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STEM-Talk

Episode 22: Dr. Kerry Emanuel Discusses Hurricane Prediction and Projection

Dr. Kerry Emanuel // Oct 11, 2016

Hurricanes are a leading source of insured losses, and a major cause of human and economics loss in the world. But from an insider’s view, they are also breathtakingly beautiful. Dr. Kerry Emanuel, a leading hurricane expert, compares flying into the eye of a hurricane to being inside a white Coliseum, thirty to forty miles wide, with walls resembling “a cascade of ice crystals.”

That’s just one of the fascinating tidbits from this episode of STEM-Talk, with Dr. Emanuel, whom Time Magazine named as one of the 100 most influential people in 2006. The following year, Dr. Emanuel was elected a member of the U.S. National Academy of Sciences.

He is a professor of meteorology at MIT, where he also completed his Ph.D. When he returned to teach there, he taught a course in meteorology of the tropics, and discovered that the existing theory of hurricanes was partly wrong. He’s spent the better part of his career disproving that theory and coming up with better theories of hurricane development and progression.

Dr. Emanuel is also a book author of “What We Know About Climate Change,”<http://amzn.to/2cWYQ7O> and “Divine Wind: The History and Science of Hurricanes.”<http://amzn.to/2dPXrNb>

His recent lecture at IHMC is entitled “Hurricane Risk: Past, Present and Future”:  https://www.ihmc.us/lectures/20160324/

STEM-Talk Host Dawn Kernagis interviews Dr. Emanuel about his career, the future of climate change and its impact on hurricane development, and the future of hurricane projection and prediction.

1:11: Ken Ford mentions that he met Kerry in 2005-06 when Ford was on the National Science Board’s Hurricane Task Force, which he co-chaired with Kelvin Droegemeier (also a previous STEM-Talk guest: https://www.ihmc.us/stemtalk/episode-13/). That NSF report was entitled “Hurricane Warning: The Critical Need for a National Hurricane Research Initiative: http://www.nsf.gov/nsb/publications/2007/hurricane/initiative.pdf

2:24: Ken reads a 5-star review from “Wheelsuker”: “I’m not always curious, but when I am, I love STEM-Talk, and the deeply learned folks at IHMC. Subjects range from human physiology to the exploration of space, with thoughtful and probing questions that simultaneously teach and entertain. Highly recommended subscription.”

4:53: Dawn introduces Kerry Emanuel.

5:05: Kerry says his older brother told him that as a toddler, Kerry would get excited about thunder storms at home in Ohio.

6:08: His academic interest in science, and weather, developed in high school: “I started reading more professional meteorology books in high school; I got interested in physics and math. By the time I went to MIT [as an undergraduate], I realized you could put those things together.”

6:33: Kerry describes his academic journey: “I was an undergraduate at MIT, and I also did my Ph.D. there in 1978. Then I went and taught at UCLA and was there for three years. I came back to MIT, and I’ve been there ever since.”

7:00: At MIT, he taught about hurricanes in a course called meteorology of the tropics. “Not only did I not understand the existing theory [about hurricanes], but the existing theory had to be wrong, so I had to go about setting it right.”

7:35: The existing theory didn’t pay any attention to transfer of energy from ocean to the atmosphere. “Ironically, earlier scientists thought that was the guiding principle.” He picked up where they left off.

9:43: “Hurricanes cannot arise out of small fluctuations in atmosphere like a thunderstorm or winter storm. Hurricanes are generated by a pretty big push.” He describes it as a giant engine that takes heat out of the ocean and transfers it to the atmosphere whenever water evaporates.

10:54: “The tropical atmosphere has a different temperature than the tropical ocean. What we don’t understand is how they [hurricanes] get started.”

11:30: In the Atlantic, African-Easterly waves flow from East to West. When they move out over the ocean, they will sometimes trigger hurricanes.

12:49: He describes the feedback loop that propels hurricane intensity: once you get the starter engine going, as the winds accelerate at the surface, the evaporation of sea water occurs faster. The stronger the wind blows the more heat is transferred to atmosphere—until you get up to peak intensity.

14:00: Kerry talks about his roughly 10 flights into the eye of hurricanes. “I think everyone should do it. It’s magnificent,” he says—especially the sight of the eye of the hurricane from the inside.

14:30: “When you’re flying in, it’s just like flying in bad weather in a commercial airline. It’s turbulent, but it’s never been as turbulent as I’ve experienced on commercial airliners. Hurricane pilots really know what they’re doing.”

15:52: The eye of the hurricane is actually calm. He compares it to being inside the Roman Coliseum, except it’s white, and instead of a few hundred feet across, it’s 30 or 40 miles across. Sometimes there’s a cascade of ice crystals on the inside of the eye wall.

16:17: “I have fantasized about starting a hurricane safari operation after I retire.”

16:45: The physics of a hurricane is angular momentum conservation. “If you have a spinning body, when you take some part of the mass and move it towards the axis, the spin increases. The classic illustration for that is a spinning ice skater who draws in her arms; by that mechanism, her speed increases; that’s the conservation of angular momentum.” Likewise, in a hurricane, air spirals towards the center of the hurricane within a few thousand feet of the ocean’s surface; once it has moved in so far, it goes rocketing up, forming the wall of the eye.

19:35: The primary remaining challenge associated with hurricane forecasting is knowing the intensity of the hurricane right now. “For most storms, we don’t have aircraft. Just looking at a satellite image doesn’t show you wind speed.”

22:10: Two things prevent most hurricanes from moving up to potential: wind shear (a dampening force that imports dry air into the core of the hurricane—like throwing water on a fire). And the hurricane’s ability to churn up cold water from deeper in the ocean.

23:24: We don’t know much about temperature of the ocean beneath the surface; that limits our ability to forecast.

24:44: Kerry describes Argo robots that submerge more than a mile into the ocean recording temperature information, and then surface and transmit this newly collected data to satellites.

26:08: Kerry explains the difference between hurricane prediction: whereby you take an existing hurricane and predict where it will go; and hurricane projection, which projects a weak or strong hurricane season based on climate change.

27:00: Prediction of the track of path of hurricanes is a wonderful success story. Predicting intensity has been much less successful.

27:57: In forecasting anything at all, you have to know where you’re starting from. It’s a fine art.

30:32: The atmosphere is chaotic, and getting the initial condition right is the really hard part…we can’t computationally resolve all the things that are physically important in the atmosphere.

31:16: There’s an enormous amount of work that goes into computational modeling; the diversity of models gives you a better forecast/appreciation for how uncertain that forecast is likely to be.

31:46: To analyze the current state of the atmosphere, we start with an old forecast. You update it by incorporating measures in present, which is data assimilation. Every forecast has a little bit of history in it.

33:33: If I didn’t have computers/understanding of physics, I’d say, ‘Let’s look for some close analogies in the past.’  This is called analog forecasting.  We know from theoretical work this is not a promising approach. Chaos will always ensure there are differences.

34:25: Computational weather prediction has pulled far ahead of any analog forecasting.

34:32: Commercial break: STEM-Talk is an educational service of the Florida Institute for Human and Machine Cognition, a not-for-profit research lab pioneering ground-breaking technologies aimed at leveraging human cognition, perception, locomotion and resilience.

35:07: “We’ve gotten steadily better by all metrics at predicting the track that hurricanes will take. On the other hand, we haven’t gotten much better at forecasting how strong a hurricane will be.”

36:13: “Hurricanes are creatures of warm, tropical ocean waters, and the Gulf of Mexico is a great example of that.” Hurricanes often form in the tropical Atlantic and the Caribbean and then strengthen as they move into the warm Gulf waters.

37:15: “If we look at geological records … we think actually the region (Gulf Coast) has been pretty lucky over the last century compared to what’s been true over the last few thousand years.”

38:40: Dawn asks if the current trend of planetary warming is likely to have any effect on hurricane formation and intensity over the long run.

39:10:  Effect of planetary warming on hurricane formation and intensity: “It’s not a solved problem, but there is a kind of consensus developing about what we think will happen.  The key points of that consensus are this, we think the frequency of very high-category hurricanes will go up as you warm the climate; but at the same time, there’s a little bit more controversy about the frequency of weaker hurricanes. Most studies suggest that the frequency of these will go down.”

40:00: Eighty percent of the damage in the U.S. has been done by category-3 or greater hurricanes. The consensus is that there will be more of these strong storms in the future. They are associated with strong storm surges. In practice they kill a lot of people. There is also a very strong consensus that fresh water flooding from heavy rains is going to get worse, almost for sure as the climate warms.

42:43: “The theory of chaos is often described as a kind of practical limit on what you can forecast … but it’s much more profound than that, it’s not just a practical limit, it’s a theoretical limit that you cannot go beyond not matter what resources you throw at it.”

44:19: For all practical purposes, the system is not deterministic beyond two weeks.  Thus, we will never be able to make precise forecasts beyond that time horizon.

45:25: Discussing how good a forecast is likely to be: “We can forecast how skillful our forecasts are. That is a very profound thing to be able to do.  What we have not mastered is how to convey that to the public.  We struggle with that everyday.”

47:42: To improve forecasting, we need better measurements, better computer models, and better ways of assimilating improved measurements into the better models. High level research on this is taking place all over the world.

48:30: While this should be a cooperative international enterprise, European governments have monetized weather data. “The bad boys are the Europeans—their governments decided they could make money from selling weather data…. Even at the peak of the Cold War, the US and USSR were freely sharing weather observations.”

49:22: Some of best computer forecasts are generated by the Europeans, from the European Center for Medium-Range Weather Forecasts. “If we want to see them, we have to pay through the nose for them. Everybody else subscribes to the older idea that since the taxpayer has paid for this data, it should be freely available to all.”

50:33: Economists have demonstrated that even if the only thing you are concerned with is how much money the government would make, it’s an inferior model. The freedom of data has led to small enterprises doing specialized forecasting based on the available data. Those companies create jobs and are taxed; the U.S. government gets more money that way, than the Europeans do trying to sell environmental data. Kerry says there are efforts to get Europeans on board with this “more gracious, economic model of sharing environmental data.”

53:19: On quantifying the risk of climate change: If it’s one degree warming by the end of the century, there’s not much difference. If it’s four to five degrees, the world could erupt in a conflict over water and food shortages.

54:03: In thinking about what we should do, if anything, to reduce the rate of warming, it is rational to consider both risk and the possible consequences.

56:10: Look on bright side [of climate change]: “We have an opportunity here to transform our energy systems ahead of the curve.”   If there were no climate change, we would still eventually run out of fossil fuel.

56:45:  Discusses the shortcomings of solar and wind energy.  The wind does not always blow and the sun does not always shine … and we are not very good a storing energy.

57:10: Kerry discusses the positive potential of next generation fission energy. Fourth generation fission reactors can consume the waste that’s been stockpiling around the world and turn it into much safer waste that can be safely buried.  These next generation plants cannot meltdown, they are physical incapable of it.

58:12: Discussing why more fourth-generation nuclear plants are not being built in the U.S.: “It’s almost a “no-brainer” and yet the word ‘nuclear’ is such a red flag for environmentalists and others that the political barriers are immense; the technical barriers are not.”

58:50: “In thirty years are we going to be buying clean energy from China and India or selling it to them? That’s our choice now.”

59:07: Once you put carbon monoxide in the atmosphere, it takes thousands of years for it to go away; unless we develop technology to pull it out of the atmosphere. In next decade or two important decisions will be made.

1:00:06: “If I had a large budget, on the practical side, I would come up with much better ways of monitoring and forecasting hurricanes. One of the great tragic limitations … is we do pretty bad job of estimating their initial intensity. I’d field a fleet of solar powered robotic aircraft in the stratosphere launching pods on parachutes … down into the troposphere to measure the intensity of hurricanes to improve their forecasts.”

1:01:25:   Dawn thanks Dr. Emanuel for joining her on STEM-Talk.

1:01:35:   Ford comments on the interview: “Kerry is incredibly engaging and insightful about the future of weather and hurricane forecasting. He’s truly at the forefront of this increasingly important field.”

1:01:49:  Dawn says that she is eager to follow-up with Dr. Emanuel on his retirement plans to give air tours on hurricanes.

1:01:57: Ford says he also flew into a hurricane when he was in the Navy.

1:02:15: Dawn and Ken sign off.