introduction to meteorology raed abu saadeh senior...

Introduction to Meteorology

Raed Abu SaadehSenior Meteorologist

FIA Meteorological Office

Meteorology

Meteorology is the study of

Earth's atmosphere.

Climate is the average of

weather in a region over long

periods (30 years)of time.

Weather is the state of the

atmosphere at any given time

and place

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Layers of the Atmosphere

The Atmosphere is a layer of gases surrounding Earth & held by gravity.

The atmosphere is divided into 4 different layers.

1. Troposphere

o This part of the atmosphere is the most dense. Almost all weather occurs in this layer.

2. Stratosphere

o Which has ozone layer, that absorbs and scatters the solar ultraviolet radiation.

3. Mesosphere

o Meteors (a small rocky or metallic body in outer space) burn up in this layer.

4. Thermosphere

o Aurora occur in this layer

o .satellites also are orbiting in this layer.

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Weather Elements

What do we needs to observe?• Temperature.

• Pressure .

• Surface Wind.

- speed/direction and variation

• Clouds

– Type, amount, altitude

• Precipitation?

– Type, amount, location

• Visibility

- In Meters or Kilometres

- Weather Phenomena reduces Visibility

e.g. Rain, fog, Mist, haze, dust... etc.

• Humidity

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Temperature

• Temperature is the quantity that tellsus how hot or cold something isrelative to some set standard value.

• Surface temperatures are measuredusing mercury thermometers housedin a Stevenson screen.

• It is held 4 ft above the ground so the temperature won’t be adversely affected by the ground temperature

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ATMOSPHERIC PRESSURE

• Atmospheric pressure is the force per

unit area exerted by the molecules of

air over a specific surface(Area).

• The unit of pressure in use is known as

the Pascal (Pa).

• QNH : The value of atmospheric

pressure, converted to the MSL in

accordance with the ICAO standard.

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ICAO International Standard Atmosphere

(ISA)

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Wind speed / direction

• The wind is the horizontal

movement of air.

• The wind direction—the direction

from which the wind is blowing in

degrees .

• The wind speed—the rate at which

the air is moving .

• The wind speed is given in knots or

kilometers per hour and meters per

second.

• 1kt = 1.85km/hr = 0.514 m/s

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Visibility

The greatest horizontal distance atwhich an object can be recognized byan observer with normal eyesight.

Visibility Reducers

Water Droplets (low clouds , mist /fog, rain).

Fog , Vis < 1000 m .

Mist Vis (1000 – 5000 m).

Solid Particles ( Sand , dust , haze, smoke) , Vis (1000 – 5000 m)

Ice (Ice Crystals , Snow m Hail)

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Humidity

• Humidity refers to the amount of water vapor in the

air. It is often expressed as a percentage and is

known as relative humidity.

• Relative Humidity is measured using a psychomotor

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Sky Condition / Clouds

• A cloud is made of water drops

or ice crystals floating in the

sky

• Cloud amount is measured in

Oktas (eights) of the sky Dome

covered by clouds.

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Cloud Amounts

Clouds types / altitude

The Metrological conditions, needed for cloud

formation:

1) The saturation of air, when the air is cooled to its dew-point

temperature.

2) Cloud condensation nuclei as a surface on which the water vapor

can condense.

– The cloud condensation nuclei (CCN) are microscopic dust smoke, and salt

particles, suspended in atmosphere. Their importance occurs from that fact if

they are absent, the condensation process can not be happen even if the relative

humidity is 100%.

– The most effective CCN are hygroscopic (water seeking) nuclei like sea salt.

– The sources of CCN: Dust storms, volcanic eruption, pollen, combustion of

forest, coal burning.

Condensation Level

There are many types of cooling

mechanisms ( Vertical Motion)

1- Turbulence.

2- Orographic uplift.

3- Convection.

4- Slow, widespread

ascent (frontal uplift).

5- Convergence.

Orographic Clouds

Two cases of Orographic

clouds are considered:

1- stable conditions.

2- unstable conditions.

Orographic clouds with stable conditions:

• When weak to moderate air flow meets a ridge of high

ground it will be forced to rise.

– If the air is sufficiently humid the condensation level will appear

below the crest of the ridge and cloud will form and precipitation

occurs. On the LEE side the cloud base is higher than on the

windward side and the wind descent warmer ( Fohn effect).

– If the air is dryer the cloud base will be above the ridge and

lenticular cloud appears .

Orographic clouds with unstable

conditions:

• Lifting in unstable conditions can produce Cu or

Cb clouds and thunderstorms if the air is

enough humid.

• Strong winds with moist air can cause

convective instability and Cb and thunderstorms.

Convection Clouds

• Critical or convection temperature: the surface air

temperature, required for the air to be lifted to the condensation

level and for the cloud to form.

• Actually, it is originated from surface warming ,which is able to

rise the air parcel aloft to be cooled to its dew point to form

clouds, but is still warmer than surrounding to continue its lifting

with SALR.

• Two particulate cases are produced:

– Fair weather Cu, which often forms early in the morning.

– Large Cu,Cb which often occur later in the day.

• The main characteristics of convective cloud that ,when the

temperature rises during the day the cloud base is found at

higher altitude and the cloud depth increases, but when the

temperature falls the cloud dissipates.

Convection Clouds

• When Turbulence occurs withconvection the SC can form (the Cubeing spread out to form the layercloud).

• Instability is required

• Pure convection cloud can not form overthe sea, but where there is cold airmoving over a warm surface the air willbecome unstable and convection cloudcan form.

• So, the convective cloud formed overland by surface heating, but soondissipates at night when insulation stopsand the cloud dropletsevaporate.(Energy is needed)

Convection Clouds

Critical Temperature The formation of Convection

Clouds

Widespread Ascent (Frontal Uplift)

• At a warm front when the warm air comes into contact with cold air

so general stable layer is formed with slow widespread lifting , layer

clouds are formed.

• In the cold front case, when cold air approaches to area heap clouds

form due to strong widespread lifting

Convergence Cloud

• When there is low pressure , the air is lifted causing area with low

density, so the new air is coming from all side ( convergence at the

surface) to compensate the deficiency in mass.

• Thus in depressions and troughs, where there are no actual fronts,

cloud formation occurs.

• Strong convergence at a trough, lifting can cause instability to

develop Cu, or Cb with possible thunderstorms

Cloud classification

• Clouds are three basic cloud forms:

– Cirrus: clouds are high, white and thin, they are separated and extended like

wispy fibers.

– Cumulus: clouds consists of globular individual cloud masses, they have flat

base and appear as rising domes or towers.

– Stratus: sheet or layer clouds that cover all sky.

The clouds with vertical development

• Some clouds extend vertically to pass more than one

height range, which are called "the clouds with

vertical development". Vertically developed clouds

are related to unstable air.

• There are two types of such clouds:

– Towering cumulus TCU

– Cumulonimbus Cb

• Towering Cumulus: condition of formation:

– Upward movement is triggered.

– Acceleration is powerful due to intensive atmosphere

instability.

– Sufficient humidity is enough for great vertical extend, so

the cumulus enlarges.

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The clouds with vertical development

• Cumulonimbus (Cb)

– May be the next stage of towering

cumulus

– Dark, dense, great vertical

extinction like huge towers.

– Cumulonimbus towers bases extend from

few hundred meters above the surface up to

12 km.

– The tops of these clouds frequently spread

out in the shape of anvil.

– Produce heavy precipitation with

thunderstorm and hail.

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Precipitation

• Precipitation—any form of water, either liquid or solid (rain , hail or snow), that falls from clouds and reaches the ground.

Drizzle : Fine uniform drops of water whose diameters are smaller than 0.5 mm.

RAIN : falling drop must have a diameter equal to, or greater than, 0.5 mm (0.02 in.)

Snow (SN) : Solid precipitation of ice crystals falling from a cloud.

Hail Transparent or partly or completely opaque of ice (hailstones) with a diameter generally between 5 mm and 50 mm.

Shower : short-lived and heavy, falling from convective clouds.

• Instrument that can be used to collect and measure rainfall is called a rain gauge .

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The Precipitation

• The clouds contain water droplets,the cloud droplets are very tiny andhas a diameter 0.02 mm or 20micrometer (one micrometer equals0.001 mm) A typical raindrop has adiameter of about 2 mm.

• Thus, for precipitation to form, clouddroplets must grow in volume byroughly one million times.

• Two processes are responsible forthe formation of precipitation:

– The Bergeron process, which isrelated to cold clouds.

– The Collision – Coalescenceprocess, which is related to warmclouds.

Precipitation from cold clouds

• Bergeron Theory : At high levels in the cloud, some of the water droplets will turn to ice and will grow in size by sublimation of water vapor and collision with supercooled water

• Cold Clouds: The clouds, which are formed above the freezing level and consist of water vapor, ice crystals, and super cooled water.

• Super cooled water : this is a pure water which has temperature below the freezing point , but is still in the liquid state – its temperature can reduce to – 40 C , this type of water is unstable one , and immediately will freeze after the first contact with any surface or object .

• The precipitation from cold clouds is based on the Bergeron process, which is formulated as ―The saturation vapor pressure over ice is less than over the super cooled water ―.

Bergeron Theory

The precipitation from warm clouds.

collision – coalescence process

• For the summer precipitation where the clouds are at

temperature above zero.

• The warm clouds: the clouds, which have the tops below the

freezing level, and consist of only water vapor and water

droplets without any ice – crystals.

• The presence of range of range of droplet sizes, the larger

falling faster and uniting with the smaller until reaching to

overweight drop falls out as drizzle or rain.

Precipitation Types

Precipitation Summary