Met-o prelims

• • Thermometer an instrument used to measure temperature
• • Wind Vaneused to measure the wind direction.
• • Anemometerused to measure wind velocity.
• • Hygrometer used to measure the humidity of the air. Hygrograph is a mechanical instrument makes a "continuous record" of humidity.
• • Barometeran instrument used to measure atmospheric pressure.
• Wind Sock - A light, flexible cylinder or cone mounted on a mast to show the direction and strength of the wind. Wind sock is commonly used at an airport or chemical plant. The cone-shaped bag opened at both ends so that it extends horizontally as the wind blows through it and indicates the wind direction by pointing 
• Rain Gauge - An instrument that measure the amount of rain that falls during a given time interval usually in millimetres or inches
• atmosphere is a mixture of many different gases and suspended in it are minute (tiny) liquid or solid particles.
• Troposphere – is the lowest region extending to a height of about 9 km over the poles and 16 km over the equator from the earth’s surface. This region contains the greater mass of air and almost all the water vapor present in the air.
• Tropopause – is the boundary between the troposphere and the stratosphere. The temperature varies from -54oC to -76oC.
• Stratosphere – is the next region upward and has a thickness of about 35 km from the tropopause
• Stratopause – is the boundary between the stratosphere and the mesosphere.
• Mesosphere – this is the layer next to the stratosphere
• Ionosphere – refers to the mesosphere and thermosphere and this is the electrically conducting region where the “Aurora Borealis”
• Exosphere – is the outer limit of the atmosphere that surrounds the planet earth.
• Temperature - most basic and fundamental weather element because any change of it causes a chain reaction in the other elements. 
• Clouds – refers to condensed water vapor some distance above the earth’s surface;
• Cirrus clouds (Ci) appear as scattered thin cloud of fibrous or feathery delicate filaments, silky and white with no shadows
• Cirrocumulus clouds (Cc) are thin white grain- like ripples in patches, or layers with very low vertical development
• Cirrostratus clouds (Cs) are almost transparent, whitish and like a fine veil sometimes covering the whole sky
• Altocumulus clouds (Ac) often appear as extensive cloudlets in regular patterns and sometimes forms a corona on the sun
• Altostratus clouds (At) are layers of gray and of uniform appearances, sometimes covering the whole sky and also form a corona on the sun.
• Nimbostratus Clouds (Ns) have no definite form or shape , low, dark, and thick enough to block out the sun and have a “wet look”
• Stratus clouds (St) are low layers of gray cloud with somewhat uniform bases and tops, give the sky a heavy leaden appearance
• Stratocumulus clouds (Sc) are grayish or whitish irregular layers with some dark patches and formed like rolls; they re- resembles altocumulus clouds but they are at much lower level.
• Cumulus clouds (Cb) are descibe as fair weather clouds. They are detached from each other, puffy like cotton balls and look like cauliflower's and constantly changing shapes, have a horizontal base and brilliant white in the sunlight.
• Cumulonimbus clouds (Cb) often develop from cumulus clouds when there is strong convective activity so that these clouds appear heavy, dense clouds of considerable height
• Rain- this is liquid drop falling from clouds. Drizzle is rain of very light intensity.
• Sleet- these are hard, small, clear ice pellets usually mixed with rain
• Hail or hailstone- These are bigger than sleet, sometimes as big as baseball, usually opaque white in color and occur during thunderstorm;
• Glaze- This is very cold rain that freezes immediately when it falls on objects
• Visibility - is the most important factor when the ship is underway in order to avoid accidents.
• Fog - is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface.
• Mist - is a phenomenon caused by small droplets of water suspended in air.
• Haze - is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates obscure the clarity of the sky.
• Blizzard - is that violent intensely cold wind laden with snow, which restricts visibility.
• Monsoon is essentially the seasonal reversal in wind direction, causes most of the rainfall received in India and some parts of the world
• A depression is an area of relatively low pressure with closed isobars.
• Stationary front – When neither air mass is moving.
• Cold front – When the cold air mass is advancing towards the warm air. This is represented by a blue line in a weather map