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 Asymmetric Response of the Equatorial Pacific SST to Climate Warming and Cooling

2017 ◽  
Vol 30 (18) ◽  
pp. 7255-7270 ◽  
Author(s):  
Fukai Liu ◽  
Yiyong Luo ◽  
Jian Lu ◽  
Oluwayemi Garuba ◽  
Xiuquan Wan
Keyword(s):  
Heat Flux ◽  
Heat Budget ◽  
Dominant Role ◽  
Surface Heat ◽  
Equatorial Pacific ◽  
Heat Fluxes ◽  
Shortwave Radiation ◽  
Asymmetric Structure ◽  
Linear Component ◽  
Budget Analysis

Abstract The response of the equatorial Pacific Ocean to heat fluxes of equal amplitude but opposite sign is investigated using the Community Earth System Model (CESM). Results show a strong asymmetry in SST changes. In the eastern equatorial Pacific (EEP), the warming responding to the positive forcing exceeds the cooling response to the negative forcing, whereas in the western equatorial Pacific (WEP) it is the other way around and the cooling surpasses the warming. This leads to a zonal dipole asymmetric structure, with positive values in the east and negative values in the west. A surface heat budget analysis suggests that the SST asymmetry mainly results from the oceanic horizontal advection and vertical entrainment, with both of their linear and nonlinear components playing a role. For the linear component, its change appears to be more significant over the EEP (WEP) in the positive (negative) forcing scenario, favoring the seesaw pattern of the SST asymmetry. For the nonlinear component, its change acts to warm (cool) the EEP (WEP) in both scenarios, also favorable for the development of the SST asymmetry. Additional experiments with a slab ocean confirm the dominant role of ocean dynamical processes for this SST asymmetry. The net surface heat flux, in contrast, works to reduce the SST asymmetry through its shortwave radiation and latent heat flux components, with the former being related to the nonlinear relationship between SST and convection, and the latter being attributable to Newtonian damping and air–sea stability effects. The suppressing effect of shortwave radiation on SST asymmetry is further verified by partially coupled overriding experiments.

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 The Surface Wind Influence on the Heat Fluxes Variability on the South Atlantic

2021 ◽  
Author(s):  
Douglas Lindemann ◽  
Alvaro Avila-Diaz ◽  
Luciano Pezzi ◽  
Jackson Rodrigues ◽  
Rose Ane Freitas ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Wind ◽  
Sensible Heat Flux ◽  
South Atlantic ◽  
Heat Fluxes ◽  
Specific Humidity ◽  
Cmip5 Models ◽  
Mean Bias Error ◽  
Bias Error ◽  
The South

Abstract An adequate representation by models and reanalyzes is fundamental since the coverage by observational data on the oceans is still limited. Therefore, this paper aims to evaluate the influence of the wind near the surface on the heat fluxes during the southern winter and summer seasons. Datasets from Coupled Model Intercomparison Project Phase 5 (CMIP5) and reanalyzes were used, in comparison to Objectively Analyzed Air - sea Fluxes (OAFlux) for the South Atlantic Ocean (SAO) during 1980-2005. Results point out an overestimation on the CMIP5 models and reanalyzes to reproduce the heat flux latent and sensible fluxes of SAO, mainly at medium and high latitudes. One possibility may be related the underestimating of surface wind speed, causing an impacts on the heat exchange between ocean and atmosphere. It was also possible to verify that the representation of heat flux, specific humidity, and air and ocean temperatures shows small biases (Mean Bias Error (MBE) to specific humidity (±5 kg.kg-1) and sensible heat flux (±10 W.m-2)). To the test Root Mean Square Error (RMSE)-observations Standard deviation Ratio (RSR), air temperature values are less than 1 °C, and for the wind with values greater than 2 m.s-1. There is less precision of CMIP5 models than OAFlux, resulting in low correlation values (between -0.3 and 0.3). On the other hand, the reanalyzes show small biases in air and ocean temperatures (between ±1 °C) and significant correlations (above 0.9) with the best performances for the NCEP and ERA5.

scholarly journals The interplay of thermodynamics and ocean dynamics during ENSO growth phase

2020 ◽  
Author(s):  
Tobias Bayr ◽  
Annika Drews ◽  
Mojib Latif ◽  
Joke Lübbecke
Keyword(s):  
Heat Flux ◽  
Latent Heat Flux ◽  
Growth Phase ◽  
Climate Models ◽  
Phase Locking ◽  
Equatorial Pacific ◽  
Heat Fluxes ◽  
Ocean Dynamics ◽  
Eastern Equatorial Pacific ◽  
Atmospheric Heat

AbstractThe growth of El Niño/Southern Oscillation (ENSO) events is determined by the balance between ocean dynamics and thermodynamics. Here we quantify the contribution of the thermodynamic feedbacks to the sea surface temperature (SST) change during ENSO growth phase by integrating the atmospheric heat fluxes over the temporarily and spatially varying mixed layer to derive an offline “slab ocean” SST. The SST change due to ocean dynamics is estimated as the residual with respect to the total SST change. In observations, 1 K SST change in the Niño3.4 region is composed of an ocean dynamical SST forcing of + 2.6 K and a thermodynamic damping of − 1.6 K, the latter mainly by the shortwave-SST (− 0.9 K) and latent heat flux-SST feedback (− 0.7 K). Most climate models from the Coupled Model Intercomparison Project phase 5 (CMIP5) underestimate the SST change due to both ocean dynamics and net surface heat fluxes, revealing an error compensation between a too weak forcing by ocean dynamics and a too weak damping by atmospheric heat fluxes. In half of the CMIP5 models investigated in this study, the shortwave-SST feedback erroneously acts as an amplifying feedback over the eastern equatorial Pacific, resulting in a hybrid of ocean-driven and shortwave-driven ENSO dynamics. Further, the phase locking and asymmetry of ENSO is investigated in the CMIP5 model ensemble. The climate models with stronger atmospheric feedbacks tend to simulate a more realistic seasonality and asymmetry of the heat flux feedbacks, and they exhibit more realistic phase locking and asymmetry of ENSO. Moreover, the almost linear latent heat flux feedback contributes to ENSO asymmetry in the far eastern equatorial Pacific through an asymmetry in the mixed layer depth. This study suggests that the dynamic and thermodynamic ENSO feedbacks and their seasonality and asymmetries are important metrics to consider for improving ENSO representation in climate models.

scholarly journals Thermal Regime of Ice Covered Swedish Lakes

1996 ◽  
Vol 27 (1-2) ◽  
pp. 39-56 ◽  
Author(s):  
Lars Bengtsson ◽  
Thorbjörn Svensson
Keyword(s):  
Heat Flux ◽  
Solar Radiation ◽  
Heat Source ◽  
Lake Water ◽  
Heat Budget ◽  
Heat Content ◽  
Heat Fluxes ◽  
Late Winter ◽  
Temperature Profiles ◽  
Early Winter

Temperature conditions and heat fluxes in ice covered lakes are discussed analyzing measurements in eight Swedish lakes. Heat fluxes from sediments and heat fluxes from water to ice are determined from temperature profiles. The contribution of solar radiation is estimated from heat-budget calculations. It is found that the heat content of most of the lakes changes very little when they are ice covered, but that the lake-water temperature slightly increases. All heat fluxes are small. The heat flux from the sediments is the highest flux in early winter, but is later in the winter balanced by the heat loss from the water to the underside of the ice. Solar radiation is an important heat source in late winter, when the snow cover is thin.

Intraseasonal SST Variability and Air–Sea Interaction over the Kuroshio Extension Region during Boreal Summer

2012 ◽  
Vol 25 (5) ◽  
pp. 1619-1634 ◽  
Author(s):  
Lu Wang ◽  
Tim Li ◽  
Tianjun Zhou
Keyword(s):  
Heat Budget ◽  
Kuroshio Extension ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Shortwave Radiation ◽  
Boreal Summer ◽  
Budget Analysis ◽  
Anomalous Anticyclone ◽  
Sst Warming ◽  
The Kuroshio

The structure and evolution characteristics of intraseasonal (20–100 day) variations of sea surface temperature (SST) and associated atmospheric and oceanic circulations over the Kuroshio Extension (KE) region during boreal summer are investigated, using satellite-based daily SST, observed precipitation data, and reanalysis data. The intraseasonal SST warming in the KE region is associated with an anomalous anticyclone in the overlying atmosphere, reduced precipitation, and northward and downward currents in the upper ocean. The corresponding atmospheric and oceanic fields during the SST cooling phase exhibit a mirror image with an opposite sign. A mixed layer heat budget analysis shows that the intraseasonal SST warming is primarily attributed to anomalous shortwave radiation and latent heat fluxes at the surface. The anomalous sensible heat flux and oceanic advection also have contributions, but with a much smaller magnitude. The SST warming caused by the atmospheric forcing further exerts a significant feedback to the atmosphere through triggering the atmospheric convective instability and precipitation anomalies. The so-induced heating leads to quick setup of a baroclinic response, followed by a baroclinic-to-barotropic transition. As a result, the atmospheric circulation changes from an anomalous anticyclone to an anomalous cyclone. This two-way interaction scenario suggests that the origin of the atmospheric intraseasonal oscillation over the KE region may partly arise from the local atmosphere–ocean interaction.

Surface heat fluxes in the Western Equatorial Pacific Ocean

1995 ◽  
Vol 13 (10) ◽  
pp. 1047-1053 ◽  
Author(s):  
N. C. Wells
Keyword(s):  
Heat Flux ◽  
Pacific Ocean ◽  
Latent Heat ◽  
Longwave Radiation ◽  
Surface Heat ◽  
Equatorial Pacific ◽  
Heat Fluxes ◽  
Equatorial Pacific Ocean ◽  
Net Heat Flux ◽  
Western Equatorial Pacific

Abstract. Estimates of the components of the surface heat flux in the Western Equatorial Pacific Ocean are presented for a 22-day period, together with a critical analysis of the errors. It is shown that the errors in latent heat, and solar and longwave radiation fluxes, dominate the net heat flux for this period. It is found that the net heat flux into the ocean over the 22-day period is not significantly different from zero. It is also demonstrated that because of the variability in daily averaged values of solar radiation and the latent heat of evaporation, a large number of independent flux measurements will be required to determine with confidence the climatological net heat flux in this region. The variability of latent fluxes over the 22-day period suggest that climatological estimates based on monthly mean observations may lead to a significant underestimate of the latent heat flux.

scholarly journals On the parameterization of turbulent fluxes over the tropical Eastern Pacific

2006 ◽  
Vol 6 (3) ◽  
pp. 5251-5268
Author(s):  
G. B. Raga ◽  
S. Abarca
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Latent Heat ◽  
Turbulent Fluxes ◽  
Heat Fluxes ◽  
Eastern Pacific ◽  
Specific Humidity ◽  
Horizontal Wind ◽  
High Wind ◽  
Tropical Eastern Pacific

Abstract. We present estimates of turbulent fluxes of heat and momentum derived from low level (~30 m) aircraft measurements over the tropical Eastern Pacific and provide empirical relationships that are valid under high wind speed conditions (up to 25 ms−1). The estimates of total momentum flux and turbulent kinetic energy can be represented very accurately (r2=0.99, when data are binned every 1 ms−1) by empirical fits with a linear and a cubic terms of the average horizontal wind speed. The latent heat flux shows a strong quadratic dependence on the horizontal wind speed and a linear relationship with the difference between the air specific humidity and the saturated specific humidity at the sea surface, explaining 96% of the variance. The estimated values were used to evaluate the performance of three currently used parameterizations of turbulence fluxes, varying in complexity and computational requirements. The comparisons with the two more complex parameterizations show good agreement between the observed and parameterized latent heat fluxes, with less agreement in the sensible heat fluxes, and one of them largely overestimating the momentum fluxes. A third, very simple parameterization shows a surprisingly good agreement of the sensible heat flux, while momentum fluxes are again overestimated and a poor agreement was observed for the latent heat flux (r2=0.62). The performance of all three parameterizations deteriorates significantly in the high wind speed regime (above 10–15 ms−1). The dataset obtained over the tropical Eastern Pacific allows us to derive empirical functions for the turbulent fluxes that are applicable from 1 to 25 ms−1, which can be introduced in meteorological models under high wind conditions.

Study on the Land-Atmosphere Interaction in the Coordination Effect of Westerly Wind and Monsoon

2021 ◽  
Author(s):  
Maoshan Li ◽  
Lingzhi Wang ◽  
Wei Fu ◽  
Ming Gong ◽  
Na Chang
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Wind Direction ◽  
Wind Field ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Specific Humidity ◽  
Sensible Heat ◽  
Mount Everest ◽  
Convective Boundary

<p><strong><sup> </sup></strong><sup>Different underlying surfaces have differing diversities, complex compositions and uneven distributions and contribute to diverse and complex land surfaces. As the main input factor for atmospheric energy, the surface greatly affects the various interactions between the ground and the atmosphere and even plays a key role in local areas on the Tibetan Plateau. The characteristics of the atmospheric boundary layer structure of the plateau and the land-atmosphere interaction under the control of different wind fields in the south branch of the westerly wind and the plateau monsoon are discussed. Results show that the height of the atmospheric boundary layer at each station under the westerly south branch wind field is higher than that under the summer monsoon wind field. The height of the convective boundary layers of Mount Everest, Nyingchi, Nagqu and Shiquan River in the southwest wind field are 3250 m, 2250 m, 2760 m and 3500 m. while the height of the convective boundary layers of Mount Everest, Nyingchi, Nagqu and Shiquan River under the plateau monsoon field are 2000 m, 2100 m, 1650 m and 2000 m. The specific humidity of the surface layer at all site is larger on July than it on other months. The specific humidity of the surface layer in Linzhi area is larger than that of the other three regions, and it reaches 12.88 g·kg-1 at the maximum. The wind direction on Mount Everest over 1200 m is dominated by westerly winds in May and October. The wind direction on Nyingchi above 1500 m is dominated by westerly winds in May and October, and in July, winds above 1200 m is dominated by southerly winds. The wind direction of Shiquan River in May and October is dominated by west-southwest wind, and the wind direction of Shiquan River in July is dominated by west-northwest wind. Secondly, variation characteristics of surface fluxes were analyzed by using the eddy covariance observations from four stations of Pailong(entrance of Canyon), Danka (middle of Canyon), Kabu (end of Canyon) , and Motuo (end of Canyon) in the southeastern gorge area of Tibet. The changing trend of monthly averaged daily sensible heat flux at Kabu station is fluctuating. Sensible heat flux and latent heat flux at Motuo station have the same variation characteristics. Latent heat fluxes increase first and then decrease at all four stations. Seasonal variations of soil heat flux are obvious, characterizing positive values in spring and summer and negative values in autumn and winter. The diurnal variation intensity of net radiation flux is summer>spring>autumn>winter.   Energy closure rates of Danka, Pailong, Motuo, and Kabu stations are 70.86%, 68.91%, 69.29%, and 67.23%, respectively. Latent heat fluxes and soil heat fluxes increase, and sensible heat fluxes decrease as increasing precipitation at the four stations. The sensible heat flux and soil heat flux respond synchronously to precipitation changes, and the changes in latent heat have a significant lag in response to precipitation changes.</sup></p>

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