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Stirring and mixing in the Denmark Strait Overflow Detlef Quadfasel (Hamburg) with contributions by Kerstin Jochumsen , Nuno Nunes (Hamburg) Janin Schaffer, Torsten Kanzow , Jürgen Fischer (Kiel). 2nd NACLIM Annual Meeting, Trieste , 1.- 2. Oktober 2013.

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Presentation Transcript
slide1

Stirring and mixing in the Denmark Strait Overflow

DetlefQuadfasel (Hamburg)

with contributions by

Kerstin Jochumsen, NunoNunes (Hamburg)

Janin Schaffer, TorstenKanzow, Jürgen Fischer (Kiel)

2nd NACLIM Annual Meeting, Trieste, 1.- 2. Oktober 2013

slide2

Temperaturestructureoverflow

DenmarkStraitϴ ~ - 0.5°C, S ~ 34.95

100 km

GreenlandIceland

slide3

Downstream temperatures

DenmarkStraitϴ ~ - 0.5°C, S ~ 34.85

100 km

GreenlandIceland

1000 km downstreamϴ ~+1.5°C, S ~ 34.95

2000 km

GreenlandIreland

slide4

Strong

entrainment

Less intense but continuing entrainment

Entrainmentalongthepath

Voet & Quadfasel, 2010

slide5

Stirringthrougheddies

Voet & Quadfasel, 2010

Obs.

Model

Fischer et al., subm.

slide7

Stirringandmixing

1

Verticalmixing KH-Inst

2

3

V. van Gogh, 1889

slide8

Stirringandmixing

1

Verticalmixing KH-Inst

2

3

V. van Gogh, 1889

Eddy-stirring

J. Girton, 2001

slide9

Mixing experiment June-August 2012

MERIAN MSM 21

POSEIDON PO 451

1

2

3

CTD/lADCP/MicroStructure

Moorings

AUV CTD & MSS

slide10

Moorings

N

E

C

W

S

E

N

Mooring array (12 m.)

2 months in water

coverage 20 x 25 km

coherentfor t > 1 day

W

S

slide11

Problems ADCP (1)

ADCP

Four ADCPs in centralarray

RCM (colour) and ADCP (black) recordsat 20 m a.b.

slide12

Problems ADCP (2)

ADCP data shows velocity bias near bottom

Bias affects also older data, albeit to lesser extent

Undergoing discussion with manufacturer to understand and mitigate problem

slide13

Problems ADCP (3)

Can wetrustthelongtermtransport time seriesofoverflows?

Weareworking on theanswer.

slide14

Results: Hydrography

Verticaldistributionatcentralmooring

High coherencealongandacrossslope. Signal propagation ~ 0.6 m/s

slide17

Microstructureprofiling

Dissipation rate at top edge of DS overflow plume three orders of magnitude greater than background value (e: 10-9 → 10-6 W / Kg)

Comparable values measured by AUV crossing horizontal edges of plume(for further details, see Paka et al, 2013, Ocean Sci. Discuss.)

slide18

AUV tracksduring MSM21

AUV equippedwith ADCP, CTD andMicrostructureprobes.

Schaffer & Kanzow

slide19

Hydrographyanddissipation

Schaffer & Kanzow

slide21

Final remarks

There‘smoreworktobedonetoestimatethemixing in theplume

The ADCP biasneedstobefurtherexplored