tailieunhanh - Seamanship Techniques 2 Episode 10

Tham khảo tài liệu 'seamanship techniques 2 episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Meteorology 63 Tornado A violent whirlwind about an area of low pressure the tornado is most common in the United States where they have been known to create considerable damage. The diameter of the whirlwind area is small usually 50 200 m but wind speeds may be in excess of 200 knots about the centre. Actual wind speed in the centre is zero but updraft may lift objects into the air. Trade Winds Permanent winds which blow towards the equator trade winds usually measure between 3 and 5 on the Beaufort Scale. They are generally referred to as NE Trades when they blow over the North Atlantic and North Pacific from below latitude 30 N towards the equator and SE Trades when they blow from latitude 30 S towards the equator over areas of the South Atlantic and the South Pacific. Trough This is an extension of low pressure from a low-pressure centre. It is the opposite to a ridge which is the outward extension from a high-pressure centre. Twilight A period of reduced light which occurs after the sun dips below the horizon it is caused by the rays of sunlight being refracted in the atmosphere towards the earth. Veering See Backing . Vertex The turning point in the path of a tropical revolving storm the vertex is the position in which the path of the storm moves to an easterly from a westerly direction in the northern hemisphere. Visibility This is the maximum range at which an object is discernible. The state of visibility may be assessed by using the length of the ship when in dense or thick fog conditions. It may similarly be assessed when in poor visibility by noting the time taken for an approaching vessel to become visible making due allowance for the respective speeds of the two ships. When assessing good visibility it is not good practice to use the range of the visible horizon owing to the possibility of distortion by refraction especially in misty or hazy conditions. Excellent visibility may be ascertained when heavenly bodies are seen to be coming over or dropping