Perturbations in tropical middle atmosphere during winter, 1984–1985     

B. K. Mukherjee  K. Indira  K. K. Dani 《Meteorology and Atmospheric Physics》1987,37(1):17-26

Summary Using high altitude rocketsonde data for Thumba (8.5 N, 76.9E) and Balasore (21.5 N, 86.9E) and the stratalert messages for high latitudes for the winter (December–March) 1984–1985, an examination has been made to study the perturbations in the temperature and winds in the tropical middle atmosphere and their linkage with the dynamical events occurring over the high-latitude middle atmosphere during that winter.The results of analysis indicated occurrence of strong cooling in the mesosphere over a period of seven days (5–12 December 1984) and the depth of the cooling layer was 15 km. This incident was followed by a strong warming over a period of seven days (12–19 December 1984) and the depth of the warming layer was 13 km. The major warming event, which occurred over high latitudes during the later part of December and the first week of January, was followed by the cooling in the mesosphere and warming in the stratosphere at Thumba. Also the zonal winds were strong easterly and the meridional winds were northerly in the upper stratosphere and the lower mesosphere over tropics during the same period. Weaker zonal winds/stronger easterly winds were generally noticed to be associated with coolings/warmings over tropics.With 7 Figures  相似文献   

Interannual variability of middle atmosphere and Indian summer monsoon     

B. K. Mukherjee  K. Indira  Bh. V. Ramana Murty 《Meteorology and Atmospheric Physics》1986,35(1-2):64-69

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Free vibrations of coupled shear walls     

P. R. Mukherjee  A. Coull 《地震工程与结构动力学》1972,1(4):377-386

The continuous connection method of analysis is extended to deal with the free vibrations of a coupled shear wall structure. The natural modes and frequencies are determined from the Galerkin technique, and the dynamic response following an imposed lateral displacement is evaluated. A comparison is made between theoretical predictions of natural frequencies and the results from tests on model structures.  相似文献   

Gas interaction effects on lunar bonded particles and their implications     

Nalin R. Mukherjee 《Earth, Moon, and Planets》1976,15(3-4):403-413

Some of the bonded particles of lunar soil samples separated upon exposure to reactive gases such as oxygen, water vapor, their mixtures, acids and bases. The bondings between particles susceptible to gas-disruption seemed to be generally weak and appeared to have taken place via highly radiation-damaged layers at the particle surfaces. These amorphous layers with an average thickness of about 0.05µm were produced by the solar wind exposure of about 2000 years. Therefore, the solar wind was responsible for the formation of these weak bondings and also probably responsible for disruption of these bondings. Apollo 11 and 12 landed in the equatorial region and about 1500 km apart. Thus, the solar wind effects on materials at these sites should have been about the same and the proportion of bonded particles separated by reactive gas exposure should also have been about the same; but the number of separations observed was about 2.7 (average) times greater in the Apollo 11 soil sample than in the Apollo 12 soil sample. This finding suggests that the number of weakly bonded particles and probably the solar-wind damaged amorphous layer particles at these sites was about in the same proportion. It is, therefore, considered that materials from certain depth (practically not exposed to the solar wind) of another site were transported and mixed during recent years (considerably less than 2000 years) with the original materials of the Apollo 12 site. This is consistent with the conclusions made by other investigators.  相似文献   

Motion of charged particles in the magnetosphere     

G. K. Mukherjee  R. Rajaram 《Astrophysics and Space Science》1981,74(2):287-301

The adiabatic motion of charged particles in the magnetosphere has been investigated using Mead-Fairfield magnetospheric field model (Mead and Fairfield, 1975). Since the motion of charged particles in a dipolar field geometry is well understood, we bring out in this paper some important features in characteristic motion due to non-dipolar distortions in the field geometry. We look at the tilt averaged picture of the field configuration and estimate theoretically the parameters like bounce period, longitudinal invariant and the bounce averaged drift velocities of the charged particle in the Mead-Fairfield field geometry. These parameters are evaluated as a function of pitch angle and azimuthal position in the region of ring current (5 to 7 Earth radii from the centre of the Earth) for four ranges of magnetic activity. At different longitudes the non-dipolar contribution as a percentage of dipole value in bounce period and longitudinal invariant show maximum variation for particles close to 90° pitch angles. For any low pitch angle, these effects maximize at the midnight meridian. The radial component of the bounce averaged drift velocity is found to be greatest at the dawn-dusk meridians and the contribution vanishes at the day and midnight meridians for all pitch angles. In the absence of tilt-dependent terms in the model, the latitudinal component of the drift velocity vanishes. On the other hand, the relative non-dipolar contribution to bounce averaged azimuthal drift velocity is very high as compared to similar contribution in other characteristic parameters of particle motion. It is also shown that non-dipolar contribution in bounce period, longitudinal invariant and bounce averaged drift velocities increases in magnitude with increase in distance and magnetic activity.  相似文献   

Natural vibrations of shear wall buildings on flexible supports     

A. Coull  P. R. Mukherjee 《地震工程与结构动力学》1978,6(3):295-316

A shear wall building is considered as an assembly of plane and curvilinear shear walls tied together by floor slabs to act as a composite unit. Based on this conception and the continuous medium approach, the governing dynamic equations and boundary conditions are derived from energy principles, using Vlasov's theory of thin-walled beams. All primary and secondary inertia forces, as well as the influence of elastic foundation flexibility, have been taken into consideration. A numerical solution of the dynamic equations is achieved by employing the Ritz-Galerkin technique, yielding both natural frequencies and mode shapes. The technique is applicable to buildings containing coupled and non-coupled, open section shear walls oriented in plan in any arbitrary manner. The use of the method is illustrated by the example of a complex building with unsymmetric plan, and the analytical natural frequencies of two shear wall building models are compared with those obtained experimentally by other investigators.  相似文献   

Some thermodynamical and microphysical aspects of monsoon clouds     

A Mary Selvam  A S Ramachandra Murty  R Vijayakumar  S K Paul  G K Manohar  R S Reddy  B K Mukherjee  Bh. V. Ramana Murty 《Journal of Earth System Science》1980,89(2):215-230

The thermodynamical and microphysical characteristics of monsoon clouds in the Poona, Bombay and Rihand regions were investigated using extensive aircraft in-cloud observations. The number of clouds sampled at Poona, Bombay and Rihand is 2199, 169 and 104 respectively. The temperatures inside the cloud are colder than its environment at Poona and Rihand. The maximum difference is about 3°C at the cloud base level and the difference decreased with height. At Bombay the difference is less than 1°C and at some levels the temperatures inside the cloud are warmer than its environment. The lapse rates of temperatures inside the cloud are slightly less than those in the immediate environment of the cloud. The environmental lapse rates are nearly equal to the saturated adiabatic value. The positive increments in liquid water content (LWC) are associated with the increments in temperature inside the cloud. Similarly positive increments in temperatures inside the cloud are associated with the increments in temperature of its immediate environment at the same level or the layer immediately above. The maximum cloud lengths observed at Poona and Bombay respectively are 14 and 3 km. The horizontal cross-section of LWC showed a maximum number of 13 peaks in clouds at Poona while only 7 peaks were observed at Bombay. The location of maximum LWC in the horizontal cross-section is more or less at the centre of the cloud. The LWC profile showed an increase with height from the base of the cloud at Poona and Bombay. There is no marked variation of LWC with height at Rihand. The total droplet concentration at different altitudes at Poona and Bombay is in the range 28–82 cm^?3. The size distribution of cloud droplets experienced a broadening effect with increase in height from the cloud base at Poona. The broadening effect at Bombay is not as marked as that at Poona.  相似文献   

Discussion     

S. Mukherjee  K. L. Chakraborty 《Mineralium Deposita》1974,9(1):91-92

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New record of <Emphasis Type="Italic">Plectoidothyris</Emphasis> from the Middle Jurassic Sequence of Jaisalmer Basin,Western India: Implications on the easterly brachiopod migrations     

Debahuti Mukherjee 《Journal of the Geological Society of India》2010,76(3):267-274

The Bathonian sediments of the Jaisalmer Basin, India host a terebratulide brachiopod Plectoidothyris which has been previously known from the Bajocian rocks of the Boreal Province. The sharp and prominent plication of the anterior commissure and increased length of costae separates the Jaisalmer specimens from other known species of the genus and the population represents an endemic species — Plectoidothyris jaisalmerensis. The population was only cursorily described earlier lacking in details of precise stratigraphic control and was wrongly assigned to a different genus. The present study is based on a large number of specimens from different localities with precise stratigraphic data, coupled with this some recent findings of time-diagnostic ammonites have helped determine the Plectoidothyris jaisalmerensis duration in the Jaisalmer Basin as the Late Bathonian. Presence of lower Jurassic Boreal brachiopod genera in the Middle Jurassic rocks of Ethiopian and Indo — Madagascan biogeographic provinces has been noticed earlier whereto Plectoidothyris is a new addition while it is also the first report of the genus from the Jurassic of India. The brachiopod migrations from the north to south of the Tethys provide evidences for opening of shallow water routes in the Tethyan seaway and are probably indicative of warmer water conditions in the Indo-Madagascan and African areas during the Middle Jurassic.  相似文献   

Groundwater recharge in natural dune systems and agricultural ecosystems in the Thar Desert region, Rajasthan, India   总被引：2，自引：1，他引：1  

Bridget R. Scanlon  Abhijit Mukherjee  John Gates  Robert C. Reedy  Amarendra K. Sinha 《Hydrogeology Journal》2010,18(4):959-972

Water and nutrient availability for crop production are critical issues in (semi)arid regions. Unsaturated-zone Cl tracer data and nutrient (NO₃ and PO₄) concentrations were used to quantify recharge rates using the Cl mass balance approach and nutrient availability in the Thar Desert, Rajasthan, India. Soil cores were collected in dune/interdune settings in the arid Thar Desert (near Jaisalmer) and in rain-fed (nonirrigated) and irrigated cropland in the semiarid desert margin (near Jaipur). Recharge rates were also simulated using unsaturated zone modeling. Recharge rates in sparsely vegetated dune/interdune settings in the Jaisalmer study area are 2.7–5.6 mm/year (2–3% of precipitation, 165 mm/year). In contrast, recharge rates in rain-fed agriculture in the Jaipur study area are 61–94 mm/year (10–16% of precipitation, 600 mm/year). Minimum recharge rates under current freshwater irrigated sites are 50–120 mm/year (8–20% of precipitation). Nitrate concentrations are low at most sites. Similarity in recharge rates based on SO₄ with those based on Cl is attributed to a meteoric origin of SO₄ and generally conservative chemical behavior in these sandy soils. Modeling results increased confidence in tracer-based recharge estimates. Recharge rates under rain-fed agriculture indicate that irrigation of 20–40% of cultivated land with 300 mm/year should be sustainable.  相似文献