Tuesday, January 29, 2013

Data Love: A Visit by NOAA CO-OPs

NOAA's Mark Bailey describing how the Port Angeles water level measurement station works to students from my Fall quarter Intro to Oceanography course.

I love time-series of data. It hasn't always been like this, but there are some things that graduate school in the sciences will teach you...and one is how useful data time series are for helping us work out how the ocean works. And in my humble opinion, one of the champion data collecting organizations in the world is NOAA's Center for Oceanographic Products and Services, part of the National Ocean Service. These are the folks that collect water level data at hundreds of sites around the country. What makes that so special? They've been doing it well for well over a hundred years, and they are incredible at getting out high quality data from hundreds of sites out to the public, via their Tides and Currents website, only seconds after it is collected. So yes, if it isn't yet obvious, I have something of a science crush on CO-OPs.

I use data from water level station's on the Strait of Juan de Fuca almost every day, both for work and for play. Lately I've been having quite a bit of fun tracking the "non-tidal residuals" that are part of the winter season in this part of the world (see Jeff Adams' blog post on December's coincidence of a perigean high tide with a large non-tidal residual here).

Here, for example, is the standard plot for "preliminary" water level data from the Port Angeles water level station. There are three curves shown here. In blue is the predicted tide, or the water level that would be expected based on the large-scale, mostly astronomical, forces that "generate" tides. The red line is the actual measured water level, and then the green line...ohh, the green line how I love thee...is the difference between the two. And in this case that green line shows the transition from the very storm December that we had into a very cold and clear January...can you see it? That green line essentially shows the "non-tidal residual", or the component of the water level not predicted by the long-term average water level measured at this site over decades. In December we had consistent elevated water levels...in some case an extra two feet of water on top of already high tides. By January though, water levels were consistently LOWER than predicted. This is also called "storm surge", though in our case it isn't always associated with a "storm" proper. The thing that I love about this, is how closely the water level of the Strait of Juan de Fuca tracks the weather. Really, this is largely driven by pressure:

Here are measurements of pressure at sea level from the Port Angeles water level station. Low pressure equals, in general, stormier, while high pressure equals, in general in the winter, cold and clear. And, of course, that pressure also dramatically influences water level - higher pressure equals lower water levels, and vice versa.

I could go on...and I think I will. How about sea level trends? Much in the news these days, changing sea level is one of the threats facing coastal communities these days. And, because NOAA has been collecting water level data at some sites for well over 100 years, they are at the forefront of helping us to understand the relative risk of sea level rise around the country. Here, for example, is Seattle's relative sea level trend (relative because tide stations measure the level of the water against the land):

Seattle has a nice long water level record...over a hundred years at this point, and suggests a rising sea and something to think about. However, its useful to put things into context. Here is the same from Atlantic City, New Jersey:

here the rate of relative sea level rise over about the same time period is nearly twice as fast. This is probably due primarily to tectonic influences, possibly with a bit of help from "isostatic rebound" - more on that later. The point is - how lucky are we to have this sort of perspective on the places we live!

Okay, enough on that for now, and time to get into the real reason for this post. Prior to December 3 I had never actually seen an actual water level station, despite using the data produced from them all of the time. Well that changed, thanks to NOAA's Mark Bailey. Mark very kindly offered to come out to Port Angeles from headquarters in Seattle and provide a tour of the Port Angeles water level station for the students of my Intro to Oceanography class. He then stuck around to participate in a ocean science and technology career panel I put together for the class. The field trip was awesome! The water level station itself is non-descript, stuck in between boxes and crates on the very active Port of Port Angeles commercial pier. Really its just a small locker packed with electronics, cabled to a few instruments under the pier. But I was still impressed thinking about how useful and special these long data time-series really are (and I actually think a few of the students' were as well).

A student standing next to the "stilling well" that holds the instruments used to measure water level in Port Angeles.

1 comment:

E. Hahn said...

The sea-level rise data is an important basis for planning future infrastructure and facilities investments in (or in some cases divestitures from) coastal areas.