Technical Note: Is radiation important for the high amplitude variability of the MOC in the North Atlantic?

Abstract. Radiation is of fundamental importance to climate modeling and it is customary to assume that it is also important for the variability of North Atlantic Deep Water (NADW) formation and the meridional overturning cell (MOC). Numerous articles follow this scenario and incorporate radiation into the calculation. Using relatively old heat-flux maps based on measurements taken in the nineteen sixties, Sandal and Nof (2007) recently suggested that, even though the radiation terms are of the same order as the other heat-flux terms, they are not important for the variability of the NADW and the MOC. They proposed that only sensible and latent heat fluxes are important for the long-term variability of the convection, i.e., for processes such as Heinrich events, which supposedly correspond to turning convection on-and-off in the Atlantic. Here, we place this suggestion on a firmer ground by presenting new and accurate up-to-date heat flux maps that also suggest that the radiation is of no major consequence to the NADW variability. Also, we attribute the relative importance of sensible and latent heat fluxes and the contrasting negligible role of radiation to the fact that the latent and sensible heat fluxes are primarily proportional to the difference between the sea surface and the air temperature whereas the radiation is primarily proportional to the sea surface temperature, i.e., radiation is approximately independent of the atmospheric temperature. Due the small heat capacity ratio of air/water (1/4), the difference between the ocean temperature and the air temperature varies dramatically between the state of active and inactive MOC, whereas the ocean temperature by itself varies very modestly between a state of active and inactive convection.

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Extratropical cyclone induced sea surface temperature anomalies in the 2013/14 winter

10.5194/wcd-2019-6 ◽

2019 ◽

Author(s):

Helen F. Dacre ◽

Simon A. Josey ◽

Alan L. M. Grant

Keyword(s):

Heat Flux ◽

North Atlantic ◽

Surface Heat Flux ◽

Cold Front ◽

Winter Season ◽

Surface Heat ◽

Heat Fluxes ◽

Sea Surface ◽

Extratropical Cyclones ◽

Sst Cooling

Abstract. The 2013/14 winter averaged sea surface temperature (SST) was anomalously cool in the mid-North Atlantic region. This season was also unusually stormy with extratropical cyclones passing over the mid-North Atlantic every 3 days. However, the processes by which cyclones contribute towards seasonal SST anomalies are not fully understood. In this paper a cyclone identification and tracking method is combined with ECMWF atmosphere and ocean reanalysis fields to calculate cyclone-relative net surface heat flux anomalies and resulting SST changes. Anomalously large negative heat fluxes are located behind the cyclones cold front resulting in anomalous cooling up to 0.2 K/day when the cyclones are at maximum intensity. This extratropical cyclone induced cold wake extends along the cyclones cold front but is small compared to climatological variability. To investigate the potential cumulative effect of the passage of multiple cyclone induced SST cooling in the same location we calculate Earth-relative net surface heat flux anomalies and resulting SST changes for the 2013/2014 winter period. Anomalously large winter averaged negative heat fluxes occur in a zonally orientated band extending across the North Atlantic between 40–60° N. The anomaly associated with cyclones is estimated using a cyclone masking technique which encompasses each cyclone centre and its trailing cold front. North Atlantic extratropical cyclones in the 2013/14 winter season account for 78 % of the observed net surface heat flux in the mid- North Atlantic and net surface heat fluxes in the 2013/14 winter season account for 70 % of the observed cooling in the mid-North Atlantic. Thus extratropical cyclones play a major role in determining the extreme 2013/2014 winter season SST cooling.

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Estimating Air–Sea Heat Fluxes in Semienclosed Basins: The Case of the Gulf of Elat (Aqaba)

Journal of Physical Oceanography ◽

10.1175/2008jpo3858.1 ◽

2009 ◽

Vol 39 (1) ◽

pp. 185-202 ◽

Cited By ~ 20

Author(s):

Moshe Ben-Sasson ◽

Steve Brenner ◽

Nathan Paldor

Keyword(s):

Heat Flux ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Air Temperature ◽

Heat Balance ◽

Evaporation Rate ◽

Heat Fluxes ◽

Sea Surface ◽

Turbulent Heat ◽

The Heat Balance

Abstract Meteorological and oceanographic data collected at the head of the Gulf of Elat were used to compute the air–sea heat flux components and the heat storage in the water column, which are in turn used to estimate the heat balance of this semienclosed basin. The solar radiation was measured directly, whereas the longwave (LW) cooling and the turbulent heat fluxes (latent, LH; sensible, SH) were computed from commonly used bulk formulas. Nine formulas for LW and four formulas for LH + SH were tested for a total of 36 possible combinations. Independent estimates for the bounds on the advective heat flux through the straits and results from a one-dimensional mixed layer model provided criteria to help identify the best choice of bulk formulas for the gulf. It was concluded that the LW formula of Bignami together with the turbulent flux formulas of Kondo provide the best estimate of the heat balance of the gulf. Based on this, the annual mean evaporation is 1.6–1.8 m yr−1, with a minimum of 1 m yr−1 in (the long) summer and a maximum of 3–4 m yr−1 in (the short) winter. The increase in evaporation rate during the winter results from the instability of the atmosphere at that time when the sea surface temperature exceeds the air temperature; in the summer, when the air temperature is much higher than the sea surface temperature, evaporation nearly stops due to the atmospheric stability. This estimated evaporation rate for the gulf, which is similar for all four of the LH formulas considered, is significantly smaller than values commonly quoted in the literature. Finally, in contrast to previous studies, it is found that the advective heat flux from the Straits of Tiran is large and significant in spring, reaching an estimated value of over 125 W m−2, but its annually averaged value is only about 35–40 W m−2.

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Air–Sea Fluxes over the Gulf Stream Region: Atmospheric Controls and Trends

Journal of Climate ◽

10.1175/2010jcli3269.1 ◽

2010 ◽

Vol 23 (10) ◽

pp. 2651-2670 ◽

Cited By ~ 28

Author(s):

Jeffrey Shaman ◽

R. M. Samelson ◽

Eric Skyllingstad

Keyword(s):

Heat Flux ◽

Latent Heat ◽

North Atlantic ◽

Gulf Stream ◽

Heat Fluxes ◽

High Flux ◽

Mode Water ◽

The North ◽

Storm Frequency ◽

The North Atlantic

Abstract The intraseasonal variability of turbulent surface heat fluxes over the Gulf Stream extension and subtropical mode water regions of the North Atlantic, and long-term trends in these fluxes, are explored using NCEP–NCAR reanalysis. Wintertime sensible and latent heat fluxes from these surface waters are characterized by episodic high flux events due to cold air outbreaks from North America. Up to 60% of the November–March (NDJFM) total sensible heat flux and 45% of latent heat flux occurs on these high flux days. On average 41% (34%) of the total NDJFM sensible (latent) heat flux takes place during just 17% (20%) of the days. Over the last 60 years, seasonal NDJFM sensible and latent heat fluxes over the Climate Variability and Predictability (CLIVAR) Mode Water Dynamic Experiment (CLIMODE) region have increased owing to an increased number of high flux event days. The increased storm frequency has altered average wintertime temperature conditions in the region, producing colder surface air conditions over the North American eastern seaboard and Labrador Sea and warmer temperatures over the Sargasso Sea. These temperature changes have increased low-level vertical wind shear and baroclinicity along the North Atlantic storm track over the last 60 years and may further favor the trend of increasing storm frequency over the Gulf Stream extension and adjacent region.

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Neural Network Retrieval of Ocean Surface Parameters from SSM/I Data

Monthly Weather Review ◽

10.1175/mwr3292.1 ◽

2007 ◽

Vol 135 (2) ◽

pp. 586-597 ◽

Cited By ~ 13

Author(s):

Lei Meng ◽

Yijun He ◽

Jinnian Chen ◽

Yumei Wu

Keyword(s):

Neural Network ◽

Heat Flux ◽

Air Temperature ◽

Surface Air Temperature ◽

Heat Fluxes ◽

Sea Surface ◽

Sensible Heat ◽

The Neural Network ◽

Global Oceans ◽

Rms Errors

Abstract A new algorithm based on the multiparameter neural network is proposed to retrieve wind speed (WS), sea surface temperature (SST), sea surface air temperature, and relative humidity (RH) simultaneously over the global oceans from Special Sensor Microwave Imager (SSM/I) observations. The retrieved geophysical parameters are used to estimate the surface latent heat flux and sensible heat flux using a bulk method over the global oceans. The neural network is trained and validated with the matchups of SSM/I overpasses and National Data Buoy Center buoys under both clear and cloudy weather conditions. In addition, the data acquired by the 85.5-GHz channels of SSM/I are used as the input variables of the neural network to improve its performance. The root-mean-square (rms) errors between the estimated WS, SST, sea surface air temperature, and RH from SSM/I observations and the buoy measurements are 1.48 m s−1, 1.54°C, 1.47°C, and 7.85, respectively. The rms errors between the estimated latent and sensible heat fluxes from SSM/I observations and the Xisha Island (in the South China Sea) measurements are 3.21 and 30.54 W m−2, whereas those between the SSM/I estimates and the buoy data are 4.9 and 37.85 W m−2, respectively. Both of these errors (those for WS, SST, and sea surface air temperature, in particular) are smaller than those by previous retrieval algorithms of SSM/I observations over the global oceans. Unlike previous methods, the present algorithm is capable of producing near-real-time estimates of surface latent and sensible heat fluxes for the global oceans from SSM/I data.

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A Description of Interdecadal Time-Scale Propagating North Atlantic Sea Surface Temperature Anomalies and Their Effect on Winter European Climate, 1948–2002

Journal of Climate ◽

10.1175/jcli3646.1 ◽

2006 ◽

Vol 19 (7) ◽

pp. 1067-1079 ◽

Cited By ~ 4

Author(s):

Bablu Sinha ◽

Brenda Topliss

Keyword(s):

Heat Flux ◽

North Atlantic ◽

Surface Air Temperature ◽

Surface Heat ◽

Heat Fluxes ◽

Sea Surface ◽

Western Basin ◽

Eastern Basin ◽

The North ◽

Sst Anomalies

Abstract Eastward-propagating interdecadal time-scale sea surface temperature (SST) winter anomalies have been shown to exist at the North Atlantic subpolar/subtropical gyre boundary. Heat flux and surface air temperature signatures of these anomalies are investigated using satellite- and ship-based SST observations and atmospheric reanalysis. Using bandpass filter analysis, retaining periods between 9 and 25 yr, a succession of coherent propagating SST anomalies is identified. The size, speed, propagation path, and decay characteristics of propagating anomalies detected during the period 1948–2002 are documented. The behavior of the propagations changes between the periods 1948–70 and 1970–2002. In the former period, SST anomalies propagated from the east coast of North America to the British Isles in ∼10 yr. The anomalies displayed a well-defined life cycle, growing in the western basin (west of 40°W) and decaying in the eastern basin. During the period 1970–2002, SST anomalies did not propagate deep into the eastern basin, but grew in the western basin and then ceased propagating. Oceanic anomalies have a comparable marked signature in surface sensible and latent heat fluxes and in surface air temperature. Winter surface heat flux anomalies act to amplify SST anomalies during the middle of their lifetimes, normally in the west-central Atlantic. At other times, heat flux anomalies are associated with decay of anomalies. Surface heat fluxes do not always act to cause propagation, and it is likely that other processes such as advection play a role in the propagation mechanism. North European winter surface air temperatures are raised or lowered by up to ±0.5°C over decadal time scales (∼1/3 of the total variation over the United Kingdom) when an SST anomaly reaches the eastern boundary. A variety of processes can cause SST variation on decadal time scales at the eastern boundary, but in the 1950s and 1960s the variability at these periods was the signature of features that had propagated across the Atlantic from the North American coast.

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Using Transformation and Formation Maps to Study the Role of Air–Sea Heat Fluxes in North Atlantic Eighteen Degree Water Formation

Journal of Physical Oceanography ◽

10.1175/2009jpo3985.1 ◽

2009 ◽

Vol 39 (8) ◽

pp. 1818-1835 ◽

Cited By ~ 49

Author(s):

Guillaume Maze ◽

Gael Forget ◽

Martha Buckley ◽

John Marshall ◽

Ivana Cerovecki

Keyword(s):

Heat Flux ◽

North Atlantic ◽

Gulf Stream ◽

Spatial Information ◽

Formation Rate ◽

Heat Fluxes ◽

Subtropical Gyre ◽

Sea Surface ◽

Transformation Rate

Abstract The Walin water mass framework quantifies the rate at which water is transformed from one temperature class to another by air–sea heat fluxes (transformation). The divergence of the transformation rate yields the rate at which a given temperature range is created or destroyed by air–sea heat fluxes (formation). Walin’s framework provides a precise integral statement at the expense of losing spatial information. In this study the integrand of Walin’s expression to yield transformation and formation maps is plotted and used to study the role of air–sea heat fluxes in the cycle of formation–destruction of the 18° ± 1°C layer in the North Atlantic. Using remotely sensed sea surface temperatures and air–sea heat flux estimates based on both analyzed meteorological fields and ocean data–model syntheses for the 3-yr period from 2004 to 2006, the authors find that Eighteen Degree Water (EDW) is formed by air–sea heat fluxes in the western part of the subtropical gyre, just south of the Gulf Stream. The formation rate peaks in February when the EDW layer is thickened by convection owing to buoyancy loss. EDW is destroyed by air–sea heat fluxes from spring to summer over the entire subtropical gyre. In the annual mean there is net EDW formation in the west to the south of the Gulf Stream, and net destruction over the eastern part of the gyre. Results suggest that annual mean formation rates of EDW associated with air–sea fluxes are in the range from 3 to 5 Sv (Sv ≡ 106 m3 s−1). Finally, error estimates are computed from sea surface temperature and heat flux data using an ensemble perturbation method. The transformation/formation patterns are found to be robust and errors mostly affect integral quantities.

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Influence of North Atlantic sea surface temperature anomalies on springtime surface air temperature variation over Eurasia in CMIP5 models

Climate Dynamics ◽

10.1007/s00382-021-05826-5 ◽

2021 ◽

Author(s):

Shangfeng Chen ◽

Renguang Wu ◽

Wen Chen

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

Temperature Variation ◽

Air Temperature ◽

North Atlantic ◽

Surface Air Temperature ◽

Sea Surface ◽

Cmip5 Models ◽

Temperature Anomalies ◽

Sea Surface Temperature Anomalies

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The Effect of Soil on the Summertime Surface Energy Budget of a Humid Subarctic Tundra in Northern Quebec, Canada

Journal of Hydrometeorology ◽

10.1175/jhm-d-20-0243.1 ◽

2021 ◽

Vol 22 (10) ◽

pp. 2547-2564

Author(s):

Georg Lackner ◽

Daniel F. Nadeau ◽

Florent Domine ◽

Annie-Claude Parent ◽

Gonzalo Leonardini ◽

...

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Sensible Heat Flux ◽

Arctic Region ◽

Heat Fluxes ◽

Surface Energy Budget ◽

Turbulent Heat ◽

Turbulent Heat Fluxes

AbstractRising temperatures in the southern Arctic region are leading to shrub expansion and permafrost degradation. The objective of this study is to analyze the surface energy budget (SEB) of a subarctic shrub tundra site that is subject to these changes, on the east coast of Hudson Bay in eastern Canada. We focus on the turbulent heat fluxes, as they have been poorly quantified in this region. This study is based on data collected by a flux tower using the eddy covariance approach and focused on snow-free periods. Furthermore, we compare our results with those from six Fluxnet sites in the Arctic region and analyze the performance of two land surface models, SVS and ISBA, in simulating soil moisture and turbulent heat fluxes. We found that 23% of the net radiation was converted into latent heat flux at our site, 35% was used for sensible heat flux, and about 15% for ground heat flux. These results were surprising considering our site was by far the wettest site among those studied, and most of the net radiation at the other Arctic sites was consumed by the latent heat flux. We attribute this behavior to the high hydraulic conductivity of the soil (littoral and intertidal sediments), typical of what is found in the coastal regions of the eastern Canadian Arctic. Land surface models overestimated the surface water content of those soils but were able to accurately simulate the turbulent heat flux, particularly the sensible heat flux and, to a lesser extent, the latent heat flux.

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