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SECTION 3 CLOUDS AND FOG

PROCESS OF FORMING FOG

KINDS OF FOG

PROCESS OF FORMING CLOUD

KINDS OF CLOUD

PRECIPETATION

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-10 0 10 20 30

30

20

10

C

hPaMax. watervapour E= 100%

Process of condensation

Airparcel

T=20 Td=8

U ca. 50%

To become 100%

1) Adding watervpr

2) Cooling

3) combination

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Two (three) ways of increasing the relative

humidity1. Increasing of watervapour in the air

2. Lowering of temperature

3. Combination 1 and 2

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Condensation/freezing nuclei

When cooler and more humid air becomes saturated with

water vapour and is still cooling down, the surplus ofwater vapour has to condense.

Therefore condensation- and freezing nuclei are needed.

Condensation nuclei formed by: - polution

- (forest) fires

- vulcanic eruptions

- plants, trees, (pollen)

- Sea salt. etc

Freezing nuclei are formed by: - small parts of rocks/clay

- ice cristals

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Condensation nuclei formed by: - polution

- (forest) fires

- vulcanic eruptions

- plants, trees, (pollen)

- etc

Together we call them??

AEROSOLS (Ned. Arosolen)

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Fog

Fog (mist) is a decreasing of the visibility, due to waterdroplets (or ice cristals), to values below 1000m.

Mist (nevel) is a decreasing of the visibility, also due to

waterdroplets, to values between 1000 and 10.000m

Haze is a decreasing of the visibility due to dustparts, smoke etc.

Haze, hazy weather = mostly dry warm polluted air (Smog)

Fog is (mostly) formed in air with almost no vertical motion,

(stable) air.

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SMOG; van: Smoke & Fog

Peking: helder na regen Na dagen warm weer: SMOG

Geen Mist!! T= 30 Td=22

Beide fotos van augustus 2005, zelfde positie.

http://upload.wikimedia.org/wikipedia/commons/a/a4/Beijing_smog_comparison_August_2005.png

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Soorten SMOG:

fotochemische (zomer)

industrile

wintersmog

Altijd:

slecht zicht

ongezond

vervuilende stoffen worden opgespaard onder INVERSIE

Stoffen: Ozon, fijn stof*, zwaveldioxide, stikstofdioxide, etc.

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.

This is a Raindrop

Cloud (fog-) dropletThis is a

(Several) millions of droplets form a drop.!

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Three processes to form fog

1. Lowering of temperature

2. Mixing

3. Combination of lowering of temperature and mixing

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1. Lowering of temperature

a. Few or no clouds and weak winds (best 3-8kt*)

T Td RADIATION FOG (stralingsmist)

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1. Lowering of temperature

b. Air that is moved over a colder surface

T Td ADVECTION FOG*

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2. mixing

18C

T=7CT=7C

Steaming Fog (slootmist)E

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-10 0 10 20 30

C

hPa

30

20

10

steaming fog

arctic sea smoke

5 15

..

Mixing

Super saturation

187

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Arctic sea smoke

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3. Combination of lowering of temperature and mixing

Rain is falling trough a not saturated layer

rain will evaporate, actual vapourpressure is rising, Td >

evaporation energy is abstracted from the air, T

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Summery:

Fog: 1. Lowering of temperature: - radiation fog

- advection fog

2. Mixing: - steaming fog

- artic seasmoke

3. Combination of lowering

of temperature and mixing: - rain fog or

frontal fog

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Dissipation of fog

insolation.(instraling) T > Td

advection of warm or dry air

increasing of windspeed low clouds

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Clouds

Clouds exist of small waterdroplets and/or ice crystals and

are formed due to rising air

rising air is cooled due to adiabatic process

- T is lowering 3C/1000 ft. DALR

- Td is lowering 0.6 C/1000 ft.

Cloudbase(ft) = (T-Td).400 (Conv. Cld: CU) (blz 2.11)

.(m)= (T-Td).125

T= 20 C, Td= 10 C cloudbase= 4000 ft.

Dry air: (no clouds, but watervapor around)

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Clouds

rising air is cooled due to adiabatic process

Wet air: (Clouds!)

- T is lowering ca*. 1,8C/1000 ft. SALR

- Td is lowering SAME (T=Td)

No rule for cloudbase

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Rising motions of air

1. Forced uplifting of air:

against mountains

against a frontsheet

in centre of low pressure

due to wavepatterns in the air

2. Free uplifting of air: due to convective motion

by rising of the temperature at

the SFC*

by turbulence/mixing

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in convergentiegebieden

tegen een berghellingtegen een frontvlak

bij frontale golven

bij lijgolven

Geordende stijgende luchtbewegingen

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In wervels die door windzijn opgewekt :TURBULENTIE

in convectieve bewegingenin onstabiele lucht

Ongeordende stijgende luchtbewegingen

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Condensation levels (Ned: Condensatie Niveaus)

Convective condensation level (CCL) (Ned:CCN)

CCL (ft) = 400 * (TTd)

Lifting condensation level (LCL)(Ned: OCN

Optillings Condensatie Niveau)

Mixing Condensation Level (MCL) (Ned: MCNMengings Condensatie Niveau)

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Convective Condensation Level (CCL)

Td T Tc

CCL

Tgold*

CCL afternoon DALR

SALRCU

http://annettekapoen.punt.nl/upload/weer/zon_1.gif

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Lifting condensation level (LCL)(Ned: OCN)

berg

wind

LCL

Air moves up from groundlevel and cools DALR

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Turbulence (=mixing)

Mixing condensation level

(MCN)

inversion Wind

ELR-

TSK

FRICTION-INVERSION

T

Height friction inversion (ft) =

66 x wind speed in kt

Mixing ratio

MCNTurbulentie ST

DALR

SALR

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Teken oefening LCL (OCN)

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Teken oefening CCL (CCN)

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(development of) Precipitation (Neerslag)

Coalescention

Wegener-Bergeron-Findeisen process(WBF)*

Warm clouds: only water droplets with T>0 (below FZL)

Cold clouds : 1)only supercooled waterdroplets

2) supercooled waterdroplets AND ice crystals(Mixed clouds)

3) Only ice cristals

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Coalescention. Mostly warm cloud, no ice!

Drizzle (DZ) is mostly caused by coalescention

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-10 0 10 20 30

30

20

10

C

hPa

Max. watervapour E

e

E over water > E over ice(Ewater >Eice)

W B Fi d i (WBF)

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Best by temperature of12 a -13C (ijskiemniveau)

Ewater = 4 hPa Eice= 2 hPa

Supercooled dropplet Ice cristal

Wegener-Bergeron-Findeisen process (WBF)

Ewater >EiceVapour from water to ice

Vapour

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Ice cristal will grow at the expense of drop

E = 4 hPa E = 2 hPa

Supercooled droplet disappears ice crystal grows

WegenerBergeronFindeisen process *

Vapour

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Ice cristals grow

Waterdroplets become

smaller

More ice cristals collide

together SNOW

Snow falls and melts

blw FZL RAIN

MIND YOU: It often

snows in summer..!!!

Most rain (90 a 95%) was snow at heigher levels..!!!

Mixed Cloud

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SFC

FZL

Neg. T

Pos. T

ed C oud

ICE

ICE and

water !!

Water

Melting ice FZL ??

WBF

So in CB lower FZL !!!

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Kind of clouds

TSK (ELR) stable stratiform clouds

TSK (ELR) unstable cumuliform clouds

Classification of clouds

Level Arctic area mid latitudes tropics

low sfc- 2 km(6000 ft) sfc- 2 km(6000 ft) sfc- 2 km(6000 ft)

medium 2-4 km (6000-12000 ft) 2-6 km (6000- 18000 ft) 2-8 km (6000-24000 ft)

high 4-8 km (12000-24000 ft) 6-13 km (18000-39000 ft) 8-18km (24000-54000 ft)

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Clouds in lower level (SFC6000 ft)

Cumulus (Cu)

Cumulonimbus (Cb)

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Clouds in lower level (SFC6000 ft)

Stratocumulus (Sc)

Stratus (St)

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Clouds in the medium level (6000 ft18000 ft)

Altocumulus (Ac)

Altostratus (As)

Nimbostratus (Ns)

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Clouds in the higher level ( 18.000 fttropopauze)

Cirrocumulus (Cc)

Cirrus (Ci)

Cirrostratus (Cs)

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Summury of cloudfamily and levels

Stratiform

Stable air*

Rain

Cumuliform

Unstable*

Showers (usa Storms ! )

SFC

6000 ft

18000 ft

1000 ftSt

Sc

Ns

As

Cs

Cu

Ac

Cc

Cb

Ci

Tcu

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Precip* from Stratiform

clouds

Few vertical movementsSmall intensity

Mostly DZ or light RA or light SN

Continuous and long lasting*

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CI

CS

AS

NS

SC

ST

The typical Warmfront* shows all Stratiform

clouds (mostly)

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Strong vertical movements

Changing intensitiesRA or +RA, SN or +SN

(Showers Buien. USA: Storms!)

Risk Hail, Gusts etc

Precip from Cumuliform

clouds

Stages of a shower

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Stages of a shower

CU stage freezing Mature Dissipating stage

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Precipitation types

Regen/Rain ra shra Motregen/Drizzle dz

Sneeuw/Snow sn shsn

Soft hail gs Motsneeuw/Snowgrains sg

Hagel/Hail gr

Onderkoelde Ra/DZ fzra of fzdz

Freezing Ra/Dz

Ijsregen/Ice pellets pl

Freezing level FZRA and Ice pellets

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Freezing level, FZRA and Ice pellets

TSK *

T ??FZRA

RA

Ice triangle (IJsdriehoek!!!!)

ICE TRIANGLE AT SFC (surface)

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ICE TRIANGLE AT SFC (surface)

Neerslagbaan

5000 ft

2500 ft

5000 ft

2500 ft

IJsdriehoek

Sneeuw

Smeltende sneeuw

Regen

Onderkoelde regen

FZRA

TSK

IJSDRIEHOEK OP HOOGTE

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IJSDRIEHOEK OP HOOGTE

Neerslagbaan

10.000 ft

5000 ft

10.000 ft

5000 ft

IJsdriehoek

TSK

Sneeuw

Smeltende sneeuw Onderkoelde regen

Regen

Forming Stratus (ST) from fog

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Forming Stratus (ST) from fog

Fog

Forming Stratus (ST) from fog

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Forming Stratus (ST) from fog

Fog

http://annettekapoen.punt.nl/upload/weer/zon_1.gifhttp://annettekapoen.punt.nl/upload/weer/zon_1.gifhttp://annettekapoen.punt.nl/upload/weer/zon_1.gif

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Stratus

In Deutsch :NEBEL

Fog

HOCHNEBEL

STRATUS (ST)

http://annettekapoen.punt.nl/upload/weer/zon_1.gifhttp://annettekapoen.punt.nl/upload/weer/zon_1.gif

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STRATUS (ST)

by mixing and turbulence (MCL): Turbulence ST

by lifting of fog: ST

by through falling precip

1. Thin layer of cloud. Mostly a few hundreds of feet thick

2. Mostly below 1000 ft

3. Thick ST gives DZ

4. ST is important in airport conditions