Prediction of the Maximum Amplitude and Timing of Sunspot Cycle 24     

Nipa J. Bhatt  Rajmal Jain  Malini Aggarwal 《Solar physics》2009,260(1):225-232

Precursor techniques, in particular those using geomagnetic indices, often are used in the prediction of the maximum amplitude for a sunspot cycle. Here, the year 2008 is taken as being the sunspot minimum year for cycle 24. Based on the average aa index value for the year of the sunspot minimum and the preceding four years, we estimate the expected annual maximum amplitude for cycle 24 to be about 92.8±19.6 (1-sigma accuracy), indicating a somewhat weaker cycle 24 as compared to cycles 21 – 23. Presuming a smoothed monthly mean sunspot number minimum in August 2008, a smoothed monthly mean sunspot number maximum is expected about October 2012±4 months (1-sigma accuracy).  相似文献   

North Atlantic warming: patterns of long-term trend and multidecadal variability   总被引：1，自引：1，他引：0  

Igor V. Polyakov  Vladimir A. Alexeev  Uma S. Bhatt  Evgenia I. Polyakova  Xiangdong Zhang 《Climate Dynamics》2010,34(2-3):439-457

Climate fluctuations in the North Atlantic Ocean have wide-spread implications for Europe, Africa, and the Americas. This study assesses the relative contribution of the long-term trend and variability of North Atlantic warming using EOF analysis of deep-ocean and near-surface observations. Our analysis demonstrates that the recent warming over the North Atlantic is linked to both long-term (including anthropogenic and natural) climate change and multidecadal variability (MDV, ~50–80 years). Our results suggest a general warming trend of 0.031 ± 0.006°C/decade in the upper 2,000 m North Atlantic over the last 80 years of the twentieth century, although during this time there are periods in which short-term trends were strongly amplified by MDV. For example, MDV accounts for ~60% of North Atlantic warming since 1970. The single-sign basin-scale pattern of MDV with prolonged periods of warming (cooling) in the upper ocean layer and opposite tendency in the lower layer is evident from observations. This pattern is associated with a slowdown (enhancement) of the North Atlantic thermohaline overturning circulation during negative (positive) MDV phases. In contrast, the long-term trend exhibits warming in tropical and mid-latitude North Atlantic and a pattern of cooling in regions associated with major northward heat transports, consistent with a slowdown of the North Atlantic circulation as evident from observations and confirmed by selected modeling results. This localized cooling has been masked in recent decades by warming during the positive phase of MDV. Finally, since the North Atlantic Ocean plays a crucial role in establishing and regulating the global thermohaline circulation, the multidecadal fluctuations discussed here should be considered when assessing long-term climate change and variability, both in the North Atlantic and at global scales.  相似文献   

Porosity and permeability prediction from wireline logs using artificial neural networks: a North Sea case study   总被引：2，自引：1，他引：2  

Hans B. Helle  Alpana Bhatt  Bjørn Ursin 《Geophysical Prospecting》2001,49(4):431-444

Estimations of porosity and permeability from well logs are important yet difficult tasks encountered in geophysical formation evaluation and reservoir engineering. Motivated by recent results of artificial neural network (ANN) modelling offshore eastern Canada, we have developed neural nets for converting well logs in the North Sea to porosity and permeability. We use two separate back-propagation ANNs (BP-ANNs) to model porosity and permeability. The porosity ANN is a simple three-layer network using sonic, density and resistivity logs for input. The permeability ANN is slightly more complex with four inputs (density, gamma ray, neutron porosity and sonic) and more neurons in the hidden layer to account for the increased complexity in the relationships. The networks, initially developed for basin-scale problems, perform sufficiently accurately to meet normal requirements in reservoir engineering when applied to Jurassic reservoirs in the Viking Graben area. The mean difference between the predicted porosity and helium porosity from core plugs is less than 0.01 fractional units. For the permeability network a mean difference of approximately 400 mD is mainly due to minor core-log depth mismatch in the heterogeneous parts of the reservoir and lack of adequate overburden corrections to the core permeability. A major advantage is that no a priori knowledge of the rock material and pore fluids is required. Real-time conversion based on measurements while drilling (MWD) is thus an obvious application.  相似文献   

Geochemistry and petrology of the Main Limestone Series (Lower Carboniferous), South Wales,U.K.     

J.J. Bhatt 《Sedimentary Geology》1976,15(1):55-86

Dolomitized Main Limestone rocks of the Lower Carboniferous crop out in a narrow band of about three fourths of a mile along the south, east and northeast rims of the South Wales Coalfield Basin which encompasses the general regions of Miskin, Taffs Well and the Clydach, respectively. The thickness of these rocks varies from a maximum of 2,750 feet to nothing.The Ca/Mg ratio in the Main Limestone in general ranged from 1.7 : 1 to over 100 : 1 with less than 2 : 1 to 3.5 : 1 being the commonest. Magnesium content ranged from less than 5% to over 60% (mole percent MgCO₃), with 40–50 mole percent p.f. MgCO₃ being the commoner.Petrographic study of the Main Limestone led to recognition of six major microfacies. They are: (1) biosparite; (2) dolobiomicrite; (3) quartz-dolomicrite; (4) dolomicrite; (5) oosparite; and (6) dolorudite. In terms of their geographic distribution, dolobiomicrite predominates in the Taffs Well region, while quartz-dolobiomicrite is common in the Clydach region. In terms of their distribution in time, biosparite is common in the basal part (Lower ZC₁ zone), dolobiomicrites (including the quartz-bearing variety) in the middle part (ZC₁ and C₂S₁ zone) of the Taffs Well region and its corresponding Calcite-Mudstone Group in the Clydach region.The bulk of dolomitization in these rocks occurred in the Caninia-Seminula zone or the Calcite-Mudstone Group. In this study, it marks geochemical stage B: the sea-connected lagoonal phase similar to one observed today in South Australia. It is suggested that such a sea-connected Lagoon in the Main Limestone Sea formed largely in response to a reef barrier (or a ridge) - a remnant of which is found today between Miskin and the Taffs Well region where the transition from lime to dolomite facies occurs. The Miskin area represented the deeper-water reef flank towards the open sea whereas the Taffs Well region marked the shallow-water reef flank landward.It is concluded that the Main Limestone Series contains predominantly diagenetic dolostones whilst the syngenetic and epigenetic dolostones are restricted in time and space. The diagenetic dolostone dominates in the Taffs Well and Clydach regions.  相似文献   

Evidence of evaporite deposition in the Lower Carboniferous Main Limestone Series of South Wales,U.K.     

J.J. Bhatt 《Sedimentary Geology》1975,13(1):65-70

Petrographic examination of the dolomitized Main Limestone Series cropping out in the south, east and northeast corners of the South Wales Coalfield Basin shows evidence of the earlier presence of evaporite minerals. However, it is believed that lack of extensive evaporite deposits in these rocks may be due to the active diagenetic dissolution and oncoming humid coal conditions of post Main Limestone time.The evaporite minerals in the Main Limestone rocks seem to be overwhelmingly early diagenetic in origin in the light of the following observations: (1) calcite or dolomite pseudomorphs after gypsum crystals associated with a fine pelmicrite matrix; (2) association of such pseudomorphs with oolitic pelsparite; and (3) evaporite solution breccia texture.  相似文献   

Late Quaternary stratigraphic development in the lower Luni,Mahi and Sabarmati river basins,western India     

M. Jain  S. K. Tandon  S. C. Bhatt 《Journal of Earth System Science》2004,113(3):453-471

This study reviews the Quaternary alluvial stratigraphy in three semi-arid river basins of western India i.e., lower Luni (Rajasthan), and Mahi and Sabarmati (Gujarat alluvial plains). On the basis of OSL chronologies, it is shown that the existing intra-valley lithostratigraphic correlations require a revision. The sand, gravel and mud facies are present during various times in the three basins, however, the fluvial response to climate change, and the resulting facies associations, was different in the Thar desert as compared to that at the desert margin; this makes purely lithostratigraphic correlations unviable. It is further shown that the rivers in the Thar desert were more sensitive to climate change and had small response times and geomorphic thresholds as compared to the desert-margin rivers. This is illustrated during the early OIS 1, when the Luni river in the Thar desert was dynamic and showed frequent variations in fluvial styles such as gravel bedload braided streams, sand-bed ephemeral streams and meandering streams, all followed by incision during the early Holocene. The coeval deposits in Sabarmati, however, only show a meandering, floodplain-dominated river. Late Quaternary alluvial deposits in these basins unconformably overlie some older deposits that lack any absolute chronology. Based on the facies types and their associations, and the composition and architecture of the multistoried gravel sheets in the studied sections, it is suggested that older deposits are of pre-Quaternary age. This hypothesis implies the presence of a large hiatus incorporating much of the Quaternary period in the exposed sections  相似文献   

Committee neural networks for porosity and permeability prediction from well logs   总被引：1，自引：0，他引：1  

Alpana Bhatt †  Hans B. Helle 《Geophysical Prospecting》2002,50(6):645-660

Neural computing has moved beyond simple demonstration to more significant applications. Encouraged by recent developments in artificial neural network (ANN) modelling techniques, we have developed committee machine (CM) networks for converting well logs to porosity and permeability, and have applied the networks to real well data from the North Sea. Simple three‐layer back‐propagation ANNs constitute the blocks of a modular system where the porosity ANN uses sonic, density and resistivity logs for input. The permeability ANN is slightly more complex, with four inputs (density, gamma ray, neutron porosity and sonic). The optimum size of the hidden layer, the number of training data required, and alternative training techniques have been investigated using synthetic logs. For both networks an optimal number of neurons in the hidden layer is in the range 8–10. With a lower number of hidden units the network fails to represent the problem, and for higher complexity overfitting becomes a problem when data are noisy. A sufficient number of training samples for the porosity ANN is around 150, while the permeability ANN requires twice as many in order to keep network errors well below the errors in core data. For the porosity ANN the overtraining strategy is the suitable technique for bias reduction and an unconstrained optimal linear combination (OLC) is the best method of combining the CM output. For permeability, on the other hand, the combination of overtraining and OLC does not work. Error reduction by validation, simple averaging combined with range‐splitting provides the required accuracy. The accuracy of the resulting CM is restricted only by the accuracy of the real data. The ANN approach is shown to be superior to multiple linear regression techniques even with minor non‐linearity in the background model.  相似文献   

Magnetic fields in cometary globules – III. CG 12     

H. C. Bhatt  G. Maheswar  P. Manoj 《Monthly notices of the Royal Astronomical Society》2004,348(1):83-88

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Orbital evolution and orbital phase resolved spectroscopy of the HMXB pulsar 4U 1538-52 with RXTE-PCA and BeppoSAX     

U. Mukherjee  H. Raichur  B. Paul  S. Naik  N. Bhatt 《Journal of Astrophysics and Astronomy》2006,27(4):411-423

We report here results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U 1538-52 over several binary periods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbitial parameters determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray binary. We have carried out orbital phase resolved spectroscopy to measure changes in the spectral parameters with orbital phase, particularly the absorption column density and the iron line flux. The RXTE-PCA spectra in the 3–20 keV energy range were fitted ∼6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at ∼6.4 keV in the restricted energy range of 0.3–10.0 keV. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a spherically symmetric stellar wind from the companion star.  相似文献   

A decadal historical satellite data analysis for flood hazard evaluation: A case study of Bihar (North India)          下载免费PDF全文

Panchagnula Manjusree  Chandra Mohan Bhatt  Asiya Begum  Goru Srinivasa Rao  Veerubhotla Bhanumurthy 《Singapore journal of tropical geography》2015,36(3):308-323

Flood is one of the major recurrent natural disasters faced by the state of Bihar in north India. In the present study the authors assess the severity of flood hazard in Bihar, using 128 decadal historical satellite datasets acquired during different flood magnitudes during 1998 to 2010. The satellite‐based observations have been analysed in conjunction with the hydrological data, for assessing the frequency of inundation, severity of flood hazard and cropped land under flood hazard. This study assesses the spatial distribution of flooding and creation of systematic flood hazard database, which can be analysed from a spatial dimension in GIS. It is observed that about 24.56 lakh ha of the state's area and about 15.85 lakh ha of the cropped area are vulnerable to flood hazard. North Bihar is more vulnerable to flooding; 8 of the 10 areas identified as worst flood‐affected districts lie in this region.  相似文献