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1.
Amala Mitra 《Pure and Applied Geophysics》1966,63(1):60-67
Summary The stress and displacement throughout a homogeneous, isotropic, elastic quarterspace have been evaluated when the stress is prescribed on one of the plane boundaries and the displacement on the other. The variations of the displacement and stress on the boundaries with time and distance from the origin have been shown graphically. 相似文献
2.
Through a suite of three-dimensional, high-resolution numerical modeling experiments, we examine the role of nonhydrostatic effects on O(1 km) submesoscale processes at ocean fronts, with particular focus on the vertical velocity field. Several differences between nonhydrostatic and hydrostatic models are pointed out using a framework that enables precise comparison, but it is difficult to identify categorical differences between the model solutions at the grid resolutions afforded. The instantaneous vertical velocity structure is sensitive to the model choice and, even more so, to grid resolution, but the average vertical flux is similar in both hydrostatic and nonhydrostatic cases.When a frontal region with horizontal density gradients is perturbed by wind, a profusion of submesoscale, O(1 km), secondary circulation features develops in the upper 50 m. Narrow, elongated cells of intense up- and down-welling are found to occur close to the surface, overlying broader regions of weaker up- and down-welling associated with the mesoscale meanders of the baroclinically unstable front. The submesoscale down-welling is considerably stronger than up-welling and is concentrated in 1–2 km width filaments within which velocities can attain magnitudes as high as 200 m day−1. The submesoscale features are found to be robust at horizontal grid resolutions varying between 1 and 0.25 km and exist even in the hydrostatic model. Submesoscale circulation is difficult to observe or resolve in coarser resolution circulation models, but is likely to play a significant role in the exchange of energy and properties between the surface ocean and thermocline. Possible mechanisms for the generation of these features are investigated in a follow-on paper. 相似文献
3.
We analyze model simulations of a wind-forced upper ocean front to understand the generation of near-surface submesoscale, O(1 km), structures with intense vertical motion. The largest vertical velocities are in the downward direction; their maxima are situated at approximately 25 m depth and magnitudes exceed 1 mm/s or 100 m/day. They are correlated with high rates of lateral strain, large relative vorticity and the loss of geostrophic balance. We examine several mechanisms for the formation of submesoscale structure and vertical velocity in the upper ocean. These include: (i) frontogenesis, (ii) frictional effects at fronts, (iii) mixed layer instabilities, (iv) ageostrophic anticyclonic instability, and (v) nonlinear Ekman effects. We assess the role of these mechanisms in generating vertical motion within the nonlinear, three-dimensionally evolving flow field of the nonhydrostatic model. We find that the strong submesoscale down-welling in the model is explained by nonlinear Ekman pumping and is also consistent with the potential vorticity arguments that analogize down-front winds to buoyancy-forcing. Conditions also support the formation of ageostrophic anticyclonic instabilities, but the contribution of these is difficult to assess because the decomposition of the flow into balanced and unbalanced components via semigeostrophic analysis breaks down at O(1) Rossby numbers. Mixed layer instabilities do not dominate the structure, but shear and frontogenesis contribute to the relative vorticity and strain fields that generate ageostrophy. 相似文献
4.
A. K. Mitra M. Das Gupta R. K. Paliwal S. V. Singh 《Journal of Earth System Science》2003,112(2):223-232
A daily rainfall dataset and the corresponding rainfall maps have been produced by objective analysis of rainfall data. The
satellite estimate of rainfall and the raingauge values are merged to form the final analysis. Associated with epochs of monsoon
these rainfall maps are able to show the rainfall activities over India and the Bay of Bengal region during the BOBMEX period.
The intra-seasonal variations of rainfall during BOBMEX are also seen using these data. This dataset over the oceanic region
compares well with other available popular datasets like GPCP and CMAP. Over land this dataset brings out the features of
monsoon in more detail due to the availability of more local raingauge stations. 相似文献
5.
A. Heusel-Waltrop K. Diehl S. K. Mitra H. R. Pruppacher 《Journal of Atmospheric Chemistry》2003,44(2):211-223
Laboratory experiments have been carried out to investigate the uptake of sulfur dioxide by water drops containing heavy metal ions where the metal ions serve as catalysts to oxidise the taken up S(IV) into S(VI). During the gas uptake the drops were freely suspended at their terminal velocity in the airstream of the Mainz vertical wind tunnel. Two series of experiments were carried out, one with large millimeter size water drops containing manganese or iron ions, and the other with small water drops containing manganese ions and having radii in hundreds of micron size range. The experimental results were compared against model computations using the Kronig–Brink model and the fully mixed model, modified for the case that heavy metal ions present in the liquid phase act as catalysts for the oxidising process. The results of the model calculations show that there are only small differences between the predicted gas uptake according to the two models. In addition it was found that the experimental obtained results from the uptake of SO2 by water drops containing heavy metal ions for both, large and small water drops did agree with the model results. 相似文献
6.
The chromites from the alpine type ultramafic intrusive of Sukinda, India, display a typical partly inverse spinel form and occur in two distinct zones: Brown Ore Zone (BOZ) and Grey Ore Zone (GOZ). The host ultramafites are mostly altered and are represented by the serpentinite, tremolite-talc(chlorite) schist, talc-serpentine schist and chlorite rock. The less altered variants are dunite, harzburgite and websterite. A dyke of orthopyroxenite runs through the main ultramafic body.The composition of olivine (Fo92), orthopyroxene (En92–89) and Al2O3 contents of the parental liquid (10.40–11.45%) determined from chromites, suggest that the parent melt is of boninitic affinity. The chemical plot of TiO2 content against cr# of chromites corroborates a boninitic parental melt. The Fe–Mg partitioning in olivine and chromite depicts the temperature for chromitites as 1200 °C. A compositional plot of mg# and cr# suggests crystallization at high pressure conditions, corresponding to the kimberlite xenolith field. From the P–T diagram of pyrolite melting and mineral assemblage, the pressure of crystallization is stipulated to be ≥1.2 GPa. The fO2 values estimated from Fe3+/Cr+Al+Fe3+ ratios range from 10−8.3 to 10−9.3 for the GOZ and 10−7.1 to 10−7.3 for the BOZ. The fO2 values together with the pressure range suggest crystallization at upper mantle conditions. The heterogeneity in chemical composition and fO2 conditions for the GOZ and BOZ could be linked to heterogeneity in the upper mantle. 相似文献
7.
8.
The effect of river runoff over the northern Indian Ocean(NIO) especially over the Bay of Bengal(Bo B) has been studied using global Nucleus for European Modelling of the Ocean(NEMO). Two sensitivity experiments, with and without river runoff are conducted and the influence of river runoff on the Indian Ocean hydrography,stratification and circulation features are studied. It is found that due to river runoff surface salinity over the northern Bo B decreases by more than 5 and the East India Coastal Current strengthens by 2 cm/s during post monsoon season. The fresh river water reaches up to 15°N in the Bo B and is the main cause for low salinity there.Sea surface temperature in the northwestern Bo B increases by more than 0.2℃ due to the river runoff in summer monsoon while surface cooling upto 0.2℃ is seen in north-west part of Bo B in winter season. The seasonal mixed layer depth in the region is found to be dependent on river runoff. The effect of vertical shear and Brunt Vaisala frequency on stratification is also examined. The ocean water becomes highly stratified up to 3 035 m due to the river runoff. It is found that the energy required for mixing is high in the northern and coastal Bo B. 相似文献
9.
P. C. Padhy R. K. Nayak V. K. Dadhwal M. Salim D. Mitra S. B. Chaudhury P. R. Rao K. H. Rao C.B. S. Dutt 《Journal of the Indian Society of Remote Sensing》2016,44(1):135-143
An empirical model is developed and used with remotely sensed predictors: sea surface temperature (SST) and chlorophyll-a concentration (Chl-a), to compute surface water partial pressure of carbon dioxide (pCO2w) and air-sea fluxes of CO2 in the Hooghly estuary and its adjacent coastal oceans. In situ observations used here were based on measurements carried out in this region during winter and summer periods in 2008. The estimated pCO2w compares well with the in situ observations at root mean square error ±18 μatm. In winter, estimated pCO2w ranges between 320 and 500 μatm with large values (>400 μatm) on the south-western and south-eastern flanks of the coastal domain and lower values (340–375 μatm) on the main-channel. In summer, it remained spatially uniform at 450 μatm. Extrapolation of the results over the study region based on the Moderate Imaging Specroradiometer (MODIS) measured SST and Chl-a suggests that the region is a strong source of atmospheric CO2 during the summer with net release of 0.095 Tg C year?1 (equivalent to mean flux of 90 molC m?2 year?1) and is a weak source during the winter with net release of 0.006 Tg C yr?1 (0.5 molC m?2 year?1) from the geographical extent of 6000 Km2 area. 相似文献
10.
S. Lopez J. H. Topalian S. K. Mitra D. C. Montague 《Journal of Atmospheric Chemistry》1989,8(2):175-188
An experimental study of the scavenging of dichloromethane vapor by water drops falling at terminal velocity, has been carried out in the UCLA precipitation shaft, in order to test the predictions of theoretical washout models. Whereas good agreement between theory and experiment was found for drops of radius 0.332 mm, computed gas uptake rates for 1.253 and 2.21 mm radius drops were much slower than those measured, just as reported previously for the washout of both sulfur dioxide and acetaldehyde. An analysis shows that theory can be reconciled with all of the experimental data by replacing the compound specific aqueous phase Fickian molecular diffusion coefficient used in the theory, by an effective diffusivity, having a constant value, (3×10-4 cm2 s-1), independent of the physical and chemical nature of the absorbed species, for all drops of equivalent radii greater than 0.9 mm. 相似文献