Clouds Over Southern Indian Ocean
This image of clouds over
the southern Indian Ocean was acquired on July 23, 2007 by one of the
backward (northward)-viewing cameras of the Multi-angle Imaging
SpectroRadiometer (MISR) instrument on NASA’s polar-orbiting Terra
spacecraft. The area covered by the image is 247.5 kilometers wide and
660 kilometers long, and is shown in an approximate perspective view at
an angle of 60 degrees off of vertical. The solar zenith angle ranges
from about 83 degrees at the top of the image to 88 degrees at the
bottom, hence the lengthening of shadows cast by the clouds on the
underlying ocean surface and reddening of the hues in the foreground.
Stereoscopic analysis of the data from multiple MISR cameras indicates
that the cloud tops visible here range in altitude from about 0.6 to 2.5
miles (1 to 4 kilometers). A new university study using MISR data
revealed an overall trend of decreasing global cloud height during the
last decade. Earth's clouds got a little lower -- about one percent on average -- during the first decade of this century, finds a new NASA-funded university study based on NASA satellite data. The results have potential implications for future global climate.
Scientists at the University of Auckland in New Zealand analyzed the
first 10 years of global cloud-top height measurements (from March 2000
to February 2010) from the Multi-angle Imaging SpectroRadiometer (MISR)
instrument on NASA's Terra spacecraft. The study, published recently in
the journal Geophysical Research Letters, revealed an overall trend of
decreasing cloud height. Global average cloud height declined by around
one percent over the decade, or by around 100 to 130 feet (30 to 40
meters). Most of the reduction was due to fewer clouds occurring at very
high altitudes.
Lead researcher Roger Davies said that while the record is too short to
be definitive, it provides a hint that something quite important might
be going on. Longer-term monitoring will be required to determine the
significance of the observation for global temperatures.
A consistent reduction in cloud height would allow Earth to cool to
space more efficiently, reducing the surface temperature of the planet
and potentially slowing the effects of global warming. This may
represent a "negative feedback" mechanism – a change caused by global
warming that works to counteract it. "We don't know exactly what causes
the cloud heights to lower," says Davies. "But it must be due to a
change in the circulation patterns that give rise to cloud formation at
high altitude."
NASA's Terra spacecraft is scheduled to continue gathering data through
the remainder of this decade. Scientists will continue to monitor the
MISR data closely to see if this trend continues.
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