Introduction to atmosphere and weather

Introduction to atmosphere and weather Definition Regions Atmospheric circulation Winds Weather Hydrologic cycle Clouds and rain Monsoons Cyclone

Atmosphere Definition: The layer of gases surrounding the Earth and retained by the Earth's gravity. Protects life by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

Atmosphere Composition: Oxygen 20.9% Nitrogen 78.1% Argon 0.93% Carbon dioxide 0.034% Neon, Helium, Methane, Krypton, Hydrogen Others 1%

What are the layers of the atmosphere? Mesopause Stratopause Tropopause

Atmospheric regions are also called as ionosphere - approximately the mesosphere and thermosphere up to 550 km. exosphere - above the ionosphere, where the atmosphere thins out into space. ozone layer - approximately 10 - 50 km, where stratospheric ozone is found. magnetosphere - here the Earth’s magnetic field interacts with the solar wind from the Sun. Van Allen radiation belts - here particles from the Sun become concentrated.

Atmospheric circulation Interaction of the polar cell, the Ferrel cell and the Hadley cell. Hadley cell – carries warm, moist air from equator. Near the tropics the air returns, creating the Trade Winds. The Ferrel cell gives rise to the Westerlies, but it is not closed. The 3 cells control the global heat transport along with other factors. Tropic of Cancer Equator Tropic of Capricorn

Movement of winds Easterlies or trade winds – winds from the east Trade winds converge here, producing a narrow band of clouds and thunderstorms Westerlies or doldrums – winds from the west

What is weather? the state of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness

Water Water exists as solid, liquid and gas Ice/snow is in solid form Rain is in liquid form Water vapour is in gas form A cloud contains tiny water droplets and/or ice crystals, a snowflake is an aggregate of many ice crystals, and rain is just liquid water.

Amounts of water in the earth Reservoir % of total Oceans 97.25000 Ice caps & glaciers 2.05000 Deep groundwater 0.38000 Shallow groundwater 0.30000 Lakes 0.01000 Soil moisture 0.00500 Atmosphere 0.00100 Rivers 0.00010 Biosphere 0.00004

The Hydrologic Cycle Movement of water between the earth and the atmosphere 5 main components Evaporation Precipitation Transpiration Runoff Infiltration

Hydrologic cycle Precipitation – change of water vapour to rain or snow Evaporation – change of water from liquid to vapour Transpiration – release of water into the atmosphere by plants and animals Infiltration – movement of water from the surface into and through soil (subsurface) Runoff – movement of water on the surface of the land

Clouds The four main types of clouds are Vertically developed, e.g. cumulus – the most common type. They can grow up to more than 12 km in height. Low-level – mostly composed of water droplets since their bases generally lie below 2 km. Mid-level – bases typically appear between 2 and 6 km. They are also composed primarily of water droplets. High-level – form above 6 km. They are primarily composed of ice crystals.

Rainfall When the water droplets in the cloud become too heavy, they fall down as rain. Snowflakes can also melt and fall as raindrops. Hail is a large frozen raindrop produced by intense thunderstorms.

The Indian Monsoon Monsoon comes from the Arabic word ‘mausim’ which means ‘the season of winds’ The monsoon affects the lives of billions of people in Asia Indian monsoon is of two types – the southwest and the northeast Southwest monsoon (June – Sep, wet monsoon) brings rain to west, central and northeast India Northeast monsoon (Sep – March, dry monsoon) brings rain to peninsular and east India

How does monsoon form? 1. Land heats faster than the Indian Ocean 2. Air masses on land heat up and rise 3. Cooler, moister, heavier air from ocean moves into land 4. The cooler and moister air is pushed by winds and produces heavy rain on land 5. The northeast monsoon is dry except in peninsular India where the Bay of Bengal gives moisture for rain

Effects of monsoon Agriculture – 30% of India's gross domestic product and 67% of the labour force Weak monsoon – drought conditions Low production (kharif) and late planting (rabi) Strong monsoon – flooding, disease Better prediction Better planning

Cyclone Winds more than 120 km/hr Circulates anticlockwise about the centre in the Northern Hemisphere Brings heavy rain to the coast, esp. in east India Also results in loss of lives and damage to property Cyclone, hurricane, typhoon – they are the same, only names are different

How do cyclones form? From thunderstorms Ocean must be warmer than 26.5 oC Temperature + moisture is essential, that is why they form over warm oceans and disintegrate fast over land Less changes in wind speed and direction (along altitude) is also necessary

Where do cyclones form? Mainly along the tropics (30 oN – 30 oS) Asia N. America S. America Australia Europe Africa