On Tuesday, August 30, 2005, NASA's Multi-angle Imaging SpectroRadiometer
retrieved cloud-top heights and cloud-tracked wind velocities for Tropical
Storm Katrina, as the center of the storm was situated over the Tennessee
valley. At this time Katrina was weakening and no longer classified as a
hurricane, and would soon become an extratropical depression. Measurements
such as these can help atmospheric scientists compare results of
computer-generated hurricane simulations with observed conditions,
ultimately allowing them to better represent and understand physical
processes occurring in hurricanes.
Because air currents are influenced by the Coriolis force (caused by the
rotation of the Earth), Northern Hemisphere hurricanes are characterized
by an inward counterclockwise (cyclonic) rotation towards the center. It
is less widely known that, at high altitudes, outward-spreading bands of
cloud rotate in a clockwise (anticyclonic) direction. The image on the
left shows the retrieved cloud-tracked winds as red arrows superimposed
across the natural color view from MISR's nadir (vertical-viewing) camera.
Both the counter-clockwise motion for the lower-level storm clouds and the
clockwise motion for the upper clouds are apparent in these images. The
speeds for the clockwise upper level winds have typical values between 40
and 45 m/s (144-162 km/hr). The low level counterclockwise winds have
typical values between 7 and 24 m/s (25-86 km/hr), weakening with distance
from the storm center. The image on the right displays the cloud-top
height retrievals. Areas where cloud heights could not be retrieved are
shown in dark gray. Both the wind velocity vectors and the cloud-top
height field were produced by automated computer recognition of
displacements in spatial features within successive MISR images acquired
at different view angles and at slightly different times.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth
continuously, viewing the entire globe between 82° north and 82° south
latitude every nine days. This image covers an area of about 380
kilometers by 1970 kilometers. These data products were generated from a
portion of the imagery acquired during Terra orbit 30324 and utilize data
from blocks 55-68 within World Reference System-2 path 22.
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.