Section 4A: Atmosphere and General Circulation Flashcards
Briefly distinguish between ‘weather’ and ‘climate’.
Weather refers to short-term atmospheric conditions like temperature, precipitation, humidity, and wind which fluctuates rapidly over hours or days.
Climate describes the long-term weather patterns which represents the overall trend averaging over decades or longer periods.
For example, a cold winter is a temporary weather event, but a decades-long cooling trend would indicate a climate change.
With the aid of a sketch (graph), outline the structure and the composition of the standard atmosphere.
Troposphere
- Extends from the surface up to 6-20 km altitude
- Temperature decreases with height at a rate of ~6.5°C/km (lapse rate)
- Contains 75% of the atmosphere’s mass and most water vapor
- Weather phenomena occur in this layer
Stratosphere
- Extends from the tropopause up to ~50 km
- Temperature increases with height due to ozone absorption of UV radiation
- Very stable and dry layer
Mesosphere
- Extends from the stratopause up to ~80-85 km
- Temperature decreases with height
Thermosphere
- Extends from the mesopause up to ~600 km
- Temperature increases rapidly with height due to absorption of high-energy radiation[3]
The composition of the standard atmosphere by volume is primarily:
- Nitrogen (78%)
- Oxygen (21%)
- Argon (0.9%)
- Carbon dioxide (0.04%)
- Water vapor (variable, up to 4% near surface)
Trace gases like ozone, methane, nitrous oxide are also present in small amounts.
Define the following:
Temperature Inversion.
Isothermal Layer.
Temperature Inversion is a layer at the atmosphere where temperature increases with height instead of decreasing with height.
Isothermal Layer is a layer of air where the temperature remains constant with height.
Briefly explain what ‘adiabatic change of temperature’ of a parcel of air.
An adiabatic change of temperature is
- the cooling or warming of an air parcel due to expansion or compression
- without any heat being added or removed from the parcel.
Briefly explain Environmental Lapse Rate (ELR).
The rate at which the temperature decreases with increasing altitude in the actual atmosphere at a given time and location.
It is the temperature gradient of the surrounding air, not of a rising air parcel.
It can vary significantly depending on factors like radiation, convection, and condensation.
When the ELR is negative, meaning temperature increases with height, it is called a temperature inversion.
Briefly explain what is meant by DALR and SALR and why they have different values.
The Dry Adiabatic Lapse Rate (DALR) is the rate at which an unsaturated dry parcel of air cools as it rises and expands.
The Saturated Adiabatic Lapse Rate (SALR) is the rate at which a saturated moist parcel of air cools as it rises and condenses, releasing latent heat.
They have different values because when water vapor condenses into liquid water droplets in a rising saturated air parcel, latent heat is released. This latent heat warms the air parcel, causing it to cool at a slower rate compared to a dry unsaturated air parcel.Therefore, the SALR is lower than the DALR due to this latent heat release during condensation.
Define the following:
Absolutely stable atmosphere.
Absolutely unstable atmosphere.
Conditionally unstable atmosphere.
An absolutely stable atmosphere is when the ELR is less than the moist adiabatic lapse rate. This means a rising air parcel will always cool faster than the surrounding environment, even after reaching saturation. As a result, the air parcel will be cooler and denser than the environment at all levels, preventing it from rising further.
An absolutely unstable atmosphere occurs when the ELR is greater than the dry adiabatic lapse rate. In this case, a rising air parcel will always cool slower than the surrounding environment, even when unsaturated. The air parcel remains warmer and less dense than the environment, allowing continuous ascent.
A conditionally unstable atmosphere exists when the environmental lapse rate lies between the moist and dry adiabatic lapse rates. An unsaturated air parcel will initially resist rising as it cools faster than the environment (stable). However, if the parcel becomes saturated and continues rising, it will cool at the moist adiabatic rate, slower than the environment, becoming unstable and able to rise further.
Briefly explain what is meant by ‘diurnal variation of atmospheric temperature’. Why is it greater over land than at sea?
Diurnal variation of atmospheric temperature refers to the fluctuation in air temperature between the daily maximum and minimum temperatures over a 24-hour period.
It is greater over land than the ocean due to it’s lower heat capacity.
Define ‘Atmospheric Pressure’. Give units of measurement.
The force per unit area exerted by the weight of the atmosphere above any given point on the Earth’s surface.
SI Unit is Pascal (Pa)
Define ‘Pressure Tendency’.
Pressure tendency refers to the change in atmospheric pressure over a given period of time and indicates whether the air pressure is rising, falling or steady.
Briefly explain what is meant by the diurnal range of atmospheric pressure.
The diurnal range of atmospheric pressure refers to the regular daily cycle of rising and falling air pressure caused by atmospheric tides.
Briefly explain the three (3) methods of heat transfer from one place to another.
Conduction - Heat moves from one object to another object through direct touch.
Convection - Heat transferred through air or liquid currents.
Radiation - Heat transfer through electromagnetic waves.
Briefly explain what ‘insolation’ is.
Insolation is the amount of solar radiation received on a surface area of the Earth over a period of time.
State the major factors that affect the amount of solar radiation received at the earth’s surface.
- Sun’s output
- Latitude of the location
- Sun’s Altitude
- Hours of daylight
- Atmoshpheric transparency
Briefly explain why cloudy nights are warmer than nights with a clear sky.
Cloudy nights are warmer than clear nights because clouds act as an insulating layer that traps outgoing infrared radiation emitted by the Earth’s surface, preventing it from escaping into space. This trapped heat is then radiated back down towards the surface, keeping temperatures warmer compared to clear nights when heat can freely radiate out to space and get lost.
