[Music]
NARRATOR: NASA's Hurricane and Severe Storm Sentinel Mission, or HS3,
completed three years of airborne measurements
over tropical storms in the Atlantic
to look at the processes that contribute
to hurricane formation and intensity change.
NASA's Global Hawk unmanned aerial vehicles
and the high flying WB 57
flew six instruments above and around tropical storms
to study the role of strong thunderstorms within them
and the large scale environment surrounding them.
PAUL NEWMAN: We have done three deployments at Wallops Flight Facility.
It's been kind of quiet seasons in 2012, 2013 and 2014,
but we've actually overflown a lot of tropical storms.
And it's because of the range of the Global Hawk.
NARRATOR: HS3 flew more than 600 flight hours during the campaign
with 21 flights, over nine named storms.
SCOTT BRAUN: I think we've shown over the three years
with the cases that we've had, that
the Global Hawk platform provides a terrific way
to get measurements over storms,
to sample the large scale environments,
to get repeated observations within the inner core.
We can map out the evolution of the storm
over a large segment of its life cycle
in ways that just haven't been possible in the past.
NARRATOR: HS3 meteorological and remote sensing instruments
collected, detailed vertical profiles of cloud structure,
temperature, pressure, winds, rainfall and humidity.
One instrument called AVAPS,
the Advanced Vertical Atmospheric Profiling System,
released more than 1400 weather transmitters, called dropsondes,
during the HS3 campaign,
providing unprecedented coverage
both inside and outside tropical storms and hurricanes.
[Radio: " The sonde has left the aircraft"]
BOB ROGERS: One of the overarching scientific goals of HS3
was to study the role of deep convection
in hurricane intensification.
There has been a fair amount of debate about,
you know, is it really deep convection
that causes intensification
or is it more of a result of intensification?
So looking at the radar,
coupled with these dropsonde measurements,
we're really getting a more solid understanding
of what the structures of this convection is.
How it feeds back on to the hurricane as a whole.
And so we're getting more confidence.
I think that this deep convection does play
an important role in actually causing intensification.
NARRATOR: Another question behind tropical storm formation
and intensity change
is the impact of hot, dry, dusty air
that drifts into the Atlantic from Africa's Sahara Desert.
There is much debate about
the role of the Saharan air layer, or cell,
and whether it contributes to or suppresses storm development.
One of the longest lasting hurricanes on record
that was studied during HS3
may provide some valuable insights.
SCOTT BRAUN: Hurricane Nadine in 2012 was our best example
of the interaction of Saharan Air Layer, or SAL,
with a tropical cyclone.
In the Nadine case we saw a major outbreak
of Saharan air in the storm's environment.
One of the things that we saw in the observations
was that the dust was sort of being kept at bay
outside of the outermost rain bands of the storm.
We saw some evidence
that perhaps, even though the dust wasn't affecting
the intensity of the storm all that much,
it might have impacted the size of the storm
where the storm was smaller in the case with dust than without
with some additional simulations
I think we'll be able to come up with a much clear answer.
NARRATOR: The 2014 Atlantic hurricane season
turned out to be the best deployment year for HS3
with four storms,
two of which became major hurricanes.
MICHAEL MONTGOMERY: This 2014 season, we collected some data
that is allowing us an unprecedented look
at the early stage of what we call secondary eye walls.
And they have been long believed to kind of be a pathway
by which the inner eye wall can decay
and the outer eye wall will basically grow
and replace the inner eye wall.
We have some new data of what the wind structure
and the thermodynamic structure is during that early formation
of that outer eye wall.
It's very exciting because we have a theory
that we've developed to characterize, understand
and even predict certain features of this process.
SCOTT BRAUN: One of the things that we've done as part of HS3
that was done only in a very limited sense prior to HS3,
was looking at the structure
of the outflow layer in tropical cyclones.
That area where it spreads out in the upper troposphere
has seldom been observed
except by a few aircraft like the NOAA G4.
So the Global Hawk flying above the storms allows us
to sample storms from the lower stratosphere, above the storm,
all the way through the outflow layer
and down to the surface.
And, with the high resolution information
we are getting from the dropsondes,
coupled with the very detailed hard measurements
that we get from the Clouds Physics LIDAR,
we're able to connect what we're seeing from the dropsondes
to that CPL structure and understand
how cloud structure relates to say, vertical variations
in temperature and humidity or wind shear
in ways it hasn't really been possible in the past.
BOB ROGERS: It was a challenging set of years in terms of just
the storms that were available.
We didn't really have a lot of these classic Atlantic
tropical cyclone, you know, major hurricane developments.
Edward was one of them.
Certainly Hurricane Nadine from a couple of years ago
was surprising for how long that it lasted.
And so there has been a lot of research looking at
the processes have really helped to sustain Nadine
and prevent it from becoming too strong.
So, every storm we fly
there is always something unique about it
and that is what makes this job so exciting.
So we're really fortunate
to have the kinds of data that we can get from HS3.
PAUL NEWMAN: I think the most important thing is,
that we've learned a new way of looking at hurricanes.
We're looking at hurricanes with a platform that can fly
over hurricanes and stay on it for an extended period of time,
over at huge distances from the United States coast,
or stay on it for a long time as it approaches the coastline.
So this is a new assets, a new way of doing science
and I think we're going to see a lot of this in the future.
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