17 Air masses.
An air mass is a large mass of air that has similar characteristics of temperature and humidity within it in meteorology, large body of air having nearly uniform conditions of temperature and humidity at any given level of altitudeEncyclopedic entry. An air mass is a large volume of air in the atmosphere that is mostly uniform in temperature and moisture. the homogeneous surfaces over which air masses form are called source regions. Their air masses are classified according to the source regions,such as maritime tropical air masses,continental arctic air mass,continental tropical air,mass and maritime polar air masstropical air masses are warm and polar air masses are cold. When the air remains over homogeneous area , in terms of temperature and pressure. For a sufficiently longer time, it acquires the characteristics of that area. The homogenous regions can be the vast Ocean surface or vast plains. The air masses differ in terms of temperature and humidity….
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- CYCLONES AND ANTI-CYCLONES.
A cyclone is a system of winds rotating inwards to an area of low pressure,with an anti clockwise or clockwise circulation ..
Cyclones are also called depressioncyclones are areas of low pressure. Cyclones usually exhibit nearly circular isobars. If isobars are oblong or elongate with the lowest pressure near the center we call them troughs. A tropical cyclone is a rapid rotating storm originating over tropical oceans from where it draws the energy to develop. they bring strong winds ,rainfall or snowfall. Cyclones may be classified as:
Tropical cyclone.
Extra tropical /temperate cyclone.
🔸️what are tropical cyclone?
Tropical cyclone is an intense low pressure area or whirl in the atmosphere over tropical or subtropical waters.A tropical cyclone is a rapid rotating storm originating over tropical oceans from where it draws the energy to develop. from the centre of a cyclonic storm pressure increases outwards. The rate at which the pressure increases determines the strength of the cyclone.Over the past 50 years, 1 942 disasters have been attributed to tropical cyclones, which killed 779 324 people and caused US$ 1 407.6 billion in economic losses – an average of 43 deaths and US$ 78 million damages every day. As per the criteria adopted by the Indian meteorological department, the low pressure system classified in the following categories:
⏺ low pressure areas with maximum sustain surface wind of speed between 31 km per hr and 61 km per h are classified as tropical depression.
⏺ when the wind speed is between 119 and 221 km per h , it is called a very severe cyclonic storm.and when the wind speed is between 221 km per h,the cyclone is called a super cyclonic strom.
⏺ wind speed between 62 km per hr and 88 km per hr are called tropical cyclones. Once the wind attain such a speed the tropical cyclone is assigned the name. When the wind speed is between 89 and 118 km per h it is called a severe cyclonic storm.
🔸️ naming of tropical cyclones:
Tropical cyclones and subtropical cyclones are named by various warning centers to provide ease of communication between forecasters and the general public regarding forecasts, watches, and warnings. The names are intended to reduce confusion in the event of concurrent storms in the same basin. Moreover if at the same time two or more cyclones affect the same region, name naming can help in the identification of a particular cyclone.
Naming of tropical cyclone was first adopted in WWII In some region. By mid -1960s, all the regions except North Indian Ocean begin using name of tropical cyclone in 2003 North Indian ocean also begin the practice of naming tropical cyclones. - Www.vinayiasacademy.com
🔸️ condition for the origin of tropical cyclone:
There are sixmain requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to sustain a low pressure center,
⏺ tropical cyclone emerges over the surface of sea. The temperature requirement for the development of low pressure and high rate of evaporation is 27 degree Celsius or more ,development over the sea enables the tropical cyclone to carry large amount of moisture on account of evaporation.
⏺ Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction due to violent winds (squalls), very heavy rainfall (torrential rainfall) and storm surge.
⏺ the ITCZ(when trade wind meet) provide suitable ground for the creation of tropical cyclones. When the ITC Z beyond 5 degree latitude ,there is convergence of wind of different temperature. The warm wind rise creating vacuum for the cold wind rotate.
⏺ vertical wind that form part of tropical cyclone are uniform in nature .the wind that do not vary with height are called Low wind shear.
⏺ the rotate in anticlockwise direction in the Northern hemisphere and in clockwise direction in the southern hemisphere on account of coriolis force.coriolis force increases with latitude and is zero at the equator .beyond 5 degree latitude,z coriolis force is enough to rotate the winds however 10 degree latitude ,the temperature is not high enough to create conditions for low pressure required for tropical cyclones .thus, tropical cyclone emerge between 5 degree and 10 degree latitudes.
🔸️ characteristics of tropical cyclone:
Tropical cyclones are devastating fast circulating storms that has low pressure in the center accompanied by strong winds and a spiral arrangement of a thunderstorm which causes heavy rainfall.
⏺ size and shape:tropical cyclone are elliptical in shape.they have compact size in comparison to temperate cyclones. their size varies from 80 km to 1500 km. the pressure gradient is very high and tropical cyclone as compared to the pressure gradient in temperate cyclones ..
⏺ wind velocity: the wind velocity the tropical cyclone is higher at the margin then at the centre.Wind speed affects weather forecasting, aviation and maritime operations, construction projects, growth and metabolism rate of many plant species, and has countless other implications.
⏺ movement: it is a tropical cyclone which moves from west to east under the influence of trade winds.
⏺ structure: the centre of tropical cyclone is called the eye of the cyclone. the diameter of an eye varies from 10 to 50 km. the wind speed is minimum, and the sky is clear in this region.the region surrounding the eye called eye wall. it is made up of cumulonimbus clouds. A continuous ring cumulonimbus cloud attains great height.cumulonimbus clouds are responsible for heaviest precipitation.
Www.vinayiasacademy.com - 🔸️why does the east coast of Indian experience tropical cyclones, whereas the West Coast does not?
East coast of India experience tropical cyclones whereas the the West Coast does not becauseEast coast of India faces the Bay of Bengal while the west coast of India is situated on the shores of Arabian Sea. on the other on the other hand cyclones and develop in Arabian Sea moves under the influence of trade wind towards Africa.
🔸️why do tropical cyclone emerge in India during April to September?
Cyclones emerging over Bay of Bengal in April-May are usually weaker, and often swerve away from India’s east coast. Tropical cyclone emerge when the sea surface temperature is 27 degree Celsius or more .Such high temperature arises in the summer season over the Bay of Bengal.
The ITCZ passes through the Bay of Bengal during this time .it shifts in accordance with the maximum sun rays on the earth.
🔸️ why tropical cyclones are rare in south hemisphere ?
In Southern hemisphere ,Ocean temperature in summer are lower than those in summer in the Northern hemisphere .this is because the southern hemisphere and has lesser land mass, consequently e generating lower warming influence during summers.Tropical cyclones in the Northern Hemisphere can travel to higher latitudes than in the Southern Hemisphere because of the presence of warm clockwise oceanic currents such as the Kuroshio and the Gulf Stream. As result the high temperature required for the formation of tropical cyclone is never attained. Moreover, the absence of land mass facilitates movements of strong winds, which hamper the formation of tropical cyclone..
🔸️temperate cyclones..
Temperate Cyclones also called mid-latitudinal cyclones or extra tropical cyclones are formed due to interaction of air masses of different temperature. temperate cyclones are formed between 35 degree and 65 degree latitude in both southern and northern hemisphere. These cyclone also called extratropical or wave cyclone.
🔸️ causes of temperate cyclones:Temperate Cyclones also called mid-latitudinal cyclones or extra tropical cyclones are formed due to interaction of air masses of different temperature. The cold air mass is from the polar region and hot air mass from the temperate region. Temperate cyclones occurs when a warm humid air mass from the temperate region meets a dry , cold air mass from the polar region . The cold air mass of high density pushes the warm air mass upwards. Air off of different temperature attain different Heights in the atmosphere. then temperate cyclone are inverted v shape. This void along with coriolis force makes the wind to rotate leading to the formation of temperate cyclone.
🔸️ characteristic of temperate cyclone:
The Extra-Tropical Cyclones are storm systems emerging in the mid and high latitudes, away from the tropics. They are low-pressure systems with associated cold fronts, warm fronts, and occluded fronts. These cyclones are formed along the polar front.
⏺ size and shape: temperate cyclones are usually inverted v shape .and their size stretches from 500 to 600 km and can reach upto 2500 km.
⏺movement: temperate cyclones move under the influence of westerlies from west to east. temperate cyclones are marked by a fall in temperature and are composed of cirrus cloud .this cloud lead to drizzle.
🔸️ difference between tropical cyclone and temperate cyclone.
⏺ tropical cyclone produced and developed mainly over the sea. Whereas temperate cyclone produced over both land and sea
⏺ tropical cyclone develop during summer. temperate cyclone usually developed during winter.
⏺ shape of tropical cyclone is elliptical whereas, temperate cyclone are inverted in v shape .
⏺ pressure gradient is low and temperate cyclones where as, it is high and tropical cyclone.
⏺ rainfall in tropical cyclone is heavy but does not last beyond the few hours .in a temperate cyclone rainfall is slow and continuous for many days.
⏺ tropical cyclone Limited To small area and generally travel from east to west whereas temperate cyclone comparatively cover a larger area and generally move from west to east.
⏺ wind is claim at the centre of tropical cyclone with no rainfall whereas, wind are strong and rainfall takes place at the centre of the temperate cyclone.
⏺ tropical cyclone derives its energy from the latent heat during condensation. The latent heat arises when water vapour releases its heat to convert into water or Ice. the energy of a temperate cyclone depends on the difference in densities of the air masses .the cold wind with high density push the warm wind with low density in the upward direction.
⏺ tropical cyclone can attain high speed and and thus have high destructive capacity .temperate cyclone cannot attain such high speed and thus have low destructive capacity.
🔸️ anti -cyclones.
An anti-cyclone — also known as a high pressure area — is a large atmospheric circulation system with the wind flowing clockwise around it in the Northern Hemisphere, and counter-clockwise in the Southern Hemisphere.
Anticyclones form from air masses cooling more than their surroundings, which causes the air to contract slightly making the air more dense. Since dense air weighs more, the weight of the atmosphere overlying a locatiion increases, causing increased surface air pressure. Anticyclones are opposite of cyclones with high pressure at the centre but gentle pressure gradient .anticyclones ,normally, are associated with fine weather and these last for days before fading out. Winds in anticyclones blows outwards.
Unlike tropical cyclone ,which form at convergence of winds ,temperate cyclones emerge at divergence of winds .
