Paris Alston: This is GBH’s Morning Edition. This afternoon begins the summer solstice, the astronomical start to the season. Many of us will be spending time at the beach in the coming weeks. And as we do, one thing we’ll be paying attention to is when is high and low tide? Here for his weekly science dive is our meteorologist, Dave Epstein, and we’ll be taking a deep dive into the ocean to chat about one of the most reliable phenomena in the world: the rise and fall of our oceans’ waters. Dave, how are you? Good morning.
Dave Epstein: Good morning. Good morning and happy summer.
Alston: Happy summer to you as well. So I’m sure many beach lovers have witnessed the rise and fall of tides, but some may not know exactly how they work. So break it down for us, please.
Epstein: Yeah, it’s a little bit complicated certainly to do on the radio. I’d love to have some visuals and things like that, but let’s try to think about what you probably think — a lot of people say, hey, the moon causes the tides, and it’s that simple, and the moon pulls the water in one direction and there’s your high tide, and then it goes back and there’s your low tide. But it’s actually way more complicated than that. Because for one thing, we have high tide on both sides of the planet. So how do you get a bulge of water on one side when you’re on the opposite side from the moon? So what’s interesting is the fact that these two massive objects, the Earth as well as the moon, have gravitational pull. And as they go around each other and as the Earth is spinning, the rock, the earth, is covered by this thin layer — relatively — of water and gas, and that water gets pulled towards the moon on one side faster than the rock underneath it. So the water is moving towards the moon, the rock’s moving a little slower, and you get this bulge that occurs of water. Now why on the other side you get a bulge? It’s kind of the weight of the water. On the opposite side, it’s moving slower than the rock underneath it. And so you get a little bit of a bulge on the other side, like the rock’s moving faster and the water is left behind. So that bulges. So now if you were to look at a picture, you’d see the Earth with two bulges. So as the Earth’s rotating it’s rotating through those bulges of water. So picture the water staying stationary with the two bulges and the earth’s rotating with the water through it. And that’s kind of what’s creating those tides. Pretty cool.
Alston: Absolutely fascinating. So why is this process important to the Earth’s oceans?
Epstein: So it does a few things. I mean, number one, it’s interesting, people that make their living on the ocean have to know when high and low tides are occurring. Are you going to get your boat out? You know, if you’re going to go down to mud in a cove, you got to get your boat in and out during high tide. Also, there’s, animal and plant life that has basically created a symbiotic relationship with the tides. So, like, mussels grow along that tidal zone where they get some water coming in during high tide, but then they’re left at low tide, basically underneath seaweed or something like that so they don’t completely dry out too far out of the tide cycle, they’re not going to be able to live. Too deep they’re not going to be able to live. So there’s a lot of like interesting things that have developed in that tidal zone.
Alston: And are there any implications for what’s happening in the Earth’s atmosphere as it relates to the tides?
Epstein: Yeah, I mean, the tides are really just been going on, you know, for millennia, and it doesn’t really relate to the atmosphere. Except I will say this: when you get high tide and you’re at the beach, that sea breeze penetrates a little bit further inland because the water’s a little bit closer to the shore. Right? So what a low tide, it’s going to be a little bit hotter in that gap you have with all that sand, because the sand is heating up. And then at high tide that’s covered by water. So you do have some fluctuation in temperature right at the shoreline at high and low tide.
Alston: So while we are talking about our oceans, Dave, this week it’s obviously been hot. We’re rounding out this heat wave that we’ve had. And so obviously you feel the impact of that heat when you step outside. Does it impact the water at all?
Epstein: Yeah, absolutely does. So for one thing, the sun angle this time of the year, as a matter of fact, today it’s at its highest of the entire year. So that UV light beating down on that open water is warming it up really quickly. Also, when you have the air temperature warming up so much that the ocean temperatures respond and do warm up. So the more solar radiation we have, they’re warming up. And over time that’s seasonal. That’s been happening for thousands of years. But now as we warm up the climate, the temperature of the water on June 20th this year may be a little bit warmer than it was, say, 20, 30, 40 years ago. So how we see the ocean temperatures changing month to month, there’s also a little bit of warming there as well.
Alston: Well, there you have it. That is meteorologist Dave Epstein. And a reminder, if you ever have a plant or weather or atmospheric or oceanographic related question form, you can text it to us at (617) 300-2008. Dave, thank you so much.
Epstein: Good to be here.
Alston: Thanks, Paris. You’re listening to GBH news.
