- Good evening and welcome to Wednesday Nite @ the Lab. My name is Margaret Mooney. I'm filling in for Tom Zinnen this week, and I have the honor to introduce my colleague and friend Derrick Herndon, who works at the Cooperative Institute for Meteorological Satellite Studies here on campus. I don't know if you all know this, but NOAA, the National Oceanic and Atmospheric Administration, has cooperative institutes at about 16 places around the country. Madison is one of them. 

Of course, UW-Madison. And why do we do the satellite studies here? Because this is the satellite capital of the world, and that's a really true thing, and Derrick will talk more about that and why he is studying hurricanes from the UW-Madison. Thanks, Derrick, for talking tonight. 

(audience applauding)

- Thanks, Margaret. So, yes, I'm Derrick Herndon. I do work at the Cooperative Institute for Meteorological Satellite Studies, which is housed over at the Space Science and Engineering Center. I'm a research assistant there. My specialty is hurricanes, and, specifically, the analysis of hurricanes using satellite data. How did I come to study hurricanes? Well, when I was about seven years old, I went for a fishing trip in the Keys with my father and my grandfather. 

It was, like, one of my favorite things to do. And while we were out fishing, my grandfather pointed to the horizon and he goes, Derrick, there's something you've never seen. And it was a waterspout coming from a thunderstorm with this black, black cloud and this elephant trunk shape coming down to the water. I had never seen anything like that. And so he explained to me what that was, and I was totally enthralled. 

And a few years after that, I started just devouring books on meteorology at the library. By the time I was 11, I had my own weather station and was posting forecasts on the refrigerator every day. To let the family know what the forecast was going to be.

So, from that point forward, you know, even into high school, when I run into my high school friends and they say, wow, Derrick, it's so cool that you're doing meteorology because that's all you ever talked about. 

(audience laughing)

 And it was. It was really the only thing I wanted to do. So I feel very fortunate to be kind of living my passion and studying this work. I got my degree at Florida State. From there, I went off to Mississippi to work at a private institution, a business that was developing high resolution models for the Navy. I did some work there for a couple of years. And a colleague here came down and gave me a talk about what they do up at Wisconsin. 

I'm like, really? They study hurricanes up in Wisconsin? I get that all the time. So every time I say I work at Wisconsin, I study hurricanes, people are like, "Why are you guys studying hurricanes in Wisconsin?" So he convinced me to come up there and work at the university, and that was in 2002 and I've been there ever since.

I do mention that, you know, the Space Science and Engineering Center is an odd location, but, if you think about it, most of the work we do with hurricanes does involve satellite data. A lot of it does, or a computer model. So you really don't need to be down in the south or in the tropics to study these things. I'll just mention a little bit about the Space Science and Engineering Center. So this was established in 1965 by Vern Suomi, who we consider the pioneer of satellite meteorology. 

He developed a very cool way to stabilize satellite imagery in a way that wasn't done before. And from that point forward, he founded the Space Science and Engineering Center. We work with other universities globally, so both in the states and other countries as well. We work with NOAA, with NASA, other government agencies, the military. 

I do a lot of work with the national hurricanes specifically, but we also have people who work with the Storm Prediction Center, which primarily they do tornado watches and warnings and tornado forecasting and severe weather forecasting. In that building, we do a lot of different types of projects. Instrument development, so instruments that are actually going to go on the satellites or develop there. We have a clean room. A lot of data processing goes on. 

We push on the order of about a couple terabytes of data to people every day. A lot of algorithm development, which is what I do specifically. And then we have people who-- Once you develop all these algorithms, you have to kind of visualize this data in some way, so we have people who work on that. We're known for MICADAS and Hydra and SIFT, which is a new algorithm, newer visualization tool. 

Lots of training and teaching, so once we develop these tools, we have to go out to the various sites and tell people how they work. We do work from the tropics, obviously that's what I do, all the way up to the Arctic and Antarctic. We actually have a group in the building that deploys to the Antarctic every year to do work. And within that building we have a couple of smaller groups. 

So CIMSS is the Cooperative Institute where I work, then we have an Antarctic group, and then obviously the Atmospheric and Ocean Sciences Department. I just put our mission statement up here real quick so you can read it. Again, we're leading development in advanced space-based instrumentation, observing Earth's atmosphere, conducting research programs to improve our understanding of the atmosphere, and also the oceans. We don't just study this on the Earth. 

We also have people who do planetary meteorology and planetary science as well. We want to facilitate the transfer of knowledge into the operational world. So transitioning these things into operations is very important. We don't want to leave them just in the research world. Supporting campus research initiatives and technical administrative expertise and then supporting the university's education mission as well.

This is the CIMSS tropical web page. So this is a web page that we maintain. And one thing you'll notice about this page is that it's global. So if there is a tropical cyclone, which is a generic term that we use for hurricanes. Hurricanes have different names around the world, so the generic term is tropical cyclones. If there's a storm that's occurring anywhere in the world, it'll show up on our page here and you can click on it and look at all kinds of cool imagery. 

And then there are also some other sites on here. If you have, like, questions about storms, this a good place to go to get answers. And you can always email me directly as well. All right, what is a hurricane?

Well, they're really just strong, low pressure systems. These are low pressure systems that form over the tropical oceans. They only form over the ocean. They tend to not form over land. They can form near land sometimes, but if they're near any land, they're going to struggle. They really need to be over the open ocean. 

The water needs to be greater than 79 degrees, and that's because the energy, as it's coming into the storm, is moving toward lower pressure, it's expanding, it would tend to cool, so in order to maintain the heat flux into these storms, the water has to be warm enough.

They're made up of thunderstorms that organize in bands around a calm eye, if they're at the hurricane stage. So here we have a very classic image. This is Hurricane Maria from last year, 2017, a very damaging hurricane.

As I mentioned, we have a generic term for these because in parts of the world they call them different things. So has anyone ever been to Japan? A couple people have been to Japan. What do they call them there? Typhoons, correct. If you're off the coast of Australia, they're tropical cyclones. If you're in the Indian Ocean, they're cyclones. So just to kind of avoid confusion, we call all of these systems tropical cyclones.

The hazards associated with these, obviously most people think about the high winds. In fact, we rate hurricanes on a wind scale. But they really have other threats. And as we saw last year with Hurricane Harvey, which produced catastrophic flooding in the Houston area, heavy rainfall is definitely a threat. In addition to that, we have storm surge. 

So the storm surge is kind of a mountain of water that the hurricane is pushing ahead of it, and as that mountain kind of hits the shore, the waters will gradually rise up and surge across the shore and do damage to buildings and such. And if it wasn't bad enough, hurricanes actually have tornadoes in them too. So, pretty bad.

When we think about low pressure systems, they really don't exist in distinct character, you know, identifications. They exist on a spectrum. So at one end of the spectrum, we kind of have these what we call mid-latitude cyclones. So these are not tropical in nature. They have cold air and warm air. They're divided by funnel systems going into the low-pressure system and they're fairly large. They tend to cover large portions of the United States. 

So think about a blizzard or a nor'easter or a storm like that. That would be a mid-latitude cyclone. At the other end of this scale here, we have tropical cyclones or hurricanes. These have no fronts. There are no temperature differences across the storm. If you went and just took a boat, and I don't recommend it. Took a boat and went across the storm, the temperature would be pretty much the same all the way across. 

I say I don't recommend it because I've done it on a Navy cruiser, and it was not fun. 

(audience laughing)

 Kind of cool sometimes but the core of the storm was not fun. And then, in between, we get these, we call them hybrid systems because they don't really fit neatly into these two categories. So these are storms that have characteristics of both of these extremes here.

Hurricane Sandy would be considered such a storm. Hurricane Sandy was a hurricane, but by the time it made landfall on the east coast of the United States, it was no longer tropical in nature. In fact, the hurricane warnings were dropped. That created a bit of confusion. So the Hurricane Center changed a bit of its policy because of that. 

So they were trying to be true to the science, the scientific identification of what the storm was, but people really reacted differently to the name hurricane as opposed to just low-pressure system.

Just to kind of show the comparison, the scale. So here is a mid-latitude low pressure system. Again, a cold front and a warm front going into a broad area of low pressure. And that's the size of a hurricane. So this hurricane is off of Florida. We can see that size wise they're much smaller, but they're more compact and more powerful so that energy is concentrated in a much smaller area.

And when I say that, when we think about the winds of the hurricane, the strongest winds are really just right around the eye. Once you get away from the eye, the winds actually drop off exponentially.

Just for comparison, that's what a cluster of thunderstorms would look like. So hurricanes are made up of many clusters of thunderstorms rotating around the center. And then if we really zoom down, we could say that's the size of a tornado. Tiny, but still very, very damaging. Again, very compact and very small, but still damaging nonetheless.

The reason I bring this up is that people often confuse size with strength. When they say it's a massive storm, it could have very, very strong winds but it might be very small and compact. And so the messaging is something we really have to keep working on because we don't want that kind of confusion.

Hurricanes have some very particular characteristics. So here are some of the distinguishing features. So I'm showing you a satellite image. This is a visible satellite image. So this is light from the sun that reflects off the clouds. So if you're standing on the satellite in space looking down at the surface of the Earth, this is kind of what you would see. The things we can see here are these thunderstorms kind of bubbling up around the center. We see the very distinctive eye. 

This is Hurricane Katrina from 2005 at category five stage, so at its max intensity. We get these distinct spiral bands. So these are bands of thunderstorms that are wrapping into the storm. And the interesting thing about these spiral bands, if you've ever been through a storm like this, is that when you're on the outside at the edges here, it's actually a beautiful sunny day many times before a hurricane, but then that first band comes through and the winds rise up to get very gusty. 

They might even gust up to 30 miles per hour or so, and then they calm back down again. So as the bands come across, you keep getting these squalls. Now, if the storm is coming right at you, those squalls get stronger and stronger and stronger, the gaps in between them get smaller and smaller and smaller, and then by the time you get to the eye wall, which surrounds the eye, it's just torrential rain and continuous very strong winds.

The other distinguishing characteristic is the outflow. So as air comes into the storm, it goes up into the thunderstorms and then it gets exited out at the top. And we can see that represented by very high cirrus clouds that spread out all the way around the hurricane in all directions, if it's a healthy storm.

Now, this is that same exact storm but now we're looking in the infrared. So now we're looking at temperatures of the cloud tops, and what that tells us is how tall the clouds are. So the taller the cloud is, the higher it is in the atmosphere, the colder that cloud top is, and the satellite can measure that temperature and then represent it in this image. So we can see that all these greens and reds are very, very tall clouds, especially the reds. 

That's that ring of thunderstorms and eye wall. But notice that the eye is quite warm, and that's very characteristic of a hurricane.

If we took a slice through that storm, kind of turned it sideways, this is what it would look like. So we have air coming in at the surface of the ocean. Some of that air gets intercepted and rises in the outer bands, but a lot of it gets pulled into the center and rises up in these towers either side of the eye. Now, as these thunderstorms get stronger, they release energy. They actually release a little bit of thermal energy. And that warms the atmosphere. 

When we warm the atmosphere in the upper parts of the atmosphere, we lower the surface pressure, so the pressure gets lower. As the pressure gets lower, more air comes in and strengthens the thunderstorms. The thunderstorms get stronger, releasing more energy, the pressure continues to fall. So you can see that this is a feedback mechanism, a positive feedback mechanism. 

Now, another distinguishing characteristic here is that some of that air, when it rises to the top of the atmosphere, it hits what we call the tropopause, so you can think about the tropopause as a lid on a pot of boiling water. The boiling water is rising up but it can't go past the lid so it kind of spreads out. Some of it will escape the lid itself. In a hurricane, some of that air actually gets pushed into the center and forced to sink. 

Now, as that air sinks, it gets compressed, and as we compress air, it warms even further, which continues that pressure fall. If we do a cross-section through this storm, we can see that the pressures on the outside are fairly high, and then they fall very rapidly. As you approach the center, they bottom out, and then they begin to rise again. The winds will just rise very slowly, and then, right when you get into the eye wall, will rise extremely rapidly. 

And then, when you get into the eye, the actual winds can go calm. So I've been in the eyes of hurricanes and they really do indeed go calm. In fact, if you're on a ship on the ocean, it's not uncommon if you find yourself in the eye of the hurricane, and this happened to mariners many, many years ago, they would go into the eye and birds would be everywhere inside the eye of the hurricane. 

Well, they're there because they got pulled into the storm and they're just circling around in the eye where the winds are calm, just trying to stay aloft. So as soon as a ship or anything that they can land on would emerge into the eye, they would just land onto the ship. I don't blame them. 

(audience laughing)

 We can think of a hurricane as a heat engine. So a Carnot engine where we have an energy intake here in the lower portion, what we call the boundary layer of the storm, and then uptake and we convert that into energy and then we exhaust that energy at the top of the storm. So, very much like an engine.

These systems go through stages of a development. They don't just appear out of nowhere, which is good. We don't want storms just popping up out of nowhere. They develop as a tropical disturbance, so like a weak area of low pressure, then they transition to a tropical depression with winds of 25 to 39 miles per hour. If it gets above 39 miles per hour, we call that a tropical storm, and it gets a name. Now, in the Atlantic, we use alternating male and female names now. 

And we just use the letters of the alphabet starting with A. In 2005, we ran out of letters. So had to go the Greek alphabet. It was a very, very active year. If the storm continues to intensify, we get up to hurricane intensity. So winds greater than 73 miles per hour.

In addition to that, once the hurricane attains that intensity, it can continue to intensify. And so in order to kind of convey the magnitude and strength of the storm, Saffir and Simpson developed this hurricane intensity scale, which goes from category one to category five. So from the depression state, this is what that storm would look like. This is Katrina again. So on the left is the visible image, and on the right is that infrared image that I talked about. 

As it progresses to tropical storm, we see it becomes more organized. Category one, more organized still, and also notice that it's beginning to expand outward and actually get physically larger in its size. So it's intensifying in its winds and it's also expanding and getting bigger. And then by category five intensity, we have a monster storm just south of Louisiana here. Again, larger still. 

Now, the problem with Katrina was that it did expand in size, and it turns out that the larger the hurricane is, the more storm surge it produces. Katrina's not really known for its rainfall because it was moving very steadily. It was actually move fairly rapidly by the time it got up to the Gulf coast here. So it did produce a lot of rain but it didn't sit in one place. But what it did do is it pushed a lot of seawater onto the coast in the form of storm surge. 

That's what did the catastrophic flooding in New Orleans.

So here's an animation satellite image of Hurricane Katrina developing. It'll develop over here on the right to the east of the Bahamas. It doesn't look like much now, just a cluster of unorganized thunderstorms. It developed from a tropical wave that came across the Atlantic and really didn't do anything. It was just kind of moving along not doing much. And then as soon as it got into the Bahamas, it really began to organize very quickly. 

It became a tropical storm right about here, continued to organize. Notice one thing that you see here is that it's kind of pulsing and almost breathing. That's a new scientific realization that we have is that these storms kind of have a breathing to them. They pulse in and outward. And we're not really sure what drives that. So that's a new area of research that we're working on. Across the coast of Florida there, that was, that part of the forecast was not a great forecast. 

But the forecast going into Louisiana, the National Hurricane Center absolutely nailed it. Three days before the hurricane made landfall on the Gulf coast, they said anywhere between Pensacola and New Orleans was the area that would be landfall, and that's exactly where the storm went. And they also did a fairly good job on the intensity forecast. Unfortunately, despite the good forecast, a lot of people still died. So here we have the very well-defined eye. 

Now, watch what happens as the hurricane begins to hit land. It begins to lose that eye. The eye kind of fills in. It weakens. So, you can very clearly see that once it loses its heat source in the form of the ocean, it weakens very rapidly.

We talked about sizes of low-pressure systems and how they kind of compare to each other, but it turns out that hurricanes actually vary in size as well. From the extreme, which was Typhoon Tip in 1970, this is a very massive cyclone. Obviously it wasn't over the United States, but I've place it over the United States for scale so you can kind of see how big that was. All the way down to tiny, little Cyclone Tracy. So this was a very, very small tropical cyclone. 

Sorry, Tip was '79, Tracy was 1970. You can see the difference in the size of these two storms. And we continued, again, to struggle in conveying to the public what that size means.

Cyclone Tracy, despite its size, was a category four cyclone.

Typhoon Tip is the strongest tropical cyclone on record in terms of its pressure. Unfortunately, we don't know what the winds were in Tip because the data wasn't quite as good in the aircraft in those days when they were flying out in the western Pacific. Okay, a little quiz. Here are two hurricanes. Both of them are near Florida. We have a hurricane here and we have a hurricane there. This one's a smaller hurricane, that one's a bigger hurricane. 

Which one is stronger? The one on the left? Who says the one on the left?

Okay, we have a fair number of answers for the left. Who thinks the stronger storm is on the right?

Okay. So, now, who thinks they're the same intensity? 

(audience laughing)

 Ah-ha. They are the same intensity. Both of these are category four hurricanes that have the same exact winds. Now I'm going to ask you a different question.

If I told you that the range of the hurricane force winds extended out that far in these two storms, now tell me which hurricane is going to produce the most damage.

The one on the left? No takers. The one on the right? Fairly unanimous. And the answer is right.

So that category scale that I told you about says nothing about the size. So we are playing with some ideas on how to convey that, but condensing all this information down into a single number, it turns out, is fairly challenging. So this is Hurricane Charlie in 2004 that made landfall in southwest Florida. It did a lot of damage. That is Hurricane Floyd, which moved, actually, just off the coast of Florida and weakened before it made landfall in the Carolinas. 

But it was a very broad storm with the winds extending out a very far amount, and it did a fair amount of damage as well. Okay, we'll shift gears a little bit. We're going to talk about where do hurricanes form in the world? So this is a map of all tropical cyclone tracks from 1851 to 2006. And you can see a couple things very clearly here. For one thing, in the Atlantic, we can see they tend to form off of Africa and move up towards the west. 

They generally move to the west, and then they either make landfall in the Gulf of Mexico area or they curve out into the Atlantic. Notice that the East Pacific also has a lot of storms there, off of Baja. But notice that those tracks are very constrained in terms of their latitudinal extent compared to the Atlantic, so a big difference there. The western Pacific should stand out like a sore thumb. It turns out that we get more storms in the western Pacific than we do anywhere in the world. 

They get an average of 30 to 32 storms per year.

A lot. Okinawa, the Philippines, Taiwan, Japan, all threats from that and often get hit quite a bit there. We also get a few storms in the Indian Ocean. They tend to occur in between the monsoon seasons. And then, in the southern hemisphere, we also get a fair amount of activity around Australia and Madagascar. All of these areas where these storms are occurring are where the water is warm enough to support them. But the water near the tropics is still quite warm off of South America. Why are there no storms there? Or there is two or one. And that was a very unusual storm. But there was a big gap there. If we zoom in kind of in the Atlantic, we can see those tracks again, starting off the coast of Africa, moving the west, and then recurving. And then, again, the area off of the coast of Mexico here, a little more constrained. 

There are more storms in the eastern Pacific than there are in the Atlantic by about five.

Hurricane season runs from June until November, at the end of November, so here we are, June 27th. But notice that at this time of year we really don't see a lot of activity. Now, we've already had our first storm, and it actually formed in May. And you can see at the tails of this distribution that there are some storms that tend to form early in the season. It turns out that we think that that might be increasing. 

We think that storms might be forming earlier in the season and actually going later in the season, such that we might have to change the start of the hurricane season from June 1st to May 15th. It's still an open question. We're still looking at that, but there is some discussion about that. The big thing on this plot that I want you to take away from is the season really doesn't get going until the middle of August, that's when things really crank up. 

So that area from about the middle of August to the middle of October is the peak of the hurricane season in the Atlantic. I want to talk just real briefly about some of the specific dangers, specifically here the wind. And I want you to kind of take home the fact that, while wind is a big deal to tropical storm the category one to category two range, we really don't get the bulk of our damage in that area. And that is homes in the United States tend to be fairly well manufactured and built. 

In fact, there are building codes in Florida and other places that are at risk from hurricanes that specifically say you have to keep the roof attached to the building. We learned during Hurricane Andrew that once you lose the roof, you're going to lose the house. So there are very specific rules in place for that. But notice once we get to category three, that the wind damage increases exponentially from category three onward. So this is the dollar damage in millions here in the category scale. 

And, actually, you can see that a category one hurricane with winds of 75 miles per hour and you compare that to 150-mile-per-hour storm, so you would think the damage would be double, right? The winds are doubled, the damage should be doubled. But it doesn't work that way. The damage is 250 times that of a category one.

Anyone want to venture a guess why? I like to ask questions.

- Momentum? Momentum of the winds? Basically, kinetic energy...

- Ah, momentum of the winds. So, yeah, the force of the winds is not linear. That's a good answer. There's another one.

It turns out that once you get winds over a category three, which is winds of over 115 miles per hour, bad things start happening to buildings, even though if they're well put together. You start ripping off trees, you start ripping off pieces of buildings. That debris then flies with the wind and hits the building next to it and so on and so on and so on. 

So, catastrophic damage starts to occur after category three because buildings start to fail and those failed buildings begin crashing into other buildings. So that's part of the reason as well. And for those who didn't see, that is a two-by-four driven through a palm tree.

I mentioned that hurricanes do have tornadoes. This was Hurricane Wilma, a tornado off of Key West back in 2005. If you get a tornado with a hurricane, it tends to be out on the outer edges on the outer spiral bands. That's where the thunderstorms are actually strongest for producing tornadoes. I also mentioned the flooding threat. Before Harvey occurred, we really kind of had the standard for that area was Allison. Now, Allison wasn't even a hurricane. 

It was only a tropical storm, but it still produced 20 inches of rain in Houston. That doesn't actually sound like much now, but at that time it was catastrophic flooding for that area because the Houston area, and many metropolitan areas, it's all asphalt and concrete. There's nowhere for that water to go. Hurricane Mitch made landfall in Central America. 

And, the problem with Mitch was that it was a powerful storm but it made landfall in a mountainous region, and the mountains just simply aggravate the rainfall situation.

In terms of ingredients, how do we get a hurricane in the first place? You have to start off with a disturbance. So I kind of mentioned that these storms progress to this phase starting with the disturbance phase. We get about 100 tropical waves that come off the African coast every year. But only about one in 10 of those waves develop. Okay? So we have about an average of about 10 storms per year in the Atlantic. You also need a lot of moisture. 

So we have these thunderstorms, they thrive on moisture. If the air is too dry, they won't develop. So this is an image, actually taken from a G5 on a research mission that I was on, looking at the genesis of storms off of Africa. And you can actually see the dust, the brown, dirty dust as we're looking down towards the ocean. So this is not an environment that's conducive for developing hurricanes. 

We were studying this very specifically because we want to understand the microphysics of how dust interacts with these storms. And I mentioned that we need water more than 79 degrees. This is a product that we did develop at the Cooperative Institute. This is what we call the Saharan Air Layer. What this does is it allows us to use satellite data to identify areas where the air is dry. 

So areas where we have oranges and reds is dry air, and areas that don't have those colors is fairly moist air. And you can see areas where those oranges and reds exist, there really are no clusters of thunderstorms.

If we look at a global view of moisture, we can see a couple distinctive features here. So this is a total precipitable water product. It's an integrated quantity of the amount of water moisture that's in the atmosphere. We can see a very distinctive ribbon along the equator. So we call that the Intertropical Convergence Zone, and it's very common for those thunderstorms to be in that position because we have converging wind flows there. 

And then oftentimes we'll get waves that will come off of that area and develop into tropical cyclones. Notice that the areas to the south of South America here are very dry in this area here.

The other ingredient we need is we have to have favorable upper level winds. Now, when we talk about tornadoes and severe thunderstorms, we want strong wind shear to get those storms rotating. But the opposite is true with hurricanes. We want the winds to be light in the upper levels. So what we want is this here, on the left. We want the thunderstorms to stay vertical. It turns out that the hurricane is more efficient that way. 

If it gets tilted over by strong upper level winds, then some of the energy gets blown away from the hurricane, and it doesn't tend to develop further. And if it's a strong storm, if we get wind shear like that, the storm will weaken. When we talk about wind shear, we're talking about a difference between the winds in the lower part of the atmosphere and the winds in the upper part of the atmosphere. By that I mean between about 5,000 feet and up around 30,000-40,000 feet or so.

Another product we have that we've developed is we can take the satellite image and we can look at a snapshot, and then we can take another image a few minutes later and compare those two images. We can actually track features of those clouds as they move. It's cool because when you do that, you can actually create wind flow from that. By looking at where those clouds are moving, we can create wind fields in the upper part of the atmosphere. 

So the Hurricane Center uses these products to identify areas that are favorable for hurricane development.

When we do get a hurricane, as I mentioned earlier, we often use satellite data to analyze it. And I just showing the electromagnetic spectrum here, and just kind of showing you kind of the areas of imagery that we are most interested in. Primarily we look at the visible spectrum, the infrared spectrum, and it turns out that we can use microwave, as well.

Microwave is a fairly newish type of satellite imagery that was developed in the late '80s. It really came into its own in the 1990s and the 2000s. So that's the visible image I've shown you. That's an infrared image of that storm. And then this is a microwave image. And notice that you can identify different features from each one of these images. Okay? So the visible image is really good at looking at the banding and the structure around the storm. 

The infrared tells us how tall the thunderstorms are. But the thing is if you have clouds covering the whole storm, it's very difficult to see what's happening underneath. That's where the microwave comes in. The microwave can actually penetrate those clouds and look at the actual structures of the rain bands and the eye and how big the eye is beneath the clouds.

So this is a microwave product that was developed at the university. The problem is, for the microwave satellites, they only come over, they're polar orbiting satellites, so they only come over every couple of hours. Whereas, with geostationary images, we can now get images every 30 seconds now with the new satellite. So having those images from the polar orbiters be sporadic makes identifying the image changes of the storm hard, so we developed this technique to look at those images. 

What I want you to take away from this is that this is Hurricane Ivan, and it's undergoing what we call an eye wall replacement cycle. So the storm starts off with an eye in the center, a primary eye. I'll let this cycle back.

And then it develops another eye around it. That eye encircles the inner eye and it chokes off the inner eye and then it becomes the new eye wall So this structure change is very important, it turns out, because what this tends to do is it weakens the storm temporarily. And it would be good to know when that's going to happen. So we're developing tools to alert the forecasters when this process is going to occur in real time so that they can adjust their forecast accordingly. 

The other thing with eye wall replacement cycles is that they tend to make the storm larger. So Ivan underwent five of these. By the time it got into the Gulf of Mexico, it was a very large storm. I want to shift to kind of some of the improvements we've made over the last few years. I'm going to start with some satellite imagery. So this is GOES-16, which was just launched back in late of 2016, became operational in 2017.

And it's very cool because it has additional channels on it to allow us to look at different things. And it also has better resolution, both spatially and temporally. And I'm going to show you a quick comparison here. So look at these two animations. This is the new satellite, that's the old satellite. A lot more information in this one.

So this was, I mentioned that we can compute these wind values from the satellite imagery. This is the old satellite that we had, the old geostationary satellite. And this is the number of wind plots that we were able to produce from that image. With the new satellite, that's the data we get.

Now, this data goes into computer models to help us improve our forecasts. Which one do you want? Do you want that one, or do you want that one? I'm going with that one. The downside to this is actually that there's so much information here that the models haven't even caught up, really, with what to do with this. So that's work to be done.

Another cool thing that this new satellite has is it has a lightning mapper. So we can actually look at the lightning that's occurring in the storm in real time and animate it.

Interestingly, there's not a lot of lightning in the interior of tropical cyclones. So look at this image of Harvey. All the lightning flashes, which are the yellows and oranges, are primarily in those outer bands. That's because those bands, those thunderstorms that are in the outer bands, actually tend to be more energetic in terms of their upward vertical motion. Now, that's not to say that the storms in the center are weak. They're just not of the type that produce a lot of lightning.

I just will mention one more on this is that when we do see shifts in the distribution of the lightning in the storm that tells us that something is changing with the storm's character. So this is going to be great information, we think, going forward. Okay, so I'm going to shift to forecasting here and hurricane predictions. And they're a challenge. I won't lie. I was a forecaster in the Navy for eight years, several of that on a ship where we did typhoon avoidance. 

Did not have all the tools that we have today. There was no internet. There were very few models at the time. Yeah, so it turns out that a lot of people think it's really more art than science. But I'm assuring you, it's a lot of science.

So we'll start with another question here. What's the temperature in Madison right now?

- Where? 
(audience laughing)

- We'll get to that. Last time I checked, I think it was 79. Okay? But the question of where is a very valid question. Is it 75? Is it 81? 74 on the isthmus? Maybe it's 79 at the airport. Where's the official observation for Madison?
- Airport. 
- At the airport.

But what if you're over in Lake Mendota?

It turns out that the computer models only know about the observation at the airport. They don't know about all this other information necessarily. So what I'm trying to drive home here is that, in terms of our observing, we cannot observe the entire atmosphere, the whole atmosphere at all levels. There's a lot of uncertainty in our observations. But at the end of the day, it's that observation at the airport that's going to go into the model. 

Why is that important? We've made a lot of advancements in hurricane forecasting. A lot of those have come from computer modeling, developing ways to track where the hurricane's going to go. Hurricanes move with the flow of the atmosphere. So think about a leaf. You throw it into a river, the hurricane is like that leaf. It's just going to flow along with the river. Okay? It will modify its environment a little bit, but primarily it's going to go with the flow. 

So one of the ways that we can address this idea of uncertainty is that we can take lots of models. So we have an American model, we have a European model, we have a UK model, we have Australian models, Japanese models. All of these people, agencies run models. And then there are models that run within the United States. All of these models will give a different answer. And it turns out there's a lot of information in that. There's a lot of information in that variance. 

The other idea we can do is we can say, well let's take the model that we have, in this case we'll talk about the American model, and let's run that model many, many times and try to incorporate that information. So we run the model with the temperature of 79 degrees. We get an answer. We then run the model with, say, "Well wait, it could be 68 degrees." We get a different answer. So we keep doing this many, many times.

And then what that does is it gives us a variety of tracks. So, in this case, we have an example of multiple models for Tropical Storm Isaac, which was south of Hispaniola I'll tell you that that track ends at the five-day range. So this is a five-day forecast. I'm going to tell you that that's a pretty good looking forecast to me as a forecaster. It's fairly tightly clustered. There is some variance. But it's fairly narrow in terms of the Gulf coast landfall. 

You're fairly confident that this hurricane is probably going to make landfall somewhere up in that area. Then you get cases like this.

This was Hurricane Sandy. So as Hurricane Sandy was coming out of the Caribbean Sea, this was some of the model solutions we were getting. And notice that some of those hit the United States. A little concerning. But other models were taking it out to sea. So which one do you pick? So this is kind of the problem that we have. This is actually a weather forecast for today. Actually starting from last night. 

And I'm just taking one particular line in the atmosphere that's of interest If we step forward 24 hours, it's still pretty tightly clustered. Another 24 hours, another day, another day, another day. Starting to get some spread here and uncertainty. If we keep doing this all the way out to the end of the forecast, this is what we get. 
(audience laughing)

Now, I'm not telling you this to say, "Oh my God, "you guys have no idea what you're doing." What I'm telling you is that there's a limit to our predictability. And we can actually define that to some degree. And we can say, you know what? We're fairly confident in this forecast. Or we can say, you know what? We are not confident in that forecast.

This is a case for Joaquin. So it turned out with Hurricane Sandy, I should probably tell you the end result of that. Hurricane Sandy, many of the models were showing the storm going out to sea. The European model was extremely stubborn in saying that no, it's going to go out to sea and then it's going to hook back and come back to the United States. Now, initially, we didn't put much faith in that because all the other models were doing something different. 

But then all the other models started kind of moving toward that direction. And it turned out that ECMWF, the European model, was right.

So that gets us to this forecast, where we have another storm, very similar position to Sandy. Very divergent forecast. Very much like Sandy. Now we have American models taking it to the coast. This time, the European model is going out to sea.

So kind of we learn from these results, and the other thing we can do is we can say, "Look, this is an uncertain forecast." And we can convey that to the public. As we step forward in time, you can see that the models started to come around.

Now they're moving all out to sea.

And eventually this storm actually did stay well away from the United States and was never a threat. Unfortunately, when people see this on their Facebook pages, they see this. 
(audience laughing)

 And I get this every year. People share this with me every year on my Facebook page. They're like, "Yeah, this is what you guys are doing." Like, you guys were actually never meant to see any of this. 
(audience laughing)

 This tended to be within the realm of forecasters. This was the information that we used to make the forecast. It was never really meant to be made public. But the genie's out of the bottle, we can't put it back in, so we're left with what we have. And that really gets back to the messaging.

We can improve on this if we have enough computer power.

And it turns out that every advancement we've made in computer power has been matched. In fact, many of you may not know that the very first use of supercomputers was solving the equations for the atmosphere. The equations for the atmosphere could be solved on paper. It took you 36 hours to do a 24-hour forecast, but you would get an answer. Okay? Twelve hours late.

But when computers were first developed, this was one of the first things we put them to task. We can improve this because we can improve computer power, but there is a limit. How much are you willing to give? If you make the computer-- If you try to get the resolution too small and try to resolve too much detail, it takes so long for the computer to get you the answer that the forecast will be late. So we'll do a little test here. 

Think about your camera, which has megapixels, and you want to get the next camera which has more megapixels, more resolution. So your old camera, and I actually just had a flip phone not that long ago before I had an iPhone, took pictures kind of like that. What is that? 
(muffled chatter)
 A what? 
(muffled chatter)
 What if I give you a little more information?
- [Together] A dog?
- [Derrick] Are you sure it's a dog?
- A monkey.
- Some say it's a dog. Some say it's a monkey. I thought I heard bear. What about now?
- [Together] Dog.

- I think we have consensus on dog. It turns out, yes, it is a dog. The question is, at what point is it good enough? At what point are you willing to settle for the answer? Because I can get you that fairly quickly, but if you want that, you're going to have to wait. So, again, we continue to work on advancing computer power to improve our computer models.

As I mentioned, even though we've been able to increase computer power to resolve this ever increasing detail of the atmosphere and smaller and smaller scales, one of the things we're finding is that, actually, the models are starting to show us things that we didn't know existed. It used to be that we understood the physics and then we wrote the physics down to write the code for the computer models. 

But now the computer models are so good that they're starting to show us things we've never seen before, and it's starting to guide our research. We're starting to see things that are very interesting and we want to investigate by doing observation campaigns. For hurricanes, our focus right now is trying to understand what's going on in the boundary layer. The boundary layer is that lowest portion of the atmosphere. And that's the part where the winds meet the sea and produce a lot of sea spray. 

We don't completely understand the role of the sea spray from the ocean and how it energizes hurricanes but we think we're making good progress on that but there's still some work to be done. I mentioned this idea of eye wall replacement cycles. These are important changes in the structure of the storm. So we want to continue to investigate that with model simulations. The models actually do a fairly good job of representing those structures. 

They will show us eye wall replacement cycles that look very, very realistic, but they do it at the wrong time, which isn't super helpful. A lot of these computer models in the past were running at such coarse resolution that we had to make some big assumptions. We call those parameterizations. So we want to kind of peel those away and get away from parameterizations if we can. 

And, really, the best work that's being done in terms of track forecasting, where hurricanes were going to go, and even intensity forecasting to some degree, is this idea of ensemble forecasts. I've already showed you ensembles. That's where we run many, many models or we run the same model many, many times. And what we can do with that data is we can run these models, we can look at where the uncertainty is, and where the uncertainty is the greatest we can say, well let's back that up. 

Where did that uncertainty come from? So if you're over the United States, a lot of the uncertainty exists. Well, we'll ask a question. So we're over the United States. We launch upper air balloons. We have lots of airports and stuff, but we get a lot of uncertainty because weather moves from west to east, so our uncertainty is where?

- The west coast.

- The west coast but even farther than that.

- Hawaii.

- Hawaii.

Over the ocean. Over the ocean. We don't have a lot of observations over the ocean. We don't have airports. We don't have balloon launches. There are some aircraft and a few ship observations and buoys, but we have huge gaps. Now, we do have satellite data, as I've shown you. But we do still have some gaps in that area.

It's all not bad news. We have made a lot of progress. This is the track forecaster from the National Hurricane Center for hurricane forecast tracks over the last couple decades. And you can see for the different forecast time frames that those errors have gotten smaller and smaller and smaller.

In fact, the five-day forecast is now as accurate as the four-day forecast was like 20 or 30 years ago.

And you can actually quantify that. You can say, well, back in 2008, the size of the uncertainty cone was in the blue. The size of the cone dictates how many people we have to evacuate. Okay? So this forecast is trying to take into account the uncertainty, and that's why the cone gets larger over time. But that cone has gotten smaller and smaller and smaller, which is great. So we have to evacuate fewer and fewer people. That's good for them because they don't have to evacuate. 

They can stay home with their families. It's also good for the economy because evacuating all these people costs a lot of money. All these businesses have to shut down. So there's no doubt that there's an economic impact from this that we are able to reduce.

However, we're fighting a bit of a battle here. For every time that we improve the forecast, more people move to the coast. So you can see in this plot here, this is a density plot of the various counties along the areas where hurricanes impact, and you can see some of these counties have had 500% growth in these counties from 1960 to 2008. And I'll tell you, since 2008, that hasn't stopped. Even though hurricanes continue to make landfall, people continue to move towards the coast. 

So even though we continue to make improvements and track forecasts, because so many people are on the coast and because the roads are still limited in terms of how many people we can move out, it takes longer to get those people out.

The advancements that we've made in forecasting where hurricanes are going to go has not been matched by our intensity forecasts. So this is that same plot for that same period that I just showed you for track forecasts, but this is for forecasting intensity. And you can see that it's fairly flat. We haven't made a whole lot of progress. 

Now, I did actually just see a new plot of this that goes beyond 2010, and, actually, it's showing a little bit of improvement We think that the computer models are now good enough that they're actually able to resolve the inner core of the storm, which is fairly small. And by being able to resolve that inner core of the storm, we're starting to be able to get the intensity forecast a little bit better. But we still have a lot of work to do on this.

This is a cumulative percentage distribution showing the forecast errors. And so the error in knots, so a knot is about a mile per hour, a little bit smaller than a mile per hour. So, say, 40 knots is about 45 miles per hour. You can see that we just do still get some fairly large errors of 45, 60, and even sometimes almost 90-mile-per-hour forecast errors. Now, remember what I said, that, you know, category one hurricanes, 75 miles per hour. 

So there are times when our forecasts are off by more than a couple categories.

That's especially dangerous when the storm is developing near the coast. If the storm was well out to sea, we have plenty of time. Even if it rapidly intensifies and we blow the forecast, we have time to warn the people at the coast. But Hurricane Harvey was not that case. Hurricane Harvey went from a tropical storm to a category four hurricane in less than two days. Less than two days. Not a lot of time to get the word out.

Okay, big shift here. We've talked about kind of observations, modeling, forecasting, but I know some of you here are interested in the climate aspect of this, so I wanted to add this to the talk. So I'm going to pose a couple of thoughts here. So if a tree falls in a forest and no one is around to hear it, does it make a sound? Very, very deep and philosophical.

I'll change that around a little bit and I'll say this. If a hurricane moves through the Atlantic and no one observed it, did it exist?

The reason I say that is that our hurricane data record is very short when we think about geological time scales. And it really is the best in the satellite era, which is fairly recent.

Here are hurricane tracks from 1851.

One thing you'll notice is that most of these tracks are near land. That's not a coincidence.

I mentioned earlier that we average about 10 storms per year. I count one, two, three, four, five.

What was going on out there?

Who knew? No ships out there, or very few. And it turns out ships don't like hurricanes. So if they see them, have any indication that they're out there, they're, like, going the other direction. They run away, which is a good idea.

I'm showing this because back in the 2000s and the 1990s when there was a lot of discussion about global warming, some people said, "Wow, I wonder what impact this is having on hurricanes." I know, let's see if hurricanes are increasing in numbers. Wow, look! From 1880 to the 2000s, they've really, really increased.

Well, as I just showed you, we don't actually know a whole lot about hurricanes in this time period. And we probably were missing at least two to three hurricanes per year during then. So trying to draw this conclusion from this data is not a good idea.

I can expand that further globally and show you that if you look at the total number of storms around the globe from 1940 until 2010, you can see this kind of cumulative increase. So this includes not just storms in the Atlantic but the eastern Pacific, the western Pacific, Indian Ocean, southern hemisphere. The Joint Typhoon Warning Center out in Hawaii does this work. They report this out in Guam. We have about 80 storms per year. We know that that's a very solid number. 

It occurs every year, about 80 storms. Not 10.

So we have this very heterogeneous record of data of hurricane, you know, storms in terms of numbers of storms. So this is a difficult thing to look at when we're trying to look at trend analysis because the satellite record really begins in the 1960s and 1970s. And that's primarily in the Atlantic and the United States area. It took a while for other countries to launch their own satellites. 

So, really, our most confident data record exists from about 1979 onward, which is not a very long period.

But we could still look at that and say, "Well, we have pretty confidence "in that data from 1986 until now. "What does it look like?" So this is a climatological scale in terms of climatology. We look at 30-year periods when we talk about climatology.

Looks like an increase in both hurricanes but especially it looks like an increase in major hurricanes. That kind of makes sense physically to us. If the atmosphere Earth/ocean system is indeed warming and the ocean specifically is warming and hurricanes derive their energy from ocean heat, if the ocean gets warmer, hurricanes should get stronger. That kind of makes sense.

All things being equal.

One way we can fill in the gaps in that old hurricane record, and some people are working on this, are some very novel ideas. One guy came up with the idea that, you know what, some of these inland lakes that are close to the coast? What if we, like, dig down into the sediment and take a look in there and look and see if there's any kind of evidence. And it turns out that there is. 

And what they found is that when the storm surge comes in and pushes all that sand over the land and into the water, you get these layers of muck, sand, muck, sand, muck, sand. Each layer of sand represents a storm. And so they can go around the world and look at these core samples and say there were hurricanes here on these dates, plus or minus. The coolest thing I saw in the last two weeks was this study. 

Some folks in Japan came up with the idea, I have no idea how, to look at the shell growth of this giant clam, Tridacna maxima. And it turns out that the clam, its shell growth changes with water temperatures. When a hurricane moves over the ocean, it churns that water. 

Churns it up, so there's warm water at the top but below there, there's a lot of cold water, and when it churns that water, that cold water gets mixed up to the top, and it changes the temperature of the water throughout a fairly large depth. The clams respond to that by changing their shell thickness. So they're looking at that.

The question that often is asked "Is human activity impacting hurricanes, "tropical cyclones in some relevant way?" "Can we even detect those trends?" "And, if so, can we attribute some part of that "to human activities?" One of the things that we want to do is that if we think that that's true and we develop models to look at it, they have to be able to at least reproduce what happened in the past.

I mentioned that the hurricane record has these large heterogeneities in it and makes it very difficult to look at these trends, especially with respect to intensity because we didn't even know where storms were back in the record, much less how strong they were. But there is something we can look at that's not sensitive to that. We can look at their maximum intensity through their whole life. 

Where did they attain that maximum intensity? It doesn't matter how strong they were because we're just looking at where the peak occurred. And when we look at that and look at that trend over the satellite record, it appears to us that hurricanes are attaining that intensity at higher and higher latitudes, farther and farther away from the equator. So they're moving north in northern hemisphere and south in the southern hemisphere. Not by a lot but by a statistically significant amount.

If we look at that record and kind of expand it back to 1940, again that part of the record is a little more uncertain but we can see this trend and then we can take a climate model and run it and see what the trend is in the climate model. And it turned out that the climate model's results looked a lot like what's been happening in the past.

That tropical cyclones are obtaining their maximum intensity farther away from the equator.

Another thing that we can look at that's also fairly insensitive to the hurricane data record is the rainfall and also how storms are moving, whether they're slowing down or not. And the reason that this was brought up, and Jim Cossum, one of my colleagues who did the previous study and also this one, looked at this and thought this idea that we're having warming but the warming is not uniform in the atmosphere, most of the warming is occurring in the poles. 

So the poles are warming faster than the tropics are. Well, if you think about it, the jet stream is driven by the difference in temperature between the poles and the equator. And if that temperature difference is decreasing, then the jet stream would also be decreasing. And if the jet stream is decreasing and hurricanes move with that flow, they should be slowing down. So it turns out that that's true. Hurricanes, tropical cyclones do appear to be slowing down. 

Why is that important? Well, as I mentioned earlier, we have a couple of storms that produced tremendous rainfall.

The intensity of the storm is not strongly correlated with the amount of rainfall it produces. What is strongly correlated is how fast the storm is moving. A storm that is moving very slowly will produce a lot more rainfall. And it makes sense, if you had a thunderstorm parked over your house all day, it would dump rain all day on you, right? Because it's not moving. Same thing with hurricanes. If they're moving very slowly, they produce a lot of rain. 

Hurricanes are very, very efficient at converting moisture in the atmosphere into raindrops and producing rainfall.

The other thing that happens is that if you warm the environment, you evaporate more moisture into it. So the amount of warming that we have observed in the atmosphere we think corresponds to about a 6% increase in the amount of moisture. So some of that moisture certainly has turned into rainfall. We think that some of that was manifested in the catastrophic event that occurred in Houston. So here we have the rainfall plot for Houston. We can see a broad area of greater than 40 and 50 inches. 

And there were peaks in this area of more than 60 inches of rainfall. Now, I was just there last week doing some hurricane recovery work in some of these damaged areas, and that area is still very, very damaged. There's still a lot of wet drywall being ripped out and houses being repaired in that area. It's going to take them probably at least another year to recover from that storm. 

We could also put this into some historical context and say, "Well, how unusual is a 60-inch rainfall in Houston?" Maybe it happens a lot. Well, we don't think it happens very much. We think it has a return period of about thousand years. So, not very often there. So it kind of piques our interest. 

We think, you know, with this idea of slowing storms and increased moisture, how much of a global warming signal is in Hurricane Harvey? It's very difficult to attribute global warming impacts on specific storms, but we have some confidence in here that at least some of the rainfall that occurred in Harvey does have a footprint of the global warming signal in it. Now, you might think 6% increase, that's not a big deal, that's not a lot of rain. 

Well, it could mean the difference between stopping at the top of the dam or going over the top of the dam.

So, with that, I'll end. I covered a lot of material there, a lot of different areas of hurricanes. I hope what you found was interesting, and I think I have some time to take a couple questions. 
(audience applauding)