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.

Tropical Cells and a Secondary Circulation near the Northern Front of the Equatorial Pacific Cold Tongue*

2010 ◽  
Vol 40 (9) ◽  
pp. 2091-2106 ◽  
Author(s):  
Renellys C. Perez ◽  
Meghan F. Cronin ◽  
William S. Kessler
Keyword(s):  
Mixed Layer ◽  
Equatorial Pacific ◽  
Secondary Circulation ◽  
Subsurface Water ◽  
Surface Mixed Layer ◽  
Cold Tongue ◽  
Near Surface ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
The Mean

Abstract Shipboard measurements and a model are used to describe the mean structure of meridional–vertical tropical cells (TCs) in the central equatorial Pacific and a secondary circulation associated with the northern front of the cold tongue. The shape of the front is convoluted by the passage of tropical instability waves (TIWs). When velocities are averaged in a coordinate system centered on the instantaneous position of the northern front, the measurements show a near-surface minimum in northward flow north of the surface front (convergent flow near the front). This convergence and inferred downwelling extend below the surface mixed layer, tilt poleward with depth, and are meridionally bounded by regions of divergence and upwelling. Similarly, the model shows that, on average, surface cold tongue water moves northward toward the frontal region and dives below tilted front, whereas subsurface water north of the front moves southward toward the front, upwells, and then moves northward in the surface mixed layer. The model is used to demonstrate that this mean quasi-adiabatic secondary circulation is not a frozen field that migrates with the front but is instead highly dependent on the phase of the TIWs: southward-upwelling flow on the warm side of the front tends to occur when the front is displaced southward, whereas northward-downwelling flow on the cold side of the front occurs when the front is displaced northward. Consequently, when averaged in geographic coordinates, the observed and simulated TCs appear to be equatorially asymmetric and show little trace of a secondary circulation near the mean front.

scholarly journals Temperature Advection by Tropical Instability Waves

2006 ◽  
Vol 36 (4) ◽  
pp. 592-605 ◽  
Author(s):  
Markus Jochum ◽  
Raghu Murtugudde
Keyword(s):  
Mixed Layer ◽  
Heat Budget ◽  
Basic Mechanism ◽  
Tropical Pacific Ocean ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
Temperature Advection ◽  
Mixed Layer Heat Budget ◽  
Oscillatory Temperature ◽  
The Tropical Pacific

Abstract A numerical model of the tropical Pacific Ocean is used to investigate the processes that cause the horizontal temperature advection of tropical instability waves (TIWs). It is found that their temperature advection cannot be explained by the processes on which the mixing length paradigm is based. Horizontal mixing of temperature across the equatorial SST front does happen, but it is small relative to the “oscillatory” temperature advection of TIWs. The basic mechanism is that TIWs move water back and forth across a patch of large vertical entrainment. Outside this patch, the atmosphere heats the water and this heat is then transferred into the thermocline inside the patch. These patches of strong localized entrainment are due to equatorial Ekman divergence and due to thinning of the mixed layer in the TIW cyclones. The latter process is responsible for the zonal temperature advection, which is as large as the meridional temperature advection but has not yet been observed. Thus, in the previous observational literature the TIW contribution to the mixed layer heat budget may have been underestimated significantly.

Effect of tropical instability waves on the eastern tropical Pacific basin: damping of TIWs in a high-resolution ocean circulation model

2021 ◽  
Author(s):  
Lisa Maillard ◽  
Julien Boucharel ◽  
Lionel Renault
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Heat Budget ◽  
Tropical Pacific ◽  
Eastern Tropical Pacific ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
Equatorial Wave ◽  
Modelling Studies ◽  
The Impact

<p>Tropical instability waves (TIWs) are oceanic cusp-like features propagating westward along the northern front of the tropical pacific cold tongue. Observational and modelling studies suggest that TIWs may have a large impact on the eastern tropical Pacific background state from seasonal to interannual time-scales, through heat advection and mixing. However, observations are coarse or limited to surface data, and modelling studies are often based on the comparison of low- vs. high-resolution simulations. In this study, we perform a set of regional high-resolution ocean simulations (CROCO 1/12°) in which we strongly damp (NUDG-RUN) or not (CTRL-RUN) TIWs propagation, by nudging the mixed layer meridional current velocities in the TIWs active region toward their climatological values. We first show that this approach do not alter the model internal physics, in particular related to the equatorial wave dynamics. The impact of TIWs on the oceanic mean state (zonal current and heat budget) is then assessed by comparing CTRL-RUN to NUDG-RUN. This approach allows quantifying for the first time the rectified effect of TIWs without degrading the model horizontal resolution, and may lead to a better understanding of ENSO asymmetry and the development of accurate TIWs parameterizations in Earth system models.</p>

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.

scholarly journals Impact of Cyclonic Ocean Eddies on Upper Ocean Thermodynamic Response to Typhoon Soudelor

2019 ◽  
Vol 11 (8) ◽  
pp. 938 ◽  
Author(s):  
Jue Ning ◽  
Qing Xu ◽  
Han Zhang ◽  
Tao Wang ◽  
Kaiguo Fan
Keyword(s):  
Vertical Mixing ◽  
Heat Content ◽  
Mesoscale Eddies ◽  
Upper Ocean ◽  
Surface Cooling ◽  
Ocean Eddies ◽  
Horizontal Advection ◽  
Content Change ◽  
Order Of Magnitude ◽  
The Impact

By using multiplatform satellite datasets, Argo observations and numerical model data, the upper ocean thermodynamic responses to Super Typhoon Soudelor are investigated with a focus on the impact of an ocean cyclonic eddy (CE). In addition to the significant surface cooling inside the CE region, an abnormally large rising in subsurface temperature is observed. The maximum warming and heat content change (HCC) reach up to 4.37 °C and 1.73 GJ/m2, respectively. Moreover, the HCC is an order of magnitude larger than that calculated from statistical analysis of Argo profile data in the previous study which only considered the effects caused by typhoons. Meanwhile, the subsurface warming outside the CE is merely 1.74 °C with HCC of 0.39 GJ/m2. Previous studies suggested that typhoon-induced vertical mixing is the primary factor causing subsurface warming but these studies ignored an important mechanism related to the horizontal advection caused by the rotation and movement of mesoscale eddies. This study documents that the eddy-induced horizontal advection has a great impact on the upper ocean responses to typhoons. Therefore, the influence of eddies should be considered when studying the responses of upper ocean to typhoons with pre-existing mesoscale eddies.

scholarly journals U.K. HiGEM: The New U.K. High-Resolution Global Environment Model—Model Description and Basic Evaluation

2009 ◽  
Vol 22 (8) ◽  
pp. 1861-1896 ◽  
Author(s):  
L. C. Shaffrey ◽  
I. Stevens ◽  
W. A. Norton ◽  
M. J. Roberts ◽  
P. L. Vidale ◽  
...  
Keyword(s):  
High Resolution ◽  
Tropical Pacific ◽  
Model Description ◽  
Small Scale ◽  
Environmental Model ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
Global Environmental ◽  
The Impact ◽  
The Tropical Pacific

Abstract This article describes the development and evaluation of the U.K.’s new High-Resolution Global Environmental Model (HiGEM), which is based on the latest climate configuration of the Met Office Unified Model, known as the Hadley Centre Global Environmental Model, version 1 (HadGEM1). In HiGEM, the horizontal resolution has been increased to 0.83° latitude × 1.25° longitude for the atmosphere, and 1/3° × 1/3° globally for the ocean. Multidecadal integrations of HiGEM, and the lower-resolution HadGEM, are used to explore the impact of resolution on the fidelity of climate simulations. Generally, SST errors are reduced in HiGEM. Cold SST errors associated with the path of the North Atlantic drift improve, and warm SST errors are reduced in upwelling stratocumulus regions where the simulation of low-level cloud is better at higher resolution. The ocean model in HiGEM allows ocean eddies to be partially resolved, which dramatically improves the representation of sea surface height variability. In the Southern Ocean, most of the heat transports in HiGEM is achieved by resolved eddy motions, which replaces the parameterized eddy heat transport in the lower-resolution model. HiGEM is also able to more realistically simulate small-scale features in the wind stress curl around islands and oceanic SST fronts, which may have implications for oceanic upwelling and ocean biology. Higher resolution in both the atmosphere and the ocean allows coupling to occur on small spatial scales. In particular, the small-scale interaction recently seen in satellite imagery between the atmosphere and tropical instability waves in the tropical Pacific Ocean is realistically captured in HiGEM. Tropical instability waves play a role in improving the simulation of the mean state of the tropical Pacific, which has important implications for climate variability. In particular, all aspects of the simulation of ENSO (spatial patterns, the time scales at which ENSO occurs, and global teleconnections) are much improved in HiGEM.

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 Heat Balance and Eddies in the Caribbean Upwelling System

2013 ◽  
Vol 43 (5) ◽  
pp. 1004-1014 ◽  
Author(s):  
Julien Jouanno ◽  
Julio Sheinbaum
Keyword(s):  
High Resolution ◽  
Mixed Layer ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Warm Pool ◽  
Upwelling System ◽  
Mixed Layer Heat Budget ◽  
The Caribbean ◽  
Surrounding Areas ◽  
Surface Jets

Abstract The upper-ocean heat budget of the Caribbean upwelling system is investigated during the onset of the Atlantic warm pool (June–September) using high-resolution observations of sea surface temperature and a high-resolution (°) regional model. Vertical mixing is found to be the major cooling contribution to the mixed layer heat budget in the nearshore and offshore Colombia Basin. Numerical results show that intense mesoscale eddies in the Colombia Basin significantly shape the turbulent cooling and may participate in the maintenance of cooler temperature in this region compared to surrounding areas. Indeed, increased mixing at the base of the mixed layer occurs below energetic surface jets that form on the downstream side of the eddies. These jets generally flow offshore and may arise from the deformation of the surface mesoscale field. It is shown that significant contribution of horizontal advection to the mixed layer heat budget is limited to a radius of 300 km around the Guajira and Margarita upwelling zones.

scholarly journals Langmuir Circulation: An Agent for Vertical Restratification?

2012 ◽  
Vol 42 (11) ◽  
pp. 1945-1958 ◽  
Author(s):  
Ke Li ◽  
Zhexuan Zhang ◽  
Greg Chini ◽  
Glenn Flierl
Keyword(s):  
Surface Waves ◽  
Mixed Layer ◽  
Vertical Mixing ◽  
Surface Mixed Layer ◽  
Symmetric Mode ◽  
Instability Mode ◽  
Two Dimensional ◽  
Langmuir Circulation ◽  
The Stability ◽  
The Impact

Abstract Comparably little is known about the impact of down-front-propagating surface waves on the stability of submesoscale lateral fronts in the ocean surface mixed layer. In this investigation, the stability of lateral fronts in gradient–wind balance to two-dimensional (down-front invariant) disturbances is analyzed using the stratified, rotating Craik–Leibovich (CL) equations. Through the action of the CL vortex force, the surface waves fundamentally alter the superinertial, two-dimensional linear stability of these fronts, with the classical symmetric instability mode being replaced by a hybrid Langmuir circulation/symmetric mode. The hybrid mode is shown to exhibit much larger growth rates than the pure symmetric mode, to exist in a regime in which the vertical Richardson number is greater than 1, and to accomplish significant cross-isopycnal transport. Nonhydrostatic numerical simulations reveal that the nonlinear evolution of this hybrid instability mode can lead to rapid, that is, superinertial, vertical restratification of the mixed layer. Paradoxically, Langmuir circulation—generally viewed as a prominent vertical mixing mechanism in the upper ocean—may thus play a role in mixed layer restratification.

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