Cyclic Heat Flux Research Articles

Implications of the salt and heat budgets of the Gulf of Thailand

Hydrographic data collected during 1959 and 1960 in the Gulf of Thailand, combined with supporting climatological data, have been used to investigate the salt and heat budgets of the Gulf. A simple model including mixing, net precipitation, local river run-off and Ekman flux predicts the flushing time of the Gulf, associated with processes other than the Ekman flux, to be 12.0 months, but predicts too small a magnitude and the wrong phase for the observed seasonal salinity cycle. Adding the discharge from the Mekong River reduces the flushing time to 5.4 months and improves the fit to the magnitude of the observed salinity cycle. The phase matches if a 2-month delay in the time for the Mekong discharge to reach the Gulf is allowed. The Mekong River appears to be a vital source of fresh water to the Gulf. Using the flushing time required to balance the salt budget and a model for temperature which incorporates the climatological net heat flux values, the Gulf is predicted to be warmer than observed. The annual cycle of net heat flux required to match the observed temperature cycle has a mean and an amplitude both of which are smaller than the published climatological values, but only by about 10 W/m 2 (annual net heat flux). Our simple model, using half the Mekong discharge, suggests that a uniformly distributed tracer would be flushed (90% removal) from the Gulf in 7 to 9 months, with the Ekman and non-Ekman exchange processes of approximately equal importance.

Analysis of the mean annual cycle of the dissolved oxygen anomaly in the World Ocean

A global climatology of the dissolved oxygen anomaly (the excess over saturation) is created with monthly resolution in the upper 500 m of the ocean. The climatology is based on dissolved oxygen, temperature and salinity data archived at the National Oceanographic Data Center. Examination of this climatology reveals statistically significant annual cycles throughout the upper 500 m of the World Ocean, though seasonal variations are most coherent in the North Atlantic, where data density is greatest. Vertical trends in the phase and amplitude of the annual cycle are noted. The cycle in surface waters is characterized by a summer maximum and a winter minimum, consistent with warming and high rates of photosynthesis during the summer, and cooling and entrainment of oxygen-depleted water during the winter. In low and middle latitudes, the amplitude increases with depth and the maximum occurs later in the year, a trend consistent with the seasonal accumulation of oxygen associated with the shallow oxygen maximum. At a depth that varies between about 30 and 130 m, the phase of the annual cycle undergoes an abrupt shift. We call this depth the oxygen nodal depth. Below the nodal depth, the annual cycle is characterized by an early-spring maximum and a late-fall minimum, consistent with a cycle dominated by respiration during the spring and summer and replenishment of oxygen from the atmosphere by ventilation during the fall and winter. Below the nodal depth, the amplitude of the annual cycle generally decreases with depth, indicative of decreasing respiration and ventilation rates, or less seasonality in both processes. We postulate that the nodal depth in middle and high latitudes corresponds closely to the summertime compensation depth, where photosynthesis and net community respiration are equal. With this interpretation of the nodal depth and a simple model of the penetration of light in the water column, a compensation light intensity of 1 W m -2 (4 μE m -2 s -1 ) is deduced, at the low end of independent estimates. Horizontal trends in the phase and amplitude of the annual cycle are also noted. We find that the nodal depth decreases toward the poles in both hemispheres and is generally greater in the Southern Hemisphere, patterns found to be consistent with light-based estimates of the compensation depth. The amplitude of the annual cycle in the oxygen anomaly increases monotonically with latitude, and higher latitudes lag lower latitudes. In the North Atlantic and North Pacific, the amplitude of the annual cycle tends to increase from east to west at all depths and latitudes, as expected considering that physical forcing has greater seasonal variability in the west. The tropics and the North Indian Ocean have features that distinguish them from other regions. Below about 75 m, these waters have pronounced annual cycles of the oxygen anomaly that are shown to be caused mainly by wind-driven adiabatic displacements of the thermocline. A semiannual cycle of the oxygen anomaly is found in the surface waters of the North Indian Ocean, consistent with the known semiannual cycle of surface heat flux in this region.

Surface heat flux in the Gulf of Maine

The surface heat flux in the Gulf of Maine is estimated on a daily basis for the period 1979–1987 by combining air temperature, water temperature and wind speed data measured at a NOAA buoy in the central Gulf with insolation data from coastal stations and climatological parameters. The heat flux is compared with water column temperatures measured during the same period. The mean annual cycle of heat flux is similar to that reported by Bunker (1976) and to the rate of change in the heat content of the upper 100 m of the water column across the Gulf. The interannual variability in heat flux is dominated by the latent and sensible heat flux terms during winter and by insolation variability during summer. In the western Gulf the interannual variability in water temperature is significantly correlated with the heat flux variations. In the eastern Gulf, no relationship is found and the temperature variability is believed dominated by advective changes.

Seasonal heat balance in the Gulf of California

Most of the available hydrographic data (1939–1988) from the Gulf of California are used to describe the seasonal cycle of heat storage in the upper 400 m of water. The seasonal cycle of surface heat flux is obtained by using the sea surface temperature from the hydrographic data bank and meteorological data from coastal stations along the gulf. Monthly values of surface heat flux and heat storage are fitted to a mean value plus an annual harmonic. The longitudinal (i.e., along‐gulf) heat flux is then obtained by integrating the difference between the rate of change of heat storage and the surface heat flux. It is found that the surface heat flux has a positive (into the sea) annual mean all along the gulf; the average annual net surface heat flux for the whole gulf being ∼118 W m−2. The southern part of the gulf gains more heat (∼130 W m−2) than the northern part (∼100 W m−2), owing to the larger loss by evaporation in the latter (∼0.6 m/yr versus ∼1 m/yr) caused by lower humidity and stronger winds. These values are in agreement with previous estimates for the northern gulf. The amplitude of the seasonal signal shows a maximum of ∼230 W m−2 in the central part. Winter heat losses occur only from the middle of the gulf, the Guaymas Basin, to its head. There is a strong annual signal superimposed on the average longitudinal heat flux, whose amplitude is larger than the annual harmonic of the surface heat flux. Input of heat from the Pacific Ocean occurs from mid‐March to mid‐July, with a maximum at the mouth in May (21×1012 W). Attempts to explain this flux by diffusive processes were unsuccessful. The proposition that advection is the main longitudinal heat carrier is congruent with the generally accepted circulation patterns.

Isopycnal and diapycnal circulation of the upper equatorial Atlantic Ocean in 1983–1984

Isopycnal circulation and diapycnal processes in the equatorial Atlantic Ocean are investigated using eight cruises from November 1982 to July 1984. An eastward decrease of the transport of the equatorial undercurrent is observed averaging 18.2 106 m3 s−1 at 35°W to 10.2 106 m3 s−1 at 4°W. There is also a meridional convergence at the undercurrent level and a larger meridional divergence in the surface layer of 15 106 m3 s−1 between 35°W and 4°W. In the eastern equatorial Atlantic, the undercurrent core density as well as the salinity above the undercurrent experience a large seasonal cycle. During the season where the eastern Atlantic thermocline is closest to the surface and surface waters are coldest, the current peaks in denser waters and subsurface salinity maximum are weaker. An analysis of the salinity on isopycnal surfaces indicates that there is significant diapycnal mixing in the upper thermocline. In the eastern Atlantic, the upper thermocline vertical heat diffusivity coefficient scaled over 1° of latitude varies between 3 cm2 s−1 during the upwelling season and nearly 0 early in the year. This seasonal mixing is an important element of undercurrent dynamics. The turbulent heat flux at the base of the surface layer averages 50 W m−2 between 1.5°N and 1.5°S. The surface layer heat budget implies an average oceanic gain of 60 W m−2 between 1.5°N and 1.5°S which could result from exchanges with the atmosphere. The heat flux and fresh water seasonal cycles needed to close the budgets are not realistic, however. The eastern equatorial Atlantic thermocline seasonal upwelling is associated with a large inflow into the surface layer. Over the two years, this flow averaging 11–12 × 106 m3 s−1 originates from the upper thermocline, and diapycnal transports near the core of the undercurrent or below are found to be small. Below the core of the undercurrent, we also find that mixing is not intense: for instance, at σθ = 26.5, in the upper part of the thermostad, vertical heat diffusivity is only 0.6 cm2 s−1 (assuming that mixing takes place over 1° of latitude). The uncertainties on these budgets are however large, and assumptions on the dynamics that were used could not be checked.

Response to high heat fluxes and metallurgical examination of a brazed carbon-fiber-composite/refractory-metal divertor mock-up

As a feasibility-study an actively cooled divertor mock-up has been subjected to high heat flux loading in electron beam simulation. The divertor design concept is based on a carbon-fiber-composite material (Aerolor 05) brazed onto a TZM/Mo41Re heat sink. The plasma facing carbon armor is divided in seven tiles to allow variable loading parameters - and repeated destructive tests. The mock-up has survived high heat flux loading up to about 12 MW/m 2 surface heat flux in steady-state conditions. One armor tile showed no change in the thermal response even after 500 s at ∼ 14 MW/m 2. To estimate the general thermal response of the mock-up design, numerical methods were applied. The predicted behavior was confirmed by the experimental results. The loading experiments were followed by a detailed metallurgical investigation of the loaded sample regions and the braze joints. The typical damages after high heat flux testing and cycling were failure (i.e. detachment) in the Zr brazed carbon/TZM joint, and failure in the CuPd bonded TZM/TZM joint due to an excess of the melting temperature of the brazes. The microstructural changes in the braze regions and the recrystallization behavior of the refractory alloys are discussed. Only in one case the loaded surface of the carbon armor shows considerable erosion, caused by a partial detachment along a braze joint and thus loss of the good thermal contact during the last applied loading shots. The thermal analyses and high heat flux performance of the Aerolor-05 armored mock-up are compared to the thermal response of a previously tested mock-up of corresponding geometry with armor tiles of isotropic graphite.

An energy balance climate model with hydrological cycle: 1. Model description and sensitivity to internal parameters

A thermodynamical model designed to illustrate the effect of a hydrological cycle on climate sensitivity is presented. The model contains three climatic variables: two temperatures referring to an idealized atmosphere and ocean, respectively, and atmospheric humidity. The independent variables are time and latitude. Atmosphere and ocean are coupled by radiation and convection at their interface. Some structure of the atmospheric circulation is retained by differentiating between the dynamics of a low latitude zone (0° ‐ ϕH) and that of a high latitude zone (ϕH‐90°), where ϕH ≈ 30° is the intersection of meridional temperature gradient and critical gradient for baroclinic instability. The atmospheric transport is split into an advective and a diffusive part, while the oceanic transport is approximated by pure diffusion. The coefficients associated with horizontal and vertical motion are modelled in terms of temperature gradients. The predicted water vapor gives rise to precipitation and clouds and influences (via cloud cover and greenhouse effect) the radiation balance of the system. The model is integrated for annual mean conditions until an asymptotic equilibrium is reached. The free (internal) parameters of the system are determined by optimization methods so that simulated temperature, heat flux and hydrological cycle are in close agreement with observations. The sensitivity of the model is governed by radiation parameters. Of these, the cloud albedo is the most sensitive quantity. By contrast, the model is relatively little affected by parameters associated with horizontal and vertical transport of heat.

The Annual Cycle of Meridional Heat Flux in the Atlantic Ocean at 26.5°N

Abstract Total meridional heat flux through a zonal oceanic section at 26.5°N in the Atlantic Ocean is computed from hydrographic, direct current and surface wind observations. The oceanic current and temperature fields are decomposed into depth-averaged and depth-dependent (including Ekman and geostrophic) components to perform the calculation. The mean annual boat flux is estimated to be 1.21 ± 0.34 PW. Mean monthly values of net heat flux are also computed from the data. The annual cycle of net heat flux determined from these values ranges from a minimum of 0.69 PW in February to a maximum of 1.86 PW in July. Thus, in contrast to an earlier estimate of the annual cycle of oceanic heat flux derived indirectly from surface energy fluxes and upper-layer heat content changes, there is no net southward heat flux during the Call. Results from a simulation of the circulation of the North Atlantic give an annual cycle of heat flux similar to our calculations with a summer maximum and winter minimum. However, t...

Large-Scale SST Variability in the Western North Atlantic Subtropical Convergence Zone during FASINEX. Part II: Upper Ocean Heat Balance and Frontogenesis

Abstract We analyzed the influence of wind-deriven horizontal heat advection on the large-scale [O(1000) km wavelength] variability of both the upper-ocean mixed-layer heat content and the subtropical frontal zone (SFZ) within an 11° by 10° domain in the western North Atlantic Ocean during FASINEX (January through June 1986). By estimating heat advection due to both Ekman transport and interior geostrophic (Sverdrup minus Ekman) transport from a slab mixed layer heat balance equation using satellite-derived sea surface temperature (Ts) and wind analysis maps, it was found that these processes could not account for the observed variability in either beat content or the SFZ. The annual cycle of surface vertical heat flux had the dominant influence on the heat content. Even when the average heat balance was analyzed during a 4-month time interval when the net influence of the annual cycle was nearly zero (mid-January to mid-May 1986), westward-propagating Ts spatial anomaly features with peak-to-peak scales ...

The latent and sensible heat fluxes over the western tropical pacific and its relationship to ENSO

In this paper the Bulk Aerodynamic Formulas are used to compute the latent and sensible heat fluxes over the area 8°S-20°N, 130°-180°E for each month from January 1950 through December 1979 by using the data set of COADS supplied by NOAA of USA. The annual and monthly geographical distributions and the seasonal cycle of heat fluxes are carried out and a seasonal change of heat fluxes for ENSO year is also obtained by compositing individual ENSO year including 1951, 1953, 1957, 1963, 1965, 1969, 1972 and 1976. It is found that during ENSO episodes positive anomalies of heat fluxes appeared during the period of March to July and negative anomalies from August to March of the following year. The time series of sum of heat fluxes for March, April, May, June and July in each year from 1950 through 1979 had a significant link to the eastern tropical Pacific SST index (Wright, 1983). The correlation coefficient was 0.56. As it is found that in the latter half of each ENSO year (August—December) the frequency of typhoon formation in the area studied is less than normal, we suggest that the negative anomalies of heat fluxes during the same period be a mechanism for the decreased frequency of typhoon formation.

Ocean/atmosphere heat fluxes within the Agulhas Retroflection region

The southern section of the Agulhas western boundary current system exhibits unique characteristics as regards ocean/atmosphere heat flux processes. The Agulhas Retroflection region's high heat flux core from 37°S to 41°S, 16°E to 22°E does not demonstrate a distinct annual cycle of turbulent heat fluxes (latent and sensible) as is characteristic of its northern hemisphere counterparts. Rather, a weak semiannual heat flux cycle is found with maximum average losses during winter and summer (200 and 211 W/m2 ) and minimum losses during spring and autumn (185 and 162 W/m2 ). Upstream where the Agulhas Current is closer to land, winter heat losses exceed those of summer, but the differences are small. This behavior contrasts with that encountered at the poleward ends of northern hemisphere western boundary currents where winter heat fluxes are several times those of summer. The main reason for this difference is persistent westerly and southwesterly wind flow over the Agulhas Retroflection region throughout the year which ensures that cold, unsaturated maritime air repeatedly forces loss of heat from the ocean's surface. Spatial heat flux gradients associated with the Agulhas‐Subtropical Convergence surface temperature front are more pronounced in summer than in winter, indicating that cyclogenesis locally may be less seasonally dependent than in the northern hemisphere situation. Average oceanic cooling rates in the core region of the Retroflection, based on net heat flux calculations and a mixed surface layer of 75 m, range from 1.35°C/month during winter to 0.25°C/month during summer. Interannual variability in ocean/atmosphere heat fluxes within the Agulhas Retroflection region often exceeds the variability illustrated by the annual cycle. West of the Agulhas Retroflection core region, interannual sea surface temperature (SST) anomalies are more influential in the generation of heat flux anomalies by virtue of their large temporal variability. This high SST variability is primarily attributed to interannual changes in flux of Agulhas Current water into the southeast Atlantic Ocean. Oceanic heat loss within this warm water zone is an important modifying influence to both ocean and atmosphere, thus meriting further research.

Surface heat flux in the northern Gulf of California

Recent coastal meteorological data (1979–1986) are used to evaluate the seasonal cycle of surface heat fluxes in the northern Gulf of California. Although net heat loss occurs from October to January, the annual mean of the net surface heat flux was found to be into the sea (69 W m−2 near the coast and 83 W m−2 offshore), with a mean evaporation rate ≃0.9 m yr−1. These results require an oceanic export of heat and salt out of the northern gulf to achieve a balance, and imply that the annual mean thermohaline circulation must have an inflowing component at depth, thus enriching the central and northern parts of the gulf. These results differ from previous meteorological estimates, which suggested a net surface heat loss, but confirm those based on hydrographic data.

Reduction of energy dissipations at thermally distorted pressed contacts

The macroscopic constriction that a heat flux experiences in passing between ‘isothermally flat’ stainless steel and copper surfaces, which are pressed together, can be alleviated by the insertion of a copper gauze. The overall joint conductance is usually increased (except with small heat fluxes for which the enhanced micro-constriction, due to the presence of the gauze, exceeds the macro-constriction it alleviates). A design is proposed for an insert that aids energy transfer across distorted contacts which may be exposed to prolonged heat flux and thermal cycling.

Thermal Regime of a Prairie Snowcover

AbstractAn energy budget approach was used to study the melting of a shallow prairie snowpack. In the analysis, all the terms of the energy budget were determined independently. The major source of energy for the melt was the net radiation flux. Over a continuous snowcover the contribution of sensible heat to the melt could not be represented by a simple low‐level temperature index, but was dependent on the energy content of the air mass. The latent heat flux responded to the radiation flux, with daytime evaporation and nighttime condensation, however the net daily flux was evaporative. Nighttime refreezing of the snowpack limited the runoff, with approximately 40% of the daily meltwater being retained or refrozen in the snowpack. Beneath the melting snowcover the diurnal cycle of soil heat flux was almost completely eliminated. Monitoring of soil moisture changes during the melt period showed that very little infiltration occurred until the soil had thawed.

Título en español.

Se realizó un breve análisis de las características climáticas e hidrológicas de Puerto Rico, interrelacionadas entre sí. Mediante la selección de estaciones típicas de las regiones norte, sur, central, valles interiores y del oeste, se presenta el curso anual de las temperaturas máximas y mínimas medias, así como el correspondiente cuadro pluviométrico. Todos los valores presentados representan promedios mensuales hasta 1970, inclusive, (20 a 70 años). Se discute brevemente la incidencia de sequías y se ofrece un enfoque agrícola del balance hidrológico. Se discute, además, la aplicabilidad de índices representativos de la disponibilidad de lluvia para las cosechas.

Calculations of temperature regime and heat budget of sea ice in the central Arctic

The equation of heat conduction, including variable thermal conductivity and specific heat, an internal heat source diminishing with depth, and an advective term, is integrated numerically for sea ice of equilibrium thickness. The annual cycle of thickness (ablation-accretion) is imposed as an external parameter. The boundary values for temperature and the vertical distribution of ice salinity are taken from empirical data. The computed temperature field is in good agreement with observations. The thermal history of individual particles of ice, the relative effect of the internal heat source (penetrating solar radiation), heat storage, and the annual cycle of heat flux by conduction at various depths are described. The observed maximum of brine volume at 40- to 70-cm depth is explained as the combined effect of salinity profile and internal absorption of radiation. The requirement that heat flux in the ice plus the heat equivalent of surface ablation equal the heat flux in the atmospheric boundary layer is well met by Badgley's values of radiative and turbulent heat transfer. During the melting season, June 15 to August 20, the surface of the ice receives about 4.5 kcal/cm2 and loses, during the freezing season, August 21 to June 14, an only slightly greater amount of heat to the atmosphere. The annual sum of heat conduction at the base of the ice is 3.6 kcal/cm2. Of this, 2.0 kcal/cm2 originates from ice accretion and 1.6 kcal/cm2 is drawn from the ocean. The atmosphere over the central Arctic receives an annual total of 2.5 kcal/cm2, which is mainly the heat of fusion of exported ice.