Subsurface warm biases in the tropical Atlantic and their attributions to the role of wind forcing and ocean vertical mixing

2022 ◽  
pp. 1-28
Keyword(s):  
Climate Models ◽  
Heat Budget ◽  
Thermal Structure ◽  
Vertical Mixing ◽  
Wind Forcing ◽  
Climate Simulation ◽  
Tropical Atlantic ◽  
Warm Bias ◽  
Budget Analysis ◽  
Almost All

Abstract Realistic ocean subsurface simulations of thermal structure and variation are critically important to the success in climate prediction and projection; currently, substantial systematic subsurface biases still exist in the state-of-the-art ocean and climate models. In this paper, subsurface biases in the tropical Atlantic (TA) are investigated by analyzing simulations from OMIP and conducting POP2-based ocean-only experiments. The subsurface biases are prominent in almost all OMIP simulations, characterized by two warm bias patches off the equator. By conducting two groups of POP2-based ocean-only experiments, two potential origins of the biases are explored, including uncertainties in wind forcing and vertical mixing parameterization, respectively. It is illustrated that the warm bias near 10° N can be slightly reduced by modulating prescribed wind field, and the warm biases over the entire basin are significantly reduced by reducing background diffusivity in the ocean interior in ways to match observations. By conducting heat budget analysis, it is found that the improved subsurface simulations are attributed to the enhanced cooling effect by constraining the vertical mixing diffusivity in terms of the observational estimate, implying that the overestimation of vertical mixing is primarily responsible for the subsurface warm biases in the TA. Since the climate simulation is very sensitive to the vertical mixing parameterization, more accurate representations of ocean vertical mixing are clearly needed in ocean and climate models.

scholarly journals A Numerical Study on the Impact of High-Frequency Winds on the Peru Upwelling System during 2014–2016

2019 ◽  
Vol 7 (5) ◽  
pp. 161
Author(s):  
Linhui Wang ◽  
Huiwang Gao ◽  
Jie Shi ◽  
Lian Xie
Keyword(s):  
High Frequency ◽  
Numerical Study ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Ocean Modeling ◽  
Wind Forcing ◽  
Regional Ocean Modeling System ◽  
Upwelling System ◽  
Budget Analysis ◽  
The Impact

The contribution of high-frequency wind to the Peruvian upwelling system during 2014–2016 was studied using the Regional Ocean Modeling System (ROMS), forced by four different temporal resolution (six-hourly, daily, weekly, and monthly) wind forcing. A major effect of the high-frequency wind is its warming of the water at all depths along the Peruvian coast. The mechanism for the temperature changes induced by high-frequency wind forcing was analyzed through heat budget analysis, which indicated a three-layer structure. Vertical advection plays a leading role in the warming of the mixed layer (0–25 m), and enhanced vertical mixing balances the warming effect. Analysis suggests that around the depths of 25–60 m, vertical mixing warms the water by bringing heat from the surface to deeper depths. In waters deeper than 60 m, the effect of vertical mixing is negligible. The differences among the oceanic responses in the sensitivity experiments suggest that wind forcing containing variabilities at higher than synoptic frequencies must be included in the atmospheric forcing in order to properly simulate the Peru upwelling system.

scholarly journals An Ocean Modeling Study To Quantify Wind Forcing and Oceanic Mixing Effects on The Tropical North Pacific Subsurface Warm Bias in CMIP and OMIP Simulations

2021 ◽  
Author(s):  
Yuchao Zhu ◽  
Rong-Hua Zhang ◽  
Delei Li
Keyword(s):  
Boundary Layer ◽  
North Pacific ◽  
Thermal Structure ◽  
Vertical Mixing ◽  
Upper Ocean ◽  
Subsurface Temperature ◽  
Mixing Processes ◽  
Warm Bias ◽  
The Past ◽  
Upper Boundary

Abstract Sea surface temperature (SST) bias in the climate models has been a focus in the past, but subsurface temperature biases have not been received much attention yet. In this study, subsurface temperature biases in the Tropical North Pacific (TNP) are investigated by analyzing the CMIP6, CMIP5 and OMIP products, and performing ocean model simulations. It is found that almost all the CMIP and OMIP simulations have a pronounced subsurface warm bias (SWB) in the northeastern tropical Pacific (NETP), and the model developments over the past decade do not indicate obvious improvements in bias pattern and magnitude from CMIP5 to the latest version CMIP6. This SWB is primarily caused by the model deficiencies in the simulated surface wind stress curl (WSC) in the NETP, which is too weak to produce a sufficient Ekman upwelling, a bias that also exists in OMIP simulations. The uncertainties in the parameterizations of the oceanic vertical mixing processes also make a great contribution, and it is demonstrated that the estimated oceanic vertical diffusivities are overestimated both in the upper boundary layer and the interior in the CMIP and OMIP simulations. The relationship between the SWB and the misrepresented oceanic vertical mixing processes are investigated by conducting several ocean-only experiments, in which the upper boundary layer mixing is modified by reducing the wind stirring effect in the Kraus-Turner type bulk mixed-layer approach, and the interior mixing is constrained by using the Argo-derived diffusivity. By applying these modifications to oceanic vertical mixing schemes, the SWB is greatly reduced in the NETP. The consequences of this SWB are further analyzed. Because the thermal structure in the NETP can influence the simulations of oceanic circulations and equatorial upper-ocean thermal structure, the large SWB in the CMIP6 models tends to produce a weak equatorward water transport in the subsurface TNP, a weak equatorial upwelling and a warm equatorial upper ocean.

scholarly journals Seasonal prediction in northern Atlantic Ocean and Norwegian Seas

2021 ◽  
Author(s):  
Noel Keenlyside ◽  
Sunil Pariyar ◽  
Ingo Bethke ◽  
Yiguo Wang ◽  
Francois Counillon
Keyword(s):  
Heat Budget ◽  
Vertical Mixing ◽  
Low Frequency ◽  
Seasonal Prediction ◽  
Boreal Summer ◽  
Budget Analysis ◽  
Low Frequency Variability ◽  
Operational Systems ◽  
High Degree ◽  
High Skill

<p>Recent operational systems are able to predict sea surface temperature (SST) on seasonal timescales in the extra-tropical North Atlantic and Nordic Seas to a high-degree and as high as in the tropical Pacific. While prediction on multi-year timescales is well documented, the source of the high skill on seasonal timescales is unclear and somewhat unexpected. Here, using the Norwegian Climate Prediction model, we show that the skill on seasonal timescales is associated primarily with low-frequency variability (timescales longer than five years). Consistently, there is high skill in predicting SST anomalies six seasons in advance, although there is a skill drop across boreal summer that seems associated with reduced vertical mixing. External forcing and initialized ocean variability contribute similarly to skill on seasonal timescales, as assessed through a heat budget analysis. Skill on these timescales can benefit fisheries and aqua culture.</p>

Mean and Variability of the Tropical Atlantic Ocean in the CCSM4*

2012 ◽  
Vol 25 (14) ◽  
pp. 4860-4882 ◽  
Author(s):  
Ernesto Muñoz ◽  
Wilbert Weijer ◽  
Semyon A. Grodsky ◽  
Susan C. Bates ◽  
Ilana Wainer
Keyword(s):  
Atlantic Ocean ◽  
Wind Stress ◽  
Heat Budget ◽  
South Atlantic ◽  
Tropical Atlantic ◽  
Climate System Model ◽  
Tropical Atlantic Ocean ◽  
Modes Of Variability ◽  
Sst Variability ◽  
Budget Analysis

Abstract This study analyzes important aspects of the tropical Atlantic Ocean from simulations of the fourth version of the Community Climate System Model (CCSM4): the mean sea surface temperature (SST) and wind stress, the Atlantic warm pools, the principal modes of SST variability, and the heat budget in the Benguela region. The main goal was to assess the similarities and differences between the CCSM4 simulations and observations. The results indicate that the tropical Atlantic overall is realistic in CCSM4. However, there are still significant biases in the CCSM4 Atlantic SSTs, with a colder tropical North Atlantic and a hotter tropical South Atlantic, that are related to biases in the wind stress. These are also reflected in the Atlantic warm pools in April and September, with its volume greater than in observations in April and smaller than in observations in September. The variability of SSTs in the tropical Atlantic is well represented in CCSM4. However, in the equatorial and tropical South Atlantic regions, CCSM4 has two distinct modes of variability, in contrast to observed behavior. A model heat budget analysis of the Benguela region indicates that the variability of the upper-ocean temperature is dominated by vertical advection, followed by meridional advection.

scholarly journals Circulation and heat budget in a regional climatological simulation of the Southwestern Tropical Atlantic.

2009 ◽  
Vol 37 (1-2) ◽  
Author(s):  
Marcus SILVA ◽  
Moacyr ARAÚJO ◽  
Jacques SERVAIN ◽  
Penven Pierrick
Keyword(s):  
Ocean Circulation ◽  
Heat Budget ◽  
Thermal Structure ◽  
Climatic Variability ◽  
Mixing Layer ◽  
Upper Ocean ◽  
Western Boundary ◽  
Tropical Atlantic ◽  
The South ◽  
Data Set

Surface and vertical thermal structures, heat budget in the surface mixing layer, and mass transports are explored in the south-western tropical Atlantic (5oS-25oS / 20oW-47oW). That region, where part of the South Equatorial Current (SEC) enters at its eastern border, is of prime interest by feeding many western boundary currents along the eastern Brazilian edge, and by contributing to the climatic variability over the Northeast Brazil. The Regional Ocean Model System (ROMS) is used here to simulate a seasonal cycle of the ocean circulation with an isotropic horizontal grid resolution of 1/12o and 40 terrain-following layers. Such a high-resolution regional model allows illustrating the complexity of meso-scales phenomena which occur in that region. Model results are compared with the very first annual series of observed thermal profiles available in the region thanks to the three PIRATA-SWE moorings recently deployed. Simulated thermal structure at the upper ocean layers agrees with in-situ data set. Seasonal evolutions of atmospheric and oceanic balances involving in the mixing layer heat budget are locally discussed. The magnitude of oceanic components (mainly the vertical diffusion and the horizontal advection) is about of the same order than of atmospheric forcing, and practically always opposes to it, with some local and seasonal timing differences. Simulated meridional transports across three zonal sections extending from continent to PIRATA sites provide new insight in the knowledge of the western boundary current system. Another section running along the PIRATA-SWE array indicates how the divergence of SEC is complex. This result encourages the need and future expansion of the observational PIRATA array system in that region. Keywords: South Western Tropical Atlantic, Upper Ocean layers, Ocean heat budget, PIRATA-SWE moorings, ROMS

On the Bias in Simulated ENSO SSTA Meridional Widths of CMIP3 Models

2013 ◽  
Vol 26 (10) ◽  
pp. 3173-3186 ◽  
Author(s):  
Wenjun Zhang ◽  
Fei-Fei Jin ◽  
Jing-Xia Zhao ◽  
Jianping Li
Keyword(s):  
Climate Models ◽  
Southern Oscillation ◽  
Heat Budget ◽  
Coupled Model ◽  
Equatorial Region ◽  
Ocean Reanalysis ◽  
Trade Winds ◽  
Budget Analysis ◽  
Coupled Climate Models ◽  
Damping Rate

Abstract The fidelity of coupled climate models simulating El Niño–Southern Oscillation (ENSO) patterns has been widely examined. Nevertheless, a systematical narrow bias in the simulated meridional width of the sea surface temperature anomaly (SSTA) of ENSO has been largely overlooked. Utilizing the preindustrial control simulations of 11 coupled climate models from phase 3 of the Coupled Model Intercomparison Project (CMIP3), it was shown that the simulated width of the ENSO SSTA is only about two-thirds of what is observed. Through a heat budget analysis based on simulations and ocean reanalysis datasets, it is demonstrated that the SSTA outside of the equatorial strip is predominantly controlled by the anomalous meridional advection by climatological currents and heat-flux damping. The authors thus propose a simple damped-advective conceptual model to describe ENSO width. The simple model indicates that this width is primarily determined by three factors: meridional current, ENSO period, and thermal damping rate. When the meridional current is weak, it spreads the equatorial SSTA away from the equator less effectively and the ENSO width thus tends to be narrow. A short ENSO period allows less time to transport the equatorial SSTA toward the off-equatorial region, and strong damping prevents expansion of the SSTA away from the equator, both of which lead to the meridional width becoming narrow. The narrow bias of the simulated ENSO width is mainly due to a systematical bias in weak trade winds that lead to weak ocean meridional currents, and partly due to a bias toward short ENSO periods.

scholarly journals A data assimilative perspective of oceanic mesoscale eddy evolution during VOCALS-REx

2013 ◽  
Vol 13 (6) ◽  
pp. 3329-3344 ◽  
Author(s):  
A. C. Subramanian ◽  
A. J. Miller ◽  
B. D. Cornuelle ◽  
E. Di Lorenzo ◽  
R. A. Weller ◽  
...  
Keyword(s):  
Large Scale ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Mesoscale Eddy ◽  
Ocean Model ◽  
Height Anomaly ◽  
Depth Range ◽  
Mixing Processes ◽  
Budget Analysis ◽  
The Cost

Abstract. Oceanic observations collected during the VOCALS-REx cruise time period, 1–30 November 2008, are assimilated into a regional ocean model (ROMS) using 4DVAR and then analyzed for their dynamics. Nonlinearities in the system prevent a complete 30-day fit, so two 15-day fits for 1–15 November and 16–30 November are executed using the available observations of hydrographic temperature and salinity, along with satellite fields of SST and sea-level height anomaly. The fits converge and reduce the cost function significantly, and the results indicated that ROMS is able to successfully reproduce both large-scale and smaller-scale features of the flows observed during the VOCALS-REx cruise. Particular attention is focused on an intensively studied eddy at 76° W, 19° S. The ROMS fits capture this eddy as an isolated rotating 3-D vortex with a strong subsurface signature in velocity, temperature and anomalously low salinity. The eddy has an average temperature anomaly of approximately −0.5 °C over a depth range from 50–600 m and features a cold anomaly of approximately −1 °C near 150 m depth. The eddy moves northwestward and elongates during the second 15-day fit. It exhibits a strong signature in the Okubo-Weiss parameter, which indicates significant nonlinearity in its evolution. The heat balance for the period of the cruise from the ocean state estimate reveals that the horizontal advection and the vertical mixing processes are the dominant terms that balance the temperature tendency of the upper layer of the ocean locally in time and space. Areal averages around the eddies, for a 15-day period during the cruise, suggest that vertical mixing processes generally balance the surface heating. Although, this indicates only a small role for lateral advective processes in this region during this period, this quasi-instantaneous heat budget analysis cannot be extended to interpret the seasonal or long-term upper ocean heat budget in this region.

scholarly journals Do CMIP5 Models Show El Niño Diversity?

2020 ◽  
Vol 33 (5) ◽  
pp. 1619-1641 ◽  
Author(s):  
Jie Feng ◽  
Tao Lian ◽  
Jun Ying ◽  
Junde Li ◽  
Gen Li
Keyword(s):  
El Niño ◽  
El Nino ◽  
Heat Budget ◽  
Equatorial Pacific ◽  
Cmip5 Models ◽  
Budget Analysis ◽  
Future Global Warming ◽  
Central Equatorial Pacific ◽  
The Future ◽  
Sst Gradient

AbstractWhether the state-of-the-art CMIP5 models have different El Niño types and how the degree of modeled El Niño diversity would be impacted by the future global warming are still heavily debated. In this study, cluster analysis is used to investigate El Niño diversity in 30 CMIP5 models. As the method does not rely on any prior knowledge of the patterns of El Niño seen in observations, it provides a practical way to identify the degree of El Niño diversity in models. Under the historical scenario, most models show a poor degree of El Niño diversity in their own model world, primarily due to the lopsided numbers of events belonging to the two modeled El Niño types and the weak compactness of events in each cluster. Four models are found showing significant El Niño diversity, yet none of them captures the longitudinal distributions of the warming centers of the two El Niño types seen in the observations. Heat budget analysis of the sea surface temperature (SST) anomaly suggests that the degree of modeled El Niño diversity is highly related to the climatological zonal SST gradient over the western-central equatorial Pacific in models. As the gradient is weakened in most models under the future high-emission scenario, the degree of modeled El Niño diversity is further reduced in the future. The results indicate that a better simulation of the SST gradient over the western-central equatorial Pacific might allow a more reliable simulation/projection of El Niño diversity in most CMIP5 models.

scholarly journals A Polar Low Pair over the Norwegian Sea

2009 ◽  
Vol 137 (8) ◽  
pp. 2559-2575 ◽  
Author(s):  
Burghard Brümmer ◽  
Gerd Müller ◽  
Gunnar Noer
Keyword(s):  
Heat Budget ◽  
Cloud Layer ◽  
Sea Surface ◽  
Cloud Base ◽  
Aircraft Measurements ◽  
Polar Lows ◽  
The North ◽  
Polar Low ◽  
Upper Level Jet ◽  
Almost All

Abstract During the Lofotes cyclone experiment (LOFZY 2005), two polar lows developed one behind the other inside a cold-air outbreak from the north in the lee of Spitsbergen on 7 March 2005. Buoys, ship, and aircraft measurements as well as satellite imagery are applied to analyze the polar low bulk properties, the horizontal and vertical structure, and the mass, moisture, and heat budget. The lifetime of the system until landfall at northern Norway was 12 h. The generation occurred under the left exit region of an upper-level jet with 70 m s−1. Both polar lows had a radius of 100–130 km and extended to a height of about 2.5 km. The propagation speeds were within 14–17 m s−1 and correspond to the vertically averaged wind velocity of the lowest 2.5 km. In the polar low centers the pressure was about 2–3 hPa lower and the air was 1–2 K warmer and drier than in the surroundings. Aircraft measurements in the second of the two polar lows show an embedded frontlike precipitation band north of the center. Here, the highest low-level winds with 25 m s−1 and the largest fluxes of sensible and latent heat with 290 and 520 W m−2, respectively, were measured (areal averages amounted to 115 and 190 W m−2). Aircraft data show mass convergence in the subcloud layer (0–900 m) and divergence in the cloud layer (900–2500 m). Moisture supply by evaporation from the sea surface was about twice as large as that by convergence in the subcloud layer. The condensation rate in the cloud layer nearly equaled the rate of evaporation at the sea surface. Almost all condensed cloud water was converted to precipitation water. Only half of the precipitation at the cloud base reached the sea surface.

scholarly journals A New Double-Moment Microphysics Parameterization for Application in Cloud and Climate Models. Part II: Single-Column Modeling of Arctic Clouds

2005 ◽  
Vol 62 (6) ◽  
pp. 1678-1693 ◽  
Author(s):  
H. Morrison ◽  
J. A. Curry ◽  
M. D. Shupe ◽  
P. Zuidema
Keyword(s):  
Climate Models ◽  
Heat Budget ◽  
Number Concentration ◽  
The Arctic ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Radiative Fluxes ◽  
Arctic Clouds ◽  
Single Column ◽  
Double Moment

Abstract The new double-moment microphysics scheme described in Part I of this paper is implemented into a single-column model to simulate clouds and radiation observed during the period 1 April–15 May 1998 of the Surface Heat Budget of the Arctic (SHEBA) and First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment–Arctic Clouds Experiment (FIRE–ACE) field projects. Mean predicted cloud boundaries and total cloud fraction compare reasonably well with observations. Cloud phase partitioning, which is crucial in determining the surface radiative fluxes, is fairly similar to ground-based retrievals. However, the fraction of time that liquid is present in the column is somewhat underpredicted, leading to small biases in the downwelling shortwave and longwave radiative fluxes at the surface. Results using the new scheme are compared to parallel simulations using other microphysics parameterizations of varying complexity. The predicted liquid water path and cloud phase is significantly improved using the new scheme relative to a single-moment parameterization predicting only the mixing ratio of the water species. Results indicate that a realistic treatment of cloud ice number concentration (prognosing rather than diagnosing) is needed to simulate arctic clouds. Sensitivity tests are also performed by varying the aerosol size, solubility, and number concentration to explore potential cloud–aerosol–radiation interactions in arctic stratus.

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