Changes In Heat Storage Research Articles

The dynamics of ocean heat transport variability

The north‐south heat transport is the prime manifestation of the ocean's role in global climate, but understanding of its variability has been fragmentary owing to uncertainties in observational analyses, limitations in models, and the lack of a convincing mechanism. We review the dynamics of global ocean heat transport variability, with an emphasis on timescales from monthly to interannual. We synthesize relatively simple dynamical ideas and show that together they explain heat transport variability in a state‐of‐the‐art, high‐resolution ocean general circulation model. Globally, the cross‐equatorial seasonal heat transport fluctuations are close to ±3 × 1015 W, the same amplitude as the cross‐equatorial seasonal atmospheric energy transport. The variability is concentrated within 20° of the equator and dominated by the annual cycle. The majority of the variability is due to wind‐induced current fluctuations in which the time‐varying wind drives Ekman layer mass transports that are compensated by depth‐independent return flows. The temperature difference between the mass transports gives rise to the time‐dependent heat transport. It is found that in the heat budget the divergence of the time‐varying heat transport is largely balanced by changes in heat storage. Despite the Ekman transport's strong impact on the time‐dependent heat transport, the largely depth‐independent character of its associated meridional overturning stream function means that it does not affect estimates of the time‐mean heat transport made by one‐time hydrographic surveys. Away from the tropics the heat transport variability associated with the depth‐independent gyre and depth‐dependent circulations is much weaker than the Ekman variability. The non‐Ekman contributions can amount to a 0.2–0.4 × 1015 W standard deviation in the heat transport estimated from a one‐time hydrographic survey.

The Surface-Layer Heat Balance in the Equatorial Pacific Ocean. Part II: Interannual Variability*

The surface-layer heat balance on interannual timescales in the equatorial Pacific has been examined in order to determine the processes responsible for sea surface temperature (SST) variability associated with warm and cold phases of the ENSO cycle (El Niño and La Niña). Principal datasets include multiyear time series of surface winds, upper-ocean temperature, and velocity obtained from the Tropical Atmosphere Ocean buoy array at four locations along the equator in the western (165°E), central (170°W), and eastern (140°W and 110°W) Pacific. A blended satellite/in situ SST product and surface heat fluxes based on the Comprehensive Ocean–Atmosphere Data Set are also used. Changes in heat storage, horizontal heat advection, and heat fluxes at the surface are estimated directly from data; vertical fluxes of heat out of the base of the mixed layer are calculated as a residual. Results indicate that all terms in the heat balance contribute to SST change on interannual timescales, depending on location and time period. Zonal advection is important everywhere, although relative to other processes, it is most significant in the central Pacific. The inferred vertical heat flux out of the base of the mixed layer is likewise important everywhere, especially so in the eastern equatorial Pacific where the mean thermocline is shallow. Meridional advection (primarily due to instability waves in this analysis) is a negative feedback term on SST change in the eastern equatorial Pacific, tending to counteract the development of warm and cold anomalies. Likewise, the net surface heat flux generally represents a negative feedback, tending to damp SST anomalies created by ocean dynamical processes. The implications of these results for ENSO modeling and theory are discussed.

A Coupled Ocean–Atmosphere System of SST Modulation for the Indian Ocean*

The net heat flux into the northern Indian Ocean is between 75 and 100 W m 22 during the boreal spring and early summer but only 10‐20 W m22 in the western Pacific during the entire year. The differences in the net surface heat fluxes arise from the radiation shielding by deep convective clouds over the western Pacific and the near absence of clouds over the northern Indian Ocean during spring. Despite the strong heat flux during the boreal spring and early summer, the northern Indian Ocean only warms by 38C over a 4-month period, much smaller than the 128C estimated using single ocean column models. Similarly, the cooling of the North Indian Ocean during the boreal winter is less than can be explained from thermodynamic processes. The tropical western Pacific Ocean sea surface temperature (SST), on the other hand, varies by only 18C throughout the year. Despite the different net surface fluxes of heat into the two warm pools, the magnitude of the annual cycle of SST in each basin is very small and is confined to lie between 268 and 308C. It is argued that SST regulation in the Pacific Ocean occurs as a combination of local thermodynamic balance with significant contributions from large-scale atmospheric circulations forced by SST gradients. On the other hand, the northern Indian Ocean SST is regulated by strong oceanic advection across the equator, southward during the boreal spring and early summer and northward during the boreal winter, and by changes in heat storage of the upper ocean. Cross-equatorial transports of heat vary from 0.5 PW southward in spring to 1.5 PW in summer. During the boreal winter, the heat fluxes reverse, averaging about 1 PW toward the north. Large oscillations of ocean heat transport are also noted on timescales of 20‐50 days. It is concluded that ocean heat transports are an essential process in the annual cycle of the Indian Ocean heat balance. Last, the results of the study are used to propose a coupled ocean‐atmosphere dynamic regulatory system for the annual cycle of the monsoon and the SST in the Indian Ocean.

An improved estimation of mean body temperature using combined direct calorimetry and thermometry.

The conventional method used to estimate the change in mean body temperature (dMBT) is by taking X% of a body core temperature and (1-X)% of weighted mean skin temperature, the value of X being dependent upon ambient temperature. This technique is used widely, despite opposition from calorimetrists. In the present paper we attempt to provide a better method. Minute-by-minute changes in dMBT, as assessed using calorimetry, and 21 (20 if esophageal temperature was unavailable) various regional temperatures (dRBTs), as assessed using thermometry, including 6 subcutaneous measures, were collected from 7 young male adults at 6 calorimeter temperatures. Since a calorimeter measures only changes in heat storage, which can be converted to dMBT, all body temperatures are expressed as changes from the reasonably constant pre-exposure temperatures. The following three aspects were investigated. (1) The prediction of dMBT from the 21 (or 20) dRBTs with multi-linear regression analysis (MLR). This yields two results, model A with rectal temperature (dTre) alone, and model B with dTre and esophageal temperature (dTes). (2) The prediction of dMBT from dTre with or without dTes and 13 skin surface temperatures combined to one weighted mean skin temperature (dTsk), using MLR. This results in models C and D. Six more models (E-J) were added, representing the above two sets in various combinations with four factors. (3) The conventional method calculated with four values for X. Model A predicted better than 0.3 degree C in 70% of the cases. Model I was the best amongst the models with 13 weighted skin temperatures (better than 0.3 degree C in 60% of the cases). The conventional method was erratic.

The Surface-Layer Heat Balance in the Equatorial Pacific Ocean. Part I: Mean Seasonal Cycle*

Abstract The surface-layer heat balance in the equatorial Pacific is examined in order to determine the processes responsible for the mean seasonal cycle of sea surface temperature (SST). Principal datasets include multiyear time series of surface winds, upper-ocean temperature, and velocity obtained from Tropical Atmosphere Ocean (TAO) buoy array at four locations along the equator in the western (165°E), central (170°W), and eastern (140° and 110°W) Pacific. A blended satellite–in situ SST product and climatological surface heat fluxes based on the Comprehensive Ocean–Atmosphere Data Set are also used. Changes in heat storage, horizontal heat advection, and heat fluxes at the surface are estimated directly from data; vertical fluxes of heat out of the base of the mixed layer are calculated as a residual. Results indicate that, of the terms that can be directly estimated, the net surface heat flux is generally the largest term in heat balance. Zonal heat advection is important at all locations and is gen...

Measuring very low frequency sea level variations using satellite altimeter data

Very low frequency (VLF) sea level variations are an important indicator of global climate change, and their measurement can provide important information for determining the socioeconomic impact of sea level change on coastal land use. The prospect of measuring VLF sea level variations has been assessed using approximately 5 years of satellite altimeter data from the TOPEX/POSEIDON (T/P) mission, where synoptic mapping of the geocentric height of the ocean surface is routinely achieved with a point-to-point accuracy of better than 4 cm. The global mean sea level variations measured by T/P every 10 days have an RMS of 4 mm and a rate of change +3.1±1.3 mm/year, after accounting for an average instrument drift computed using the global tide gauge network by Mitchum (1998). A likely cause of the observed instrument drift is the microwave radiometer, which provides the water vapor delay correction, which results in a revised estimate of +2.5 mm/year if the error is assumed to be linearly related to the mean water vapor delay. Approximately half of this rise appears related to an increase in sea level that began in mid-1996, thus it is unlikely to be sustained over the long term. Estimates of sea level change over the major ocean basins reveal that the North Atlantic has risen over the T/P mission, and this is believed to be related to decadal changes in heat storage. Maps of the geographic variability of the observed sea level trends are currently dominated by ENSO variations, and thus the climate change signals cannot currently be isolated. These results suggest that T/P, when combined with tide gauge monitoring of the satellite instruments, is achieving the necessary accuracy to distinguish sea level rise caused by climate change from the natural `background' rate of sea level rise, although a longer time series is necessary to average out possible interannual and decadal variations. A longer time series will also reduce the errors in estimates of the altimeter calibration, providing an important constraint on any long-term instrument drift. Future research will focus on establishing a more realistic error budget for these measurements of global mean sea level, so that they can be put in the proper context with other observations of global climate change. In addition, the study of the spatial variability of the sea level rise signal will become increasingly important as a longer time series is collected.

Modifying a Mesoscale Meteorological Model to Better Incorporate Urban Heat Storage: A Bulk-Parameterization Approach

Abstract A simple bulk-parameterization scheme is implemented in modifying a mesoscale meteorological model to better incorporate urban heat storage. The objective is to improve the quantification of the fluxes associated with heat storage change and to more explicitly account for the integrated effect of urban canopy layer fluxes on the overlying boundary layer. The approach involves integrating an Objective Hysteresis Model with a meteorological model, which, in this case, is the Colorado State University Mesoscale Model (CSUMM). When the resulting modified version of the model (MM) is applied to the Atlanta, Georgia, region, larger daytime urban heat islands are predicted (∼1.5°C larger) than with the nonmodified version of CSUMM. The largest simulated summer daytime Atlanta heat island for the modeling episode of 25–27 July is 1.4°C with CSUMM and 2.9°C with MM. The impacts of surface modifications, such as changes in urban albedo, on air temperature are slightly larger in MM than in CSUMM.

水温躍層調節とENSO位相変化における北西太平洋風変動の役割

Analysis of 17 years (1980-1996) of tropical Pacific thermocline variations indicates that short period (about 18 months) cycles in the early 1990s exhibit a relatively small meridional scale. The long period (4-5 year) cycles in the 1980s, associated with major basic-wide warming/cooling events, have much wider meridional scales. The dominant mode of interannual variation of thermocline depth can be approximately described by a basin-scale east-west seesaw oscillation, with an eastward propagation of thermocline depth anomalies occurring in the equatorial waveguide during the transition phases. The long-period ENSO cycles associated with the major basic-wide warming/cooling events involve a substantial change of heat storage in the western North Pacific (WNP) (5-15°N, 130-170°E). The tendency of thermocline displacement and local wind stress curl in the WNP exhibit a coherent, broad spectral peak on a 8-20 month time scale. The deepening (rising) of the thermocline occurs in phase with the local anticyclonic (cyclonic) wind stress forcing, suggesting the essential roles of the in situ wind forcing in thermocline adjustment. The surface wind variation in the western Pacific is found to play a critical role in the phase transition of ENSO cycles. During the mature phases of major warm episodes, there is a rapid establishment of an anomalous anticyclonic wind stress curl over the WNP. The anticyclonic wind stress deepens the WNP thermoline and starts a recharge of heat content in the warm pool. Meanwhile, the easterly anomalies to the south of the anticyclonic center elevate the thermocline in the equatorial western Pacific, and trigger an eastward migration of the rising thermocline along the equator, leading to cooling in the east. The transition from cooling to warming during the mature phases of cold episodes involves a similar process, but with opposite anomalies.

Simulation of heat storages and associated heat budgets in the Pacific Ocean: 2. Interdecadal timescale

We use a primitive equation isopycnal model of the Pacific Ocean to simulate and diagnose the anomalous heat balance on interdecadal timescales associated with heat storage changes observed from 1970–1988 in the expendable bathythermograph (XBT) data set. Given the smallness of the interdecadal signals compared to the El Niño‐Southern Oscillation (ENSO) signal, the agreement between model and observations is remarkably good. The total anomalous heat balance is made up of two parts, the diabatic part (from the model temperature equation) and the adiabatic part (from the model mass conservation equation) due to thermocline heave. We therefore describe our analysis of both the total and diabatic anomalous heat balances in four areas of the tropical and subtropical North Pacific Ocean in the upper 400 m. The interdecadal total (diabatic plus adiabatic) heat balance in the North Pacific Ocean is characterized by a complicated interplay of different physical processes, especially revealed in basin‐scale averages of the heat budget components that have comparable amounts of variance. In smaller subregions, simpler balances hold. For example, in the western equatorial Pacific (area 1) the total heat content tendency term is nearly zero, so that a simple balance exists between surface heat flux, vertical heat transport, and horizontal mixing. In the western subtropical Pacific the total heat content tendency balances the three‐dimensional divergence of the heat flux. We speculate that this complexity is indicative of multiple physical mechanisms involved in the generation of North Pacific interdecadal variability. The diabatic heat balance north of 24°N, a region of special interest to The World Ocean Circulation Experiment (WOCE), can be simplified to a balance between the tendency term, surface heat flux, and meridional advection, the last term dominated by anomalous advection of mean temperature gradients. For the western equatorial region the diabatic heat content tendency is nearly zero and the steady balance involves simply horizontal advection and the surface heat flux, which at these latitudes has a damping role in the model. An important finding of this study is the identification of two interdecadal timescales, roughly 10 and 20 years, both similar to those reported by other investigators in recent years. [Tourre et al., 1998; Latif and Barnett, 1994; Robertson, 1995; White et al, 1997; Gu and Philander, 1997; Jacobs et al., 1994]. The 20‐year timescale is only present in diabatic heat budget components, while the 10‐year timescale is present in both diabatic and adiabatic components. The 10‐year timescale can also be seen in the surface heat flux time series, but it occurs in the ocean adiabatic components which demonstrates the importance of oceanic adjustment through Rossby wave dynamics on decadal timescales.

Simulation of heat storages and associated heat budgets in the Pacific Ocean: 1. El Niño‐Southern Oscillation timescale

We use a primitive equation isopycnal model of the Pacific Ocean to simulate and diagnose the anomalous heat balance on El Niño‐Southern Oscillation, ENSO, timescales associated with heat storage changes observed in the expendable bathythermograph (XBT) data set. We focus on the analysis of the total (diabatic plus adiabatic) and diabatic anomalous heat balances in six areas of the tropical and subtropical North Pacific Ocean in the upper 400 m. The diabatic (i.e., from the model conservation temperature equation) and adiabatic (i.e., from the model mass conservation equation) anomalous heat balances add up to the total anomalous heat balance. We computed the adiabatic/diabatic ratios to infer the relative importance of both contributions in different areas and found that they are smaller than 2.0 in only two regions (western equatorial and central North Pacific). The larger ratios (>2) were found along the corridor where adiabatic anomalies propagate westward in the form of Rossby waves and at the eastern equatorial Pacific. For those areas where the adiabatic/diabatic ratio is higher than about 2 the total anomalous heat balance is dominantly between the temporal change of heat and the three‐dimensional divergence of the heat flux. At the central North Pacific area the total anomalous heat balance is between the temporal changes in anomalous heat, the surface heat flux and the vertical advection of heat. Different ENSO events are not always controlled by the same physical processes in the different areas. In many cases these differences are associated with the relative importance of adiabatic to diabatic processes. For instance, the western equatorial Pacific is controlled in general by diabatic processes, while the eastern equatorial Pacific is dominated by adiabatic physics most of the time.

Global upper ocean heat storage response to radiative forcing from changing solar irradiance and increasing greenhouse gas/aerosol concentrations

We constructed gridded fields of diabatic heat storage changes in the upper ocean from 20°S to 60°N from historical temperature profiles collected from 1955 to 1996. We filtered these 42 year records for periods of 8 to 15 years and 15 to 30 years, producing depth‐weighted vertical average temperature (DVT) changes from the sea surface to the top of the main pycnocline. Basin and global averages of these DVT changes reveal decadal and interdecadal variability in phase across the Indian, Pacific, Atlantic, and Global Oceans, each significantly correlated with changing surface solar radiative forcing at a lag of 0±2 years. Decadal and interdecadal changes in global average DVT are 0.06°±0.01°K and 0.04°K±0.01°K, respectively, the same as those expected from consideration of the Stefan‐Boltzmann radiation balance (i.e., 0.3°K per W m−2) in response to 0.1% changes in surface solar radiative forcing of 0.2 W m−2 and 0.15 W m−2, respectively. Global spatial patterns of DVT changes are similar to temperature changes simulated in coupled ocean‐atmosphere models, suggesting that natural modes of Earth's variability are phase‐locked to the solar irradiance cycle. A trend in global average DVT of 0.15°K over this 42 year record cannot be explained by changing surface solar radiative forcing. But when we consider the 0.5 W m−2 increase in surface radiative forcing estimated from the increase in atmospheric greenhouse gas and aerosol (GGA) concentrations over this period [Intergovernmental Panel on Climate Change, 1995], the Stefan‐Boltzmann radiation balance yields this observed change. Moreover, the sum of solar and GGA surface radiative forcing can explain the relatively sharp increase in global and basin average DVT in the late 1970's.

Measuring heat storage changes in the equatorial Pacific: A comparison between TOPEX altimetry and Tropical Atmosphere‐Ocean buoys

Heat storage variations in the equatorial Pacific have been studied from December 1992 through February 1997, using sea level data from the TOPEX altimeter and temperatures measured by 42 tethered buoys that are part of the Tropical Ocean‐Atmosphere (TAO) array. The TOPEX measurements are converted to heat storage anomalies using a coefficient determined from mean climatological values. For 30‐day averages the two measurements agree well over most of the region, except for the southwestern quadrant of the warm pool and a small region of the north‐central equatorial Pacific. In the southwestern quadrant the TOPEX measurements indicate a smaller long‐term heating rate than the TAO measurements, differing by as much as 30%. After examining conductivity‐temperature‐depth data in this region, it appears that the difference is due to a change in ocean salinity which is reflected in the TOPEX sea level measurements but not in the TAO heat measurements. The signal in the north‐central region is predominately at an annual period, but there is not enough external measurements to determine what the source of the difference is. In the remainder of the equatorial Pacific, the agreement between the data suggests that the TOPEX measurements can be used to measure heat storage variations in the upper layer with reasonable accuracy. Thus TOPEX altimeter data can provide information about the heat budget of the equatorial Pacific in regions where there are few or no direct measurements.

Seasonal Cycles of Meridional Overturning and Heat Transport of the Indian Ocean

A general circulation model of the Indian Ocean is fitted to monthly averaged climatological temperatures, salinities, and surface fluxes using the adjoint method. Interannual variability is minimized by penalizing the temporal drift from one seasonal cycle to another during a two-year integration. The resultant meridional overturning and heat transport display large seasonal variations, with maximum amplitudes of 18 and 22 (× 106 m3 s−1) for the overturning and 1.8 and 1.4 (× 1015 W) for heat transport near 10°S and 10°N, respectively. A dynamical decomposition of the overturning and heat transport shows that the time-varying Ekman flow plus its barotropic compensation can explain a large part of the seasonal variations in overturning and heat transport. The maximum variations at 10°N and 10°S are associated with monsoon reversal over the northern Indian Ocean and changes of the easterlies over the southern Indian Ocean. An external mode with variable topography has a moderate contribution where the Somali Current and the corresponding gyre reverse direction seasonally. Contribution from vertical shear (thermal wind and ageostrophic shear) is dominant near the southern boundary and large near the Somali Current latitudes. The dominant balance in the zonally integrated heat budget is between heat storage change and heat transport convergence except south of 15°S. Optimization with seasonal forcings improves estimates of sea surface temperatures, but the annual average overturning and heat transport are very similar to previous results with annual mean forcings. The annual average heat transport consists of roughly equal contributions from time-mean and time-varying fields of meridional velocities and temperatures in the northern Indian Ocean, indicating a significant rectification to the heat transport due to the time-varying fields. The time-mean and time-varying contributions are primarily due to the overturning and horizontal gyre, respectively. Inclusion of TOPEX data enhances the seasonal cycles of the estimated overturning and heat transport in the central Indian Ocean significantly and improves the estimated equatorial zonal flows but leads to unrealistic estimates of the velocity structure near the Indonesian Throughflow region, most likely owing to the deficiencies in the lateral boundary conditions.

Long‐period ocean heat storage rates and basin‐scale heat fluxes from TOPEX

Over 3 years of TOPEX altimeter data have been used to estimate annual heat storage and long‐period heat storage rates in 1° grids over the global oceans (65°S to 65°N). The mean annual heat storage rates computed from the TOPEX data agree with those computed from monthly‐mean temperatures to within 30 W m2. The accuracy of long‐term heat storage rates is estimated to be less than 10 W m2 over mid and low latitudes. Regional heat storage rates are larger than this error in many regions, most notably in the tropical Pacific and Indian Oceans and in the northern Atlantic Ocean. The heat storage changes associated with the 1991–1993 El Niño event are evident and agree with values computed from in situ measurements collected by the Tropical Ocean‐Global Atmosphere program Tropical Atmosphere Ocean array moorings. The heat storage rates inferred from TOPEX data are also shown to qualitatively agree with sea surface temperature rates computed over the same time period. Finally, heat storage rates are integrated over ocean gyres to estimate atmosphere‐ocean heat fluxes. Results suggest that from 1993 to 1995 the North Atlantic and the southern hemisphere gained heat from the atmosphere at a rate of between 1.5 and 2 W m2, while the North Pacific either lost heat or maintained zero net flux. However, the estimated error on this measurement is of the order of 1.5 W m2 indicating the true flux could be from 0 to 3 W m2. Both the TOPEX and temperature measurements suggest that the North Atlantic gained more heat per unit area than the North Pacific between 1992 and 1995.

Acoustic thermometry of ocean climate

The purpose of ATOC is to study climate variability in the oceans using three related techniques: (i) satellite altimetry, (ii) acoustic thermometry, and (iii) climate modeling. Satellite altimetry is related to ocean temperature by thermal expansion (melting glaciers are a secondary factor) with each mm of sea level rise corresponding to 15 to 30 mJ/m2 of stored thermal energy. Acoustic thermometry is associated with the temperature dependence of the speed of sound, and relates changes in the interior heat storage with small changes in acoustic travel times (10 ms at 5000 km, say). The THETIS experiment (Send, 1995; Menemenlis and Wunsch, 1996) in the western Mediterranean gives consistent results for the seasonal heat storage when all three techniques are combined; model prediction alone does not account for the observed changes. Fu and associates at JPL have reported on the changes in sea level measured by TOPEX-POSEIDON for the period 1992–5. For a global spatial average they obtain an astounding (but preliminary) 6 mm/year, but with regional departures by an order of magnitude. Some of the departures can be related to decadal variability. A comparison between the satellite and acoustic measurements is needed for interpretation. [Work supported by SERDP/ARPA.]

Sensitivity of the heat budget in a midlatitude ocean model to variations in atmospheric forcing

The rate of change of total heat storage in the ocean is determined primarily by the net heat fluxes across the air‐sea interface. In the context of a wind‐ and heat‐driven ocean model the long‐term mean heat budget was examined in a series of perturbation experiments in which atmospheric forcing parameters (surface winds and surface air temperature) were systematically varied. The thermodynamic effect of increasing surface wind speed is to take heat out of the mixed layer and thus cool the ocean. However, this wind‐induced cooling is overwhelmed by wind‐induced mechanical deepening of the mixed layer. A mixed layer deepened in this way is also cooler, so heat loss to the atmosphere is reduced. This ultimately leads to a warmer vertically integrated ocean. A change in wind stress forcing has little effect on total heat storage. Surface air temperatures are typically cooler than sea surface temperatures, so warmer air temperatures result in less heat flux out of the ocean, a warmer mixed layer, and more oceanic heat storage. The seasonal cycle is dominated by changes in radiative forcing to which the model responds exactly as it does to surface air temperature changes. As a result the model ocean stores less heat in winter (February–April) than in summer (August–October). The dependence of this seasonal change on mixed‐layer depth, mixed‐layer temperature and deep ocean temperature is quantified. Mixed‐layer depth is by far the most important controlling factor. Comparisons with climatological data from the North Atlantic and North Pacific Oceans confirm this general picture, although the comparisons suggest that the model mixed‐layer depth varies too much between seasons. The climatological data also indicate that the northern oceans store more heat in winter than in summer around 25°N. Possible explanations for this are discussed.

Inferring interannual changes in global upper ocean heat storage from TOPEX altimetry

Good agreement is found between global patterns of TOPEX dynamic height and expendable bathythermograph (XBT) heat storage anomalies from approximately 30°S to 60°N for the 2‐year period from 1993 to 1994, with both variables dominated by the biennial signal. This is due to the physical dependence of absolute dynamic height upon relative steric height (i.e., an alias of heat storage). Regression finds these two variables correlated from 0.5 to 0.8 over the global ocean, with slopes of regression ranging from 0.05 to 0.15×109 W−s m−2 cm−1. While these statistics are not definitive, they do provide representative estimates of regression error, sampling error, and sampling frequencies for determining the role that TOPEX altimetry can play in estimating upper ocean heat storage over large portions of the global ocean. We examine this role within the framework of optimum interpolation methodology (Gandin, 1963), finding regression errors for inferred heat storage anomalies larger than instrumental errors expected from XBT heat storage estimates but of the same order as uncertainties incurred from subgrid ambient noise. While this increases the noise‐to‐signal ratio of the inferred heat storage anomalies by a factor of 2, the greater density of TOPEX observations reduces the interpolation errors for gridded fields of upper ocean heat storage anomalies to half those incurred from the smaller density of XBT sampling. So, when inferred heat storage anomalies are used to compute the time sequence in upper ocean heat storage anomaly over large portions of the global ocean during 1993–1994, errors of ±2 W m−2 are half those achieved with XBT sampling. Moreover, the time rate of change in upper ocean heat storage anomalies becomes statistically significant, with inferred heat storage anomalies in the North Atlantic Ocean remaining constant for 1993–1994 but increasing in both the Indian and Pacific Oceans. The latter dominate the time rate of change of upper ocean heat storage anomaly over the global ocean, yielding an average rate of 3 W m−2 over the 2‐year period.

Seasonal heat storage in the North Pacific: 1976–1989

Volunteer observing ship expendable bathythermograph data obtained during the period 1976–1989, from 30°N to 40°N in the North Pacific, were used to compute the rate of change of heat storage to a fixed upper ocean temperature surface. The variability of the storage rate in the seasonal timescale, computed on a 5° latitude by 5° longitude spatial scale, is compared to the net surface heat flux computed from available surface marine weather data to the same spatial and temporal resolution. Averaged across the entire basin, the difference between the average monthly heat storage rate and the average monthly heat flux is 3.76 Wm−1. The average basin‐wide absolute heat storage rate agrees to within 7.5% of the average absolute heat flux for the whole basin. An empirical orthogonal decomposition of the spatial patterns of the difference between the heat storage rate and the net heat flux reveals no obvious trends in the heat flux computation or possible physical processes responsible for the difference. Instead, the eddies shed by the warm boundary current, the Kuroshio, is probably responsible for the major part of the difference patterns in locations where the difference values are maximum. The most important results of this study are that the heat storage rate computed to a fixed isotherm matches the net heat flux extremely well at the chosen locations and across the whole basin; and the heat storage rate computation is sensitive to the isotherm choice and to the space scale involved.

Including the heat storage term in sap flow measurements with the stem heat balance method

The importance of the change in stem temperature and therefore the heat storage term in the stem heat balance method of measuring sap flow is examined. Results from a range of measurements on a model stem, potted sunflower plants in a glasshouse, and Guiera senegalensis shrubs in the Sahel, Niger, are presented. A novel analysis of the heat balance in zero flow conditions allows the accurate determination of the gauge radial conductance and the stem segment heat capacity, both of which are required for accurate sap flow measurement with good dynamic resolution in low flow conditions. In high sap flow conditions the change in heat storage constitutes only a small component of the balance, and can be neglected, especially for small stems. The improved accuracy and dynamic resolution for stems of any size if heat storage is included allowed the measurement of low night-time flows during rehydration, and of redistribution of water between stems of G. senegalensis bushes in the field following rain.

The physiology of heat regulation

Heat regulation is presented as the physiological method of handling metabolic heat, instead of temperature regulation. Experimental evidence of heat regulation from the literature is reviewed, including more than 20 years of calorimetric studies by the author. Changes in heat production are followed by slow exponential changes in heat loss, which produce changes in body heat storage. Heat balance occurs at many levels of heat production throughout the day and night, and at each level there is a related level of rectal temperature. Heat flow can be sensed by the transcutaneous temperature gradient. The controller for heat loss appears to operate like a servomechanism, with feedback from heat loss and possibly feedforward from heat production. Physiological responses defend the body heat content, but heat content varies over a range that is related to heat load. Changes in body heat content drive deep body temperatures.