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Coordination compounds of Co(II) , Ni(II), Cu(II) and Zn(II) of the type [M(L1-2)2(H2O)2] were obtained from Schiff base ligands [HL1-2] by the condensation reaction of 5-bromosalicyldehyde/5-chlorosalicyldehyde with 4-amino quinoline using methanol as a solvent in (1:1) molar ratio. The metal complexes were synthesized by reacting the aqueous methanolic solution of metal acetates M(CH3COO)2xH2O with the hot methanolic solution of their respective Schiff base ligands in (1:2) molar ratio. Various physicochemical techniques i.e. elemental analysis, molar conductance measurements, magnetic moment studies and different spectral studies (1H NMR, 13C NMR, UV–Vis, FT-IR, ESR) and mass spectrometry were used for characterization of compounds. The spectral data confirmed the bidentate nature (NO) of Schiff base ligands coordinating through nitrogen atom of azomethine group and oxygen atom of hydroxyl group resulting in the formation of octahedral geometry of all metal complexes. The Schiff base ligands and their transition metal complexes were screened against two gram-positive bacterial species i.e. (S. aureus, B. subtilis), two-gram negative bacterial species i.e. (E. coli, P. aeruginosa) and two fungal species (A. niger and C. albicans) using serial dilution method with ciprofloxacin and fluconazole as reference drug. The results obtained from antimicrobial studies showed that metal complexes are more active than their respective Schiff base ligands. Complex 5 and 6 are potent antimicrobial agent.

Modi Rural Municipality is one of the commercial vegetable pocket areas under temperate climate. A study was carried out during July 2021 in three vegetable growing areas: Tilahar, Deupur and Bajung of Modi Rural Municipality. A total number of nine quadrates (10×10) m2 were laid, including three replicating quadrates in each area with 500m differences from each quadrates in the sampling site. Overall, 18 farmers were interviewed to collect information about vegetables grown, insect pests that affected vegetables and their management practices. The total number of 24 insect pests were recorded belonging to five orders from 14 vegetable crops. Greater Sorensen's similarity index of insects was recorded in Tilahar and Deupur (ß=0.52) because there was similarity in environment, habitats, larval host plants and visiting plants of insects. Lower Sorensen's similarity index (ß=0.25) was recorded in Deupur and Bajung as there was less similarity in environment, habitats, larval host plants and visiting plants of insects. Insect pests and diseases on vegetables were the major problems in the study areas. The use of chemical insecticides was the means to control adopted by most of farmers while a few of them used other control methods. Insecticides on pests were applied considering fewer precautions. The study clearly indicated that the farmer’s knowledge towards Integrated Pest Management (IPM) was null and thus necessary action should be taken by concerned agencies to increase rate of vegetable production, avoid the heavy use of chemicals and allied consequences.

This paper examines long-term (more than four solar cycles) temporal and spatial fluctuations in the solar rotation by investigating radio-emission escapes from various layers of the solar atmosphere during the years 1967–2010. The flux modulation approach can also be used to investigate variations in solar rotation, which is a contentious topic in solar physics. This study makes use of a time-series of radio flux data at various frequencies (245–15 400 MHz) obtained at Sagamore Hill Solar Radio Observatory in Massachusetts, USA, and at other observatories from 1967 to 2010. The periodicity present in the temporal variation of the time-series is estimated through a Lomb–Scargle periodogram. The rotation period estimated for five radio emissions (606, 1415, and 2695 MHz from the corona, and 4995 and 8800 MHz from the transition region) through a statistical approach shows continuous temporal and spatial variations throughout the years. The smoothed rotation period shows the presence of periodic ∼22-yr and ∼11-yr components. The 22-yr component could be linked to the reversal of the solar magnetic field (Hale) cycle, while the 11-yr component is most likely related to the sunspot (Schwabe) cycle. In addition to these two components, random components are also prominently present in the analysed data. The cross-correlation between the sunspot number and the rotation period obtained shows a strong correlation with the 11-yr Schwabe and 22-yr Hale cycle. The corona rotates faster or slower than the transition region in different epochs. The alternation of the faster rotation speed between the corona and transition region also follows the 22-yr cycle.

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...

Fine particulate matter (PM2.5, aerodynamic diameter ≤2.5 µm) impacts the climate, reduces visibility and severely influences human health. The Indo-Gangetic Plain (IGP), home to about one-seventh of the world’s total population and a hotspot of aerosol loading, observes strong enhancements in the PM2.5 concentrations towards winter. We performed high-resolution (12 km × 12 km) atmospheric chemical transport modeling (WRF-Chem) for the post-monsoon to winter transition to unravel the underlying dynamics and influences of regional emissions over the region. Model, capturing the observed variations to an extent, reveals that the spatial distribution of PM2.5 having patches of enhanced concentrations (≥100 µgm−3) during post-monsoon, evolves dramatically into a widespread enhancement across the IGP region during winter. A sensitivity simulation, supported by satellite observations of fires, shows that biomass-burning emissions over the northwest IGP play a crucial role during post-monsoon. Whereas, in contrast, towards winter, a large-scale decline in the air temperature, significantly shallower atmospheric boundary layer, and weaker winds lead to stagnant conditions (ventilation coefficient lower by a factor of ~4) thereby confining the anthropogenic influences closer to the surface. Such changes in the controlling processes from post-monsoon to winter transition profoundly affect the composition of the fine aerosols over the IGP region. The study highlights the need to critically consider the distinct meteorological processes of west-to-east IGP and changes in dominant sources from post-monsoon to winter in the formulation of future pollution mitigation policies.

Dry deposition is a major sink for tropospheric ozone; nevertheless, studies on its effects on ozone distribution are very limited over the rapidly developing South Asian region. We performed numer...

The atmospheric motion vectors (AMV) are derived by tracking cloud and moisture features in the subsequent images of geostationary as well as polar satellites. The heights of the AMVs are nothing b...

The present work has been carried to analyze the changes in trend of temperature, water vapor and ozone profiles at different atmospheric layers, total column integrated methane (TCH4) and total column integrated carbon-monoxide (TCO) over the Indian region. The atmospheric column was divided into few atmospheric layers: surface-850 hPa, 850–500 hPa, 500–100 hPa, 100–50 hPa and 50–1 hPa. Monthly averages of these parameters were calculated from AIRS Level 2 Standard Products for a decade from 2003 to 2012. A non-parametric statistical test with seasonal modification was applied to check the trends of various parameters. Monthly means were used to examine the seasonal dependency in the trend, and allowing more information from the data to be used. The layer average temperature in surface-850 hPa layer has shown significant increase in overall annual trend over eastern part, southern part and averaged over whole India with an increase of 0.041 K/year, 0.034 K/year and 0.034 K/year, respectively. The overall trend was decreasing over all but southern parts in 100–50 hPa layer at the rate of 0.079 K/year over whole India. For water vapor trends, it has been found that layer integrated water vapor (LIWV) in surface-850 hPa layer has significant overall increasing trend over western part, southern part and averaged over whole India with the rate of increase of 0.555%/year, 0.598%/year and 0.486%/year respectively. For LIWV (850–500 hPa), only western part has significant increasing trend at a rate of 0.879%/year. However, LIWV in 500–100 hPa layer does not show any significant trend. Total water vapor (TWV) has shown significant annual increasing trend over all the parts except over the central part. The increasing trend has been estimated as 0.962%/year over whole India. The layer integrated ozone (LIOZ) in surface-850 hPa has significant increasing trend over western part (0.062%/year) and southern part (0.071%/year). In 500–100 hPa layer, the LIOZ has statistically significant decreasing trend over whole India at a rate of 0.112%/year. For LIOZ averaged over whole India in 100–50 hPa, there is significant decreasing trend with a rate of 0.273%/year. Overall, the ozone concentration is increasing near surface, whereas it is decreasing in lower stratosphere. The total column ozone (TOZ) has not shown any significant trend. The column integrated methane has shown an increasing trend (0.366%/year) over all parts of the country, whereas, TCO has not shown any significant trend.

The present study focuses on investigating the impacts of a sudden dust storm on the atmospheric boundary layer (ABL) over Ahmedabad (23.02°N, 72.57°E), an urban site located in the western region of India. The accumulation of dust in the atmosphere during the dust storm, originating from the Thar Desert in Rajasthan, led to the decrease in surface temperature as a consequence of dust-radiation interaction. Ambient particulate matter data obtained from Air Quality (AQ) station at Ahmedabad showed a spike of 118.5% and 44.5% in PM10 and PM2.5 concentrations, respectively during the event in comparison to the previous control day. Sudden exposure to an anomalous increase in particulate aerosols may cause severe impacts on human health. These surface forcing have been reflected in the stable nocturnal ABL. Backscatter signals recorded by ground-based Ceilometer Lidar at Physical Research Laboratory (PRL), showed that ABL was shallow and collapsed during the dust storm episode. Turbulence was detected in the ABL during the event which further assisted in the vertical mixing of dust aerosols in the ABL. These aerosols got trapped within the residual layer, preventing further percolation in the free atmosphere. Such sub-grid scale changes in the ABL during the dust storm were not reflected in the boundary layer height (BLH) obtained from the ERA-5 reanalysis dataset. A significant association between the ABL and the local radiative budget has been found. It has been substantiated by Coupled Ocean-Atmosphere Radiative Transfer Model (COART) simulations that showed a cooling of the surface. Thus, this study is important as it can be taken as feedback to improve local climate models with respect to dust storm meteorology.

Mesoscale convection weather events, associated with deep cumulonimbus clouds transport moisture, energy and momentum to upper troposphere and lower stratosphere (UTLS), affect the energetics and general circulation of the middle atmosphere. Therefore, it is necessary to understand the atmospheric dynamics during pre–monsoon periods (when strong mesoscale convective events occur) for improving the parameterization of model physics. The present study attempts to investigate the characteristics of high-frequency gravity waves (GWs) generated over Gadanki (13.5° N, 79.2° E), India during one such severe convection event in the pre–monsoon period. For this purpose, the Mesosphere Stratosphere Troposphere (MST) radar at Gadanki was operated continuously for the period of ∼10 h during 27–28 May 2015. A wide spectrum of high frequency GWs with different generation mechanisms are found during this convective event whose vertical propagation characteristics fulfill the non-hydrostatic GWs dispersion relation. The temperature and wind data of ERA (ECMWF Re-Analysis)-interim reanalysis and GPS radiosonde, launched at Gadanki, are also analyzed for ten days around the event day to determine the background atmospheric thermodynamical conditions. Strong up- and downdrafts are observed in the altitude range of ∼3.6–20 km (radar limited top height); presence of which even up to ∼20 km height is quite rare. The WRF (Weather Research and Forecasting) model simulated relative humidity on 27–28 May 2015 clearly depicts the mid-tropospheric moisture intrusion. Presence of moisture is also observed at the higher heights ∼17–18 km which could be due to strong low level convergence leading to high divergence value of deep cumulonimbus clouds in UTLS region. Furthermore, this is supported by the Doppler Weather Radar (DWR) and simulated reflectivity of WRF model reaching the tropopause height of ∼18 km. The altitude profiles of phase of some oscillations during convection period depict that the sources of these waves are near ∼20 km which is first of its kind outcome and it is corroborated with high resolution WRF model simulations.

The vertical wavenumber (VWN) characteristics during sudden stratospheric warming (SSW) events (2003–2016) is investigated for the first time using temperature observation of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on-board Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite (for the altitude range of 20–70 km) and ERA-Interim reanalysis data (for the altitudes of 0.1–20 km). Highly negative VWN spectral slope value (approximately) of −4.82 (at 25° N, 77° E) and −4.41 (at 35° N, 77° E) at 40–50 km altitude is observed during the 2013 SSW event, a sort of which is not perceived in any other SSW events (2003–2016). The combined effect of planetary waves (PWs) with wavenumber 1 and 2 during 2013 SSW may be responsible for such distinctive observation near the peak temperature altitude. This study elicits the importance of polar vortex portraying that lower latitudes are affected if only the vortex splits and presents the first of its kind VWN characteristics during SSW events.

Urban areas emit large amounts of methane (CH4) to the atmosphere from landfills, wastewater treatment facilities, waste dump and consumption and infrastructure of natural gas. CH4 emissions from India are increasing, especially from the urban regions due to fast socioeconomic developments. Therefore, the total emissions of all greenhouse gases (GHGs) from these regions need to be continuously monitored. However, the systematic measurements of GHGs at urban regions in India are lacking to record the current emission scenarios. We have initiated high-frequency measurements of atmospheric CH4 dry-air mole fraction (DMF), along with carbon dioxide (CO2) and carbon monoxide (CO) at Ahmedabad, a representative urban site in western India, using laser-based cavity ring down spectrometer from July 2014 to July 2015. The time series analysis suggests that the study region exerts very high emissions of CH4, and the tracer-tracer correlations of CH4:CO2 and CH4:CO indicate that the combustion related anthropogenic and fugitive sources are the two main sources of CH4 in the study region. The seasonally high (low) values of CH4 DMF are observed during October–February (May–August) months, and the diurnally high (low) CH4 are observed during midnight (afternoon) hours. We compute the total CH4 emission from Ahmedabad to be ∼58 ± 16 Gg for the year 2014, which is ∼45% higher than the EDGARv4.2 FT2010 inventory estimates. The observed time series are compared to simulations from two global atmospheric chemistry-transport models (i.e. ACTM and LMDzINCA). Both of the models perform very well in simulating the seasonal cycle of CH4 when the afternoon mean observations are used but fail to simulate the evening to mid-night build-up in CH4 owing to coarse resolutions of the global models and limitations in capturing the dynamical and physical processes in the boundary layer.

A comprehensive statistical analysis of the cloud base height (CBH) measured by ground-based Vaisala ceilometer (CL31) has been performed to study different layers of the cloud in the lower troposphere up to 7.5 km height over Ahmedabad, western India during 2014 and 2015. The total observations (∼69%) of cloud by using ceilometer show annual cloud occurrence frequency of around 64%. Seasonal variation of CBH and cloud occurrence frequency reveal that the maximum/minimum cloud cover is found during southwest (SW) Indian summer monsoon/pre-monsoon season. Three CBHs (CBH1, CBH2, and CBH3) are presented in monsoon period due to high cloud occurrence, and two CBHs (CBH1 and CBH2) are observed in other seasons due to low cloud occurrence by ceilometer over the observational site. The CBH1 (∼100–2000 m) and CBH2 (500–3000 m) are observed during SW monsoon and summer season, respectively. The CBH3 is occurred usually in SW monsoon season. Moreover, the cloud cover during the day and night time shows that the occurrence of cloud is more frequent in daytime than nighttime during pre-monsoon and post-monsoon season. The statistical analysis of cloud with ground-based observations is also performed in this study that may be useful for the development/improvement of regional weather and climate models to reduce the uncertainty in the prediction.

A diagnostic investigation of an extreme rainfall episode that occurred over the central and north Indian region is carried out in this study using data from a suite of observations from space-borne instruments and the reanalysis datasets. This event is unique in the sense that the organized tropical and extratropical forcing stimulated the intense rainfall on 01 Jan 2012. The WindSat (multi-frequency polarimetric microwave radiometer) observations indicate the source of the moisture flux coming from the adjoining tropical Ocean. The dynamical and thermo-dynamical contributions are evaluated based on the atmospheric instability analysis using the Atmospheric Infrared Sounder (AIRS) and reanalysis datasets by computing various stability indices such as total totals (TT) index, Potential Vorticity (PV), static stability and the Convective Available Potential Energy (CAPE). High TT index values (>40 K) are observed both in satellite and reanalysis data indicating thermodynamic instability. PV intrusion to low latitudes is also observed with extreme rainfall occurrence ahead of the PV tongue. The vertical structure of PV intrusion shows remarkable features with enhanced upward motions ahead of the intrusion representing the dynamical instability. The reduced static stability, increased CAPE and upper-level cyclonic anomalies together with enhanced moisture in the lower troposphere coming from the adjoining tropical Indian Ocean regulate the amplitude and region of occurrence of the extreme rainfall. Therefore, this study identifies the significant implications of tropical and extra-tropical influences that generate the thermodynamical and dynamical instabilities for the occurrence of the extreme rainfall event over the Central and Northern parts of India.

In this article, a series of coordination complexes of Co(II), Ni(II), Cu(II) and Zn(II) metals were prepared by four novel Schiff base ligands (E)-N’-(4-(prop-2-yn-1-yloxy)benzylidene)benzohydrazide (HL1), (E)-4-chloro-N’-(4-(prop-2-yn-1-yloxy)benzylidene)benzohydrazide (HL2), (E)-N’-((2-(benzyloxy)naphthalen-1-yl)methylene)benzohydrazide (HL3), (E)-N’-((2-(benzyloxy)naphthalen-1-yl)methylene)-4-chlorobenzohydrazide (HL4) obtained by the condensation reaction of benzoic acid hydrazide/4-chloro benzoic acid hydrazide with oxy derivatives of 2-hydroxy-1-napthaldehyde/4-hydroxy benzaldehyde. The proposed structure of the complexes have been established by spectroscopic and analytical techniques like C, H, N and metal analysis, FT-IR, 1H and 13C NMR, mass, UV-Vis, EPR, fluorescence, molar conductance, magnetic susceptibility and TGA which concluded that Schiff bases act as bidentate NO donor ligands coordinating through nitrogen atom of azomethine linkage and uninegative oxygen atom of carbonyl group in enolic form and resulting in complexes of the type [M(L1–4)·(CH3COO)·3H2O] in 1:1 molar ratio. The synthesized compounds were screened for their in vitro antimicrobial activities against two gram +ve bacteria i.e. S. aureus and S. gordonii; two gram -ve bacteria i.e. E. coli and P. aeruginosa and two fungal strains i.e. A. niger and C. albicans and found that metal chelates were more noxious than their parent Schiff bases. The copper(II) complex 19 was found to be the highest noxious antimicrobial active compound. The compounds were also assessed for their antioxidant activity and found that the complexes are more potent and show excellent efficiency in decolorizing the DPPH purple colored solution than their free ligands. The complexes 6, 7, 10, 11, 14, 15, 18, 19 were found to be excellent antioxidants and copper(II) complexes were the most potent antioxidant compounds with lowest IC50 values (2.04–2.56 µM)) among all the tested compounds. Total 20 compounds of Schiff bases transition metal complexes were synthesized and characterized. The copper complex (19) was found to be highest antimicrobial against Streptococcus gordonii, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger, Candida albicans. The copper(II) complex (11) exhibits outstanding and highest antioxidant activity (IC50 = 2.04 µM).

The study focusses to investigate the variations in aerosol characteristics, concentrations and radiative properties due to the burning of firecrackers during Diwali festival event followed with New year festival celebrations over a representative urban environment. A six day's long intensive in situ measurements of Black Carbon, Particulate Matter and Aerosol Optical Depth were collected to capture pre to post-Diwali and New Year festival celebrations marked with massive fireworks. We observed an increase of 286%, 89.5%, and 60.5%, in BC, PM10, and PM2.5 concentrations, respectively on festival night as compared to pre-event days. An increase in in situ measured AOD is comparable with concurrent satellite derived AOD. Angstrom exponent, α > 1.0 along with high turbidity coefficient; β estimated for the festival period clearly implies the abundance of fine-mode particles, probably the smoke aerosols loading from fireworks. The Mie-scattered return signals received by the ground based Raman LiDAR at 532 nm showed an increased concentration of ‘anthropogenic aerosols’, attributed to the increased crackers activity. Space based CALIPSO LiDAR observations also validate the presence of ‘polluted dust’ and ‘smoke’ types aerosols at the near surface to 5 km altitude over the study area. A sharp increase in gaseous air pollutants like SO2 and NOx concentrations exceeding the National Ambient Air Quality Standards is also observed. The COART model run simulations in SWIR region showed an increased ‘cooling’ at the surface (−125 Wm−2 to −185 Wm−2) as compared to ‘warming’ in the atmosphere during the event period. A maximum heating rate (1.9 Kday−1) due to total aerosol radiative forcing is also estimated. These investigations provide useful insights into the impact of burning firecrackers on urban air quality besides radiative impacts at a regional scale. Such celebration induced air pollution events may lead to severe health impacts; particularly respiratory and cardiovascular ailments in the resident population.

In this study, decadal trend analysis of atmospheric temperature, water vapour, ozone, methane and carbon-monoxide has been presented over few major cities of India using Aqua-AIRS products from 2003 to 2012. The atmospheric column is studied in few atmospheric layers, viz., surface-850, 850–500, 500–100, 100–50 and 50–1 hPa for temperature, water vapour and ozone. However, CH4 and CO results are presented in total column amounts. Non-parametric Mann–Kendall test has been applied to investigate the trends of annual means of parameters and Sen’s slope estimate has been used to find the rate of the change, if there is a trend. The layer average temperature (LAT) has been found to be increasing in lower troposphere (surface-850 hPa) and decreasing in lower stratosphere (100–50 hPa). The warming trend over Chennai is found to be not limited in lower tropospheric region, but extended in 850–500 hPa layer also. However, LAT (850–500 hPa) has decreasing trend over Thiruvananthapuram. LAT in 500–100 hPa has significant decreasing trend only over Ahmedabad. The decreasing LAT trend in 100–50 hPa is quite prominent with significant decreasing trends over Mumbai, Ahmedabad, Kolkata and Hyderabad. The layer integrated water vapour (LIWV) is found be increasing mainly in surface-850 hPa and 850–500 hPa layers. The decreasing trend of LIWV has been observed only over Ahmedabad in 500–100 hPa layer. For total column water vapour, the trends are mostly increasing, however, it is statistically significant only over Hyderabad. The layer integrated ozone has been found to be increasing in troposphere and decreasing in lower stratosphere. The increasing trend of ozone in troposphere is most prominent in lower-mid tropospheric region (850–500 hPa layer). No significant trend has been observed for total column ozone. Total column methane has shown significant increasing trend over all cities with very good significance level. However, for total column carbon-monoxide, the trends are decreasing and the decreasing trends are significant over Delhi and Mumbai.

Fog is a meteorological phenomenon in which cloud has its base near to the surface which disrupts public health and transportation due to decrease in visibility. In the present study, a collective ...

Long term variations of the middle atmospheric thermal structure in the upper stratosphere and lower mesosphere (20–90 km) have been studied over Ahmedabad (23.1°N, 72.3°E, 55 m amsl), India using SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) onboard TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics) observations during year 2002 to year 2014. For the same period, three different atmospheric models show over-estimation of temperature (∼10 K) near the stratopause and in the upper mesosphere, and a signature of under-estimation is seen above mesopause when compared against SABER measured temperature profiles. Estimation of monthly temperature anomalies reveals a semiannual and ter-annual oscillation moving downward from the mesosphere to the stratosphere during January to December. Moreover, Lomb Scargle periodogram (LSP) and Wavelet transform techniques are employed to characterize the semi-annual, annual and quasi-biennial oscillations to diagnose the wave dynamics in the stratosphere-mesosphere system. Results suggested that semi-annual, annual and quasi-biennial oscillations are exist in stratosphere, whereas, semi-annual and annual oscillations are observed in mesosphere. In lower mesosphere, LSP analyses revealed conspicuous absence of annual oscillations in altitude range of ∼55–65 km, and semi-annual oscillations are not existing in 35–45 km. Four monthly oscillations are also reported in the altitude range of about 45–65 km. The temporal localization of oscillations using wavelet analysis shows strong annual oscillation during year 2004–2006 and 2009–2011.

A preliminary study was performed to investigate the quality of total column ozone (TCO), water vapour (WV) and aerosol optical thickness (AOT) available from satellite and reanalysis from atmospheric models along with in situ observations over Ahmedabad (23.03 ° N, 72.5 ° E, 55 m above mean sea level), India. Ground-based measurements from a MICROTOPS II ozonometer as well as space-based satellite retrieved products from the moderate resolution imaging spectroradiometer (MODIS) and an ozone monitoring instrument were analysed during December 2014 to March 2015. The European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-Interim) created TCO and WV were also used to assess the skill of global model reanalysis over the western part of India. An increasing trend was found in the TCO and WV parameters from the winter to summer period. Investigations showed that MODIS satellite retrieved and ERA-Interim reanalysis WV are able to capture the trends compared with ground-based hand-held MICROTOPS II observations. Higher TCO was found in the MODIS data, whereas the ERA-Interim and ozone monitoring instrument TCO matched well with ground-based observations. Larger differences were found with the MODIS AOT in comparison to MICROTOPS II AOT observations. Further, analysis showed that ERA-Interim has sufficient potential to be used for various meteorological applications over the western Indian region. Furthermore, the variations of TCO, WV and AOT were studied over the orographic region of Mount Abu (∼110 km aerial distance from Ahmedabad), located in the Aravali range of mountains. Ground-based measurements at different altitudes (0.3, 1.1 and 1.67 km above mean sea level) revealed significant variations in WV and AOT. The WV varies 17.1% (30.3%) and the AOT varies 53.8% (57.5%) in 1.1 km (1.67 km), whereas no noteworthy variations are observed in the TCO in this field campaign.

The Stratospheric Sudden Warming (SSW) is one of the most spectacular phenomena in the atmosphere and has impacts on the Earth’s lower, middle, and upper atmospheres. In this study, two major SSW episodes associated with vortex displacement and vortex splitting that occurred in the years 1998 and 1999, respectively, are investigated for the first time over Mt. Abu using lidar observations. Analyses show that ground-based lidar and satellite observations from the Halogen occultation experiment (HALOE) on board the upper atmospheric research satellite (UARS) can capture the effect of SSW events. Lidar measurements are able to capture SSW warming and its decay very accurately. The impact of SSW is further investigated in the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim-reanalysed potential vorticity. Moreover, a detailed study has been presented to understand the latitudinal variation of SSW warming and the associated mesospheric cooling over the Indian region. The results showe...

Equatorial atmospheric regions are unique and one of the most important parts of the Erath’s atmosphere. These regions receive maximum energy from the Sun and are highly turbulent. Height of the tropopause is maximum over the equatorial regions and several complex processes are taking place all the times. Further, they are always influenced by the processes of Northern Hemisphere as well as by the Southern Hemisphere. Atmospheric temperature is one the most sensitive parameters and having imprints of dynamical, radiative and chemical processes. Thermal structure, seasonal variability and atmospheric oscillations occurring in the equatorial middle atmosphere have been studied using temperature measurements obtained from the Sounding of the Atmosphere using the Broadband Emission Radiometry (SABER) instrument on-board Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite during January 2002 to December 2015 (14 years). In the present work, three geographical locations have been chosen, considering 5° × 15° latitude-longitude grid between the altitudes ranging from 20 to 100 km. These locations are named as site 1, site 2 and site 3 and are spread over Equatorial latitudes and ± 120° longitude. A detailed time series and climatology have been established over these regions and significant longitudinal differences has been observed. Characteristics of Semiannual oscillations (SAO), Annual Oscillations (AO) and Quasi Biennial Oscillation (QBO) have been investigated using Lomb Scargle Periodogram and wavelet transform analysis techniques. Form the analysis it is observed that, SAO is showing highest amplitude at 45 km and 75-85 km and QBO is showing significance amplitude in the lower stratosphere. At higher altitudes, amplitudes of all the oscillations (SAO, AO and QBO) are very weak, and temperatures also not revealing any particular pattern. Moreover, from the climatology and time series of the temperature measurements higher temperature (-260 K) has been noticed at 55-65 km height range. In addition to that, seasonal variations over these three regions have been studied and the strength of seasonal difference is found to be about 9 K (summer-winter) at higher altitudes. Furthermore, these satellite-based results are augmented and compared using the MACC (Monitoring Atmospheric Composition and Climate) reanalysis and simulations using a climate model EMAC (ECHAM5/MESSy Atmospheric Chemistry) over the equatorial regions.

Tropospheric ozone plays a key role in controlling the oxidation capacity of the atmosphere, and is a Short-Lived Climate forcing Pollutant (SLCP). Rapid changes in the emissions, land use, and regional climate are anticipated to intensify the tropospheric chemistry in South Asia during last two decades. Owing to the tropical convection together with strong horizontal winds aloft, the changes in tropospheric chemistry over South Asia influence the global atmospheric composition especially in the Upper Troposphere and Lower Stratosphere (UTLS). However, in situ observations in the free troposphere are highly sparse over South Asia to study the long-term changes in this region and their impacts downwind. Here, we combine satellite retrievals (Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) on board the Aura spacecraft), model reanalysis (MACC; Monitoring Atmospheric Composition & Climate), and a regional climate model (WRF-Chem; Weather Research and Forecasting coupled with Chemistry) to investigate the tropospheric ozone climatology and long-term trend over South Asia during 2005-2017 period. Satellite retrievals show elevated tropospheric ozone loading (∼50 DU) along the Indo-Gangetic Plain (IGP) during both pre-monsoon and the summer monsoon, and reveal strong inter-annual variations of 10–15 DU. A general increase in the Tropospheric Column Ozone (TCO) is observed across the South Asia in all the seasons. Wintertime TCO shows an increase over the western India and Northwest Indo-Gangetic Plain (IGP) with a statistically significant (p 2 , and HCHO. Sensitivity simulations using a regional chemistry climate model (WRF-Chem) are being performed to analyze the role of large-scale dynamics, besides the regional photochemistry.

The present study investigates the characteristics of elevated aerosol layer (EAL) using high spatio-temporal Boundary Layer Lidar observations over Manora Peak (29.4° N; 79.2° E; 1958m above mean sea level), Nainital located in the Himalayan region. We have chosen four EAL cases on June 17, 2006 (C1); December 12, 2007 (C2); February 06 (C3) and May 07, 2008 (C4) over the observational site. The occurrence of EAL is generally found at an altitude ~ 2–4 km above ground level over the site. It is found that the westerly/northwesterly winds with magnitudes of about 6–9 ms−1 are conducive for the generation and strengthening of EAL. A 7-days airmass backward trajectory analysis reveals that the lower (higher) altitude source originates from the west coast (northwest) regions. Furthermore, the atmospheric radiative forcing estimated using Santa Barbara DISORT (discrete ordinates radiative transfer) Atmospheric Radiative Transfer (SBDART) model reveals that the atmosphere heats up with 1.35 K day−1 and 1.32 K day−1 due to the presence of EAL on C1 and C4, respectively. Our results confirm that the occurrence of EALs causes atmospheric warming, that can impact on the regional radiation budget over the Himalayan region.

International audience; The temperature retrieved from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during January 2002 to September 2015 are used in this study to delineate the differences of middle atmospheric thermal structure in the Northern Hemisphere (NH) and Southern Hemisphere (SH). Two stations namely Mt. Abu (24.59°N, 72.70°E) in NH and Reunion Island (21.11°S, 55.53°E) in SH are chosen over sub-tropical regions. Temperature climatology from SABER observations suggests that stratopause is warmer, and upper mesosphere is cooler in NH as compared to SH. Three atmospheric models are used to understand the monthly thermal structure differences for different altitudes. Moreover, semi-annual, annual and quasi-biennial oscillations are studied using Lomb Scargle Periodogram and Wavelet transform techniques. Over NH, summer and winter season are warmer (~4 K) and cooler (~3 K) respectively in stratosphere as compared to SH. It is important to note here that Mt. Abu temperature is warmer (~9 K) than Reunion Island in winter but in summer season Mt. Abu temperature is cooler in upper mesosphere and above mesosphere NH shows warming. Results show that annual oscillations are dominated in both hemisphere as compared to semi-annual and quasi-biennial oscillations. In upper mesosphere, strength of annual oscillations is substantial in NH, while semi-annual oscillations are stronger in SH. Wavelet analyses found that annual oscillations are significant in NH near mesopause, while semi-annual oscillations are strengthening in SH.

Cloud is one of the most crucial parameters, which influences the predictive ability of the weather models. This study is first of its kind to assess the efficiency of the numerical weather prediction (NWP) models to simulate the cloud types over Indian region. Two broadly used NWP models named as European Centre for Medium Range Weather Forecast (ECMWF) Reanalysis Interim (ERAI) and Weather Research and Forecasting (WRF) model are chosen to compare analyses and forecasts of cloud types along with cloud base height (CBH) measured from ceilometer over Ahmedabad (23.03°N, 72.5°E, 55 m amsl), India. Three months of the Indian summer monsoon period (July to September, 2014) are used for initial verifications. Results show that both the ERAI and WRF models are able to capture the cloud cover correctly over this region. This investigation has shown that the WRF model shows mostly mid-level cloud as low-level cloud, which needs further modification in WRF physics to improve the skills of cloud forecast. ...

The geomagnetic storm of November 1998 is a unique event where IMF-Bz remained southward with values exceeding –15 nT for more than a day. The SYM/H index decreased from about 07 hr on 13 November 1998 reaching a minimum of about –120 nT around midnight of 13–14 November 1998. Features of the equatorial electrojet in the Indian region are studied during the geomagnetic storm event of 13–14 November 1998, based on the geomagnetic data from the chain of observatories in India. Sudden northward turning of IMF-Bz for a very short duration around 08 hr on 13 November 1998 resulted in a small and very short duration counter electrojet. A strong (–50 nT) and a long duration counter electrojet, right from 08 to 13 hr on 14 November 1998 was observed resulting in the absence of equatorial Es at Thumba. Absence of the equatorial ionization anomaly was also observed as seen from the ionograms over Thumba and ionspheric data from Ahmedabad. The delayed effect on 14 November 1998 is due to the disturbance dynamo effect.

Characteristics of Mesospheric Temperature Inversions (MTIs) are studied using ~290 nights of Rayleigh Lidar data collected over Mt. Abu (24.5°N, 72.7°E) during the period of 1997 to 2004 for the first time from an Indian sub-tropical location. Three MTI events have been investigated and statistical analysis has also been performed. A strong MTI event, with amplitude of about 30 K, at altitudes between 60 and 70 km was observed on 30 December 2003. It was accompanied by strongly perturbed mesospheric zonal winds as observed by TIMED Doppler Interferometer (TIDI) onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED). Two MTI episodes during March and December 2000 have been investigated, which showed that MTI can persist for few days and its amplitude varies gradually. Ozone observed by Halogen Occultation Experiment (HALOE) onboard Upper Atmospheric Research Satellite (UARS) also showed significantly higher variability during strong MTI events. A statistical analysis of MTI occurrence and their characteristics have been done using Lidar data (1997–2004), HALOE on board UARS (1997–2004) and SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) on board TIMED (2002–2004). The frequency of occurrence of MTIs is maximum during winter and minimum during summer and average magnitude of MTIs is ~20 K with prominent seasonal variability. SABER and Lidar observed occurrence statistics is showing very similar pattern and SABER is able to capture stronger MTIs (~50 K). The average bottom height of MTIs from Lidar is having strong seasonality (lower height during winter) in contrast to satellites observed heights of MTIs.

Convective clouds are the sources of severe weather and extreme precipitation events which often produce flooding, landslides and other disasters. The physical characteristics of convective clouds influence the distribution of radiative heating/cooling in the troposphere. They play a crucial role in atmospheric circulation and the hydrological cycle. Present study deals with the detection of convective clouds using multispectral observations at split window channels (near 11 and 12 µm) and water vapour absorption channels (near 6.7 µm) from EUMETSAT (Meteosat 7) data. Results are compared with the observations (reflectivity-based threshold) from Precipitation Radar (PR) on-board Tropical Rainfall Measuring Mission (TRMM). The Results have also been validated against convective clouds derived from rain gauge based precipitation product from the IMD data. Validation results show a correlation coefficient (cc) of 0.79 and Root Mean Square Error (RMSE) of 2.61 (%) against rain gauge based observations of convective clouds.

Temporal and spectral characteristics of X-ray emission from 60 flares of intensity $\ge$C class observed by Solar X-ray Spectrometer (SOXS) during 2003-2011 are presented. We analyse the X-ray emission observed in four and three energy bands by the Si and CZT detectors, respectively. The number of peaks in the intensity profile of the flares varies between 1 and 3. We find moderate correlation (R$\simeq$0.2) between the rise time and the peak flux of the first peak of the flare irrespective to energy band, which is indicative of its energy-independent nature. Moreover, magnetic field complexity of the flaring region is found to be anti-correlated (R=0.61) with the rise time of the flares while positively correlated (R=0.28) with the peak flux of the flare. The time delay between the peak of the X-ray emission in a given energy band and that in the 25-30 keV decreases with increasing energy suggesting conduction cooling to be dominant in the lower energies. Analysis of 340 spectra from 14 flares reveals that the peak of Differential Emission Measure (DEM) evolution delays by 60-360 s relative to that of the temperature, and this time delay is inversely proportional to the peak flux of the flare. We conclude that temporal and intensity characteristics of flares are energy dependent as well as magnetic field configuration of the active region., Accepted for Publication in Research in Astronomy and Astrophysics (RAA) Journal. arXiv admin note: text overlap with arXiv:1210.4210 by other authors

The subject of pre-earthquake ionospheric signatures has always been contentious and debatable. Some of the previous reports have documented unforeseen and unusual variations in some of the atmospheric and ionospheric parameters well before an earthquake. Here, we analyze the ionospheric response from the Indian Subcontinent to Nepal Gorkha Earthquakes occurred between April and May 2015, which were the most powerful and disastrous natural calamities in past ~80 years over the Himalayan region left ~9000 causalities and more than ~20000 people injured with the property damage of the order of several billion dollars. In view of severe earthquakes occurrences, their prior information on the shorter time scales are warranted for mitigation of associated disasters. Here, we report for the first time, a case which shows a strong link in anomalous variations between VLF sub-ionospheric signal and mesospheric ozone prior to both April 25, 2015 (Mw = 7.8) earthquake and its biggest aftershock on May 12, 2015 (Mw = 7.3). Observations show an unusual variation in VLF signals amplitude /shift in terminator time (TT) strongly linked with positive (negative) mesospheric ozone anomaly in D-region altitudes prior to the Gorkha Nepal earthquakes. It is surmised that simultaneous continuous observations of both VLF waves and mesospheric ozone can be considered as an important tool to identify the prior earthquake signatures in the vicinity of the extremely earthquake-prone zone such as Himalayan region. In this context, the current report opens up a new dimension in lithosphere-atmosphere-ionosphere coupling during the earthquake preparation processes itself.

On 16 June 2013, intense and continuous rainfall together led to the collapse of moraine-dammed lake (Chorabari Lake) and devastated the entire land of Uttarakhand, Himalaya. This caused heavy floods in Uttarakhand (28°43′−31°27′ latitudes and 77°34′–81°02′ longitudes) along with unprecedented damage to life and property. Timely prediction and warning of such severe local weather systems over complex terrain are the first step towards disaster mitigation and bears huge societal impact. In this study, weather research and forecasting (WRF) model was configured at high spatial resolution (2 km) to simulate the Kedarnath heavy rainfall event over Uttarakhand region of India during 16–17 June 2013. Results showed that the WRF model was able to predict the Kedarnath heavy rainfall. Location and intensity of heavy rainfall were captured by the WRF model when verified with in situ measurements and satellite-retrieved rainfall products. Moreover, the explicit impact of topography in triggering this extreme weather event has been discussed using a diagnostic model which demonstrated that orographic component of rain rate is quite high over this region.

Increased concentration of greenhouse gases due to anthropogenic activities warm the troposphere and have a cooling effect in the middle and upper atmosphere. Ionospheric densities and heights are affected due to cooling. Carbon dioxide is one of the most dominant gases for the cause of long term ionospheric trends along with other radiatively active greenhouse gases. Regular ionospheric soundings are made over Ahmedabad (23.1°N, 72.7°E), since 1953. Long term changes in the ionosphere as a consequence of the cooling of the mesosphere and thermosphere due to the increased concentration of greenhouse gases have been studied. Ionospheric observations over Ahmedabad, a low latitude station in the anomaly crest region, for the years 1955–2003 are examined to study the long term changes in the critical frequencies of the various ionospheric layers and the height of the maximum ionization as characterized by h P F 2 . A decrease in f o F 2 (1.9 MHz for midday, 1.4 MHz for midnight) and h P F 2 (18 km for midday, 17 km for midnight) during about five decades are noted. An increase is noted in f o F 1 (0.4 MHz). The f o F 2 data are also examined over an equatorial station Kodaikanal (10.2°N, 77.5°E), situated near the magnetic equator for the years 1960–1995 and a decrease of 0.5 MHz for midday and 0.7 MHz for midnight are noted in ~35 years.

General characteristics of sub-tropical middle atmospheric temperature structure over a high altitude station, Mt. Abu (24.5°N, 72.7°E, altitude ~1670 m, above mean sea level (amsl)) are presented using about 150 nights observational datasets of Rayleigh Lidar. The monthly mean temperature contour plot shows two distinct maxima in the stratopause region (~45–55 km), occurring during February-March and September-October, a seasonal dependence similar to that reported for mid- and high-latitudes respectively. Semi-Annual Oscillation (SAO) are stronger at an altitude ~60 km in the mesospheric temperature in comparison to stratospheric region. A comparison with the satellite (Halogen Occultation Experiment, (HALOE)) data shows qualitative agreement, but quantitatively a significant difference is found between the observation and satellite. The derived temperatures from Lidar observations are warmer ~2–3 K in the stratospheric region and ~5–10 K in the mesospheric region than temperatures observed from the satellite. A comparison with the models, COSPAR International Reference Atmosphere (CIRA)-86 and Mass Spectrometer Incoherent Scatter Extended (MSISE)-90, showed differences of ~3 K in the stratosphere and ~5–10 K in the mesosphere, with deviations somewhat larger for CIRA-86. In most of the months and in all altitude regions model temperatures were lower than the Lidar observed temperature except in the altitude range of 40–50 km. MSISE-90 Model temperature overestimates as compared to Lidar temperature during December-February in the altitude region of 50–60 km. In the altitude region of 55–70 km both models deviate significantly, with differences exceeding 10–12 K, particularly during equinoctial periods. An average heating rate of ~2.5 K/month during equinoxes and cooling rate of ~4 K/month during November-December are found in altitude region of 50–70 km, relatively less heating and cooling rates are found in the altitude range of 30–50 km. The stratospheric temperature derived from the Lidar and columnar ozone observed by the Total Ozone Mapping Spectrometer (TOMS) over Mt. Abu shows good correlation (r 2 = 0.61) and indicates the association of ozone with the temperature.

Rain plays a significant role in satellite communication link design as attenuation caused by rain is severe in Ku and Ka bands which degrade the performance of the system. This paper mainly focuses on predicting the attenuation caused by rain in five Indian zones through the ITUR model in the frequency range of 12–40 GHz. It further emphasizes on attenuation predicted through SAM (simple attenuation model) and Garcia-Lopez Model followed by a comparison between the various proposed models for rain prediction. The platform used for implementation is MATLAB.

Here we report in depth reanalysis of a paper by Vats et al. (2001) [Astrophys. J. 548, L87] based on the measurements of differential rotation with altitude as a function of observing frequencies (as lower and higher frequencies indicate higher and lower heights, respectively) in the solar corona. The radial differential rotation of the solar corona is estimated from daily measurements of the disc-integrated solar radio flux at 11 frequencies: (275, 405, 670, 810, 925, 1080, 1215, 1350, 1620, 1755 MHz and 2800 MHz). We use the same data as were used in Vats et al. (2001), but instead of the 12th maxima of autocorrelograms used there, we use the 1st secondary maxima to derive the synodic rotation period. We estimate synodic rotation by Gaussian fit of the 1st secondary maxima. Vats et al. (2001) reported that the sidereal rotation period increases with increasing frequency. The variation found by them was from 23.6 to 24.15 days in this frequency range with a difference of only 0.55 days. The present study finds that sidereal rotation period increases with decreasing frequency. The variation range is from 24.4 to 22.5 days and difference is about three times larger (1.9 days). However, at 925 MHz both studies give similar rotation period. In Vats et al. (2001) the Pearson factor with trend line was 0.86 whereas present analysis obtained a ~ 0.97 Pearson factor with the trend line. Our study shows that the solar corona rotates slower at higher altitudes, which is in contradiction to the findings reported in Vats et al. (2001). Key words: Solar radio flux- flux modulation method- Gaussian fit- sidereal rotation period., 10 pages 4 figures solar physics journal

International audience; The transition regions in thermal structure viz. Tropopause, stratopause and mesopause play a vital role in the vertical coupling of the Earth’s atmosphere. For the first time, interhemispheric characteristics of the transition regions over two subtropical regions are studied using temperature observations from the SABER onboard TIMED satellite and the ERA Interim reanalysis during year 2002 to 2015. Results show that tropopause height is higher over Reunion Island (21.11S, 55.53E) in the Southern Hemisphere (SH) as compared to Mt. Abu region (24.59°N, 72.70°E) in the Northern Hemisphere (NH). Temporal variation of tropopause temperature reveals a decreasing (* 4 K) trend from year 2002 to 2008 and beyond this, an increasing (* 1.5 K) trend is found in tropopause temperature. These features are reinforcing for Mesopause as compared to tropopause temperature. The SH shows stronger variations in Mesopause temperature (* 7 K) compared to NH during year 2002 to 2008.The occurrence frequency of mesopause and stratopause height shows that the maximum occurrence frequency (* 60%) of mesopause at * 100 km in NH, while frequency is found to be * 55% in the SH. Results show that stratopause (mesopause) is cooler (warmer) in NH as compared SH. Moreover, Lomb Scargle Periodogram and wavelet transform techniques are used to investigate the periodicity of mesopause, stratopause and tropopause temperatures and heights. Investigations revealed prominent annual oscillations in the tropopause and stratopause temperatures in both hemispheres. These findings will be of immense use for the vertical and inter-hemispheric atmospheric coupling studies.

The present study primarily focused on the characteristics of the planetary scale waves in the middle atmosphere during different phases of Quasi-Biennial Oscillation (QBO), a dominant oscillation in the low-latitude stratospheric region. The temperature profiles retrieved from the Rayleigh lidar measurements have been utilized for the 11 winter periods between 1998 and 2009 over a low-latitude station, Gadanki (13.5oN 79.2oE). The spectral analysis of temperature anomalies indicates two dominant planetary-scale modes, namely, quasi 12-day and quasi 16-day waves. The existence of these waves in the middle atmosphere is strongly controlled by the westerly and easterly phases of QBO. For instance, the 12-day wave is mainly observed in the QBO westerly phase, while the 16-day wave peaks at two heights; 30–40 km and above 60 km with large spread in the mesosphere due to Doppler shifting in presence of westerly winds. The QBO easterly phase indicates low wave activity with 16-day wave indicating appreciable amplitudes in the upper stratosphere and mesosphere and is absent in the lower altitudes. This indicates that the 16-day wave might be generated through some in-situ mechanism due to gravity breaking or instability in the mesospheric region. Moreover, the refractive index of the two dominant planetary waves are strongly negative in the easterly phase relative to the westerly phase of QBO in the lower troposphere and stratosphere. This indicates the high probability of the planetary wave vertical propagation in the westerly phase of QBO. Therefore, the presented report re-emphasizes the importance of QBO controlling the middle atmospheric dynamics through vertical propagation of planetary scale waves in low-latitudes.