Pramitha M.,National Atmospheric Research Laboratory NARL |
Venkat Ratnam M.,National Atmospheric Research Laboratory NARL |
Taori A.,National Atmospheric Research Laboratory NARL |
Krishna Murthy B.V.,B1 |
And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2015
Sources and propagation characteristics of high-frequency gravity waves observed in the mesosphere using airglow emissions from Gadanki (13.5° N, 79.2° E) and Hyderabad (17.5° N, 78.5° E) are investigated using reverse ray tracing. Wave amplitudes are also traced back, including both radiative and diffusive damping. The ray tracing is performed using background temperature and wind data obtained from the MSISE-90 and HWM-07 models, respectively. For the Gadanki region, the suitability of these models is tested. Further, a climatological model of the background atmosphere for the Gadanki region has been developed using nearly 30 years of observations available from a variety of ground-based (MST radar, radiosondes, MF radar) and rocket- and satellite-borne measurements. ERA-Interim products are utilized for constructing background parameters corresponding to the meteorological conditions of the observations. With the reverse ray-tracing method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas for five other events the waves terminated in the mesosphere itself. Uncertainty in locating the terminal points of wave events in the horizontal direction is estimated to be within 50-100 km and 150-300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in the tidal amplitudes. Prevailing conditions at the terminal points for each of the 14 events are provided. As no convection in and around the terminal points is noticed, convection is unlikely to be the source. Interestingly, large (~9 ms-1 km-1) vertical shears in the horizontal wind are noticed near the ray terminal points (at 10-12 km altitude) and are thus identified to be the source for generating the observed high-phase-speed, high-frequency gravity waves. © Author(s) 2015.
Sahu L.K.,Physical Research Laboratory PRL
Indian Journal of Geo-Marine Sciences | Year: 2014
In the earth-ocean-atmosphere system, the halogenated species take part in the cycles of several key processes involving both gas and heterogeneous interactions. The atmospheric cycles of reactive halogens are very complex specifically for those emitted from natural sources. As far as their roles in the tropospheric chemistry, the halogen compounds particularly those containing bromine (Br) and chlorine (Cl) play key roles. The reaction rate constants of many trace gases with halogen radicals are faster than those with hydroxyl radicals (OH). Near the source regions, however, halogen radicals can greatly influence the oxidizing capacity of the troposphere due to their reactive behaviors. In the lower troposphere, particularly in the marine boundary layer (MBL) and polar boundary layer, the reactive halogen compounds cause substantial destruction of ozone. The in-situ observations are available only for very limited geographical regions mainly in the mid- and high- latitudes of the northern hemisphere. One of the reasons for the lack of studies could be the technological constraint owing to very reactive nature of halogens hence the uncertainty in detection and quantification. Nonetheless, it is imperative to study the photochemistry of halogens in global troposphere for the better understanding of chemistry-climate interactions. Many theoretical aspects related to photochemistry of halogenated species in the troposphere need to be verified by the observations. Present study highlighted recent scientific progress about the roles of reactive halogens and their measurements in the troposphere. In spite of greater scientific opportunities in atmospheric studies of halogens, study over Indian subcontinent and surrounding marine regions are almost nil. © 2014, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.
Lupker M.,French National Center for Scientific Research |
France-Lanord C.,French National Center for Scientific Research |
Galy V.,Woods Hole Oceanographic Institution |
Lave J.,French National Center for Scientific Research |
And 6 more authors.
Geochimica et Cosmochimica Acta | Year: 2012
We present an extensive river sediment dataset covering the Ganga basin from the Himalayan front downstream to the Ganga mainstream in Bangladesh. These sediments were mainly collected over several monsoon seasons and include depth profiles of suspended particles in the river water column. Mineral sorting is the first order control on the chemical composition of river sediments. Taking into account this variability we show that sediments become significantly depleted in mobile elements during their transit through the floodplain. By comparing sediments sampled at the Himalayan front with sediments from the Ganga mainstream in Bangladesh it is possible to budget weathering in the floodplain. Assuming a steady state weathering regime in the floodplain, the weathering of Himalayan sediments in the Gangetic floodplain releases ca. (189±92)×10 9 and (69±22)×10 9mol/yr of carbonate bound Ca and Mg to the dissolved load, respectively. Silicate weathering releases (53±18)×10 9 and (42±13)×10 9mol/yr of Na and K while the release of silicate Mg and Ca is substantially lower, between ca. 0 and 20×10 9mol/yr. Additionally, we show that sediment hydration, [H 2O +], is a sensitive tracer of silicate weathering that can be used in continental detrital environments, such as the Ganga basin. Both [H 2O +] content and the D/H isotopic composition of sediments increases during floodplain transfer in response to mineral hydrolysis and neoformations associated to weathering reactions. By comparing the chemical composition of river sediments across the floodplain with the composition of the eroded Himalayan source rocks, we suggest that the floodplain is the dominant location of silicate weathering for Na, K and [H 2O +]. Overall this work emphasizes the role of the Gangetic floodplain in weathering Himalayan sediments. It also demonstrates how detrital sediments can be used as weathering tracers if mineralogical and chemical sorting effects are properly taken into account. © 2012 Elsevier Ltd.
Sahu L.K.,Physical Research Laboratory PRL |
Sheel V.,Physical Research Laboratory PRL
Journal of Atmospheric Chemistry | Year: 2014
In this study, we have investigated the seasonality and long-term trends of major biomass burning (BB) sources over South and Southeast Asia (S-SE Asia). The activities of BB and related emissions show bi-modal seasonality in S-SE Asia. From January to May period, the BB dominates in the northern hemisphere parts of S-SE Asia. From July to September, the activities shift to the southern hemisphere where the emissions from Indonesian and Malaysian islands make largest contributions. Overall, the activities of BB are lowest during October-December period in S-SE Asia. The seasonality of BB intensity and rain are just opposite in the phase over India. The climatological (1997-2008) emissions of carbon monoxide (CO), oxides of nitrogen (NOx) and non-methane hydrocarbons (NMHCs) show strong spatio-temporal variation. The trends show large inter-annual variations with highest and lowest values during years 1997 and 2000, respectively. In the southern hemisphere parts of S-SE Asia mainly in Indonesia, the intensity of biomass fires has been modulated by the large scale climatic phenomena like El Niño and Southern Oscillation (ENSO). The annual emissions of trace gases in southern hemisphere region during the El Niño years exceed to those for the normal years. The estimates for northern hemisphere region during the La Niña years were significantly higher than those for the normal years. The Model for Ozone And Related Chemical Tracers (MOZART) simulations of columnar CO and NOx tend to capture the prominent features of BB emissions in S-SE Asia. The impacts of extensive fires in Indonesia during El Niño year of 2006 compared to a normal year of 2005 were clearly seen in the MOZART-4 simulations of both CO and NOx. © 2013 Springer Science+Business Media.
Chakrabortty J.,Physical Research Laboratory PRL |
Ghosh P.,Autonomous University of Madrid |
Rodejohann W.,Max Planck Institute for Nuclear Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012
New data on the lepton mixing angle θ 13 imply that the eμ element of the matrix m νmν†, where m ν is the neutrino Majorana mass matrix, cannot vanish. This implies a lower limit on lepton flavor violating processes in the eμ sector in a variety of frameworks, including Higgs triplet models or the concept of minimal flavor violation in the lepton sector. We illustrate this for the branching ratio of μ→eγ in the type II seesaw mechanism, in which a Higgs triplet is responsible for neutrino mass and also mediates lepton flavor violation. We also discuss processes like μ→eēe and μ→e conversion in nuclei. Since these processes have sensitivity on the individual entries of m ν, their rates can still be vanishingly small. © 2012 American Physical Society.