STRUCTURE OF ATMOSPHERE

STRUCTURE OF ATMOSPHERE
From the earth's surface upward to an altitude of about 80 km, the chemical composition of atmosphere is uniform in terms of the proportions of its component gases. This layer is the homosphere. The homosphere can be divided into layers on the basis of temperatures and zones of tempera­ture change. Above 80 kIn, atmospheric composition tends to be independent of height.
TROPOSPHERE It is the lowermost atmospheric layer extending from about 8 km ,at the poles and 16 kIn at equator. It is characterised by almost uniform decrease of
temperature with a rise in altitude (about 1°C per 165"
metres).

All phenomena of weather and climate which physically affect man take place within this layer. Tropo­sphere contains water vapour which mixes perfectly with air and in its various proportions gives rise to the different phenomena like ,rain, snow, hail or sleet. Dust particles present in this layer hold the water vapour and contribute to the occurrence' of twilight and the red colours of sunrise and sunset and distribute insolation.

STRATOSPHERE The second layer of atmosphere is called the stratosphere. The level at which the troposphere gives way to stratosphere is called tropopause. (At this level, the fall in temperature stops.) Within the stratosphere, the increase in temperature with altitude is slow and constant at lower sections but becomes rapid at higher altitudes The upper limit of this layer is called stratopause. Withir the stratosphere, temperature increases fropt about -600( at tropopause to about O°C at stratopause. Little weathe is generated here as there is very little water vapour anc virtually no dust present. Ozone is produced in tropica and mid-latitudes of stratosphere. The stratosphere pro vides ideal conditions for flying aeroplanes.

MESOSPHERE Mesosphere is the atmospheric laye extending between the stratopause (at an altitude c about 50 kIn) and mesopause-the upper limit of mesc sphere (at about 80-90 km). Within mesosphere, th temperature decreases with altitude from about OOC "
stratopause to about -100°C at mesopause. Vertical ai currents are not strongly inhibited here and formatio of ice crystal clouds called the noctilucent clouds tak~ place occasionally in the upper regions of the layer.

THERMOSPHERE AND EXOSPHERE Thermosphere: the uppermost layer of the atmosphere, extending frO! the mesosphere at an altitude of about 85 km to 400 kJ of the atmosphere. Within it, the temperature increaSE with altitude from about -100°C at the mesosphere f over 150°C. Exosphere is the boundary between tl earth's atmosphere and the interplanetary space. It e: tends from about 400 km above the earth's surface.