lapse rates & stability
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DESCRIPTIONLapse Rates & Stability. Learning outcomes: - What are condensation nuclei? - What is the difference between DALR & SALR? - What are the different states of air stability?. Condensation nuclei. Large numbers of these in atmosphere Hygroscopic nuclei (attract water) Volcanic dust - PowerPoint PPT Presentation
Lapse Rates & StabilityLearning outcomes:- What are condensation nuclei?- What is the difference between DALR & SALR?- What are the different states of air stability?
Condensation nuclei Large numbers of these in atmosphereHygroscopic nuclei (attract water)Volcanic dustDust from windblown soilSmoke urb & indSulphuric acid urb & indSalt from sea sprayOver cities 1 mill nuclei per cubic cmOver oceans 10 nuclei per cubic cm* If large quantities of nuclei, condensation occurs at low RH e.g. 75% RH = smog in Los Angeles
If air is pure:
No particles or condensation nucleiAir can be cooled below its dew pointAir can have more than 100% RHLab tests have cooled air to -40 before condensation / sublimation
Pure air is very rare
Environmental Lapse Rate (ELR)ELR varies with local air conditions:HeightTime of yearType of surface that the air is over (land or sea)
Decrease intemperature withheight6.5 oC / 1000m
Adiabatic Lapse Rate (ALR)
Decrease in temp
Increase in volume
Decrease in pressure
Parcel of air risesSinking air
Air warms up
There are 2 ALRs1. Dry Adiabatic Lapse Rateenergy (heat) used up by expansion causes fall in tempno condensation, air not saturated
9.8oC / 1000mAver. 1oC / 100m
Adiabatic Lapse RatesSaturated Adiabatic Lapse Rate (SALR)Happens when enough uplift to reach Dew Point Temp Cooling causes saturationCondensation occursLatent heat is releasesThis partly compensates for loss of temp with heightSALR varies with air temp 4-9oC / 1000mAverage 5.4oC / 1000m, about 0.5oC / 100m
Freezing Adiabatic Lapse RateHappens when temp below zeroSame rate as DALRVery little moisture at low temps, as no evaporation
STABILITYPARCEL OF WARM AIR COOLS ATDALR (9.8oC/1000M)
Ground level temp 20oC1000m up parcel of aircools to 10.2oCSurrounding air Cools at ELR6.5oC / 1000mSurrounding air 14oC at 1000mWill the parcel of air continue to rise above 1000m? Why?What will happen to the parcel?
StabilityParcel will sink because..
No clouds formed because..
Creates stable conditions because.
Weather conditions associated with.
InstabilityCommon on hot daysSurrounding air heated by conductionELR increasesParcel of rising air remains warmer and lighterRises above DPTLatent heat released so it continues to riseCumulonimbus form, thunderstorms likely
Conditional Instability- most common in Britain- instability is conditional upon the air being forced to rise in the first place, until condensation triggers the SALR and further unforced uplift- gives cloudy and showery weatherOver mountain or cold air mass
SummaryLearning outcomes:- What are condensation nuclei?- What is the difference between DALR & SALR?- What are the different states of air stability?