Temperature Rainfall Wind WEATHER AND CLIMATE

Relevance of Weather

Definitions Meteorologists define ‘weather’ as the condition of the atmosphere at a particular place over a short period of time Climate refers to the weather pattern of a place over a long period of time, usually 30 years or more The basic elements of weather and climate: Temperature Rainfall Wind

The Atmosphere Atmosphere held to the earth by gravitational forces. Why is most of the atmosphere concentrated nearer the earth’s surface? Constituents of the atmosphere: 1.Various gases (water vapour, ozone carbon dioxide) – their significance? 2.Dust particles and other pollutants

The Atmosphere The atmosphere is divided into 4 layers according to zones of temperature change:

Troposphere  Home of the biosphere.  Region of principal weather activity.  90% of the total mass of water vapour, clouds, weather, air pollution and life forms are contained within the troposphere.  Upper limit is called the tropopause.  Temperature decreases rapidly with increasing average of 6.5°C/km (normal lapse rate)  Actual lapse rate varies with local weather conditions (environmental lapse rate)

Troposphere

Stratosphere  Extends from 18 to 50 km from Earth’s surface.  Temperatures increase with altitude throughout the stratosphere (due to prevalence of UV radiation from the sun).  Outer boundary is called the stratopause.

Mesosphere  The areas from 50 to 80 km above earth.  Outer boundary is known as the mesopause, which is the coldest portion of the atmosphere, averaging -90°C.  Very low pressure.  Sometimes receives cosmic or meteoric dust which acts as condensation nuclei around which ice crystals form.  Observers may see bands of crystals glow in rare and unusual night clouds called noctilucent clouds.

Thermosphere  Also known as the “heat sphere”.  Extends from about km of the atmosphere to about 480 km (extent).  Upper limit of thermosphere is called the thermopause.  Temperature rises sharply to 1200°C and higher (due to absorption of UV radiation).  However the thermosphere is not “hot” in the way we expect because of low density of molecules.

Earth’s Energy Budget

Earth’s Heat Balance Sun: provider of energy to all living systems on the earth. Energy received is in the form of shortwave radiation. Only 45% of incoming solar radiation is absorbed by the ground. The rest is reflected and scattered back to space by ground surface, clouds and air molecules

Earth’s Heat Balance Solar radiation absorbed by the earth’s surface is changed into heat energy that warms the ground. Re-radiated energy: long wave radiation Out-going terrestrial radiation mainly absorbed by water vapour and carbon dioxide and re- radiated back to earth. This process brings about constant motion of the atmosphere – changes in weather conditions