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51.
52.
This paper deals with the morphotectonic evaluation of the Delhi region in northern India to understand its impact on land use and urban development. To accommodate heavy urbanization and population rise (being the capital of India), the area has undergone tremendous environmental degradation resulting from a mismatch between adopted land use and morphotectonic considerations. The geomorphic and drainage signatures of the region have evolved out of interaction of varied geological parameters including neotectonic activities. We have evaluated the changes in the drainage pattern of the Yamuna River in the Delhi region to underline its significance in geomorphic evolution and subsequent land use and/or land suitability. The Yamuna River has shown variations both in channel position and geometry over the last two centuries. The observed migration pattern of the river (shifting of confluences, position and disposition of palaeochannels, etc.,) cannot be attributed to normal river phenomenon and appears to have been effected by neotectonic changes. In addition, some case studies are discussed to underline the significance of geomorphic factors in urban development. 相似文献
53.
General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations
without a large extent of ver- tical flow. Vertical flow, however, plays an important role in the formation of local breezes,
such as urban heat island induced breezes that have great significance in the ventilation of large cities. The effects of
atmospheric stratification, anelasticity and Coriolis force must be taken into account in such simulations. We introduce a
general method for adapting pressure based CFD solvers to atmospheric flow simulations in order to take advantage of their
high flexibility in geometrical modelling and meshing. Compressibility and thermal stratification effects are taken into account
by utilizing a novel system of transformations of the field variables and by adding consequential source terms to the model
equations of incompressible flow. Phenomena involving mesoscale to microscale coupled effects can be analyzed without model
nesting, applying only local grid refinement of an arbitrary level. Elements of the method are validated against an analytical
solution, results of a reference calculation, and a laboratory scale urban heat island circulation experiment. The new approach
can be applied with benefits to several areas of application. Inclusion of the moisture transport phenomena and the surface
energy balance are important further steps towards the practical application of the method. 相似文献
54.
Erika?Kaufmann Günter?Kargl Norbert?I.?K?mleEmail author Manfred?Steller Johann?Hasiba Florian?Tatschl Stefan?Ulamec Jens?Biele Marc?Engelhardt Jens?Romstedt 《Earth, Moon, and Planets》2009,105(1):11-29
One possibility to explore the subsurface layers of icy bodies is to use a probe with a “hot tip", which is able to penetrate
ice layers by melting. Such probes have been built and used in the past for the exploration of terrestrial polar ice sheets
and may also become useful tools to explore other icy layers in the Solar System. Examples for such layers are the polar areas
of Mars or the icy crust of Jupiter’s moon Europa. However, while on Earth a heated probe launched into an ice sheet always
causes melting with subsequent refreezing, the behaviour of such a probe in a low pressure environment is quite different.
We report on the results of some experiments with a simple “melting probe" prototype with two different kinds of hot tips
in a vacuum environment. For one of the tips the probe moved into two types of ice samples: (i) compact water ice and (ii)
porous water ice with a snow (firn) like texture. It was also found that the penetration behaviour was basically different
for the two sample types even when the same kind of tip was used. While in the porous sample the ice was only subliming, the
phase changes occurring during the interaction of the tip with the compact ice are much more complex. Here alternating phases
of melting and sublimation occur. The absence of the liquid phase has severe consequences on the performance of a “melting
probe" under vacuum conditions: In this environment we find a high thermal resistance between the probe surface and the underlying
ice. Therefore, only a low percentage of the heat that is generated in the tip is used to melt or sublime the ice, the bulk
of the power is transferred towards the rear end of the probe. This is particularly a problem in the initial phases of an
ice penetration experiment, when the probe has not yet penetrated the ice over its whole length. In the compact ice sample,
phases could be observed, where a high enough gas pressure had built up locally underneath the probe, so that melting becomes
possible. Only during these melting periods the thermal contact between the probe and the ice is good and in consequence the
melting probe works effectively. 相似文献
55.
The evolution of east coast of India sis discussed within the ambit of clearly identifiable four major tectonic stages which
had a profound effect in shaping the tectonic grain of the east coast basins. The evolutionary process began with rift related
crustal extension between India and Sri Lanka as a consequence of Africa-Antarctica rifting and development of Natal Basin.
An arm of this rift led to initial extension in the Cauvery Basin and failed. Later, the India-West Australia rift propagated
further in southwesterly direction initiating Mahanadi and Krishna-Godavari Basins. This extension was an oblique one with
Nayudupeta high acting as pivot. The oblique extension followed by asymmetric seafloor spreading developed transpression along
India-Sri Lanka and Antarctica junction, resulting in a NNW-SSE trending transcurrent fault along which Antarctica moved southward.
Subsequently, entire east coast evolved through a more or less uniform post rift stage. 相似文献
56.
Krzysztof Pleskot Rik Tjallingii Mirosław Makohonienko Norbert Nowaczyk Witold Szczuciński 《Journal of Paleolimnology》2018,59(4):443-459
Western Poland is located in the central European climatic transition zone, which separates the mild and humid Atlantic climate of Western Europe and the East European continental climate. This region is sensitive to lateral shifts of the European climate zones and is particularly suitable for reconstructing Holocene climate variability. This paper presents detailed analyses of the sedimentary record from Lake Strzeszyńskie since the Late Pleistocene. These include smear-slide and thin-section observations, X-ray fluorescence core scanning, magnetic susceptibility measurements, pollen analyses, and radiocarbon dating. The sediment record reveals three distinct sedimentary units consisting of: (1) an alternation of sand layers and laminated silt and clay deposits accumulated prior to 14,600 cal yr BP; (2) faintly laminated calcareous sediments intercalated with organic matter-rich layers deposited between 14,600 and 10,200 cal yr BP; and (3) massive calcareous mud deposited after 10,200 cal yr BP. The Holocene period is marked by nine phases of organic-rich sedimentation and enhanced Fe deposition, which occurred at ca. 10.1, 9.3, 6.4–6.1, 5.5–5.1, 4.7–4.5, 2.7–2.4, 1.3–1.2, 0.8–0.6, 0.4–0.2 kyr cal BP. These phases are associated with high lake levels and correspond with wet periods recognized in several other records from Poland and central Europe. These phases partly coincide with North Atlantic cold periods, which may suggest that high lake levels are triggered by an ocean-continent linking mechanism. 相似文献
57.
Leonhard Gantner Vera Maurer Norbert Kalthoff Olga Kiseleva 《Boundary-Layer Meteorology》2017,162(3):475-502
A method to simulate characteristics of wind speed in the boundary layer of tropical cyclones in an idealized manner is developed and evaluated. The method can be used in a single-column modelling set-up with a planetary boundary-layer parametrization, or within large-eddy simulations (LES). The key step is to include terms in the horizontal velocity equations representing advection and centrifugal acceleration in tropical cyclones that occurs on scales larger than the domain size. Compared to other recently developed methods, which require two input parameters (a reference wind speed, and radius from the centre of a tropical cyclone) this new method also requires a third input parameter: the radial gradient of reference wind speed. With the new method, simulated wind profiles are similar to composite profiles from dropsonde observations; in contrast, a classic Ekman-type method tends to overpredict inflow-layer depth and magnitude, and two recently developed methods for tropical cyclone environments tend to overpredict near-surface wind speed. When used in LES, the new technique produces vertical profiles of total turbulent stress and estimated eddy viscosity that are similar to values determined from low-level aircraft flights in tropical cyclones. Temporal spectra from LES produce an inertial subrange for frequencies \(\gtrsim \)0.1 Hz, but only when the horizontal grid spacing \(\lesssim \)20 m. 相似文献
58.
Lalmani Babu Madhu Kaul Kumar Rajou Singh Rajesh Singh Krishna Kumar 《Earth, Moon, and Planets》1999,84(3):151-162
The propagationmechanism of low latitude daytime whistlers is investigated on the basis of ground measurements made continuously
during daytime in North India at Jammu (geomag. lat. 22°26°N;L = 1.17). On February 14, 1998 extremely small dispersion (ESD)
whistlers with dispersion varying from 5–10 sec1/2 in surprisingly large numbers were recorded at Jammu during daytime in the late afternoon. The results of a study of the
characteristics of ESD whistlers are presented and the discussion indicates that ESD whistlers recorded are the VLF waves
radiated from the return stroke of the lightning discharge launched at the ionosphere with different initial wave normal angles,
propagated upwards under eitherquasi-longitudinal conditions or pro-longitudinal whistler mode, turned around at different
heights due to quasi-transverse propagation and received at Jammu with the dispersion of the order of 5–10 sec1/2. The validity of this suggestion has been tested by performing actualray-tracing computations in thepresence of equatorial
anomaly model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
59.
Sushma Prasad Norbert Marwan Deniz Eroglu Bedartha Goswami Praveen K. Mishra Birgit Gaye A. Anoop N. Basavaiah Martina Stebich Arshid Jehangir 《地球表面变化过程与地形》2020,45(15):3842-3853
Extreme climate events have been identified both in meteorological and long-term proxy records from the Indian summer monsoon (ISM) realm. However, the potential of palaeoclimate data for understanding mechanisms triggering climate extremes over long time scales has not been fully exploited. A distinction between proxies indicating climate change, environment, and ecosystem shift is crucial for enabling a comparison with forcing mechanisms (e.g. El-Niño Southern Oscillation). In this study we decouple these factors using data analysis techniques [multiplex recurrence network (MRN) and principal component analyses (PCA)] on multiproxy data from two lakes located in different climate regions – Lonar Lake (ISM dominated) and the high-altitude Tso Moriri Lake (ISM and westerlies influenced). Our results indicate that (i) MRN analysis, an indicator of changing environmental conditions, is associated with droughts in regions with a single climate driver but provides ambiguous results in regions with multiple climate/environmental drivers; (ii) the lacustrine ecosystem was ‘less sensitive’ to forcings during the early Holocene wetter periods; (iii) archives in climate zones with a single climate driver were most sensitive to regime shifts; (iv) data analyses are successful in identifying the timing of onset of climate change, and distinguishing between extrinsic and intrinsic (lacustrine) regime shifts by comparison with forcing mechanisms. Our results enable development of conceptual models to explain links between forcings and regional climate change that can be tested in climate models to provide an improved understanding of the ISM dynamics and their impact on ecosystems. © 2020 John Wiley & Sons, Ltd. 相似文献
60.
Studia Geophysica et Geodaetica - The gravity database for the IAG African Geoid Project contains significantly large data gaps. These large data gaps affect the interpolation precision of the... 相似文献