Heat Flux, Freshwater Flux, and Climate

This study investigates the physical processes controlling the mixed layer buoyancy using a regional configuration of an ocean general circulation model. Processes are quantified by using a linearized equation of state, a mixed-layer heat, and a salt budget. Model results correctly reproduce the observed seasonal near-surface density tendencies. The results indicate that the heat flux is located poleward of 10° of latitude, which is at least three times greater than the freshwater flux that mainly controls mixed layer buoyancy. During boreal spring-summer of each hemisphere, the freshwater flux partly compensates the heat flux in terms of buoyancy loss while, during the fall-winter, they act together. Under the seasonal march of the Inter-tropical Convergence Zone and in coastal areas affected by the river, the contribution of ocean processes on the upper density becomes important. Along the north Brazilian coast and the Gulf of Guinea, horizontal and vertical processes involving salinity are the main contributors to an upper water change with a contribution of at least twice as much the temperature. At the equator and along the Senegal-Mauritanian coast, vertical processes are the major oceanic contributors. This is mainly due to the vertical gradient of temperature at the mixed layer base in the equator while the salinity one dominates along the Senegal-Mauritania coast.

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A New Analytical Model for Heinrich Events and Climate Instability

Journal of Physical Oceanography ◽

10.1175/2007jpo3722.1 ◽

2008 ◽

Vol 38 (2) ◽

pp. 451-466 ◽

Cited By ~ 8

Author(s):

Cathrine Sandal ◽

Doron Nof

Keyword(s):

Heat Flux ◽

Air Temperature ◽

Sensible Heat Flux ◽

Greenland Ice Sheet ◽

Atmospheric Temperature ◽

Freshwater Flux ◽

Ocean Temperature ◽

Algebraic Equations ◽

Humid Atmosphere ◽

Heinrich Events

Abstract The authors focus on Heinrich events and the question of whether the arrest and restart of convection can explain the associated sudden changes in oceanic and atmospheric temperature. For this purpose, a new (mixed) dynamical-box model is developed in which the ocean and atmosphere communicate via both Ekman layers and convection. The conservation of heat, salt, volume flux, and a “convection condition” yields a system of algebraic equations that are solved analytically. As expected, it is found that as the freshwater flux increases, the convective ocean temperature decreases. The heat flux from the ocean to the atmosphere, the transport of the oceanic meridional overturning cell (MOC), and the corresponding atmospheric flow generated by the heat flux from the ocean all decrease. However, the outgoing air temperature increases with increasing freshwater flux. This counterintuitive increase is because a decreased latent and sensible heat flux (to a humid atmosphere) means a reduced temperature difference between the warmer ocean and the cooler atmosphere, implying a cooler ocean and warmer atmosphere. For each wind speed, there is a critical freshwater flux beyond which the convection collapses and the temperatures of both the ocean and the air plunge because equatorial water is no longer flowing northward to replace the frigid northern waters. The above points to a potentially new instability process that was probably active during glaciation periods—when ice and snow are abundant, even the smallest amount of freshwater flux will cause local warming which, in turn, will cause increased melting, resulting in an ever-increased freshwater flux until the critical flux is reached and the MOC collapses. The model suggests that switching convection on and off changed the glacial ocean temperature by 4°C and the glacial air temperature by 12.5°C, both consistent with the Greenland Ice Sheet Project (GISP II) ice core record and the Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement (CEREGE) alkenone record.

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Oceanic Fluxes in the South Atlantic

Journal of Physical Oceanography ◽

10.1175/jpo-2666.1 ◽

2005 ◽

Vol 35 (1) ◽

pp. 109-122 ◽

Cited By ~ 28

Author(s):

Elaine L. McDonagh ◽

Brian A. King

Keyword(s):

Heat Flux ◽

Ocean Circulation ◽

World Ocean ◽

South Atlantic ◽

Freshwater Flux ◽

Intermediate Water ◽

The South ◽

Cape Basin ◽

Small Gain ◽

The Difference

Abstract A box inverse of the World Ocean Circulation Experiment A10 (30°S) and A11 (nominally 45°S) sections in the South Atlantic Ocean was undertaken. The authors find a heat flux across A10 of 0.22 ± 0.08 PW, consistent with previous studies, and a heat flux of 0.43 ± 0.08 PW across A11. The A11 heat flux is lower than some previous analyses of this section but implies a plausible oceanic heat convergence (heat loss to the atmosphere) of 0.21 ± 0.10 PW. The difference is principally due to adding a cyclonic component to the circulation in the Cape Basin. As compared with the solution of other studies, the anticyclonic circulation in the surface and intermediate water of the subtropical gyre is weakened. The circulation of the deep water is cyclonic rather than anticyclonic; this is in better agreement with previously published circulation schemes based on examination of water properties. A southward freshwater flux of 0.7 Sv (1 Sv ≡ 106 m3 s−1) at A11, consistent with previous inverse studies, is still inconsistent with the net Atlantic evaporation inferred from integrated surface climatologies. Results suggest a small gain of freshwater (0.2 ± 0.1 Sv) between the sections.

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Intensified Atlantic vs. weakened Pacific meridional overturning circulations in response to Tibetan Plateau uplift

10.5194/cp-2017-110 ◽

2017 ◽

Author(s):

Baohuang Su ◽

Dabang Jiang ◽

Ran Zhang ◽

Pierre Sepulchre ◽

Gilles Ramstein

Keyword(s):

Heat Flux ◽

Tibetan Plateau ◽

Large Scale ◽

Meridional Overturning Circulation ◽

Freshwater Flux ◽

Deep Water Formation ◽

Overturning Circulation ◽

The North ◽

Water Formation ◽

Meridional Overturning

Abstract. The role of the Tibetan Plateau (TP) in maintaining large-scale overturning circulation in the Atlantic and Pacific is investigated using a coupled atmosphere–ocean model. For the present day with a realistic topography, model simulation shows a strong Atlantic meridional overturning circulation (AMOC) but a near absence of a Pacific meridional overturning circulation (PMOC), which is in good agreement with present observations. In contrast, the simulation without the TP depicts a collapsed AMOC and a strong PMOC that dominates deep water formation. The switch in deep water formation between the two basins results from changes in the large-scale atmospheric circulation and atmosphere–ocean feedback in the Atlantic and Pacific. The intensified westerly winds and increased freshwater flux over the North Atlantic cause an initial slowdown of the AMOC, but the weakened East Asian monsoon circulation and associated decreased freshwater flux over the North Pacific enhance initial intensification of the PMOC. The further decreased heat flux and the associated increase in sea-ice fraction promote the final AMOC collapse over the Atlantic, while the further increased heat flux leads to the final PMOC establishment over the Pacific. Although the simulations were done in a cold world, it still importantly implicates that the uplift of the TP alone could have been a potential driver for the reorganization of PMOC–AMOC between the Late Eocene and Early Oligocene.

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Accuracy of the IMET Sensor Package in the Subtropics

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2009jtecho667.1 ◽

2009 ◽

Vol 26 (9) ◽

pp. 1867-1890 ◽

Cited By ~ 64

Author(s):

Keir Colbo ◽

Robert A. Weller

Keyword(s):

Heat Flux ◽

Momentum Flux ◽

Barometric Pressure ◽

Absolute Error ◽

Shortwave Radiation ◽

Freshwater Flux ◽

Near Surface ◽

Sensor Package

Abstract The accuracies of the meteorological sensors (air temperature, relative humidity, barometric pressure, near-surface temperature, longwave and shortwave radiation, and wind speed and direction) that compose the Improved Meteorological (IMET) system used on buoys at long-term ocean time series sites known as ocean reference stations (ORS) are analyzed to determine their absolute error characteristics. The predicted errors are compared to in situ measurement discrepancies and other observations (direct flux shipboard sensors) to confirm the predictions. The meteorological errors are then propagated through bulk flux formulas and the Coupled Ocean–Atmosphere Response Experiment (COARE) algorithm to give predicted errors for the heat flux components, the freshwater flux, and the momentum flux. Absolute errors are presented for three frequency bands [instantaneous (1-min sampling), diurnal, and annual]. The absolute uncertainty in the annually averaged net heat flux is found to be 8 W m−2 for conditions similar to the current ORS deployments in the subtropics.

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A Decade of Ocean Changes Impacting the Ice Shelf of Petermann Gletscher, Greenland

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0181.1 ◽

2018 ◽

Vol 48 (10) ◽

pp. 2477-2493 ◽

Cited By ~ 7

Author(s):

P. Washam ◽

A. Münchow ◽

K. W. Nicholls

Keyword(s):

Heat Flux ◽

Steady State ◽

Freshwater Flux ◽

Ice Shelf ◽

Hydrographic Data ◽

Ocean Stratification ◽

Freshwater Fluxes ◽

Subsurface Ocean ◽

Grounding Line ◽

Seasonal Signal

AbstractHydrographic data collected during five summer surveys between 2002 and 2015 reveal that the subsurface ocean near Petermann Gletscher, Greenland, warmed by 0.015° ± 0.013°C yr−1. New 2015–16 mooring data from beneath Petermann Gletscher’s ice shelf imply a continued warming of 0.025° ± 0.013°C yr−1 with a modest seasonal signal. In 2015, we measured ocean temperatures of 0.28°C near the grounding line of Petermann Gletscher’s ice shelf, which drove submarine melting along the base of the glacier. The resultant meltwater contributed to ocean stratification, which forced a stronger geostrophic circulation at the ice shelf terminus compared with previous years. This increased both the freshwater flux away from the sub–ice shelf cavity and the heat flux into it. Net summertime geostrophic heat flux estimates into the sub–ice shelf cavity exceed the requirement for steady-state melting of Petermann Gletscher’s ice shelf. Likewise, freshwater fluxes away from the glacier exceed the expected steady-state meltwater discharge. These results suggest that the warmer, more active ocean surrounding Petermann Gletscher forces “non steady state” melting of its ice shelf. When sustained, such melting thins the ice shelf.

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A Conceptual Model of Polar Overturning Circulations

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0139.1 ◽

2020 ◽

Author(s):

Thomas W. N. Haine

Keyword(s):

Heat Flux ◽

Sea Ice ◽

Conceptual Model ◽

The Arctic ◽

Global Ocean ◽

Freshwater Flux ◽

Ice Surface ◽

Freshwater Fluxes ◽

Weak Constraints ◽

Polar Water

AbstractThe global ocean overturning circulation carries warm, salty water to high latitudes, both in the Arctic and Antarctic. Interaction with the atmosphere transforms this inflow into three distinct products: sea ice, surface Polar Water, and deep Overflow Water. The Polar Water and OverflowWater formestuarine and thermal overturning cells, stratified by salinity and temperature, respectively. A conceptual model specifies the characteristics of these water masses and cells given the inflow and air/sea/land fluxes of heat and freshwater. The model includes budgets of mass, salt, and heat, and parametrizations of Polar Water and Overflow Water formation, which include exchange with continental shelves. Model solutions are mainly controlled by a linear combination of air/sea/ice heat and freshwater fluxes and inflow heat flux that approximates the meteoric freshwater flux plus the sea ice export flux. The model shows that for the Arctic, the thermal overturning is likely robust, but the estuarine cell appears vulnerable to collapse via a so-called heat crisis that violates the budget equations. The system is pushed towards this crisis by increasing AtlanticWater inflow heat flux, increasing meteoric freshwater flux, and/or decreasing heat loss to the atmosphere. The Antarctic appears close to a so-called Overflow Water emergency with weak constraints on the strengths of the estuarine and thermal cells, uncertain sensitivity to parameters, and possibility of collapse of the thermal cell.

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Freshwater Flux (FWF)-Induced Oceanic Feedback in a Hybrid Coupled Model of the Tropical Pacific

Journal of Climate ◽

10.1175/2008jcli2543.1 ◽

2009 ◽

Vol 22 (4) ◽

pp. 853-879 ◽

Cited By ~ 49

Author(s):

Rong-Hua Zhang ◽

Antonio J. Busalacchi

Keyword(s):

Heat Flux ◽

Interannual Variability ◽

Coupled Model ◽

Tropical Pacific ◽

Freshwater Flux ◽

Atmosphere System ◽

Ocean Atmosphere ◽

Hybrid Coupled Model ◽

Sst Anomalies ◽

The Tropical Pacific

Abstract The impacts of freshwater flux (FWF) forcing on interannual variability in the tropical Pacific climate system are investigated using a hybrid coupled model (HCM), constructed from an oceanic general circulation model (OGCM) and a simplified atmospheric model, whose forcing fields to the ocean consist of three components. Interannual anomalies of wind stress and precipitation minus evaporation, (P − E), are calculated respectively by their statistical feedback models that are constructed from a singular value decomposition (SVD) analysis of their historical data. Heat flux is calculated using an advective atmospheric mixed layer (AML) model. The constructed HCM can well reproduce interannual variability associated with ENSO in the tropical Pacific. HCM experiments are performed with varying strengths of anomalous FWF forcing. It is demonstrated that FWF can have a significant modulating impact on interannual variability. The buoyancy flux (QB) field, an important parameter determining the mixing and entrainment in the equatorial Pacific, is analyzed to illustrate the compensating role played by its two contributing parts: one is related to heat flux (QT) and the other to freshwater flux (QS). A positive feedback is identified between FWF and SST as follows: SST anomalies, generated by El Niño, nonlocally induce large anomalous FWF variability over the western and central regions, which directly influences sea surface salinity (SSS) and QB, leading to changes in the mixed layer depth (MLD), the upper-ocean stability, and the mixing and the entrainment of subsurface waters. These oceanic processes act to enhance the SST anomalies, which in turn feedback to the atmosphere in a coupled ocean–atmosphere system. As a result, taking into account anomalous FWF forcing in the HCM leads to an enhanced interannual variability and ENSO cycles. It is further shown that FWF forcing is playing a different role from heat flux forcing, with the former acting to drive a change in SST while the latter represents a passive response to the SST change. This HCM-based modeling study presents clear evidence for the role of FWF forcing in modulating interannual variability in the tropical Pacific. The significance and implications of these results are further discussed for physical understanding and model improvements of interannual variability in the tropical Pacific ocean–atmosphere system.

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Understanding Bjerknes Compensation in Atmosphere and Ocean Heat Transports Using a Coupled Box Model

Journal of Climate ◽

10.1175/jcli-d-15-0281.1 ◽

2016 ◽

Vol 29 (6) ◽

pp. 2145-2160 ◽

Cited By ~ 16

Author(s):

Haijun Yang ◽

Yingying Zhao ◽

Zhengyu Liu

Keyword(s):

Heat Flux ◽

Energy Conservation ◽

Heat Transport ◽

Thermohaline Circulation ◽

Box Model ◽

Climate Feedback ◽

Freshwater Flux ◽

Realistic Situation ◽

Close Relationship ◽

Local Feedback

Abstract A coupled box model is used to study the compensation between atmosphere and ocean heat transports. An analytical solution to the Bjerknes compensation (BJC) rate, defined as the ratio of anomalous atmosphere heat transport (AHT) to anomalous ocean heat transport (OHT), is obtained. The BJC rate is determined by local feedback between surface temperature and net heat flux at the top of atmosphere (TOA) and the AHT efficiency. In a stable climate that ensures global energy conservation, the changes between AHT and OHT tend to be always out of phase, and the BJC is always valid. This can be demonstrated when the climate is perturbed by freshwater flux. The BJC in this case exhibits three different behaviors: the anomalous AHT can undercompensate, overcompensate, or perfectly compensate the anomalous OHT, depending on the local feedback. Stronger negative local feedback will result in a lower BJC rate. Stronger positive local feedback will result in a larger overcompensation. If zero climate feedback occurs in the system, the AHT will compensate the OHT perfectly. However, the BJC will fail if the climate system is perturbed by heat flux. In this case, the changes in AHT and OHT will be in phase, and their ratio will be closely related to the mean AHT and OHT. In a more realistic situation when the climate is perturbed by both heat and freshwater fluxes, whether the BJC will occur depends largely on the interplay among meridional temperature and salinity gradients and the thermohaline circulation strength. This work explicitly shows that the energy conservation is the intrinsic mechanism of BJC and establishes a specific link between radiative feedback and the degree of compensation. It also implies a close relationship between the energy balance at the TOA and the ocean thermohaline dynamics.

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Siphon Flows in Stratified Coronal Loops

International Astronomical Union Colloquium ◽

10.1017/s0252921100025288 ◽

1994 ◽

Vol 144 ◽

pp. 185-187

Author(s):

S. Orlando ◽

G. Peres ◽

S. Serio

Keyword(s):

Heat Flux ◽

Scaling Laws ◽

Flow Model ◽

Supersonic Flows ◽

Coronal Loops ◽

Characteristic Parameters

AbstractWe have developed a detailed siphon flow model for coronal loops. We find scaling laws relating the characteristic parameters of the loop, explore systematically the space of solutions and show that supersonic flows are impossible for realistic values of heat flux at the base of the upflowing leg.

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