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