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Information about Precipitation

Published on November 3, 2013

Author: zohairmagsi



precipitation,ppt,forms of precipitation

Group Members Zohaib Hassan B-15077 Muhammad Zohair B-15086 Mubasher Rasheed B-15107 A.Saeed Sajid B-15576

Definition All types of moisture reaching the surface of earth from atmosphere. Precipitation is the basic input to the hydrology  Factors determining precipitation or the amount of atmospheric moisture over a region  Climate  Geography  Ocean surfaces is the chief source of moisture for precipitation .

Forms of precipitation

Rain Rain is the most common type of precipitation in our atmosphere. Rain is when liquid droplets fall to the surface of the Earth. There are two different forms of rain, either in the form of showers drizzles Showers are heavy, large drops of rain and usually only last a period of time. Drizzles however usually last longer and are made up of smaller droplets of water. Rain can either be formed as ice crystals melt or it can be smaller water droplets. Light I = 2.5mm/hr Moderate I = 2.8-7.6mm/hr Heavy I > 7.6 mm/hr

Snow  Snow is the second most common precipitation in the North East.  Snow forms when water vapor turns directly into ice without ever passing through a liquid state. This happens as water condenses around an ice crystal. Density of freshly fallen snow varies between 125500mm of snow required to equal 25mm of liquid water Average density gravity) = 0.1 (specific

Hail  Hail is created when moisture and wind are together. Inside the cumulonimbus clouds ice crystals form, and begin to fall towards the surface of Earth. When this starts to happen wind gusts start to pick up the ice crystals pushing them up high into the clouds. As they start to fall down again they continue to grow in size. A wind gust might catch the hail stone again which will push it back up into the cloud. This whole process gets repeated several times before the hail stone becomes so big that it is too heavy for the wind to carry so it must fall towards Earth. Shapes of hail particles 1.Spherical 2.Conical 3.Irregular Diameter range 5 to 125 mm Specific gravity = 0.8 Average density (specific gravity) = 0.1

Fog  There is really no different between fog and the clouds that are high in the sky. In simple terms fog is; a cloud that has formed near the surface of the Earth.  There are four main types of fog,  radiation fog  advection fog  upslope fog  evaporation fog

Dew  The small drops of water which can be found on cool surfaces like grass in the morning.  This is the result of atmospheric vapor condensing on the surface in the colder night air.  Dew Point is the temperature in which condensation starts to take place or when dew is created.

Mist / Drizzle Mist is a bunch of small droplets of water which are in the air. This occurs with cold air when it is above a warm surface, for example water. Fog and mist are very similar, the only difference is their visibility. If you cannot see 1 kilometer or less you know you're dealing with fog. You can see visuals through mist and it is more haze looking than a thicker substance. Diameter range between 0.1 and 0.5 mm/hr

Glaze  Glaze is the ice coating, generally clear and smooth, formed on exposed surfaces by the freezing of super cooled water deposited by rain or drizzle. Specific gravity may be as high as 0.8-0.9

Sleet Sleet consists of transparent, globular, solid grains of ice formed by the freezing of raindrops or freezing of largely melted ice crystals falling through a layer of sub freezing air near the earth’s surface.

Measurement of Precipitation  1. Amount of precipitation  2. Intensity of precipitation  3. Duration of precipitation  4. Arial extent of precipitation

Measurement Methods Measurement of precipitation (Rain and Snow) can be done by various devices. These measuring devices and techniques are; Rain Gauges Snow Gauges Radars Satellites Scratching of snow packs Water equivalent in snow packs

RAIN GAGES  Rain gages are most commonly used for the measurement of precipitation, both in terms of rain fall and snow.

Types of rain gages  There are two main types of rain gages which are used to measure the precipitation. These are;  1. Non recording rain gages  2. Recording rain gages

Non recording rain gauges  It is a rain gage which does not provide the distribution of amount of precipitation in a day. It simply gives the amount of precipitation after 24 hours (daily precipitation).

Recording rain gauges  These rain gauges are also called integrating rain gauges since they record cumulative rainfall. In addition to the total amount of rainfall at a station, it gives the times of onset and cessation of rains (thereby gives the duration of rainfall events)

Types of recording Rain gauges  There are three main types of recording rain gauges  1. Float type rain gages  2. Tipping bucket type rain gages  3. Weighing type rain gages

1. Tipping bucket gauges  A tipping bucket rain gauge is used for measurement of rainfall. It measures the rainfall with a least count of 1 mm and gives out one electrical pulse for every millimeter of rainfall

2. Weighing type gauges It consists of a storage bin, which is weighed to record the mass. It weighs rain or snow which falls into a bucket, set on a platform with a spring or lever balance. The increasing weight of the bucket and its contents are recorded on a chart. The record shows accumulation of precipitation.

3. Float recording gauges  The rise of float with increasing catch of rainfall is recorded. Some gauges must be emptied manually while others are emptied automatically using self starting siphons. In most gauges oil or mercury is the float and is placed in the receiver, but in some cases the receiver rests on a bath of oil or mercury and the float measures the rise of oil or mercury displaced by the increasing weight of the receiver as the rainfall catch freezes. Float may get damaged by rainfall catch freezer

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