Surface-layer features with different prevailing wind directions for two distinct seasons (Southwest Monsoon and Northeast Monsoon) on the west coast of India are studied using data obtained from tower-based sensors at a site located about 500 m from the coast. Only daytime runs have been used for the present analysis. The surface boundary-layer fluxes have been estimated using the eddy correlation method. The surface roughnessz0 obtained using the stability-corrected wind profiles (Paulson, 1970) has been found to be low for the Southwest monsson season. For the other season,z0 is relatively high. The drag coefficientCD varies with height in the NE monsoon season but not in the season with lowz0. This aspect is reflected in the wind profiles for the two seasons and is discussed in detail. The scaling behaviour of friction velocityu* and the turbulence intensity of longitudinal, lateral and vertical winds u, v and w, respectively) are further examined to study their dependence on fetch. Our study shows that for the non-dimensional case, u/u* and v/u* do not show any surface roughness dependence in either season. On the other hand, for w/u* for the season with lowz0, the values are seen to agree well with that of Panofskyet al. (1977) for homogeneous terrain whereas for the other season with highz0, the results seem to conform more to the values observed by Smedman and Högström (1983) for coastal terrain. The results are discussed in the light of observations by other investigators. 相似文献
Summary This paper presents an examination of the statistical relationship between summer monsoon rainfall over all India, and two sub-regions (north west India and peninsular India) and the indices of mid-latitude (35° to 70° N) zonal circulation at 500 hPa level, over different sectors of the hemisphere, based on 19 years (1971–1989) data. The results indicate that summer monsoon rainfall (June–September) over India shows; (i) a significant and direct relationship with the strength of the zonal circulation index during concurrent July over the sector 90° E to 160° E. (ii) a significant inverse relationship with the strength of the zonal index during the previous April over the sector 160° E to 45° W and a similar relationship with the whole northern hemisphere and (iii) a significant and direct relationship with the frequency of the zonal index during the previous January over the sector 45° W to 90° E.Significant relationships are also observed between the zonal circulation indices of the above mentioned months and sectors with the 500 hPa ridge location in April at 75° E over India.With 4 Figures 相似文献
This paper presents a participatory approach to investigate vulnerability and adaptive capacity to climate variability and water stress in the Lakhwar watershed in Uttarakhand State, India. Highly water stressed microwatersheds were identified by modelling surface runoff, soil moisture development, lateral runoff, and groundwater recharge. The modelling results were shared with communities in two villages, and timeline exercises were carried out to allow them to trace past developments that have impacted their lives and livelihoods, and stimulate discussion about future changes and possible adaptation interventions. 相似文献
Southwest Pacific nations are among some of the worst impacted and most vulnerable globally in terms of tropical cyclone (TC)-induced flooding and accompanying risks. This study objectively quantifies the fractional contribution of TCs to extreme rainfall (hereafter, TC contributions) in the context of climate variability and change. We show that TC contributions to extreme rainfall are substantially enhanced during active phases of the Madden–Julian Oscillation and by El Niño conditions (particularly over the eastern southwest Pacific region); this enhancement is primarily attributed to increased TC activity during these event periods. There are also indications of increasing intensities of TC-induced extreme rainfall events over the past few decades. A key part of this work involves development of sophisticated Bayesian regression models for individual island nations in order to better understand the synergistic relationships between TC-induced extreme rainfall and combinations of various climatic drivers that modulate the relationship. Such models are found to be very useful for not only assessing probabilities of TC- and non-TC induced extreme rainfall events but also evaluating probabilities of extreme rainfall for cases with different underlying climatic conditions. For example, TC-induced extreme rainfall probability over Samoa can vary from ~ 95 to ~ 75% during a La Niña period, if it coincides with an active or inactive phase of the MJO, and can be reduced to ~ 30% during a combination of El Niño period and inactive phase of the MJO. Several other such cases have been assessed for different island nations, providing information that have potentially important implications for planning and preparing for TC risks in vulnerable Pacific Island nations.
The contribution of atmospheric pressure and local wind to sea level variability at Goa (West coast of India) for the period
2007–2008 is investigated. Sea level data from a tide gauge are compared with measured local surface meteorological as well
as oceanographic data. Multilinear regression analysis is used to resolve the dependence of sea level on various forcing parameters.
The multilinear regression analysis performed over approx. 2-year data shows that the local surface meteorological data and
water temperature account for the sea level variability only up to 6%. The accounted sea level variability increases to 25%,
when the local wind and the surface currents obtained from satellite altimetry in the near vicinity of the study area are
incorporated in the regression analysis. The contribution of local wind increases substantially when the regression is performed
over a 2-month duration, and it is variable within the year. During the summer monsoon season (May–September), the sea level
variability attributable to wind is up to 47% and 75%, respectively, for 2007 and 2008; however, it reduces to <20% during
the winter monsoon (November–February) season. A significant part of the variability observed in sea level remains unaccounted
for and is attributed to remote forcing. 相似文献
Geophysical flows of practical interest encompass turbulent boundary layer flows. The velocity profile in turbulent flows
is generally described by a log- or a power-law applicable to certain zones of the boundary layer, or by wall-wake law for
the entire zone of the boundary layer. In this study, a novel theory is proposed from which the power-law velocity profile
is obtained for the turbulent boundary layer flow. The new power-law profile is based on the conservation of mass and the
skin friction within the boundary layer. From the proposed theory, analytical expressions for the power-law velocity profile
are presented, and their Reynolds-number dependency is highlighted. The velocity profile, skin friction coefficient and boundary
layer thickness obtained from the proposed theory are validated by the reliable experimental data for zero-pressure gradient
turbulent boundary layers. The expressions for Reynolds shear stress and eddy viscosity distributions across the boundary
layer are also obtained and validated by the experimental data. 相似文献
The predatory potentiality of G. affinis and P. reticulata fishes on cyclops was tested by ‘no-choice’ and ‘choice’ experiments. In ‘no-choice’ experiments predation increased significantly with the number of cyclops exposed (1, 3, 5, 7 and 10 preys) and decreased with the increase in the water volume (1, 2 and 3 litres) in case of both the fishes. A similar trend for cyclops predation was observed in ‘choice’ experiments. The relative rate of predation of G. affinis and P. reticulata was more in ‘no-choice’ as compared to in ‘choice’ experiments. However, the predatory efficacy of G. affinis was relatively higher than that of P. reticulata in all the experiments. The comparative rate of predation on three zooplanktons by G. affinis and P. reticulata showed that Daphnia spec. was most susceptible to predation by both the fishes. It was followed by calanoids and the least preferred prey being cyclops. 相似文献
This paper presents the effects of soil layering on the characteristics of basin-edge induced surface waves and associated
strain and aggravation factor. The simulated results revealed surface wave generation near the basin-edge. The first mode
of induced Love wave was obtained in models having increasing velocity with depth and a large impedance contrast between the
soil layers. Amplitude amplification or de-amplification of body waves was proportional to the impedance contrast between
the soil layers. The average aggravation factor was inversely proportional to the impedance contrast between the soil layers
in case of increasingvelocity models and proportional in case of decreasing-velocity basinedge models. On the other hand,
the maximum strain was inversely proportional to the impedance contrast between the soil layers in both cases. On the average,
strain was greater in case of increasing-velocity models but the average aggravation factor was greater in case of decreasingvelocity
models. 相似文献
When a turbulent shear flow above a plane sand surface entrains sand grains,it generates a variety of sand patterns.Fluvial sand forms two major interfacial patterns:meso-scale dunes and antidunes,and large-scale bars.Measurements have evidenced that under erosive conditions,meso-scale patterns either change to or coexist with large-scale patterns.However,it remains elusive what exactly drives the switching of interfacial patterns and how the switching occurs.Here,we showdcombing a flow model with a grain transport model,allowing for both the surface and suspended sand fluxes dthat the switching of patterns emerges from the shear-driven complex feedback between grain transport and topographic perturbations.The switching predominantly depends on the magnitudes of the Rouse number and the grain size to undisturbed flow depth ratio.The model offers quantitative predictions of the maximum amplification of sand patterns and unveils a new attraction erepulsion phenomenon. 相似文献