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NASA Chat: Getting a 'GRIP' on Hurricane Forecasting
Hurricane Isabel, seen from the International Space Station Hurricane Isabel, seen from the International Space Station. (NASA)
Hurricane Katrina eyewall swirls. Hurricane Katrina's powerful eyewall. (Lieutenant Mike Silah/courtesy NOAA)
Hurricane Katrina cloud and rainfall data chart Atmospheric data of Hurricane Katrina. (NASA)

More Information
Wikipedia: Global Climatology of Tropical Cyclones Note: This link is per a request in the live chat.
NASA Worldbook: Hurricanes
Link: NASA Hurricane Web Site
Link: GRIP Mission Page
Video: Watch Hurricane Katrina Form
Link: No One Can Hear You Scream
Link: NASA's "Summer Science Camp"
Every summer, tens of thousands of people follow the spinning, counterclockwise drama that plays out across their television screens. Satellite images show a tropical depression forming off the coast. Will it become one of the most powerful storms on Earth? Will it turn into a hurricane?

The Genesis and Rapid Intensification Processes mission, or GRIP, will use 15 cutting edge instruments to get a daring new look at some of the world’s fiercest storms. Scientists will study how storms form, strengthen, and weaken, and try to better understand how tropical storms develop into major hurricanes.

On Thursday, July 29, atmospheric scientist Tim Miller from NASA's Marshall Space Flight Center answered your questions about hurricanes and the upcoming NASA study.

More About Chat Expert Tim Miller

As a research scientist and Team Lead in the Earth Science Office at NASA/Marshall Space Flight Center, Dr. Tim Miller’s scientific expertise lies mainly in atmospheric modeling and dynamics. Miller was born and grew up on a farm in Blanchester, Ohio, and he received his PhD from the University of Arizona.

His experience includes being a Mission Scientist for ATLAS-2 and ATLAS-3, which were Space Shuttle (Spacelab) missions to study stratospheric chemistry in collaboration with UARS. He was appointed Principle Investigator of the Hurricane Imaging Radiometer (HIRAD) project in 2008. He has published work in numerical study of the stability, wavenumber selection, and vacillation of 3D baroclinic systems and in symmetric instability.

When not studying science, he plays the Mandolin.

Chat Transcript

(Moderator Brooke): Welcome to today’s Web chat with NASA atmospheric scientist Tim Miller. Our topic today is hurricanes, and how missions such as Genesis and Rapid Intensification Processes, or GRIP, can help us better understand the workings of these powerful storms. Please remember to stay on topic! This is a moderated chat. It may take a few moments for the queue to catch up to your question, so please don’t leave if you don’t see your question right away.

Tim: Hi everyone! I'm really excited about our upcoming hurricane research mission GRIP (Genesis and Rapid Intensification Processes). I'm here to try to answer any questions you might have about it, and especially about my instrument HIRAD (Hurricane Imaging Radiometer). My knowledge range beyond HIRAD is fairly limited, so while I can talk about the GRIP and HIRAD objectives, I'll probably have to pass on specific questions about the other instruments. Just giving you fair warning. :)

justmk10: Hello, I was wondering, what is a "Cape Verde" hurricane?

Tim: A Cape Verde hurricane is one generated in the Eastern Atlantic Ocean near the Cape Verde islands. Usually the formation (genesis) occurs in that region and the storm develops to hurricane strength as it moves westward.

Tomsneweather: Are you the expert tim?

Tim: Rather than answer that directly...I'm the lead scientist for HIRAD: Hurricane Imaging Radiometer, that will measure winds in the storms from the WB-57. Involved with hurricane research for about three years, so I'm not as expert as some of the others!

Tomsneweather: Atrong tropical waves moving across the atlantic now..NHC put out a 20% and a 10%.

Tim: GRIP forecasters are keeping an eye on these.

Tim(P) You'll hear a lot about GRIP on this chat. You can learn more about it at:

Katherine: Greetings from the UK!

Tim: Hello UK! Do you have a question?

Dell_Conagher: What was your first impression of the "anechoic chamber"?

Tim: Pretty weird. Mostly black and dark blue foam walls, black floors, just a few lights. Very starkly lit with a few lights while we're in there, then we turn the lights off when we're running the tests.

Wigi: Tim, what exactly does your instrument do, and how does it fit into the project as a whole?

Tim: HIRAD measures ocean surface wind speed by sensing microwave emissions from the ocean surface and from the rain column. It also measures rain rate as a byproduct. Also, measurements similar to HIRAD are being done operationally, except that they are only one point beneath the aircraft (creating a line of measurements) whereas HIRAD measures a ful swath of winds about 60 km wide.

MeredithM: What do you test in an anechoic chamber? Why do the lights have to be off?

Tim: We test our antenna patterns and the system's ability to discriminate the different wavelengths and polarizations. This data provides calibration for when we fly the instrument and verifies performance. The lights are off to avoid any extraneous microwave emissions.

bhagenau: Which aircraft will carry your instrument for the hurrican flights? Beth

Tim: The WB-57.

lionoalfa: hello i am steve i have one question how the radiometer take the syclone and analize them?

Tim: Hi Steve. Microwave emissions from the ocean surface are very dependent on the presence of sea foam. The stronger the winds, the more sea foam and the stronger the microwave emissions.

Hunter_Cutting: Hi Tim, thanks for doing this chat. Can you tell us: given that model predict that Atlantic Hurricanes will become stronger in the coming decades due to climate change (Cat 4/5 hurricanes to double), how will your research tease out the interplay of factors such as SST and wind shear that affect formation such that we can make long-term impacts of climate change better understood?

Tim: The objectives of GRIP don't really include investigating effects of climate change, per se. We're trying to better understand the physics of hurricanes and in particular how to better predict them. But from this, perhaps someone will be able to apply what we learn to address your question.

esalmon: Will HIRAD fly on the Global Hawk or the "manned" aircraft?

Tim: WB-57 is a manned aircraft. Only two people are on it: the pilot and the "back-seater." They have to wear pressurized suits because they fly at 60,000 feet.

norapeq: Hi Tim, I am Nora I want to ask what does it mean "the lifecycle "? I mean, how do you know the start and the end?

Tim: Nora, if you mean an individual storm, a tropical depression becomes a tropical storm when winds are at 40 mph. Frequently the storm will dissipate after landfall, although sometimes one can follow a low pressure system for quite some time. For example, Katrina was evidenced across land for quite some time until after it re-entered the Atlantic Ocean.

Tomsneweather: Tim i live in New England, what are your thoughts on a hurricane strike there?

Tim: Hurricanes can strike New England, though certainly not as often as further south. They're usually not still as strong as when in warmer waters.

Wigi: How does your instrument differentiate between the ocean surface, rain and cloud droplets (or does it?)

Tim: HIRAD senses radiation in four microwave channels -- four, five, six, and 6.6 GHz. The lower frequencies are less affected by rain, so by collecting all four frequencies, we can back out both the wind speed and rain data. Cloud droplets only minimally (hardly at all) affect the emissions at those frequencies.

longsheryl: How big are these hurricanes you see?

Tim: HIRAD can measure winds up to 85 meters per second, or greater than 170 mph.

spacecamper: Does your instrument help in making better hurricane forecasts or is it primarily for analysing the hurricanes?

Tim: Good question! First, we expect improvement in the analyses, then as we gain more experience, we think this data will enable numerical prediction models to make better forecasts, in particular regarding the storm intensity and structure.

FNancy: What's it like flying through a storm?

Tim: I've never done that, and I don't expect to. :) And the WB-57 will fly -- without me! -- over the storm, not through it.

(Moderator Brooke): We're working to get through all of the great questions you've asked us. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Miguel(Q) how does form a Hurricane ?

Tim: I only have time for a short answer, but ... some of the factors needs are warm SSTs (sea surface temps), latitude short distance from the equator (not ON the equator), lack of wind shear (winds strongly changing with height). If these factors are present, and if there's a region of low level convergence of air flow, and a development of strong convection, then there's a chance that a tropical cyclone can be developed. If that becomes strong enough (74 mph) then we call it a hurricane in this part of the world.

mamali_astronomer: hello.can some one tell me how to do chat here?

Tim: You're doing it. :) Do you have a question?

(Moderator Brooke): To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Dell_Conagher: Will HIRAD be taking measurements during the day, night, or both? If during both, will measurements be more difficult during the day, because of the small amount of microwaves from the sun?

Tim: HIRAD can measure either night or day. The main effect of the sun is simply the warming of the ocean surface. Not much effect on the emissions at these frequencies.

GeoGuru: How did they get that picture of the eyewall? Wouldn't that be a dangerous place to fly?

Tim: NOAA and Air Force aircraft routinely fly through hurricanes, including the eye and eye wall. The eye is actually quite calm compared to the eye wall.

rahulr96: What determines the level of the hurricane? Like how strong it is?

Tim: That's a good question -- that's what the GRIP campaign is trying to address. We hope to have the most detailed dataset of a few tropical storms, to specifically address your question. Couple of factors that are well-known are warm SSTs (sea surface temps) and low wind shear.

spacecamper: Why isn't there hurricanes in Europe?

Tim: The sea surface temps (SSTs) aren't warm enough and/or there's not room or the supporting large-scale flow.

rahulr96: Why do no hurricanes strike where I live (New Jersey)? If they ever do strike it is at the level of a week storm.

Tim: By the time they get there, the storms have weakened because the sea surface temps (SSTs) are cooler, plus the presence of the continent reduces the source of heat and moisture.

mamali_astronomer: hi Tim I live in Iran,what do you think about hurricanes here?

Tim: There's a great Web page for that. We'll post it in this page after the chat!

Hunter_Cutting: Can you say more about your research on rainfall rates, given that the other impact of climate change that models predict for hurricanes is increased rainfall? Will your research be able to identify increases in rainfall rates, and, separately, provide attribution?

Tim: Well, stronger storms mean more rainfall, so indeed if the storms get stronger, there will be more rain. But there's still a lot more that we need to learn before we can answer that question.

Katherine: Britain has been known to get the remnants of storms though - David in 79, Charley in 1986, Grace last year...

Tim: True. By then they've made the transition to "extratropical" status.

Miguel: Hello this is Miguel from Chile and my question is . could occur a hurricane in Chile?

Tim: Try this Web site;

GeoGuru: What's the first thing you do ifyou har that a hurricane is coming?

Tim: Listen to the advice of local emergency services. :)

tapesit: What would say is the most surprising discovery about hurricanes in the last 10 years? Also, is the bluegrass mandolin you play or some other type?

Tim: No, I play Celtic and old-time. :) On the hurricane discoveries, I'm still learning myself. What's surprising to me is how much we DON'T know about them.

norapeq: What kind of models do you make? do you make them with statistical data? Is there other kinds of models based in PDE's?

Tim: The prediction models I'm familiar with are indeed based on PDEs, or partial differential equations.They basically apply Newton's second law (a=f/m) to the fluid (air) system.

JAC: Will HIRAD data be able publicly on the web?

Tim: We'll have some quick-look data available fairly soon after the mission, but it won't be fully calibrated and verified for a few months. We'll definitely put some images of HIRAD data on the GRIP Web site at some point:

(Moderator Brooke): We're working to get through all of the great questions you've asked us. Keep them coming!

science: Why not use satellites to study the hurricane? What's so beneficial about being right on top of the storm?

Tim: Great question. Satellites are much further away, so the spatial resolution with which they observe the storm is much coarser than we can do with aircraft.

Christopher: What kind of real time data will be available to the National Hurricane Center and also to the general public as well from the GRIP project? Will the public be able to see the various measurements you take in real time or are these missions mostly for research to be conducted after the flight? I'm wondering what the data will be like in comparison to the real time data the public can get from the NOAA and Air Force hurricane hunters.

Tim: Most of the data is for research purposes and won't be available real-time. I think the lightning data on the LIP (lightning instrument package) on the Global Hawk wil be made available real-time to the GRIP science team. That could include the National Hurricane Center folks, if they wish. LIP is a fairly mature technology, having flown several times in the past.

tapesit: How is it that, though most hurricanes are redirected by a front, some can cross through?

Tim: It depends on how strong the front is.

Kenny: I wish there were a way to harness the energy developed in a hurricane and use it for something productive. Any projects/technology for such things in the future?

Tim: I wish that too! But I don't think it's practical.

Dell_Conagher: Do tropical cyclones not develop on the equator because of the Coriolis effect?

Tim: That's correct, Dell.

norapeq: What about twisters? are they related whit hurricanes?? Thanks

Tim: Occasionally tornados do develop in hurricanes, especially after landfall. It could be that the higher number of observed tornados (waterspouts over water) is because they're easier to observe there than they are over the ocean.

esalmon: How do you "tease apart" the signal from the ocean surface and the rain column? do the ocean surface emissions have different "signatures" that can be detected through the rain column?

Tim: HIRAD senses radiation in four microwave channels -- four, five, six, and 6.6 GHz. The lower frequencies are less affected by rain, so by collecting all four frequencies, we can back out both the wind speed and rain data. Cloud droplets only minimally (hardly at all) affect the emissions at those frequencies.

Elaine: Hi Tim. What factors decide the path of a Hurricane? And will your research help to better forecast the path of a hurricane?

Tim: The path is mostly determined by the larger-scale ("environment") flow. of course, the hurricane interacts with that flow, so it does have some influence on its own path.

DEsteve: Is there any predictors your looking at that could help to tell if a given season will be a Gulf and Florida season vs a East Coast or Out to the Atlantic Season

Tim: You're asking about seasonal forecasting. We're not really addressing that with GRIP, but rather short-term prediction. But, we do hope that what we learn can be applied by people studying seasonal forecasts.

(Moderator Brooke): To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

stephanielynnroesner: Why do hurricanes form most in the E.Atlantic?

Tim: Actually, there are more powerful tropical storms (called typhoons, same thing just a different name) in the East Pacific. The factors determining the predominant locations are related to the latitude, the ocean circulation of that basin -- which determines the sea surface temps -- as well as the larger-scale flow.

curious_george: Do hurrianes always turn counterclockwise? Why (or why not)?

Tim: In the Northern hemisphere they turn counterclockwise due to the direction of the Coriolis force. In the Southern hemisphere, they turn clockwise. The Coriolis force represents conservation of momentum as the Earth rotates beneath the air flow.

Katherine: What I'd like to masochistically do one year is to go on a hurricane chase like Jim Edds or Richard Horodner. Is there such a thing as 'safe' chasing?

Tim: It sure would be expensive for an individual. :)

deejayh: Have you done any work with correlation between lightning activity/intensity as it relates to the strengh of Hurricanes?

Tim: I haven't, but some other folks in my office have. There's definitely a relationship due to the fact that lightning exists in strong and deep convection in which ice particles exist in the upper regions of the storm.

JAC: Will you be looking specifically at how hot-towers influence TC genesis and intensification?

Tim: That's a major objective for GRIP. However, HIRAD's specialty is measuring the strong winds that occur in major hurricanes, so I'm not quite as involved in that part.

mamali_astronomer: A few minutes ago,I asked you one question about hurricanes in Iran and you said there is a good webpage about please send me the link of the webpage.

Tim: This is one, but we'll also post a link to a better one on this page later, after the chat. I have to dig a little to find that one.

stephanielynnroesner: Is a hurricane just a larger storm of a tornado? Because a tornado consistes of wind and rain? Like a hurricane?

Tim: No, but there are some common characteristics. They both are cyclones, meaning circulation around a low pressure center; they both have strong winds; but that's where the resemblance ends. Tornados can be spun off from hurricanes (which are produced over water), or they can be spun off from other strong storms that are produced on the continent.

echoofthunder: This may have been brought up already but, quickstat, when or if will a replacement be sent up?

Tim: I wish I knew the answer to that. It was a very valuable satellite. However, it couldn't measure the strongest winds within major hurricanes, as HIRAD will be able to do.

alberto: Will 90l become a hurricane?

Tim: I'm really not following that, but the GRIP forecasters probably are.

Enock: Are Hurricanes assigned magnitudes?

Tim: We talk about "categories" of hurricanes from 1-5.

jozsef: tim u can direct Kathrine to the Skywarn spotters.

Tim: Sure: Thanks for the suggestion!

Dell_Conagher: Are there other applications that a device of HIRAD's abilities could be used for?

Tim: A microwave radiometer at HIRAD's frequences can also observe sea ice. This could be valuable in studies of global change, if implemented on a satellite.

Katherine: Fascinating chat - goodnight (it's 21:00 UK Time)!

Tim: Good night Katherine -- thanks for joining the chat!

JAC: Will you be measuring ozone to determine tropopause height and trying to correlate it to TC genesis and intensification.

Tim: That might be something done after the mission using satellite data.

stephanielynnroesner: why is it that hurricanes have a eye?

Tim: The eye is a region of descending air that's a result of the ascent in the eye wall becoming so strong that it needs someplace else to go other than outward.

Enock: What do each of the categories mean?

Tim: This is a good link for further research on that:

jstn: What is the singlest biggest mystery surrounding hurricanes? If you hope to learn one thing from the mission, what would it be?

Tim: Two things: how to better predict rapid intensification of existing storms, and how to predict which groups of fledgling thunderstorms will evolve into hurricanes.

hjnueva: I jwhat is the modern way of detecting hurricane

Tim: Satellites!!

CanuckChick: I'm a dummy when it comes to this stuff, like most ppl lol but is there still a so-called 'Hole in the Ozone?' And, does CO2 have anything to do with Hurricanes?

Tim: No, those are good questions. The ozone hole still exists. It appears every southern hemisphere spring over Antarctica, but we believe that our reductions of CFC use have resulted in the hole's stabilizing and possibly shrinking. There's some research indicating that hurricanes are strengthening due to warming resulting from CO2, but nothing is proven yet.

DESteve: Tim Im trying to understand the relationship between PREDICT ( and GRIP could you explain that .. is there one ?

Tim: GRIP is collaborating with PREDICT and may have some common storm targets. PREDICT is studying genesis in the Atlantic Ocean all the way to the East Atlantic, and genesis is also one of the major objectives of GRIP as well.

Tim: Thanks for all of the great questions, everyone! Keep an eye out for GRIP:

(Moderator Brooke): Thanks to all of you for the great questions, and thanks to our guest scientist, Tim Miller. Check back in the next day or two for a posted transcript of today’s chat. Have a great afternoon.

Dell_Conagher: Thank you for the chat! =D

Tim: My pleasure.

Enock: Thank you

Tim: Very welcome!

CanuckChick: Thanks Tim! I respect you ppl!

Tim: And I appreciate those great questions you asked.
Kim Newton, 256-544-0371
Marshall Space Flight Center, Huntsville, Ala.
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