Monday, May 8, 2017

The World According To Measurements

Fig. 1 All in
Sometimes we describe the world, or parts of it, by measurements.

So, how much or how little should we measure?

The most we can measure is "all we can."

We see this "all we can" quantity working in measurements, or the lack thereof, at the polar regions where the surface conditions can be harsh ("It is currently winter in Antarctica, therefore direct visual observation is extremely difficult." - Antarctic Ice Shelf Crack).

The same can be said of many areas of the ocean that are not visited often because of distance from shore, or distance to the bottom.

Fig. 2 Ice Sheet fingerprints
So, we form our world view in large part from the measurements we can manage to take and record.

A recent Dredd Blog post focused on the reaction of scientists to puzzling measurement results in tide gauge station records from around the world (Golden 23 Zones Revisited).

They solved what they saw as a problem by selecting tide gauge stations that are used to be representative of how the global ocean behaves, thereby developing the notion of  "sea level fingerprints."

How sea level changes and leaves "fingerprints" in measurements taken at those stations is said to be a general indication of where the water came from.

Today, as a follow up I present graphs generated by a new software module I wrote, which uses CTD & PFL measurements from all ocean depths in all WOD zones where they have been recorded.

It combines all the relevant (CTD & PFL) WOD and (monthly & annual) PSMSL measurements into one CSV file that represents the entire world ocean (not just the zones and the layers) over the years shown.

But remember, that representation ends up being "the world ocean according to measurements" recorded in the premiere (CTD & PFL) datasets of the WOD database.

The graph at Fig. 1 shows (pane one, upper left) sea level rise based on all Permanent Service for Mean Sea level measurements downloaded into my SQL database (PSMSL).

The result is reasonably close to "the Golden 23" sea level rise graphs made from far fewer measurements which are touted as a good general representation of the world oceans.

It also shows ocean temperatures, ocean salinity, and calculated steric, thermal expansion and contraction values downloaded from the World Ocean Database (WOD) (CTD & PFL dataset) measurements into my SQL database.

These graphs, made from real-life measurements, also confirm that thermal expansion is a minor player in the global sea level change dynamics (Fig. 2).

Thus confirming, with real-world measurements, the world view expressed in an ongoing Dredd Blog series (On Thermal Expansion & Thermal Contraction, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18).

The next post in this series is here.

1 comment:

  1. Be sure to remember that these graphs show CHANGES in values, not the actual values.