Based on analysis of both observational data and data‐assimilation model product, it is shown that there exists a gap‐leaping path of the Kuroshio in the Luzon Strait. Numerical results of two sets ...of Hybrid Coordinate Ocean Model twin experiments indicate that bottom topography and islands in Luzon Strait exert control of Kuroshio's gap‐leaping behavior, especially existence of sharp northeast cape of Philippine Island is one of the most important factors for the gap‐leaping Kuroshio path in model simulation. Corresponding to the gap‐leaping Kuroshio, there is steep westward shoaling of thermocline in Luzon Strait. The enhanced upper‐layer stratification in South China Sea due to westward shoaling thermocline results in strong zonal potential vorticity (PV) gradient (one order higher than ß‐induced planetary PV gradient), and PV isolines are always parallel to the gap‐leaping path of the Kuroshio. This PV front acts as a dynamic barrier in the Luzon Strait, blocking the westward propagating Rossby waves and eddies from Pacific. This blocking effect is verified through sea‐surface height anomaly spectrum analysis, Radon Transform based Feature‐Tracking method, and eddy identification and tracking method. Numerical twin experiments demonstrate from another point of view that the gap‐leaping Kuroshio can efficiently block the westward propagating Rossby wave and eddy energy, while the fluctuating Kuroshio is less efficient for blocking.
Key Points
topography in Luzon Strait controls Kuroshio gap‐leaping behavior.gap‐leaping Kuroshio blocks the westward propagating Rossby wave and eddy.gap‐leaping Kuroshio and corresponding PV front form the dynamic barrier effect.
The role of background wind and moisture in the atmospheric response to oceanic eddies during winter in the Kuroshio Extension (KE) region is examined by numerical experiments (EXPs) using the ...Weather Research and Forecasting (WRF) model. We designed two sets of parallel experiments (dry and wet EXPs). The dry EXPs exclude the moisture in the air and the evaporation process. Each experiment differs only in the background wind speed during the initial condition. The wet EXPs include humidity in the initial condition and evaporation during the integration; the other settings are the same as the dry EXPs. The atmosphere in the two sets of EXPs are forced by the same mesoscale sea surface temperature anomaly which resembles the oceanic warm eddy in KE region. The results of these EXPs confirm that under weak background wind conditions, the atmospheric secondary circulation over oceanic eddies is driven by the pressure adjustment process due to weak advection. In the case of the dry run, the increase in background wind enhances the sea surface wind (SSW) by increasing vertical mixing. The convergence of SSW induces vertical motion and heating in the boundary layer, which further decreases the instability. The atmospheric secondary circulation in the dry run remains within the boundary layer. In wet EXPs, the atmospheric response is similar to that in dry runs when the background wind is very weak. When the background wind speed is increased to the climatology value (in KE region) or higher, the vertical motion triggers the precipitation process and diabatic heating above the boundary layer, and the heating in turn reinforces the upward flow.
Experimental outputs of 11 Atmospheric Model Intercomparison Project （AMIP） models from phase 5 of the Coupled Model Intercomparison Project （CMIP5） are analyzed to assess the atmospheric circulation ...anomaly over Northern Hemisphere induced by the anomalous rainfall over tropical Pacific and Indian Ocean during boreal winter.The analysis shows that the main features of the interannual variation of tropical rainfall anomalies,especially over the Central Pacific （CP） （5°S-5°N,175°E-135°W） and Indo-western Pacific （IWP） （20°S-20°N,110°-150°E） are well captured in all the CMIP5/AMIP models.For the IWP and western Indian Ocean （WIO） （10°S-10°N,45°-75°E）,the anomalous rainfall is weaker in the 11 CMIP5/AMIP models than in the observation.During El Ni（n）o/La Ni（n）a mature phases in boreal winter,consistent with observations,there are geopotential height anomalies known as the Pacific North American （PNA） pattern and Indo-western Pacific and East Asia （IWPEA） pattern in the upper troposphere,and the northwestern Pacific anticyclone （cyclone） （NWPA） in the lower troposphere in the models.Comparison between the models and observations shows that the ability to simulate the PNA and NWPA pattern depends on the ability to simulate the anomalous rainfall over the CP,while the ability to simulate the IWPEA pattern is related to the ability to simulate the rainfall anomaly in the IWP and WIO,as the SST anomaly is same in AMIP experiments.It is found that the tropical rainfall anomaly is important in modeling the impact of the tropical Indo-Pacific Ocean on the extratropical atmospheric circulation anomaly.
Background:
Whether statins can reduce the incidence of cancers has been an interesting topic in recent years. This meta-analysis aimed to determine the relationship between statin treatment with the ...risk of hepatocellular carcinoma.
Methods:
Studies published up to July 2019 were screened from databases. The data from approved studies were pooled. Random-effects or fixed-effects model was used to calculate the relative risk with 95% CIs in the overall group and subgroups. Sensitivity and meta-regression analyses were performed, and publication bias was evaluated.
Results:
A total of 18 studies involving 1 611 596 patients were included in this meta-analysis. The overall result showed a significantly reduced risk of hepatocellular carcinoma (relative risk = 0.54, 95% CI: 0.42-0.66) in statin users. In comparison to the risk in nonstatin users, the risk of hepatocellular carcinoma was reduced in all subgroups. The dose of statins and their pharmacokinetics can partly explain the heterogeneity in the overall meta-analysis (I
2 = 94.6%, P = .000). A dose-dependent effect of statin use for the reduced risk of hepatocellular carcinoma was found.
Conclusions:
Findings from this meta-analysis support that statin use can significantly reduce the incidence of hepatocellular carcinoma.
Previous studies have indicated that a high-level wave train from the tropical Indo–Western Pacific to East Asia (IWP-EA, expressed as geopotential height at 200 hPa) is triggered by dipolar ...convective activity anomalies over the IWP during the boreal winter. The current study highlights the relative importance of sea surface temperature forcing versus atmospheric internal variability on the IWP-EA pattern, based on an Atmospheric Model Intercomparison Project (AMIP) experiment with 30 integrations. It was found that the SST-forcing component can reproduce the observed IWP–EA pattern and the related rainfall dipole well, for both the spatial features and temporal evolutions. The internal variability of the rainfall dipole is strong in the southern and eastern Indian Ocean and region north of Australia, while the internal variability of height generally increases with latitude. The signal-to-noise ratios are just over 1 over the northernmost lobe of the IWP-EA (Japan and the region to its east), while ratios over the other centers reach values greater than 3. An inter-member EOF analysis of the rainfall dipole indicates that the variability associated with the first two modes can explain more than 70% of the total spread over most regions with large spread for both rainfall dipole and IWP-EA, including the region over Japan. Thus, some parts of internal variability of rainfall dipole and IWP-EA are connected.
The mixed layer is deep in January-April in the Kuroshio Extension region. This paper investigates the response in this region of mixed layer depth （MLD） and the spring bloom initiation to global ...warming using the output of 15 models from CMIP5. The models indicate that in the late 21st century the mixed layer will shoal and the MLD reduction will be most pronounced in spring at about 33~N on the southern edge of the present deep-MLD region. The advection of temperature change in the upper 100 m by the mean eastward flow explains the spatial pattern of MLD shoaling in the models. Associated with the shoaling mixed layer, the onset of spring bloom inception is projected to advance due to the strengthened stratification in the warming climate.
Most previous studies have proven the local negative heat flux feedback (the surface heat flux response to SST anomalies) in the midlatitude areas. However, it is uncertain whether a nonlocal heat ...flux feedback can be observed. In this paper, the generalized equilibrium feedback assessment (GEFA) method is employed to examine the full surface turbulent heat flux response to SST in the North Atlantic Ocean using NCEP–NCAR reanalysis data. The results not only confirm the dominant local negative feedback, but also indicate a robust nonlocal positive feedback of the Gulf Stream Extension (GSE) SST to the downstream heat flux in the subpolar region. This nonlocal feedback presents a strong seasonality, with response magnitudes of 16 W m−2K−1in winter and 1.2 W m−2K−1in summer. Further study indicates that the nonlocal effect is initiated by the adjustments of the downstream surface wind to the GSE SST anomalies.
The responses of Sea Surface Temperature（SST） to greenhouse gas（GHG） and anthropogenic aerosol in the North Pa- cific are compared based on the historical single and all-forcing simulations with ...Geophysical Fluid Dynamics Laboratory Climate Model version 3（GFDL CM3）. During 1860–2005, the effect of GHG forcing on the North Pacific SST is opposite to that of the aerosol forcing. Specifically, the aerosol cooling effect exceeds the GHG warming effect in the Kuroshio Extension（KE） region dur- ing 1950–2004 in the CM3 single forcing. The mid-latitude response of ocean circulation to the GHG（aerosol） forcing is to enhance（weaken） the Subtropical Gyre. Then the SST warming（cooling） lies on the zonal band of 40？N because of the increased（reduced） KE warm advection effect in the GHG（aerosol） forcing simulations, and the cooling effect to SST will surpass the warming effect in the KE region in the historical all-forcing simulations. Besides, the positive feedback between cold SST and cloud can also strengthen the aerosol cooling effect in the KE region during boreal summer, when the mixed layer depth is shallow. In the GHG（aerosol） forcing simulations, corresponding to warming（cooling） SST in the KE region, the weakened（enhanced） Aleutian Low appears in the Northeast Pacific. Consequently, the SST responses to all-forcing in the historical simulations are similar to the re- sponses to aerosol forcing in sign and spatial pattern, hence the aerosol effect is quite important to the SST cooling in the mid-latitude North Pacific during the past 55 years.
Analysis of the Simple Ocean Data Assimilation product reveals that the central North Pacific (28°N–35°N, 150°E–170°W) is one of the main formation regions for low potential vorticity water of ...density between 25.4σθ and 25.8σθ. It is found that the low potential vorticity water is transported from the central North Pacific toward the east of Taiwan Island along a subsurface pathway following the subtropical gyre circulation, and it takes approximately 12 years. Propagation of pycnocline thickness anomalies is detected along the pathway, in association with the decadal variability of the subduction rate.
The response of South Pacific Eastern Subtropical Mode Water (SPESTMW) to global warming is investigated by comparing solutions from a set of Intergovernmental Panel on Climate Change (IPCC) Fourth ...Assessment Report (AR4) coupled models between a present‐day climate and a future, warmer climate. Under the warmer climate scenario, the SPESTMW extends southwestward and is significantly increased in volume. This is because all the local surface forcing mechanisms (i.e., wind stress, heat and freshwater fluxes) in the eastern subtropical South Pacific tends to de‐stratify the upper ocean and thus deepen the mixed layer. Further, a suite of process‐oriented experiments with an ocean general circulation model suggest that it is the intensified southeast trade winds under the warmer climate that promotes more heat flux from the ocean into the atmosphere that then results in a deepening of the mixed layer in the eastern subtropics of the South Pacific.
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