SBI-2005

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Vagarities of Velocity Variations

Andreas Muenchow

Graduate College of Marine Studies

University of Delaware

http://newark.cms.udel.edu/~sbi

Chr

is L

inde

r, W

HO

I

SBI-2005

2/13

• transmits sound then listens for echoes

• sound interacts with ~ 2-cm particles (zooplankton)

• backscattered sound received by transducers

Velocity:Radar + Sonar

Radar send and receiveelectromagnetic waves (radio, police)

Sonar send and receives acoustic waves (sound, whales)

Same physics.

75-kHz transducers:

SBI-2005

3/13

Zooplankton diel vertical migrations?

ADCP backscatter Beaufort slopeOct.-2004

~10 m/hr~0.28 cm/s

SBI-2005

4/13

Aagaard (1984)

SBI-2005

5/13

cm/s

Beaufort Slope Currents 2003

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6/13

Beaufort Slope Currents 2004

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7/13

•

•

t0

t0+16 hrs

east west

L

Barrow Canyon, Sept. 1993

Synoptic velocity observation in Barrow Canyon, Alaska(view is to the south):

The flow scales with the internal deformation radius, L~5-km.

Münchow and Carmack (1996)

SBI-2005

8/13

Barrow Canyon 2004

Barrow Chukchi

SBI-2005

9/13

Coastal Circulation off Wainwright,Sept.-12, 2004

as measured by75-kHz acoustic Doppler current profiler

Flow is in the opposite direction from what is the canonical view of fresh Bering Sea water entering the Arctic via Barrow Canyon

SBI-2005

10/13

I

II

III

Eddies in the ArcticSept.-22, 2004

I II III

USCGC Healy 75-kHz ADCP

L

D

SBI-2005

11/13

The only real SBI-ADCP Survey, Sept.-22/24, 2004

55-m 100-m

red dots are XBT drops (Pickart and Kosro)

Chukchishelf

Chukchishelf

SBI-2005

12/13

Warm, fresh water flows northward against gale force winds in channel while

cooler and saltier waters flow southward with the winds.

Central Channel Chukchi Shelf8-m temperature

8-m salinity

SBI-2005

13/13

How to best distribute ADCP data?How to best “explore” ADCP data?

file:///Users/a2/0309_pro/os75/www0309/index.html

Conclusions:•ADCP velocity data challenges conventional perceptions of Arctic shelf and slope circulations (strong vs. weak local forcing);

•SBI did not resolve velocity and physical property fields properly in time-space domain (with the exception of WHOI moored array)

Questions:

SBI-2005

14/13

ADCP Processing: Sorting and Screening Single Ping Data

water trackrelative to ship(true East, unsorted)

water trackrelative to ship(true North, unsorted)

water trackrelative to bottom(true North, sorted)

water trackrelative to bottom(true East, sorted)

Ensemble average

Ensemble

SBI-2005

15/13

ADCP Calibration-1:Comparing Velocity Components

… looks good,but can’t tellhow good …

Transducer misalignment in

x-y plane: 44.1 deg.

x-z plane: 1.17 deg.

y-z plane: -1.10 deg.

Scaling by 1.021158

SBI-2005

16/13

ADCP Calibrations-2:Difference of ADCP-GPS Velocity Components

North

East

Histogram Integrated Histogram

SBI-2005

17/13

Barotropic Tidal Currents5-km data assimilation8 constituents, 2-week rms

from Erofeeva et al. (2004)