New atmospheric pCO₂ estimates from palesols during the late Paleocene/early Eocene global warming interval     

Ashish Sinha  Lowell D. Stott 《Global and Planetary Change》1994,9(3-4)

The late Paleocene to early Eocene was one of the warmest intervals in Earth's history. Superimposed on this long-term warming was an abrupt short-term extreme warm event at or near the Paleocene/Eocene boundary and centered in the higher latitudes. This short-term climate warming was associated with a major benthic foraminiferal extinction and a dramatic 3–4% drop in the ocean's carbon isotopic composition. It has been suggested that the late paleocene/early Eocene global warming was caused by an enhanced greenhouse effect associated with higher levels of atmospheric CO₂ relative to present levels. We present carbon isotopic data from the co-existing paleosols organic matter and carbonates from a terrestrial sequence in the Paris Basin, France that contradict the notion that an increase in atmospheric CO₂ level was the cause of extreme warming for this time interval. Atmospheric pCO₂ estimates for the Late Paleocene/early Eocene estimated from the terrestrial carbon isotopic record spanning the Paleocene/Eocene transition, are indistinguishable from each other and were generally between 300 and 700 ppm.  相似文献   

Understanding Interannual Variations of the Local Rainy Season over the Southwest Indian Ocean     

Hanying LI  Peng HU  Qiong ZHANG  Ashish SINHA  Hai CHENG 《大气科学进展》2021,38(11):1852-1862

Located at the southern boundary of the tropical rainfall belt within the South Africa monsoon regime, Rodrigues Island, ～2500 km east of East Africa, is ideally located to investigate climatic changes over the southwest Indian Ocean(SWIO). In this study, we investigate the climatic controls of its modern interannual rainfall variability in terms of teleconnection and local effects. We find that increased rainfall over the SWIO tends to occur in association with anomalously warm(cold) SSTs over the equatorial central Pacific(Maritime Continent), resembling the central Pacific El Ni?o, closely linked with the Victoria mode in the North Pacific. Our analyses show that the low-level convergence induced by warm SST over the equatorial central Pacific leads to anomalous low-level divergence over the Maritime Continent and convergence over a large area surrounding the Rodrigues Island, which leads to increased rainfall over the SWIO during the rainy season. Meanwhile, the excited Rossby wave along the tropical Indian Ocean transports more water vapor from the tropical convergence zone into the SWIO via intensified northwest wind. Furthermore, positive feedback induced by the Rossby wave response to the increased rainfall in the region contributes to the large interannual variations over the SWIO.  相似文献   

Study of variation of aerosol optical properties over a high altitude station in Indian Western Himalayan region,palampur using raman lidar system     

Singh  Shishir Kumar  Radhakrishnan  S. R.  Jaswant  Mishra  Sumit Kumar  Shukla  Devesh Kumar  Ranjan  Ashish  Sharma  Chhemendra 《Journal of Atmospheric Chemistry》2022,79(2):117-139

A Raman lidar system was operated along with the Microtops sunphotometer measurements to carry out the study of the variation of the optical properties of aerosols over Palampur (32.11° N and 76.53° E), India from 17th April to 11th May 2019. The lidar system is furnished with Raman (N₂) channel and depolarization channel allowing independent measurement of Lidar Ratio (LR) and linear depolarization ratio. The study reveals that the majority of the aerosols approximately were restricted within the planetary boundary layer (PBL) and very less loading was present in the free troposphere over the study location. The particle loading over the study period was found to be very less with aerosol backscatter coefficient (at 355 nm) ranging from ～0.13 Mm^?1sr^?1 to ～7.25 Mm^?1sr^?1 with mean value of 2.67?±?0.82 Mm^?1sr^?1 and it is well supplemented by the mean aerosol optical depth (AOD) of 0.37?±?0.13 obtained from Microtops Sunphotometer. The average lidar ratio values for 0-1 km altitude (L1) 72?±?13sr, for 1-2 km (L2) altitude 55?±?8sr, for 2-3 km (L3) 54?±?15sr were observed as suggesting dominance of the biomass burning aerosols and anthropogenic aerosols. The particle depolarization ratio (355 nm) values were found from approximately 4.8?±?2.7% to 11.5?±?1.9% with the mean value of 7?±?1.3% suggesting the presence of non-spherical particles. To trace the sources of the pollution, we derived the HYSPLIT trajectory which shows the majority of the movement was from local sources.

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Using second-order approximation to incorporate GCM uncertainty in climate change impact assessments     

Sajjad Eghdamirad  Fiona Johnson  Ashish Sharma 《Climatic change》2017,142(1-2):37-52

This study presents a method to incorporate uncertainty of climate variables in climate change impact assessments, where the uncertainty being considered refers to the divergence of general circulation model (GCM) projections. The framework assesses how much bias occurs when the uncertainties of climate variables are ignored. The proposed method is based on the second-order expansion of Taylor series, called second-order approximation (SOA). SOA addresses the bias which occurs by assuming the expected value of a function is equal to the function of the expected value of the predictors. This assumption is not valid for nonlinear systems, such as in the case of the relationship of climate variables to streamflow. To investigate the value of SOA in the climate change context, statistical downscaling models for monthly streamflow were set up for six hydrologic reference stations in Australia which cover contrasting hydro-climate regions. It is shown that in all locations SOA makes the largest difference for low flows and changes the overall mean flow by 1–3%. Another advantage of the SOA approach is that the individual contribution of each climate variable to the total difference can be estimated. It is found that geopotential height and specific humidity cause more bias than wind speeds in the downscaling models considered here.  相似文献   

Evaluation of cloud properties in the NCEP CFSv2 model and its linkage with Indian summer monsoon     

Anupam Hazra  Hemantkumar S. Chaudhari  Ashish Dhakate 《Theoretical and Applied Climatology》2016,124(1-2):31-41

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Estimation of runoff for hilly catchment using satellite data     

Ashish Pandey  P. P. Dabral 《Journal of the Indian Society of Remote Sensing》2004,32(2):235-240

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Understanding fluid mud in a dynamic environment   总被引：1，自引：0，他引：1  

Ashish J. Mehta 《Geo-Marine Letters》1991,11(3-4):113-118

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Mineralogy and geochemistry of picro-dolerite dykes from the central Deccan Traps flood basaltic province,India, and their geodynamic significance     

Dongre  Ashish  Viljoen  K. S.  Rathod  A. 《Mineralogy and Petrology》2018,112(2):267-277

Mineralogy and Petrology - Constituent mineral compositions and whole rock major element geochemistry of picro-dolerite dykes from the central part of the Deccan flood basalt province are presented...  相似文献   

Erratum to: Stochastic ground-motion simulation of two Himalayan earthquakes: seismic hazard assessment perspective     

Ashish Harbindu  Mukat Lal Sharma  Kamal 《Journal of Seismology》2012,16(2):371-371

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Stochastic ground-motion simulation of two Himalayan earthquakes: seismic hazard assessment perspective     

Ashish Harbindu  Mukat Lal Sharma  Kamal 《Journal of Seismology》2012,16(2):345-369

The earthquakes in Uttarkashi (October 20, 1991, M _w 6.8) and Chamoli (March 8, 1999, M _w 6.4) are among the recent well-documented earthquakes that occurred in the Garhwal region of India and that caused extensive damage as well as loss of life. Using strong-motion data of these two earthquakes, we estimate their source, path, and site parameters. The quality factor (Q _β ) as a function of frequency is derived as Q _β (f) = 140f ^1.018. The site amplification functions are evaluated using the horizontal-to-vertical spectral ratio technique. The ground motions of the Uttarkashi and Chamoli earthquakes are simulated using the stochastic method of Boore (Bull Seismol Soc Am 73:1865–1894, 1983). The estimated source, path, and site parameters are used as input for the simulation. The simulated time histories are generated for a few stations and compared with the observed data. The simulated response spectra at 5% damping are in fair agreement with the observed response spectra for most of the stations over a wide range of frequencies. Residual trends closely match the observed and simulated response spectra. The synthetic data are in rough agreement with the ground-motion attenuation equation available for the Himalayas (Sharma, Bull Seismol Soc Am 98:1063–1069, 1998).  相似文献