金星的複雜氣候 Complex meteorology at Venus
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http://www.esa.int/SPECIALS/Venus_Express/SEM65OV74TE_1.html
Radiation from below the Venusian cloud deck
In its relentless probing of Venus's atmosphere, ESA's Venus Express
keeps revealing new details of the Venusian cloud system. Meteorology
at Venus is a complex matter, scientists say.
New night-side infrared images gathered by the Ultraviolet, Visible and
Near-Infrared Mapping Spectrometer (VIRTIS) in July 2006, clearly show
new details of a complex cloud system.
The first (false colour) view - the composite of three infrared images
acquired by VIRTIS, was taken on 22 July when the spacecraft was flying
around the apocentre of its orbit (point of maximum distance from the
planet surface) at about 65 000 kilometres altitude. Venus was in the
night side.
Using its capability to observe at 1.7-micrometre wavelenght, VIRTIS
could probe at about 15-20 kilometres altitude, below the thick cloud
deck situated at about 60 kilometres from the surface. The thermal
radiation coming from the oven-hot surface of Venus is represented by
the intensity of the colours: the brighter the colour (towards white),
the more radiation comes from the surface, so the less cloudy the region
in the line of sight between the view and the spacecraft is.
The edge of the images, taken at a time interval of about 30 minutes
from each other, do not precisely match. This is due to the fact that
clouds on Venus move very rapidly and constantly vary their shape.
Venus's atmosphere is certainly the most dynamic among the terrestrial
planets that have one, taking only four days to completely rota
te around the planet.
"Clouds at Venus present repetitive patterns and recurrent features, but
they are very variable in position both on short and long time scales,"
said Giuseppe Piccioni who, with Pierre Drossart, is the instrument co-
Principal Investigator. "This makes meteorology a very complex matter
for this planet."
Since the thermal radiation from the surface of Venus is in practice
modulated by the presence of the clouds, taking the negative of the
image it is possible to see directly the clouds structure on the night
side, and so study its morphology and dynamics.
This was done for this other night-side image, acquired by VIRTIS on 29
July around apocentre from a distance of about 65 000 kilometres from
the surface.
http://www.esa.int/SPECIALS/Venus_Express/SEM65OV74TE_1.html#subhead1
Cloud structures at Venus
The 2.3-micrometre wavelength used for this image brought the 'view'
again down below the cloud deck. The large cloud visible in the centre
of the image and extending toward the bottom-right part is about 2000
kilometres long and 500 kilometres wide.
This cloud presents the familiar and peculiar shape of clouds at Venus.
They are usually elongated due to the very high-speed winds – reaching
up the formidable velocity of 360 kilometres per hour and being caused
by the 'super-rotation' of the atmosphere.
The very cloudy region visible at the top-right of the image is
situated beyond 60o South latitude, and represents the transition to the
region where the atmosphere is dominated by the effects of the powerful
South double polar vortex.
For more information
Hakan Svedhem, ESA Venus Express Project Scientist
Email: hakan.svedhem @ esa.int
Giuseppe Piccioni, VIRTIS co-Principal Investigator, IASF-INAF,
Rome, Italy
Email: giuseppe.piccioni @ iasf-roma.inaf.it
Pierre Drossart, VIRTIS co-Principal Investigator, Observatoire
de Paris, France
Email: pierre.drossart @ obspm.fr
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歐洲航太總署（ESA）金星特快車號（Venus Express）太空船持續監測金星大
氣，不僅呈現出金星的雲系的細節，而且發現金星的氣候相當複雜。
金星特快車號於2006年7月22日恰好位在離金星最遠的軌道點上，離金星約
65000公里遠，且當時恰好是在金星的夜晚一面。以紫外光、可見光和近紅外
光譜儀（Ultraviolet, Visible and Near-Infrared Mapping Spectrometer，
VIRTIS）拍攝了許多金星夜間部分的紅外波段影像。由於是利用1.7微米的波
段進行觀測，因此可以偵測到金星濃厚雲頂以下約15～20公里身的雲底狀況。
http://www.tam.gov.tw/news/2006/200610/Orbit_93_night_17_full_H.jpg
金星的雲頂高度平均距離金星地表約60公里高。上圖雲底的顏色，反映了金星
表面的熱輻射強度，顏色愈亮愈白、來自表面的輻射就愈強，這個區域的雲朵
數量就愈少。
上圖中間的暗線是拍攝間隔30分鐘的3張影像合成的結果，可見因金星的表面
風速是所有類地行星中最強的，僅4天便可繞行金星一週，雲系的變化非常快，
因此三張影像邊緣的雲系形狀並無法重疊的很好。科學家表示：雖然金星的雲
系型態與特徵會重複出現，可是在短時間與長時間的尺度上，它們的位置卻變
化得非常快，而且受到時速高達360公里的風速影響，金星上的雲系通常被拉
成長橢圓狀。
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來源：ESA
http://www.esa.int/SPECIALS/Venus_Express/SEM65OV74TE_0.html
TAM
http://www.tam.gov.tw/news/2006/200610/06101502.htm
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