The surface heat flux feedback. Part I: estimates from observations in the Atlantic and the North Pacific

Abstract. The development of wintertime ozone buildup over the Northern Hemisphere (NH) midlatitudes and its connection with the mean meridional circulation in the stratosphere are examined statistically on a monthly basis from October to March (1980–2002). The ozone buildup begins locally in October with positive ozone tendencies over the North Pacific, which spread eastward and westward in November and finally cover all midlatitudes in December. During October–January a longitudinal distribution of the ozone tendencies mirrors a structure of quasi-stationary planetary waves in the lower stratosphere and has less similarity with this structure in February–March when chemistry begins to play a more important role. From November to March, zonal mean ozone tendencies (50°–60° N) show strong correlation (|r|=0.7) with different parameters used as proxies of the mean meridional circulation, namely: eddy heat flux, the vertical residual velocity (diabatically-derived) and temperature tendency. The correlation patterns between ozone tendency and the vertical residual velocity or temperature tendency are more homogeneous from month to month than ones for eddy heat flux. A partial exception is December when correlation is strong only for the vertical residual velocity. In October zonal mean ozone tendencies have no coupling with the proxies. However, positive tendencies averaged over the North Pacific correlate well, with all of them suggesting that intensification of northward ozone transport starts locally over the Pacific already in October. We show that the NH midlatitude ozone buildup has stable statistical relation with the mean meridional circulation in all months from October to March and half of the interannual variability in monthly ozone tendencies can be explained by applying different proxies of the mean meridional circulation.

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Skillful Subseasonal Prediction of United States Extreme Warm Days and Standardized Precipitation Index in Boreal Summer

Journal of Climate ◽

10.1175/jcli-d-20-0878.1 ◽

2021 ◽

pp. 1-34

Author(s):

Douglas E. Miller ◽

Zhuo Wang ◽

Bo Li ◽

Daniel S. Harnos ◽

Trent Ford

Keyword(s):

United States ◽

Heat Flux ◽

Soil Moisture ◽

Statistical Model ◽

North Pacific ◽

Standardized Precipitation Index ◽

Boreal Summer ◽

The North ◽

Moisture Conditions ◽

The North Pacific

AbstractSkillful subseasonal prediction of extreme heat and precipitation greatly benefits multiple sectors, including water management, public health, and agriculture, in mitigating the impact of extreme events. A statistical model is developed to predict the weekly frequency of extreme warm days and 14-day standardized precipitation index (SPI) during boreal summer in the United States (US). We use a leading principal component of US soil moisture and an index based on the North Pacific sea surface temperature (SST) as predictors. The model outperforms the NCEP’s Climate Forecast System version 2 (CFSv2) at weeks 3-4 in the eastern US. It is found that the North Pacific SST anomalies persist several weeks and are associated with a persistent wave train pattern (WTZ500), which leads to increased occurrences of blocking and extreme temperature over the eastern US. Extreme dry soil moisture conditions persist into week 4 and are associated with an increase in sensible heat flux and decrease in latent heat flux, which may help maintain the overlying anticyclone. The clear sky conditions associated with blocking anticyclones further decrease soil moisture conditions and increase the frequency of extreme warm days. This skillful statistical model has the potential to aid in irrigation scheduling, crop planning, reservoir operation, and provide mitigation of impacts from extreme heat events.

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Spatiotemporal Characteristics of the Dominant Modes of Surface Air Temperature Interannual Variations over South China during the Spring-to-Summer Transition

Atmosphere ◽

10.3390/atmos10020065 ◽

2019 ◽

Vol 10 (2) ◽

pp. 65

Author(s):

Fen Wang ◽

Yaokun Li ◽

Jianping Li

Keyword(s):

Heat Flux ◽

Air Temperature ◽

South China ◽

Surface Heat Flux ◽

Surface Air Temperature ◽

Surface Heat ◽

Shortwave Radiation ◽

Northerly Wind ◽

The North ◽

Land Surfaces

The surface air temperature (SAT) interannual variability during the spring-to-summer transition over South China (SC) has been decomposed into two dominant modes by applying empirical orthogonal function (EOF) analysis. The first EOF mode (EOF1) is characterized by homogenous SAT anomalies over SC, whereas the second EOF mode (EOF2) features a dipole SAT anomaly pattern with opposite anomalies south and north of the Yangtze River. A regression analysis of surface heat flux and advection anomalies on the normalized principle component time series corresponding to EOF1 suggests that surface heat flux anomalies can explain SAT anomalies mainly by modulating cloud-shortwave radiation. Negative cloud anomalies result in positive downward shortwave radiation anomalies through the positive shortwave cloud radiation effect, which favor warm SAT anomalies over most of SC. For EOF2, the distribution of advection anomalies resembles the north–south dipole pattern of SAT anomalies. This suggests that wind-induced advection plays an important role in the SAT anomalies of EOF2. Negative SAT anomalies are favored by cold advection from northerly wind anomalies over land surfaces in high-latitude regions. Positive SAT anomalies are induced by warm advection from southerly wind anomalies over the ocean in low-latitude regions.

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

Journal of Climate ◽

10.1175/jcli-d-19-0642.1 ◽

2020 ◽

Vol 33 (17) ◽

pp. 7503-7522 ◽

Cited By ~ 1

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.

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

Journal of Climate ◽

10.1175/jcli3521.1 ◽

2005 ◽

Vol 18 (21) ◽

pp. 4582-4599 ◽

Cited By ~ 76

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.

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Air–Sea Interactions in the Tropical Atlantic: A View Based on Lagged Rotated Maximum Covariance Analysis

Journal of Climate ◽

10.1175/jcli3498.1 ◽

2005 ◽

Vol 18 (18) ◽

pp. 3874-3890 ◽

Cited By ~ 29

Author(s):

Claude Frankignoul ◽

Elodie Kestenare

Keyword(s):

Heat Flux ◽

Surface Heat Flux ◽

Surface Heat ◽

Covariance Analysis ◽

Atmospheric Response ◽

Tropical Atlantic ◽

Maximum Covariance Analysis ◽

Wind Response ◽

Sst Anomaly ◽

Heat Flux Feedback

Abstract The dominant air–sea feedbacks that are at play in the tropical Atlantic are revisited, using the 1958–2002 NCEP reanalysis. To separate between different modes of variability and distinguish between cause and effect, a lagged rotated maximum covariance analysis (MCA) of monthly sea surface temperature (SST), wind, and surface heat flux anomalies is performed. The dominant mode is the ENSO-like zonal equatorial SST mode, which has its maximum amplitude in boreal summer and is a strongly coupled ocean–atmosphere mode sustained by a positive feedback between wind and SST. The turbulent heat flux feedback is negative, except west of 25°W where it is positive, but countered by a negative radiative feedback associated with the meridional displacement of the ITCZ. As the maximum covariance patterns change little between lead and lag conditions, the in-phase covariability between SST and the atmosphere can be used to infer the atmospheric response to the SST anomaly. The second climate mode involves an SST anomaly in the tropical North Atlantic, which is primarily generated by the surface heat flux and, in boreal winter, wind changes off the coast of Africa. After it has been generated, the SST anomaly is sustained in the deep Tropics by the positive wind–evaporation–SST feedback linked to the wind response to the SST. However, north of about 10°N where the SST anomaly is largest, the wind response is weak and the heat flux feedback is negative, thus damping the SST anomaly. As the in-phase maximum covariance patterns primarily reflect the atmospheric forcing of the SST, simultaneous correlations cannot be used to describe the atmospheric response to the SST anomaly, except in the deep Tropics. Using instead the maximum covariance patterns when SST leads the atmosphere reconciles the results of recent atmospheric general circulation model experiments with the observations.

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Circulation and Heat Flux along the Western Boundary of the North Pacific

Journal of Ocean University of China ◽

10.1007/s11802-020-4168-z ◽

2019 ◽

Vol 19 (1) ◽

pp. 1-12

Author(s):

Xia Ju ◽

Chao Ma ◽

Xuejun Xiong ◽

Yanliang Guo ◽

Long Yu

Keyword(s):

Heat Flux ◽

North Pacific ◽

Western Boundary ◽

The North ◽

The North Pacific

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PDO-Related Heat and Temperature Budget Changes in a Model of the North Pacific

Journal of Climate ◽

10.1175/jcli4229.1 ◽

2007 ◽

Vol 20 (10) ◽

pp. 2092-2108 ◽

Cited By ~ 12

Author(s):

Jordan T. Dawe ◽

Lu Anne Thompson

Keyword(s):

Heat Flux ◽

North Pacific ◽

Heat Budget ◽

Heat Content ◽

Ocean Dynamics ◽

Upper Ocean ◽

The North ◽

Atmospheric Heat ◽

The Kuroshio ◽

The North Pacific

Abstract Heat and temperature budget changes in a ⅓° model of the North Pacific driven by an idealized Pacific decadal oscillation (PDO) atmospheric forcing are diagnosed to determine the roles of atmospheric heat flux and ocean dynamics in upper-ocean heat content and mixed layer temperature (MLT) changes. Changes in MLT and heat content during the transition between negative and positive PDOs are driven primarily by atmospheric heat fluxes, with contributions from ageostrophic advection and entrainment. Once the new PDO state is established, atmospheric heat flux in the central North Pacific works to mitigate the MLT change while vertical entrainment and ageostrophic advection act to enhance it. Upper-ocean heat content is affected in a similar matter, except that vertical processes are not important in the heat budget balance. At the same time, changes in wind stress curl cause the subtropical gyre to spin up and the subpolar gyre boundary to migrate southward. These circulation changes cause a large increase in the geostrophic advective heat flux in the Kuroshio region. This increase results in more heat flux to the atmosphere, demonstrating an active role for ocean dynamics in the upper-ocean heat budget. Eddy heat flux divergence along the Kuroshio Extension doubles after the transition, due to stronger eddy activity related to increased Kuroshio transport.

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