scholarly journals Modeling the Surface Heat Flux Response to Long-Lived SST Anomalies in the North Atlantic

1995 ◽  
Vol 8 (9) ◽  
pp. 2161-2180 ◽  
Author(s):  
S. B. Power ◽  
R. Kleeman ◽  
R. A. Colman ◽  
B. J. McAvaney
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
The North ◽  
The North Atlantic ◽  
Flux Response ◽  
Sst Anomalies

scholarly journals Observational Assessment of Nonlocal Heat Flux Feedback in the North Atlantic by GEFA

2013 ◽  
Vol 52 (3) ◽  
pp. 645-653 ◽  
Author(s):  
Na Wen ◽  
Zhengyu Liu ◽  
Qinyu Liu
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Surface Wind ◽  
Turbulent Heat ◽  
Observational Assessment ◽  
The North ◽  
The North Atlantic ◽  
Flux Response ◽  
Sst Anomalies ◽  
Heat Flux Feedback

AbstractMost previous studies have proven the local negative heat flux feedback (the surface heat flux response to SST anomalies) in the midlatitude areas. However, it is uncertain whether a nonlocal heat flux feedback can be observed. In this paper, the generalized equilibrium feedback assessment (GEFA) method is employed to examine the full surface turbulent heat flux response to SST in the North Atlantic Ocean using NCEP–NCAR reanalysis data. The results not only confirm the dominant local negative feedback, but also indicate a robust nonlocal positive feedback of the Gulf Stream Extension (GSE) SST to the downstream heat flux in the subpolar region. This nonlocal feedback presents a strong seasonality, with response magnitudes of in winter and in summer. Further study indicates that the nonlocal effect is initiated by the adjustments of the downstream surface wind to the GSE SST anomalies.

Global Pattern Formation of Net Ocean Surface Heat Flux Response to Greenhouse Warming

2020 ◽  
Vol 33 (17) ◽  
pp. 7503-7522 ◽  
Author(s):  
Shineng Hu ◽  
Shang-Ping Xie ◽  
Wei Liu
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Greenhouse Warming ◽  
Global Pattern ◽  
Passive Advection ◽  
The North ◽  
The North Atlantic ◽  
Circulation Changes

AbstractThis study examines global patterns of net ocean surface heat flux changes (ΔQnet) under greenhouse warming in an ocean–atmosphere coupled model based on a heat budget decomposition. The regional structure of ΔQnet is primarily shaped by ocean heat divergence changes (ΔOHD): excessive heat is absorbed by higher-latitude oceans (mainly over the North Atlantic and the Southern Ocean), transported equatorward, and stored in lower-latitude oceans with the rest being released to the tropical atmosphere. The overall global pattern of ΔOHD is primarily due to the circulation change and partially compensated by the passive advection effect, except for the Southern Ocean, which requires further investigations for a more definitive attribution. The mechanisms of North Atlantic surface heat uptake are further explored. In another set of global warming simulations, a perturbation of freshwater removal is imposed over the subpolar North Atlantic to largely offset the CO2-induced changes in the local ocean vertical stratification, barotropic gyre, and the Atlantic meridional overturning circulation (AMOC). Results from the freshwater perturbation experiments suggest that a significant portion of the positive ΔQnet over the North Atlantic under greenhouse warming is caused by the Atlantic circulation changes, perhaps mainly by the slowdown of AMOC, while the passive advection effect can contribute to the regional variations of ΔQnet. Our results imply that ocean circulation changes are critical for shaping global warming pattern and thus hydrological cycle changes.

Ocean climate response to anomalous surface buoyancy and momentum fluxes

2020 ◽  
Author(s):  
Rene Navarro-Labastida ◽  
Riccardo Farneti
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Surface Heat ◽  
High Latitudes ◽  
Temperature Changes ◽  
Ocean Climate ◽  
The North ◽  
Anomalous Surface ◽  
Low Latitudes ◽  
The North Atlantic

<p>The aim of the project is to evaluate the response of the global ocean climate to anomalous surface fluxes in terms of ocean heat uptake and circulation changes. All simulations have been performed with the NOAA-GFDL Modular Ocean Model (MOM) version 5. Ocean-only MOM has been integrated toward a near-equilibrium state using as multicentinal initial conditions derivated from a former CORE-I protocol implementation (Griffies et al., 2009). After equilibrium, a restored control simulation has been obtained by a further 70 years of integration while effective total air-sea heat fluxes and freshwater fluxes were stored at daily intervals. A second control simulation has been obtained by the prescription of these storage fluxes. Differences between the restored and prescribed fluxes controls are rather small. Explicit flux sensitivity experiments are proposed by the Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) in which prescribed surface flux perturbations are applied to the ocean in separated simulations (Gregory et al., 2016). Experiments are 70 years long and branch from piControl conditions. Both wind stress and freshwater anomalies implies nearly-to-zero temperature changes in volume mean temperature. Only the last implies a rather small cooling effect after year 50 of integration. In contrast, anomalous heat flux causes significant volume mean temperature changes. Observed total temperature changes are solely determined by the local addition of heat implying vanishing of the redistribution effect in the entire ocean by inter-basin exchanges and vertical mixing. So far, surface heat anomalies produce the most notable zonal-mean change in ocean temperature. Strong positive temperature change is observed along the top ocean while deepening of temperature anomalies occurs at high latitudes in both hemispheres. Both added and redistributed temperature tracers show maxima in the same area. In most cases, both processes are proportionally inverse. Except for the northern ocean, added temperature tracer is roughly limited to the first 1000 m deep. In contrast, redistributed temperature tracer shows the cooling of subtropical areas and the warming of both the tropical and southern ocean. Maximum at the North Atlantic is possibly due to atmosphere-sea feedbacks, while near-surface tropical and subtropical changes are due to redistribution processes. Heat is mainly taken as a passive tracer in the North Atlantic Ocean and along the entire Southern Ocean. Warming up of mid and low latitudes by redistribution processes is due to the weakening of the Atlantic Meridional Overturning Circulation (AMOC). In turn, changes in AMOC are dominated by surface heat flux changes. The reduction of northward heat transport cools down high latitudes near the surface causing low latitudes to warm up.</p><p> </p>

Estimation of the Surface Heat Flux Response to Sea Surface Temperature Anomalies over the Global Oceans

2005 ◽  
Vol 18 (21) ◽  
pp. 4582-4599 ◽  
Author(s):  
Sungsu Park ◽  
Clara Deser ◽  
Michael A. Alexander
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Surface Heat Flux ◽  
Surface Wind ◽  
Surface Heat ◽  
Radiative Flux ◽  
Turbulent Heat ◽  
Global Oceans ◽  
Sst Anomalies ◽  
Heat Flux Feedback

Abstract The surface heat flux response to underlying sea surface temperature (SST) anomalies (the surface heat flux feedback) is estimated using 42 yr (1956–97) of ship-derived monthly turbulent heat fluxes and 17 yr (1984–2000) of satellite-derived monthly radiative fluxes over the global oceans for individual seasons. Net surface heat flux feedback is generally negative (i.e., a damping of the underlying SST anomalies) over the global oceans, although there is considerable geographical and seasonal variation. Over the North Pacific Ocean, net surface heat flux feedback is dominated by the turbulent flux component, with maximum values (28 W m−2 K−1) in December–February and minimum values (5 W m−2 K−1) in May–July. These seasonal variations are due to changes in the strength of the climatological mean surface wind speed and the degree to which the near-surface air temperature and humidity adjust to the underlying SST anomalies. Similar features are observed over the extratropical North Atlantic Ocean with maximum (minimum) feedback values of approximately 33 W m−2 K−1 (9 W m−2 K−1) in December–February (June–August). Although the net surface heat flux feedback may be negative, individual components of the feedback can be positive depending on season and location. For example, over the midlatitude North Pacific Ocean during late spring to midsummer, the radiative flux feedback associated with marine boundary layer clouds and fog is positive, and results in a significant enhancement of the month-to-month persistence of SST anomalies, nearly doubling the SST anomaly decay time from 2.8 to 5.3 months in May–July. Several regions are identified with net positive heat flux feedback: the tropical western North Atlantic Ocean during boreal winter, the Namibian stratocumulus deck off West Africa during boreal fall, and the Indian Ocean during boreal summer and fall. These positive feedbacks are mainly associated with the following atmospheric responses to positive SST anomalies: 1) reduced surface wind speed (positive turbulent heat flux feedback) over the tropical western North Atlantic and Indian Oceans, 2) reduced marine boundary layer stratocumulus cloud fraction (positive shortwave radiative flux feedback) over the Namibian stratocumulus deck, and 3) enhanced atmospheric water vapor (positive longwave radiative flux feedback) in the vicinity of the tropical deep convection region over the Indian Ocean that exceeds the negative shortwave radiative flux feedback associated with enhanced cloudiness.

How does aerosol forcing drive a strengthening of the AMOC in CMIP6 historical simulations?

2021 ◽  
Author(s):  
Jon Robson ◽  
Matthew Menary ◽  
Jonathan Gregory ◽  
Colin Jones ◽  
Bablu Sinha ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Loss ◽  
North Atlantic ◽  
Surface Heat ◽  
Meridional Overturning Circulation ◽  
Radiation Budget ◽  
Anthropogenic Aerosols ◽  
The North ◽  
Aerosol Forcing ◽  
The North Atlantic

<p>Previous work has shown that anthropogenic aerosol emissions drive a strengthening in the Atlantic Meridional Overturning Circulation (AMOC) in CMIP6 historical simulations over ~1850-1985. However, the mechanisms driving the increase are not fully understood. Previously, forced AMOC changes have been linked to changes in surface heat fluxes, changes in salinity, and interhemispheric energy imbalances. Here we will show that across CMIP6 historical simulations there is a strong correlation between ocean heat loss from the subpolar North Atlantic and the forced change in the AMOC. Furthermore, the model spread in the surface heat flux change explains the spread of the AMOC response and is correlated with the strength of the models’ aerosol forcing.  However, the AMOC change is not strongly related to changes in downwelling surface shortwave radiation over the North Atlantic, showing that anthropogenic aerosols do not drive AMOC change through changes in the local surface radiation budget. Rather, by separating the models into those with ‘strong’ and ‘weak’ aerosol forcing, we show that aerosols appear to predominantly imprint their impact on the AMOC through changes in surface air temperature over the Northern Hemisphere and the consequent impact on latent and sensible heat flux. This thermodynamic driver (i.e. more heat loss from the North Atlantic) is enhanced both by the increase in the AMOC itself, which acts as a positive feedback, and by a response in atmospheric circulation. </p>

scholarly journals Extratropical-cyclone-induced sea surface temperature anomalies in the 2013–2014 winter

2020 ◽  
Vol 1 (1) ◽  
pp. 27-44 ◽  
Author(s):  
Helen F. Dacre ◽  
Simon A. Josey ◽  
Alan L. M. Grant
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Cold Front ◽  
Environmental Flow ◽  
Surface Heat ◽  
Sea Surface ◽  
The North ◽  
Sst Cooling ◽  
The North Atlantic ◽  
Anomalous Heat

Abstract. The 2013–2014 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 d. However, the processes by which cyclones contribute towards seasonal SST anomalies are not fully quantified. In this paper a cyclone identification and tracking method is combined with European Centre for Medium-Range Weather Forecasts (ECMWF) atmosphere and ocean reanalysis fields to calculate cyclone-relative net surface heat flux anomalies and resulting SST changes. Anomalously large negative heat flux is located behind the cyclones' cold front, resulting in anomalous cooling up to 0.2 K d−1 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 in the SSTs. 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 flux occurs in a zonally orientated band extending across the North Atlantic between 40 and 60∘ N. The 2013–2014 winter SST cooling anomaly associated with air–sea interactions (ASIs; anomalous heat flux, mixed layer depth and entrainment at the base of the ocean mixed layer) is estimated to be −0.67 K in the mid-North Atlantic (68 % of the total cooling anomaly). The role of cyclones is estimated using a cyclone-masking technique which encompasses each cyclone centre and its cold wake. The environmental flow anomaly in 2013–2014 sets the overall tripole pattern of heat flux anomalies over the North Atlantic. However, the presence of cyclones doubles the magnitude of the negative heat flux anomaly in the mid-North Atlantic. Similarly, the environmental flow anomaly determines the location of the SST cooling anomaly, but the presence of cyclones enhances the SST cooling anomaly. Thus air–sea interactions play a major part in determining the extreme 2013–2014 winter season SST cooling anomaly. The environmental flow anomaly determines where anomalous heat flux and associated SST changes occur, and the presence of cyclones influences the magnitude of those anomalies.

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

2020 ◽  
Author(s):  
Helen Dacre ◽  
Simon Josey ◽  
Alan Grant
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Cold Front ◽  
Environmental Flow ◽  
Surface Heat ◽  
Sea Surface ◽  
The North ◽  
Sst Cooling ◽  
The North Atlantic ◽  
Anomalous Heat

<p>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 quantified. 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 flux is located behind the cyclones cold front resulting in anomalous cooling up to 0.2K/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 in the SST's.  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 flux occurs in a zonally orientated band extending across the North Atlantic between 40-60 <sup>o</sup>N. The 2013/2014 winter SST cooling anomaly associated with air-sea interactions (anomalous heat flux, mixed layer depth and entrainment at the base of the ocean mixed layer) is estimated to be -0.67 K in the mid-North Atlantic (68% of the total cooling anomaly).  The role of cyclones is estimated using a cyclone masking technique which encompasses each cyclone centre and its trailing cold front. The environmental flow anomaly in 2013/2014 sets the overall tripole pattern of heat flux anomalies over the North Atlantic.  However, the presence of cyclones doubles the magnitude of the negative heat flux anomaly in the mid-North Atlantic.  Similarly, the environmental flow anomaly determines the location of the SST cooling anomaly but the presence of cyclones enhances the SST cooling anomaly.  Thus air-sea interactions play a major part in determining the extreme 2013/2014 winter season SST cooling anomaly. The environmental flow anomaly determines where anomalous heat flux and associated SST changes occur and the presence of cyclones influences the magnitude of those anomalies.</p>

scholarly journals The Central Role of Ocean Dynamics in Connecting the North Atlantic Oscillation to the Extratropical Component of the Atlantic Multidecadal Oscillation

2017 ◽  
Vol 30 (10) ◽  
pp. 3789-3805 ◽  
Author(s):  
Thomas L. Delworth ◽  
Fanrong Zeng ◽  
Liping Zhang ◽  
Rong Zhang ◽  
Gabriel A. Vecchi ◽  
...  
Keyword(s):  
Heat Flux ◽  
North Atlantic ◽  
Atlantic Multidecadal Oscillation ◽  
Ocean Dynamics ◽  
The North ◽  
Decadal Scale ◽  
The North Atlantic ◽  
Slab Ocean ◽  
The North Atlantic Oscillation ◽  
Sst Anomalies

Abstract The relationship between the North Atlantic Oscillation (NAO) and Atlantic sea surface temperature (SST) variability is investigated using models and observations. Coupled climate models are used in which the ocean component is either a fully dynamic ocean or a slab ocean with no resolved ocean heat transport. On time scales less than 10 yr, NAO variations drive a tripole pattern of SST anomalies in both observations and models. This SST pattern is a direct response of the ocean mixed layer to turbulent surface heat flux anomalies associated with the NAO. On time scales longer than 10 yr, a similar relationship exists between the NAO and the tripole pattern of SST anomalies in models with a slab ocean. A different relationship exists both for the observations and for models with a dynamic ocean. In these models, a positive (negative) NAO anomaly leads, after a decadal-scale lag, to a monopole pattern of warming (cooling) that resembles the Atlantic multidecadal oscillation (AMO), although with smaller-than-observed amplitudes of tropical SST anomalies. Ocean dynamics are critical to this decadal-scale response in the models. The simulated Atlantic meridional overturning circulation (AMOC) strengthens (weakens) in response to a prolonged positive (negative) phase of the NAO, thereby enhancing (decreasing) poleward heat transport, leading to broad-scale warming (cooling). Additional simulations are used in which heat flux anomalies derived from observed NAO variations from 1901 to 2014 are applied to the ocean component of coupled models. It is shown that ocean dynamics allow models to reproduce important aspects of the observed AMO, mainly in the Subpolar Gyre.

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

2006 ◽  
Vol 19 (7) ◽  
pp. 1067-1079 ◽  
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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