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Scott Braun Interview About Upcoming Hurricane Campaign For NASA

August 2, 2012
Image Caption: This Global Hawk unmanned aircraft is one of two that are used by NASA for Earth science missions and by Northrop Grumman for follow-on developmental testing. Credit: NASA/Tony Landis

Scott Braun is the Hurricane Severe Storm Sentinel (HS3) mission principal investigator and a research meteorologist at NASA’s Goddard Space Flight Center in Greenbelt, Md. Scott studies hurricanes from the inside out.

HS3 is a five-year mission specifically targeted to investigate hurricanes in the Atlantic Ocean basin. In his role as Principal Investigator, Scott leads a diverse team of hurricane and instrument scientists to design and conduct experiments using NASA’s two Global Hawk unmanned aircraft to understand better the meteorological conditions that favor storm formation and often lead to the development of major hurricanes. The campaign is set to take to the sky this September from Wallops Island, Va. Scott recently answered some questions about the HS3 mission:

Q: What is the biggest difference between past NASA hurricane field campaigns and HS3? Will the two Global Hawks have different instruments onboard?

A: The key differences from previous NASA hurricane field campaigns is that HS3 is a multi-year (2012-2014) rather than single year effort.It will utilize two of the unmanned Global Hawk aircraft flying from the U. S. east coast rather than one Global Hawk flying from the west coast as was the case during the Genesis and Rapid Intensification Processes (GRIP) campaign in 2010. (For information about GRIP, go to: www.nasa.gov/GRIP).

Three of the instruments flying on the HS3 mission had flown in GRIP, but on two separate aircraft. Now they will fly together on one Global Hawk (called the over-storm aircraft) to observe the inner-core region of hurricanes. The second Global Hawk (called the environmental aircraft) will be equipped with instruments that were not part of previous campaigns and will sample the large-scale environment of storms to see if conditions are favorable for storm formation and intensification.

Q: How will the mission work? Every time a hurricane is approaching, will the Global Hawk fly to meet it? How far and how long the planes will fly?

A: We will not be flying every storm, but will select storms that are likely to yield the best science. We are in the field for only five weeks and have science flight hours for only about 10-11 flights. Depending on how we use the flight hours, we could do five flights each for two storms or two flights each for five storms, or something like that.

A lot will depend on the storms that occur and whether we think they are events from which we have a lot to learn. In previous campaigns with manned aircraft based in a specific location, we had to wait for storms to come close to the U.S. Because the Global Hawks can fly for up to about 26-28 hours and have a range of more than 12,000 miles, we can reach anywhere in the Atlantic Ocean basin, so we can either choose to spend a smaller amount of time over a storm in the Central Atlantic or spend a great deal more time over storms in the Western Atlantic, Caribbean, or Gulf of Mexico.

Q: How these unmanned aircraft are controlled? They are equipped with all instruments on every flight?

A: The aircraft are controlled from a flight operations room on the ground. Normal autonomous control of the Global Hawk is conducted via the aircraft´s autopilot system using a pre-programmed mission plan. However, to accommodate changes in flight path requested by mission scientists, the pilot can alter the flight path at any time and conduct precise manual aircraft navigation with the insertion of custom “way points.” At all times, however, the aircraft is under the control of the onboard mission computer that ensures that the aircraft is under controlled flight.

Since we have two [Global Hawk] aircraft with different instrument payloads, the instruments on a given flight will depend on whether we send our environmental or over-storm aircraft out to a storm. Often we may start with the environmental aircraft and then immediately upon landing, send out the over-storm aircraft. Depending on how the storm changes, we might then decide to repeat the sequence or alter the order of flights or stop flights all together.

Q: What is the Saharan Air Layer, and why do you think it has an impact on the intensity change of hurricanes? What is the importance of studying it?

A: The Saharan Air Layer, or SAL for short, is a very warm, dry dusty air mass that comes off of the Saharan desert along with the African Easterly Waves that often spawn hurricanes. There have been some studies in the past that have argued that the SAL actually enhances thunderstorm activity in such a way as to favor the growth of the waves and eventually tropical cyclones. More recently, several studies have reached the opposite conclusion and have argued that the SAL actually suppresses storm development, so we are going out to try to determine what effect, if any, the SAL really has on Atlantic storms.

Q: How will you map the deep convection (rising air that forms thunderstorms) in the inner core? Will the Global Hawk fly through a hurricane?

A: The Global Hawk will not fly through the hurricanes. Because its flight altitude is about 18-19 km (11.1 to 11.8 miles), it will actually fly above the storms with sophisticated instruments that will be able to measure the precipitation and wind structure within the storm.

The most important of these on the over-storm aircraft is the High-altitude Imaging Wind and Rain Airborne Profiler (HIWRAP), which is a Doppler radar capable of mapping out the three-dimensional patterns of winds and rain in the storm.

Also onboard will be a microwave radiometer that measures the surface rain and wind speed that will help to map out the extent of the strong surface winds in the core of the storm and another microwave instrument that will measure temperature and humidity in the near environment of the storm and the warming temperatures in the eye of the storm.

Q: Which of the instruments is the most important or precise? Why?

A: On the over-storm aircraft, the HIWRAP radar is the most important because of its ability to map the three-dimensional structure of the winds and rain in the eyewall and rainbands of the storm. It will provide the most information on how the storm is intensifying and the role that intense thunderstorms play in that process.

On the environmental aircraft, the most important instrument is the dropsonde system. It releases an instrument package from the aircraft that then descends down to the surface while measuring temperature, humidity, and winds. We can drop up to 88 of these over the course of a flight to map out the structure of the environment around the storm. Dropsondes are never released near land or when other aircraft are in the vicinity, so there is no hazard to anyone beneath the aircraft.

Q: Will instruments only be on the Global Hawks, or will there be some on the ground? How will all the data gathered be examined?

The HS3 mission only involves data collected from the aircraft, but of course, researchers will utilize all data available including any land-based observations and especially satellite observations. It is difficult to describe the method by which the data is analyzed since different researchers may use different methodologies. However, the data will be combined usually by placing all of the observations in a reference frame that moves with the storm. In some cases, sophisticated software is used to merge all of the different types of data into a single analysis. In other cases, the data might be combined with a numerical forecast model through a process known as data assimilation. This approach uses the model information and observations to produce the best possible analysis and, in some cases, simulations of storms that can then be used for analysis of the physical processes involved in storm formation and intensification.

Q: After the mission ends, will it be possible to better predict a hurricane’s intensity and track?

It is certainly our goal to improve our understanding of how hurricanes form and what processes control their intensity, knowledge that should prove beneficial to predicting hurricanes. We expect the data will be used to improve the numerical forecast models that are used as guidance to forecast intensity changes, but which currently do not show sufficient skill. The observations may reveal shortcomings in the model physics or in the way the [computer] models describe the initial structure of the storm or its environment. We also hope to demonstrate the utility of the Global Hawk and the instruments as an observing platform that could be used by operational agencies to better monitor storms in the future.

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Source: Rob Gutro, NASA's Goddard Space Flight Center, Greenbelt, Md.



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