scholarly journals Vertical Mixing in the Ocean and Its Impact on the Coupled Ocean–Atmosphere System in the Eastern Tropical Pacific*

2009 ◽  
Vol 22 (13) ◽  
pp. 3703-3719 ◽  
Author(s):  
Kelvin J. Richards ◽  
Shang-Ping Xie ◽  
Toru Miyama
Keyword(s):  
Vertical Mixing ◽  
Tropical Pacific ◽  
Intertropical Convergence Zone ◽  
General Character ◽  
Convergence Zone ◽  
Ocean Mixing ◽  
Cold Tongue ◽  
Eastern Tropical Pacific ◽  
Ocean Atmosphere ◽  
The Impact

Abstract The zonal and meridional asymmetries in the eastern tropical Pacific (the eastern equatorial cold tongue and the northern intertropical convergence zone) are key aspects of the region that are strongly influenced by ocean–atmosphere interactions. Here the authors investigate the impact of vertical mixing in the ocean on these asymmetries, employing a coupled ocean–atmosphere regional model. Results highlight the need to study the impact of processes such as vertical mixing in the context of the coupled system. Changes to the vertical mixing in the ocean are found to produce large changes in the state of the system, which include changes to the surface properties of the ocean, the ocean currents, the surface wind field, and clouds and precipitation in the atmosphere. Much of the strength of the impact is through interactions between the ocean and atmosphere. Increasing ocean mixing has an opposite effect on the zonal and meridional asymmetries. The zonal asymmetry is increased (i.e., a colder eastern equatorial cold tongue and increased easterly winds), whereas the meridional asymmetry is decreased (a reduced north–south temperature difference and reduced southerlies), with the impact being enhanced by the Bjerknes and wind–evaporation–sea surface temperature feedbacks. Water mass transformations are analyzed by consideration of the diapynic fluxes. Although the general character of the diapycnic transport remains relatively unchanged with a change in ocean mixing, there are changes to the magnitude and location of the transport in density space. Oceanic vertical mixing impacts the balance of terms contributing to the heating of the ocean surface mixed layer. With reduced mixing the advection of heat plays an increased role in areas such as the far eastern tropical Pacific and under the intertropical convergence zone.

The Impact of SST Specification on ECMWF Surface Wind Stress Fields in the Eastern Tropical Pacific

2005 ◽  
Vol 18 (4) ◽  
pp. 530-550 ◽  
Author(s):  
Dudley B. Chelton
Keyword(s):  
Wind Stress ◽  
Weather Prediction ◽  
Surface Wind ◽  
Cold Season ◽  
Numerical Weather Prediction Model ◽  
Tropical Pacific ◽  
Stress Fields ◽  
Eastern Tropical Pacific ◽  
Ocean Atmosphere ◽  
The Impact

Abstract The impact of SST specification on low-level winds in the operational ECMWF numerical weather prediction model is investigated in the eastern tropical Pacific from comparisons of ECMWF wind stress fields with QuikSCAT satellite scatterometer observations of wind stress during the August–December cold seasons of 2000 and 2001. These two time periods bracket the 9 May 2001 change from the Reynolds SST analyses to the Real-Time Global SST (RTG_SST) analyses as the ocean boundary condition in the ECMWF model. The ocean–atmosphere interaction in the eastern tropical Pacific that is clearly evident in QuikSCAT wind stress divergence and curl fields is also evident in the ECMWF winds, but is more than twice as strong in the 2001 cold season as in the 2000 cold season, due primarily to the improved spatial and temporal resolution of the RTG_SST analyses compared with the Reynolds SST analyses. While a significant improvement compared with 2000, the response of the 2001 ECMWF wind stress field to SST is only about half as strong as the coupling inferred from QuikSCAT data and satellite observations of SST from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). It is concluded that the underrepresentation of the ocean–atmosphere coupling is attributable partly to underrepresentation of SST gradients in the RTG_SST fields and partly to inadequacies of the ECWMF model. The latter may be due to errors in the parameterization of boundary layer processes or to insufficient horizontal or vertical resolution in the model.

scholarly journals Reducing Climatology Bias in an Ocean–Atmosphere CGCM with Improved Coupling Physics

2005 ◽  
Vol 18 (13) ◽  
pp. 2344-2360 ◽  
Author(s):  
Jing-Jia Luo ◽  
Sebastien Masson ◽  
Erich Roeckner ◽  
Gurvan Madec ◽  
Toshio Yamagata
Keyword(s):  
Wind Stress ◽  
Surface Current ◽  
Ocean Surface ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Eastern Pacific ◽  
Cold Tongue ◽  
Easterly Wind ◽  
Ocean Atmosphere ◽  
The Tropical Pacific

Abstract The cold tongue in the tropical Pacific extends too far west in most current ocean–atmosphere coupled GCMs (CGCMs). This bias also exists in the relatively high-resolution SINTEX-F CGCM despite its remarkable performance of simulating ENSO variations. In terms of the importance of air–sea interactions to the climatology formation in the tropical Pacific, several sensitivity experiments with improved coupling physics have been performed in order to reduce the cold-tongue bias in CGCMs. By allowing for momentum transfer of the ocean surface current to the atmosphere [full coupled simulation (FCPL)] or merely reducing the wind stress by taking the surface current into account in the bulk formula [semicoupled simulation (semi-CPL)], the warm-pool/cold-tongue structure in the equatorial Pacific is simulated better than that of the control simulation (CTL) in which the movement of the ocean surface is ignored for wind stress calculation. The reduced surface zonal current and vertical entrainment owing to the reduced easterly wind stress tend to produce a warmer sea surface temperature (SST) in the western equatorial Pacific. Consequently, the dry bias there is much reduced. The warming tendency of the SST in the eastern Pacific, however, is largely suppressed by isopycnal diffusion and meridional advection of colder SST from south of the equator due to enhanced coastal upwelling near Peru. The ENSO signal in the western Pacific and its global teleconnection in the North Pacific are simulated more realistically. The approach as adopted in the FCPL run is able to generate a correct zonal SST slope and efficiently reduce the cold-tongue bias in the equatorial Pacific. The surface easterly wind itself in the FCPL run is weakened, reducing the easterly wind stress further. This is related with a weakened zonal Walker cell in the atmospheric boundary layer over the eastern Pacific and a new global angular momentum balance of the atmosphere associated with reduced westerly wind stress over the southern oceans.

scholarly journals AMO Forcing of Multidecadal Pacific ITCZ Variability

2018 ◽  
Vol 31 (14) ◽  
pp. 5749-5764 ◽  
Author(s):  
Aaron F. Z. Levine ◽  
Dargan M. W. Frierson ◽  
Michael J. McPhaden
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Atlantic Multidecadal Oscillation ◽  
Intertropical Convergence Zone ◽  
Hadley Cell ◽  
Convergence Zone ◽  
Proxy Record ◽  
Temperature And Precipitation ◽  
The Pacific ◽  
The Impact

The Atlantic multidecadal oscillation (AMO) has been shown to play a major role in the multidecadal variability of the Northern Hemisphere, impacting temperature and precipitation, including intertropical convergence zone (ITCZ)-driven precipitation across Africa and South America. Studies into the location of the intertropical convergence zone have suggested that it resides in the warmer hemisphere, with the poleward branch of the Hadley cell acting to transport energy from the warmer hemisphere to the cooler one. Given the impact of the Atlantic multidecadal oscillation on Northern Hemisphere temperatures, we expect the Atlantic multidecadal oscillation to have an impact on the location of the intertropical convergence zone. We find that the positive phase of the Atlantic multidecadal oscillation warms the Northern Hemisphere, resulting in a northward shift of the intertropical convergence zone, which is evident in the Pacific climate proxy record. Using a coupled climate model, we further find that the shift in the intertropical convergence zone is consistent with the surface energy imbalance generated by the Atlantic multidecadal oscillation. In this model, the Pacific changes are driven in large part by the warming of the tropical Atlantic and not the extratropical Atlantic.

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 Factors that modulate the seasonal variability of the sea surface temperature of the Eastern Tropical Pacific

2009 ◽  
Vol 48 (3) ◽  
Author(s):  
A. L. Flores-Morales ◽  
A. Parés-Sierra ◽  
S. G. Marinone
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Seasonal Variability ◽  
Baja California ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Eastern Tropical Pacific ◽  
Data Set ◽  
Ocean Atmosphere

Se estudiaron los principales factores que modulan la variabilidad estacional de la temperatura superficial del mar (TSM) en el Pacífico Tropical Oriental. Para ello se analizaron las siguientes bases de datos: TSM y viento de la base Comprehensive Ocean-Atmosphere Data Set de 1978 a 1997, campos climatológicos de temperatura y salinidad de LEVITUS y alturas del nivel del mar de los altímetros TOPEX/Poseidon de 1993 a 2002. Como factores locales importantes que modulan esta variabilidad se identificaron: (1) la influencia del Golfo de California junto con el desplazamiento estacional de la Corriente de California, que se extiende desde la boca del Golfo hacia el sur y oeste unos 200 km y por el lado occidental de la península de Baja California hacia el norte aproximadamente 300 km; (2) la influencia del Golfo de Tehuantepec y del Golfo de Papagayo, donde, debido al comportamiento de los vientos, se genera un enfriamiento local de la superficie durante el invierno; (3) surgencias en el Ecuador, frente a Cabo Corrientes y frente a las costas de Baja California; (4) la variación espacial y temporal de la Zona de Convergencia Intertropical y su relación con el ecuador térmico; (5) la propagación de señales remotas y (6) la variación estacional del sistema de corrientes ecuatoriales.

scholarly journals Coastal Sea Salt Chlorine Deposition Linked to Intertropical Convergence Zone (ITCZ) Oscillation in French Guiana

2020 ◽  
Vol 77 (5) ◽  
pp. 1723-1731 ◽  
Author(s):  
M. L. Gobinddass ◽  
J. Molinie ◽  
S. Richard ◽  
K. Panechou ◽  
A. Jeannot ◽  
...  
Keyword(s):  
Wind Speed ◽  
French Guiana ◽  
Chloride Concentration ◽  
Essential Element ◽  
Intertropical Convergence Zone ◽  
Sea Salt ◽  
Chlorine Concentration ◽  
Convergence Zone ◽  
Low Level ◽  
The Impact

Abstract Sea salt chloride is a major component of atmospheric aerosol and its behavior is an essential element in determining the climate. Two atmospheric chlorine deposition measurement procedures were performed between 2004 and 2008 by the French Guiana Regional Air Observatory (ORA), in the coastal plain of Sinnamary. The main goal was to determine the background spatial distribution of marine chlorine in order to evaluate the impact of Ariane rocket hydrogen chloride emission. To determine the chlorine concentration level, weekly samples from 10 sites were analyzed. A seasonal pattern was identified. For every site, a high sea salt chlorine deposition level was observed from December to April and a low level from July to October. The ratio of high to low mean chloride concentration RHC/LC shows that just under half of the variation in chlorine deposition can be linked to the variation of sea salt production with low-level wind speed. Equations relating mean sea salt chlorine concentration and the distance to shore were studied, taking into account parameters found in other tropical regions, with a focus on neighboring Brazil. The wind rotation between the two seasons, and the sea salt chlorine loss per kilometer equation found for dry deposition, were used to calculate RHC/LC. It appears that the observed rotation (60°) explains 88% of RHC/LC. Finally, inland sea salt chlorine deposition behavior in this region was linked to intertropical convergence zone oscillation through variations in wind speed and direction.

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