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The Earth’s Atmosphere Contents Part 6

Tầng đối lưu: từ bề mặt trái đất tới độ cao 7-17 km, phụ thuộc theo vĩ độ (ở 2 vùng cực là 7-10km) và các yếu tố thời tiết, nhiệt độ giảm dần theo độ cao đạt đến -50 °C. Không khí trong tầng đối lưu chuyển động theo chiều thẳng đứng và nằm ngang rất mạnh làm cho nước thay đổi cả 3 trạng thái, gây ra hàng loạt quá trình thay đổi vật lý. | Weather Forecasting Methods and Tools 235 from a geostationary satellite are distorted because of the low angle at which the satellite sees this region. Polar orbiters also circle the earth at a much lower altitude about 850 km or 530 mi than geostationary satellites and provide detailed photographic information about objects such as violent storms and cloud systems. Continuously improved detection devices make weather observation by satellites more versatile than ever. Early satellites such as TIROS I launched on April 1 1960 used television cameras to photograph clouds. Contemporary satellites use radiometers which can observe clouds during both day and night by detecting radiation that emanates from the top of the clouds. Additionally the new generation Geostationary Operational Environmental Satellite GOES series has the capacity to obtain cloud images and at the same time provide vertical profiles of atmospheric temperature and moisture by detecting emitted radiation from atmospheric gases such as water vapor. In modern satellites a special type of advanced radiometer called an imager provides satellite pictures with much better resolution than did previous imagers. Moreover another type of special radiometer called a sounder gives a more accurate profile of temperature and moisture at different levels in the atmosphere than did earlier instruments. In the latest GOES series the imager and sounder are able to operate independently of each other. The forecaster can obtain information on cloud thickness and height from satellite photographs. Visible photographs show the sunlight reflected from a cloud s upper surface. Because thick clouds have a higher reflectivity than thin clouds they appear brighter on a visible satellite photograph. However high middle and low clouds have just about the same reflectivity so it is difficult to distinguish among them simply by using visible light photographs. To make this distinction infrared cloud pictures are used. Such .