dimes: diapycnal and isopycnal mixing experiment in the southern
TRANSCRIPT
DIMES: Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean
• A US+UK experiment • Diapycnal diffusion and isopycnal dispersion and eddy fluxes • Improve eddy parameteriza>ons in models of the MOC for climate variability
WHOI
FSU
SIO
UW/APL
UEA
BAS
NOC Southampton
SAMS (Scotland) Read all about it: http://dimes.ucsd.edu/
Why K? Dominant momentum balances:
V = net meridional volume flux, τo = wind stress η = layer thickness, p = pressure, pb = bottom pressure
Surface -fV1 = τo
-fV2 = η'1p'1x - η'2p'2x
-fV3 = - hpbx “blocked” layer
ρ1
ρ2
ρ3
…adapted from Olbers
Side view of the ACC
zonally open
τo
Why K? Dominant momentum balances:
V = net meridional volume flux, τo = wind stress η = layer thickness, p = pressure, pb = bottom pressure
Surface -fV1 = τo
-fV2 = η'1p'1x - η'2p'2x ≈ K dq/dy
-fV3 = - hpbx
zonally open
“blocked” layer
ρ1
ρ2
ρ3
…adapted from Olbers
Side view of the ACC τo
DIMES Overview
X X
UK2.5
The tracer
• Trifluoromethyl-‐sulphur-‐pentafluoride.
• Inert, non-‐toxic. • 1 milligram is detectable in a cubic kilometer of seawater, by gas chromatography with electron capture detec>on.
CF3SF5
Ledwell Watson
R/V Revelle, 5 Jan to 1 Mar 2009
US1 Cruise Track and Deployments
Sound sources
Tracer release
CTD surveys Float deployments
SoSo large blue Solo small blue Rafos black CTD red
Injec>on patch on P18 Sec>on
Mean Concentra>on versus Depth (using mean density vs depth from CTD)
Tracer Simula>on 22 Feb 2010
Now wait a year… …but follow the evolution of the tracer with altimetry
X
Cruise Track R/V Thompson 15 Jan–5 Mar 2010
US2
Tracer Transects Column Integral
Horizontal structure
Ini>al & 12-‐month profiles
kz = 0.13 cm2/s
Vertical structure
Sco>a Sea
RRS James Cook UK2 Dec 2010 – Jan 2011
JC054 Sta>ons
2 years later
Average Profiles
0 500 1000 1500 2000 2500 3000 3500 4000 4500 -1800
-1700
-1600
-1500
-1400
-1300
West of DP
East of DP
US2
Normalized Concentration
DP kz ~ 1 cm2/s
DIMES Floats
• 11 sound sources for acous>c array • ~ 150 Argos and Iridium Rafos floats
R/V Revelle, 5 Jan to 1 Mar 2009
US1 Cruise Track and Deployments
Sound sources
Tracer release
CTD stations (red) Float deployments in triplets
SoSo large blue Solo small blue Rafos black CTD red
Neutral Density Sec>on at 105 W Deployment on 2 isopycnal surfaces
X
DIMES Floats as of Sept 2011
US1 1
US1 2US1 3
US1 4
US1 5
US1 6UK1 1
UK1 2UK1 3
UK1 4
110oW 100oW 90oW 80oW 70oW 60oW 50oW
65oS
60oS
55oS
50oS
Dimes Trajectories (43) Orsi fronts
Drake Passage Fronts and Floats
SOSE mean speed AVISO 7 yr mean speed + real floats + bathymetry
100oW
90oW 80oW 70oW
60oW
60o S
55o S
50o S
1000 2000 3000 4000 5000 6000Depth (m)
Tracer-‐Float Spreading
All stations Deep float surfacings
60 50 40 30 20 10 0 10 200
1
2
3
4
5
6
7
SSH(cm)
Num
ber o
f Par
ticle
s
Starting DF
100 80 60 40 20 0 20 400
1
2
3
4
5
6
SSH(cm)
Num
ber o
f Par
ticle
s
Ending DF
PDFs
Kdiff = σ2/2Δt = (400km)2/4yrs ≈ 1200 m2/s Also, d<X2>/dt ~ 1000m2/s and dKSSH/dz <0
−120 −100 −80 −60 −40 −20 0 20 40 600
100
200
300
400
500
600
700
800
900
1000
1100
SSH (cm)
Column Integral (pmol/m2) & Floats
Year 2
Tracer: blue Floats: green
Ver>cal Structure
Klocker et al; Speer et al.
i-----------------------------I
Ver>cal Structure
Klocker et al
1000 K 0
Conclusions 1. Deep isopycnal mixing in the ACC is
-‐ about 1200 m2/s (uncertain>es TBD) -‐ associated with f/H -‐ weaker away from topography?
2. DIMES float trajectories will provide direct but limited
diffusivity es>mates and other quan>>es, state es>mates necessary
3. Need to observe ver>cal structure of mixing to discriminate
theories 4. Flow spligng and merging: braided jets