"How Do I Decode the Pacific Ocean Wave Report?" v.960318
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Question:
> Wondering if someone around there could provide me a little insight [on]
> how to interpret wave gauge data to estimate swell height...
>
> i.e. how would someone take this...
>
> MISSION BAY BUOY
> 080106 183.8 0.1 0.2 0.7 2.9 13.3 22.2 17.4 28.7 14.9
>
> And determine the surf is 6.0.3 feet at Mission Bay?
Answer:
PERCENT ENERGY/ANGULAR DISTRIBUTION IN PERIOD BANDS
PST SIG.HT/ANGLE(T) BAND PERIOD LIMITS (SECS)
DDHHMM (CM.) 22+ 22-18 18-16 16-14 14-12 12-10 10-8 8-6 6-4
080106 183.8 0.1 0.2 0.7 2.9 13.3 22.2 17.4 28.7 14.9
I think the interpretation of the report you cited (above) is:
080106 June 8 at 0806 UTC (June 8 at 0106 PDT)
183.8 Significant wave height 183.8 cm (72.4 inches)
The rest (0.1 0.2 0.7 2.9 13.3 22.2 ...) shows the percent
of total wave energy in each discrete time band. For instance, the
majority (28.7, 17.4, and 22.2 or 68.3%) of the wave energy in your
observation is in the 6 to 12 second bands (6-8, 8-10, and 10-12).
Take a look at the column headers I listed above.
Overall, it looks like fairly nice waves at fairly crappy intervals.
But then, I'm not a surfer...
Some of the buoys have paired observations, one for wave height and
energy (labeled ENERGY) and the other for the DIRECTION of travel.
I think this gives the direction TOWARD which most of the energy
in that time band is heading. This must have been set up by a
physicist. We climatologists expect to see it the other way round.
SANTA CRUZ HARBOR ARRAY, DIRECTION
241041 61 057 061 040 041 044 067 075 081
SANTA CRUZ HARBOR ARRAY, ENERGY
241041 38.9 6.1 2.6 1.6 4.8 23.5 8.0 14.0 22.2 17.7
Question:
> I [think] you avoided (from the looks of the decoding method)
> explaining the swell direction decode method.
Answer:
Sorry about that, I frequently forget that not everyone understands
how to decode compass directions. Direction of movement is decoded
using a 360 degree circle running clockwise from true north.
For example, the direction for the peak energy band at Santa Cruz
(in this case, 12 to 14 seconds) is 041. This means that most of
the energy in the 14-12 band is moving just barely (4 degrees) north
of northeast. The eight main compass directions are:
000/360 north 180 south
045 northeast 225 southwest
090 east 270 west
135 southeast 315 northwest
Caveat: 000/360 north - In meteorology, 360 designates movement
while 000 designates NO movement. whether or not that holds true
here, I don't know. My guess is that they would never designate
a no movement condition. In that case, you should see one or the
other, but never both.
If someone (who knows more about this report than I do) reads it and
disagrees with what I'm saying, please tell me where I'm wrong.
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-----===(* Climate's what we expect, but weather's what we get. *)===-----
Larry Riddle : Climate Research Division : Scripps Institution of Oceanography
University of California, San Diego : La Jolla, California 92093-0224
Phone: (619) 534-1869 : Fax: (619) 534-2240 : E-Mail: lriddle@ucsd.edu