scholarly journals Scale Dependence of Midlatitude Air–Sea Interaction

2017 ◽  
Vol 30 (20) ◽  
pp. 8207-8221 ◽  
Author(s):  
Stuart P. Bishop ◽  
R. Justin Small ◽  
Frank O. Bryan ◽  
Robert A. Tomas
Keyword(s):  
Climate Models ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Balance Model ◽  
Western Boundary ◽  
Surface Heat Fluxes ◽  
Functional Relationships ◽  
Sst Variability ◽  
Temporal Smoothing ◽  
Circumpolar Current

Abstract It has traditionally been thought that midlatitude sea surface temperature (SST) variability is predominantly driven by variations in air–sea surface heat fluxes (SHFs) associated with synoptic weather variability. Here it is shown that in regions marked by the highest climatological SST gradients and SHF loss to the atmosphere, the variability in SST and SHF at monthly and longer time scales is driven by internal ocean processes, termed here “oceanic weather.” This is shown within the context of an energy balance model of coupled air–sea interaction that includes both stochastic forcing for the atmosphere and ocean. The functional form of the lagged correlation between SST and SHF allows us to discriminate between variability that is driven by atmospheric versus oceanic weather. Observations show that the lagged functional relationship of SST–SHF and SST tendency–SHF correlation is indicative of ocean-driven SST variability in the western boundary currents (WBCs) and the Antarctic Circumpolar Current (ACC). By applying spatial and temporal smoothing, thereby dampening the signature SST anomalies generated by eddy stirring, it is shown that the oceanic influence on SST variability increases with time scale but decreases with increasing spatial scale. The scale at which SST variability in the WBCs and the ACC transitions from ocean to atmosphere driven occurs at scales less than 500 km. This transition scale highlights the need to resolve mesoscale eddies in coupled climate models to adequately simulate the variability of air–sea interaction. Away from strong SST fronts the lagged functional relationships are indicative of the traditional paradigm of atmospherically driven SST variability.

Sea Surface Temperature Variability along the Path of the Antarctic Circumpolar Current

2006 ◽  
Vol 36 (7) ◽  
pp. 1317-1331 ◽  
Author(s):  
Ariane Verdy ◽  
John Marshall ◽  
Arnaud Czaja
Keyword(s):  
Antarctic Circumpolar Current ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Heat Advection ◽  
Surface Heat Fluxes ◽  
Sst Variability ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Sst Anomalies

Abstract The spatial and temporal distributions of sea surface temperature (SST) anomalies in the Antarctic Circumpolar Current (ACC) are investigated, using monthly data from the NCEP–NCAR reanalysis for the period 1980–2004. Patterns of atmospheric forcing are identified in observations of sea level pressure and air–sea heat fluxes. It is found that a significant fraction of SST variability in the ACC can be understood as a linear response to surface forcing by the Southern Annular Mode (SAM) and remote forcing by ENSO. The physical mechanisms rely on the interplay between atmospheric variability and mean advection by the ACC. SAM and ENSO drive a low-level anomalous circulation pattern localized over the South Pacific Ocean, inducing surface heat fluxes and Ekman heat advection anomalies. A simple model of SST propagating in the ACC, forced with heat fluxes estimated from the reanalysis, suggests that surface heat fluxes and Ekman heat advection are equally important in driving the observed SST variability. Further diagnostics indicate that SST anomalies, generated mainly upstream of Drake Passage, are subsequently advected by the ACC and damped after a couple of years. It is suggested that SST variability along the path of the ACC is largely a passive response of the oceanic mixed layer to atmospheric forcing.

scholarly journals On the Interpretation of the North Atlantic Averaged Sea Surface Temperature

2020 ◽  
Vol 33 (14) ◽  
pp. 6025-6045
Author(s):  
Jing Sun ◽  
Mojib Latif ◽  
Wonsun Park ◽  
Taewook Park
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
Climate Models ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
The North ◽  
Sst Variability ◽  
The North Atlantic ◽  
Different Time Scales

AbstractThe North Atlantic (NA) basin-averaged sea surface temperature (NASST) is often used as an index to study climate variability in the NA sector. However, there is still some debate on what drives it. Based on observations and climate models, an analysis of the different influences on the NASST index and its low-pass filtered version, the Atlantic multidecadal oscillation (AMO) index, is provided. In particular, the relationships of the two indices with some of its mechanistic drivers including the Atlantic meridional overturning circulation (AMOC) are investigated. In observations, the NASST index accounts for significant SST variability over the tropical and subpolar NA. The NASST index is shown to lump together SST variability originating from different mechanisms operating on different time scales. The AMO index emphasizes the subpolar SST variability. In the climate models, the SST-anomaly pattern associated with the NASST index is similar. The AMO index, however, only represents pronounced SST variability over the extratropical NA, and this variability is significantly linked to the AMOC. There is a sensitivity of this linkage to the cold NA SST bias observed in many climate models. Models suffering from a large cold bias exhibit a relatively weak linkage between the AMOC and AMO and vice versa. Finally, the basin-averaged SST in its unfiltered form, which has been used to question a strong influence of ocean dynamics on NA SST variability, mixes together multiple types of variability occurring on different time scales and therefore underemphasizes the role of ocean dynamics in the multidecadal variability of NA SSTs.

Covariability of SST and surface heat fluxes in reanalyses and CMIP3 climate models

2009 ◽  
Vol 36 (3-4) ◽  
pp. 589-605 ◽  
Author(s):  
Bin Yu ◽  
G. J. Boer ◽  
F. W. Zwiers ◽  
W. J. Merryfield
Keyword(s):  
Climate Models ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Surface Heat Fluxes

scholarly journals Mechanisms of Internal Atlantic Multidecadal Variability in HadGEM3-GC3.1 at Two Different Resolutions

2021 ◽  
pp. 1-60
Author(s):  
J. I. Robson ◽  
L. J. Wilcox ◽  
N. Dunstone
Keyword(s):  
Ocean Circulation ◽  
Low Frequency ◽  
Heat Fluxes ◽  
The Arctic ◽  
Western Boundary ◽  
Atlantic Multidecadal Variability ◽  
Surface Heat Fluxes ◽  
Ocean Salinity ◽  
Circulation Changes ◽  
Sst Anomalies

Abstract This study broadly characterises and compares the key processes governing internal AMV in two resolutions of HadGEM3-GC3.1: N216ORCA025, corresponding to ~ 60km in the atmosphere and 0.25° in the ocean, and N96ORCA1 (~ 135km / 1°). Both models simulate AMV with a timescale of 60-80 years, which is related to low frequency ocean and atmosphere circulation changes. In both models, ocean heat transport convergence dominates polar and subpolar AMV, whereas surface heat fluxes associated with cloud changes drive subtropicalAMV. However, details of the ocean circulation changes differ between the models. In N216 subpolar subsurface density anomalies propagate into the subtropics along the western boundary, consistent with the more coherent circulation changes and widespread development of SST anomalies. In contrast, N96 subsurface density anomalies persist in the subpolar latitudes for longer, so circulation anomalies and the development of SST anomalies are more centred there. The drivers of subsurface density anomalies also differ between models. In N216, the NAO is the dominant driver, while upper-ocean salinity-controlled density anomalies that originate from the Arctic appear to be the dominant driver in N96. These results further highlight that internal AMV mechanisms are model dependent and motivate further work to better understand and constrain the differences.

scholarly journals Enhanced Persistence of Equatorial Waves via Convergence Coupling in the Stochastic Multicloud Model

2015 ◽  
Vol 72 (12) ◽  
pp. 4701-4720 ◽  
Author(s):  
Noah D. Brenowitz ◽  
Yevgeniy Frenkel ◽  
Andrew J. Majda
Keyword(s):  
Large Scale ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Theoretical Studies ◽  
Equatorial Waves ◽  
Moist Convection ◽  
Kelvin Wave ◽  
Surface Heat Fluxes ◽  
Walker Cell ◽  
Conditional Instability

Abstract Recent observational and theoretical studies show a systematic relationship between tropical moist convection and measures related to large-scale convergence. It has been suggested that cloud fields in the column stochastic multicloud model compare better with observations when using predictors related to convergence rather than moist energetics (e.g., CAPE) as per Peters et al. Here, this work is extended to a fully prognostic multicloud model. A nonlocal convergence-coupled formulation of the stochastic multicloud model is implemented without wind-dependent surface heat fluxes. In a series of idealized Walker cell simulations, this convergence coupling enhances the persistence of Kelvin wave analogs in dry regions of the domain while leaving the dynamics in moist regions largely unaltered. This effect is robust for changes in the amplitude of the imposed sea surface temperature (SST) gradient. In essence, this method provides a soft convergence coupling that allows for increased interaction between cumulus convection and the large-scale circulation but does not suffer from the deleterious wave–conditional instability of the second kind (CISK) behavior of the Kuo-type moisture-convergence closures.

Sea Surface Heat Fluxes and Fortnightly Modulation of the Surface Temperature within the Ballenas Channel, Gulf of California

2013 ◽  
Vol 292 ◽  
pp. 1400-1412 ◽  
Author(s):  
A. Martínez-Díaz-de-León ◽  
Rubén Castro ◽  
E. Santamaría-del-Ángel ◽  
I. Pacheco-Ruiz ◽  
R. Blanco-Betancourt
Keyword(s):  
Surface Temperature ◽  
Gulf Of California ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Surface Heat Fluxes

scholarly journals Precipitation Sensitivity to Surface Heat Fluxes over North America in Reanalysis and Model Data

2013 ◽  
Vol 14 (3) ◽  
pp. 722-743 ◽  
Author(s):  
Alexis Berg ◽  
Kirsten Findell ◽  
Benjamin R. Lintner ◽  
Pierre Gentine ◽  
Christopher Kerr
Keyword(s):  
North America ◽  
Rainfall Variability ◽  
Surface Flux ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Eastern United States ◽  
Convective Rainfall ◽  
Surface Heat Fluxes ◽  
Functional Relationships ◽  
The Impact

Abstract A new methodology for assessing the impact of surface heat fluxes on precipitation is applied to data from the North American Regional Reanalysis (NARR) and to output from the Geophysical Fluid Dynamics Laboratory’s Atmospheric Model 2.1 (AM2.1). The method assesses the sensitivity of afternoon convective rainfall frequency and intensity to the late-morning partitioning of latent and sensible heating, quantified in terms of evaporative fraction (EF). Over North America, both NARR and AM2.1 indicate sensitivity of convective rainfall triggering to EF but no appreciable influence of EF on convective rainfall amounts. Functional relationships between the triggering feedback strength (TFS) metric and mean EF demonstrate the occurrence of stronger coupling for mean EF in the range of 0.6 to 0.8. To leading order, AM2.1 exhibits spatial distributions and seasonality of the EF impact on triggering resembling those seen in NARR: rainfall probability increases with higher EF over the eastern United States and Mexico and peaks in Northern Hemisphere summer. Over those regions, the impact of EF variability on afternoon rainfall triggering in summer can explain up to 50% of seasonal rainfall variability. However, the AM2.1 metrics also exhibit some features not present in NARR, for example, strong coupling extending northwestward from the central Great Plains into Canada. Sources of disagreement may include model hydroclimatic biases that affect the mean patterns and variability of surface flux partitioning, with EF variability typically much lower in NARR. Finally, the authors also discuss the consistency of their results with other assessments of land–precipitation coupling obtained from different methodologies.

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