Atmosphere and Weather

Flashcards covering key vocabulary terms related to atmospheric processes and the global energy budget.

Diurnal Energy Budget

The balance between energy inputs and outputs over a 24-hour period. It explains why temperature rise during the day and fall at night and how different surfaces respond to incoming solar radiation.

Incoming Solar Radiation (Insolation)

Shortwave radiation from the sun in the form of visible light, UV, and near-infrared.

what affects incoming solar radiation (5)

time of day (midday = highest intensity)

season (higher in summer)

Latitude (closer to Eqautor = more intense)

cloud cover (blocks and reflects solar radiation)

atmospheric transparency (dust, pollution reduce intensity)

percentages of incoming solar radiation

5% is scattered by the atmosphere

24% reflected into space by atmosphere

23% absorbed by atmospheric gasses

48% absorbed by Earths surface

reflected solar radiation (albedo)

The proportion of solar radiation that is reflected back into space by surfaces of the Earth, such as ice, water, and vegetation, often expressed as a percentage.

percentages of reflected solar radiation (albedo)

snow/ice - 70-90%

water - 50-80%

grass/forset - 10-25%

asphalt - 5-15%

lighter surfaces reflect more, reducing heat absorption while urban areas with dark surfaces have low albed, increasing heat absorption

energy absorbed into surface and subsurface

The remaining solar radiation that is not reflected is absorbed by the Earths surface

the energy is stored as heat and then:

-conducted into the soil or water

-re-emitted later as longwave radiation

-used in evaporation or warming the air

soil and water have different thermal properties as water has a high specific heat capacity, so it takes longer to heat up and cool down. In contrast soill heats up rapidly due to lower thermal mass, but also loses heat quickly. These influence daily temperature variation and inland areas show greater extremes than coastal areas.

Longwave Radiation (Terrestrial Radiation)

The Earth emits longwasve (infared) radiation as it cools down, especially at night

this energy escapes into the atmosphere unless it is absorbed by clouds or greenhouse gasses (which trap heat and warm the atmosphere).

cloudy nights are warmer due to this trapping effect

smog in urban areas can behave like low-level clouds, absorbing and re-emitting longwave radiation at night. this traps heat and contributes to the urban heat effect, especially in CBDs.

greenhouse gassees (CO2, CH4, water vapour) absorb longwave radiation and re-radiate to Earth, this is the basis of the natural greenhouse effect.

Sensible Heat Transfer

The process by which heat is transferred from the ground to the air through conduction and convection.

“sensible“ means its felt as a temperature change

convection currents carry heat away from the surface to the atmosphere

stongest during the day, especially over land with little vegetation or moisture

Latent Heat Transfer

Occurs when water changes state (e.g., from liquid to vapor)

evaporation requires energy, so this “hidden” or latent in the water vapour

when condensation occurs (e.g cloud formation), this latent heat is released from the water vapour

Dew Formation

at night, surface temperature cool rapidly through radiation loss

when surfaces temperature drops below dew point, condensation occurs, so dew forms

this process releases latent heat, slightly warming the surrounding air

however, net energy loss still dominates leading to nighttime cooling

factors influencing the diurnal energy budget

Cloud Cover - Reflects solar radiation (cooler days) and traps longwave radiation (warmer nights).

Surface Type (Water vs. Land) - Heats (and cools) slower than land; urban areas store more heat.

Wind - Enhances sensible and latent heat transfer; can speed up cooling.

vegetation - Increases evapotranspiration, leading to more latent heat loss and a cooler surface.

humidity - More water vapor leads to more condensation and more trapped heat at night.

altitude - Higher altitudes cool faster at night due to thinner air and less greenhouse effect.

convection

the transfer of heat through the movement of fluids and gases, where warmer, less dense air rises and cooler, denser air sinks, causing convection currents that circulate energy and heat in the atmosphere. Due to the particles vibrating more

conduction

is the transfer of heat through direct contact of molecules, where energy is passed from one molecule to another without any movement of the material as a whole.

Global Energy Budget

The imbalance between incoming and outgoing radiation energy across the Earth. Due to the Earths tilt and shape, energy is not evenly ditributed, leading to variations in climate and weather patterns.

radiation surplus (equator to 35°c)

more imncoming solar radiation than outgoing longwave radiation.

the sun is directly overhead, so energy is concentrated over a small area

the atmosphere is thinner, so less energy is lost

radiation deficit (poles to 35°c)

less incoming solar radiation than outgoing longwave radiation, leading to a net energy loss in the atmosphere.

sun at low angle and spreads over a large area

ice and snow reflect much of the incoming energy (high elbedo)

global heat balance

The equilibrium between incoming solar radiation and outgoing terrestrial radiation, determining the Earth's climate.

Pressure Variations

Air moves from high to low pressure.

surface pressure

low pressure in equatorial regions, as warm air rises and leaves the surface. higher pressures seen in polar regions, where cool air descends.

surface wind belts

Patterns of wind circulation that occur due to the Earth's rotation and varied surface temperatures. They influence weather patterns and ocean currents.

Ocean Conveyor Belts

Cold, salty water sinks from polar regions and moves towards the Equator, where warm water gives its heat away to surface winds.

seasonal variation (latitude)

between the tropics (23.5 N/S) the sun is more directly overhead so:

shortwave radiation is more intense and leads to more consistent warm temperatures year-round. In contrast, areas further from the equator experience greater seasonal fluctuations in temperature due to the angle of sunlight. also atmosphere is thinner, so less radiation is lost

seasonal variation (land vs sea) (4 each)

Land has:

lower albedo

heat confined to the surface

low specfic heat capacity (5x as much heat to raise temperature of water by 2 degrees)

less evaporation

sea has:

higher albedo

solar energy pentration goes deeper due to transparency

high specific heat capacity

more evaporation as energy is diverted into latent heat, cooling effect

seasonal variation (altitude)

higher altitudes experince cooler temperatures because the thinner atmosphere holds less heat, leading to a decrease in temperature with increasing elevation. air at high altitudes expands and cools as pressure drops (adiabatic cooling)

pressure belts (3-cell model influence)

solar heating creates distinct pressure belts, where warm air rises at the equator, low pressure zone (ITCZ)

air then moves aloft and sinks at 30 degrees, subtropical high pressure zones

cool air descends at the poles, high pressure zones, influencing global wind patterns and climate.

pressure gradient

air moves from high to low pressure due to the pressure gradient force which causes wind.

wind belts (global circulation ceels)

large-scale patterns of wind circulation caused by the differential heating of the Earth's surface, influencing especially the (ITCZ), which influence weather, monsoon systems and climate.

coriolis force

The Coriolis force is an apparent force caused by the Earth's rotation, which affects the direction of winds and currents, causing them to curve rather than move in a straight line. to the right in the northern hemisphere and to the left in the southern hemisphere

isobar

these are lines connecting points of equal atmospheric pressure.

geographic balance and winds

when gradient force and coriolis force balance the effects of wind, resulting in geostrophic winds that flow parallel to isobars.

friction and surface winds

Friction reduces the speed of winds near the Earth's surface, causing them to flow at an angle across isobars towards low pressure, causing inflow (convergence) and potential uplift. Greater roughness = more friction (e.g. cities and forests). over oceans, friction is lower, so smoother airflow

jet streams

fast moving air in the atmosphere, near the tropopause. occurs where temperature gradients and pressure gradients are steepest e.g. between Hadley and Ferrel cells. strongest in winter, as temperature contrasts are greater. move west to east and influnce weather systems.

hadley cell

adjacent to the ITCZ, where insolation is most intense. Doldrums created (permanent low pressure belt) due to constant rising air, trade winds are drawn in. Air subsides around 30 degrees and is deflected right or left depending on hemisphere.

ferrel cell

not thermally induced but a result of adjacent cells, creating a cog-like system. air is forced to rise at the polar front and forced to sink at the high-pressure zone, where it meets the hadley cell

polar cell

a circulation cell found at high latitudes, where cold air descends at the poles, creating high pressure, then moves equatorward before rising at the polar front, interacting with the Ferrel cell. low pressure zone created at 60 degrees

depresion

a depression (or low-pressure system) , often associated with cloud formation, precipitation, and stormy weather. It occurs when warmer, moist air rises and cools, leading to condensation.

evaporation

the process by which liquid water is converted into water vapor, resulting water gains enough energy to escape the air

conditions favouring evaporation

include high temperatures, low humidity, large surface area (lake, ocean), solar radiation and increased wind speed, allowing moisture to escape from surfaces more readily.

evaporations role in the atmosphere

transfers water vapour into the atmosphere. uses energy (latent heat of vaporisation) which cools the surface. contributes to cloud formation.

condensation

the process by which water vapor in the air cools and changes back into liquid water, forming clouds and precipitation.

how condensation happens

air rises then cools down adiabatically, expanding as pressure increase and once dew point is reached, condensation nuclei (dust, salt, smoker) allows vapour to condence into water droplets

freezing

the process where liquid water turns into solid ice as temperatures drop below 0°C under pressure.

occurs when raindrops or cloud droplets freeze (e.g. supercooled water turns into ice)

also happens at the surface (e.g lakes freezing or frost formation)

releases latent heat fusion, as molecules loose energy to solidify

melting

the process where solid ice turns back into liquid water as temperatures rise above 0°C. This occurs when ice absorbs heat, causing the molecules to gain energy and transition to a liquid state.

absorbs latent heat of fusion

slows temperature rise in spring, hence why snow melt takes time

depostion

the process where water vapor transitions directly to solid ice without becoming a liquid, such as in the formation of frost (e.g on grass or windowpanes).

releases latent heat, helping maintain cloud buoyancy

importancet in the Bergeron process (cold cloud precipitation)

sublimation

the process where solid ice transitions directly to water vapor without becoming a liquid. This process absorbs latent heat, causing temperature drops and is significant in various atmospheric phenomena. it occurs in glaciers, mountain slopes and polar regions.

convectional uplift

triggered by solar heating of the Earth's surface, causing warm air to rise, cool, and form clouds and precipitation.

occurs in equatorial/tropical areas (e.g. Amazon or Congo) and summer in temprate areas (e.g SE USA, India before monsoon)

formation of convectional uplift

1 sun heats the ground, especially in the afternoon

2 ground heats air above it, air becomes less dense and rises

3 as air rises, it expands and cools adibatically

4 reaches dew point, condensation begins forming cumulus or cumulonimbus clouds form

5 water droplets grow leading to heavy convectional rainfall (could be torrential and short-lived)

fronatal uplift

the process that occurs when two air masses meet, with the denser, colder air pushing the lighter, warmer air upward. This upward movement can lead to cloud formation and precipitation, often associated with weather fronts. could be warm front where cold air lifts warm air (stratus), or a cold front where warm air is forced to rise rapidly (cumulonimbus clouds).

occurs in mid latitude depressions (e.g UK, USA east coast) and along polar fronts.

orographic (relief) uplift

the process that occurs when moist air is lifted over a mountain range or hill, leading to cooling and precipitation on the windward side, while creating a rain shadow on the leeward side. This phenomenon is common in mountainous regions (e.g Andes mountains).

radiation cooling

the process where the Earth's surface loses heat at night through longwave radiation, leading to a decrease in air temperature.

formation of radiation cooling

1 air near the surface cools below dew point

2 condensation occurs close to the ground

3 forms dew, fog or frost depending on temperature

clouds

are visible masses of condensed water vapor floating in the atmosphere, formed when moist air rises and cools, leading to condensation. forms when air becomes saturated (relative = 100%) and condensation begins.

requires condensation nuclei (dust,salt,pollution) to form droplets

types of clouds (4)

cumulus - fluffy, white clouds with a flat base, often signaling fair weather. needs convectional uplift

cumulonimbus - tall, towering clouds that can produce thunderstorms and heavy precipitation. needs deep convection

stratus - gray, uniform clouds that cover the sky, often bringing steady rain or drizzle. needs fronatal or radiation cooling

cirrus - thin, wispy clouds high in the atmosphere, indicating fair weather but can signal a change in the weather.

rain (bergeron)

A process where ice crystals form in supercooled clouds and grow larger, eventually falling to the ground as precipitation when they become too heavy. depends on temperature (if below 0 degress)

rain (coalesence)

A process where small water droplets collide and merge to form larger droplets in warm clouds, ultimately falling to the ground as precipitation. depends on temperature (if above 0 degress)

snow

Precipitation that occurs when water vapor freezes into ice crystals in the atmosphere. It typically forms in cold temperatures below 0 degrees.

hail

Precipitation that consists of balls or irregular lumps of ice, formed within powerful thunderstorms when updrafts carry water droplets upwards into extremely cold areas of the atmosphere. falls when too heavy to updraft

fog

A weather phenomenon characterized by low-level clouds composed of tiny water droplets suspended in the air, reducing visibility. It typically forms when warm, moist air cools and condenses. 3 differnet types of fog include radiation fog (clear, calm nights, gorund coold air above), advection fog (warm,moist air moves over cooler surfaces), and valley fog (cold air sinks and pools in low areas).

main greenhouse gases and human sources

The primary greenhouse gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), CFCs, and water vapor, which trap heat in the atmosphere. Major human sources include fossil fuel combustion, agriculture, and deforestation.

evidencce of global warming

sea level rising (3.1 mm/year)

ocean temperature rise (+0.11 per decade)

ice loss (artic ice shrunk 65% since 1975)

ocean acidity increasing ( increased 26% since 1975)

weather (increased intensity of floods, heatwaves, hurricanes and more)

global temperature increase (increase of 1.1 degrees since pre-industrial era)

extreme weather events (more frequents/intense storms, floods have killed 500,000 and 2.8 billion affected)

agriculture (35% drop in African yield with 3 degrees rise and $10 billion loss in Texas and Oklahoma) (although longer growing season)

drought and water scarcity

health and disease (malaria)

wildlife and bidivrsity (risk of extiction)

tourism (ski resorts may become unavailable) (although new destinations may become available e.g artic cruise)

economic cost (climate chance could cost 5-20% of global GDP per year) (although early mitigation may limit cost to just 1% of GDP)

human causes of global warming

fossil fuel combusion

deforestation (less carbon absorption + higher albedo

agriculture and industy producing fumes)

natural causes of global warming

orbital changes (milankovitch cycles)

solar output variations

volcanic eruptions

EL Nino, La Nina cucles (affect temperature cycles short-term)

urban climate (temperature - higher)

it is caused by low albedo(absorbs more heat)

high rise buildings (traps radiation (urban canyon effect))

reduced evapotranspiration (less cooling from vegetation)

anthropogenic heat (heating systems like traffuc and industry increase the heat to upto 50%)

urban areas cna increse 3-7 degrees, especially at night

urban climate (humidity - lower)

lower daytime humidity (less vegetation = reduced transpiration)

higher night time relative humidity (warm air holds more moisture; slower cooling=more condensation)

drianage systems (remove water quickly, reducing evaporation sources)

urban climate (precipitation - higher)

increased precipitation due to urban heat islands, which enhance convection and cloud formation. Urban surfaces also alter airflows, leading to localized heavy rainfall.

London, New York, Tokyo often experince more summer thunderstorms than surrounding rural areas

urban climate (wind patterns - higher)

lower wind speeds due to surface roughness (buildings increase friction). Tall buildings can redirect winds, resulting in enhanced turbulence and occasional wind tunnel effects in urban areas.

urban climate (other effects)

less snowfall

insolation differences, (pollution reduces incoming solar radiation, leads to cooler mornings and warmer afternoons)

micro-anomilies (slightly cooler zones over water bodies, e.g rivers, canals)

urban climate (mitigation stratedgies)

urban forests (3-5 degress cooling due to shade plus evapotranspiration)

living/green roofs (reduces surface temperature, improves air quality)

cool roofing materials (reflects more solar radiation)

more green spaces (reduce urban heat effects, inceeases infiltration and improve biodiversity. )

transport policies (ULEZ) fewer condensation nuclei

use of reflective materials (e.g white roofs)