Understanding the wet season variations over Florida     

Vasubandhu Misra  S. M. DiNapoli 《Climate Dynamics》2013,40(5-6):1361-1372

The wet season of Florida is well defined and is invariably centered in the boreal summer season of June–July–August. In this observational study we objectively define the Length of the Wet Season (LOWS) for Florida and examine its variations with respect to El Niño and the Southern Oscillation (ENSO) and the Atlantic Warm Pool (AWP). Our study reveals that ENSO variability has a profound influence on the LOWS especially over south Florida and parts of panhandle Florida prior to 1976. In the post-1976 era the influence of ENSO has significantly diminished. Our results show that in this pre-1976 era, warm (cold) ENSO events in the boreal winter are followed by long (short) LOWS over the region. This variation is consistent with warm (cold) ENSO events influencing early (late) onset of the wet season in the region. There is significant relationship of the LOWS in south and northeast Florida with the variation of the AWP. Unlike the teleconnection with ENSO the relationship of the demise of the wet season with AWP is stronger in the post-1976 period compared to the pre-1976 period. Furthermore the variability of the LOWS has increased in the post-1976 period.  相似文献   

Evaluation of twentieth-century Atlantic Warm Pool simulations in historical CMIP5 runs     

Michael E. Kozar  Vasubandhu Misra 《Climate Dynamics》2013,41(9-10):2375-2391

State-of-the-art coupled global climate models are evaluated for their simulation of the Atlantic Warm Pool (AWP). Historical runs from 17 coupled climate models included in the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5) serve as the basis for this model evaluation study. The model simulations are directly compared to observations and reanalysis data to evaluate the climatological features and variability of the AWP within each individual model. Results reveal that a select number of models—namely the GISS-E2-R, CSIRO-Mk3.6, and MPI-ESM-LR—are successful at resolving an appropriately sized AWP with some reasonable climatological features. However, these three models exhibit an erroneously broad seasonal peak of the AWP, and its variability is significantly underestimated. Furthermore, all of the CMIP5 models exhibit a significant cold bias across the tropical Atlantic basin, which hinders their ability to accurately resolve the AWP.  相似文献   

Long term optical variability of bright X-ray point sources in elliptical galaxies     

V.Jithesh  Ranjeev Misra  P.Shalima  K.Jeena  C.D.Ravikumar  B.R.S.Babu 《中国天文和天体物理学报》2014,(10)

We present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with the Chandra Advanced CCD Imaging Spectrometer array(ACIS-S) and observations from the Hubble Space Telescope(HST) Advanced Camera for Surveys.Out of the 46 bright(X-ray counts 60)sources that are in the common field of view of the Chandra and HST observations,34 of them have potential optical counterparts,while the rest of them are optically dark.After taking into account systematic errors,estimated using optical sources in the field as a reference,we find that four of the X-ray sources(three in NGC 1399 and one in NGC 1427) have variable optical counterparts at a high level of significance.The X-ray luminosities of these sources are ~ 10~(38) erg s~(-1) and are also variable on similar time scales.The optical variability implies that the optical emission is associated with the X-ray source itself rather than being the integrated light from a host globular cluster.For one source,the change in optical magnitude is 0.3,which is one of the highest reported for this class of X-ray sources and this suggests that the optical variability is induced by the X-ray activity.However,the optically variable sources in NGC 1399 have been reported to have blue colors(g- z 1).All four sources have been detected in the infrared(IR) by Spitzer as point sources,and their ratios of 5.8 to 3.6 μm flux are 0.63,indicating that their IR spectra are like those of Active Galactic Nuclei(AGNs).While spectroscopic confirmation is required,it is likely that all four sources are background AGNs.We find none of the X-ray sources having optical/IR colors different from AGNs to be optically variable.  相似文献   

Self-consistent computation of γ-ray spectra due to proton–proton interactions in black hole systems     

S. Bhattacharyya  N. Bhatt  R. Misra 《Monthly notices of the Royal Astronomical Society》2006,371(1):245-251

In the inner regions of an accretion disc around a black hole, relativistic protons can interact with ambient matter to produce electrons, positrons and γ-rays. The resultant steady-state electron and positron particle distributions are self-consistently computed taking into account Coulomb and Compton cooling,  e⁻ e⁺  pair production (due to γ–γ annihilation) and pair annihilation. While earlier works used the diffusion approximation to obtain the particle distributions, here we solve a more general integro-differential equation that correctly takes into account the large change in particle energy that occurs when the leptons Compton scatter off hard X-rays. Thus this formalism can also be applied to the hard state of black hole systems, where the dominant ambient photons are hard X-rays. The corresponding photon energy spectrum is calculated and compared with broad-band data of black hole binaries in different spectral states. The results indicate that the γ-ray spectra  ( E > 0.8 MeV)  of both the soft and hard spectral states and the entire hard X-ray/γ-ray spectrum of the ultrasoft state could be due to p–p interactions. These results are consistent with the hypothesis that there always exists in these systems a γ-ray spectral component due to p–p interactions that can contribute between 0.5 and 10 per cent of the total bolometric luminosity. The model predicts that GLAST would be able to detect black hole binaries and provide evidence for the presence of non-thermal protons, which in turn would give insight into the energy dissipation process and jet formation in these systems.  相似文献   

X-ray spectral evolution of the extragalactic Z source LMC X-2     

V. K. Agrawal  R. Misra 《Monthly notices of the Royal Astronomical Society》2009,398(3):1352-1360

We present the results obtained by a detailed study of the extragalactic Z source LMC X-2, using broad-band Suzaku data and a large (∼750 ks) data set obtained with the proportional counter array (PCA) onboard the Rossi X-ray Timing Experiment ( RXTE ). The PCA data allow the study of the complete spectral evolution along the horizontal, normal and flaring branches of the Z track. Comparison with previous studies shows that the details of spectral evolution (like the variation of Comptonizing electron temperature) are similar to those of GX 17+2 but unlike those of Cyg X-2 and GX 349+2. This suggests that Z sources are a heterogeneous group, with perhaps LMC X-2 and GX 17+2 being members of a subclass. However, non-monotonic evolution of the Compton y parameter seems to be generic to all sources. The broad-band Suzaku data reveal that the case in which the additional soft component of the source is modelled as disc blackbody emission is strongly preferred over the one where it is taken to be a blackbody spectrum. This component, as well as the temperature of seed photons, does not vary when the source goes into flaring mode, and the entire variation can be ascribed to the Comptonizing cloud. The bolometric unabsorbed luminosity of the source is constrained to be  ∼2.23 × 10³⁸ erg s⁻¹  , which, if the source is Eddington-limited, implies a neutron star mass of  1.6 M_⊙  . We discuss the implications of these results.  相似文献   

Rhodophycean algae from the Lower Cretaceous of the Cauvery Basin,South India     

P. K. Misra  S. Kishore  S. K. Singh  A. K. Jauhri 《Journal of the Geological Society of India》2009,73(3):325-334

The present paper records eight Rhodophycean taxa from the Kallakudi limestone of the Uttatur Group (Lower Cretaceous) exposed in the quarries at Kallakudi and Olaipadi near Govindarajapatnam of the Cauvery Basin, south India. Of these, four species (Melobesioideae gen. et sp. indet 1, Melobesioideae gen. et sp. indet 2, Lithophyllum alternicellum and Pseudoamphiroa propria) belong to corallinaceae family, one species (Polystrata alba) is assigned to Peyssonneliaceae family, two species (Solenopora urgoniana and Parachaetetes asvapatii) are placed under Solenoporaceae; and one species (Sporolithon sp.) is referable to Sporolithaceae family. Among these, three taxa (Solenopora urgoniana, Lithophyllum alternicellum and Pseudoamphiroa propria) are recorded for the first time from India. The study also includes observations on ultrastructural morphological features of Parachaetetes asvapatii. The observations reveal absence of cell fusions, which confirms its affinities with Solenoporaceae. Palaeoecological data indicate that the assemblage from the sequence at the Kallakudi quarry is characteristic of lagoonal to reefal environment, whereas the Olaipadi quarry sequence near Govindarajapatnam points to 20 m to 30 m deep environment characterized by high- to moderate energy conditions.  相似文献   

Simple Approaches to Oil Spill Detection Using Sentinel Application Platform (SNAP)-Ocean Application Tools and Texture Analysis: A Comparative Study     

A. Misra  R. Balaji 《Journal of the Indian Society of Remote Sensing》2017,45(6):1065-1075

Effective and efficient monitoring of oil spills that originate from ships, offshore platforms and any accidents are of immense importance from the viewpoint of public safety and environmental protection. Detection of spilled oil is also essential to estimate the potential spread and drift from the source to the nearby coastal areas. In this regard, utilization of SAR data for the detection and monitoring of oil spills has received considerable attention in recent times, due to their wide area coverage, day-night and all-weather capabilities. In this paper, two oil spills incidents along the coast of Mumbai, India are investigated; (1) The 2010 oil spill that occurred after the MV MSC Chitra and MV Khalijia-3 collided and (2) the oil spill caused due to sinking of MV RAK carrier in 2011. Two simple and relatively quick approaches for oil spill detection have been applied to VV polarized Radarsat-2 imagery of the incidents and a comparison is made of the results obtained. The first approach utilizes the oil spill detection tool of Sentinel Application Platform (SNAP) and the second explores texture analysis using Grey Level co-occurrence matrix (GLCM). The results of the study show that texture analysis proves to be an efficient method for oil spill detection as compared to the SNAP oil spill detection tool. Nevertheless, both the proposed methodologies are useful for detection of oil spills and for subsequent utilization of the results, timely and cost effectively, for the calibration and validation of numerical models that predict oil spill dispersion trajectories.  相似文献   

Spatial-Correlation Based Persistent Scatterer Interferometric Study for Ground Deformation     

Kousik Biswas  Debashish Chakravarty  Pabitra Mitra  Arundhati Misra 《Journal of the Indian Society of Remote Sensing》2017,45(6):913-926

Interferometric Synthetic Aperture Radar (InSAR), nowadays, is a precise technique for monitoring and detecting ground deformation at a millimetric level over large areas using multi-temporal SAR images. Persistent Scatterer Interferometric SAR (PSInSAR), an advanced version of InSAR, is an effective tool for measuring ground deformation using temporally stable reference points or persistent scatterers. We have applied both PSInSAR and Small Baseline Subset (SBAS) methods, based on the spatial correlation of interferometric phase, to estimate the ground deformation and time-series analysis. In this study, we select Las Vegas, Nevada, USA as our test area to detect the ground deformation along satellite line-of-sight (LOS) during November 1992–September 2000 using 44 C-band SAR images of the European Remote Sensing (ERS-1 and ERS-2) satellites. We observe the ground displacement rate of Las Vegas is in the range of ?19 to 8 mm/year in the same period. We also cross-compare PSInSAR and SBAS using mean LOS velocity and time-series. The comparison shows a correlation coefficient of 0.9467 in the case of mean LOS velocity. Along this study, we validate the ground deformation results from the satellite with the ground water depth of Las Vegas using time-series analysis, and the InSAR measurements show similar patterns with ground water data.  相似文献   

Downscaling future climate change projections over Puerto Rico using a non-hydrostatic atmospheric model     

Amit Bhardwaj  Vasubandhu Misra  Akhilesh Mishra  Adrienne Wootten  Ryan Boyles  J. H. Bowden  Adam J. Terando 《Climatic change》2018,147(1-2):133-147

We present results from 20-year “high-resolution” regional climate model simulations of precipitation change for the sub-tropical island of Puerto Rico. The Japanese Meteorological Agency Non-Hydrostatic Model (NHM) operating at a 2-km grid resolution is nested inside the Regional Spectral Model (RSM) at 10-km grid resolution, which in turn is forced at the lateral boundaries by the Community Climate System Model (CCSM4). At this resolution, the climate change experiment allows for deep convection in model integrations, which is an important consideration for sub-tropical regions in general, and on islands with steep precipitation gradients in particular that strongly influence local ecological processes and the provision of ecosystem services. Projected precipitation change for this region of the Caribbean is simulated for the mid-twenty-first century (2041–2060) under the RCP8.5 climate-forcing scenario relative to the late twentieth century (1986–2005). The results show that by the mid-twenty-first century, there is an overall rainfall reduction over the island for all seasons compared to the recent climate but with diminished mid-summer drought (MSD) in the northwestern parts of the island. Importantly, extreme rainfall events on sub-daily and daily time scales also become slightly less frequent in the projected mid-twenty-first-century climate over most regions of the island.  相似文献   

Impacts of SW Monsoon on Phytoplankton Community Structure Along the Western Coastal BOB: an HPLC Approach     

Debasmita Bandyopadhyay  Haimanti Biswas  V. V. S. S. Sarma 《Estuaries and Coasts》2017,40(4):1066-1081

The major Indian rivers bring significant amount of freshwater along with inorganic nutrients and sediment load in to the northern Bay of Bengal (BOB) during the southwest monsoon (SWM); the southern bay does not experience equal freshening. This contrasting pattern may considerably impact the physicochemical features and phytoplankton community composition in this bay and was investigated during a coastal cruise during the SWM covering eight river plumes from both northern and southern bay; phytoplankton pigments and physicochemical parameters were analysed from different depths (0, 10, 25, and 50 m). Significant freshening, stratification and warmer waters were noticed in the northern bay relative to its southern part. Phytoplankton pigment analysis and diagnostic pigment-based size class analysis revealed the dominance of microphytoplankton (mainly diatoms) in the northern bay and were mostly confined to the surface waters. Their abundance was positively correlated with dissolved silicate (DSi) concentrations and inversely with salinity. Nanophytoplankton and picophytoplankton (prymnesiophytes, chrysophytes and cyanophytes) were mostly noticed in the subsurface waters and dominated the southern bay. This finding suggests that the dominance of microphytoplankton in the northern bay may significantly contribute to higher particle flux which has been reported earlier. Therefore, any modification in future river discharge, which is in turn related to the intensity of Indian summer monsoon, will alter the phytoplankton community structure in the coastal BOB and may be further cascaded to the other vital ecosystem components like fisheries resources, organic carbon export flux and benthic production.  相似文献