3 - The thermodynamics of the atmosphere Flashcards
What is latent heat?
The energy consumed or released during phase transition(e.g. liquid to ice) - it is an efficient way to heat or cool the atmosphere
How does latent heat transport connect to water transport?
Water vapour stores latent heat from EV
Cloud formation releases latent heat to atmosphere
Re-evaporation of clouds or rain transfer heat to latent heat
How does vapour saturation occur?
Consider flat surface of water in contact with atmosphere
Molecules of water constantly exchanged at water surface between air above and water below
Saturation occurs when an equal amount of water molecules evaporate and condense at the surface
At a given temp, water vapour saturation is defined by an exact concentration of water molecules in air
What is Saturation Vapour Pressure(SVP)?
SVP is vapour pressure at which air is saturated - if exceeded, vapour condenses until SVP is reached again.
SVP only depends on temperature e.g. if T = 100C, SVP = 1013 mb
How does water vapour vary in the atmosphere?
0.1% to 4% in troposphere depending on local conditions & generally more water vapour at higher temperatures
How does pressure change with height?
The higher you go, the less air there is to produce pressure - pressure halves for every 5.5 km increase in height
How does temperature change with height?
The atmosphere is heated from below
Radiation and heat conduction alone would lead to cold(dense) air above warm(less dense) air below
Warm air with lower density rises above colder air with higher density
Conduction(vertical mexiting) dominates lower part of the atmosphere(troposphere)
Radiative processes dominate temperature profile above troposphere
What is the first law of thermodynamics?
Change of internal energy = externally added heat + energy used to do work against the surroundings
Change of internal energy for ideal gas = heat capacity x change of temp
Energy for work against surroundings = pressure x change in volume
What is the dry adiabatic lapse rate?
It is the rate at which the temperature of unsaturated air decreases as it rises in the atmosphere - it is ~9.8C/1000m
What is the saturated adiabatic lapse rate?
It is the rate at which saturated air cools as it rises in the atmosphere - ~49C/1000m
What occurs when the true atmospheric lapse rate is greater than the dry atmospheric lapse rate?
Adiabatically lifted parcel cools with the dry atmospheric lapse rate - cools slower than environment, therefore warmer & less dense, therefore continues to rise.
This is an unconditionally unstable situation and an example is thermals near the surface.
What occurs when the saturated atmospheric lapse rate is greater than the true atmospheric lapse rate?
Adiabatically lifted parcel cools with dry rate - cools faster than env, therefore colder & more dense, therefore returns to its original position and latent heat release insufficient to destabilise
This is an unconditionally stable situation and an example is a temperature inversion due to nocturnal near surface longwave cooling.
What occurs when the dry atmospheric lapse rate is greater than true rate which is greater than the saturated rate?
Adiabatically lifted parcel cools with either the dry or saturated rate - it is stable as long as no latent heat release occurs, however, it is unstable as soon as latent heat release occurs.
This is a conditionally unstable situation and some examples include cumulus clouds, thunderstorm clouds and other convective clouds.
What is moist convection and what processes is it important for?
Moist convection occurs when the true atmospheric lapse rate>saturated rate - this is important for cloud formation & precipitation - tropical precipitation(& mid-latitude during summer) dominated by moist convection
Why is there a temperature increase with altitude in the stratosphere?
Ozone heating - very stable air here with the only transfer of air being waves
