scholarly journals Understanding the Equatorial Pacific Cold Tongue Time-Mean Heat Budget. Part I: Diagnostic Framework

2018 ◽  
Vol 31 (24) ◽  
pp. 9965-9985 ◽  
Author(s):  
Sulagna Ray ◽  
Andrew T. Wittenberg ◽  
Stephen M. Griffies ◽  
Fanrong Zeng
Keyword(s):  
Heat Flux ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Surface Mixed Layer ◽  
Cold Tongue ◽  
Radiative Forcings ◽  
Surface Warming ◽  
Leading Role ◽  
Diagnostic Framework ◽  
Highly Correlated

The Pacific equatorial cold tongue plays a leading role in Earth’s strongest and most predictable climate signals. To illuminate the processes governing cold tongue temperatures, the upper-ocean heat budget is explored using the GFDL-FLOR coupled GCM (the forecast-oriented low ocean resolution version of CM2.5). Starting from the exact temperature budget for layers of time-varying thickness, the layer temperature tendency terms are studied using hourly-, daily-, and monthly-mean output from a 30-yr simulation driven by present-day radiative forcings. The budget is then applied to 1) a surface mixed layer whose temperature is highly correlated with SST, in which the air–sea heat flux is balanced mainly by downward diffusion of heat across the layer base, and 2) a thicker advective layer that subsumes most of the vertical mixing, in which the air–sea heat flux is balanced mainly by monthly-scale advection. The surface warming from shortwave fluxes and submonthly meridional advection and the subsurface cooling from monthly vertical advection are both shown to be essential to maintain the cold tongue thermal stratification against the destratifying effects of vertical mixing. Although layer undulations strongly mediate the tendency terms on diurnal-to-interannual scales, the 30-yr-mean tendencies are found to be well summarized by analogous budgets developed for stationary but spatially varying layers. The results are used to derive practical simplifications of the exact budget, to support the analyses in Part II of this paper, and to facilitate broader application of heat budget analyses when evaluating and comparing climate simulations.

scholarly journals Understanding the Equatorial Pacific Cold Tongue Time-Mean Heat Budget. Part II: Evaluation of the GFDL-FLOR Coupled GCM

2018 ◽  
Vol 31 (24) ◽  
pp. 9987-10011 ◽  
Author(s):  
Sulagna Ray ◽  
Andrew T. Wittenberg ◽  
Stephen M. Griffies ◽  
Fanrong Zeng
Keyword(s):  
Heat Transport ◽  
Wind Stress ◽  
Heat Budget ◽  
Model Development ◽  
Vertical Mixing ◽  
Heat Fluxes ◽  
Thermocline Depth ◽  
Surface Mixed Layer ◽  
Cold Tongue ◽  
Coupled Gcm

The heat budget of the Pacific equatorial cold tongue (ECT) is explored using the GFDL-FLOR coupled GCM (the forecast-oriented low ocean resolution version of CM2.5) and ocean reanalyses, leveraging the two-layer framework developed in Part I. Despite FLOR’s relatively weak meridional stirring by tropical instability waves (TIWs), the model maintains a reasonable SST and thermocline depth in the ECT via two compensating biases: 1) enhanced monthly-scale vertical advective cooling below the surface mixed layer (SML), due to overly cyclonic off-equatorial wind stress that acts to cool the equatorial source waters; and 2) an excessive SST contrast between the ECT and off-equator areas, which boosts the equatorward heat transport by TIWs. FLOR’s strong advective cooling at the SML base is compensated by strong downward diffusion of heat out of the SML, which then allows FLOR’s ECT to take up a realistic heat flux from the atmosphere. Correcting FLOR’s climatological SST and wind stress biases via flux adjustment (FA) leads to weaker deep advective cooling of the ECT, which then erodes the upper-ocean thermal stratification, enhances vertical mixing, and excessively deepens the thermocline. FA does strengthen FLOR’s meridional shear of the zonal currents in the east Pacific, but this does not amplify either the simulated TIWs or their equatorward heat transport, likely due to FLOR’s coarse zonal ocean resolution. The analysis suggests that to advance coupled simulations of the ECT, improved winds and surface heat fluxes must go hand in hand with improved subseasonal and parameterized ocean processes. Implications for model development and the tropical Pacific observing system are discussed.

scholarly journals Modulation of cross-isothermal velocities with ENSO in the tropical Pacific cold tongue

2021 ◽  
Author(s):  
Anna-Lena Deppenmeier ◽  
Frank O. Bryan ◽  
William Kessler ◽  
LuAnne Thompson
Keyword(s):  
El Niño ◽  
Cold Water ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Tropical Pacific ◽  
Cold Tongue ◽  
Diabatic Processes ◽  
The Tropical Pacific

AbstractThe tropical Pacific cold tongue (CT) plays a major role in the global climate system. The strength of the CT sets the zonal temperature gradient in the Pacific that couples with the atmospheric Walker circulation. This coupling is an essential component of the El Niño Southern Oscillation (ENSO). The CT is supplied with cold water by the equatorial undercurrent that follows the thermocline as it shoals toward the east, adiabatically transporting cold water towards the surface. As the thermocline shoals, its water is transformed through diabatic processes producing water mass transformation (WMT) that allows water to cross mean isotherms. Here, we examine WMT in the cold tongue region from a global high resolution ocean simulation with saved budget terms that close its heat budget exactly. Using the terms of the heat budget, we quantify each individual component of WMT (vertical mixing, horizontal mixing, eddy fluxes, solar penetration), and find that vertical mixing is the single most important contribution in the thermocline, while solar heating dominates close to the surface. Horizontal diffusion is much smaller. During El Niño events, vertical mixing, and hence cross-isothermal flow as a whole, is much reduced, while during La Niña periods strong vertical mixing leads to strong WMT, thereby cooling the surface. This analysis demonstrates the enhancement of diabatic processes during cold events, which in turn enhances cooling of the CT from below the surface.

scholarly journals Diapycnal heat flux and mixed layer heat budget within the Atlantic Cold Tongue

2014 ◽  
Vol 43 (11) ◽  
pp. 3179-3199 ◽  
Author(s):  
Rebecca Hummels ◽  
Marcus Dengler ◽  
Peter Brandt ◽  
Michael Schlundt
Keyword(s):  
Heat Flux ◽  
Mixed Layer ◽  
Heat Budget ◽  
Cold Tongue ◽  
Mixed Layer Heat Budget ◽  
Atlantic Cold Tongue

scholarly journals Surging of Global Surface Temperature due to Decadal Legacy of Ocean Heat Uptake

2020 ◽  
Vol 33 (18) ◽  
pp. 8025-8045
Author(s):  
Bablu Sinha ◽  
Florian Sévellec ◽  
Jon Robson ◽  
A. J. George Nurser
Keyword(s):  
Thermal Gradient ◽  
Climate Model ◽  
Heat Budget ◽  
Global Climate ◽  
Global Climate Model ◽  
Vertical Mixing ◽  
Base Layer ◽  
Ocean Heat Uptake ◽  
Surface Warming ◽  
Global Surface

AbstractGlobal surface warming since 1850 has consisted of a series of slowdowns (hiatus) followed by surges. Knowledge of a mechanism to explain how this occurs would aid development and testing of interannual to decadal climate forecasts. In this paper a global climate model is forced to adopt an ocean state corresponding to a hiatus [with negative interdecadal Pacific oscillation (IPO) and other surface features typical of a hiatus] by artificially increasing the background diffusivity for a decade before restoring it to its normal value and allowing the model to evolve freely. This causes the model to develop a decadal surge that overshoots equilibrium (resulting in a positive IPO state), leaving behind a modified, warmer climate for decades. Water-mass transformation diagnostics indicate that the heat budget of the tropical Pacific Ocean is a balance between large opposite-signed terms: surface heating/cooling resulting from air–sea heat flux is balanced by vertical mixing and ocean heat transport divergence. During the artificial hiatus, excess heat becomes trapped just above the thermocline and there is a weak vertical thermal gradient (due to the high artificial background mixing). When the hiatus is terminated, by returning the background diffusivity to normal, the thermal gradient strengthens to prehiatus values so that the mixing (diffusivity × thermal gradient) remains roughly constant. However, since the base layer just above the thermocline remains anomalously warm, this implies a warming of the entire water column above the trapped heat, which results in a surge followed by a prolonged period of elevated surface temperatures.

scholarly journals The Onset of the Indonesian–Australian Summer Monsoon Triggered by the First-Branch Eastward-Propagating Madden–Julian Oscillation

2019 ◽  
Vol 32 (17) ◽  
pp. 5453-5470 ◽  
Author(s):  
Yongliang Duan ◽  
Hongwei Liu ◽  
Weidong Yu ◽  
Lin Liu ◽  
Guang Yang ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Heat Budget ◽  
Sea Surface ◽  
Specific Humidity ◽  
Surface Mixed Layer ◽  
Madden Julian Oscillation ◽  
Northern Australia ◽  
Surface Warming ◽  
Australian Summer Monsoon ◽  
Australian Summer

Abstract The Madden–Julian oscillation (MJO) often causes the onset of the Indonesian–Australian summer monsoon (IASM) over Indonesia and northern Australia. In the present study, a composite analysis is conducted to reveal the detailed IASM onset process and its air–sea interactions associated with the first-branch eastward-propagating MJO (FEMJO) based on 30-yr ERA-Interim data, satellite-derived sea surface temperature (SST), outgoing longwave radiation (OLR), and SODA3 ocean reanalysis. The results distinctly illustrate the phase-locked relationships among the persistent sea surface warming north of Australia, the FEMJO, and the established westerlies. It is found that the SST to the north of Australia reaches its annual maximum just before the onset of the summer monsoon. The oceanic surface mixed layer heat budget discloses that this rapid warming is primarily produced by the enhanced surface heat flux. In addition, this premonsoon sea surface warming increases the air specific humidity in the low-level troposphere and then establishes zonal moisture asymmetry relative to the FEMJO convection. This creates a more unstable atmospheric stratification southeast of the FEMJO and favors convection throughout the vicinity of northern Australia, which ultimately triggers the onset of the IASM. The results in this study thus may potentially be applicable to seasonal monsoon climate monitoring and prediction.

The Impact of Horizontal Resolution on the Tropical Heat Budget in an Atlantic Ocean Model

2005 ◽  
Vol 18 (6) ◽  
pp. 841-851 ◽  
Author(s):  
Markus Jochum ◽  
Raghu Murtugudde ◽  
Raffaele Ferrari ◽  
Paola Malanotte-Rizzoli
Keyword(s):  
Heat Flux ◽  
General Circulation ◽  
Heat Budget ◽  
Circulation Model ◽  
Warm Pool ◽  
Shear Instability ◽  
Entrainment Rate ◽  
Cold Tongue ◽  
Coarse Resolution ◽  
The Impact

Abstract An ocean general circulation model (OGCM) of the tropical Atlantic is coupled to an advective atmospheric boundary layer model. This configuration is used to investigate the hypothesis that resolving tropical instability waves (TIWs) in OGCMs will remove the equatorial cold bias that is a feature common to coarse-resolution OGCMs. It is shown that current eddy parameterizations cannot capture the TIW heat flux because diffusion in coarse-resolution OGCMs removes heat from the warm pool to heat the equatorial cold tongue, whereas TIWs draw their heat mostly from the atmosphere. Thus, they can bring more heat to the equatorial cold tongue without cooling the warm pool, and the SST in the warm pool is higher and more realistic. Contrary to expectations, the SST in the equatorial cold tongue is not significantly improved. The equatorial warming due to TIWs is slightly greater than the warming due to diffusion, but this increased equatorial heat flux in the high-resolution experiment is compensated by increased equatorial entrainment there. This is attributed to the Equatorial Undercurrent being stronger, thereby increasing the entrainment rate through shear instability. Thus, higher resolution does not significantly increase the total oceanic heat flux convergence in the equatorial mixed layer.

A Modeling Study of the Impact of Tropical Instability Waves on the Heat Budget of the Eastern Equatorial Pacific

2006 ◽  
Vol 36 (5) ◽  
pp. 847-865 ◽  
Author(s):  
Christophe E. R. Menkes ◽  
Jérôme G. Vialard ◽  
Sean C. Kennan ◽  
Jean-Philippe Boulanger ◽  
Gurvan V. Madec
Keyword(s):  
Mixed Layer ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Leading Edge ◽  
Cold Tongue ◽  
Instability Waves ◽  
Horizontal Advection ◽  
Vertical Advection ◽  
Tropical Instability Waves ◽  
The Impact

Abstract A numerical simulation is used to investigate the mixed layer heat balance of the tropical Pacific Ocean including the equatorial cold tongue and the region of vortices associated with tropical instability waves (TIWs). The study is motivated by a need to quantify the effects that TIWs have on the climatological heat budget of the cold tongue mixed layer; there has been some discrepancy between observations indicating very large equatorward heat transport by TIWs and models that disagree on the full three-dimensional budget. Validation of the model reveals that the TIW-induced circulation patterns are realistic but may have amplitudes about 15% weaker than those in the observations. The SST budget within tropical instabilities is first examined in a frame of reference moving with the associated tropical instability vortices (TIVs). Zonal advection of temperature anomalies and meridional advection of temperature by current anomalies dominate horizontal advection. These effects strongly heat the cold cusps and slightly cool the downwelling areas located at the leading edge of the vortices. Cooling by vertical mixing is structured at the vortex scale and almost compensates for horizontal advective heating in the cold cusps. In contrast to some previous studies, TIW-induced vertical advection is found to be negligible in the SST budget. Cooling by this term is only significant below the mixed layer. The effect of TIWs on the climatological heat budget is then investigated for the region bounded by 2°S–6°N, 160°–90°W, where instabilities are most active. TIW-induced horizontal advection leads to a warming of 0.84°C month−1, which is of the same order as the 0.77°C month−1 warming effect of atmospheric fluxes, while the mean currents and vertical mixing cool the upper ocean by −0.59°C month−1 and −1.06°C month−1, respectively. The cooling effect of TIW-induced vertical advection is also negligible in the long-term surface layer heat budget and only becomes significant below the mixed layer. The results above, and in particular the absence of cancellation between horizontal and vertical TIW-induced eddy advection, are robust in three other sensitivity experiments involving different mixing parameterizations and increased vertical resolution.

scholarly journals An Intermodel Approach to Identify the Source of Excessive Equatorial Pacific Cold Tongue in CMIP5 Models and Uncertainty in Observational Datasets

2015 ◽  
Vol 28 (19) ◽  
pp. 7630-7640 ◽  
Author(s):  
Gen Li ◽  
Yan Du ◽  
Haiming Xu ◽  
Baohua Ren
Keyword(s):  
Heat Flux ◽  
Heat Budget ◽  
Equatorial Pacific ◽  
Heat Fluxes ◽  
Specific Humidity ◽  
Cmip5 Models ◽  
Climate Projections ◽  
Cold Tongue ◽  
Budget Analysis ◽  
Dynamic Cooling

Abstract An excessive cold tongue error in the equatorial Pacific has prevailed in several generations of climate models. However, the causes of this problem remain a mystery, partly owing to uncertainty and/or a lack of observational datasets. Based on the multimodel ensemble from phase 5 of the Coupled Model Intercomparison Project (CMIP5), this study introduces a novel intermodel approach to identify the bias source by going beyond comparison with observational datasets. Intermodel statistics show that the excessive cold tongue bias could be traced back to a too strong oceanic dynamic cooling linked to a too shallow thermocline along the equatorial Pacific. A heat budget analysis suggests that the excessive oceanic dynamic cooling is balanced by the surface latent heat flux (LHF) adjustment. This is consistent with a variety of oceanic and atmospheric observations but at odds with the popular objectively analyzed air–sea heat fluxes (OAFlux) products. Further analyses suggest an alarming overestimation of OAFlux net surface heat flux (Qnet) into the tropical Pacific, mainly ascribed to observational uncertainly in air specific humidity. Implications for intermodel statistics in assessing model processes, validating observational data, and regulating future climate projections are discussed.

scholarly journals Interannual Variability of Sea Surface Temperature off Java and Sumatra in a Global GCM*

2008 ◽  
Vol 21 (11) ◽  
pp. 2451-2465 ◽  
Author(s):  
Yan Du ◽  
Tangdong Qu ◽  
Gary Meyers
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Mixed Layer ◽  
Heat Budget ◽  
Sea Surface ◽  
Surface Mixed Layer ◽  
Horizontal Advection ◽  
Cold Anomaly ◽  
Sst Anomalies

Abstract Using results from the Simple Ocean Data Assimilation (SODA), this study assesses the mixed layer heat budget to identify the mechanisms that control the interannual variation of sea surface temperature (SST) off Java and Sumatra. The analysis indicates that during the positive Indian Ocean Dipole (IOD) years, cold SST anomalies are phase locked with the season cycle. They may exceed −3°C near the coast of Sumatra and extend as far westward as 80°E along the equator. The depth of the thermocline has a prominent influence on the generation and maintenance of SST anomalies. In the normal years, cooling by upwelling–entrainment is largely counterbalanced by warming due to horizontal advection. In the cooling episode of IOD events, coastal upwelling–entrainment is enhanced, and as a result of mixed layer shoaling, the barrier layer no longer exists, so that the effect of upwelling–entrainment can easily reach the surface mixed layer. Horizontal advection spreads the cold anomaly to the interior tropical Indian Ocean. Near the coast of Java, the northern branch of an anomalous anticyclonic circulation spreads the cold anomaly to the west near the equator. Both the anomalous advection and the enhanced, wind-driven upwelling generate the cold SST anomaly of the positive IOD. At the end of the cooling episode, the enhanced surface thermal forcing overbalances the cooling effect by upwelling/entrainment, and leads to a warming in SST off Java and Sumatra.

Eddy Modulation of Air–Sea Interaction and Convection

2008 ◽  
Vol 38 (1) ◽  
pp. 65-83 ◽  
Author(s):  
Ivana Cerovečki ◽  
John Marshall
Keyword(s):  
Heat Flux ◽  
Heat Budget ◽  
Formation Rate ◽  
Mean Flow ◽  
Mode Water ◽  
Ocean Eddies ◽  
Eddy Heat Flux ◽  
Water Formation ◽  
Transformed Eulerian Mean

Abstract Eddy modulation of the air–sea interaction and convection that occurs in the process of mode water formation is analyzed in simulations of a baroclinically unstable wind- and buoyancy-driven jet. The watermass transformation analysis of Walin is used to estimate the formation rate of mode water and to characterize the role of eddies in that process. It is found that diabatic eddy heat flux divergences in the mixed layer are comparable in magnitude, but of opposite sign, to the surface air–sea heat flux and largely cancel the direct effect of buoyancy loss to the atmosphere. The calculations suggest that mode water formation estimates based on climatological air–sea heat flux data and outcrops, which do not fully resolve ocean eddies, may neglect a large opposing term in the heat budget and are thus likely to significantly overestimate true formation rates. In Walin’s watermass transformation framework, this manifests itself as a sensitivity of formation rate estimates to the averaging period over which the outcrops and air–sea fluxes are subjected. The key processes are described in terms of a transformed Eulerian-mean formalism in which eddy-induced mean flow tends to cancel the Eulerian-mean flow, resulting in weaker residual mean flow, subduction, and mode water formation rates.

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