Mean Surface Heat Flux Research Articles

A two-way nested-grid ocean-circulation model for the Meso-American Barrier Reef System

A two-way nested-grid ocean-circulation model is developed for the Meso-American Barrier Reef System (MBRS), using a newly developed two-way interactive nesting technique. The unique feature of this new nesting technique is its use of the semi-prognostic method (Sheng et al. 2001) to exchange information between different grids through the model momentum equations. The nested-grid model for the MBRS has a fine-resolution inner model embedded in a coarse-resolution outer model. The outer model is the western Caribbean Sea model developed by Sheng and Tang (2003), with a horizontal resolution of roughly 19 km. The inner model domain covers the northwest Caribbean Sea (NWCS) between 79°W and 89°W and between 15.5°N and 22°N, with a horizontal resolution of roughly 6 km. The nested-grid ocean model is initialized with the January mean temperature and salinity and forced by the monthly mean COADS (comprehensive ocean-atmosphere data set) wind stress and surface heat flux. The model sea-surface salinity is restored to the monthly mean climatology. The nested-grid model is integrated for 2 years and the second-year model results are presented in this paper. The model-calculated annual-mean near-surface currents over the NWCS agree reasonably well with the time-mean near-surface currents inferred by Fratantoni (2001) from trajectories of the satellite-tracked 15-m drogued drifters in the 1990s. The two-way nested model is also used to quantify the role of local wind stress, local density gradients and boundary forcings of the outer model in driving the annual-mean circulation in the region.

A preferred scale for landscape forced mesoscale circulations?

The Regional Atmospheric Modeling System was used in two previous studies to simulate mesoscale circulations forced by surface heterogeneity in the Central U. S. and Amazonia. In this work, spectral analysis is used to compare the horizontal length scales of these simulated circulations with the scale of the surface heterogeneity. For both cases, the organized mesoscale circulations are confined within a preferred length scale range (10–20 km) that is significantly different from the dominant length scale of the surface heterogeneity. Multiscale landscape patchiness in these two regions tend to produce eddies at a wide range of scales, but the land‐atmosphere interaction processes act as a medium‐pass filter to select intermediate‐scale circulations. This scale of response remains relatively unchanged despite significant day‐to‐day variations in the synoptic situation and the mean surface heat flux.

The thermal state and composition of the lithospheric mantle beneath the Leizhou Peninsula, South China

Two localities on the Leizhou Peninsula, southern China (Yingfengling and Tianyang basaltic volcanoes) yield a wide variety of mantle-derived xenoliths including Cr-diopside series mantle wall rocks and two distinct types of Al-augite series pyroxenites. Metapyroxenites have re-equilibrated granoblastic microstructures whereas pyroxenites with igneous microstructures have not thermally equilibrated to the mantle conditions. An abundant suite of megacrysts and megacrystic aggregates (including garnet, plagioclase, clinopyroxene, ilmenite and apatite) is interpreted as the pegmatitic equivalents of the igneous pyroxenite suite. Layered spinel lherzolite/spinel websterite xenoliths were formed by metamorphic differentiation caused by mantle deformation, inferred to be related to lithospheric thinning. Some metapyroxenites have garnet websterite assemblages that allow calculation of their mantle equilibration temperatures and pressures and the construction of the first xenolith geotherm for the southernmost China lithosphere. Heat flow data measured at the surface in this region yield model conductive geotherms (using average crustal conductivity values) that are consistent with the xenolith geotherm for the mantle. The calculated mean surface heat flux is 110 mW/m 2. This high heat flux and the high geotherm are consistent with young lithospheric thinning in southern China, and with recent tomography results showing shallow low-velocity zones in this region. The xenolith geotherm allows the construction of a lithospheric rock type section for the Leizhou region; it shows that the crust–mantle boundary lies at about 30 km, consistent with seismic data, and that the lithosphere–asthenosphere boundary lies at about 100 km.

Climate from borehole data: Energy fluxes and temperatures since 1500

Variations in the Earth's surface energy balance are recorded in the ground as perturbations of the subsurface thermal regime. Here I apply singular value decomposition (SVD) inversion methods to 826 temperature‐depth profiles distributed world wide, in order to reconstruct ground surface temperature histories (GSTH) and surface heat flux histories (SHFH) from the temperature and heat flux anomalies detected in the shallow subsurface. Inversions yielded a mean ground surface temperature and surface heat flux histories for the Earth's continents for the last 500 years. Results indicate that the global average ground temperature and ground heat flux have increased an average of 0.45°K and 18.0 mWm2 respectively over the last 200 years, and 0.9°K in the last five centuries.

Air-sea interaction over the Indian Ocean due to variations in the Indonesian throughflow

The effects of the Indonesian throughflow on the upper thermocline circulation and surface heat flux over the Indian Ocean are presented for a 3-D ocean model forced by two different monthly wind–stress climatologies, as they show interesting differences, which could have implications for long-term variability in the Indian and Australasian monsoons. The effects are determined by contrasting a control run with a run in which the throughflow is blocked by an artificial land-bridge across the exit channels into the Indian Ocean. In the model forced by ECMWF wind stresses, there is little impact on the annual mean surface heat flux in the region surrounding the throughflow exit straits, whereas in the model forced by SSM/I-based wind stresses, a modest throughflow of less than 5 ×106 m3s–1 over the upper 300 m induces an extra 10–50 Wm–2 output. In the SSM/I-forced model, there is insignificant penetration of the throughflow into the northern Indian Ocean. However, in the ECMWF-forced model, the throughflow induces a 5–10 Wm–2 reduction in heat input into the ocean, i.e., an effective output, over the Somali Current in the annual mean. These differences are attributed to differences in the strength and direction of the Ekman transport of the ambient flow, and the vertical structure of the transport and temperature anomalies associated with the throughflow. In both models, the throughflow induces a 5–30 Wm–2 increase in net output over a broad swathe of the southern Indian Ocean, and a reduction in heat output of 10–60 Wm–2 in a large L-shaped band around Tasmania. Effective increases in throughflow-induced net output reach up to 40 (60) Wm–2 over the Agulhas Current retroflection in the ECMWF (SSM/I)-forced model. Seasonal variations in the throughflow's effect on the net surface heat flux are attributed to seasonal variations in the ambient circulation of the Indian Ocean, specifically in coastal upwelling along the south Javan, west Australian, and Somalian coasts, and in the depth of convective overturning between 40°S to 50°S, and its sensing of the mean throughflow's thermal anomaly. The seasonal anomalies plus annual mean yield maximum values for the throughflow-induced net surface heat output in boreal summer. Values may exceed 40 Wm–2 in the southern Indian Ocean interior in both models, exceed 60 Wm–2 over the Agulhas retroflection and immediate vicinity of the exit channels in the SSM/I-forced model, and reach 30 Wm–2 over the Somali jet in the ECMWF-forced model.

Impact of the AVHRR sea surface temperature on atmospheric forcing in the Japan/East Sea

The impact of high resolution sea surface temperature (SST) data on the atmospheric forcing in the Japan/East Sea (JES) is investigated using a high‐resolution mesoscale atmospheric model. We use the Advanced Very High Resolution Radiometer (AVHRR) Pathfinder SST (PFSST) and the operational NCEP (National Center for Environmental Prediction) global SST analysis (NCEPSST) as the lower boundary conditions for two numerical experiments. A sharp SST gradient associated with the subpolar front in JES, well‐resolved by PFSST, has a significant influence on both synoptic scale and monthly mean surface winds and heat fluxes in JES. These results have an important implication for research related to coastal atmosphere and ocean circulation and air‐sea interactions.

A numerical study of the seasonal variability in the circulation off central Chile

The Princeton Ocean Model is used to study the coastal ocean circulation off central Chile (between 30° and 45°S) and its seasonal transitions in response to monthly mean climatological wind stress and surface heat flux. The model reproduces many of the dominant circulation features, including an equatorward coastal current, coastal upwelling, and a poleward undercurrent. To get the correct seasonal variability in the undercurrent, it was necessary to prescribe the inflow of the undercurrent on the northern model boundary. Meanders and eddies form throughout the simulation period seaward of the coastal current in response to baroclinic instability of the flow. The flow associated with the meanders shows upwelling in the shoreward flow and downwelling in the seaward flow. This upwelling/downwelling pattern is explained by conservation of relative vorticity in the flow. The upwelling velocity associated with the meanders corresponds to a vertical migration of 15–30 m over a typical timescale of the meanders of 1–2 months. It is argued that this upwelling may be important for maintaining observed high phytoplankton biomass and primary production seaward of the coastal zone directly affected by wind‐driven upwelling.

The influence of tectonic plates on mantle convection patterns, temperature and heat flow

SUMMARY The dynamic coupling between plate motion and mantle convection is investigated in a suite of Cartesian models by systematically varying aspect ratios and plate geometries. The aim of the study presented here is to determine to what extent plates affect mantle flow patterns, temperature and surface heat flux. To this end, we compare numerical convection models with free-slip boundary conditions to models that incorporate between one and six plates, where the geometries of the plates remain fixed while the plate velocities evolve dynamically with the flow. We also vary the widths of the plates and the computational domain in order to determine what constraint these parameters place on the mean temperature, heat flux and plate velocity of mantle convection models. We have investigated the influence of plates for three whole-mantle convection cases that differ in their heating modes (internally heated and basally heated) and rheologies (isoviscous and depth-dependent viscosity). We present a systematic investigation of over 30 models that exhibit increasingly complex behaviour in order to understand highly time-dependent systems using the insight gained from simpler models. In models with aspect ratios from 0.5 to 12 we find that for the same heating mode, variations in temperature can be as much as 40 per cent when comparing calculations with unit-width plates to models incorporating plates with widths equal to five times the model depth. Mean surface heat flux may decrease by 60 per cent over the same range of plate widths. We also find that internally heated mantle convection models incorporating plates exhibit novel behaviour that, we believe, has not been described previously in mantle convection studies. Specifically, in internally heated models, plate motion is characterized by episodic reversals in direction driven by changes in the mantle circulation from clockwise to counterclockwise and vice versa. These flow reversals occur in internally heated convection and are caused by a build-up of heat in the interiors of wide convection cells close to mantle downwellings. We find that flow reversals occur rapidly and are present in both single-plate and multiple-plate models that include internal heating. This behaviour offers a possible explanation for why the Pacific plate suddenly changed its direction some 43 Ma.

Atmospheric Response To Spatial Variations In Concentration And Size Of Polynyas In The Southern Ocean Sea-Ice Zone

Although it is well known that sea-ice regions are important components of the Earth's climate system, the exchanges of energy between ocean, ice and atmosphere are not well understood. The majority of past observational and modelling studies of atmosphere-surface interactions over sea-ice regions were primarily concerned with airflow over a single, isolated area of open water. The more realistic situations of multiple polynyas within a sea-ice field and different areal concentrations of sea ice were studied here. Spatial structure of the atmospheric boundary layer in response to this surface was simulated using a high-resolution numerical model. A sea-ice concentration of 80%, typical of the Southern Ocean sea-ice zone, was maintained within a 100-km wide domain. The effects of three polynya characteristics were assessed: their horizontal extent; local concentration of sea ice (LCI); and their arrangement with ice floes. Over polynyas of all sizes distinct plumes of upward heat flux, their width and height closely linked to polynya width, resulted in mixed layers 600 to 1000 m deep over and downwind of the polynyas, their depth increasing with polynya width. Mean surface heat flux (MSHF) increased with size in polynyas less than 30 km wide. The air-to-ice MSHF over the first 10 km of sea-ice downwind of each polynya and the domain-average surface heat flux increased linearly with polynya width. Turbulent kinetic energy plumes occurred over all polynyas, their heights and widths increasing with polynya widths. Downward flux of high momentum air in the plumes caused increased wind speeds over polynyas in the layer from about 300–1000 m above the surface, the depth varying directly with polynya width. MSHFs decreased as LCIs increased. The arrangement of polynyas had relatively little effect on the overall depth of the modified layer but did influence the magnitude and spatial structure of vertical heat transfer. In the two-polynya case the MSHF over the polynyas was larger when they were closer together. Although the MSHF over the sea ice between the polynyas decreased in magnitude as their separation increased, the percentage of the polynya-to-air heat recaptured by this ice floe increased fivefold.

Analysis of a 3 year meteorological record from the ablation zone of Morteratschgletscher, Switzerland: energy and mass balance

AbstractSince 1 October 1995, an automatic weather station has been operated on the tongue of Morteratschgletscher, Switzerland. The station stands freely on the ice, and sinks with the melting glacier surface. It is located at 2100 m a.s.l., and measures air temperature, wind speed and direction, incoming and reflected solar radiation, pressure and snow temperature. A sonic ranger, mounted to stakes drilled into the ice, measures surface height from which melt rates and snow accumulation can be derived. In this paper the data for the period 1 October 1995 to 30 September 1998 are used to evaluate the surface energy balance. The turbulent energy fluxes are calculated with the bulk method. The turbulent exchange coefficient Ch is used as a control parameter. With Ch = 0.00127 the calculated melt equals the observed melt, which is 17.70 m w.e. over the 3 years. When averaged over the time when melting occurs (i.e. 35% of the time), the mean surface heat flux equals 191 W m−2. Net shortwave radiation contributes 177 W m−2, net longwave radiation −25 W m−2, the sensible-heat flux 31 W m−2 and the latent-heat flux 8 W m−2.

An Evaluation of the Large-Eddy Simulation Option of the Regional Atmospheric Modeling System in Simulating a Convective Boundary Layer: A FIFE Case Study

Abstract A large-eddy simulation (LES) model was used to simulate the convective boundary layer (CBL) that developed on 1 July 1987, over the domain of the First International Satellite Land Surface Climatology Project Field Experiment (FIFE). Three simulations were produced using different boundary conditions at the ground surface, namely, (i) spatial distribution of topography and spatial distribution of surface heat fluxes; (ii) spatial distribution of topography but mean surface heat fluxes; and (iii) no topography and mean surface heat fluxes. The diurnal variation of mean surface fluxes and their spatial distribution were derived from the FIFE network of observations. In all cases, the model was initialized with the atmospheric sounding observed in this domain at 0700, and run until 1500 local time. The resulting mean profiles of temperature and specific humidity were compared to those observed with atmospheric soundings at 0900, 1030, and 1230 local time. The simulated structure of turbulence was q...

Heat transfer response of free convection flow from a vertical heated plate to an oscillating surface heat flux

An investigation is undertaken of the unsteady response of two-dimensional laminar free convection boundary layer flow of a viscous incompressible fluid along a semi-infinite vertical heated plate where the mean surface heat flux oscillates with a small amplitude about a steady profile. The buoyancy forces are favourable, resulting from a positive flux of heat from the surface of the plate into the fluid. The interaction of the time-periodic heat flux with the usual boundary-layer flow is examined by using a linearized theory. Solutions are obtained using three distinct methods, namely an extended series expansion method for low frequencies, an asymptotic series expansion method for high frequencies and a fully numerical finite difference method for general frequencies. Calculations have been carried out for a wide range of parameters to examine the solutions in terms of the amplitude and phase angle of the fluctuating parts of the surface shear stress and the surface temperature. It has been found that the amplitude and phase angle of both the shear stress and the surface temperature predicted by these three methods are in very good agreement in their respective ranges of validity.

Heat budget in the Japan Sea

The long-term mean (31-year mean) surface heat fluxes over the Japan Sea are estimated by the bulk method using the most of the available vessel data with the resolution of 1o×1o. The long-term annual mean net heat flux is about −53 W m−2 (negative sign means upward heat flux) with the annual range from 133 W m−2 in May to −296 W m−2 in December. The small gain of heat in the area near Vladivostok seems to indicate the existence of cold water flowing from the north. In that area in winter, the mean loss of heat attains about 200 W m−2, and the Bowen's ratio is over the unity. The largest insolation occurs in May in the Japan Sea, and the upward latent heat flux becomes the largest in November in this area. The heat flux of Haney type is also calculated, and the result, shows that the constantQ 1 has the remarkable seasonal and spatial variation, while the coefficientQ 2 has relatively small variation throughout all seasons. Under the assumption of constant volume transport of 1.35×106 m3s−1 through the Tsugaru Strait, the long-term averages of the volume transport through the Tsushima and Soya Straits are estimated to be about 2.20 and 0.85×106 m3s−1 from the result of the mean surface heat flux, respectively.

Surface Heat Fluxes Using Satellite Observations: A Case Study in the Northwest Pacific

Abstract Satellite-observed surface-level meteorological parameters are used to derive 10-day mean surface heat fluxes of solar, longwave, sensible, and latent heat fluxes in the northwest Pacific. Cloud amount in tenths were taken from Geostationary Meteorological Satellite cloud data, published by the Japan Meteorological Agency. Sea surface temperature (SST) was derived from the NOAA Advanced Very High Resolution Radiometer observations using the cross-product SST. Surface wind speed was obtained from the Special Sensor Microwave/Imager (SSM/I). Air temperature and surface level humidity were derived statistically from the SSM/I precipitable water. Synoptic flux estimates using satellite observations are compared with earlier estimates for this region (same season) derived from in situ data and were found to be reasonable. While the Kuroshio regime shows large net heat loss toward the south, it decreases and has heat surplus. For an evaluation of the satellite-derived heat fluxes, these are compared wi...

Driving the meridional overturing in the Indian Ocean

Accumulating evidence points toward the surprising and puzzling conclusion that the overall deep upwelling velocity in the Indian Ocean is several times bigger than that in the Pacific. Recent bulk-formula calculations suggest that the mean surface heat flux per unit area may be much greater into the Indian than into the Pacific Ocean. The hypothesis is therefore offered that the anomalously large meridional overturning in the Indian Ocean, an element of the global thermohaline circulation, is driven locally by anomalously large heat-flux differential. A simple two-layered, two-dimensional model of the process is developed in order to compare relative upwelling rates to imposed heat fluxes. The comparison is promising, despite ambiguities in the upwelling evidence and gross uncertainties in present heat-flux estimates.

Analytical and experimental evaluations of simulated sweeping heat load on the divertor plate for ITER

The magnitude of the heat flux on the surface of the divertor plate of ITER is one of the most limiting constraints on its lifetime. A technique for sweeping the separatrix across the divertor surface will be applied to reduce the mean surface heat fluxes and erosion damages due to intense fluxes over 15 MW/m 2. As a first step for the evaluation of the sweeping effects, the thermal response of the divertor plate has been analyzed under the ITER relevant heat flux conditions that a peak heat flux on the divertor plate and full width at half maximum are expected to be 30 MW/m 2 and 3 cm, respectively. The analytical results show that the application of sweeping is very effective for reducing the surface temperature of the divertor plate. To realize these benefits for ITER, the divertor separatrix must be swept with a frequency of higher than 3.0 Hz over a distance of ± 10 cm. Based on the analytical results, thermal response experiments with a divertor mock-up are carried out using the JAERI Electron Beam Irradiation Stand (JEBIS). The conditions for this experiment were a peak heat flux of 30 MW/m 2 with a sweeping frequency of 1.0 Hz over a distance of ± 10 cm for a 30 s long cycle. Experimental results show that the divertor mock-up has successfully endured for more than 1000 major thermal cycles without an increase of the surface temperature. Therefore, it has been experimentally demonstrated that application of the sweeping technique is very effective for improvement of the power handling capability of the divertor plate. Experimental results showed a good agreement with analytical results.

Annual mean surface heat fluxes in the Arabian Gulf and the net heat transport through the Strait of Hormuz

Abstract An attempt is made to assess the climatological air‐sea fluxes in the Arabian (Persian) Gulf using meteorological observations. The annual mean values of upward heat transfer due to solar radiation, sensible heat, latent heat and infrared radiation fluxes are ‐212, ‐1, 168 and 66 W m−2, respectively. Based on the surface inflow and subsurface outflow through the Strait of Hormuz, the annual average heat transport into the Gulf is 25 W m−2. This is in fair agreement with the resulting upward flux of 21 W m−2 at the sea surface in the Gulf.

The Use of Mean Atmospheric Parameters in the Calculation of Modeled Mean Surface Heat Fluxes over the World's Oceans

There are a number of atlases that display the distribution of ocean-atmosphere sensible and latent heat fluxes over various regions. Many are based on the “classical” method, in which time mean quantities are used in the bulk aerodynamic formulas, rather than the more accurate “sampling” method, which computes the mean of the instantaneous fluxes. Much of the justification for the use of this approximation comes from some studies conducted in the North Pacific and Atlantic oceans. How valid is it when applied globally? In this study we use large datasets, generated by January and July simulations of a general circulation model of the atmosphere, to examine comprehensively the differences between the two methods. We find that the ocean zonal averages of the two fluxes differ by less than 10 W m−2 at most latitudes in both months. However, at high southern latitudes in winter the sensible heat fluxes north of the Antarctic ice pack are up to 17 W m−2 (25%) greater when calculated with the sampling method. We show that the two methods differ due to four temporal covariances of various atmospheric quantities Some of the covariances contribute up to 12 W m−2 to the zonal mean fluxes. The fact that the classical and sampling methods give similar results over most of the globe is due, in large part, to the near cancellation of the covariances. However, this is not always true around the periphery of Antarctica.

Four-equation turbulence model for prediction of the turbulent boundary layer affected by buoyancy force over a flat plate

Turbulent convective heat transfer with appreciable buoyancy effect over a heated or cooled horizontal flat plate is numerically analyzed by solving four equations for mean square temperature variance θ 2 , its rate of destruction ε θ , turbulent kinetic energy κ and the rate of kinetic energy dissipation ε. Turbulent time-scale ratio R of temperature fluctuations relative to velocity fluctuations defined by ( θ 2 ε θ ) ( 2κ ε ) is found to vary widely across the boundary layer. For both highly stable and highly unstable conditions, the ‘four-equation’ model yields better results for mean temperature profile and surface heat flux than the two-equation model. It is also found that the magnitude of thermal von Karman constant κ θ is not a universal constant but it depends on the thermal stratification of the boundary layer.

Heat flow and age of the Gulf of Oman

We present the results of twenty heat flow stations in the Gulf of Oman which are used to infer the first reliable age estimates for the basin. A mean surface heat flux of 42.6±3.6 mW m −2 exhibits no significant regional variation. After correction for thick and rapidly deposited sediments this yields an age of 70 to 100 Ma according to oceanic thermal models. This age is also consistent with the sediment corrected basement depths of 5.5–6.0 km and with formation during the Cretaceous quiet zone. The latter can explain the absence of magnetic sea-floor spreading lineations. Heat flow measurements are also used to confirm the presence of gas hyrdate layers. The measured thermal gradient yields a depth for the solid to free gas phase transition which is the same as that deduced from “bright spots” seen on seismic reflection profiles.