3194 research outputs found
Sort by
Aerosol optical properties and their relationship with meteorological parameters during wintertime in Delhi, India
No full textIn situ and columnar measurements of aerosol optical properties (AOPs) [Aerosol optical depth (AOD), Angstrom Exponent (AE), Aerosol scattering (σscat) and absorption (σabs) coefficients and single scattering albedo (SSA)] along with soot particles (Black carbon: BC) and fine particles (PM2.5: d ≤ 2.5) were continuously measured at an urban site in Delhi, India during winter period (December 2011 to March 2012). Average values of AOD, σscat, σabs, and SSA at 500 nm; and AE for the observation period were found to be 0.95 ± 0.32, 1027.36 ± 797.1 Mm− 1, 85.95 ± 73.2 Mm− 1 and 0.93 ± 0.03; and 0.94 ± 0.19, respectively. Higher values of σscat and σabs were occurred in the month of December (1857 and 148 Mm− 1) while relatively lower values of σscat (585 Mm− 1) and σabs (44 Mm− 1) were occurred in March and February respectively. SSA, however, was higher during January (0.94) and lower in March (0.89). The mass concentration of PM2.5 and BC were 195.34 ± 157.99 and 10.11 ± 8.83 μg m− 3 respectively during study period. Bimodal distributions were observed in σscat and σabs coefficients during 0800 and 0900 h LT (traffic rush hours) and at 2200 and 2300 h LT (low boundary layer conditions) with lower values during daytime between 1500 and 1700 h LT, respectively. The σscat peak in morning may be attributed to large emissions of aerosol in the traffic rush hours and production of secondary aerosols with increasing solar radiation and temperature. During study period, the σscat (mean) coefficient was 13% lower during daytime as compared to nighttime. An interesting feature was seen in monthly analysis of σscat in between day and nighttime which was 18% and 22% higher in December and January in nighttime however ~ 4% lower during February and March; it is due to effect of local meteorology. The impact of meteorological parameters such as wind speed (WS), wind direction (WD), visibility (VIS) and mixed layer depths (MLDs) on AOPs along with fine and soot particles were studied. A clear negative significant correlation between atmospheric visibility with σscat (− 0.64); σabs (− 0.57) and PM2.5 (− 0.56) were observed. During foggy days (VIS ≤ 1000 m), the AOPs, fine and soot particles were substantially (~ 1.8 times) higher as compared to clean days, however, it was ~ 2.3 times higher during dense foggy days (VIS ≤ 500 m). Similarly higher (~ 2 times) AOPs and aerosol concentrations were also seen below 200 m MLDs. In addition to this, ~ 4 times higher AOPs and aerosol mass concentrations were observed when WS was below 1 m/s. In view of the above results and regression analysis, we can say that the meteorological parameters play a crucial role in enhancement of aerosols at ground level during winter period over Delhi
Identification of aerosol types over Indo-Gangetic Basin: implications to optical properties and associated radiative forcing
No full textThe aerosols in the Indo-Gangetic Basin (IGB) are a mixture of sulfate, dust, black carbon, and other soluble and insoluble components. It is a challenge not only to identify these various aerosol types, but also to assess the optical and radiative implications of these components. In the present study, appropriate thresholds for fine-mode fraction and single-scattering albedo have been used to first identify the aerosol types over IGB. Four major aerosol types may be identified as polluted dust (PD), polluted continental (PC), black carbon-enriched (BCE), and organic carbon-enriched (OCE). Further, the implications of these different types of aerosols on optical properties and radiative forcing have been studied. The aerosol products derived from CIMEL sun/sky radiometer measurements, deployed under Aerosol Robotic Network program of NASA, USA were used from four different sites Karachi, Lahore, Jaipur, and Kanpur, spread over Pakistan and Northern India. PD is the most dominant aerosol type at Karachi and Jaipur, contributing more than 50 % of all the aerosol types. OCE, on the other hand, contributes only about 12–15 % at all the stations except at Kanpur where its contribution is ∼38 %. The spectral dependence of AOD was relatively low for PD aerosol type, with the lowest AE values (1.0). SSA was found to be the highest for OCE (>0.9) and the lowest for BCE (<0.9) type aerosols, with drastically different spectral variability. The direct aerosol radiative forcing at the surface and in the atmosphere was found to be the maximum at Lahore among all the four stations in the IGB
Mesoscale and intraseasonal air-sea CO2 exchanges in the western Arabian Sea during boreal summer
No full textIntraseasonal variability, considered a coupled phenomenon, typically occurs in the 20-to-90 day-band and is seen in several of the air–sea interaction parameters over the Indian Ocean. The corresponding variability in the air–sea CO2 exchanges and oceanic pCO2 are not widely studied. In this study, we focus on the boreal summer season to find that there is a strong air–sea interaction of carbon cycle over the Somali region of the western Arabian Sea where the intraseasonal variability during this season is clearly evident in the intense variability in winds, the strength of the upwelling and the evolution of meso-scale eddies. The oceanic pCO2 variability in this intraseasonal band over the Somali region is also remarkably consistent with the other variables and is found to be driven by sea surface temperatures (SST) albeit with a counteracting but relatively minor influence from the dynamics of dissolved inorganic carbon (DIC). The 20-to-90 day-band in pCO2 accounts for about 40% of the monthly mean variability of the sea-to-air CO2 fluxes of this region in boreal summer. Ocean dynamic control on the atmospheric wind response at these mesoscales has been reported before and this study demonstrates that the ocean dynamics also control the seawater pCO2 and the air–sea CO2 fluxes in this region. Other regions with similar meso-scale dynamics must be analyzed for processes that determine air–sea CO2 exchanges and to determine whether the mesoscale fluxes contribute to the low-frequency CO2 fluxes. The role of the intraseasonal variability in atmospheric pCO2 in this exchange is not quantified here due to the lack of data at such high resolutions and needs to be considered in further observational and modeling efforts
Long term characterization of aerosol optical properties: Implications for radiative forcing over the desert region of Jodhpur, India
No full textAOT data for eight years period (2004–2012) using the MICROTOPS II Sun photometer has been used to study the wavelength dependent optical characteristics of aerosols over Jodhpur, situated in the desert region in NW India. The daily mean AOT at 500 nm for the present study period was 0.66 ± 0.14 with an average Angstrom exponent as 0.71 ± 0.20. Linear regression analysis of monthly AOT and Angstrom Exponent indicated an increasing trend of both. Seasonal variations of daily AOT and α as well as spectral dependence of seasonal mean AOT are presented. Diurnal variation of AOT and α in different season is studied. Impact of dust storm events on the aerosol characteristics over Jodhpur during the study period is studied. AOT values derived from MICROTOPS II were cross checked with Sun Sky Radiometer (Model POM-01, Prede Inc.) data for the period from May 2011 to April 2012 and were found to be in good agreement. Short wave aerosol radiative forcing (ARF) was computed for one year period of May 2011 to April 2012. Spectral variation of AOT, SSA and ASP showed more AOT and ASP during pre monsoon period when SSA was comparatively low; indicating towards more prevalence of coarse size absorbing dust in this period. The ARF at SUF and TOA was negative during all the seasons indicating dominance of scattering type aerosols mainly dust particles whereas that at ATM was positive in all the seasons indicating heating of the atmosphere, especially more during pre monsoon (+40.5 W/m2) than during rest of the year (+19.5 W/m2). A high degree of correlation between ARF at the SUF with AOT (R2 = 0.94) indicated that ARF is a strong function of AOT. The radiative forcing efficiency inferred to scattering nature of aerosols at SUF (−4.2 W/m2/AOD) and TOA (−63.2 W/m2/AOD) indicating cooling at surface and top of the atmosphere whereas, there was warming of the atmosphere in between (+59 W/m2/AOD). The atmospheric heating rates varied from 0.49 K/day in post monsoon to 1.13 K/day in pre monsoon. This study has enabled us to understand the long term nature and physical characteristics of atmospheric aerosols over Jodhpur
Rethinking Indian monsoon rainfall prediction in the context of recent global warming
Get PDFPrediction of Indian summer monsoon rainfall (ISMR) is at the heart of tropical climate prediction. Despite enormous progress having been made in predicting ISMR since 1886, the operational forecasts during recent decades (1989–2012) have little skill. Here we show, with both dynamical and physical–empirical models, that this recent failure is largely due to the models’ inability to capture new predictability sources emerging during recent global warming, that is, the development of the central-Pacific El Nino-Southern Oscillation (CP–ENSO), the rapid deepening of the Asian Low and the strengthening of North and South Pacific Highs during boreal spring. A physical–empirical model that captures these new predictors can produce an independent forecast skill of 0.51 for 1989–2012 and a 92-year retrospective forecast skill of 0.64 for 1921–2012. The recent low skills of the dynamical models are attributed to deficiencies in capturing the developing CP–ENSO and anomalous Asian Low. The results reveal a considerable gap between ISMR prediction skill and predictability
A mathematical study of an eco-epidemiological system on disease persistence and extinction perspective
No full textA prey-predator system with disease in prey is proposed. The proposed system is an extension of the model analyzed by Bhattacharyya and Mukhopadhyay (2011) which did not consider the density of fish population as a dynamic variable which significantly influence the dynamics of the system. The coexistence equilibria of the system is determined and the dynamic behavior of the system is investigated around coexistence equilibria. Incidence rate of the disease is considered as a bifurcation parameter to examine the occurrence of Hopf bifurcation in the neighborhood of the co-existing equilibria. Sufficient conditions are derived for the global stability of the system around coexistence equilibria. Uniform strong persistence of the system is discussed in order to ensure long-term survival of the species. The obtained results are useful to extract the criteria for disease extinction and persistence. Finally, some numerical simulations are given to verify the analytical results, and the system is analyzed through graphical illustrations
Evaluation of Aquarius Sea Surface Salinity with Argo Sea Surface Salinity in the Tropical Indian Ocean
No full textThe performance of sea surface salinity (SSS) obtained from the Aquarius satellite is evaluated. Daily, weekly, and monthly Aquarius SSS data between September 2011 and August 2013 from the tropical Indian Ocean (TIO) are compared with the surface most salinity observations ( 0.6) was observed everywhere, except the coast of Oman, western equatorial Indian Ocean, and south of 20° S. A seasonal comparison has also revealed that both Aquarius and Argo are in agreement; in addition, the Aquarius SSS clearly shows the seasonal salinity cycle of the TI
Improved Spread–Error Relationship and Probabilistic Prediction from the CFS-Based Grand Ensemble Prediction System
No full textThis study describes an attempt to overcome the underdispersive nature of single-model ensembles (SMEs). As an Indo–U.S. collaboration designed to improve the prediction capabilities of models over the Indian monsoon region, the Climate Forecast System (CFS) model framework, developed at the National Centers for Environmental Prediction (NCEP-CFSv2), is selected. This article describes a multimodel ensemble prediction system, using a suite of different variants of the CFSv2 model to increase the spread without relying on very different codes or potentially inferior models. The SMEs are generated not only by perturbing the initial condition, but also by using different resolutions, parameters, and coupling configurations of the same model (CFS and its atmosphere component, the Global Forecast System). Each of these configurations was created to address the role of different physical mechanisms known to influence error growth on the 10–20-day time scale. Last, the multimodel consensus forecast is developed, which includes ensemble-based uncertainty estimates. Statistical skill of this CFS-based Grand Ensemble Prediction System (CGEPS) is better than the best participating SME configuration, because increased ensemble spread reduces overconfidence errors
Shape and oscillations of the water drops freely suspended in horizontal electric field: A wind tunnel study
No full textThe time-averaged axis ratios, frequency and amplitude of oscillations of water drops of 2.67–6.6 mm diameter were determined by suspending them in a vertical wind tunnel in the absence and presence of horizontal electric fields using a high speed camera at 1000 frames per second. A systematic decrease in the drop's axis-ratio is observed with increase in its diameter and/or horizontal electric field. The results revealed with high speed photography are in good agreement with earlier results. The drop distortion due to horizontal electric field is more pronounced for the drops in the size-range of 3.36–6 mm diameter showing that the electrical forces progressively enhance the horizontal elongation of the drop resulting in its instability at 6.6 mm. The drop oscillation frequency computed from temporal variation of axis ratio, decreases with increase in drop size but shows no significant change in oscillation frequency in the horizontal electric field of ≤500 kV m−1. However, the oscillation amplitude increases with increase in drop size up to a threshold value and then flatten-off in the electric field of ≤300 kV m−1 demonstrating the nonlinear effect of net forces acting on such large drops. In higher electric field of 500 kV m–1, gradual increase in the amplitude of oscillation with an increase in drop diameter has been observed. Moreover, for a particular drop size, the amplitude of oscillation decreases with increase in the electric field upto 500 kV m−1. The oscillation frequency of the waterdrops experiences multimode oscillations. The dominant fundamental mode of oscillations (2,0) always exists for all drops in our experiments along with the coexistence of higher modes of oscillations i.e. (2,1) and (2,2) mode. Possible effects of electrical forces on shape parameters and their implications on cloud microphysics and in radar meteorology are discussed
Lightning activity and its association with rainfall and convective available potential energy over Maharashtra, India
No full textThis work presents the association of flash rate density (FRD) with surface air temperature, rainfall and convective available potential energy (CAPE) using satellite-based flash count grid (0.5° × 0.5°) data from 1998 to 2007 over Maharashtra, India. We investigate monthly to seasonal variations in lightning activity with rainfall and CAPE. The first peaks for FRD and rainfall found in June and July, respectively, followed by next peaks in September. The difference in peaks for FRD and rainfall of 1 month (June–July) attributed to the onset phase of summer monsoon in June (relatively less wet period favorable for more convective and lightning activity), thereafter, heavy rainfall in July over Maharashtra. The annual variations show that the September peaks for both FRD and rainfall are higher than that in June for FRD and for rainfall in July. FRD is moderately correlated with rainfall (r = 0.51 at significant level <0.0001). There is good parallelism in the variation of FRD, and CAPE as the correlation coefficient in between them is 0.78 at significant level <0.0001