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Simultaneous measurements of black carbon and PM2.5, CO, and NOx variability at a locally polluted urban location in India
No full textBlack carbon, which is a by-product of incomplete combustion of carbon containing fuels, can alter atmospheric radiation property and make adverse impacts on human health. This paper shows the comparative study of particles and associated gaseous pollutants measurements at five observatories dispersed across central part of megacity Delhi, India, with high-temporal resolution (5 min) measurements. The mean ± SD concentrations of black carbon (BC), fine particles (PM2.5), carbon monoxide (CO), and oxides of nitrogen (NO x ) of the all five stations were 13.4 ± 10, 149.6 ± 109 µg m−3, 3.4 ± 2 ppm, and 81.8 ± 79 ppb, respectively. The mean mass concentration of PM2.5 was approximately four times and ten times in excess of annual average standards of Indian air quality (40 µg m−3) and USEPA (15 µg m−3) levels. Highest BC mass concentrations were recorded during winter (December) due to consistent with a shallower atmospheric boundary layer, lower wind speeds, and possibly larger biofuel burning in the coldest period. Also, the strong diurnal dynamics in boundary layer height had a large impact on the ground-level concentrations of all the pollutants. A significant difference in the emissions of atmospheric pollutants was observed over Delhi during weekdays and weekends during study period. There was a strong diurnal effect on BC and the other pollutants, presumably with mixing height as a strong driver. The 24-h cycle is characterized throughout the study by maximum concentrations around midnight and lowest concentrations at 1500–1700 hours local time (LT), with a local maximum between 0800 and 1000 hours LT, presumably due to morning rush hour. While the amplitude of the BC excursion was a factor of 2–3, the mixing height decreased by a factor of 12–14 from day to night. This monitoring program contributed to insights into the levels and dynamics of atmospheric pollutants in the New Delhi megacity over a 5-month period. The concentrations are varying over several timescales, consistent with both atmospheric mixing and variations in presumed emission source strengths
Observed interannual variability of near-surface salinity in the Bay of Bengal
No full textAn in situ gridded data of salinity, comprising Argo and CTD profiles, has been used to study the interannual variability of near-surface salinity (within 30 m from sea surface) in the Bay of Bengal (BoB) during the years 2005-2013. In addition to the broad agreement with earlier studies on the north-to-south gradient of surface salinity and general features of seasonal variability of salinity, the data also revealed few episodes of enhanced freshening in the BoB. The observations showed distinct anomalous low salinity (< 2 psu) waters in the northern BoB during June-February of the years 2006-2007 (Y67), 2011-2012 (Y12), and 2012-2013 (Y23). The anomalous freshening during these years showed similar life cycle, such as, it starts in the northern BoB during July-September of current summer and extends up to February-March of next winter with a southward propagation. Analysis showed that the oceanic and atmospheric conditions associated with positive Indian Ocean Dipole (pIOD) lead to these freshening events, and IOD rather than El Niño/Southern Oscillation (ENSO) controls the interannual variability of salinity in the BoB. The mixed layer salt budget analysis indicated the dominant role of local fresh water flux (horizontal advection) on the observed salinity tendency during summer (winter) monsoon season. Enhanced precipitation associated with pIOD lead to enhanced freshening in northern BoB during June-September, which remained to this region with prevailing summer monsoon circulation. The weakening or absence of southward east India coastal current (EICC) during October-December of these freshening years trapped anomalous freshwater in the northern BoB. Key Points Anomalous freshening observed in BoB in 3 years Positive IOD initiate the freshening events in northern BoB Salt budget analysis resolve contributions from different processes © 2015. American Geophysical Union. All Rights Reserved
Utility of Sea Surface Height anomaly (SSHa)in determination of Potential Fishing Zones
Get PDFPhysical processes in the oceans can be monitored by altimeters well before a radiometer can in terms of temperature or chlorophyll concentration. Herein we show the importance of Sea Surface Height anomaly (SSHa, retrieved with altimeter) in demarcating potential fishing
zones. We also show how SSHa can help predict tuna movements, horizontally as well as vertically in the water column. Moreover, we prove these prediction with positively
correlating SSHa to tuna hooking rates. In the end, we list out present and potential future sources from where SSHa can be retrieved in order to provide improved fishery advisories
Ecological sustainability of an optimal controlled system incorporating partial closure for the populations
No full textThis paper describes a prey-predator fishery model incorporating partial closure for the populations. It is assumed that the predator population partially dependent on a logistically growing resource with Beddington-De Angelis type functional response. The proposed system also reflects the dynamic interaction between the net economic revenue and the fishing effort used to harvest the populations. The steady states of the system are determined and the dynamic behavior of the system is discussed. The existence of Hopf bifurcation phenomenon is examined at the interior equilibrium point of the proposed system. We have adopted partial closure for the populations as a controlling instrument to regulate the harvesting of the populations. A dynamic framework towards the optimal utilization of the resource is developed using Pontryagin's maximum principle. The optimal system is numerically solved using an iterative method with Runge-Kutta fourth-order scheme. Simulation results show that the optimal control scheme can achieve a sustainable ecosystem. Results are analyzed with the help of graphical illustrations
Influence of extratropical sea-surface temperature on the Indian summer monsoon: an unexplored source of seasonal predictability
No full textBased on extensive analysis of observations and a series of climate model experiments, here we establish that slow variations of northern hemispheric extratropical sea-surface temperature (SST) anomalies can augment seasonal predictability of the south Asian monsoon. The SST conditions and performance of the south Asian monsoon during 2013 boreal summer months (June–September) led us to hypothesize that the strong extratropical SST anomalies in the North Pacific and North Atlantic in conjunction with weak tropical SST anomalies (weak La Niña) were responsible for the above-normal rainfall over India during 2013. We also argue that the 2013 SST pattern and above-normal monsoon condition are not unique but occurred on several occasions in the past. Further, we show that there is a complementary pattern of strong extratropical SST and weak tropical SST that is associated with below-normal south Asian monsoon rainfall. We also show that the extratropical SST pattern in the Northern Hemisphere is associated with a low-frequency interdecadal mode of variability indicating potential predictability associated with such extratropical SST forcing. Extensive experiments with an atmospheric general circulation model forced by such SST conditions elucidate the mechanism through which the extratropical SSTs influence the Indian monsoon. The SST anomalies affect the north–south temperature gradient and lead to a local displacement of the jet stream, setting up a quasi-stationary wave. Such a stationary wave, in turn, affects the tropospheric temperature (TT) over southern Eurasia, influencing the north–south TT gradient in the region and thereby the Indian monsoon. Our discovery of this additional source of potential predictability together with the fact that the new-generation coupled ocean–atmosphere models are capable of predicting the extratropical SST anomalies brightens the prospect of south Asian monsoon prediction
Interannual variability of the Arabian Sea Warm Pool: observations and governing mechanisms
No full textThe near-surface layers in the Arabian Sea progressively warm up from February to early May resulting in the formation of pool of warm waters popularly known as the Arabian Sea Warm Pool (ASWP). The availability of high quality TMI sea surface temperature (SST) data for the years 1998-2010 is exploited to describe the evolution of the ASWP on seasonal and interannual time scales and to explain the associated mechanisms. The multi-year (1998-2010) averaged TMI SSTs during April-May show peak values of the ASWP in excess of 30 °C with its core >30.5 °C extending offshore as a well-marked southwestward tongue stretching from the southwest coast of India. The ASWP shows both seasonal and interannual variability in the evolution of spatio-temporal characteristics such as amplitude, phase and spatial extent. Among these 13 years, the ASWP was most (least) pronounced during 1998, 2003 and 2010 (1999, 2000, 2001 and 2008). The mechanisms that govern the observed interannual variability of the ASWP are examined addressing the most relevant issues such as-(1) dynamic pre-conditioning: background pycnocline topography influenced by the westward propagating Rossby waves during October-May, (2) thermal pre-conditioning: background SST/heat content signal during October-January influenced by the strength of the preceding year's summer monsoon and the post-monsoon cyclones during October-December, (3) haline pre-conditioning: near-surface vertical salinity stratification during November-February influenced by the advection of low saline waters from the Bay of Bengal, (4) influence of surface net heat flux forcing during February-May, and (5) influence of El Nino/La Nina
Modeling Storm Surge and its Associated Inland Inundation Extent Due to Very Severe Cyclonic Storm Phailin
No full textA hindcast simulation of storm surge and inundation from tropical cyclone Phalin, which made landfall at Odisha, India, on 12 October 2013, was carried out using ADCIRC model. Model-simulated inundation extent matched well with field surveys at Ganjam, Odisha, within a few days of landfall. Further, the model reproduced the temporal evolution of the surge residual with respect to observations from a tide gauge at Paradip (correlation 0.8, RMSE 0.26 m). However, the model marginally underestimated the magnitude with respect to observations, which can be attributed to the lack of wave setup in the model and uncertainty in wind and pressure information. The experiment also involved the use of two idealized scenarios, that is, variation of landfall timings with the ebbing and high tide phase. These scenarios were required for better understanding the sensitivity of inundation to the phase of tide in the model. Simulation with landfall at flooding (ebbing) tide showed greater (lower) inundation than the real scenario. Results from idealized scenarios confirmed the significance of the accuracy needed in forecasting landfall time. Our results clearly indicate that the overall performance of the model is good and therefore is of potential use as a tool to forewarn disaster management authorities
Predictability of Global Monsoon Rainfall in NCEP CFSv2
No full textThis study evaluates the actual and potential prediction skill of the global monsoon rainfall using hindcast simulations by NCEP CFSv2 at zero to three lead forecast months (L0–L3). It is shown that the model has moderate skill in global monsoon rainfall (GMR) prediction, where the boreal summer monsoon rainfall forecast is more skillful than that of the austral summer. In general, the prediction skill of the GMR (actual and potential) increases with the decrease in lead forecast time, which is true for the all major regional monsoons, except the Australian monsoon. Over the Australian monsoon region, both actual and potential prediction skills in rainfall increase with increase in lead forecast. The forecast skill of tropical SST during austral summer is a maximum at 3 months lead forecast (i.e. July initial conditions) and that is associated with spring predictability barrier. Using partial least square (PLS) regression method, it is shown that the major predictor (first latent vector) of the boreal and austral summer monsoon rainfall variability is ENSO, and the influence of ENSO on rainfall variability is much stronger in the model as compared to the observation. The second PLS regression mode is associated with the non-ENSO variability like tropical Atlantic, Indian, subtropical northwest Pacific Ocean variability, midlatitude interactions etc. However, the model has very poor skill in reproducing the second mode, particularly during the boreal summer monsoon season. It is also shown that a significant part of the Indian summer monsoon rainfall variability is controlled by other than ENSO variability and the model has limited success in capturing that
Monsoon-extratropical circulation interactions in Himalayan extreme rainfall
No full textExtreme precipitation and flood episodes in the Himalayas are oftentimes traced to synoptic situations involving connections between equatorward advancing upper level extratropical circulations and moisture-laden tropical monsoon circulation. While previous studies have documented precipitation characteristics in the Himalayan region during severe storm cases, a comprehensive understanding of circulation dynamics of extreme precipitation mechanisms is still warranted. In this study, a detailed analysis is performed using rainfall observations and reanalysis circulation products to understand the evolution of monsoon-extratropical circulation features and their interactions based on 34 extreme precipitation events which occurred in the Western Himalayas (WEH) during the period 1979–2013. Our results provide evidence for a common large-scale circulation pattern connecting the extratropics and the South Asian monsoon region, which is favorable for extreme precipitation occurrences in the WEH region. This background upper level large-scale circulation pattern consists of a deep southward penetrating midlatitude westerly trough, a blocking high over western Eurasia and an intensifying Tibetan anticyclone. It is further seen from our analysis that the key elements of monsoon-midlatitude interactions, responsible for extreme precipitation events over the WEH region, are: (1) midlatitude Rossby wave breaking, (2) west-northwest propagation of monsoon low-pressure system from the Bay of Bengal across the Indian subcontinent, (3) eddy shedding of the Tibetan anticyclone, (4) ageostrophic motions and transverse circulation across the Himalayas, and (5) strong moist convection over the Himalayan foothills. Furthermore, high-resolution numerical simulations indicate that diabatic heating and mesoscale ageostrophic effects can additionally amplify the convective motions and precipitation in the WEH region
High concentration of acidic species in rainwater at Varanasi in the Indo-Gangetic plains, India
No full textThe Indo-Gangetic Plains (IGP), straddling the northeastern parts of India near the foothills of the Himalayas, are one of the most densely populated and polluted regions on the globe, with consequent large anthropogenic emissions. In particular, the use of traditional biofuels in the rural areas along the plains leads to strong emissions of various pollutants. Due to this importance, a comprehensive study on the chemical characteristics of rainwater was carried out during southwest summer monsoon season of 2009 at two different locations over Varanasi, India, located in the middle of IGP region in the eastern part of Uttar Pradesh. The rainwater samples were analyzed for major chemical constituents along with pH and its electric conductivity. The pH values ranged from 5.18 to 7.08 with a mean of 5.82 ± 0.45 suggest the alkaline nature of rainwater over Varanasi. During the study period, ~14 % rainwater samples were found to be acidic when the winds blew from south–southeast direction. The weighted mean pH and electric conductivity were found higher (5.92 ± 0.45) and (24.59 µS/cm) at Maldahiya site than Banaras Hindu University (5.89 ± 0.46) and (17.16 µS/cm) due to dominance of soil-derived particles. The equivalent concentration of ionic species is of the order: Ca2+ > SO42− > NO3− > Cl− > Mg2+ > Na+ > HCO3− > NH4+ > K+ > F− > H+. The weighted mean concentration of dominant ions in rainwater over Varanasi was Ca2+ (67.1 ± 56 µeq/l), SO42− (37 ± 23 µeq/l) and NO3− (27.1 ± 28 µeq/l). Significant correlation (r = 0.81; P < 0.001) between the sum of major cations (NH4+ + Ca2+ + Mg2+) and the sum of acidic species (SO42− + NO3−) corroborates that these alkaline species may act as a neutralizing agent for the acidity of rainwater. The source contribution of SO42− in rainwater was estimated and was ~95 % by man-made activities, which is mainly derived from burning of fossil/biofuels over this region. The source of nitrate (11 %) emissions was mainly from automobiles and biomass burning. Statistical analysis such as principle component analysis was performed to find out possible sources of measured ions. First factor accounted for ~54 % variance suggested that most of the ions were from natural sources especially soil dust and sea; however, factor 2 accounted only for ~12 % variance suggests their sources from burning of fossil fuel and biomass. The third factor also indicates the mixed sources into the atmosphere