Measuring Sea Level Change NSF DRL-1316782. What is sea level? Or should we say what is mean sea...
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Transcript of Measuring Sea Level Change NSF DRL-1316782. What is sea level? Or should we say what is mean sea...
Measuring Sea Level Change
NSF DRL-1316782
What is sea level?
Or should we say what is mean sea level?
Mean Sea Level
Before we answer the question “What is mean sea level?” let’s take a closer look at how sea level changes.
• Daily – Sea level rises and
falls – Called ocean tides
• Seasonally– In Tampa Bay,
water level tends to be higher in the summer and lower in the winter
Sea Level Variations
Sea Level Variations: Multi-year changes
Sea level also varies in terms of years
e.g., during El Niño years, the sea level along the US Pacific coast tends to be higher than during La Niña years.
When we say global sea level rise, what do we really mean?
Mean sea level -- The average of the sea level of a large region, or even the entire earth.How do we “get” the mean sea level?– Before we can get the “mean sea
level”, how do we get “just” the sea level?
– We measure sea level using scientific instruments• Measuring is not very difficult. • It has been done for several
hundreds of years.
History & Technology of measuring sea level
In the past, we used a stilling well.As the water level rises and falls• the float rises and falls. • mechanical device (at the
top) “draws” the sea level on a roll of paper
• Small holes near the bottom are designed to “filter” out the wave motion
History & Technology of measuring sea level
The water level is measured with sound (called acoustic sensor), which is like sonar.The drum recorder is replaced by a computer.
Today, we use much more sophisticated equipment but the principal concept remains similar.
A modern water level measurement station
Housing to keep the computer and equipment out of the weather
Sensor to measure wind speed and direction
Solar panel to supply power
Satellite antenna to send the data to the internet
Computer to process and store data
Acoustic sensor to measure water level
Stilling well to “filter” out wave motion
The previous slides illustrate how we measure water level at the coast, then how do we measure water level out in the ocean?• We could not measure
water level in the deep ocean until about 20 years ago.
Now satellites can accurately measure elevation using satellite altimetry.
What causes sea level change?
What causes sea level change?
Climate change (warming) will result in the following:• Thermal expansion – Water expands when
becomes warmer • For example, a 0.03
expansion results in a sea level rise of 1.2 m (or 4 ft).
• Continental ice melting adds water to the ocean