an additional peak at 19 h on 10 May. The loading over this region has more fine-mode aerosols than coarse-mode particles. Further, findings from ground-based lidar have been compared with MACC-II model simulations and Cloud-Aerosol Lidar with Orthogonal Polarization on-board Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observational. Back-trajectory analysis showed majority of the influx came from middle-east, carrying mineral dust and traces of marine aerosols from Arabian Sea, except for 11 May, where low-level dust carrying trajectories and also coarser dust particles were not seen. This type of manifestation has also been observed while classifying aerosols over Ahmedabad using Lidar Depolarization Ratio and Lidar Ratio obtained from Raman Lidar. Fine mode aerosols have been characterized as industrial, vehicular and marine, while coarser as mineral dust and biomass burning. This study focuses on local variation and classification of aerosols based on size and type, which will further help in better estimation of radiative budget and other impacts of aerosols.
During recent years, an increase in the intensity of pre‐monsoon tropical cyclones (TCs) is observed over the Arabian Sea. This study suggests that this increase is due to epochal variability in the ...intensity of TCs and is associated with epochal variability in the storm‐ambient vertical wind shear and tropical cyclone heat potential (TCHP). There is a significant increase (0.53 kJ cm−2 year−1) of TCHP during recent years. The warmer upper ocean helps TCs to sustain or increase their intensity by an uninterrupted supply of sensible and latent heat fluxes from the ocean surface to the atmosphere.
This study examines the link between upper-tropospheric planetary-scale Rossby waves and surface meteorological parameters based on the observations made in association with the Ganges Valley Aerosol ...Experiment (GVAX) campaign at an extratropical site at Aryabhatta Research Institute of Observational Sciences, Nainital (29.45° N, 79.5° E) during November–December 2011. The spectral analysis of the tropospheric wind field from radiosonde measurements indicates a predominance power of around 8 days in the upper troposphere during the observational period. An analysis of the 200 hPa meridional wind (v200 hPa) anomalies from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis shows distinct Rossby-wave-like structures over a high-altitude site in the central Himalayan region. Furthermore, the spectral analysis of global v200 hPa anomalies indicates the Rossby waves are characterized by zonal wave number 6. The amplification of the Rossby wave packets over the site leads to persistent subtropical jet stream (STJ) patterns, which further affects the surface weather conditions. The propagating Rossby waves in the upper troposphere along with the undulations in the STJ create convergence and divergence regions in the mid-troposphere. Therefore, the surface meteorological parameters such as the relative humidity, wind speeds, and temperature are synchronized with the phase of the propagating Rossby waves. Moreover, the present study finds important implications for medium-range forecasting through the upper-level Rossby waves over the study region.
In this paper, two logarithmic non-linearities are proposed for a new four-dimensional chaotic system. The phase portrait, Lyapunov exponent, bifurcation, stability, and other dynamical features of ...the new chaotic system are all discussed. The multi-stability of the new chaotic system with coexisting attractors has been established. The adaptive backstepping control approach with proper Lyapunov functions is used in the control application to retrieve the unknown parameters of the system. To synchronise the states between the drive-response system, non-linear feedback control is used, as well as backstepping control to synchronise the states on the system's error dynamics. Op-amp circuits are used to create the electronic circuit design for a new chaotic system. The system's efficiency is confirmed using MATLAB numerical simulation.
In this study, we investigate the causative processes responsible for the observed enhancement in the tropospheric and surface ozone during December 09–11, 2008 orography induced gravity wave event ...over Himalayan region. The analysis is done using surface ozone measurements and satellite datasets from Atmospheric Infrared Sounder/Advanced Microwave Sounding Unit-A (AIRS/AMSU-A), COSMIC, TES and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Observations depict a two fold increase in surface and tropospheric ozone during the event as compared to normal days in both AIRS and TES ozone measurements. COSMIC temperature perturbations show generation of shorter vertical wavelengths efficient for the sub-tropical tropopause folding due to orography induced gravity waves. Moreover, the intense tropopause folding as evidenced by upward-downward vertical velocities couplet could trigger the intrusion of stratospheric ozone rich air into upper tropospheric ozone poor air as also confirmed by high values of potential vorticity during the observational period. Hence, present study reemphasizes the importance of wave induced atmospheric dynamics on atmospheric constituents' especially tropospheric ozone over Himalayan region.
•Tropospheric ozone enhancement observed by multi-space borne sensors•Tropopause folding due to orography induced short vertical wavelength gravity waves.•Importance of STE process in tropospheric ozone over Himalayan region
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