Lesson 4 - Precipitation

Precipitation

the water that falls from the atmosphere in either liquid or solid form

Precipitation

results from the condensation of moisture in the atmosphere due to the cooling of a parcel of air

Dynamic/Adiabatic Lifting

the most common cause of cooling of the air

Adiabatic Lifting

means that a given parcel of air is caused to rise with resultant cooling and possible condensation into very small cloud droplets that forms into precipitation if they coalesced and become of sufficient in size to overcome the air resistance

• topography/region/space

• temporal/time

What are the factors affecting the type, properties, and behavior of precipitation?

Meteorological Factors

weather elements that affect precipitation

Meteorological Factors

wind, temperature, humidity, pressure in the volume region enclosing the clouds and ground surface at the given place

Precipitation

denotes all forms of water that reach the earth from the atmosphere

Precipitation

the basic input in hydrology

• The atmosphere must have moisture

• There must be sufficient nuclei present to aid condensation

• Water conditions must be good for condensation of water vapor to take place

• The products of condensation must reach the earth

What must be the conditions for precipitation to form?

• Rain

• Snow

• Hail

• Fog

• Dew

• Mist

• Glaze

What are the forms of precipitation?

Rain

the most common type of precipitation in our atmosphere

Rain

is when liquid droplets fall to the surface of the earth

Rainfall

used to describe precipitation in the form of water drops

• Showers

• Drizzles

What are the two different forms of rain?

Showers

heavy, large drops of rain and usually only last a period of time

Drizzles

usually last longer and are made up of smaller droplets of water

• Light Rain - 2.5 mm/h

• Moderate Rain - 2.5 mm/h to 7.5 mm/hr

• Heavy Rain - > 7.5 mm/hr

What are the types of rain, and what are their intensity?

Snow

the second most common precipitation

Snow

consists of ice crystal which usually combine to form flakes

Snow

forms when the water vapor turns directly into ice without ever passing through a liquid state which happens as water condenses around ice crystals

0.06 to 0.15 g/cm³, 0.1 g/cm³

When fresh snow has an initial density varying from _____ and an average density of _____.

Hail

a showery precipitation in the form of irregular pellets or lumps of ice of size ranging from 5 to 125 mm

Hails

occur in violent thunderstorms in which vertical currents are very strong

Hail

is created when moisture and wind are together

cumulonimbus clouds

Inside the _____ ice crystals forms, and begin to fall towards the surface of earth.

• Spherical

• Conical

• Irregular

What are the shapes of hail particles?

Fog

a cloud that has formed near the surface of the earth

Dew

the small drops of water which can be found on cool surfaces like grass in the morning

Dew

the result of atmospheric vapor condensing on the surface in the colder night air

Dew Point

the temperature in which condensation starts to take place or when dew is created

Mist

a bunch of small droplets of water which are in the air

Mist

occurs with cold air when it is above a warm surface, for example water

Mist

very similar to fog, but difference with visibility

Fog

If you can see 1 kilometer or less, what are you dealing with?

mist, haze

You can see visuals through _____ and it is more _____ looking than a thicker substance.

Glaze

the ice coating, generally clear and smooth, formed on exposed surfaces by freezing of super cooled water deposited by rain or drizzle

Front

the interface between two distinct air masses

front

Under certain favorable conditions when warm air mass and cold air mass meet, the warmer air mass is lifted over the colder one with the formation of a _____.

Cyclone

a large low pressure region with circular wind motion

• Tropical Cyclones

• Extratropical Cyclones

What are the two types of cyclones that are recognized?

• Typhoon

• Cyclone

• Hurricane

What is a tropical cyclone called in Southeast Asia, India, and the USA?

Tropical Cyclone

a wind system with an intensely strong depression

100 - 200 km

What is the diameter of the normal areal extent of a cyclone?

Tropical Cyclones

the isobars are closely spaced and the winds are anticlockwise in the northern hemisphere

Eye

the center of the storm

10 - 50 km

For a tropical cyclone, what is the diameter that its eye may extend to?

Extratropical Cyclones

cyclones formed in locations outside the tropical zone

Extratropical Cyclones

associated with frontal system, they possess a strong counter-clockwise wind circulation in the norther hemisphere

Extratropical Cyclones

the magnitude of precipitation and wind velocities are relatively lower than those of a tropical cyclone

Anticyclones

regions of high pressure, usually of large extent

Anticyclones

cause clockwise wind circulation in northern hemisphere

Anticyclones

winds are moderate speed, cloudy and precipitation conditions exist

• Cyclonic Precipitation

• Warm Front Precipitation

• Cold Front precipitation

• Convective Precipitation

• Orographic Precipitation

What are the types of cyclone precipitation?

Cyclonic Precipitation

lifting of air converging into a low pressure area; also known as a cyclone

Warm Front Precipitation

warm air advancing upward over a colder air mass

Warm Front Precipitation

has a slow rate of ascent

Cold Front Precipitation

warm air forced upward by an advancing cold air mass

Cold Front

What is the leading edge of the cold air mass in cold front precipitation?

Cold Front Precipitation

has a faster rate of ascent

Cold Front Precipitation

rainfall is showery in nature or high precipitation rate

Convective Precipitation

rising of warmer, lighter air in colder, denser surroundings

Convective Precipitation

there is a change in temperature such as unequal heating at the surface or unequal cooling at the top of the air layer

Convective Precipitation

may experience a scattered rain showers and cloud bursts

Orographic Precipitation

mechanical lifting of air mass over mountain barriers

Artificially Induced Precipitation

conducted to modify and control weather condition

Cloud Seeding/Modification

a type of artificially induced precipitation to dissipate cloud or stimulate precipitation

• Dry Ice

• Silver Iodide

Seeding Agents

• Static

• Dynamic

Two General Approaches in Cloud Seeding:

Static

one artificial nucleus per liter of cloud air

Dynamic

massive seeding

• Yield Point Data

• Areal Data

Classification of Measuring Precipitation:

Yield Point Data

commonly uses rain gauge since the area considered in measuring the precipitation is about 20 cm only

Yield Point Data

done in small regions

Point Precipitation Analysis

analysis of data from a single gauge

Areal Data

uses radar where the area covered for measurement is at around 2.5 km²

depth

Precipitation is expressed in terms of the _____ to which rainfall water stand in an area if all the rain were collected on it.

1 cm, 1 sq. km, 10 × 10

_____ of rainfall over a catchment area of _____ represents a volume of water equal to _____ .

Raingauge

How is precipitation collected and measured in?

• Pluviometer

• Ombrometer

• Hyetometer

What are the terms that are also sometimes used to designate a raingauge?

Recording Gauges

produce a continuous plot of rainfall against time to provide valuable data of intensity and duration of rainfall for hydrological analysis of storms

• The ground must be level and in the open and the instrument must present a horizontal catch surface.

• The gauge must be set as near the ground as possible to reduce wind effects but it must be sufficiently high to prevent splashing, flooding, etc.

• The instrument must be surrounded by an open fenced area of at least 5.5 m by 5.5 m. No object should be nearer to the instrument than 30 m or twice the height of the obstruction.

Consideration for Setting Up a Raingauges:

• Non Recording Raingauges

• Recording Raingauges

Categories of Raingauges:

• Simons’ Gauge

What is the type of raingauge under non recording gauges?

Simons’ Gauge

it essentially consists of a circular collecting area of 12.7 cm (5 inches) diameter connected to a funnel

• Tipping-Bucket Type

• Weighing-Bucket Type

• Natural-Syphon Type (Float-Type Gauge)

What are the types of raingauges under recording gauges?

Tipping-Bucket

not applicable for snow

Tipping-Bucket

30.5 cm size raingauge

Tipping-Bucket

the catch from the funnel falls onto one pair of small buckets

Tipping-Bucket

it measures the rainfall with at least count of 1 mm and gives out one electrical pulse for every mm of rainfall

Weighing Type Gauge

records the weight of the snow or rain

Weighing Type Gauge

the catch from the funnel empties into a bucket mounted on a weighing scale

Weighing Type Gauge

the weight of the bucket and its contents are recorded on a clock-word-driven chart

Natural-Siphon Type

also known as float-type gauge

Natural-Siphon Type

the rainfall collected by a funnel-shaped collector is led into a float chamber causing a float to rise, where a pen attached to the float through a lever system records the elevation of the float on a rotating drum driven by a clock-word mechanism

DOST PAG-ASA Automated Rain Gauge (ARG)

developed to gather and record the amount of rainfall over a set of period of time and automatically sends the data to a central based station on a predetermined interval basin

DOST PAG-ASA Automated Rain Gauge (ARG)

rainfall data are sent wirelessly through the cellular network as a text message or Short Messaging System (SMS)

DOST PAG-ASA Automated Rain Gauge (ARG)

is designed to be rugged and standalone, the station can be deployed even in the harshest remote areas and can operate continuously, as it gets power from the sun, backed up by the internal rechargeable battery

10%, simple arithmetic average procedure

If the normal annual precipitations at various stations are within about _____ of the annual precipitation at station X, then a _____ is followed to estimate P_x.

P_x = 1/M [P₁ + P₂ + … + P_m]

Simple Arithmetic Average Procedure