on eac anticyclonic eddies: insights from observations and...
TRANSCRIPT
Tatiana Rykova1
Gabriela S. Pilo1, 2 et al1CSIRO Marine and Atmospheric Research 2Institute for Marine and Antarctic Studies
On EAC anticyclonic eddies: insights from observations and models
Outline
1. Merging of East Australian Current eddies observed by Argo float and glider – Tatiana Rykova
2. Vertical velocity induced by eddy distortion – Gabriela Pilo
2 |
Historically …
Question: If we only have two examples in 30 years, does it mean that these types of eddies are uncommon … or did we just not notice
them?
EAC sandwich-like eddies with complex two-core structure were first observed in 1982 (Creswell)
EAC+Bass Strait Water two-core eddy was first described in 2012 (Baird and Ridgway)
We observe 2 two-layered eddies in the Tasman Sea in November-December 2009: From Argo … showing warm, salty waters to depths
of > 800 m
T S
Two-layer eddies …
T S
We observe 2 two-layered eddies in the Tasman Sea in November-December 2009: From Argo … showing warm, salty waters to depths
of > 800 m
Two-layer eddies …
T S r N2
T S
S anom
Nov 2009 Dec 2009
We observe 2 two-layered eddies in the Tasman Sea in November-December 2009: From Argo … showing warm, salty waters to depths
of > 800 m
From a glider … showing a double pycnocline and sub-surface T/S anomalies
… at the same time in a different eddy
Two-layer eddies …
In September, the Argo float sampled an anticyclonic eddy with one layer
Eddy A
SLA
r @ 50 m
Two anticyclonic eddies merge … and stack – one on top of the other
Potential density at 50m derived from SynTS
Eddy A Eddy B Eddy A Eddy B Eddy A+B
T=t T=t+1 week T=t+2 weeks
• Potential density at 50m shows that two adjacent anticyclonic eddies
have very different density over the upper ocean
• Eddy B is subducted beneath Eddy A
• @ T=t+5 weeks, we observe the two-layer eddy with Argo
?
• We observe two examples (1 with gliders, 1 with Argo) of double-core eddies. These may be more common than we think.
• When merging – the eddy with a denser core may subduct under the eddy with the lighter core
• Next step – use BRAN2016 … because it’s very good (see poster)
Take home message from observations
9 |
Come see our BRAN poster!
Outline
1. Merging of East Australian Current eddies observed by Argo float and gliders – Tatiana Rykova
2. Vertical velocity induced by eddy distortion – Gabriela Pilo
10 |
Patterns in eddy vertical speed
Is vertical velocity related to eddy distortion? | Gabriela S Pilo et al11 |
Red = upwellingBlue = downwelling
0.1 m SLA
EAC anticyclonic eddies tracked in OFAM3 (Pilo et al., 2015 - JGR)
Nardelli, 2013 - JGRMartin & Richards, 2013 - JGR
Idealised model data derived (ω-eq)
Is vertical velocity related to eddy distortion? | Gabriela S Pilo et al
Vertical speed explained by eddy distortion
12 |
ζ = relative vorticityh = layer thickness𝜕ρ
ρ= difference between depth layers
ρ = mean density between these layers
Eddy distortion = change in eddy shape
ΔSLAΔSLA
ΔSLA changes layers below: StretchingSqueezing
If we consider f and h constant:
Verticalspeed
UP
UPDOWN
DOWN
For an anticyclonic eddy in the Southern Hemisphere!
We use ΔSLA as a proxy for eddy distortion
ΔSLA w
• We see a coherent pattern in eddy w –> alternating cells
• w alternating cells are induced by eddy distortion …
• … and can be explained by simple theoretical arguments
Take home message from models
Is vertical velocity related to eddy distortion? | Gabriela S Pilo et al13 |
Outward = downwellingInward = upwelling
Come see me at my poster!
