FRONTAL MEANDERS IN THE KUROSHIO EXTENSION PO25D-05 · frontal meanders w ∼ 100-200 m d-1-mainly...
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KESS Unstable 3. Case Study: Stable Period (upper & deep, four bands) 4. Case Study: Unstable Period (upper & deep, four bands) FRONTAL MEANDERS IN THE KUROSHIO EXTENSION D. Randolph Watts, Karen L. Tracey, and Kathleen A. Donohue Unfiltered Bandpassed Vertical Velocity Deep (u,v) [email protected] www.po.gso.uri.edu/dynamics/KESS www.uskess.org Band: 30-15d PO25D-05 KESS is funded by National Science Foundation grants OCE02-21008 and OCE08-51246. Large scale meanders of the Kuroshio Extension are quasi-stationary. However smaller scale meanders, or frontal waves, continually propagate eastward. The downstream propagation of these frontal waves can even be resolved when the path is highly convoluted. 1. Kuroshio Extension 5. Dispersion Curve The Kuroshio Extension System Study (KESS) spanned a transition between relatively stable and unstable meandering states. The CPIES array mapped the upper and deep streamfunctions daily with mesoscale resolution for a 16-month period. One of many frontal waves during Jun-Nov 2004. Shown: upper and deep, unfiltered and filtered Ψ. • 15-7d & 7-3d features propagate eastward along front with highs and lows vertically aligned upper and deep. • 30-15d strong features north of 35 o N are associated with a WCR propagating westward, not frontal waves. 2. Space-time Plots of Upper & Deep Streamfunction Ψ (Band-pass Filtered) Stable Period Unstable Period One of many frontal waves in Jan-Sep 2005. Shown: upper and deep, unfiltered and filtered Ψ. 30-15d and 15-7d features propagate downstream, References James,C., M. Wimbush, H. Ichikawa, 1999. JPO, 29:259-272. Kontoyiannis, H., D.R.Watts, 1994. JPO, 24:1999-2013. Kouketsu, S., I. Yasuda, Y. Hiroe, 2007. JPO, 37:644-656. Lee, T., P. Cornillon, 1996. JPO, 26:205-224. Mizuno,K., 1985. Bull. Tohoku Reg. Fish. Res. Lab., 47:59-68. In the following plots, the upper and deep streamfunctions were band-pass filtered in 30-15d, 15-7.5d and 7.5-3.75d period bands to characterize the eastward-propagating frontal meanders. Deep lows highs Upper Gulf Stream KW94 LC96 Kuroshio JWI99 KYH07 M85 KESS Stable Deep lows highs Upper Upper Deep highs lows 15-7.5d 7.5-3.75d Vertical Velocity, w Vertical Velocity, w unfiltered unfiltered w caused mainly by cross-front motion in quasi- stationary trough, w ∼ 100-200 m d -1 -mainly advection V n •(∂ Z 12 /∂ n) w caused by rapid-propagating frontal meanders w ∼ 100-200 m d -1 -mainly tendency (∂ Z 12 /∂ t) along the front. Mean path: 20 cm s -1 grows downstream decays downstream grows downstream decays downstream decays downstream SUMMARY • Upper and deep meanders propagate jointly downstream along the path. • Smooth changes of (λ, T, c) ≈ (220km, 5d, 44km/d) to (350km, 20d, 17km/d). • Substantial vertical velocities in frontal waves, by tendency and advection, ~ 100-200 m d -1 down- and up-welling entering trough and crest. Frontal waves propagate eastward jointly in upper and deep layers during Stable and Unstable Periods. •At times, the deep expression of frontal waves is obscured by external eddies approaching from NNE. - Greene et al. (poster PO25D-04) discuss vertical coupling induced by these external eddies, particularly 30-60d periods. •Joint CEOF analyses of upper and deep Ψ in boxed regions find the deep perturbations lead upper by ΔΦ ≈ 0-30 o for 30-15d; 37 o -57 o for 15-7d; 70 o -72 o for 7-3d. Some waves grow or decay downstream in all 3 bands; usually the longer (shorter) periods tend to grow (decay). Comparison symbols show estimates from references cited below. Phase speed vs wavenumber and wavelength from CEOF analysis of along- path upper Ψ in boxed regions (Topic 2). Speeds equal those in Gulf Stream within statistical confidence. Methodologies differ: - Propagation is along-path so distance ds is longer, with larger ds/dt. - Propagation is zonal in the other studies. Paths from Aviso SSH products CPIES
Transcript of FRONTAL MEANDERS IN THE KUROSHIO EXTENSION PO25D-05 · frontal meanders w ∼ 100-200 m d-1-mainly...
KESS Unstable
3. Case Study: Stable Period (upper & deep, four bands) 4. Case Study: Unstable Period (upper & deep, four bands)
FRONTAL MEANDERS IN THE KUROSHIO EXTENSIOND. Randolph Watts, Karen L. Tracey, and Kathleen A. Donohue
Unfiltered Bandpassed Vertical Velocity Deep (u,v)
[email protected] www.po.gso.uri.edu/dynamics/KESS www.uskess.org
Band:
30-15d
PO25D-05
KESS is funded by National Science Foundation grants OCE02-21008 and OCE08-51246.
Large scale meanders of the Kuroshio Extension are quasi-stationary. However smaller scalemeanders, or frontal waves, continually propagate eastward. The downstream propagation ofthese frontal waves can even be resolved when the path is highly convoluted.
1. Kuroshio Extension
5. Dispersion Curve
The Kuroshio Extension System Study (KESS) spanned a transition between relatively stable andunstable meandering states. The CPIES array mapped the upper and deep streamfunctions dailywith mesoscale resolution for a 16-month period.
One of many frontal waves during Jun-Nov 2004.Shown: upper and deep, unfiltered and filtered Ψ.• 15-7d & 7-3d features propagate eastward alongfront with highs and lows vertically aligned upperand deep.• 30-15d strong features north of 35oN areassociated with a WCR propagating westward, notfrontal waves.
2. Space-time Plots of Upper & Deep Streamfunction Ψ (Band-pass Filtered) Stable Period Unstable Period
One of many frontal waves in Jan-Sep 2005.Shown: upper and deep, unfiltered and filtered Ψ.
30-15d and 15-7d features propagate downstream,
References James,C., M. Wimbush, H. Ichikawa, 1999. JPO, 29:259-272. Kontoyiannis, H., D.R.Watts, 1994. JPO, 24:1999-2013. Kouketsu, S., I. Yasuda, Y. Hiroe, 2007. JPO, 37:644-656. Lee, T., P. Cornillon, 1996. JPO, 26:205-224. Mizuno,K., 1985. Bull. Tohoku Reg. Fish. Res. Lab., 47:59-68.
In the following plots, the upper and deep streamfunctions were band-pass filtered in 30-15d,15-7.5d and 7.5-3.75d period bands to characterize the eastward-propagating frontal meanders.
Deep
lows
highs
Upper
Gulf Stream KW94 LC96
Kuroshio JWI99 KYH07 M85
KESS Stable
Deep
lows
highs
Upper
Upper Deep
highs
lows
15-7.5d
7.5-3.75d
VerticalVelocity, w
VerticalVelocity, w
unfiltered unfiltered
w caused mainly by cross-front motion in quasi- stationary trough,w ∼ 100-200 m d-1
-mainly advection Vn•(∂Z12 /∂n)
w caused byrapid-propagating frontal meanders w ∼ 100-200 m d-1
-mainly tendency (∂Z12/∂ t)
along the front.
Mean path:
20 cm s-1
grows downstream
decays downstream
grows downstream decays downstream
decays downstream
SUMMARY• Upper and deep meanders propagate jointly downstream along the path.• Smooth changes of (λ, T, c) ≈ (220km, 5d, 44km/d) to (350km, 20d, 17km/d).• Substantial vertical velocities in frontal waves, by tendency and advection, ~ 100-200 m d-1 down- and up-welling entering trough and crest.
Frontal waves propagate eastward jointly in upper and deep layers during Stable and Unstable Periods.•At times, the deep expression of frontal waves is obscured by external eddies approaching from NNE.
- Greene et al. (poster PO25D-04) discuss vertical coupling induced by these external eddies, particularly 30-60d periods. •Joint CEOF analyses of upper and deep Ψ in boxed regions find the deep perturbations lead upper by ΔΦ ≈ 0-30o for 30-15d; 37o-57o for 15-7d; 70o-72o for 7-3d.
Some waves grow or decay downstream in all 3 bands; usually the longer (shorter) periods tend to grow (decay).
Comparison symbols show estimates from references cited below.
Phase speed vs wavenumber and wavelength from CEOF analysis of along-path upper Ψ in boxed regions (Topic 2).Speeds equal those in Gulf Stream within statistical confidence.
Methodologies differ: - Propagation is along-path so distance ds is longer, with larger ds/dt. - Propagation is zonal in the other studies.
Paths from Aviso SSH productsCPIES
![Ensemble forecast of the Kuroshio meanderingengan.cmes.ehime-u.ac.jp/xguo/paper/Miyazawa2005JGR.pdf · The theoretical studies [e.g., Masuda, 1982] suggest that the Kuroshio can possess](https://static.fdocuments.net/doc/165x107/5f971cd0bf26f91b450a9c6f/ensemble-forecast-of-the-kuroshio-the-theoretical-studies-eg-masuda-1982-suggest.jpg)
