scholarly journals Characteristics of Mesoscale Eddies in the Kuroshio–Oyashio Extension Region Detected from the Distribution of the Sea Surface Height Anomaly

2010 ◽  
Vol 40 (5) ◽  
pp. 1018-1034 ◽  
Author(s):  
Sachihiko Itoh ◽  
Ichiro Yasuda
Keyword(s):  
Kuroshio Extension ◽  
Mesoscale Eddies ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Height Anomaly ◽  
Asymmetric Distribution ◽  
Spatial Coverage ◽  
Sea Surface Height Anomaly ◽  
North And South ◽  
The Kuroshio

Abstract This study investigates the distribution of the sea surface height anomaly (SSHA) with the aim of quantifying the characteristics of mesoscale eddies in the Kuroshio–Oyashio extension region (KOER), where intense mesoscale eddies are commonly observed during hydrographic surveys. Dense distributions of both anticyclonic eddies (AEs) and cyclonic eddies (CEs) are detected for the first time in KOER with sufficient temporal and spatial coverage, using the Okubo–Weiss parameter without smoothing. Their contribution to the total SSHA variance is estimated to be about 50%. The zones of highest amplitudes are located north and south of the axis of the Kuroshio Extension (KE) for AEs and CEs, which represent warm-core and cold-core rings, respectively; the areas extend poleward along the Japan and Kuril–Kamchatka Trenches, especially for AEs. Eddies of both polarities and with moderate amplitudes are also recognized along the Subarctic Front (SAF). Eddies in areas north and south of the KE generally propagate westward, at a mean rate of 1–5 cm s−1; those along the trenches south of 46°N and along the SAF propagate poleward at mean rates of 1–2 and 0.5–1 cm s−1, respectively. Because of the asymmetric distribution of the AEs and CEs in the areas north and south of the KE, and the asymmetric amplitude of them along the Japan and Kuril–Kamchatka Trenches, there exist significant eddy fluxes of vorticity, heat, and salinity in these areas.

scholarly journals Mesoscale SST Dynamics in the Kuroshio–Oyashio Extension Region

2019 ◽  
Vol 49 (5) ◽  
pp. 1339-1352 ◽  
Author(s):  
Zhao Jing ◽  
Ping Chang ◽  
Xuan Shan ◽  
Shengpeng Wang ◽  
Lixin Wu ◽  
...  
Keyword(s):  
Kuroshio Extension ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Reanalysis Data ◽  
Sea Surface ◽  
Height Anomaly ◽  
Theoretical Expression ◽  
Surface Salinity ◽  
Density Anomaly ◽  
The Kuroshio

Abstract Mesoscale eddies have been extensively studied based on the sea surface height anomaly (SSHA). However, it is the sea surface temperature anomaly (SSTA) that is vital to the mesoscale eddy–atmosphere interactions. In this study, we analyze the amplitude relationship between SSHA and SSTA (referred to as the H-T amplitude relationship) in the Kuroshio–Oyashio extension (KOE) region using both observational and reanalysis data. It is found that the spatial distribution of mesoscale SSHA variance is not coincident with mesoscale SSTA variance. The former peaks in the Kuroshio extension around 35°N whereas the latter is strongest in the Oyashio extension around 40°N. Regression analyses indicate that the rate of SSTA change per SSHA change is 1.8°C m−1 in the Kuroshio extension (145°–160°E, 34°–36°N) but increases drastically by a factor of 3–4 to 6.2°C m−1 in the Oyashio extension (145°–160°E, 39°–41°N). A theoretical expression for the H-T amplitude relationship is derived. Analyzing this expression suggests that the stronger H-T amplitude relationship in the Oyashio extension than the Kuroshio extension is mainly attributed to 1) the smaller thermal expansion coefficient due to the colder background SST, 2) the stronger salinity compensation effect that works against the contribution of SSTA change to sea surface density anomaly (SSDA) change, and 3) the shallower vertical structure of mesoscale eddies. The second factor is ascribed to the strong surface salinity front in the Oyashio extension, while the third factor is found to be qualitatively consistent with the shallower baroclinically unstable modes due to the shallower density front there.

scholarly journals Global Interannual Trends and Amplitude Modulations of the Sea Surface Height Anomaly from the TOPEX/Jason-1 Altimeters

2008 ◽  
Vol 21 (12) ◽  
pp. 2824-2834 ◽  
Author(s):  
Paulo S. Polito ◽  
Olga T. Sato
Keyword(s):  
Time Series ◽  
Rossby Waves ◽  
Mesoscale Eddies ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Global Ocean ◽  
Height Anomaly ◽  
Western Boundary ◽  
Regional Variability ◽  
Sea Surface Height Anomaly

Abstract This study uses the global Ocean Topography Experiment (TOPEX)/Jason-1 altimeters’ time series to estimate the 13-yr trend in sea surface height anomaly. These trends are estimated at each grid point by two methods: one fits a straight line to the time series and the other is based on the difference between the average height between the two halves of the time series. In both cases the trend shows large regional variability, mostly where the intense western boundary currents turn. The authors hypothesize that the regional variability of the sea surface height trends leads to changes in the local geostrophic transport. This in turn affects the instability-related processes that generate mesoscale eddies and enhances the Rossby wave signals. This hypothesis is verified by estimates of the trend of the amplitude of the filtered sea surface height anomaly that contains the spectral bands associated with Rossby waves and mesoscale eddies. The authors found predominantly positive tendency in the amplitude of Rossby waves and eddies, which suggests that, on average, these events are becoming more energetic. In some regions, the variation in amplitude over 13 yr is comparable to the standard deviation of the data and is statistically significant according to both methods employed in this study. It is plausible that in this case, the energy is transferred from the mean currents to the waves and eddies through barotropic and baroclinic instability processes that are more pronounced in the western boundary current extension regions. If these heat storage patterns and trends are confirmed on longer time series, then it will be justified to argue that the warming trend of the last century provides the energy that amplifies both Rossby waves and mesoscale eddies.

ASSIMILATION OF SEA SURFACE HEIGHT ANOMALIES INTO HYCOM WITH AN OPTIMAL INTERPOLATION SCHEME OVER THE ATLANTIC OCEAN METAREA V

2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Clemente Augusto Souza Tanajura ◽  
Filipe Bitencourt Costa ◽  
Renato Ramos da Silva ◽  
Giovanni Abdelnur Ruggiero ◽  
Victor Bastos Daher
Keyword(s):  
Interpolation Method ◽  
Maximum Error ◽  
Sea Surface Height ◽  
Volume Transport ◽  
Ocean Model ◽  
Sea Surface ◽  
Height Anomaly ◽  
Optimal Interpolation ◽  
Sea Surface Height Anomaly ◽  
The Impact

Along-track sea surface height anomaly (SSHA) data from the Jason-1 and Jason-2 satellites were assimilated into the ocean model HYCOM from July 1, 2009 until December 31, 2009. A new and simple approach to overcome the bias between the model and observed SSHA was proposed. It focuses on the meso-scale differences between the data and the model along each satellite track. An optimal interpolation method and the Cooper and Haines (1996) scheme (C&H) were employed to produce a SSHA analysis field and to adjust model layer thicknesses over the Atlantic METAREA V. The corrected model state was used as initial condition for the next assimilation cycle. SSHA data with a 7-day window were assimilated in 3-day intervals centered in the SSHA data window and the C&H scheme was applied taking the SSHA analysis. A control run without assimilation was also performed. The results showed that the model SSHA was completely reorganized by the end of the experiment. The modifications of SSHA were compared to the American Navy HYCOM+NCODA system and AVISO data. Maximum error was reduced from 0.7 m to 0.2 m by assimilation. Comparisons were also made with the Argo temperature and salinity vertical profiles. Improvements in the currents and volume transport were also produced by assimilation. The impact in temperature was in general positive, but there was no substantial modification in salinity.

Sea surface height anomaly and upper ocean temperature over the Indian Ocean during contrasting monsoons

2016 ◽  
Vol 75 ◽  
pp. 1-21 ◽  
Author(s):  
Anitha Gera ◽  
A.K. Mitra ◽  
D.K. Mahapatra ◽  
I.M. Momin ◽  
E.N. Rajagopal ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Height Anomaly ◽  
Upper Ocean ◽  
Ocean Temperature ◽  
The Indian Ocean ◽  
Sea Surface Height Anomaly

scholarly journals Enhanced Warming and Intensification of the Kuroshio Extension, 1999–2013

2019 ◽  
Vol 11 (1) ◽  
pp. 101 ◽  
Author(s):  
You-Lin Wang ◽  
Chau-Ron Wu
Keyword(s):  
Kuroshio Extension ◽  
Height Anomaly ◽  
Upstream Region ◽  
Climate Regime ◽  
Aleutian Low ◽  
Wind Stress Curl ◽  
The Pacific ◽  
Poleward Shift ◽  
Sea Surface Height Anomaly ◽  
The Kuroshio

The Pacific climate regime has anomalous warm and cool periods every decade associated with atmospheric circulation changes, which are known to have modulated the tropical and subtropical Pacific during the recent Pacific hiatus regime (1999–2013). However, the influence of the hiatus regime on the Kuroshio Extension (KE) remains unclear. Here, we show that the KE jet underwent enhanced warming (increased 1–1.5 °C), intensification (8–19%) and northward migration (0.5–1°). The KE jet became more perturbed in the upstream region (increased by 70%, west of 146°E) but became stable downstream (perturbation decreased 5–11%, east of 146°E). A poleward shift of the mid-latitude jet stream and weakened Aleutian Low (AL) contributed to the northward migration and intensification of the KE jet, respectively. The weakened AL was associated with negative wind stress curl (WSC) in the eastern Pacific, and this WSC generated an underlying positive sea surface height anomaly that propagated westward, intensifying the KE jet when it reached the KE region. Since the recent Pacific hiatus regime ended after 2013, these changes of the KE jet may reverse during the ongoing warming regime.

Sign in / Sign up

Export Citation Format

Share Document