c2.1:L1 earth-atmosphere system and the tropics Flashcards
energy from the sun
insolation; shortwave radiation
radiative transfer
by infrared radiation between the surface, the atmosphere, and space
non radiative transfer
convection, conduction, latent heat of evaporation
inputs into the system
arriving insolation: 100%
albedo reflects: 31%
absorption by atmospheric clouds and radiation: 3%
direct and diffuse radiation: 45%
outputs from the system
re-rediates 69% into space; terrestrial radiation: 21%(atmosphere heating)+45%(surface heating)+3%(ozone emission)
processes
absorption, reflection, scattering, conduction and convection, latent heat transfer
what is absorption
assimilation of radiation by molecules of matter and its conversion from one form of energy to another
e.g. infrared radiation or chemical energy (photosynthesis)
where does absorption take place
land and water surfaces, atmospheric gases, dust, cloud, and stratospheric ozone
explain the process of absorption on the surface of the earth
- when earth surface is heated up, it releases heat energy and warms the air above via radiation, conduction and convection
- radiation emitted by warmed surface is known as terrestrial radiation; longwave radiation
explain the process of absorption by components of the atmosphere
certain molecules absorb radiation.
e.g. oxygen absorbs short wave
water vapour and co2 absorbs long wave(green house effect); long wave radiation that travels back to earth known as counter radiation
reflection
influenced by albedo of a surface
albedo
is the reflective quality of a surface
colour and albedo relationship
dark colours; low albedo
light colours; high albedo
smoothness of surface and albedo relationship
smooth: increased albedo
rough: reduced albedo
scattering process
- insolation encounters increasing density of atmospheric gases as it travels to surface
- gas molecules absorb and reemit the radiation; represents 7% of the earth’s albedo
- dust particles, pollutants, ice , cloud droplets, water vapour produce further scattering
- this is known as diffused radiation
conduction process
- molecule to molecule transfer of heat energy as it diffuses through a substance
- molecule warm, vibration increase, cause collisions that produce motion in neighbouring molecules, transfers heat from warm to cool materials
convection
energy transfer through gases and liquids by movements that occur when physical mixing involves strong vertical motion
e.g. warmer masses rise, cooler masses sink
latent heat definition
changing of state of matter during a “constant temperature”
evaporation vs condensation
evaporation: gain heat, break bonds, surrounding lose heat
condensation: lose head, form bonds, surrounding gains heat
net radiation
refers to the balance of all incoming and outgoing radiation at the earth’s surface.
net radiation across latitudes
equator: net gain
tropics: net gain
net gain decreases and becomes negatives towards poles
global imbalance of radiation causes?
poleward transfer of heat; global atmospheric circulation pattern; wind(75%), ocean currents(25%)
characteristics of tropics
- mean temp of coolest month is 18’c
- area between tropics of cancer and tropics of capricorn(23’N, 23’S)
- mostly humid and arid/semiarid climates
what causes high temp in the tropics
- high solar angle/ angle of incidence
- dist solar radiation through atmosphere
- length of day: affected by axial tilt
how does high solar angle affect temp
since insolation is dependent on the angle of the sun above the horizon, it is the greatest when the sun is overhead in the tropics. the tropics receive incoming light at a 90’ angle(subpolar point), it concentrates to a small area and increases it ability to heat the surface, hence energy is distributed to a more intense energy per unit area
how does distance solar radiation travels through atmosphere affect temperature?
insolation received in tropics is concentrated over a smaller area and passes through a shallower layer of atmosphere
how does axial tilt affect length of day which in turns affects temp
axial tilt produces seasonal differences in insolation at any given latitude. tropical latitudes never receive high daily maxima reached near the poles, but receive relatively large amounts of solar radiation throughout the year. there is also little variation in length of day and midday solar angle, so energy receipts exhibit little change through the year
