On the length and time scales of the power supply to the ocean between the meso-scale and the synoptic-scale

2020 ◽  
Author(s):  
Achim Wirth
Keyword(s):  
Gulf Stream ◽  
Kuroshio Extension ◽  
Surface Wind ◽  
Coarse Graining ◽  
Power Input ◽  
Ocean Dynamics ◽  
Synoptic Scale ◽  
Surface Wind Stress ◽  
Using Data ◽  
The Kuroshio

<p> The input of mechanical power to the ocean due to the surface wind-stress, in regions which correspond to different regimes of ocean dynamics, is considered using data from satellites observations. Its dependence on the coarse-graining range of the atmospheric and oceanic velocity in space from 0.5° to 10° and time from 6h to 40 days is determined.  In the area of the Gulf Stream and the Kuroshio extensions the dependence of the power-input on space-time coarse-graining  varies over tenfold for the coarse-graining considered. It decreases over twofold for the Gulf Stream extension and threefold for the Kuroshio extension, when the coarse-graining length-scale passes from a few degrees to 0.5° at a temporal coarse-graining scale of a few days. It increases over threefold in the Gulf Stream and the Kuroshio extensions when the coarse-graining passes from several days to 6h at a spatial coarse graining of a few degrees. The power input is found to increase monotonically with shorter coarse-graining in time. Its variation with coarse graining in space has no definite sign. Results show that including the dynamics at scales below a few degrees reduces considerably the power input by air-sea interaction in regions of strongly non-linear ocean currents.<br>  When the ocean velocities are not considered in the shear calculation the power-input is considerably (up to threefold) increased. The dependence of the power input on coarse graining in space and time is close to being multiplicatively separable in all regions and for most of the coarse-graining domain considered.</p>

scholarly journals Determining the dependence of the power supply to the ocean on the length and time scales of the dynamics between the meso-scale and the synoptic-scale, from satellite data

2020 ◽  
Author(s):  
Achim Wirth
Keyword(s):  
Gulf Stream ◽  
Kuroshio Extension ◽  
Surface Wind ◽  
Coarse Graining ◽  
Power Input ◽  
Ocean Dynamics ◽  
Synoptic Scale ◽  
Surface Wind Stress ◽  
Using Data ◽  
The Kuroshio

Abstract. The input of mechanical power to the ocean due to the surface wind-stress, in regions which correspond to different regimes of ocean dynamics, is considered using data from satellites observations. Its dependence on the coarse-graining range of the atmospheric and oceanic velocity in space from 0.5° to 10° and time from  6 h to 40 days is determined. In the area of the Gulf Stream and the Kuroshio extensions the dependence of the power-input on space-time coarse-graining varies over tenfold for the coarse-graining considered. It decreases over twofold for the Gulf Stream extension and threefold for the Kuroshio extension, when the coarse-graining length-scale passes from a few degrees to 0.5° at a temporal coarse-graining scale of a few days. It increases over threefold in the Gulf Stream and the Kuroshio extensions when the coarse-graining passes from several days to 6 h at a spatial coarse graining of a few degrees. The power input is found to increase monotonically with shorter coarse-graining in time. Its variation with coarse graining in space has no definite sign. Results show that including the dynamics at scales below a few degrees reduces considerably the power input by air-sea interaction in regions of strongly non-linear ocean currents. When the ocean velocities are not considered in the shear calculation the power-input is considerably (up to threefold) increased. The dependence of the power input on coarse graining in space and time is close to being multiplicatively separable in all regions and for most of the coarse-graining domain considered.

scholarly journals On the Relationship between Synoptic Wintertime Atmospheric Variability and Path Shifts in the Gulf Stream and the Kuroshio Extension

2009 ◽  
Vol 22 (12) ◽  
pp. 3177-3192 ◽  
Author(s):  
Terrence M. Joyce ◽  
Young-Oh Kwon ◽  
Lisan Yu
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Western Boundary ◽  
Atmospheric Variability ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

Abstract Coherent, large-scale shifts in the paths of the Gulf Stream (GS) and the Kuroshio Extension (KE) occur on interannual to decadal time scales. Attention has usually been drawn to causes for these shifts in the overlying atmosphere, with some built-in delay of up to a few years resulting from propagation of wind-forced variability within the ocean. However, these shifts in the latitudes of separated western boundary currents can cause substantial changes in SST, which may influence the synoptic atmospheric variability with little or no time delay. Various measures of wintertime atmospheric variability in the synoptic band (2–8 days) are examined using a relatively new dataset for air–sea exchange [Objectively Analyzed Air–Sea Fluxes (OAFlux)] and subsurface temperature indices of the Gulf Stream and Kuroshio path that are insulated from direct air–sea exchange, and therefore are preferable to SST. Significant changes are found in the atmospheric variability following changes in the paths of these currents, sometimes in a local fashion such as meridional shifts in measures of local storm tracks, and sometimes in nonlocal, broad regions coincident with and downstream of the oceanic forcing. Differences between the North Pacific (KE) and North Atlantic (GS) may be partly related to the more zonal orientation of the KE and the stronger SST signals of the GS, but could also be due to differences in mean storm-track characteristics over the North Pacific and North Atlantic.

scholarly journals Influential Role of Moisture Supply from the Kuroshio/Kuroshio Extension in the Rapid Development of an Extratropical Cyclone

2015 ◽  
Vol 143 (10) ◽  
pp. 4126-4144 ◽  
Author(s):  
Hidetaka Hirata ◽  
Ryuichi Kawamura ◽  
Masaya Kato ◽  
Taro Shinoda
Keyword(s):  
Diabatic Heating ◽  
Rapid Development ◽  
Kuroshio Extension ◽  
Lower Troposphere ◽  
Active Role ◽  
Conveyor Belt ◽  
Synoptic Scale ◽  
Warm Front ◽  
The Kuroshio

Abstract This study focused on an explosive cyclone migrating along the southern periphery of the Kuroshio/Kuroshio Extension in the middle of January 2013 and examined how those warm currents played an active role in the rapid development of the cyclone using a high-resolution coupled atmosphere–ocean regional model. The evolutions of surface fronts of the simulated cyclone resemble the Shapiro–Keyser model. At the time of the maximum deepening rate, strong mesoscale diabatic heating areas appear over the bent-back front and the warm front east of the cyclone center. Diabatic heating over the bent-back front and the eastern warm front is mainly induced by the condensation of moisture imported by the cold conveyor belt (CCB) and the warm conveyor belt (WCB), respectively. The dry air parcels transported by the CCB can receive large amounts of moisture from the warm currents, whereas the very humid air parcels transported by the WCB can hardly be modified by those currents. The well-organized nature of the CCB plays a key role not only in enhancing surface evaporation from the warm currents but also in importing the evaporated vapor into the bent-back front. The imported vapor converges at the bent-back front, leading to latent heat release. The latent heating facilitates the cyclone’s development through the production of positive potential vorticity in the lower troposphere. Its deepening can, in turn, reinforce the CCB. In the presence of a favorable synoptic-scale environment, such a positive feedback process can lead to the rapid intensification of a cyclone over warm currents.

scholarly journals Processes Shaping the Frontal-Scale Time-Mean Surface Wind Convergence Patterns around the Kuroshio Extension in Winter

2020 ◽  
Vol 33 (1) ◽  
pp. 3-25
Author(s):  
Ryusuke Masunaga ◽  
Hisashi Nakamura ◽  
Bunmei Taguchi ◽  
Takafumi Miyasaka
Keyword(s):  
Kuroshio Extension ◽  
Surface Wind ◽  
Convective Precipitation ◽  
Western Boundary ◽  
Boundary Currents ◽  
Sst Front ◽  
Atmospheric Structure ◽  
Mean Convergence ◽  
Daily Scale ◽  
The Kuroshio

AbstractHigh-resolution satellite observations and numerical simulations have revealed that climatological-mean surface wind convergence and precipitation are enhanced locally around the midlatitude warm western boundary currents (WBCs) with divergence slightly to their poleward side. While steep sea surface temperature (SST) fronts along the WBCs have been believed to play an important role in shaping those frontal-scale atmospheric structures, the mechanisms and processes involved are still under debate. The present study explores specific daily scale atmospheric processes that are essential for shaping the frontal-scale atmospheric structure around the Kuroshio Extension (KE) in winter, taking advantage of a new product of global atmospheric reanalysis. Cluster analysis and case studies reveal that a zonally extending narrow band of surface wind convergence frequently emerges along the KE, which is typically observed under the surface northerlies after the passage of a developed synoptic-scale cyclone. Unlike its counterpart around the cyclone center and associated cold front, the surface convergence tends to be in moderate strength and more persistent, contributing dominantly to the distinct time-mean convergence/divergence contrast across the SST front. Accompanying ascent and convective precipitation, the band of convergence is a manifestation of a weak stationary atmospheric front anchored along the SST front or generation of a weak meso-α-scale cyclone. By reinforcing the ascent and convergence, latent heating through convective processes induced by surface convergence plays an important role in shaping the frontal-scale atmospheric structure around the KE.

scholarly journals Wind Speed and Stability Effects on Coupling between Surface Wind Stress and SST Observed from Buoys and Satellite

2012 ◽  
Vol 25 (5) ◽  
pp. 1544-1569 ◽  
Author(s):  
Larry W. O’Neill
Keyword(s):  
Stress Response ◽  
Wind Speed ◽  
Wind Stress ◽  
Stress Responses ◽  
Gulf Stream ◽  
Surface Wind ◽  
Equatorial Pacific ◽  
Satellite Observations ◽  
Actual Surface ◽  
Surface Wind Stress

The surface wind and stress responses to sea surface temperature (SST) are examined using collocated moored buoy and satellite observations in the Gulf Stream and the eastern equatorial Pacific. Using 17 buoy pairs, differences in the wind speed, 10-m equivalent neutral wind speed (ENW), and surface wind stress magnitude between two buoys separated by between 150 and 350 km were all found to be highly correlated to, and satisfy linear relations with, the SST difference on time scales longer than 10 days. This wind–SST coupling is consistent with previous analyses of spatially high-pass-filtered satellite ENW and SST fields. For all buoy pairs, the ENW and wind speed responses to SST differ by only 10%–30%, indicating that the ENW and stress responses to SST are attributable primarily to the response of the actual surface wind speed to SST rather than to stability. This result clarifies the dynamical pathway of the wind–SST coupling on the oceanic mesoscale. This buoy-pair methodology is used further to evaluate the ENW–SST coupling derived from collocated satellite observations of ENW by the Quick Scatterometer (QuikSCAT) and SST by the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) on board the Aqua satellite. Overall, the satellite and buoy ENW responses to SST compare well, with normalized mean differences (satellite minus buoy) of 17% over the Gulf Stream and −31% and 2% over the southern and northern sides of the equatorial Pacific, respectively. Finally, seasonal variability of the large-scale ENW is shown to modulate the wind stress response to SST, whereby stronger winter wind enhances the stress response by a factor of ~2 relative to the ENW response.

scholarly journals Winter Extreme Flux Events in the Kuroshio and Gulf Stream Extension Regions and Relationship with Modes of North Pacific and Atlantic Variability

2015 ◽  
Vol 28 (12) ◽  
pp. 4950-4970 ◽  
Author(s):  
Xiaohui Ma ◽  
Ping Chang ◽  
R. Saravanan ◽  
Dexing Wu ◽  
Xiaopei Lin ◽  
...  
Keyword(s):  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Propagation Path ◽  
Northwestern Pacific ◽  
Boreal Winter ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

Abstract Boreal winter (November–March) extreme flux events in the Kuroshio Extension region (KER) of the northwestern Pacific and the Gulf Stream region (GSR) of the northwestern Atlantic are analyzed and compared, based on NCEP Climate Forecast System Reanalysis (CFSR), NCEP–NCAR reanalysis, and NOAA Twentieth Century Reanalysis data, as well as the observationally derived OAFlux dataset. These extreme flux events, most of which last less than 3 days, are characterized by cold air outbreaks (CAOs) with an anomalous northerly wind that brings cold and dry air from the Eurasian and North American continents to the KER and GSR, respectively. A close relationship between the extreme flux events over KER (GSR) and the Aleutian low pattern (ALP) [east Atlantic pattern (EAP)] is found with more frequent occurrence of the extreme flux events during a positive ALP (EAP) phase and vice versa. A further lag-composite analysis suggests that the ALP (EAP) is associated with accumulated effects of the synoptic winter storms accompanied by the extreme flux events and shows that the event-day storms tend to have a preferred southeastward propagation path over the North Pacific (Atlantic), potentially contributing to the southward shift of the storm track over the eastern North Pacific (Atlantic) basin during the ALP (EAP) positive phase. Finally, lag-regression analyses indicate a potential positive influence of sea surface temperature (SST) anomalies along the KER (GSR) on the development of the extreme flux events in the North Pacific (Atlantic).

Revisit of the Occurrence of the Kuroshio Large Meander South of Japan

2021 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen
Keyword(s):  
Kuroshio Extension ◽  
Surface Wind ◽  
Wind Forcing ◽  
Dynamic State ◽  
Large Meander ◽  
Subtropical Countercurrent ◽  
Eddy Generation ◽  
Anticyclonic Eddies ◽  
The Kuroshio

AbstractA unique characteristic by the Kuroshio off the southern coast of Japan is its bimodal path variations. In contrast to its straight path that follows coastline, the Kuroshio takes a large meander (LM) path when its axis detours southward by as much as 300 km. Since 1950, eight Kuroshio LM events took place and their occurrences appeared random. By synthesizing available in-situ/satellite observations and atmospheric reanalysis product, this study seeks to elucidate processes conducive for the LM occurrence. We find both changes in the inflow Kuroshio transport from the East China Sea and in the downstream Kuroshio Extension dynamic state are not determinant factors. Instead, intense anticyclonic eddies with transport > 20 Sv emanated from the Subtropical Countercurrent (STCC) are found to play critical roles in interacting with Kuroshio path perturbations southeast of Kyushu that generate positive relative vorticities along the coast and lead the nascent path perturbation to form a LM. Occurrence of this intense cyclonic{anticyclonic eddy interaction is favored when surface wind forcing over the STCC is anticyclonic during the positive phasing of Pacific decadal oscillations (PDOs). Such wind forcing strengthens the meridional Ekman flux convergence and enhances eddy generation by the STCC, and seven of the past eight LM events are found to be preceded by 1 ~ 2 years by the persistent anticyclonic wind forcings over the STCC. Rather than a fully random phenomenon, we posit that the LM occurrence is regulated by regional wind forcing with a positive PDO imprint.

Atlantic coastal sea level variability and synoptic-scale meteorological forcing

2021 ◽  
Keyword(s):  
Sea Level ◽  
Atmospheric Circulation ◽  
Tide Gauge ◽  
Surface Wind ◽  
High Tide ◽  
The United States ◽  
Ocean Dynamics ◽  
Flood Events ◽  
Synoptic Scale ◽  
Sea Level Variability

Abstract Anomalous sea levels along the Mid- and South- Atlantic coasts of the United States are often linked to atmosphere- ocean dynamics, remote- and local- scale forcing and other factors linked to cyclone passage, winds, waves, and storm surge. Herein, we examine sea level variability along the U.S. Atlantic coast through satellite altimeter and coastal tide gauge data within the context of synoptic-scale weather pattern forcing. Altimetry, derived from sea level anomaly (SLA) data between 1993 and 2019 were compared with Self Organizing Map (SOM)-based atmospheric circulation and surface wind field categorizations to reveal spatiotemporal patterns and their inter-relationships with high water-level conditions at tide gauges. Regional elevated sea level patterns and variability were strongly associated with synergistic patterns of atmospheric circulation and wind. Recurring atmospheric patterns associated with high-tide flooding events and flood risk were identified, as were specific regional oceanographic variability patterns of SLA response. The incorporation of combined metrics of wind and circulation patterns further isolate atmospheric drivers of high tide flood events and may have particular significance for predicting future flood events over multiple spatial and temporal scales.

Different cyclone characteristics along the Gulf Stream and Kuroshio SST front regions

2021 ◽  
Author(s):  
Leonidas Tsopouridis ◽  
Clemens Spensberger ◽  
Thomas Spengler
Keyword(s):  
Gulf Stream ◽  
Kuroshio Extension ◽  
Northwest Pacific ◽  
Western Boundary ◽  
Cold Side ◽  
Sst Front ◽  
The North ◽  
Relative Contribution ◽  
Upper Level ◽  
The Kuroshio

<p>The Northwest Atlantic and the Northwest Pacific are regions of strong temperature gradients and hence favourable locations for wintertime cyclone intensification co‐located with the storm tracks. Although the Gulf Stream and the Kuroshio Extension are both western boundary currents with similar characteristics, the SST gradient is markedly stronger across the Gulf Stream. Further, upper-level flow is stronger and more zonal over the Kuroshio Extension. To estimate the relative contribution of the SST front to the evolution of cyclones and to identify the mechanisms for cyclone intensification in the two regions, we track individual cyclones and categorise them depending on their propagation relative to the SST front. We focus on cyclones staying either on the cold (C1) or warm (C2) side of the SST front, and on cyclones that cross the SST front from the warm to the cold side (C3).  Comparing these categories, we find that low-level baroclinicity, particularly arising from the land–sea contrast, drives the higher intensification of cyclones in C1 and C3 in the Gulf Stream region, with the propagation of those cyclones near the left exit region of the North Atlantic jet contributing to the higher intensification and precipitation. In the Kuroshio region on the other hand, the land–sea contrast plays a less prominent role for the low‐level baroclinicity. Cyclones remaining on the warm side of the Kuroshio SST front (C2), as well as those crossing the SST front from the warm to the cold side (C3) are characterized by higher intensification, associated with a stronger upper-level jet in the Pacific. Comparing the different cyclone categories, there is no direct effect of the SST front on cyclone intensification in both regions. However, the SST front contributes to the climatological low‐level baroclinicity, providing a conducive environment for cyclone intensification for the cyclones crossing the SST front.</p>

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