observations of storms off the west coast in 2012 from seafloor data david atkinson, uvic dept. of...

Observations of Storms off the West Coast in 2012 from Seafloor Data

David Atkinson, UVic Dept. of GeographySteve Mihaly, ONCDilumie Abeysirigunawardena, ONCMartin Heesemann, ONC

2013 CSAS State of Ocean Workshop February 20, 2013

Series of storm events, Jan 19 – 26, 2012:

- Synoptic overview

- La Perouse traces

- ONC Folger Passage (Deep) data:- surface waves

- Start with annual variance and comparison, 2011 vs 2012- BPR power spectra trace, late summer period

- spring period close-up- storm period close-up

- ADCP currents- storm event response

- oxygen - storm event response

Series of storm events, Jan 19 – 26, 2012:

Synoptic overview. - point to note: potential for different wave source regions during these events

January 19 2012 00Z

M

Typical progression:- “parent” system moves off jet into GoA-Dynamically linked systems generated, moved towards coast and to NE -Support from aloft = rapid increases in strength

January 19 2012 06Z

6,4

La Perouse Bank buoyDirectionWspd,Hs

M

January 19 2012 12Z

10,4

M

January 19 2012 18Z

7,3

M

1

January 20 2012 00Z

6,2.5

M

1

January 20 2012 06Z

11,3

M

1

January 20 2012 12Z

15,3

M

1

January 20 2012 18Z

15,4

M1

January 21 2012 00Z

16,5

M1

January 21 2012 06Z

960

12,4

M

1

2

January 21 2012 12Z

960

11,4

M

1

2

January 21 2012 18Z

11,5

M

2

January 22 2012 00Z

10,6

M

2

January 22 2012 06Z

11,6

M

2

January 22 2012 12Z

977 18,6

M

2

January 22 2012 18Z

977

20,7

M

2

3

January 23 2012 00Z

977

22,9

M

2

3

January 23 2012 06Z

10,7

M

2

3

January 23 2012 12Z

7,6

M

3

4

January 23 2012 18Z

9,4

M

3

4

January 24 2012 00Z

10,4

M

4

5

January 24 2012 06Z

14,4

M

4

5

January 24 2012 12Z

14,6

M

4

5

January 24 2012 18Z

13,6

4

5

967

972

January 25 2012 00Z

12,5

4

5

964

968

January 25 2012 06Z

15,6

4

5

964

968

January 25 2012 12Z

10,8

4 5

January 25 2012 18Z

8,8

45

La Perouse traces

Wave height peaks >8m

Max sustained wind ~23m/s(gust 30m/s)

Note direction shifts

ONC Folger Passage (Deep) data : Wave activity expressed as variance

log

Annual: 2011

log

Annual: 2011

More energetic, more variable winter season Less energetic/variable

summer season

log

Annual: 2011

February – activity appeared to be winding down- Kicked back in for an active March

log

Annual: 2012

log

Annual: 2012Similar in general form to 2011 – winter active, summer quieter

log

Annual: 2012Timings – 2011 winter ended fairly suddenly; 2012 dragged out

log

Annual: 2012Timings – both years – late July/August very quiet, September sees increasing activity

July/Aug. Sept.

First three weeks of September 2012 locally were (very) storm free

Observed energy can not be local.

Use a running spectral power plot of Folger BPR data to assess wave dispersion - angled tracks between 25s-10s indicate long period waves arriving well before shorter = wave trains pumped out by distant storms

Sept 12012

Sept 212012

Sept 142012

Sept 72012

Wave Period

Relative power

log

Annual: 2012Late Jan. Stormy period – most active single week in 2012

log spring

Spring: 2011Closer look at variance traces for stormy period

JAN 01 FEB 01 MAR 01

log spring

Spring: 2011

Note pattern – waves often exhibit rapid onset, slow decline- Cordillera blocks eastern progression of storms- move in fast, but stall and die slowly

JAN 01 FEB 01 MAR 01

log spring

Spring: 2011

Note pattern – waves often exhibit rapid onset, slow decline- Cordillera blocks eastern progression of storms- move in fast, but stall and die slowly

JAN 01 FEB 01 MAR 01

log spring

Spring: 2011

Can also observe fairly regular synoptic timing 3 – 7 days between events in mid-latitudes at this time of year

JAN 01 FEB 01 MAR 01

log spring

Spring: 2012

JAN 01 FEB 01 MAR 01

Similar general pattern but a higher level of activity persisted - no February slow-down as in 2012

Storm period

log storms

JAN 18 JAN 21 JAN 24

Stormy period: Jan 19-27, 2012Three peaks in local activity, two major (22-23rd and 26th)

ONC Folger Passage (Deep) data : ADCP vector currents

Stormy period: Jan 19-27, 2012ADCP current vector data, daily averages, filtered

North

South

East

West

Stormy period: Jan 19-27, 2012ADCP current vector data, daily averages, filtered

North

South

East

West

Rapid wind shift

Bottom return current

Direction maintained,Speed dropped off

Stormy period: Jan 19-27, 2012ADCP current vector data, daily averages, filtered

North

South

East

West

Possible Barkley Sound outflow?

Upper ~40m entrained during these events

ONC Folger Passage (Deep) data : Oxygen

Stormy period: Jan 19-27, 2012Oxygen data at 94m

Stormy period: Jan 19-27, 2012Oxygen data at 94m compared with ADCP vector currents

Stormy period: Jan 19-27, 2012Oxygen data at 94m compared with ADCP vector currents Presumably return

flow at depth draws from oxygenated upper flow

Upwelling?(SE flow)

Summary

- 2012 – surface forcing from Folger BPR:- more active and longer winter/spring- quiet mid-July/Aug, - Sept showed activity due to distant storms- Strong storm period in late Jan

- Folger data show in general- very high resolution overview of wave activity

- spectral tracks great for ID storm distance- depth of entrainment of surface water- indications of overturning flow due to storm-surge forcing/

interactions with Barkley Sound and bathy- resulting oxygenation at depth- short lived upwelling events ?

Analysis chart detail, Jan 22-23