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Abstract
Building on recent observational evidence showing disproportionate increases in temperature and aridity over land in a warming climate, this study examines simulated land–ocean contrasts in fully coupled projections from the Third Coupled Model Intercomparison Project (CMIP3) archive. In addition to the projection of disproportionate changes in temperature and moisture over land, the analysis reveals contrasts in clouds and radiative fluxes that play a key role in the eventual equilibration of the planetary energy budget in response to forcing. Despite differences in magnitude, the nature of the feedbacks governing the land–ocean contrast are largely robust across models, notwithstanding the large intermodel differences in cloud parameterizations, and suggest the involvement of fundamental constraints.
The model responses are consistent with previously proposed ideas maintaining that relative humidity (RH) over land decreases with warming because precipitation and the hydrological cycle are governed primarily by transports of moisture from the oceans, where increases in lower-tropospheric temperature and saturated humidity fail to keep pace with those over land. Here, it is argued additionally that constraints on RH imply systematic changes in the cloud distribution and radiative feedbacks over land, as decreased RH raises the lifting condensation level, even as moist instability increases, and suppresses convective clouds. This effect is shown to be particularly strong at low latitudes where the dynamical influence of competing sources of maritime deep convection may further suppress convection. It is found that as a result of the coincidence between strong warming and a muted net greenhouse feedback associated with decreases in RH and clouds, the mean increase in outgoing longwave radiation (OLR) over land (1.0 W m−2 K−1) in transient simulations at 2200 is almost double that over the ocean (0.6 W m−2 K−1), and a strong negative net top-of-atmosphere (TOA) radiative perturbation emerges as the simulations approach and attain equilibrium. However, over the oceans a positive radiative imbalance persists and the increase in water vapor and other greenhouse gases does not allow a local TOA equilibration to occur. The contrast results in an increase in the transport of energy from ocean to land relative to the twentieth century that is accompanied by lasting increases in both OLR and absorbed shortwave radiation globally.
A conceptual model to describe the simulated variability is proposed that involves the following: 1) the differing albedos and lower-tropospheric lapse rates over land and ocean, 2) the nonlinearity of the saturated lapse rate in a warming environment, and 3) the disproportionate response in temperature, moisture, clouds, and radiation over land versus ocean. It is noted that while the land–ocean contrast plays a key role in achieving global radiative equilibrium, it entails disproportionate increases in temperature and aridity over land and therefore is likely to be associated with substantial environmental impacts.
Abstract
Building on recent observational evidence showing disproportionate increases in temperature and aridity over land in a warming climate, this study examines simulated land–ocean contrasts in fully coupled projections from the Third Coupled Model Intercomparison Project (CMIP3) archive. In addition to the projection of disproportionate changes in temperature and moisture over land, the analysis reveals contrasts in clouds and radiative fluxes that play a key role in the eventual equilibration of the planetary energy budget in response to forcing. Despite differences in magnitude, the nature of the feedbacks governing the land–ocean contrast are largely robust across models, notwithstanding the large intermodel differences in cloud parameterizations, and suggest the involvement of fundamental constraints.
The model responses are consistent with previously proposed ideas maintaining that relative humidity (RH) over land decreases with warming because precipitation and the hydrological cycle are governed primarily by transports of moisture from the oceans, where increases in lower-tropospheric temperature and saturated humidity fail to keep pace with those over land. Here, it is argued additionally that constraints on RH imply systematic changes in the cloud distribution and radiative feedbacks over land, as decreased RH raises the lifting condensation level, even as moist instability increases, and suppresses convective clouds. This effect is shown to be particularly strong at low latitudes where the dynamical influence of competing sources of maritime deep convection may further suppress convection. It is found that as a result of the coincidence between strong warming and a muted net greenhouse feedback associated with decreases in RH and clouds, the mean increase in outgoing longwave radiation (OLR) over land (1.0 W m−2 K−1) in transient simulations at 2200 is almost double that over the ocean (0.6 W m−2 K−1), and a strong negative net top-of-atmosphere (TOA) radiative perturbation emerges as the simulations approach and attain equilibrium. However, over the oceans a positive radiative imbalance persists and the increase in water vapor and other greenhouse gases does not allow a local TOA equilibration to occur. The contrast results in an increase in the transport of energy from ocean to land relative to the twentieth century that is accompanied by lasting increases in both OLR and absorbed shortwave radiation globally.
A conceptual model to describe the simulated variability is proposed that involves the following: 1) the differing albedos and lower-tropospheric lapse rates over land and ocean, 2) the nonlinearity of the saturated lapse rate in a warming environment, and 3) the disproportionate response in temperature, moisture, clouds, and radiation over land versus ocean. It is noted that while the land–ocean contrast plays a key role in achieving global radiative equilibrium, it entails disproportionate increases in temperature and aridity over land and therefore is likely to be associated with substantial environmental impacts.
Abstract
Using the National Center for Atmospheric Research Community Climate Model, version 3, radiation transfer model and a realistic tropospheric environment including the International Satellite Cloud Climatology Project cloud fields, all-sky radiative sensitivity to water vapor is assessed. The analysis improves upon previous clear-sky and model-based studies by using observed clouds, assessing realistic vertically varying perturbations, and considering spatial gradients in sensitivity through the Tropics and subtropics. The linearity of sensitivity is also explored. The dry zones of the subtropics and the eastern Pacific Ocean are found to be particularly sensitive to the water vapor distribution, especially for variations in the upper troposphere. The cloud field is instrumental in determining spatial gradients in sensitivity both at the top of the atmosphere and the surface. Throughout the Tropics, outgoing longwave radiation is most sensitive to water vapor in the upper troposphere, especially when perturbations characteristic of either natural variations or measurement uncertainties are considered. In contrast, surface radiative fluxes are everywhere most sensitive to specific humidity variations in the lower troposphere.
Abstract
Using the National Center for Atmospheric Research Community Climate Model, version 3, radiation transfer model and a realistic tropospheric environment including the International Satellite Cloud Climatology Project cloud fields, all-sky radiative sensitivity to water vapor is assessed. The analysis improves upon previous clear-sky and model-based studies by using observed clouds, assessing realistic vertically varying perturbations, and considering spatial gradients in sensitivity through the Tropics and subtropics. The linearity of sensitivity is also explored. The dry zones of the subtropics and the eastern Pacific Ocean are found to be particularly sensitive to the water vapor distribution, especially for variations in the upper troposphere. The cloud field is instrumental in determining spatial gradients in sensitivity both at the top of the atmosphere and the surface. Throughout the Tropics, outgoing longwave radiation is most sensitive to water vapor in the upper troposphere, especially when perturbations characteristic of either natural variations or measurement uncertainties are considered. In contrast, surface radiative fluxes are everywhere most sensitive to specific humidity variations in the lower troposphere.
Abstract
The warm tropical oceans underlie the most convective regions on earth and are a critical component of the earth’s climate, yet there are differing opinions on the processes that control warm pool SST. The Indo–Pacific warm pool is characterized by large-scale variations in SST approaching 30°C on intraseasonal timescales. In this study, surface heat flux anomalies associated with composite warm episodes over three spatial scales in both the Pacific and Indian Ocean basins are examined.
The current study benefits from the recently available National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset that enables the examination of variability in surface evaporation with moderate confidence. Solar flux estimates from the reanalysis are somewhat less reliable than evaporation estimates, however, and two techniques that infer surface shortwave radiation from satellite retrievals of cloud properties are considered. Error in all measurements is quantified.
Both shortwave and evaporative flux variability play significant roles in modifying the temperature of the warm pool, though the relative importance of individual flux anomalies depends on SST tendency and geographical location. There also exist differences in the relative heating roles of the flux anomalies among episodes within a fixed location, though in instances the resolved differences are less than likely flux estimation error. Differences also exist between the ocean basins. A more pronounced annual cycle exists in the eastern Indian Ocean, and SST there is less sensitive to surface thermal forcing. Finally, the analysis offers evidence that SST is not regulated by a simple atmospheric thermodynamic response to the surface. Instead, the relationship between warm pool variability and large-scale dynamical features of the Tropics (e.g., intraseasonal oscillation and the seasonal monsoon) is demonstrated. The conclusions are shown to be robust to spatial scale and are consistent with a recent analysis of Tropical Oceans and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment observations.
Abstract
The warm tropical oceans underlie the most convective regions on earth and are a critical component of the earth’s climate, yet there are differing opinions on the processes that control warm pool SST. The Indo–Pacific warm pool is characterized by large-scale variations in SST approaching 30°C on intraseasonal timescales. In this study, surface heat flux anomalies associated with composite warm episodes over three spatial scales in both the Pacific and Indian Ocean basins are examined.
The current study benefits from the recently available National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset that enables the examination of variability in surface evaporation with moderate confidence. Solar flux estimates from the reanalysis are somewhat less reliable than evaporation estimates, however, and two techniques that infer surface shortwave radiation from satellite retrievals of cloud properties are considered. Error in all measurements is quantified.
Both shortwave and evaporative flux variability play significant roles in modifying the temperature of the warm pool, though the relative importance of individual flux anomalies depends on SST tendency and geographical location. There also exist differences in the relative heating roles of the flux anomalies among episodes within a fixed location, though in instances the resolved differences are less than likely flux estimation error. Differences also exist between the ocean basins. A more pronounced annual cycle exists in the eastern Indian Ocean, and SST there is less sensitive to surface thermal forcing. Finally, the analysis offers evidence that SST is not regulated by a simple atmospheric thermodynamic response to the surface. Instead, the relationship between warm pool variability and large-scale dynamical features of the Tropics (e.g., intraseasonal oscillation and the seasonal monsoon) is demonstrated. The conclusions are shown to be robust to spatial scale and are consistent with a recent analysis of Tropical Oceans and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment observations.
Abstract
Meridional structure and transports of energy in the atmosphere, ocean, and land are evaluated holistically for the mean and annual cycle zonal averages over the ocean, land, and global domains, with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and Earth’s Radiant Energy System (CERES) are used along with estimates of energy storage and transport from two global reanalysis datasets for the atmosphere. Three ocean temperature datasets are used to assess changes in the ocean heat content (OE ) and their relationship to the net upward surface energy flux over ocean (F o S ), which is derived from the residual of the TOA and atmospheric energy budgets. The surface flux over land is from a stand-alone simulation of the Community Land Model forced by observed fields.
In the extratropics, absorbed solar radiation (ASR) achieves a maximum in summer with peak values near the solstices. Outgoing longwave radiation (OLR) maxima also occur in summer but lag ASR by 1–2 months, consistent with temperature maxima over land. In the tropics, however, OLR relates to high cloud variations and peaks late in the dry monsoon season, while the OLR minima in summer coincide with deep convection in the monsoon trough at the height of the rainy season. Most of the difference between the TOA radiation and atmospheric energy storage tendency is made up by a large heat flux into the ocean in summer and out of the ocean in winter. In the Northern Hemisphere, the transport of energy from ocean to land regions is substantial in winter, and modest in summer. In the Southern Hemisphere extratropics, land − ocean differences play only a small role and the main energy transport by the atmosphere and ocean is poleward. There is reasonably good agreement between F o S and observed changes in OE , except for south of 40°S, where differences among several ocean datasets point to that region as the main source of errors in achieving an overall energy balance. The winter hemisphere atmospheric circulation is the dominant contributor to poleward energy transports outside of the tropics [6–7 PW (1 petawatt = 1015 W)], with summer transports being relatively weak (∼3 PW)—slightly more in the Southern Hemisphere and slightly less in the Northern Hemisphere. Ocean transports outside of the tropics are found to be small (<2 PW) for all months. Strong cross-equatorial heat transports in the ocean of up to 5 PW exhibit a large annual cycle in phase with poleward atmospheric transports of the winter hemisphere.
Abstract
Meridional structure and transports of energy in the atmosphere, ocean, and land are evaluated holistically for the mean and annual cycle zonal averages over the ocean, land, and global domains, with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and Earth’s Radiant Energy System (CERES) are used along with estimates of energy storage and transport from two global reanalysis datasets for the atmosphere. Three ocean temperature datasets are used to assess changes in the ocean heat content (OE ) and their relationship to the net upward surface energy flux over ocean (F o S ), which is derived from the residual of the TOA and atmospheric energy budgets. The surface flux over land is from a stand-alone simulation of the Community Land Model forced by observed fields.
In the extratropics, absorbed solar radiation (ASR) achieves a maximum in summer with peak values near the solstices. Outgoing longwave radiation (OLR) maxima also occur in summer but lag ASR by 1–2 months, consistent with temperature maxima over land. In the tropics, however, OLR relates to high cloud variations and peaks late in the dry monsoon season, while the OLR minima in summer coincide with deep convection in the monsoon trough at the height of the rainy season. Most of the difference between the TOA radiation and atmospheric energy storage tendency is made up by a large heat flux into the ocean in summer and out of the ocean in winter. In the Northern Hemisphere, the transport of energy from ocean to land regions is substantial in winter, and modest in summer. In the Southern Hemisphere extratropics, land − ocean differences play only a small role and the main energy transport by the atmosphere and ocean is poleward. There is reasonably good agreement between F o S and observed changes in OE , except for south of 40°S, where differences among several ocean datasets point to that region as the main source of errors in achieving an overall energy balance. The winter hemisphere atmospheric circulation is the dominant contributor to poleward energy transports outside of the tropics [6–7 PW (1 petawatt = 1015 W)], with summer transports being relatively weak (∼3 PW)—slightly more in the Southern Hemisphere and slightly less in the Northern Hemisphere. Ocean transports outside of the tropics are found to be small (<2 PW) for all months. Strong cross-equatorial heat transports in the ocean of up to 5 PW exhibit a large annual cycle in phase with poleward atmospheric transports of the winter hemisphere.
Abstract
The energy budget of the modern-day Southern Hemisphere is poorly simulated in both state-of-the-art reanalyses and coupled global climate models. The ocean-dominated Southern Hemisphere has low surface reflectivity and therefore its albedo is particularly sensitive to cloud cover. In modern-day climates, mainly because of systematic deficiencies in cloud and albedo at mid- and high latitudes, too much solar radiation enters the ocean. Along with too little radiation absorbed at lower latitudes because of clouds that are too bright, unrealistically weak poleward transports of energy by both the ocean and atmosphere are generally simulated in the Southern Hemisphere. This implies too little baroclinic eddy development and deficient activity in storm tracks. However, projections into the future by coupled climate models indicate that the Southern Ocean features a robust and unique increase in albedo, related to clouds, in association with an intensification and poleward shift in storm tracks that is not observed at any other latitude. Such an increase in cloud may be untenable in nature, as it is likely precluded by the present-day ubiquitous cloud cover that models fail to capture. There is also a remarkably strong relationship between the projected changes in clouds and the simulated current-day cloud errors. The model equilibrium climate sensitivity is also significantly negatively correlated with the Southern Hemisphere energy errors, and only the more sensitive models are in the range of observations. As a result, questions loom large about how the Southern Hemisphere will actually change as global warming progresses, and a better simulation of the modern-day climate is an essential first step.
Abstract
The energy budget of the modern-day Southern Hemisphere is poorly simulated in both state-of-the-art reanalyses and coupled global climate models. The ocean-dominated Southern Hemisphere has low surface reflectivity and therefore its albedo is particularly sensitive to cloud cover. In modern-day climates, mainly because of systematic deficiencies in cloud and albedo at mid- and high latitudes, too much solar radiation enters the ocean. Along with too little radiation absorbed at lower latitudes because of clouds that are too bright, unrealistically weak poleward transports of energy by both the ocean and atmosphere are generally simulated in the Southern Hemisphere. This implies too little baroclinic eddy development and deficient activity in storm tracks. However, projections into the future by coupled climate models indicate that the Southern Ocean features a robust and unique increase in albedo, related to clouds, in association with an intensification and poleward shift in storm tracks that is not observed at any other latitude. Such an increase in cloud may be untenable in nature, as it is likely precluded by the present-day ubiquitous cloud cover that models fail to capture. There is also a remarkably strong relationship between the projected changes in clouds and the simulated current-day cloud errors. The model equilibrium climate sensitivity is also significantly negatively correlated with the Southern Hemisphere energy errors, and only the more sensitive models are in the range of observations. As a result, questions loom large about how the Southern Hemisphere will actually change as global warming progresses, and a better simulation of the modern-day climate is an essential first step.
Abstract
Monthly net surface energy fluxes (FS ) over the oceans are computed as residuals of the atmospheric energy budget using top-of-atmosphere (TOA) net radiation (RT ) and the complete atmospheric energy (AE ) budget tendency (δ AE /δ t) and divergence (∇ · F A ). The focus is on TOA radiation from the Earth Radiation Budget Experiment (ERBE) (February 1985–April 1989) and the Clouds and Earth’s Radiant Energy System (CERES) (March 2000–May 2004) satellite observations combined with results from two atmospheric reanalyses and three ocean datasets that enable a comprehensive estimate of uncertainties. Surface energy flux departures from the annual mean and the implied annual cycle in “equivalent ocean energy content” are compared with the directly observed ocean energy content (OE ) and tendency (δOE /δt) to reveal the inferred annual cycle of divergence (∇ · F O ). In the extratropics, the surface flux dominates the ocean energy tendency, although it is supplemented by ocean Ekman transports that enhance the annual cycle in ocean heat content. In contrast, in the tropics, ocean dynamics dominate OE variations throughout the year in association with the annual cycle in surface wind stress and the North Equatorial Current. An analysis of the regional characteristics of the first joint empirical orthogonal function (EOF) of FS , δOE /δt, and ∇ · F O is presented, and the largest sources of uncertainty are attributed to variations in OE . The mean and annual cycle of zonal mean global ocean meridional heat transports are estimated. The annual cycle reveals the strongest poleward heat transports in each hemisphere in the cold season, from November to April in the north and from May to October in the south, with a substantial across-equatorial transport, exceeding 4 PW in some months. Annual mean results do not differ greatly from some earlier estimates, but the sources of uncertainty are exposed. Comparison of annual means with direct ocean observations gives reasonable agreement, except in the North Atlantic, where transports from the ocean transects are slightly greater than the estimates presented here.
Abstract
Monthly net surface energy fluxes (FS ) over the oceans are computed as residuals of the atmospheric energy budget using top-of-atmosphere (TOA) net radiation (RT ) and the complete atmospheric energy (AE ) budget tendency (δ AE /δ t) and divergence (∇ · F A ). The focus is on TOA radiation from the Earth Radiation Budget Experiment (ERBE) (February 1985–April 1989) and the Clouds and Earth’s Radiant Energy System (CERES) (March 2000–May 2004) satellite observations combined with results from two atmospheric reanalyses and three ocean datasets that enable a comprehensive estimate of uncertainties. Surface energy flux departures from the annual mean and the implied annual cycle in “equivalent ocean energy content” are compared with the directly observed ocean energy content (OE ) and tendency (δOE /δt) to reveal the inferred annual cycle of divergence (∇ · F O ). In the extratropics, the surface flux dominates the ocean energy tendency, although it is supplemented by ocean Ekman transports that enhance the annual cycle in ocean heat content. In contrast, in the tropics, ocean dynamics dominate OE variations throughout the year in association with the annual cycle in surface wind stress and the North Equatorial Current. An analysis of the regional characteristics of the first joint empirical orthogonal function (EOF) of FS , δOE /δt, and ∇ · F O is presented, and the largest sources of uncertainty are attributed to variations in OE . The mean and annual cycle of zonal mean global ocean meridional heat transports are estimated. The annual cycle reveals the strongest poleward heat transports in each hemisphere in the cold season, from November to April in the north and from May to October in the south, with a substantial across-equatorial transport, exceeding 4 PW in some months. Annual mean results do not differ greatly from some earlier estimates, but the sources of uncertainty are exposed. Comparison of annual means with direct ocean observations gives reasonable agreement, except in the North Atlantic, where transports from the ocean transects are slightly greater than the estimates presented here.
Abstract
As observations and atmospheric reanalyses have improved, the diagnostics that can be computed with confidence also increase. Accordingly, a new formulation of the energetics of the atmosphere is laid out, with a view to advancing diagnostic studies of Earth’s energy budget and flows. It is utilized to produce assessments of the vertically integrated divergences in both the atmosphere and ocean. Careful conservation of mass is required, with special attention given to the hydrological cycle and redistribution of mass associated with precipitation and evaporation, and a new method for ensuring this is developed. It guarantees that the atmospheric divergence is associated with moisture and precipitation, unlike previous methods. A new term, identified as associated with the enthalpy of precipitation, is included in a preliminary way. It is sensitive to the formulation, and the use of temperature in degrees Celsius instead of Kelvin greatly reduces errors and produces the extra term with values up to about ±5 W m−2. New results for 2000 to 2016 are presented for the vertical-mean and annual-mean diabatic atmospheric heating, atmospheric moistening, and total atmospheric energy divergence. Results for the atmospheric divergence are combined with top-of-atmosphere radiation observations to deduce total surface energy fluxes. Along with estimates of changes in ocean heat content, the Atlantic Ocean meridional heat transports are recomputed for March 2000 through 2013. The new results are compared with previous estimates and an assessment is made of the effects of the new mass balance, change in temperature scale, and the extra precipitation enthalpy term.
Abstract
As observations and atmospheric reanalyses have improved, the diagnostics that can be computed with confidence also increase. Accordingly, a new formulation of the energetics of the atmosphere is laid out, with a view to advancing diagnostic studies of Earth’s energy budget and flows. It is utilized to produce assessments of the vertically integrated divergences in both the atmosphere and ocean. Careful conservation of mass is required, with special attention given to the hydrological cycle and redistribution of mass associated with precipitation and evaporation, and a new method for ensuring this is developed. It guarantees that the atmospheric divergence is associated with moisture and precipitation, unlike previous methods. A new term, identified as associated with the enthalpy of precipitation, is included in a preliminary way. It is sensitive to the formulation, and the use of temperature in degrees Celsius instead of Kelvin greatly reduces errors and produces the extra term with values up to about ±5 W m−2. New results for 2000 to 2016 are presented for the vertical-mean and annual-mean diabatic atmospheric heating, atmospheric moistening, and total atmospheric energy divergence. Results for the atmospheric divergence are combined with top-of-atmosphere radiation observations to deduce total surface energy fluxes. Along with estimates of changes in ocean heat content, the Atlantic Ocean meridional heat transports are recomputed for March 2000 through 2013. The new results are compared with previous estimates and an assessment is made of the effects of the new mass balance, change in temperature scale, and the extra precipitation enthalpy term.
Abstract
The mean and annual cycle of energy flowing into the climate system and its storage, release, and transport in the atmosphere, ocean, and land surface are estimated with recent observations. An emphasis is placed on establishing internally consistent quantitative estimates with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth’s Radiant Energy System (CERES) are used, while in the atmosphere the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) estimates are used. The net upward surface flux (FS ) over ocean is derived as the residual of the TOA and atmospheric energy budgets, and is compared with direct calculations of ocean heat content (OE ) and its tendency (δOE /δt) from several ocean temperature datasets. Over land, FS from a stand-alone simulation of the Community Land Model forced by observed fields is used. A depiction of the full energy budget based on ERBE fluxes from 1985 to 1989 and CERES fluxes from 2000 to 2004 is constructed that matches estimates of the global, global ocean, and global land imbalances. In addition, the annual cycle of the energy budget during both periods is examined and compared with ocean heat content changes.
The near balance between the net TOA radiation (RT ) and FS over ocean and thus with OE , and between RT and atmospheric total energy divergence over land, are documented both in the mean and for the annual cycle. However, there is an annual mean transport of energy by the atmosphere from ocean to land regions of 2.2 ± 0.1 PW (1 PW = 1015 W) primarily in the northern winter when the transport exceeds 5 PW. The global albedo is dominated by a semiannual cycle over the oceans, but combines with the large annual cycle in solar insolation to produce a peak in absorbed solar and net radiation in February, somewhat after the perihelion, and with the net radiation 4.3 PW higher than the annual mean, as it is enhanced by the annual cycle of outgoing longwave radiation that is dominated by land regions. In situ estimates of the annual variation of OE are found to be unrealistically large. Challenges in diagnosing the interannual variability in the energy budget and its relationship to climate change are identified in the context of the episodic and inconsistent nature of the observations.
Abstract
The mean and annual cycle of energy flowing into the climate system and its storage, release, and transport in the atmosphere, ocean, and land surface are estimated with recent observations. An emphasis is placed on establishing internally consistent quantitative estimates with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth’s Radiant Energy System (CERES) are used, while in the atmosphere the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) estimates are used. The net upward surface flux (FS ) over ocean is derived as the residual of the TOA and atmospheric energy budgets, and is compared with direct calculations of ocean heat content (OE ) and its tendency (δOE /δt) from several ocean temperature datasets. Over land, FS from a stand-alone simulation of the Community Land Model forced by observed fields is used. A depiction of the full energy budget based on ERBE fluxes from 1985 to 1989 and CERES fluxes from 2000 to 2004 is constructed that matches estimates of the global, global ocean, and global land imbalances. In addition, the annual cycle of the energy budget during both periods is examined and compared with ocean heat content changes.
The near balance between the net TOA radiation (RT ) and FS over ocean and thus with OE , and between RT and atmospheric total energy divergence over land, are documented both in the mean and for the annual cycle. However, there is an annual mean transport of energy by the atmosphere from ocean to land regions of 2.2 ± 0.1 PW (1 PW = 1015 W) primarily in the northern winter when the transport exceeds 5 PW. The global albedo is dominated by a semiannual cycle over the oceans, but combines with the large annual cycle in solar insolation to produce a peak in absorbed solar and net radiation in February, somewhat after the perihelion, and with the net radiation 4.3 PW higher than the annual mean, as it is enhanced by the annual cycle of outgoing longwave radiation that is dominated by land regions. In situ estimates of the annual variation of OE are found to be unrealistically large. Challenges in diagnosing the interannual variability in the energy budget and its relationship to climate change are identified in the context of the episodic and inconsistent nature of the observations.
Abstract
An accurate diagnosis of ocean heat content (OHC) is essential for interpreting climate variability and change, as evidenced for example by the broad range of hypotheses that exists for explaining the recent hiatus in global mean surface warming. Potential insights are explored here by examining relationships between OHC and sea surface height (SSH) in observations and two recently available large ensembles of climate model simulations from the mid-twentieth century to 2100. It is found that in decadal-length observations and a model control simulation with constant forcing, strong ties between OHC and SSH exist, with little temporal or spatial complexity. Agreement is particularly strong on monthly to interannual time scales. In contrast, in forced transient warming simulations, important dependencies in the relationship exist as a function of region and time scale. Near Antarctica, low-frequency SSH variability is driven mainly by changes in the circumpolar current associated with intensified surface winds, leading to correlations between OHC and SSH that are weak and sometimes negative. In subtropical regions, and near other coastal boundaries, negative correlations are also evident on long time scales and are associated with the accumulated effects of changes in the water cycle and ocean dynamics that underlie complexity in the OHC relationship to SSH. Low-frequency variability in observations is found to exhibit similar negative correlations. Combined with altimeter data, these results provide evidence that SSH increases in the Indian and western Pacific Oceans during the hiatus are suggestive of substantial OHC increases. Methods for developing the applicability of altimetry as a constraint on OHC more generally are also discussed.
Abstract
An accurate diagnosis of ocean heat content (OHC) is essential for interpreting climate variability and change, as evidenced for example by the broad range of hypotheses that exists for explaining the recent hiatus in global mean surface warming. Potential insights are explored here by examining relationships between OHC and sea surface height (SSH) in observations and two recently available large ensembles of climate model simulations from the mid-twentieth century to 2100. It is found that in decadal-length observations and a model control simulation with constant forcing, strong ties between OHC and SSH exist, with little temporal or spatial complexity. Agreement is particularly strong on monthly to interannual time scales. In contrast, in forced transient warming simulations, important dependencies in the relationship exist as a function of region and time scale. Near Antarctica, low-frequency SSH variability is driven mainly by changes in the circumpolar current associated with intensified surface winds, leading to correlations between OHC and SSH that are weak and sometimes negative. In subtropical regions, and near other coastal boundaries, negative correlations are also evident on long time scales and are associated with the accumulated effects of changes in the water cycle and ocean dynamics that underlie complexity in the OHC relationship to SSH. Low-frequency variability in observations is found to exhibit similar negative correlations. Combined with altimeter data, these results provide evidence that SSH increases in the Indian and western Pacific Oceans during the hiatus are suggestive of substantial OHC increases. Methods for developing the applicability of altimetry as a constraint on OHC more generally are also discussed.
Abstract
The flows of energy and water from ocean to land are examined in the context of the land energy and water budgets, for land as a whole and for continents. Most atmospheric reanalyses have large errors of up to 15 W m−2 in the top-of-atmosphere (TOA) energy imbalance, and none include volcanic eruptions. The flow of energy from ocean to land is more reliable as it relies on analyzed wind, temperature, and moisture fields. It is examined for transports of the total, latent energy (LE), and dry static energy (DSE) to land as a whole and as zonal means. The net convergence of energy onto land is balanced by the loss of energy at TOA, measured by Clouds and the Earth’s Radiant Energy System (CERES), and again there are notable discrepancies. Only the ECMWF Interim Re-Analysis (ERA-I) is stable and plausible. Strong compensation between variations in LE and DSE transports onto land means that their sum is more stable over time, and the net transport of energy onto land is largely that associated with the hydrological cycle (LE). A more detailed examination is given of the energy and water budgets for Eurasia, North and South America, Australia, and Africa, making use of Gravity Recovery and Climate Experiment (GRACE) data for water storage on land and data on river discharge into the ocean. With ERA-I, the new land estimates for both water and energy are closer to achieving balances than in previous studies. As well as the annual means, the mean annual cycles are examined in detail along with uncertainty sampling estimates, but the main test used here is that of closure.
Abstract
The flows of energy and water from ocean to land are examined in the context of the land energy and water budgets, for land as a whole and for continents. Most atmospheric reanalyses have large errors of up to 15 W m−2 in the top-of-atmosphere (TOA) energy imbalance, and none include volcanic eruptions. The flow of energy from ocean to land is more reliable as it relies on analyzed wind, temperature, and moisture fields. It is examined for transports of the total, latent energy (LE), and dry static energy (DSE) to land as a whole and as zonal means. The net convergence of energy onto land is balanced by the loss of energy at TOA, measured by Clouds and the Earth’s Radiant Energy System (CERES), and again there are notable discrepancies. Only the ECMWF Interim Re-Analysis (ERA-I) is stable and plausible. Strong compensation between variations in LE and DSE transports onto land means that their sum is more stable over time, and the net transport of energy onto land is largely that associated with the hydrological cycle (LE). A more detailed examination is given of the energy and water budgets for Eurasia, North and South America, Australia, and Africa, making use of Gravity Recovery and Climate Experiment (GRACE) data for water storage on land and data on river discharge into the ocean. With ERA-I, the new land estimates for both water and energy are closer to achieving balances than in previous studies. As well as the annual means, the mean annual cycles are examined in detail along with uncertainty sampling estimates, but the main test used here is that of closure.
