GG 140: The Atmosphere, the Ocean, and Environmental Change

Lecture 01.?Introduction to Atmospheres

https://oyc.yale.edu/geology-and-geophysics/gg-140/lecture-1

Course Overview [00:06:56]

The course simply has to do with how the atmosphere and the ocean work. How does the air and the water move and mix in the atmosphere? That's the winds. Also,?the different kinds of storms: thunderstorms, frontal cyclones, tropical cyclones.?So we're very interested in the basic physics of how the atmosphere and the ocean move. In the atmosphere, we're going to be studying clouds. How do clouds form? What is a cloud made of? And why do very few clouds precipitate?

We certainly want to understand how climate varies around the globe. Why does Central Africa have a different climate than Connecticut, which is different from Southern California, which is different from?any place? There's a distribution of climates around the planet that controls how people live, how they do their agriculture, how they live their daily lives. A?key part of this course is understanding the distribution of climates and the impact on human beings around the globe.

New Haven Weather Data during Hurricane Irene [00:12:39]

There's time on this axis and feet above mean low water. So this is the record of tides for New Haven Harbor. It's at the coast guard station right on the east side of the harbor there. And the blue curve is what was predicted for the tides based on the moon and the sun. The moon and the sun produce--their gravitational pull produces a tide in the ocean. Here in New Haven and most places around the world, it's a semi-diurnal tide, that is to say it's a twice a day tide, two high tides and two low tides. And that's what you see in the blue curve.

The red curve is what's actually measured. They've got a water level gauge there. And as it goes up, they record that. And now this date goes back to the twenty-eighth and the twenty-seventh, which was last weekend. And what you see here is that the sea water level rose quite a bit above what was predicted from the normal tides. And of course, that's what's called the storm surge.

So as Hurricane Irene came up the coast and with the winds blowing counterclockwise around it, as it approached, the winds were from the east. In fact, that's on this curve. I'll show it to you in just a minute. Well, that wind from the east pushed water into Long Island. And the water level rose. And they subtracted one curve from the other to get the green curve. So that's the difference between the observed water level and the predicted tide level. And you see that it rose about four feet above normal, and then dropped a couple of feet below, and then came back to normal. So that's a typical example of what happens with sea level as the hurricane comes up.

Now, here's the wind data. It's too small for you read from the back, so I'll try to walk through it. The same time scale is on the bottom. You're spanning about three or four days. This is in knots, which is a traditional unit of wind speed. Unfortunately, it's not the one we'll use primarily. We'll use meters per second. But knots is a traditional speed. A knot is a nautical mile per hour. So it's kind of like a mile per hour but a little bit greater.

So the wind speed increased as the--Hurricane Irene approached. And from the little vectors that you can see, the wind was from the east. It reached a peak of about thirty, thirty-two knots. And then as the storm moved away, the wind speed decreased. But then the wind was from the west.?

So here we are in New Haven. And the cyclone is like this, winds going around in that direction. As it approaches us, the winds are going to be from the east. And then as it passes by a day later, it's up here, the winds have the same direction around it. Suddenly, the winds are from the west. So you're seeing that pattern there. And then, of course, that's what's reflected in the storm surge. First, it pushes water into Long Island Sound. Then it pushes the water back out of Long Island.?

So here's another one. If you go on to water data USGS, that's the United States Geological Survey, and hit on the Quinnipiac River, which is the main river that comes down through New Haven, there's three rivers, we're going to do a field trip along the Quinnipiac as part of lab two or three. So you'll learn a lot about the Quinnipiac. But I went on just after the hurricane to get this data. This is the river discharge. It's in cubic feet per second. That's how much water is coming down the river.?This is a logarithmic scale. So that's a really big increase in the amount of water coming down the rivers. And of course, that's because of the heavy rain that fell from the hurricane.

Radar is a microwave signal that gets sent out from the radar antenna. It scatters off raindrops and then comes back to the receiver. And from the time it takes for the signal to go out and back, you get the distance. And from how the antenna was aimed, you know the azimuth angle, so you could figure out where that is. And it's put together in a nice map like this.

This was taken just as the front part of the cyclone was coming into Southern New England. And you see this nice heavy rain shield out here. The eye of the storm is probably about here. It wasn't a very well developed eye. But the center of it was probably about here. And the backside was fairly dry, surprisingly dry. Some people think that it was transitioning away from a tropical cyclone to a different type of a storm at this point.?

Another great one, of course, is the satellites. And there's a picture of Irene. Now there's lots of ways to get at the satellite data.?www.goes.noaa.gov?is one way to do it. And GOES stands for Geostationary Environmental Satellite. That means it's a satellite that is--it's over the equator. And it takes twenty-four hours to go around its orbit, just like the Earth takes twenty-four hours to spin on its axis.

So it stays over the same point on the equator. So we say it's geostationary. It's like it's parked right up there. And it's the best satellite for watching cloud patterns develop and move. Because you're not just getting an occasional snapshot when the satellite comes back around. No, that satellite is there. And it's taking a picture about every ten minutes. So you get a really good way to follow the structure of these cloud patterns as they're swirling around. So there's a good example.

Now, also notice these clouds are quite different than the ones up here. The radar shows that these were not precipitating, but these were. So the deeper clouds with the big anvils on them were precipitating, but these low level clouds were not at that moment.

This is?the balloon sounding. So the National Weather Service launches balloons--weather balloons--twice a day from a couple of hundred places around the United States and 400 or 500 around the globe. And they're all accessible.

The balloons are launched at 00:00 and 12:00 universal time. You're going to have to become familiar with what we call universal time. Sometimes we call it Greenwich Mean Time. In the military, it's called Zulu Time. We'll most of the time call it just universal time. And so 00:00 and 12:00 universal time, when we're on Eastern Daylight Time, like we're on right now, it would be 8 o'clock in the morning and 8 o'clock in the evening. So those balloons are launched at 8 o'clock in the morning, 8 o'clock in the evening. And they take about--they'll launch them a few minutes before that time because they take a couple hours to rise.

What's plotted here is, well, I'll say altitude. But really it's pressure because that's how we know how high the balloon is from the pressure that it is recording. Pressure decreases as you go up in the atmosphere. So it's a convenient way to keep track of your altitude.

And then on this scale is temperature. And two lines are plotted, one is the air temperature, one is the dew point. So when they're close together, that means the air is saturated with water. So that's not a surprise, that as this hurricane was coming over us, the air was saturated at least three or four miles up in the atmosphere. Maybe that's not saturated, but it probably is too. Probably that's just an instrument error or something to do with ice versus water. It's probably saturated all the way up.

And then the winds are given over here in a traditional, meteorological wind barb. It's a little feather that you draw--a little arrow with feathers on it. And the number of feathers tell you how fast the wind is blowing. And the direction tells you what direction the wind is blowing. So for example, here, the wind was, I think, thirty knots from the east. That's when the storm was approaching. So here in Southern Connecticut or Long Island, the wind is from the east.

And then as the storm was moving away, we had forty knots from the west. That was taken twelve hours later, 00Z on the twenty-eighth and 00Z on the twenty-ninth. That kind of brackets the hurricane passage. And then you can see this begins to dry out a little bit aloft. You saw those low clouds in the satellite image. That's this saturated air. But then it was drier aloft. So you can understand that vertical cloud structure we saw in the satellite image by looking at the balloon sounding.

What is an Atmosphere? [00:31:01]

My answer is going to be that it's a layer of gas held to a planet by its gravitational field. So that's my definition of an atmosphere.

I've got a planet here. It has some mass, M, has no atmosphere. But I've got an alien. I've hired this alien to bring in an atmosphere. And he's over here, and he's got a box of air. And the molecules are there. And he's far away from Earth. So it doesn't feel the gravitational field of the planet yet.

And so these molecules are going to be uniformly distributed through the box. They don't feel the tug yet from the planet that's going to maybe want to squeeze them towards this corner of the box. They're too far away for that. So they're just sitting there freely bouncing around in the box having a good time.

Then we bring that box down to Earth. Now it feels the gravity field of that planet. Now the molecules are still moving around. They're bouncing. There's pressure in that gas. But the gravity field is going to play a role too. So more of those molecules are going to sink to the bottom. There's going to be a few up here at the top. But most of them are going to be down at the bottom simply because of that gravitational field.

And then the final step of this experiment is I'm just going to open a door. When I open the door, that gas is just going to flow right out. The box is going to become empty, and I'm going to have an atmosphere. Obviously, it's held to the planet by that gravitational field. Just like it was in the box here, there's going to be few more molecules down below and fewer up at the top. So you're going to have that gradient because of the gravity field. But basically, it's going to be held there by the gravity field.

So that's what I mean by layer of gas held to the planet by the gravity field. Now, a couple of things that I've already misled you about. First of all, of course, that isn't how planets get their atmospheres. They're not brought in by aliens. There are two leading theories for how a planet really gets its atmosphere.

One is that it is a so-called primordial atmosphere. That is to say it was formed with the condensing planet. When the planet was first formed, it was formed from material out in space that was collected together gravitationally, kind of a gravitational inflow. And at the same time, there would have been lighter molecules out there that didn't want to become incorporated in the solid planet's surface. But they would have been attracted too.

And so you would have formed the solid atmosphere from the heavier compounds or ones that like to bond together. And the lighter molecules or the ones that don't like to bond together would have formed this envelope of gas around it. So that's one possibility.

The other is that--well, maybe there was an atmosphere formed in this way. But maybe it was lost. After all, the earth is almost 6 billion years old. So whatever atmosphere it had at the beginning isn't necessarily the same atmosphere we have today.?But even if the planet--the atmosphere was never there or was lost, the planet could still, over geologic time, give off additional gases from its interior. I'll just call that outgassing.

For example, if you go to a volcano today, you could measure gases coming out of the planet into the atmosphere. So this is an active dynamic ongoing process where gases come from the interior of the planet out into the atmosphere itself. So either one or some combination of the two is where the Earth and the other planets actually got their atmosphere from.

Now, I misled you in another way too, the way I've drawn that. I've drawn the atmosphere relatively thick that distance. If I call the radius of the planet capital R and the thickness of the atmosphere, let me call that little d, I've drawn them with the ratio about five or six to one. Actually, the ratio is much smaller than that.

If I take the ratio of d to R for the Earth, the radius is about 6,370 kilometers. Whereas the depth of the atmosphere--it's a little bit hard to define the depth of the atmosphere because it has a gradual top. There isn't suddenly a level where suddenly the atmosphere stops. But I'll make a rough estimate and say 100 kilometers.

The atmosphere has a great moderating influence on our climate.?Were it not for our atmosphere, the temperature of the surface of our earth would be much, much colder than it is, colder than we than we could survive. That's a long-term effect, but the atmosphere is very important for that.?And the atmosphere protects us also from X-rays, ultraviolet radiation, small micro particles coming into the atmosphere. They burn up in the atmosphere. So the atmosphere has a great protective role to play in allowing us to exist on this planet.