A possible new mechanism for northward propagation of boreal summer intraseasonal oscillations based on TRMM and MERRA reanalysis     

S. Abhik  M. Halder  P. Mukhopadhyay  X. Jiang  B. N. Goswami 《Climate Dynamics》2013,40(7-8):1611-1624

Boreal summer intraseasonal oscillations (BSISOs) manifest in the active and break spells and act as the primary building block of the Indian summer monsoon. Although recent research has evolved a basic framework for understanding the scale selection and northward propagation of the BSISO, the role of different hydrometeors in modulating these processes remains poorly explored. In this study, TRMM-2A12 retrievals and Modern Era Retrospective-analysis for Research and Applications reanalysis data are examined to establish relationship between cloud hydrometeors and other atmospheric dynamical parameters with the northward propagation of the BSISOs. The study reveals that the cloud liquid water leads the deep convection during the northward propagation of BSISOs in the lower troposphere, while the cloud ice slightly lags the convection. This distribution indicates the occurrence of a possible mechanism of the lower level moistening through the large scale moisture advection in lower atmosphere and boundary layer (PBL) convergence, followed by triggering of the deep convection. The analyses of moisture advection and the dynamical fields with respect to the convection center show that low level moistening is a manifestation of the barotropic vorticity and PBL convergence of moisture anomaly north of the convection center. A new internal dynamical-thermodynamical mechanism is unraveled to understand the reason behind the middle tropospheric heating maximum and its role on the northward propagation. It is shown that the enhanced moisture perturbation in lower levels together with the heat transport by the sub-grid scale eddies within the PBL induces lower level instability required to precondition the lower atmosphere for triggering the deep convection. Vigorous upward motion inside the deep convection uplifts the liquid hydrometeors to upper levels and the formation of precipitable ice leads to the heating maxima in the middle troposphere. To check the robustness of the proposed hypothesis, similar analysis is performed for the weak northward propagating BSISO cases.  相似文献   

First megafossil evidence of Cyatheaceous tree fern from the Indian Cenozoic     

Subir Bera  Sudha Gupta  Mahasin Ali Khan  Aniruddha De  Radhanath Mukhopadhyay 《Journal of Earth System Science》2014,123(6):1433-1438

A part of the compressed tree fern axis with leaf and adventitious root scars in unusual arrangement from Plio–Pleistocene sediments of Arunachal Pradesh, India is described as Cyathea siwalika sp. nov. This record suggests that Cyathea was an important component of tropical evergreen forest in the area during the Plio–Pleistocene and this group subsequently declined in importance within the local vegetation.  相似文献   

New insights into the carrier phase(s) of extraterrestrial He in geologically old sediments     

S. Mukhopadhyay  K.A. Farley 《Geochimica et cosmochimica acta》2006,70(19):5061-5073

To better understand the composition, characteristics of helium diffusion, and size distribution of interplanetary dust particles (IDPs) responsible for the long-term retention of extraterrestrial ³He, we carried out leaching, stepped heating, and sieving experiments on pelagic clays that varied in age from 0.5 Ma to ∼90 Myr. The leaching experiments suggest that the host phase(s) of ³He in geologically old sediments are neither organic matter nor refractory phases, such as diamond, graphite, Al₂O₃, and SiC, but are consistent with extraterrestrial silicates, Fe-Ni sulfides, and possibly magnetite. Stepped heating experiments demonstrate that the ³He release profiles from the magnetic and non-magnetic components of the pelagic clays are remarkably similar. Because helium diffusion is likely to be controlled by mineral chemistry and structure, the stepped heating results suggest a single carrier that may be magnetite, or more probably a phase associated with magnetite. Furthermore, the stepped outgassing experiments indicate that about 20% of the ³He will be lost through diffusion at seafloor temperatures after 50 Myrs, while sedimentary rocks exposed on the Earth’s surface for the same amount of time would lose up to 60%. The absolute magnitude of the ³He loss is, however, likely to depend upon the ³He concentration profile within the IDPs, which is not well known. Contrary to previous suggestions that micrometeorites in the size range of 50-100 μm in diameter are responsible for the extraterrestrial ³He in geologically old sediments [Stuart, F.M., Harrop, P.J., Knott, S., Turner, G., 1999. Laser extraction of helium isotopes from Antarctic micrometeorites: source of He and implications for the flux of extraterrestrial ³He flux to earth. Geochim. Cosmochim. Acta63, 2653-2665], our sieving experiment demonstrates that at most 20% of the ³He is carried by particles greater than 50 μm in diameter. The size-distribution of the ³He-bearing particles implies that extraterrestrial ³He in sediments record the IDP flux rather than the micrometeorite flux.  相似文献   

Uncertainty of soil erosion modelling using open source high resolution and aggregated DEMs     

Arun Mondal  Deepak Khare  Sananda Kundu  Sandip Mukherjee  Anirban Mukhopadhyay  Surajit Mondal 《地学前缘(英文版)》2017,8(3):425-436

Digital Elevation Model (DEM) is one of the important parameters for soil erosion assessment. Notable uncertainties are observed in this study while using three high resolution open source DEMs. The Revised Universal Soil Loss Equation (RUSLE) model has been applied to analysis the assessment of soil erosion uncertainty using open source DEMs (SRTM, ASTER and CARTOSAT) and their increasing grid space (pixel size) from the actual. The study area is a part of the Narmada river basin in Madhya Pradesh state, which is located in the central part of India and the area covered 20,558 km². The actual resolution of DEMs is 30 m and their increasing grid spaces are taken as 90, 150, 210, 270 and 330 m for this study. Vertical accuracy of DEMs has been assessed using actual heights of the sample points that have been taken considering planimetric survey based map (toposheet). Elevations of DEMs are converted to the same vertical datum from WGS 84 to MSL (Mean Sea Level), before the accuracy assessment and modelling. Results indicate that the accuracy of the SRTM DEM with the RMSE of 13.31, 14.51, and 18.19 m in 30, 150 and 330 m resolution respectively, is better than the ASTER and the CARTOSAT DEMs. When the grid space of the DEMs increases, the accuracy of the elevation and calculated soil erosion decreases. This study presents a potential uncertainty introduced by open source high resolution DEMs in the accuracy of the soil erosion assessment models. The research provides an analysis of errors in selecting DEMs using the original and increased grid space for soil erosion modelling.  相似文献   

Ferrobasalts from the Central Indian Ocean Basin     

S. D. Iyer  R. Mukhopadhyay  D. C. Popko 《Geo-Marine Letters》1999,18(4):297-304

 We report the occurrence of ferrobasalts recovered from the Central Indian Ocean Basin crust generated at the Southeast Indian Ridge during a phase of moderate to fast spreading accretion (∼110–190 mm/yr, full rate).The rocks are rich in plagioclase, FeO^* (13–19%), and TiO₂ (2.27–2.76%), poor in olivine and MgO (3.44–6.20%), and associated with topographic highs and increased amplitude magnetic anomalies corresponding to chrons A25 and A24. We suggest that secon dary eruptions from ancient N-MORB magma, which may have been trapped at a shallow depth in a horizon of neutral buoyancy, could have produced the ferrobasalts. Received: 27 January 1998 / Revision received: 25 May 1998  相似文献