Atmosphere Flashcards
lectures 1, 2 and 3
weather vs climate
Weather - day to day condition of atmosphere - temperature, rainfall and wind
Climate - average weather conditions of a place, measured over one year or month
climate and weather determinants
Climate is determined by location on east/west coast of large continent
Weather is determined by local weather system, however it is not independent of local climate
climate as a system of interacting spheres
Atmosphere
Hydrosphere
Cryosphere
Geosphere
Biosphere
solar radiation value
342 W/m^2
geothermal 0.6
black body
emission of radiation only dependent on temperature
perfect emitter and absorber
plancks law
intensity of emitted radiation as a function of temperature and wavelength
sun is an example
hotter object emits more radiation at shorter wavelengths
stephan-boltzman law
total energy emitted across all wavelengths -
E = T^4 x sigma
follows inverse square law and so receive
E-total / 4pi x distance^2
milankovitch cycles
eccentricity, obliquity, precession
eccentricity - how strong the eliptical shape is
obliquity - 41,000 years long, variations in angle between rotational axis and orbital plane. stronger = stronger seasons
precession - shortest cycles, determines when seasons occur
black body temp of earth vs actual temp
BB - 255K
actual - 288K
worked out using ((1−α)⋅S/4sigma) to the power of 1/4
alpha = 0.3
white body
refelcts all radiation irrespective of wavelength
albedo of 1
solar radiation reflection
earths surface - brighter surfaces such as deserts or snow have most
cloud droplets and aerosol particles
gas molecules - rayleigh scattering
earth has albedo of around 0.3
solar constant
1368 w per m squared
dependent on total radiation emitted by sun, and sun-earth distance
earths surface receives 1/4 of solar constant per surface area
radiation travelling through the atmosphere
- transmission, no interaction (mostly solar)
- scattering, gas molecule or particle, changes direction (only solar)
- absorption, converted to heat, inc temp of matter or gas, then emit radiation (solar and terrestrial - gh effect)
how much of 341 W/M^2 is reflected
102
can use albedo to work out
absorption
2x amount of radiation is absorbed at surface than the atosphere
means that atmosphere is heated from below
scattering
rayleigh scattering is wavelength dependent
shorter wavelengths (blue), scatter more efficiently, produces blue sky when looking away from the sun
aerosols both scatter and absorb, needed as nucleation sites for cloud droplets to form
clouds
water droplets and ice crystals
most important scatterer in atm
dominate planetary albedo
UV
most absorbed by ozone layer 20-25km
visible light
little absorption in ozone
main absorber is water vapor
infared
terrestiral radiation
gases absorbing infared are greenhouse gases
net absorption
0.9W/m^2
due to theramal inertia of oceans and declining albedo
thermal inertia - resistance of a system to changes in temp due to its ability to store heat
atmosphetre adjusts rapidly to changes (low heat capacity)
ocean has slower response
deep ocean even slower, slow mixing, heat capacity
prolongs effects of global warming
% of radiation emmited at surface that is absorbed by GHG or clouds
90%
then heats atmosphere
emits radiation up and down
10% emitted to space through atmospheric window
solar vs terrestrial radiation
atm is largely transparent for solar
opaque for terrestrial
absorption of T traps heat in atm
to achieve balance, more needs to be emitted at surface
what is responsible for absorption of longwave raduation in the atm
99% of atm is either nitrogen or oxygen
nitrogen does not absorb shortwave or longwave raditation
oxygen absorbs shortest wavelenght of UV (production of ozone)
neither contirbute but do contribute to rayleigh scattering threfore albedo
water vapour, co2, methane, nitrous oxide
radiative forcing
artificial imbalance or difference between outgoing and incoming radiation
warming is positive forcing
methane and forcing
oxidises CO2 therefore water vapour and increase in ozone
aerosols
scattering of solar radiation producess cooling
soot i excetion, absorbs radiation therefore warming
produce more cloud droplets, smaller and brighter therefore cooling
thermostat effect
cloud feedback effect
warmer climate, more ET, more clouds
clouds reflect, cools, reduces intital warming
overall, clouds have postive feedback
stephan boltzman law feedback
a negative feedback since any warming will lead
to a very strong increase in the emitted radiation. This will quickly limit any further
temperature increases. Thus, the fourth power in the Stefan-Boltzmann law restricts
the temperature change that a forcing will produce.
What happens during evaporation and condensation?
Evaporation: More water molecules transition from liquid to vapour.
Condensation: More water molecules transition from vapour to liquid.
What is saturation in the context of water and air?
Saturation occurs when there is a zero net flux of water molecules between liquid and vapour, meaning as many molecules evaporate as condense. The atmosphere is then in saturation with respect to liquid water.
What determines the saturation vapour concentration or saturation vapour pressure?
The saturation vapour concentration or pressure depends only on temperature.
How does the saturation vapour pressure over ice compare to that over liquid water?
The saturation vapour pressure over ice is lower than that over liquid water for temperatures below freezing.
What effect does the curvature of water droplets have on saturation vapour pressure?
The curvature of very small droplets increases saturation vapour pressure. However, for most cloud and all rain droplets, the surface behaves like a flat surface, so evaporation and condensation occur similarly to over a lake.
What is the saturation vapour pressure?
The saturation vapour pressure is the partial pressure at which air becomes saturated with water vapour. It represents the contribution of water vapour to the total atmospheric pressure.
How does saturation vapour pressure change with temperature?
The saturation vapour pressure increases approximately exponentially with temperature. It rises slowly at low temperatures and much faster at higher temperatures.
How does a 10ºC temperature drop affect saturation vapour pressure at warm vs. cold temperatures?
From 30ºC to 20ºC: Saturation vapour pressure drops significantly, leading to much more condensation and latent heat release.
From 0ºC to -10ºC: The change in saturation vapour pressure is much smaller.
This difference explains why cloud formation is more vigorous in the tropics than in polar regions.
What happens when saturated air cools, and why is this important?
When saturated air cools, it becomes supersaturated, causing condensation and cloud formation to restore saturation. In warmer regions, more vigorous condensation occurs, releasing more latent heat, which affects vertical temperature profiles in low and high latitudes.
What does the hydrostatic assumption state about pressure at a particular altitude?
The hydrostatic assumption states that pressure at a particular altitude is determined only by the weight of the fluid above that altitude.
In which systems is the hydrostatic assumption a good approximation, and where can deviations occur?
The hydrostatic assumption is a good approximation in the atmosphere and the ocean. Deviations can occur on small spatial scales, especially in the presence of topography.
equation used to calculate how pressure changes with altitude?
dP=-pgdz
How does pressure change in the ocean with depth, and what is the rate of change?
In the ocean, pressure changes linearly with depth. The pressure increases by approximately 1 bar for every 10 meters of depth.
What factors cause slight variations in ocean water density?
Ocean water density varies slightly due to temperature and salt content.
How does air density depend on pressure and temperature?
Air density is proportional to pressure and inversely proportional to temperature:
Twice the pressure means twice the density.
Twice the temperature means half the density.
How does atmospheric pressure change with altitude at constant temperature?
Atmospheric pressure changes exponentially with altitude.
Where is most of the solar radiation absorbed, and how does this affect atmospheric heating?
Most solar radiation is absorbed at the Earth’s surface, causing the atmosphere to be primarily heated from below.
Why are radiation and heat conduction insufficient to remove heat from the Earth’s surface?
Radiation and heat conduction alone cannot transfer heat effectively upward, so vertical motion is necessary to carry heat through the atmosphere.
What process carries heat upward in the lower atmosphere, and why does it occur?
Convection carries heat upward because warmer air, which has a lower density than colder air, rises.
What dominates heat transfer at higher altitudes, and how does this differ from the lower atmosphere?
At higher altitudes, radiative processes play a larger role in heat transfer, unlike the lower atmosphere where convection dominates.
What does the first law of thermodynamics state about the internal energy of a gas?
The first law of thermodynamics states that the internal energy of a gas can change when heat is added externally or when the gas does work against the environment.
How is the internal energy of an ideal gas calculated?
The internal energy of an ideal gas is given by:
Internalenergy
=
Temperature
×
Heatcapacityatconstantvolume
Internalenergy=Temperature×Heatcapacityatconstantvolume
Intermolecular forces like Van der Waals forces are ignored for an ideal gas.
What are some ways heat can be added externally to air in the atmosphere?
Heat can be added externally through processes like radiation absorption or the release of latent heat during condensation.
What is an adiabatic process in the atmosphere?
An adiabatic process is when air moves without exchanging energy with the environment. In a dry adiabatic process, we also ignore latent heat release or consumption due to phase changes
What is the dry adiabatic lapse rate
The dry adiabatic lapse rate is the rate at which temperature decreases with altitude during a dry adiabatic process.
What is the value of the dry adiabatic lapse rate, and how does it relate to altitude?
The dry adiabatic lapse rate is approximately 1 Kelvin per 100 meters, meaning the temperature drops by 1 Kelvin for every 100 meters of altitude increase.
Prompt:
What does the dry adiabatic lapse rate represent in terms of atmospheric cooling?
The dry adiabatic lapse rate represents the strongest cooling that can occur in the atmosphere without generating vertical motion or cloud formation.
What happens to air as it rises and reaches saturation?
As air rises and cools, the saturation vapour pressure drops. When saturation is reached, further cooling causes cloud formation, which releases latent heat from condensation.
How does latent heat release affect the lapse rate of rising air?
Latent heat release heats the air as it rises, reducing the dry adiabatic lapse rate to form the saturated adiabatic lapse rate (or moist adiabatic lapse rate).
What is the relationship between the saturated and dry adiabatic lapse rates?
The saturated adiabatic lapse rate is smaller than the dry adiabatic lapse rate because latent heat release reduces the rate of cooling as air rises.
Why does the saturated adiabatic lapse rate approach the dry adiabatic lapse rate at colder temperatures?
Since the saturation vapour pressure changes more slowly at colder temperatures, less latent heat is released. As a result, the saturated adiabatic lapse rate becomes closer to the dry adiabatic lapse rate in colder conditions, such as in polar clouds.
How does temperature affect the difference between the lapse rates in tropical and polar clouds?
In tropical clouds, the temperature decreases more slowly with altitude because of higher latent heat release. In polar clouds, less latent heat is released, so the temperature drops faster, approaching the dry adiabatic lapse rate.
What is the saturation mixing ratio?
The saturation mixing ratio is the mass of water vapour per mass of air at saturation. It changes depending on temperature and affects the amount of latent heat released.
What is atmospheric stability?
Atmospheric stability describes whether air will move vertically on its own. In unstable conditions, air rises freely due to buoyancy. In stable conditions, air resists vertical movement unless forced.
What determines whether air will rise or remain stable in the atmosphere?
The comparison between the observed atmospheric lapse rate (γ) and the dry adiabatic lapse rate (γdry):
If γ > γdry, the atmosphere is unstable.
If γ < γdry, the atmosphere is stable.
What happens when the observed atmospheric lapse rate (γ) is larger than the dry adiabatic lapse rate (γdry)?
The air parcel cools less (at γdry) than the surrounding atmosphere. This makes the parcel warmer and less dense, causing it to rise due to positive buoyancy. This is an unconditionally unstable situation.
What is an example of an unconditionally unstable situation in the atmosphere?
Thermals near the surface, where strong surface heating creates pockets of air that become buoyant and rise within the atmosphere.
What happens when the observed atmospheric lapse rate (γ) is smaller than both the dry adiabatic lapse rate (γdry) and the saturated adiabatic lapse rate (γmoist)?
The atmosphere is unconditionally stable. Vertically displaced air cools more than its surroundings, whether it follows the dry or saturated lapse rate, and it sinks back to its original position due to negative buoyancy
What characterizes an unconditionally stable atmosphere?
An atmosphere is unconditionally stable when the observed lapse rate is less than both the dry and moist adiabatic lapse rates, making displaced air colder and denser than the surrounding air, leading to its return to the original position.
What is an example of an unconditionally stable atmospheric condition?
Temperature inversions near the surface, where radiative cooling at night creates colder temperatures near the ground than higher up, resulting in a stable atmosphere.
What happens when the observed atmospheric lapse rate (γ) lies between the dry adiabatic lapse rate (γdry) and the moist adiabatic lapse rate (γmoist)?
his describes a conditionally unstable atmosphere. Initially, the lifted air cools dry adiabatically and is stable. Upon reaching saturation, it cools at the moist adiabatic lapse rate, leading to instability because the atmospheric lapse rate is larger than the moist lapse rate.
What is required for instability in a conditionally unstable atmosphere?
The occurrence of saturation is required for instability, as the air parcel then follows the moist adiabatic lapse rate, creating positive buoyancy.
What type of clouds form under conditionally unstable conditions?
Vertically developing or convective clouds, such as thunderstorm clouds, form under conditionally unstable conditions.
What is the typical lapse rate in the lower atmosphere under conditionally unstable conditions
he lapse rate is close to the moist adiabatic lapse rate, around 0.65 K per 100 metres for surface temperatures near the global mean.
What is atmospheric convection, and how is it classified?
Atmospheric convection refers to vertical motion due to positive buoyancy caused by local instability. It is classified as:
Dry convection: No clouds involved.
Moist convection: Clouds form, and latent heat release occurs, which is crucial for atmospheric heating.
Why is moist convection important?
Moist convection is important because it:
Heats the atmosphere through latent heat release.
Dominates precipitation in the tropics and mid-latitude summers.
What roles does convection play in the atmosphere besides heating?
Removes instability by redistributing heat and moisture vertically.
Transports momentum and pollutants vertically.
Why is there little net transport of mass by atmospheric convection?
Convective updrafts are largely compensated by downdrafts in nearby regions, resulting in very little net mass transport. This makes convection distinct from the atmospheric mean circulation.
What is the troposphere, and what characterizes its temperature profile?
he troposphere is the lowest 12 km of the atmosphere, characterized by:
Vertical mixing through convection.
A mean lapse rate of 0.65 K per 100 m.
It ends at the tropopause.
What causes the temperature increase in the stratosphere?
In the stratosphere, temperature increases due to:
Absorption of solar radiation by the ozone layer.
This layer is extremely stable and ends at the stratopause (~48 km altitude).
What defines the mesosphere, and how does its temperature change?
The mesosphere lies between the stratopause and mesopause (~80 km altitude).
Temperature decreases with altitude.
Dominated by dry adiabatic processes, with some heating from radiation and atmospheric waves.
Why does temperature rise in the thermosphere?
In the thermosphere (~80 km and above), temperature rises due to:
Absorption of solar radiation at very short wavelengths by oxygen.
At higher altitudes, air density becomes so low that temperature is less well defined.
How does radiation transport heat in the atmosphere?
Radiation transports heat through:
Emission (causes cooling).
Absorption (causes heating).
Radiation can also be scattered or transmitted, influencing where absorption occurs.
What is turbulence, and how does it transport heat?
Turbulence is caused by friction at the surface.
Produces turbulent eddies that mix heat vertically and horizontally.
Dominates in the boundary layer (lowest ~1 km of the atmosphere).
Transports heat that enters the atmosphere via surface conduction.
What is advection, and how does it transport heat?
Advection involves the horizontal transport of air over large scales (kilometers and above).
Horizontal convergence/divergence leads to vertical transport.
Driven by temperature differences and reduces temperature gradients.
Includes heat transport from equator to poles by global circulation.
