哈勃观测到一个新的土星风暴英文原文
译:
Jack


    HST发现了在土星的赤道处有一个特别的白色箭头状的稀有的风暴。这个风暴是由一个暖气流上升形成的,类似于地球上(雷暴前常见的)圆块积云。这个风暴东西方向的长度等于地球的直径(月7,900英里)。哈勃望远镜向我们提供了这次土星风暴中占主导地位的气流的新的细节。这张新的照片说明了这个风暴的运动和大小与1994年9月发现它的时候并没有太大的区别。

           


    这次风暴是宽视场行星照相机2用宽视场模式于1994年12月1日当土星离地球907,000,000英里时拍摄的。为了展现这颗行星的“真彩色”,哈勃的照相机用了不同颜色的滤镜,花了6分钟的时间才合成了这张照片。照片中,土星右边蓝色的分枝是在照片曝光时,为了补偿行星自转而人工加上去的。

    土星风暴中,占主导地位的气流就像是一个黑色的楔,插入例如图中西边(左边)亮的中心云层,在这张哈勃的高清晰度照片中,我们可以十分清晰地看到这一点。土星中最强的气流(从航海者号太空船于1980~1981年拍摄的照片中分析,气流的速度约为1000英里每小时)和那个“楔”在同一纬度。

    在箭头状物的北方,气流相对减弱,使得风暴中心相对于本地来说是向东移动的。云层向风暴的北方扩张,从高于气流的纬度上掠过。楔状物附近的强气流在风暴的北部刮过,在风暴的东边(有方)中心造成了暗白色、次级的扰动。

    风暴中白色的云层是暖空气上升的过程中,挤压了土星云层的最上部而形成的晶体状的固态氨。这次的风暴,要比那个白色的云层和经常被报道的次级风暴的总和还要来得大。

    哈勃这次仔细光测了于1990年9月出现的风暴,也是近两个世纪中最重要的三个风暴之一。虽然这些风暴两两相距57年(对土星来说,是2年),但是,它们好有一个共同的周期规律——当土星的南半球是夏天时便会有风暴产生。

 

   译自 哈勃网站(http://oposite.stsci.edu

HUBBLE OBSERVES A NEW SATURN STORM
Chinese Version


  This NASA Hubble Space Telescope image of the ringed planet Saturn 
shows a rare storm that appears as a white arrowhead-shaped feature 
near the planet's equator. The storm is generated by an upwelling of 
warmer air, similar to a terrestrial thunderhead. The east-west extent of 
this storm is equal to the diameter of the Earth (about 7,900 miles). 
Hubble provides new details about the effects of Saturn's prevailing 
winds on the storm. The new image shows that the storm's motion 
and size have changed little since its discovery in September, 1994.

  The storm was imaged with Hubble's Wide Field Planetary Camera 2 
(WFPC2) in the wide field mode on December 1, 1994, when Saturn 
was 904 million miles from the Earth. The picture is a composite of 
images taken through different color filters within a 6 minute interval 
to create a "true-color" rendition of the planet. The blue fringe
on the right limb of the planet is an artifact of image processing 
used to compensate for the rotation of the planet between exposures.

  The Hubble images are sharp enough to reveal that Saturn's prevailing 
winds shape a dark "wedge" that eats into the western (left) side of the 
bright central cloud. The planet's strongest eastward winds (clocked at 
1,000 miles per hour from analysis of Voyager spacecraft images taken in 
1980-81) are at the latitude of the wedge.

  To the north of this arrowhead-shaped feature, the winds decrease so 
that the storm center is moving eastward relative to the local flow. The 
clouds expanding north of the storm are swept westward by the winds 
at higher latitudes. The strong winds near the latitude of the dark 
wedge blow over the northern part of the storm, creating a secondary 
disturbance that generates the faint white clouds to the east (right) of 
the storm center.

  The storm's white clouds are ammonia ice crystals that form when 
an upward flow of warmer gases shoves its way through Saturn's 
frigid cloud tops. This current storm is larger than the white clouds 
associated with minor storms that have been reported more frequently 
as bright cloud features. 

  Hubble observed a similar, though larger, storm in September 1990, 
which was one of three major Saturn storms seen over the past two 
centuries. Although these events were separated by about 57 years 
(approximately 2 Saturnian years) there is yet no explanation why they 
apparently follow a cycle -- occurring when it is summer in Saturn's
northern hemisphere.

 

   From Hubble Web(http://oposite.stsci.edu

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