Met 2204 meteorology
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MET 2204 METEOROLOGY. Presentation 5: Moisture, Cloud Formation, & Precipitation. Recapitulate. Lets recap what we have done last week: What is the Wind? Concept of Convection How the air move? Use of Isobar The force acting on the wind: PGF, GF, Friction

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MET 2204 METEOROLOGY

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Met 2204 meteorology

MET 2204METEOROLOGY

Presentation 5:

Moisture, Cloud Formation, & Precipitation.

Presented by Mohd Amirul for AMC


Recapitulate

Recapitulate

  • Lets recap what we have done last week:

    • What is the Wind?

    • Concept of Convection

    • How the air move?

    • Use of Isobar

    • The force acting on the wind: PGF, GF, Friction

    • Major Wind: Geostrophic and Gradient Wind

    • Jet Stream

    • Local and Minor Surface Wind: mountain and Valley; Katabatic; Land and Sea.

    • Wind Shear

Presented by Mohd Amirul for AMC


Presentation outline

Presentation Outline

  • Introduction

  • Water Vapor

  • Change of State

  • Cloud Formation

  • Cloud Identification.

  • Precipitation

  • Land and Water Effects

  • Conclusion

Part 1

Part 2

Presented by Mohd Amirul for AMC


Learning outcomes

Learning Outcomes

  • At the end of this session, student should be able to:

    • Identify the physical processes related to the transfer of heat and moisture

    • Explain change of state

    • Understand the background of formation of cloud and its classification.

Presented by Mohd Amirul for AMC


Introduction

Introduction

  • Moisture in atmosphere creates a variety of hazards.

  • Water can be solid, liquid, and gaseous states.

  • What is the difference between moisture and humidity?

    • Moisture: caused by water(usually can be seem)

    • Humidity: the amount of water vapor inside atmosphere. (usually can’t be seem)

Presented by Mohd Amirul for AMC


Water vapor

Water Vapor

Presented by Mohd Amirul for AMC


Water vapor1

Water Vapor

  • Invisible

  • Can be measured in TWO ways:

    • Relative Humidity

    • Dew Points

Presented by Mohd Amirul for AMC


I relative humidity

i. Relative Humidity

  • Express in percent

  • Relative humidity: express the degree of saturation.

    • 100% - Saturated.

    • Below 100% - unsaturated.

  • ‘Relative’ means relates the actual water vapor present that which could be present.

    • E.g. 50% humidity means the air could hold twice as much water vapor as it actually present.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • In fact, warm air can hold more water than cool air.

    • Temperature determine the maximum amount of water vapor air can hold

    • Temperature increase, water vapor increase, relative humidity decrease.

  • When air is cooled, can’t hold more water vapor (water becomes liquid/solid)

    • Condensation/sublimation begins to occur - SATURATED (100% Rel. Humidity)

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

Presented by Mohd Amirul for AMC


Ii dew points

ii. Dew Points

  • Dew Points: Temperature to which air must be cooledto become saturated by the water vapor already present in the air.

    (Temperature at which water vapor becomes saturated and condensation begins.)

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Temperature-dew point spread.

    • Aviation weather reports normally include air temperature and dew point temperature.

    • Temperature-dew point spread: difference between temperature and dew point.

    • As SPREAD less, relative humidity increase.

    • Spread will be 100% when temperature and dew point are same.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Has a little bearing about precipitation but important in anticipating (predicting) fog.

    *saturate: cause chemical compound, vapour, solution to unite with the greatest amount of another substance.

Presented by Mohd Amirul for AMC


Change of state

Change of State

Presented by Mohd Amirul for AMC


Change of state1

Change of State

  • Change of State: a change from one state (solid or liquid or gas) to another without a change in chemical composition.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Involving:

    • Evaporation: The process of becomes a vapor from liquid.

    • Condensation: The process of change from gas to liquid

    • Sublimation: The process of change directly from solid to gas or vice versa.

    • Freezing: The process of change from liquid to solid.

    • Melting: The process of change from solid to liquid.

      *Example of Sublimation: Snow/Ice crystals result from sublimation of water vapor directly to solid state.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

Presented by Mohd Amirul for AMC


Latent heat

Cont.

Latent Heat

  • Any change of state involves heat transaction.

  • Latent heat: Heat absorbed or radiated during a change of phase at a constant temperature and pressure

  • Gas have the high energy than solid. It can be prove by its rapid movement of molecules.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Types of latent heat:

    • Latent heat of vaporization

      • Involves during evaporation and condensation process

      • The heat energy restored in the water vapor and release during condensation.

    • Latent heat of fusion

      • Involves when melting and freezing

      • Heat energy restored during melting and released during freezing.

    • Latent heat of sublimation:

      • Involve sublimation

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

Presented by Mohd Amirul for AMC


Condensation nuclei

Condensation Nuclei

  • As air become saturated water vapor begins to condensed (water vapor decrease) on the nearest available surface.

  • What surface in the atmosphere on which water vapor may condense??

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Surface in the atmosphere on which water vapor may condense Condensation Surface.

  • Condensation Surface: the surface where abundance microscopic solid particles suspended in the air.

  • Theses microscopic solid particles we call as CONDENSATION NUCLEI

    • E.g. salt, dust, combustion by product.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • As the water vapor condense or sublimates on condensation nuclei, liquid or ice particles begin to grow.

  • The particle ice or liquid doesn’t depend entirely on temperature

    • E.g.: Liquid Water may be present at temperature well below freezing.

Presented by Mohd Amirul for AMC


Supercooled water

Supercooled Water

  • Supercooled: Water droplet colder than 0˚C (liquid water below freezing point)

  • When these water droplets strike on expose objectthe impact induce FREEZING!!

    • May result aircraft icing.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Some of the supercooled water left in clouds at temperature between 0˚C to -15 ˚C

    • Amount of supercooled water become less.

  • At temperature colder than -15 ˚C sublimation commonly occur.

  • Sublimation will form ice crystals/clouds/fog.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Strong vertical current may carry supercooled water to great height where temperature are much colder than -15 ˚C

Presented by Mohd Amirul for AMC


Dew and frost

Dew and Frost

  • Dew: water that has condensed on a cool surface overnight from water vapor in the air.

  • Formation of Dew:

    • During night (with wind or no wind), Flora (vegetation) cools by radiation (terrestrial radiation) to a temperature at or below the dew point of air.

      *moisture form on the leaves ambiguous to moisture form in warm room.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Frost: The formation of ice on the surface.

  • Formation of Frost:

    • Form in much same way with dew.

    • The difference is dew point of surrounding air must be colder than freezing. In this case, water vapor sublimates directly as ice crystals frost rather than condensing as dew.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • But sometimes dew forms and later freezes

    Frozen Dew

  • However, frozen dew can easily be distinguish from frost.

    • Frozen dew is hard and transparent.

    • Frost is white and opaque.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • What is the difference between frost and snow?

    • Snow-can form/fall all day long

    • Frost-form in the cold of winter morning

Presented by Mohd Amirul for AMC


Clouds

Clouds

Presented by Mohd Amirul for AMC


The clouds

The Clouds

  • Clouds: A visible mass of water or ice particles suspended at a considerable altitude.

    (A visible manifestation of condensation or deposition in the atmosphere)

  • Clouds can indicate following problem:

    • Turbulence

    • Visibility

    • Precipitation

    • Icing

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Turbulence: Unstable flow of a liquid or gas in atmosphere.

  • Fog: ‘cloud’ on the ground.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Cloud Base

    • The height of the lowest part of the cloud above the surface.

    • Similar to condensation surface/level.

    • Can be estimated using ceilometer.

      • Ceilometer: Laser beam pointing vertically and the receiver put at the same location.

Presented by Mohd Amirul for AMC


Cloud formation

Cloud Formation

  • Clouds are formed by air being lifted and cooled adiabatically (without heat transfer) until condensation occur.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Remember back Condensation Nuclei

    • atmosphere contains particles that have an affinity for water ---These serve as centers for condensation.

Cloud Condensation Nuclei (CCN)

Presented by Mohd Amirul for AMC


Met 2204 meteorology

  • The atmosphere has plenty of CCN

DustSalt Spray from Oceans

VolcanoesSulfate Particles from Phytoplankton

Forest FiresTrees

Anthropogenic Origins

Presented by Mohd Amirul for AMC


Met 2204 meteorology

  • CCN are more plentiful near the surface of the earth.

  • CCN are more plentiful over land rather than the ocean.

  • The formation of cloud droplets using CCN is called:

Heterogeneous Nucleation.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • The air must become saturated for condensation/sublimation to occur.

  • Saturation can result from

    • cooling temperature,

    • increasing dew point

    • or both

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • But the cooling is more predominant (frequent) for the air to become saturated.

  • Cooling Process:

    • 3 basics processmay cool the air to saturation:

      • Air moving over a colder surface

      • Stagnant air overlying a cooling surface

      • Expansion cooling in upward moving air

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • Expansion cooling is a major cause of cloud formation.

Presented by Mohd Amirul for AMC


Cloud classification

Cloud Classification

  • Clouds are classify as follows:

    • Heap Clouds

    • Layer Clouds

Presented by Mohd Amirul for AMC


A heap clouds

Cont.

a. Heap Clouds

  • General Characteristics:

    • Unstable

    • Isolated with large vertical and small horizontal extent.

    • Associated with changeable weathers, showers, thunderstorm and turbulence.

Presented by Mohd Amirul for AMC


Met 2204 meteorology

Cont.

  • 3 main types:

    • Cumulus (Cu)

    • Comulonimbus (Cb)

    • Altocumulus Castellanus (Acc)

Presented by Mohd Amirul for AMC


I cumulus cu

Cont.

i. Cumulus (Cu)

  • Characteristic:

    • Give heavy showers and moderate to heavy clear ice and turbulence.

    • Brilliant (striking) white to grey, denseisolated clouds.

    • Clumped or heaped shapes.

    • Field of Cu often have bases all at same (Condensation Surface) level

  • Instability cloud at cold front.

  • *Cold Front: zone where cold air replaces warm air

  • Presented by Mohd Amirul for AMC


    Ii comulonimbus cb

    Cont.

    ii. Comulonimbus (Cb)

    • Characteristics:

      • Thunderstorm Clouds

        • Severe turbulence and heavy clear icing., heavy showers, hail, thunderstorm and lightning.

      • Occur at cold front and major tropical storms

      • Huge towering cloud, dark base and white sides.

    Presented by Mohd Amirul for AMC


    Iii altocumulus acc

    Cont.

    iii. Altocumulus (Acc)

    • Characteristics:

      • Warning of unstable air and thunderstormswithin 24 hours.

      • white or grey, broken cumulus-like clouds;

      • Sometimes arranged in lines.

    Presented by Mohd Amirul for AMC


    B layer clouds

    Cont.

    b. Layer Clouds

    • General Characteristics:

      • Occur in stable condition

      • Sheets of cloud cover a wide area

      • The weather can be dull (darkened with overcast(cover by cloud)) for lengthy periods with continuous light to moderate precipitation.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Main types:

      • High level

        • Cirrus (Ci),

        • Cirro Stratus (Cs),

        • Cirro Cumulus (Cc)

      • Medium Level

        • Alto cumulus (ac)

        • alto stratus (As)

      • Low Level

        • Nimbo Stratus (Ns),

        • Strato Cumulus (Sc),

        • Stratus(St)

    Presented by Mohd Amirul for AMC


    I high level

    Cont.

    i. High Level

    • Cirrus (Ci)

      • Characteristics:

        • White, delicate, fibrous in appearance. Forms in patches(contrast) or narrow bands.

        • Cirrus clouds are formed entirely of ice crystals. These grow and evaporate slowly, leading to soft edges to clouds.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Cirro Stratus (Cs)

      • Characteristics:

        • Thin, transparent sheet or veil(hide);

        • sun clearly visible & casting shadows at surface.

        • A halo(circle of light) may be seen around the sun (or moon).

        • Sheets of cirrostratus may cover entire sky, and be up to several 1000m deep.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Cirro Cumulus

      • Characteristics:

        • Thin white patch or sheet of cloud;

        • Appears dappled or rippled.

    Presented by Mohd Amirul for AMC


    Ii medium level

    Cont.

    ii. Medium Level

    • Alto Cumulus (ac)

      • Characteristics:

        • white or grey patches arranged in sheets.

        • Shape and texture are variable.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Alto Stratus (As)

      • Characteristics:

        • A greyish sheet of cloud, may be fibrous or uniform in appearance.

        • Thin enough in parts to make out the sun, but no halo.

    Presented by Mohd Amirul for AMC


    Iii low level

    Cont.

    iii. Low Level

    • Nimbo Stratus (Ns)

      • Characteristics:

        • Dark grey, featureless, thick layer of cloud.

        • Associated with prolonged precipitation.

        • Commonly forms in frontal systems

          *Front: zone/surface of interaction between two air masses of different temperature.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Strato Cumulus (Sc)

      • Characteristics:

        • white or grey sheet of cloud

        • usually formed in mounds (laid on top of each others) or rolls.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Stratus

      • Characteristics:

        • grey featureless layer of cloud with a uniform base.

        • Often associated with drizzle or snow.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    Four latin terms form the basis for the naming of clouds:

    • Cirrus : fibrous or hair-like

    • Cumulus : a heap or pile

    • Stratus : a horizontal sheet or layer

    • Nimbus : rain-bearing

      The prefix Altois used to indicate medium altitude clouds.

    Presented by Mohd Amirul for AMC


    Precipitation

    Precipitation

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Precipitation occurs when the particles (e.g. : water droplets or ice crystals) grow in size and weight until the atmosphere no longer can suspend them and they fall.

    • Precipitation versus Cloud Thickness:

      • To produce significant precipitation, clouds usually are 4000 ft thick or more

      • Thicker Cloud  Heavier Precipitation

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • There is two ways of particles grows:

      • Growth of water droplet/ice crystal

        • Once water droplet or ice crystals forms, it continue to grow by added condensation or sublimation directly into particle

      • Collision between cloud particle/droplets

        • Rapid growth process

        • Cloud particles collide and merge into larger drop

        • Produce larger precipitation particles

        • Upward currents enhance the growth rate and support larger droplet.

        • Light rain and snow - produce by merging drops with mild upward current.

        • Heavy rain, heavy snow and hail - produce by strong upward current support larger drops and built clouds to great height.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    Growth of raindrops by collision of cloud droplets

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Precipitation types are:

      • Rain

        • Water droplets are supported by upcurrents but if the weight of water becomes too greatrain or drizzle will occur

      • Snow

        • Precipitation in the form of ice crystals

      • Hail

        • Solid balls or piece of ice

    Presented by Mohd Amirul for AMC


    Examples of precipitation

    Examples of Precipitation

    • Rain

      • Precipitation in the form of liquid water dropletsgreater than 0.5 mm. If widely scattered, the drop size may be smaller. The intensity of rain is based on rate of fall.

    • The rate of fall with respect to the intensity is as follows:

      • Slight - <0.5mm/hr

      • Moderate -0.5 – 4.0mm/hr

      • Heavy ->4.0mm/hr

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Drizzle

      • Very small, numerous, and uniformly distributed water drops that may appear to float while following air currents.

      • Unlike fog droplets, drizzle falls to the ground.

      • It usually falls from low stratus clouds and is frequently accompanied by low visibility and fog

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Hail

      • Precipitation in the form of balls or irregular lumps of ice, always produced by cumulonimbus cloud.

      • An individual unit of hail is called a hailstone.

      • By convention, hail has a diameter of 5 mm or more, while smaller particles of similar origin, formerly called small hail, may be classed as either ice pellets or snow pellets

      • The destructive effects of hailstorms- plant and animal life, buildings and property, and aircraft

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Shower

    • Precipitation from a cloud that is characterized by its sudden beginning and ending,changes in intensity, and rapid changes in the appearance of the sky. It occurs in the form of rain (SHRA), snow (SHSN), or ice (SHPE). It is reported as "SH" in an observation and on the METAR.

    • The rate of fall with respect to intensity is as follows;

    • Slight -< 2mm/hr

    • Moderate -2-10mm/hr

    • Heavy -> 10-50mm/hr

    • Violent -> 50mm/hr

    *METAR is a format for reporting weather information.

    A METAR weather report is predominantly used by pilots in fulfillment of a part of a

    pre-flight weather briefing

    Presented by Mohd Amirul for AMC


    Land and water effects

    Land and Water Effects

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Land and water can frequently affect cloud and precipitation.

      How?

    • Large body of water (e.g. oceans/large lakes) can add water vapor to the air.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Variation of season to cloudiness

      • In winter:

        • Cold air frequently moves over warm lakes/oceans  warm water adds heat and water vapor to the air  causing shower to the lake side/oceans side.

      • In other seasons:

        • Air may be warmer than lakes  air become saturatedby evaporation from water while also becoming cooler in the low levels by contact with cool water  form a fog - dense side to the lake/oceans.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    Presented by Mohd Amirul for AMC


    Met 2204 meteorology

    Cont.

    • Variation of diurnal to cloudiness

      • Day:

        • Cool air over the lake/oceans blows toward the land

        • Clouds form cloud over the land

      • Night

        • Reverse pattern.

        • Clouds tend to form over the lake

    Presented by Mohd Amirul for AMC


    Conclusion

    Conclusion

    • Water can be solid, liquid, and gaseous states.

    • Water Vapor can be measured in TWO ways: Relative Humidity and Dew Points.

    • Change of State: a change from one state (solid or liquid or gas) to another without a change in chemical composition.

    • Condensation Surface: the surface where abundance microscopic solid particles suspended in the air.

    Presented by MohdAmirul for AMC


    Met 2204 meteorology

    • Clouds: A visible mass of water or ice particles suspended at a considerable altitude.

    • Clouds are formed by air being lifted and cooled adiabatically (without heat transfer) until condensation occur.

    • Clouds are classify as follows:Heap Clouds and Layer Clouds.

    • Precipitation occurs when the particles (e.g. : water droplets or ice crystals) grow in size and weight until the atmosphere no longer can suspend them and they fall.

    Presented by Mohd Amirul for AMC


    Key points

    Key Points

    • Water vapor

    • Measurement of Water Vapor

    • Change of State

    • Evaporation, Condensation, Sublimation, Freezing, Melting

    • Latent Heat

    • Condensation Surface and Condensation Nuclei

    • Supercooled Water

    • Dew and Frost

    • Clouds

    • Clouds Base

    • Clouds Classification: Heap and Layer Clouds

    • Precipitation

    • Types of Precipitation

    • Land and Water Effect.

    Presented by Mohd Amirul for AMC


    End of presentation 5

    End of Presentation #5

    5 Minutes for Q/A session

    Presented by Mohd Amirul for AMC


    Quote of the day

    Quote of the Day

    • I'm a dreamer. I have to dream and reach for the stars, and if I miss a star then I grab a handful of clouds.

      ~Mike Tyson

    Presented by Mohd Amirul for AMC


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