Katrina颱風眼衛星照片
當大家正在注意泰利動向的同時
有空可以看看這個由NASA Terra衛星上的儀器MISR所拍到的Katrina中心影像
(這是我從一個mailing list收到的
因為還沒正式放上MISR的網頁 所以暫時放在無名大氣科學網誌的相簿裡
等到正式連結出來再改 若要引用請注意版權歸屬)
http://www.wretch.cc/album/show.php?i=atmossci&b=2&f=1125454634&p=0
下面則是照片與MISR儀器的介紹
抱歉沒有太多時間可全部翻成英文
不過整理幾個重點:
所有影像均拍攝於8/27 當時Katrina正從三級迅速增強中 (北方在左手邊)
影像是假色 陸地上的紅色是植被
圖中可以明顯看到眼牆與對流雲系 而且此時正是Katrina發生眼牆置換的時間
可以從向上突出的對流雲頂隱約看出雙眼牆的狀況
有一些對流雲向上達到18-19km的高度
在東北方的雲帶上方可看到可能由這些對流雲造成的重力波
MISR有九個鏡頭排列在俯視角向前70度到向後70度 平行衛星前進方向的平面上
約七分鐘的間隔這九個鏡頭會掃過地面上同一個點 得到不同角度拍攝的影像
這樣的設計對觀察天氣系統的立體結構非常有用
上半的圖是由俯視角90度 也就是直接向下看的鏡頭拍攝的
下半的圖則是把向前70度與向後60度鏡頭拍到的圖用影像處理疊成的全像圖
(就是要用紅藍立體眼鏡看的立體圖)
The 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° forward-viewing and 60°
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.
Image credit: NASA/GSFC/LaRC/JPL, MISR Team.
Text acknowledgment: Clare Averill (Raytheon ITSS/Jet Propulsion Laboratory),
David J. Diner, Mike Garay and Ralph Kahn (Jet Propulsion Laboratory) and
Greg McFarquhar (University of Illinois at Urbana-Champaign).
--
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之令而自均始制有名名亦既有夫亦將知止知止可以不殆 crystal.che.caltech.edu海
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