scholarly journals Decadal variability of the Kuroshio Extension: the response of the jet to increased atmospheric resolution in a coupled ocean–atmosphere model

2020 ◽  
Author(s):  
Giusy Fedele ◽  
Alessio Bellucci ◽  
Simona Masina ◽  
Stefano Pierini
Keyword(s):  
Large Scale ◽  
Decadal Variability ◽  
North Pacific Ocean ◽  
Kuroshio Extension ◽  
Low Frequency ◽  
Small Scale ◽  
The North ◽  
Ocean Atmosphere ◽  
The Impact ◽  
The Kuroshio

AbstractThe Kuroshio Extension (KE) shifts between elongated and convoluted states on interannual to decadal time scales. The nature of this low frequency variability (LFV) is still under debate since it is known to be driven by intrinsic oceanic mechanisms, but it is also synchronized with the Pacific Decadal Oscillation (PDO). In this analysis we present the results from two present-climate coupled simulations performed with the CMCC-CM2 model under the CMIP6 HighResMIP protocol and differing only by their atmospheric component resolution. The impact of increased atmospheric resolution on the KE LFV is assessed inspecting several aspects: the KE bimodality, the large-scale variability and the air–sea interactions. The KE LFV and the teleconnection mechanism that connects the KE and the PDO are well captured by both configurations. However, higher atmospheric resolution favors the occurrence of the elongated state and leads to a more realistic PDO representation. Moreover, both simulations qualitatively capture the signatures of atmosphere-driven and ocean-driven regimes over the North Pacific Ocean, even if the higher resolution induces an excessively strong ocean–atmosphere coupling that leads to an overestimation of the air–sea feedbacks. This work highlights that the small scale atmospheric variability (resolution lower than 1°) does not substantially contribute to improve the realism of the KE LFV, but causes significant differences in the air–sea interaction over the KE region likely related to the strengthening of the coupling. The eddy-permitting ocean resolution shared by both configurations is likely responsible for the degree of realism exhibited by the simulated KE LFV in the two analyzed simulations.

scholarly journals A Nonlinear Theory of the Kuroshio Extension Bimodality

2009 ◽  
Vol 39 (9) ◽  
pp. 2212-2229 ◽  
Author(s):  
Stefano Pierini ◽  
Henk A. Dijkstra ◽  
Angelo Riccio
Keyword(s):  
Decadal Variability ◽  
Nonlinear Dynamical Systems ◽  
North Pacific Ocean ◽  
Kuroshio Extension ◽  
Relaxation Oscillation ◽  
Low Frequency ◽  
Wind Forcing ◽  
Altimeter Data ◽  
Main Question ◽  
The Kuroshio

Abstract The Kuroshio Extension (KE) flow in the North Pacific Ocean displays a very distinctive decadal variability of bimodal character involving two completely different states (a large-meander “elongated” state and a small-meander “contracted” state) connected by very asymmetric temporal transitions. Although such a flow has been widely studied by means of a suite of mathematical models and by using several observational platforms, a satisfactory theoretical framework answering quite elementary questions is still lacking, the main question being whether such variability is induced by a time-varying wind forcing or, rather, by intrinsic oceanic mechanisms. In this context, the chaotic relaxation oscillation produced by a process-oriented model of the KE low-frequency variability, with steady climatological wind forcing, was recently recognized to be in substantial agreement with altimeter data. Here those model results are further compared with a comprehensive altimeter dataset. The positive result of such a comparison allows the conclusion that a minimal model for the KE bimodality has been identified and that, consequently, nonlinear intrinsic oceanic mechanisms are likely to be the main cause of the observed variability. By applying the methods of nonlinear dynamical systems theory, relevant dynamical features of the modeled flow are then explained, such as the origin of the relaxation oscillation as a consequence of a homoclinic bifurcation, the spatiotemporal character of the bimodal behavior, and the degree of predictability of the flow in the different stages of the oscillation (evaluated through a field of finite-time Lyapunov exponents and the corresponding Lagrangian time series).

scholarly journals Internal tide energy flux over a ridge measured by a co-located ocean glider and moored ADCP

2019 ◽  
Author(s):  
Rob Hall ◽  
Barbara Berx ◽  
Gillian Damerell
Keyword(s):  
Energy Flux ◽  
Large Scale ◽  
Low Frequency ◽  
Internal Tide ◽  
Small Scale ◽  
Potential Density ◽  
The North ◽  
Model Study ◽  
Continental Shelves ◽  
Alternative Approach

Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide, to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring-neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being fished-out by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimise these risks, with u measured by a low-frequency ADCP moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the M2 internal tide radiating from the Wyville Thompson Ridge in the North Atlantic. The observed energy flux (4.2 ± 0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by sub-sampling potential density in an idealised internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (

scholarly journals Importance of Resolving Kuroshio Front and Eddy Influence in Simulating the North Pacific Storm Track

2017 ◽  
Vol 30 (5) ◽  
pp. 1861-1880 ◽  
Author(s):  
Xiaohui Ma ◽  
Ping Chang ◽  
R. Saravanan ◽  
Raffaele Montuoro ◽  
Hisashi Nakamura ◽  
...  
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
Climate Model ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Small Scale ◽  
Low Resolution ◽  
The North ◽  
The North Pacific ◽  
Sst Anomalies

Abstract Local and remote atmospheric responses to mesoscale SST anomalies associated with the oceanic front and eddies in the Kuroshio Extension region (KER) are studied using high- (27 km) and low-resolution (162 km) regional climate model simulations in the North Pacific. In the high-resolution simulations, removal of mesoscale SST anomalies in the KER leads to not only a local reduction in cyclogenesis but also a remote large-scale equivalent barotropic response with a southward shift of the downstream storm track and jet stream in the eastern North Pacific. In the low-resolution simulations, no such significant remote response is found when mesoscale SST anomalies are removed. The difference between the high- and low-resolution model simulated atmospheric responses is attributed to the effect of mesoscale SST variability on cyclogenesis through moist baroclinic instability. It is only when the model has sufficient resolution to resolve small-scale diabatic heating that the full effect of mesoscale SST forcing on the storm track can be correctly simulated.

scholarly journals On the Crucial Role of Basin Geometry in Double-Gyre Models of the Kuroshio Extension

2008 ◽  
Vol 38 (6) ◽  
pp. 1327-1333 ◽  
Author(s):  
Stefano Pierini
Keyword(s):  
Crucial Role ◽  
North Pacific Ocean ◽  
Kuroshio Extension ◽  
Low Frequency ◽  
Altimeter Data ◽  
Western Boundary ◽  
Low Frequency Variability ◽  
Basin Geometry ◽  
The Kuroshio ◽  
Double Gyre

Abstract The decadal chaotic relaxation oscillation obtained in a recent double-gyre model study of the Kuroshio Extension intrinsic low-frequency variability was found to compare surprisingly well with the real variability of the jet as revealed by altimeter data, despite the high degree of idealization of the model. In this note it is shown that elements of realism in the basin geometry, present in that study and absent in previous double-gyre models applied to the Kuroshio Extension, play a crucial role in shaping the low-frequency variability of the jet, and can explain the good performance of the model. A series of numerical experiments with different basin geometries of increasing degrees of simplicity are analyzed. If the schematic western boundary representing the coastline south of Japan is removed, the strong decadal variability completely disappears and only a very weak periodic oscillation about an elongated state of the jet is found. If the large zonal width of the basin (representing correctly the extension of the North Pacific Ocean) is reduced by a half, then the total meridional Sverdrup transport is reduced by the same factor, and so is the intensity of the Kuroshio and Oyashio western boundary currents: as a result, the modeled Kuroshio Extension is totally unrealistic in shape and is steady. If both simplifications are introduced the resulting jet is, again, totally unrealistic, yielding a weak periodic bimodal cycle. On the basis of these results, two main conclusions are drawn: (i) the introduction of appropriate geometrical elements of realism in double-gyre model studies of the Kuroshio Extension is essential, and (ii) the Kuroshio Extension intrinsic low-frequency variability would be dramatically different if the southwestern coastline of Japan were more meridionally oriented.

scholarly journals Influence of the Meridional Shifts of the Kuroshio and the Oyashio Extensions on the Atmospheric Circulation

2011 ◽  
Vol 24 (3) ◽  
pp. 762-777 ◽  
Author(s):  
Claude Frankignoul ◽  
Nathalie Sennéchael ◽  
Young-Oh Kwon ◽  
Michael A. Alexander
Keyword(s):  
Atmospheric Circulation ◽  
North Pacific ◽  
Large Scale ◽  
Kuroshio Extension ◽  
Statistical Significance ◽  
The North ◽  
Enso Teleconnections ◽  
Historical Temperature ◽  
The Kuroshio ◽  
Sst Anomalies

Abstract The meridional shifts of the Oyashio Extension (OE) and of the Kuroshio Extension (KE), as derived from high-resolution monthly sea surface temperature (SST) anomalies in 1982–2008 and historical temperature profiles in 1979–2007, respectively, are shown based on lagged regression analysis to significantly influence the large-scale atmospheric circulation. The signals are independent from the ENSO teleconnections, which were removed by seasonally varying, asymmetric regression onto the first three principal components of the tropical Pacific SST anomalies. The response to the meridional shifts of the OE front is equivalent barotropic and broadly resembles the North Pacific Oscillation/western Pacific pattern in a positive phase for a northward frontal displacement. The response may reach 35 m at 250 hPa for a typical OE shift, a strong sensitivity since the associated SST anomaly is 0.5 K. However, the amplitude, but not the pattern or statistical significance, strongly depends on the lag and an assumed 2-month atmospheric response time. The response is stronger during fall and winter and when the front is displaced southward. The response to the northward KE shifts primarily consists of a high centered in the northwestern North Pacific and hemispheric teleconnections. The response is also equivalent barotropic, except near Kamchatka, where it tilts slightly westward with height. The typical amplitude is half as large as that associated with OE shifts.

Potential Impact of the Eurasian Boreal Forest on North Pacific Climate Variability*

2007 ◽  
Vol 20 (6) ◽  
pp. 981-992 ◽  
Author(s):  
Michael Notaro ◽  
Zhengyu Liu
Keyword(s):  
Boreal Forest ◽  
North Pacific ◽  
Vegetation Cover ◽  
Large Scale ◽  
Forest Cover ◽  
Kuroshio Extension ◽  
Vegetation Feedback ◽  
North Asia ◽  
The Impact ◽  
The Kuroshio

Abstract The authors demonstrate that variability in vegetation cover can potentially influence oceanic variability through the atmospheric bridge. Experiments aimed at isolating the impact of variability in forest cover along the poleward side of the Asian boreal forest on North Pacific SSTs are performed using the fully coupled model, Fast Ocean Atmosphere Model–Lund Potsdam Jena (FOAM-LPJ), with dynamic atmosphere, ocean, and vegetation. The northern edge of the simulated Asian boreal forest is characterized by substantial variability in annual forest cover, with an east–west dipole pattern marking its first EOF mode. Simulations in which vegetation cover is allowed to vary over north/central Russia exhibit statistically significant greater SST variance over the Kuroshio Extension. Anomalously high forest cover over North Asia supports a lower surface albedo with higher temperatures and lower sea level pressure, leading to a reduction in cold advection into northern China and in turn a decrease in cold air transport into the Kuroshio Extension region. Variability in the large-scale circulation pattern is indirectly impacted by the aforementioned vegetation feedback, including the enhancement in upper-level jet wind variability along the north–south flanks of the East Asian jet stream.

scholarly journals Kuroshio Extension Variability and Forcing of the Pacific Decadal Oscillations: Responses and Potential Feedback

2003 ◽  
Vol 33 (12) ◽  
pp. 2465-2482 ◽  
Author(s):  
Bo Qiu
Keyword(s):  
Pacific Ocean ◽  
North Pacific ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Kuroshio Extension ◽  
Atmospheric Forcing ◽  
Mean Flow ◽  
Wind Stress Curl ◽  
The Pacific ◽  
The Kuroshio

Abstract A forcing mechanism is sought for the large-scale circulation changes in the Kuroshio Extension region of the western North Pacific Ocean as inferred by TOPEX/Poseidon sea surface height (SSH) data. The low-frequency signal of the Kuroshio Extension over the last decade was characterized by a modulation in its zonal mean flow intensity: the mean Kuroshio Extension jet weakened progressively from 1993 to 1996 and this trend reversed after 1997. The ability to simulate the major trends in the observed SSH signals with linear vorticity dynamics leads the authors to conclude that the modulation in the zonal mean jet was remotely forced by wind stress curl anomalies in the eastern North Pacific Ocean related to the Pacific decadal oscillations (PDOs). To be specific, the weakening (strengthening) trend in 1993–96 (1997–2001) was caused by westward expansions of negative (positive) SSH anomalies south of the Kuroshio Extension and positive (negative) SSH anomalies north of the Kuroshio Extension. Emergence of oppositely signed SSH anomalies on the two sides of the Kuroshio Extension jet is due to the different propagating speeds of the baroclinic Rossby waves, which carry the wind-induced SSH anomalies generated in the eastern North Pacific at different phases of the PDOs. Hindcasting the Kuroshio Extension jet strength over the last 45 years reveals that the jet modulation has a dominant timescale of ∼12 yr. Given the location of the Kuroshio Extension jet relative to the maximum atmospheric forcing, it is found that this dominant timescale is consistent with the preferred timescale under a stochastic white-noise atmospheric forcing. It is hypothesized that this connection between the Kuroshio Extension strength and the latitudinally dependent baroclinic adjustment contributes to an increase in variance and persistence of the North Pacific midlatitude coupled system on the decadal timescale.

scholarly journals Structural and Efficiency Effects of Land Transfers on Food Planting: A Comparative Perspective on North and South of China

2021 ◽  
Vol 13 (6) ◽  
pp. 3327
Author(s):  
Zhihua Leng ◽  
Yana Wang ◽  
Xinshuo Hou
Keyword(s):  
Large Scale ◽  
Scale Effects ◽  
Division Of Labour ◽  
Market Mechanism ◽  
Small Scale ◽  
Structural Effects ◽  
The South ◽  
Operating Income ◽  
The North ◽  
The Impact

This paper uses a multi-period PSM-DID model to explore the impact of land transfers on food production from a spatial perspective and analyses the income effects, scale effects, and structural effects of such transfers. The empirical results are as follows. (1) Land transfers have reduced the proportion of food crops planted by farmers, and the planting structure has shifted towards cash crops, which has obvious structural effects. (2) The impact of land transfers on the planting structure is spatially heterogeneous. Land transfers are more common in the south than in the north. Land transfers have reduced wheat planting in the north, while rice planting has been reduced in the south. (3) Land transfers have increased the operating income of farmers and have an income effect, but the income of farmers in the north is higher than that of farmers in the south. (4) Land transfers do not have scale effects. Current land transfers among farmers are mainly conducted on a small scale and do not improve farmers’ efficiency in planting food. The following suggestions are proposed. (1) A market mechanism for land transfers should be established to promote large-scale land transfers. (2) The trend towards non-grain cultivation due to land transfers should be halted to ensure food security. (3) The different impacts of urbanization in the northern and southern regions should be considered, and the division of labour in grain-producing areas should be strengthened. (4) Land transfer models should be developed, and the development of smart agriculture should be explored.

scholarly journals Low-frequency variability of the Kuroshio Extension

2009 ◽  
Vol 16 (6) ◽  
pp. 665-675 ◽  
Author(s):  
S. Pierini ◽  
H. A. Dijkstra
Keyword(s):  
Nonlinear Dynamics ◽  
Large Scale ◽  
Rossby Waves ◽  
Kuroshio Extension ◽  
Baroclinic Instability ◽  
Low Frequency ◽  
Wave Dynamics ◽  
Low Frequency Variability ◽  
Low Dimensional ◽  
The Kuroshio

Abstract. In this paper, we provide a review of recent results targeted at the understanding of the low-frequency variability of the Kuroshio Extension. We provide the background and main arguments of two views which have recently been proposed to explain this variability. In the first view, wind-induced Rossby waves and the effects of mesocale eddies are crucial. The second view is based on low-dimensional equivalent-barotropic large-scale nonlinear dynamics, with neither Rossby wave dynamics nor baroclinic instability being important. Results from models supporting each view are discussed and confronted with results from available observations.

The Impact of Kuroshio Extension Fronts Variation on the Pacific Storm Tracks and the relationship with Temperature over North America

2020 ◽  
Author(s):  
Ziniu Xiao
Keyword(s):  
North America ◽  
Temperature Gradient ◽  
Large Scale ◽  
Kuroshio Extension ◽  
Storm Tracks ◽  
Near Surface ◽  
Intensity Index ◽  
Significant Difference ◽  
The Impact ◽  
The Kuroshio

<p>The intensity index of Kuroshio Extension and northern front zones (KEF) is defined as the area average of SST meridional gradient by using Hadley Center’s surface sea temperature dataset (1949-2014), and the Kuroshio Extension frontal intensity index (KEFI) has seasonal to interdecadal variations. In winter, the KEFI has significant positive correlation with transient variances in the North Pacific storm tracks area, and the positive relationship appears when KEFI lead storm tracks one month which indicates the intensity of KEF could influence storm tracks in winter. To investigate the possible mechanism, we found: when the winter SST front is stronger, the more significant difference between ocean-air heat flux in both sides of KEF could strengthen the near-surface temperature gradient, which maintains the near-surface baroclincity and benefits the transient heat transport, promote the develop of transient eddies at last. Additional, the large-scale circulation also be response to KEF in winter: when the KEF is stronger, the Aleutian is deepen, the subtropical high is strengthen, the 500 hPa potential high is increased (decreased) in south (north), the subtropical jet is weaker and wider. It is found that the oceanic fronts promote storm tracks by transporting heat upward and maintaining the air temperature gradient in winter. In further, the significant correlation was found between the Kuroshio Extension Oceanic Front intensity and the temperature over North America in autumn and winter.</p>

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