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1.
A steady state model of the Somali current including forcing by both the curl and the divergence of the wind stress is discussed. The model equations are linear, but the results presented are for the one nonlinear case. The grid resolution was 12 km in the zonal and 24 km in the meridional direction. The streamfunction and velocity potential of the current are presented for forcing by divergence and compared with a situation when only the curl is present. The results indicate that a two-gyre system appears in July, a representative month for the summer monsoon, only when divergence is included. Computations with available data indicate that the divergence is comparable in magnitude to the curl near the location of the Somali current. The model produces three other important features: (i) strong upwelling off the east coast of Africa, (ii) downwelling over central Arabian sea and (iii) a strong eastward current in the upper layer towards the interior of the Arabian sea near 12°N.  相似文献   

2.
In this article, the authors examine Sea surface temperature (SST), Sea surface circulation (SSC) and Vertical velocity (VV) fields from simulation of 25 layers coarse resolution Modular ocean model (MOM version 3.0) with prescribed wind forcing for the region 74.25°S to 65°N, 180°W-180°E. It is found that distribution of SST simulated by the model shows its consistency with the observed climatology. However, simulated SST in the areas of Arabian Sea, Bay of Bengal, Indonesian Throughflow (ITF) region and east of North America near equator exhibit slight warming with respect to observation, which may be due to model deficiency and forcing problems. Circulation features suggest that one of the strongest current viz. Antarctic circumpolar current (ACC) along with other major current systems viz. Gulf stream current, North and South Pacific current, Agulhas current, Labrador current, Canary current, etc are captured well by the model. In the Indian Ocean and other ocean basins, current patterns are well captured by the model simulation. Intense upwelling as well as downwelling areas is marked in the horizontal distribution of VV, which is as expected. VV show quasi-stagnant and convergent regions suggesting that floating materials may be accumulated during January/July in the real ocean and wind driven circulation may act as an important contribution for such transport of floating materials in these regions. An attempt has also been made to understand the fluctuations of the SST in NINO 3.4 region during the period of model simulation using SST anomalies.  相似文献   

3.
Several wind fields developed for Hurricane Katrina (2005) in the US Gulf of Mexico (GOM) are applied with the ADCIRC hydrodynamic model to explore the sensitivity of predictions of coastal surges to wind fields developed by alternative methods. The alternative model predictions are evaluated against water level measurements provided by gages at two coastal locations. It is found that all the post-event analyzed wind fields yield a range of predictions of only ±10% of the available peak surge measurements regardless of whether the wind fields are produced by dynamical boundary layer models, kinematic analysis methods or a blend. However, the richness of meteorological forcing data in the GOM is not typically matched in other basins affected by tropical cyclones and errors may be much larger where storm intensity and size parameters are estimated mainly from satellite data. The attributes and remaining critical deficiencies of current methods for surface wind specification in both data-rich and data-poor environments are reviewed.  相似文献   

4.
The Azores Current originating as a branch of the Gulf Stream is a highly dynamic system in the subtropical North Atlantic. The associated front forms the northeastern boundary of the North Atlantic Subtropical Gyre. In this study we analyzed 42 years of assimilated modeled temperature fields to localize the position of the Azores Front at 22°W and observed a fast north- and southward propagation between 30°N and 37°N on monthly to decadal time scales. The North Atlantic Oscillation with correlated changes of the wind direction was identified as one driving mechanism. As the front is acting as a guide for Rossby waves, the signal of the front??s propagation is transferred to the western Atlantic and, among other atmospheric forcing mechanisms, induces a shifting of the Northern Wall of the Gulf Stream with one year delay. Shallower mixed layer depths in the northern frontal region of the Azores Current caused by the rise of the isotherms lead to nutrient supply and primary production different from those found in the southern frontal region of the current system. A high interannual variability is manifested in deep ocean particle flux, derived from a sediment trap in 2000 m water depth at the mooring site KIEL276 (33°N, 22°W) from 1993 to 2008, which is directly related to the phytoplankton bloom in the euphotic zone. This variability is explained by the propagation of the front and strong variations in the catchment areas of the sediment trap due to the associated eddy activity in the frontal region.  相似文献   

5.
Thermal dynamics of lakes has a key role in chemical and biological processes in lakes including nutrient distributions and phytoplankton growth. Applications of hydrodynamic models to lakes can provide insights into possible future alterations in thermal dynamics induced by climate change. In this study, we present the calibration and validation of the newest version of the open-source hydrodynamic model GLM (General Lake Model) to the dimictic Lake Ammersee, located in south-east Germany. The simulation of lake water temperatures for the calibration period revealed an overall root mean square error of 0.65 °C and a mean error of 0.08 °C. The seasonal stratification pattern and the annual thermal structure of this dimictic lake were reproduced by the model. The model simulated the presence of winter ice cover for the only year out of 8 years simulated, when ice cover was observed. Elevated lake water temperatures were also reproduced in model simulations during a period in 2003 of unusually high air temperatures. Statistical analysis of the model calibration results for Lake Ammersee indicates a fit comparable to or better than most other well-established hydrodynamic models and provides an opportunity for continuous simulations through periods of ice cover. Our results indicate a major improvement in GLM compared with earlier model versions and demonstrate the applicability of GLM for limnophysical studies, particularly for altered forcing conditions such as climate change.  相似文献   

6.
Speed and direction of bottom currents induced by density underflow of two sediment-laden rivers were measured by oceanographic current meters in the Walensee (= Lake of Walenstadt), Switzerland. The apparently shooting flow of currents (up to 30 cm/s in this study) is suggested as an explanation for laminations in turbidite sequences. The current speed apparently stabilizes on slopes around 2°; this angle seems to correspond to the critical slope where the flow of the measured currents becomes steady. Current direction is controlled by bottom topography and direction of river inflow. Reversal of current direction observed at two sites is probably due to the underflow-induced backward motion of the overlying lake water. Underflow activity in Walensee is correlative with density peaks of the river water input. The currents are compared to Lake Mead (Southwestern U.S.) underflows and sporadic currents in some submarine canyons.  相似文献   

7.
The local weather and air quality over a region are greatly influenced by the atmospheric boundary layer (ABL) structure and dynamics. ABL characteristics were measured using a tethered balloon-sonde system over Kharagpur (22.32°N, 87.32°E, 40m above MSL), India, for the period 7 December 2004 to 30 December 2004, as a part of the Indian Space Research Organization-Geosphere Biosphere Program (ISRO-GBP) Aerosol Land Campaign II. High-resolution data of pressure, temperature, humidity, wind speed and wind direction were archived along with surface layer measurements using an automatic weather station. This paper presents the features of ABL, like ABL depth and nocturnal boundary layer (NBL) depth. The sea surface winds from Quikscat over the oceanic regions near the experiment site were analyzed along with the NCEP/NCAR reanalysis winds over Kharagpur to estimate the convergence of wind, moisture and vorticity to understand the observed variations in wind speed and relative humidity, and also the increased aerosol concentrations. The variation of ventilation coefficient (V C), a factor determining the air pollution potential over a region, is also discussed in detail.  相似文献   

8.
《Applied Geochemistry》1988,3(2):153-163
A simulated nuclear waste glass, developed by the Power Reactor and Nuclear Fuel Development Corporation of Japan, was leached at 50, 75, 95, 110, 160, 210 and 240°C under saturated vapor pressure in groundwater from a granitic terrain. Depth profiles of insoluble components in reacted glass surface were measured by EPMA, together with time-excursion of the solution composition. Except at 160 and 210°C, B, Na, Mo (as MoO42−), Li, K, Si and Cs were leached out readily, with increasing rate of leaching in this order, at all other temperatures. At the intermediate temperatures of 160 and 210°C, however, the leaching rates of the soluble components were significantly lowered. Surface layers formed on the reacted glass surface thickened and changed in composition and structure with increasing temperature of reaction. During 312 h leaching at 110°C, a leached layer, about 5 μm thick, formed which is depleted in the soluble components and enriched in immobile metals such as Ni, Mn and Fe, and in precipitated components such as Ca and Mg. At 160 and 210°C, the secondary layer is composed of two sharply defined sublayers: an inner leached layer and an outer KSiAlrich layer, probably formed on the leached layer by precipitation from solution. The 50-μm thick layer formed during 508 h of leaching at 240°C is composed of three broadly defined sublayers, an inner leached layer, an outer precipitation layer and a middle layer of intermediate composition between the former two. The significant suppression in leaching rate at 160 and 210°C is interpreted as a result of rapid formation of the precipitation layer on the glass surface which slowed the diffusive migration of solution species responsible for glass dissolution through the surface layer. At 240°C, the leaching rate of soluble species except for silica increased significantly after an initial stage of slow leaching. At this temperature, coarse crystalline analcime precipitated from solution probably in expense of the surface precipitate, thus preventing the formation of surface precipitation layer as impermeable to solution species migration as that formed at 160 and 210°C.  相似文献   

9.
The objective of this study was to investigate the effects of diurnal temperature fluctuation amplitude (DTFA) on the geothermal regime of the embankment on the Qinghai–Tibet plateau. The investigation was simulated by respectively denoting the diurnal temperatures at the embankment surface, embankment slope, and natural ground surface with sinusoidal waves. The amplitudes of the waves were denoted by 0°C, 5°C, 8°C, and 12°C, respectively. The numerical result shows that the DTFA cannot vary the frequency of the seasonal temperature fluctuation of the underlying soil, but can significantly change the magnitude of the soil’s temperature. The changes include: (1) The high DTFA, such as 12°C, can significantly lead to the warming of the soil under the embankment. (2) Interestingly, when the DTFA at ground surface is 5°C, the underlying soil is in a cooler stage compared to when such DTFA is 0°C, 8°C, or12°C. This interesting result means that the documented model which ignores the diurnal temperature rhythm overestimates the warming of the underlying soil at the low DTFA region and underestimates such warming at the high DTFA region. This result also suggests that the soil under the embankment can be cooled down if the DTFA on the ground surface was maintained at or approximately at 5°C.  相似文献   

10.
Satellite-derived sea-ice extent in the Indian Ocean Sector during the period November 1978 to December 2006 was studied in relation to the atmospheric forcing and oceanic thermohaline structure. The study revealed that sea-ice extent increased when the ocean exhibited higher stability. Low sea-ice extent was observed during 1985 to 1993, when the zonal winds and latent flux was relatively weak and when the ocean exhibited strong vertical mixing facilitated by low stability thereby, deepening the mixed layer to ∼250 m. This was reflected in the ocean surface layer temperature, which was relatively warm (−0.3°C). Winds increased during 1996 to 2000, but due to higher oceanic stability mixed layer depth shallowed (< 200 m) leading to reduced vertical mixing of deep warmer layers with the surface water, leading to an enhancement in the sea-ice extent.  相似文献   

11.
Hurricane Gilbert has been labelled the storm of the century because of the many meteorological records it set. These include size, straightness of track, atmospheric pressure, precipitation, and total energy. After ravaging Jamaica as a Force 3 storm, Gilbert made landfall in Yucatan as a Force 5, one of only three hurricanes of such magnitude to do so in North America this century. In spite of a death toll of 318 and property damage in the billions of dollars, Gilbert's impacts were eclipsed by the extensive publicity that accompanied Hurricane Hugo's landfall in South Carolina the following year (1989).  相似文献   

12.
 We have conducted H2O-undersaturated melting experiments on charges consisting of a layer of a sillimanite-bearing metapelite and a layer of garnet-bearing amphibolite, with the goal of studying how layered metamorphic rocks interact during anatexis. Experiments with the layered charges were performed at 10 kbar (1 GPa) at 900 °C (334 h), 925 °C (341 h), and 950 °C (50, 161, 332 h). Dehydration-melting of the amphibolite alone and of the pelite alone were studied at the same P-T conditions. When run alone at 900 °C, the pelite and the amphibolite yielded ca. 40 vol.% and 15 vol.% melt, respectively. Corresponding melt fractions at 950 °C were ca. 50 vol.% and 30 vol.%. When run side by side, melt abundance in the pelite is fairly uniform and ca. 20 vol.% higher than in the solo runs at all temperatures studied. In contrast, complex zoning patterns parallel to the interface develop in the amphibolite layer. Far from the interface the melt fraction is 5–10 vol.% lower than in the amphibolite-solo runs. Closer to the interface the melt fraction in the amphibolite layers are comparable to, or somewhat higher than, in the amphibolite-solo runs, and both clinopyroxene and plagioclase react-out and are replaced by orthopyroxene and quartz. Melt fraction closest to the interface reaches 65–70 vol.%, and the only crystalline phase present is garnet with hollow cores. The increase in melt fraction in the pelite layers of the layered runs is caused by transfer of Na from the amphibolite to the pelite, which forces biotite to be eliminated at lower temperature along the biotite-garnet reaction boundary. K is transferred from the pelite to the amphibolite, and the lower melt fraction in the distal end of the amphibolite layers is caused by faster diffusion of Na compared to K, which results in a net depletion of alkalies. Ca is transferred from the amphibolite to the pelite, and the resulting changes in CaO concentrations affect the stabilities of plagioclase, pyroxenes, garnet and quartz and cause the observed zoning in the amphibolite layer. Ca entering the pelite layer induces crystallization of large plagioclase neoblasts radiating from the interface into the pelite layer. These results show that diffusion of components between contiguous lithologies undergoing anatexis can cause profound changes in phase relations, melt fractions and restite compositions. Received: 21 December 1994 / Accepted: 26 June 1995  相似文献   

13.
An accurate tropical cyclone track and intensity forecast is very important for disaster management. Specialized numerical prediction models have been recently used to provide high-resolution temporal and special forecasts. Hurricane Weather Research and Forecast (HWRF) model is one of the emerging numerical models for tropical cyclone forecasting. This study evaluates the performance of HWRF model during the post monsoon tropical cyclone Nilofar on the north Indian Ocean basin. The evaluation uses the best track data provided by the Indian Meteorological Department (IMD) and the Joint Typhoon Warning Centre (JTWC). Cyclone track, central pressure, and wind speed are covered on this evaluation. Generally, HWRF was able to predict the Nilofar track with track error less than 230 km within the first 66 h of forecast time span. HWRF predicted more intense tropical cyclone. It predicted the lowest central pressure to be 922 hPa while it reached 950 hPa according to IMD and 937 hPa according to JTWC. Wind forecast was better as it predicted maximum wind speed of 122 kt while it reached 110 and 115 kt according to IMD and JTWC, respectively.  相似文献   

14.
Changes in solar constant over an 11 yr cycle suggest a certain, but limited, degree of solar forcing of climate. The high-resolution climate (oxygen isotope) record of the Greenland GISP2 (Greenland Ice Sheet Project 2) ice core has been analyzed for solar (and volcanic) influences. The atmospheric14C record is used as a proxy of solar change and compared to the oxygen isotope profile in the GISP2 ice core. An annual oxygen isotope profile is derived from centimeter-scale isotope measurements available for the post-A.D. 818 interval. Associated extreme summer and winter isotope ratios were found to yield similar climate information over the last millennium. The detailed record of volcanic aerosols, converted to optical depth and volcanic explosivity change, was also compared to the isotope record and the oxygen isotope response calibrated to short-term volcanic influences on climate. This calibration shows that century-scale volcanic modulation of the GISP2 oxygen isotope record can be neglected in our analysis of solar forcing. The timing, estimated order of temperature change, and phase lag of several maxima in14C and minima in18O are suggestive of a solar component to the forcing of Greenland climate over the current millennium. The fractional climate response of the cold interval associated with the Maunder sunspot minimum (and14C maximum), as well as the Medieval Warm Period and Little Ice Age temperature trend of the past millennium, are compatible with solar climate forcing, with an order of magnitude of solar constant change of 0.3%. Even though solar forcing of climate for the current millennium is a reasonable hypothesis, for the rest of the Holocene the century-scale events are more frequent in the oxygen isotope record than in the14C record and a significant correlation is absent. For this interval, oceanic/atmospheric circulation forcing of climate may dominate. Solar forcing during the surprisingly strong 1470 yr climate cycle of the 11,000–75,000 yr B.P. interval is rather hypothetical.  相似文献   

15.
Hurricane Gilbert made its landfall on the Yucatan peninsula on September 14, 1988, destroying valuable resort property in Cancun, Isla Mujeres, and Cozumel. Salt flats (salinas) in northern Quintana Roo and Yucatan were flooded by the storm surge and coastal marine ecosystem were devastated. Inland, the hurricane caused damages to houses, power lines, and farming land, but increased opportunities for garden hunting on destroyed fields. Twenty percent of tropical rain forest suffered losses of canopy and in the deciduous forests of north-central Yucatan noxiuous insects populations increased. Although damaging in its ultimate effects, hurricane Gilbert tested the resilience of Maya Indians and their readiness for post-disaster accommodation.  相似文献   

16.
Modelling palaeoglaciers in mountainous terrain is challenging due to the need for detailed ice flow computations in relatively narrow and steep valleys, high-resolution climate estimations, knowledge of pre-ice topography, and proxy-based palaeoclimate forcing. The Parallel Ice Sheet Model (PISM), a numerical model that approximates glacier sliding and deformation to simulate large ice sheets such as Greenland and Antarctica, was recently adapted to alpine environments. In an attempt to reconstruct the climate conditions during the Last Glacial Maximum (LGM) on Mount Dedegöl in SW Turkey, we used PISM and explored palaeoglacier dynamics at high spatial resolution (100 m) in a relatively small domain (225 km2). Palaeoice-flow fields were modelled as a function of present temperature and precipitation. Nine different palaeoclimate simulations were run to reach the steady-state glacier extents and the modelled glacial areas were compared with the field-based and chronologically well-established ice extents. Although our results provide a non-unique solution, best-fit scenarios indicate that the LGM climate on Mount Dedegöl was between 9.2 and 10.6 °C colder than today, while precipitation levels were the same as today. More humid (20% wetter) or arid (20% drier) conditions than today bring the palaeotemperature estimates to 7.7–8.8 or 11.5–13.2 °C lower than present, respectively.  相似文献   

17.
In this study, the climate changes over Arid Central Asia(ACA) during the mid-Holocene(approximately 6,000 calendar years ago, MH) and the Last Glacial Maximum(approximately 21,000 calendar years ago, LGM) were investigated using multimodel simulations derived from the Paleoclimate Modelling Intercomparison Project Phase 3(PMIP3). During the MH, the multimodel median(MMM) shows that in the core region of ACA, the regionally averaged annual surface air temperature(SAT) decreases by 0.13°C and annual precipitation decreases by 3.45%, compared with the preindustrial(PI) climate. The MMM of the SAT increases by 1.67/0.13°C in summer/autumn, whereas it decreases by 1.23/1.11°C in spring/winter. The amplitude of the seasonal cycles of the SAT increases over ACA due to different MH orbital parameters. For precipitation, the regionally averaged MMM decreases by 5.77%/5.69%/0.39%/5.24% in spring/summer/autumn/winter, respectively. Based on the analysis of the aridity index(AI), compared with the PI, a drier climate appears in southern Central Asia and western Xinjiang due to decreasing precipitation. During the LGM, the MMM shows that the regionally averaged SAT decreases by 5.04/4.36/4.70/5.12/5.88°C and precipitation decreases by 27.78%/28.16%/31.56%/27.74%/23.29% annually and in the spring, summer, autumn, and winter, respectively. Robust drying occurs throughout almost the whole core area. Decreasing precipitation plays a dominant role in shaping the drier conditions, whereas strong cooling plays a secondary but opposite role. In response to the LGM external forcings, over Central Asia and Xinjiang, the seasonal cycle of precipitation has a smaller amplitude compared with that under the PI climate. In the model-data comparison, the simulated MH moisture changes over ACA are to some extent consistent with the reconstructions, further confirming that drier conditions occurred during that period than during the PI.  相似文献   

18.
Melt-rock reaction in the upper mantle is recorded in a variety of ultramafic rocks and is an important process in modifying melt composition on its way from the source region towards the surface. This experimental study evaluates the compositional variability of tholeiitic basalts upon reaction with depleted peridotite at uppermost-mantle conditions. Infiltration-reaction processes are simulated by employing a three-layered set-up: primitive basaltic powder (‘melt layer’) is overlain by a ‘peridotite layer’ and a layer of vitreous carbon spheres (‘melt trap’). Melt from the melt layer is forced to move through the peridotite layer into the melt trap. Experiments were conducted at 0.65 and 0.8 GPa in the temperature range 1,170–1,290°C. In this P-T range, representing conditions encountered in the transition zone (thermal boundary layer) between the asthenosphere and the lithosphere underneath oceanic spreading centres, the melt is subjected to fractionation, and the peridotite is partially melting (T s ~ 1,260°C). The effect of reaction between melt and peridotite on the melt composition was investigated across each experimental charge. Quenched melts in the peridotite layers display larger compositional variations than melt layer glasses. A difference between glasses in the melt and peridotite layer becomes more important at decreasing temperature through a combination of enrichment in incompatible elements in the melt layer and less efficient diffusive equilibration in the melt phase. At 1,290°C, preferential dissolution of pyroxenes enriches the melt in silica and dilutes it in incompatible elements. Moreover, liquids become increasingly enriched in Cr2O3 at higher temperatures due to the dissolution of spinel. Silica contents of liquids decrease at 1,260°C, whereas incompatible elements start to concentrate in the melt due to increasing levels of crystallization. At the lowest temperatures investigated, increasing alkali contents cause silica to increase as a consequence of reactive fractionation. Pervasive percolation of tholeiitic basalt through an upper-mantle thermal boundary layer can thus impose a high-Si ‘low-pressure’ signature on MORB. This could explain opx + plag enrichment in shallow plagioclase peridotites and prolonged formation of olivine gabbros.  相似文献   

19.
Hydrothermal processes and the regimes of frozen soil formed in alpine regions with glaciers and lake area are complex and important for ecological environment but have not been studied in Tibet. Based on soil temperature and moisture data from October 2005 to September 2006 collected in the Nam Co lake basin, Tibetan Plateau (TP), those questions were discussed. The mean annual air temperature was −3.4°C with 8 months below 0°C. Air and soil temperature varied between −25.3~13.1°C and −10.3~8.8°C, respectively. Soil moisture variations in the active layer were small with the minimum value of 1.4%, but were influenced greatly by snowmelt, rainfall and evaporation, varying up to 53.8%. The active layer froze later, thawed earlier and was thinner, however, the lower altitude limit of permafrost is higher than that in most areas of TP. The effects of soil moisture (unfrozen water content) on soil temperature, which were estimated through proposed models, were more significant near ground surface than the other layers. The surface soil temperature decreased with snowcover, the effect of cold snow meltwater infiltration on soil thermal conditions was negligible, however, the effect of rainfall infiltration was evident causing thermal disruptions.  相似文献   

20.
松辽盆地中部深部断层影响浅部次级断层发育的数值研究   总被引：2，自引：2，他引：0  
利用Poly3D模拟了松辽盆地长垣隆起中部后裂谷期应力场,由此预测浅部次级断层的产状和密度。计算结果表明,深部断层的存在会扰乱浅部应力场,距离深部断层越近,扰动程度越明显,从而导致了浅层次级断层的走向变化和不均匀的密度分布;浅部次级断层的走向和分布与深部断层的形态和空间位置相关,它们在断层的端部、转折段及其附近变化较大。同样地,在施加远场的不同方向水平拉伸、相同应变量下,可计算出相应的浅部次级断层走向和密度的计算值。在不同反射层模拟得到的最佳伸展方向与区域分析基本相同,但此时预测断层走向和密度与实际情况仍有较大差别。考虑到模型中深部断层面的拖曳力分量均设置为零,即不存在独立的断层活动,这一差别暗示出浅部次级断层的发育不仅受远场构造作用影响,而且还受深部断层独立活动的制约。  相似文献   

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