Quick Time Movie for PIA04383
Roiling Clouds of Katrina
This image pair and animation from NASA's Multi-angle Imaging
SpectroRadiometer (MISR) shows the strong convective development of
Hurricane Katrina on Saturday, August 27 as it moved west through the
Gulf of Mexico. Over 7 minutes during which all 9 MISR cameras viewed
Katrina, the animation captures the cloud-top sides, the counterclockwise
rotation of the eyewall, and the bubbling growth of the towering cloud
structures. At this time, Katrina was undergoing rapid development -- it
had just been upgraded to a Category 3 hurricane, and within 24 hours it
would reach Category 5. On Monday morning when the eyewall made landfall
over the United States, it was again a Category 4 storm. Hurricane Katrina
is one of the most powerful and destructive storms on record for the
Atlantic Basin.
The animation progresses from MISR's most forward pointing camera, which
views the scene first, to the most backward pointing camera, which views
the scene last. It was created by registering the views from all 9 cameras
to high clouds within the eyewall. North is at the top. The convective
cloud towers, especially those along the eastern sides of the inner and
outer eyewalls, attain the highest altitudes and indicate that the storm
is strengthening. Those areas that do not exhibit cloud-top convection
are probably influenced by vertical wind shear, and tend to be lower than
the towering cloud structures.
The vertical and horizontal development of the convective clouds and the
formation of an outer ring of growing clouds (referred to as an "eyewall
replacement cycle") also indicates rapid strengthening. During this stage
of hurricane development, an outer band of clouds may gradually move
inward to replace the existing hurricane eyewall, causing the central
pressure to increase and weaken the storm in the short term, but eyewall
replacement may sometimes be a forerunner for rapid strengthening in the
longer term. This was the case with Hurricane Katrina, whose central
pressure increased slightly on Saturday, but then dropped again
significantly on Sunday when Katrina became a Category 5 storm. Observing
the development of a concentric eyewall at this spatial and temporal
resolution is a unique feature of these MISR observations.
The top panel of the still images is a false-color view (near-infrared,
red, and blue displayed as red, green and blue) from MISR's nadir
(vertically downward pointing) camera. The vegetated Alabama coast in the
upper left-hand corner appears here in red hues. The bottom panel is a
3-D stereo anaglyph created with red band data from MISR's 70-degree
forward-viewing and 60-degree forward-viewing cameras, displayed as red
and green/blue, respectively. For the still images, north is at the left.
To observe the height variations in 3-D, you will need to use red/blue
glasses. Information on ordering glasses can be found at
http://photojournal.jpl.nasa.gov/Help/VendorList.html#Glasses.
MISR stereo height retrievals (not shown here) indicate that the highest
clouds reach 18-19 kilometers. The stereo anaglyph shows relative height
variations and enhances the appearance of thin clouds, such as those that
mark the series of gravity waves north-east of the eyewall. Atmospheric
gravity waves are caused by air displacements in an otherwise stable air
layer. In this case, the gravity waves are above the hurricane arms in the
upper troposphere, and were probably generated as the towering storm
updraft tried to push into the stable air between the troposphere and the
stratosphere (known as the tropopause).Some of Katrina's cloud tops were
about 2 kilometers above the tropopause. Such high "overshooting tops" are
also characteristic of strong and rapidly growing storms.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth
continuously, viewing the entire globe between 82¡ north and 82¡ south
latitude every nine days. The still images each cover an area of about
827 kilometers by 380 kilometers, and the animation covers an area of
about 202 kilometers by 214 kilometers. The data products were generated
from a portion of the imagery acquired during Terra orbit 30280 and
utilize data from blocks 69 to 74 within World Reference System-2 path
17.
MISR was built and is managed by NASA's Jet Propulsion Laboratory,
Pasadena, CA, for NASA's Science Mission Directorate, Washington, DC.
The Terra satellite is managed by NASA's Goddard Space Flight Center,
Greenbelt, MD. JPL is managed for NASA by the California Institute of
Technology.