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1.
A high-resolution, regional coupled atmosphere–ocean model is used to investigate strong air–sea interactions during a rapidly developing extratropical cyclone (ETC) off the east coast of the USA. In this two-way coupled system, surface momentum and heat fluxes derived from the Weather Research and Forecasting model and sea surface temperature (SST) from the Regional Ocean Modeling System are exchanged via the Model Coupling Toolkit. Comparisons are made between the modeled and observed wind velocity, sea level pressure, 10 m air temperature, and sea surface temperature time series, as well as a comparison between the model and one glider transect. Vertical profiles of modeled air temperature and winds in the marine atmospheric boundary layer and temperature variations in the upper ocean during a 3-day storm period are examined at various cross-shelf transects along the eastern seaboard. It is found that the air–sea interactions near the Gulf Stream are important for generating and sustaining the ETC. In particular, locally enhanced winds over a warm sea (relative to the land temperature) induce large surface heat fluxes which cool the upper ocean by up to 2 °C, mainly during the cold air outbreak period after the storm passage. Detailed heat budget analyses show the ocean-to-atmosphere heat flux dominates the upper ocean heat content variations. Results clearly show that dynamic air–sea interactions affecting momentum and buoyancy flux exchanges in ETCs need to be resolved accurately in a coupled atmosphere–ocean modeling framework.  相似文献   

2.
The HadISST1 sea surface temperature data set is examined for two contrasting areas: the Chagos Archipelago, central Indian Ocean which has a small (approximately 3 degrees C) annual temperature fluctuation, and Abu Dhabi in the southern Arabian Gulf whose annual air temperature fluctuation of approximately 24 degrees C is the largest known for coral reef habitats. The HadISST1 data are shown to match air temperature records closely, both in terms of annual moving averages and residual analysis. Temperatures in 1998 caused massive mortality of corals in the Indian Ocean: sea surface temperature (SST) values causing this were 33.8 degrees C in the Arabian Gulf at a time when average daily air temperature was over 40 degrees C, while in Chagos the SST lethal to corals was 29.8-29.9 degrees C, when air temperatures peaked at about 31 degrees C. The HadISST1 record was searched back to 1870 for previous abnormal peaks: one of 29.7 degrees C was found for Chagos SST in 1972, though this did not cause coral mortality. Analysis of 12-month running means of the residuals from the annual cycle show that, between 1870 and 1999, the largest SST deviations occurred between October 1997 and May 1998 in Chagos and between August 1998 and July 1999 near Abu Dhabi. The event of 1998-1999 was the largest in these regions for at least 130 years. SSTs have risen over the last three decades at rates of about 0.22 degrees or 0.23 degrees per decade in both locations.  相似文献   

3.
River runoff from the four largest Siberian river basins (the Ob, Yenisei, Lena, and Kolyma) considerably contributes to freshwater flux into the Arctic Ocean from the Eurasian continent. However, the effects of variation in snow cover fraction on the ecohydrological variations in these basins are not well understood. In this study, we analysed the spatiotemporal variability of the maximum snow cover fraction (SCFmax) in the four Siberian river basins. We compared the SCFmax from 2000 to 2016 with data in terms of monthly temperature and precipitation, night-time surface temperatures, the terrestrial water storage anomaly (TWSA), the normalised difference vegetation index (NDVI), and river runoff. Our results exhibit a decreasing trend in the April SCFmax values since 2000, largely in response to warming air temperatures in April. We identified snowmelt water as the dominant control on the observed increase in the runoff contribution in May across all four Siberian river basins. In addition, we detected that the interannual river runoff was predominantly controlled by interannual variations in the TWSA. The NDVI in June was strongly controlled by the timing of the snowmelt along with the surface air temperature and TWSA in June. The rate of increase in the freshwater flux from the four Siberian rivers decreased from 2000 to 2016, exhibiting large interannual variations corresponding to interannual variations in the TWSA. However, we identified a clear increase trend in the freshwater flux of ~4 km3/year when analysing the long-term 39-year historical record (1978–2016). Our results suggest that continued global warming will accelerate the transition towards the earlier timing of snowmelt and spring freshwater flux into the Arctic Ocean. Our findings also highlight the effects of earlier snowmelt on ecohydrological changes in the Northern Hemisphere.  相似文献   

4.
We present 9 bottom222Rn profiles measured from the western and southern Indian Ocean during the 1977–1978 GEOSECS expedition. These profiles can be grouped into three cypes: one-layer, two-layer, and irregular types. The one-layer profiles with quasi-exponential distributions allow one to estimate the apparent vertical eddy diffusivity,Kv, with a simple model. The two-layer profiles show that there is a benthic boundary layer of the order of 50–100 m in which the excess222Rn distribution shows a vertical gradient much smaller than that of the layer immediately above. Within the boundary layer, the STD potential temperature (θ) and density(σ4) profiles are practically constant, and theKv values are of the order of 1000 cm2/s. The STD profiles for the water column above the boundary layer show gradients of increasing stability, and theKv values are of the order of 100 cm2/s. Modeling of the Rn data in the water column above the boundary layer indicates that there is a transition layer which effectively reduces the penetration of excess Rn from the benthic boundary layer into the upper layer.Sarmiento et al. [10] have shown that the buoyancy gradient or stability is inversely correlated with the apparent vertical eddy diffusivity, and the resulting buoyancy flux is fairly uniform, ranging from 1 to 14 × 10?6 cm2/s3 in the Atlantic and Pacific Oceans. However, Sarmiento et al. [11] show that a much higher buoyancy flux is associated with an intensified flow of the bottom water through a passage. In the Indian Ocean basins, we have found that the buoyancy flux has a comparable range (3–14 × 10?6 cm2/s3), except for a couple of stations where both stability and apparent vertical diffusivity are higher, resulting in a much higher buoyancy flux, probably indicative of rapid bottom water flow.  相似文献   

5.
Solute and runoff fluxes from two adjacent alpine streams (one glacial and one non‐glacial) were investigated to determine how the inorganic solute chemistry of runoff responded to seasonal and interannual changes in runoff sources and volume, and to differences in physical catchment properties. Intercatchment differences in solute composition were primarily controlled by differences in catchment geology and the presence of soils, whereas differences in total solute fluxes were largely dependent on specific discharge. The glacial stream catchment had higher chemical denudation rates due to the high rates of flushing (higher specific discharge). The non‐glacial Bow River had higher overall concentrations of solutes despite the greater prevalence of more resistant lithologies in this catchment. This is likely the result of both longer average water–rock contact times, and a greater supply of protons from organic soils and/or pyrite oxidation. Increases in snowpack depth/snowmelt runoff reduced the retention of nitrate in the Bow River catchment (i.e. increased nitrate export), probably by reducing net biological uptake, or by reducing the proportion of runoff that had contact with biologically active soil horizons that tend to remove nitrate. The two streams exhibited opposite solute flux responses to climate perturbations over three melt seasons (1998, 1999, and 2000). The 1998 El Niño event resulted in an unusually thin winter snowpack, and increased runoff and solute fluxes from the glacial catchment, but decreased fluxes from the Bow River catchment. Solute fluxes in the Bow River increased proportionally to discharge, indicating that increased snowmelt runoff in this catchment resulted in a proportional increase in weathering rates. In contrast, the proportional variation in solute flux in the glacial stream was only ∼70–80% of the variation in water flux. This suggests that increased ablation of glacier ice and the development of subglacial channels during the 1998 El Niño year apparently reduced the average water–rock contact time in the glacial catchment relative to seasons when the subglacial drainage system was primarily distributed in character. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

6.
A statistical evaluation of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) was performed over the Arabian Gulf region for the period, 1 August to 5 October, 2004. Verification skill scores of bias and root-mean-square error were estimated for surface variables and for vertical profiles to investigate any diurnal variations. The model predictions of boundary-layer heights are compared with the observations at Abu Dhabi, United Arab Emirates. The Middle East presents challenges to numerical weather prediction due to complex land-ocean-land mesoscale processes. An independent data set of surface measurements from 50 stations in the UAE was available from the Department of Water Resources Studies, Abu Dhabi for model verification. The results indicate a diurnal variation in the model errors. The errors are small considering the magnitudes of the observed variables. Errors in the coastal region can be attributed to the differences in the timing of the onset of sea and land breeze circulations in the simulations as compared to the observations. Errors are relatively smaller in the offshore locations.  相似文献   

7.
Abstract

This paper explores the properties of a two-dimensional, Boussinesq convection model with an ad hoc term in the buoyancy tendency equation that represents a positive external feedback process acting on the buoyancy fluctuations. Linear stability analyses and nonlinear integrations are presented for the case of constant heat flux boundary conditions. Although the large wavenumber modes grow the fastest from a state of rest, the nonlinear solutions progressively evolve to cells of small wavenumber. Applications to mesoscale cellular convection in the atmosphere are discussed.  相似文献   

8.
A coupled ocean and boundary layer flux numerical modeling system is used to study the upper ocean response to surface heat and momentum fluxes associated with a major hurricane, namely, Hurricane Dennis (July 2005) in the Gulf of Mexico. A suite of experiments is run using this modeling system, constructed by coupling a Navy Coastal Ocean Model simulation of the Gulf of Mexico to an atmospheric flux model. The modeling system is forced by wind fields produced from satellite scatterometer and atmospheric model wind data, and by numerical weather prediction air temperature data. The experiments are initialized from a data assimilative hindcast model run and then forced by surface fluxes with no assimilation for the time during which Hurricane Dennis impacted the region. Four experiments are run to aid in the analysis: one is forced by heat and momentum fluxes, one by only momentum fluxes, one by only heat fluxes, and one with no surface forcing. An equation describing the change in the upper ocean hurricane heat potential due to the storm is developed. Analysis of the model results show that surface heat fluxes are primarily responsible for widespread reduction (0.5°–1.5°C) of sea surface temperature over the inner West Florida Shelf 100–300 km away from the storm center. Momentum fluxes are responsible for stronger surface cooling (2°C) near the center of the storm. The upper ocean heat loss near the storm center of more than 200 MJ/m2 is primarily due to the vertical flux of thermal energy between the surface layer and deep ocean. Heat loss to the atmosphere during the storm’s passage is approximately 100–150 MJ/m2. The upper ocean cooling is enhanced where the preexisting mixed layer is shallow, e.g., within a cyclonic circulation feature, although the heat flux to the atmosphere in these locations is markedly reduced.  相似文献   

9.
In the present study, an attempt was made to understand the role of South China Sea (SCS) convection associated with northerly cold surges and Typhoon Peipah in initiating Cyclone Sidr in the Bay of Bengal (BoB). The variation of air sea fluxes during the entire history of Cyclone Sidr tracking before its landfall over Bangladesh was also studied. The presence of cold surges in the north SCS associated with heavy rainfall episodes has been noticed at the southern Gulf of Tonkin coast prior to the formation of Typhoon Peipah. Subsequently, these surges migrated south, which resulted in intensification of a deep convection on reaching the Vietnamese coast. During the same period in the western Pacific, Typhoon Peipah developed, propagating in the westward direction and entering the SCS. Analysis of geostationary water vapour images, mean sea level pressure, and surface wind maps clearly depicted the transport of convective cloud clusters, moisture, and westward momentum from Typhoon Peipah to the deep convection cells over the SCS. Consequently, the existing deep convection over the Vietnamese coast resulted in a westward direction and entered the Gulf of Thailand and Andaman Sea. The availability of higher latent heat fluxes, warmer sea surface temperatures, and suitable atmospheric conditions over this region favoured the formation of a tropical depression in the Andaman Sea. This depression further intensified in the southeast BoB, resulting in the formation of Cyclone Sidr. NCEP/NCAR wind fields and air-sea fluxes revealed left asymmetry surface winds and higher latent heat flux on the left side of the track during the intensification phase of Sidr.  相似文献   

10.
A recent dynamo model for Mercury assumes that the upper part of the planet's fluid core is thermally stably stratified because the temperature gradient at the core–mantle boundary is subadiabatic. Vigorous convection driven by a superadiabatic temperature gradient at the boundary of a growing solid inner core and by the associated release of light constituents takes place in a deep sub-layer and powers a dynamo. These models have been successful at explaining the observed weak global magnetic field at Mercury's surface. They have been based on the concept of codensity, which combines thermal and compositional sources of buoyancy into a single variable by assuming the same diffusivity for both components. Actual diffusivities in planetary cores differ by a large factor. To overcome the limitation of the codensity model, we solve two separate transport equations with different diffusivities in a double diffusive dynamo model for Mercury. When temperature and composition contribute comparable amounts to the buoyancy force, we find significant differences to the codensity model. In the double diffusive case convection penetrates the upper layer with a net stable density stratification in the form of finger convection. Compared to the codensity model, this enhances the poloidal magnetic field in the nominally stable layer and outside the core, where it becomes too strong compared to observation. Intense azimuthal flow in the stable layer generates a strong axisymmetric toroidal field. We find in double diffusive models a surface magnetic field of the observed strength when compositional buoyancy plays an inferior role for driving the dynamo, which is the case when the sulphur concentration in Mercury's core is only a fraction of a percent.  相似文献   

11.
Interdecadal variations in the Northern Hemisphere and the North Pacific have been documented in many studies[1 4]. The connection between the subtropical North Pacific and the tropics is regarded as the most important process triggering and maintaining t…  相似文献   

12.
The recent destructive earthquake(MS 7.4) of 17 August 1999 in the Gulf of Izmitin north-west Turkey was not a surprise, neither forits location, large magnitude or for the damage itcaused. Other, equally large magnitude earthquakeshave occurred in the past in the region but we havechosen to present in this paper the earthquake of 10July 1894 because it is one of the two large events tostrike the Gulf of Izmit in the last 105 years, and inmany respects similar to the recent earthquake of 17August 1999 in size, location, and effects.  相似文献   

13.
Seasonal patterns of di-nitrogen fluxes together with denitrification, anammox, and N-fixation rates were studied in sediment in an area subject to strong human pressure via waste water, tributaries and shellfish farming in the Mediterranean Sea (Carteau Cove, NW area of the Gulf of Lion). Ammonium concentration demonstrated no seasonal variation, however, a large increase in its concentration was observed over a 10 years period due to intense biodeposition of organic matter. In contrast, nitrate concentration demonstrated no seasonal or long-term (10 years) variation. The main processes affecting di-nitrogen flux magnitudes were denitrification and N-fixation. Anammox was only detected occasionally, nevertheless it represented at times up to 39% of the N2-flux. Nitrate reducing processes were variable and denitrification showed a 20-fold increase over the past 10 years and might actually have reached its potential maximal activity. Rates of N2 production (denitrification and anammox) were generally higher than those of N-fixation, leading to elimination of nitrogen from the ecosystem.  相似文献   

14.
The Intensive Field Phase of Indian Ocean Experiment (INDOEX, IFP-99) was carried onboard Oceanic Research Vessel Sagar Kanya during January 20–March 12, 1999 over the latitudinal range 15°N–20°S and the longitudinal range 63°E–77°E. The present study deals with the spatial variation of air–sea fluxes over the Indian Ocean during the INDOEX, IFP-99 campaign. Drag coefficient (C_D), and sensible heat (CH) and water vapor (CE) exchange coefficients are determined using an iterative scheme. The estimated values of these coefficients are utilized for the computation of air–sea fluxes using the bulk aerodynamic method. The variations of air–sea flux estimates are studied with respect to the variation of wind speed.  相似文献   

15.
The Loop Current mediating the oceanic heat and salt flux from the Caribbean Sea into the Atlantic Ocean and its interference with the Mississippi River discharge are critical for both the regional climate in the Gulf of Mexico area and the water vapor transport towards high northern latitudes. We present a 400-kyr record of sea surface temperature and local surface salinity from the northeastern Gulf of Mexico (IMAGES core MD02-2575) approximated from combined planktonic foraminiferal δ18O and Mg/Ca, which reflects the temporal dynamics of the Loop Current and its relationship to both varying Mississippi discharge and evolution of the Western Hemisphere Warm pool. The reconstructed sea surface temperature and salinity reveal glacial/interglacial amplitudes that are significantly larger than in the Western Hemisphere Warm pool. Sea surface freshening is observed during the extreme cool periods of Marine Isotope Stages 2, 8, and 10, caused by the strengthened Mississippi discharge which spread widely across the Gulf favored by the less established Loop Current. Interglacial and interstadial sea-surface conditions, instead, point to a strengthened, northward flowing Loop Current in line with the northward position of the Intertropical Convergence Zone, allowing northeastern Gulf of Mexico surface hydrographic conditions to approach those of the Caribbean. At these times, the Mississippi discharge was low and deflected westward, promoted by the extended Loop Current. Previously described deglacial megadischarge events further to the west did not affect the northeastern Gulf of Mexico hydrography, implying that meltwater routing from the Laurentide Ice Sheet via the Mississippi River is unlikely to have affected Atlantic Meridional Overturning Circulation.  相似文献   

16.
Phytoplankton biomass, community and size structure, primary production and bacterial production were measured at shelf and continental slope sites near North West Cape, Western Australia (20.5°S–22.5°S) over two summers (October–February 1997–1998 and 1998–1999), and in April 2002. The North West Cape region is characterized by upwelling-favorable, southwesterly winds throughout the summer. Surface outcropping of upwelled water is suppressed by the geostrophic pressure gradients and warm low-density surface waters of the southward flowing Leeuwin Current. Strong El Niño (ENSO) conditions (SOI <0) prevailed through the summer of 1997–1998 which resulted in lower sea levels along the northwestern Australian coast and a weaker Leeuwin Current. La Niña conditions prevailed during the 1998–1999 summer and in April 2002. During the summer of 1997–1998, the North West Cape region was characterized by a shallower thermocline (nutricline), resulting in larger euphotic zone stocks of inorganic nitrogen and silicate over the continental slope. There was evidence for episodic intrusions of upper thermocline waters and the sub-surface chlorophyll maximum onto the outer continental shelf in 1997–1998, but not in 1998–1999. Pronounced differences in phytoplankton biomass, community size structure and productivity were observed between the summers of 1997–1998 and 1998–1999 despite general similarities in irradiance, temperature and wind stress. Phytoplankton primary production and bacterial production were 2- to 4-fold higher during the summer of 1997–1998 than in 1998–1999, while total phytoplankton standing crop increased by<2-fold. Larger phytoplankton (chiefly diatoms in the >10 μm size fraction) made significant contributions to phytoplankton standing crop and primary production during the summer of 1997–1998, but not 1998–1999. Although there were no surface signs of upwelling, primary production rates near North West Cape episodically reached levels (3–8 g C m−2 day−1) characteristic of eastern boundary Ekman upwelling zones elsewhere in the world. Bacterial production (0.006–1.2 g C m−2 day−1) ranged between 0.6 and 145 percent (median=19 percent) of concurrent primary production. The observed differences between years and within individual summers suggest that variations in the Leeuwin Current driven by seasonal or ENSO-related changes in the Indonesian throughflow region may have episodic, but significant influences on pelagic productivity along the western margin of Australia.  相似文献   

17.
Vertical eddy diffusivities (Kv's) have been estimated at fourteen widely separated locations from fourteen222Rn profiles and two228Ra profiles measured near the ocean floor as part of the Atlantic and Pacific GEOSECS programs. They show an inverse proportionality to the local buoyancy gradient [(g/?)(??pot/?z)] calculated from hydrographic measurements. The negative of the constant of proportionality is the buoyancy flux [?Kv(g/?)(??pot/?z)] which has a mean of ?4 × 10?6 cm2/sec3. Our results suggest that the buoyancy flux varies very little near the ocean floor. Kv's for the interior of the deep Pacific calculated from the relationship Kv = (4 × 10?6cm2/sec3)/[(g/?)(??pot/?z)] agree well with published estimates. Kv's calculated for the pycnocline are one to two orders of magnitude smaller than upper limits estimated from tritium and7Be distributions.Heat fluxes calculated with the model Kv's obtained from the222Rn profiles average 31 μcal cm?2 sec?1 in the Atlantic Ocean and 8 μcal cm?2 sec?1 in the Pacific Ocean.  相似文献   

18.
A technique employing the resonant nuclear reaction 1H(19F, αγ) 16O has been used to measure hydrogen concentration versus depth in selected coarse fine fragments from the Apollo 11 and Apollo 15 missions, and in glass coated surface chips from two Apollo 15 rocks. The highly variable hydrogen content in the coarse fine fragments is concentrated mainly in a layer extending from the surface to a depth of 2000 ± 500A?. The hydrogen content of the surface region of the Apollo 15 rock chips is comparable to that of the coarse fine samples, but is concentrated mainly within a few hundred angstroms of the surface. The hydrogen depth distribution in a piece of platinum foil from the Apollo 16 Lunar surface Cosmic Ray Experiment was also measured in an attempt to place a limit on the flux of 10–40 keV protons associated with a solar flare event.  相似文献   

19.
Soil moisture and its isotopic composition were observed at Spasskaya Pad experimental forest near Yakutsk, Russia, during summer in 1998, 1999, and 2000. The amount of soil water (plus ice) was estimated from volumetric soil water content obtained with time domain reflectometry. Soil moisture and its δ18O showed large interannual variation depending on the amount of summer rainfall. The soil water δ18O decreased with soil moisture during a dry summer (1998), indicating that ice meltwater from a deeper soil layer was transported upward. On the other hand, during a wet summer (1999), the δ18O of soil water increased due to percolation of summer rain with high δ18O values. Infiltration after spring snowmelt can be traced down to 15 cm by the increase in the amount of soil water and decrease in the δ18O because of the low δ18O of deposited snow. About half of the snow water equivalent (about 50 mm) recharged the surface soil. The pulse of the snow meltwater was, however, less important than the amount of summer rainfall for intra‐annual variation of soil moisture. Excess water at the time just before soil freezing, which is controlled by the amount of summer rainfall, was stored as ice during winter. This water storage stabilizes the rate of evapotranspiration. Soil water stored in the upper part of the active layer (surface to about 120 cm) can be a water source for transpiration in the following summer. On the other hand, once water was stored in the lower part of the active layer (deeper than about 120 cm), it would not be used by plants in the following summer, because the lower part of the active layer thaws in late summer after the plant growing season is over. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

20.
Dynamics of a large tropical lake: Lake Maracaibo   总被引：1，自引：0，他引：1  
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