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Diving Deeper Shorts: Episode 2 (August 12, 2010) -


HOST: Today on Diving Deeper Shorts, we will revisit our previous interview on tides with Steve Gill from NOAA’s Center for Operational Oceanographic Products and Services.

Let’s listen in.

HOST: Steve, what is the difference between a tide and a current?

STEVE GILL: Well, that’s a good question and typically the first thing I cover in many of my talks with students. The word “tides” is a general term used to define the alternating rise and fall in sea level with respect to the land. So, tides are characterized by water moving up and down during the day. Currents on the other hand move horizontally rather than vertically. Currents describe the horizontal motion of the water and are driven by several factors, one of those is tides; another is the wind. The horizontal movement of water that accompanies the rising and falling of the daily tides is called the tidal current.

HOST: So basically tides move up and down and currents move back and forth. What causes tides?

STEVE GILL: Gravity is one of the major forces that causes tides. Tides are caused by the gravitational pull of the moon and the sun. The gravitational forces are counterbalanced by the outward force of inertia from the moon revolving around the Earth and Earth revolving around the sun in their orbital paths. The combination of these two forces results in the tide-producing forces. So, ocean tides are a combination of lunar tides (lunar meaning the moon) and solar tides (solar meaning the sun).

HOST: Why do we study tides?

STEVE GILL: Well, we study tides for a variety of reasons. If we know the times, heights, and extents of both the inflow and outflow of the tidal waters we can better navigate through the intracoastal waterways and within the estuaries, bays, harbors; and we can work on harbor engineering projects such as the construction of bridges and docks; and we can collect data critical to fishing, boating, surfing, and many other water-related sports. We put in tide stations to measure the tides and analyze the data so that we can predict the tides and publish tide tables. And this is just to name a few of the ways that we use tidal data to help us in our daily lives.

That’s all for today’s Diving Deeper Shorts, where we highlight a few minutes of your favorite Diving Deeper episodes.

Want to learn more? Go to and select the April 2009 podcast archive to listen to the full interview with Steve Gill on tides.

You can catch the next episode on August 26.