Tuesday, January 6, 2015

A Fall Warm Water Pulse in the Strait of Juan de Fuca

Students from this year's oceanography class construct their mooring

For the past three years my oceanography class at Peninsula College has built and deployed moorings that measure, amongst other things, water temperature around City Pier in Port Angeles Harbor. The deployments are always about a month long, and always take place around the same time...usually mid-October to mid-November.

HOBO pendants, the data collection workhorse for my class's moorings

The moorings are built around HOBO pendants, which are placed to measure both surface water temperature, and "deep" water temperature...up to about 25 feet deep in this part of the Harbor.

Mooring deployment locations around City Pier

Here is the interesting observation from this year: We captured a really dramatic spike in water temperature this fall. I'm going to show data from the deepest water HOBO available at Station D, off the very end of the Pier, simply to illustrate that this wasn't just a surface warming phenomenon. This HOBO sits at a depth of about 20 feet relative to MLLW. Here are the data from 2012 and 2013. You will note that the 2012 deployment was only 2 weeks long:

In 2014 here was the pattern (the green line). Hopefully the difference is obvious:

But in reality, given the short record in 2012, we are working with only two years of data here - not ideal. So lets turn to surface water temperature measures from the Port Angeles tide gauge to try to get a sense of how anomalous this might be. First off, here is the typical annual pattern, based on data since 1998:

This takes water temperature data from each year (hourly observations) and plots them against the day of the year. I've colored all these years the same - the key take away is that in the fall the typical pattern is to see a decline in water temperature as winter sets in.

2013 was a bit different, in that there was a one-week pulse of relatively warm water recorded in the harbor in October (around Day 275; and actually one in July as well around day 180):

At the time I thought these two pulses were very interesting (and still do). But this year's fall pulse, the one we picked up with our class HOBO's, lasted much longer and was warmer (the red line between about Day 280 and 330):

That bulge between about Day 280 and 330 is warmer, by about 2 degrees Celsius, than the "usual" warm temperature at that time of year. The only other year that exceeds it? The 1997 winter, during a strong El Nino (shown here in purple):

Here, the pulse of warm water in the harbor occurred a bit earlier in the fall, but looks very similar in terms of its magnitude and duration. The interesting thing is that NOAA currently has us on an El Nino Watch, and suggests that El Nino conditions still aren't present. Interestingly, though, they note that much of the Pacific is warmer than average, but its the atmospheric El Nino conditions that haven't materialized. No matter which way you cut it though, no once is calling this a strong El Nino like the one that materialized in Spring 1997.

Another way to look at this is to look at the monthly average temperature from the Port Angeles tide station:

So in this case the thinner line is the monthly average temperature - you can see the seasonal pattern in there quite clearly. The green thicker line is the anomoly from the average monthly temperature, in degrees celsius, and November 2014 is the peak in that green line just shy of 2015. It is the highest temperature anomoly since the 1997-1998 El Nino.

So what is going on? I'm not really sure...and would love to figure it out. Contact me if you can help me understand.

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