This document summarizes key aspects of the hydrological cycle and atmospheric processes. It describes the layers of the atmosphere, global wind belts formed by uneven heating and the Earth's rotation, cloud formation, types of precipitation including rain, snow, hail and their measurement. The hydrological cycle involves evaporation and transpiration of water from surfaces, condensation of water vapor to form clouds, and precipitation of water in different forms which completes the cycle.

1. Prepared by
B.Gowtham AP/Civil
SREC,CBE-22
Hydrological cycle

2. Weather- “the state of the atmosphere with respect
to heat or cold, wetness or dryness, calm or storm,
clearness or cloudiness”.
Climate – “the average course or condition of the
weather at a place usually over a period of years as
exhibited by temperature, wind velocity, and
precipitation”.

3. ATMOSPHERE
Troposphere
 Most of the weather occurs.
Stratosphere
 19% of the atmosphere’s gases;
 Ozone layer
Mesosphere
 Most meteorites burn up here.
Thermosphere
 High energy rays from the sun are absorbed;
 Hottest layer.
Exosphere
 Molecules from atmosphere escape into space; satellites orbit here.

5. Wind and Wind belts
 The global wind belts are formed by two main
factors: the unequal heating of the earth by
sunlight and the earth's spin.
 The unequal heating makes the tropical regions
warmer than the polar regions. As a result, there is
higher pressure at the poles and lower at the
equator.
 As the wind flows from high to low pressure, the
atmosphere tries to send the cold air toward the
equator at the surface and send warm air northward
toward the pole at higher levels.

6. The spin of the earth prevents this from being a direct
route, and the flow in the atmosphere breaks into three
zones between the equator and each pole.
 These form the six global wind belts: 3 in the Northern
Hemisphere (NH) and 3 in the Southern (SH). They are
generally known as:
 1) The Tradewinds, which blow from the northeast (NH)
and southeast SH), are found in the subtropic regions from
about 30 degrees latitude to the equator.
 2) The Prevailing Westerlies (SW in NH and NW in SH)
which blow in the middle latitudes. Most of North America
fits into this belt.
 3) The Polar Easterlies which blow from the east in the
polar regions.

8. Cloud is a visible set of drops of water and fragments
of ice suspended in the atmosphere and located at some
altitude above the earth’s surface.

9. Hydrological Cycle

10. Classification of precipitation
Based on the “mechanism” by which air is lifted.
 Frontal lifting: Warmer air is forced to go above
cooler air in equilibrium with a cooler surface.
 Orographic lifting: Air is forced to go over mountains
(and it’s the reason why windward slopes receive
more precipitation).
 Convective Lifting: Warm air rises from a warm
surface and progressively cools down.
 Cyclonic Lifting: A cyclonic storm is a large, low
pressure system that forms when a warm air mass and
a cold air mass collide.

11. Frontal lifting

12. Orographic precipitation

13. Convective Precipitation

14. Cyclonic Precipitation

15. Measurement of precipitation
Rain gauges
Recording Non-recording
Weighing bucket type
Recording Natural Siphon
Tipping bucket type
Non recording- Symon’s Rain gauge

16. Non-Recording Symon’s raingauge

17. Weighing bucket type

18. Natural Siphon type rain Gauge

19. Tipping Bucket type

20. Forms of precipitation
The common forms of precipitation are as follows:
 Rain
 Snow
 Drizzle
 Glaze
 Sleet
 Hail

21. Rain
 Principal form of precipitation in India
 Water drops size larger than 0.5 mm and maximum
size is 6mm
 The drop size greater than 6mm breaks in to
smaller sizes during it’s fall.

22. On the basis of the rainfall intensity , they are
classified as
Type Intensity
Light rain Trace to 2.5 mm/hr
Moderate rain 2.5 to 7.5 mm/hr
Heavy rain Greater than 7.5 mm/hr

23. Snow
 It consists of ice crystals which usually combine to
form flakes.
 Initial density of snow is between 0.06 to
0.15g/cm3
 Average is 0.1 g/cm3
 In India it occurs only in the Himalayan regions.

24. Drizzle
 A fine sprinkle of numerous water droplets of size
less than 0.5 mm and intensity less than 1 mm/h is
known as drizzle.
 In this the drops are so small that they appear to
float in the air.

25.  Glaze
When rain or drizzle comes in contact with cold
ground around 0ᴼc,the water drops freeze to form
an ice coating called glaze or freezing rain.

28.  Sleet
It is frozen raindrops of transparent grains which form
when rain falls through air at subfreezing temperature.

30. Hail
 Showery precipitation in the form of irregular
pellets or lumps of ice of size more than 8mm.
 It occurs in violent thunderstorms.

32.  Thank you