Atmosphere, Oceans and Ice

definition of atmopshere

layer of gases surrounding the Earth

Earth’s envelope of gases, representing the lightest, volatile products of geological an d biological fractionation retained by gravity

atmopsheric composition

oxygen - 21%

nitrogen - 78%

atmopsheric composition below 20km = 99% nitrogen and oxygen

aerosols

suspended particles in the air

particulates are microscopic solids or liquid droplets

natural = dust, fog, volcanic ash, sea spray

non natural = smoke, fumes from aerosols sprays

atmopsheric pressure and density

depends on air density, gravity and height

90% of air is below 16km

99.9% of air below 50km

vertical structure of atmosphere

layers of atmosphere based on temperature

temp decreases through troposphere to tropopause

temps increase with heigh through stratosphere to stratopause

temp falls through mesophere then increase in thermosphere

thermodynamics

warm air is less dense so rises

less dense and colder at higher altitudes, causing air parcel to expand and cool

once reaches height where temp is equal to surrounding environment, stops

decends warms and compresses

temperature inversion - radiation fog

close to surface overnight where air in contact with cooling surface

stable layer may cool to dew point, creating fog while layer above remains subsaturated

temperature inversion - smog

when a warmer air mass moves over a cooler air mass

traps polluted air and keep it close to the surface

water v

sensible heat

latent heat

energy released or absorbed by a body or a thermodynamic system during a constant temperature process

transition between gas and liquid involves 7 times as much heat enegry as transisiton betwen liquid and solid phase

water vapour

formed by evaporation

80% from oceans

20% from land surfaces and vegetation

absolute and

saturated humidity

maximum absolute humidity

decreases with temperature

greater when air temps are higher so warmer air tends to have higher absolute humidity

relative humidity

absolute humidity / saturated humidity

ratio of amount of water vapour actually in air to the maximum amount of water vapour required for saturation at that temperature

cloud formation

as rising air cools to its dew temperature, relative humidity reaches 100% and air becomes saturated

further lifting of rising air will result in condensation and latent heat is released inside the air parcel

H20 molecules meet condensation nuclei

condense and accumulate

when weight too heavy = fall

absorption

uptake of radiative energy by gases or particulate matter in the atmosphere

scattering

radiative energy is redirected by air molecules and particulate matter

transmission

radiative energy passes through the atmosphere

heat

transfer of energy from one body to another driven by a difference in temperature

temperature

measure of average speed of atoms and molecules

global energy budget

electromagnetic spectrum

radiowaves → gamma rays

types of heat transfer

thermal radiation

conduction

convection

thermal radiation

electromagnentic radiation emitted by a body with a temperature >0K

conduction

heat energy transmitted through collisions between neighnouring atoms or molecules

convection

transport of heat through vertical motion of air

solar radiation

ultraviolet, visible and near infrared radiation

absorbed by surface and atmosphere

fraction reflected into space

terrestrial radiation

intensity increases with temperature

longwave, far infrared, thermal radiation

top of atmosphere

radiative fluxes measured by satellite

incoming solar radiation nearly in radiative balance with total outgoing radiation

present day imbalance

net radiation at surface

emits 400 Wm-2 longwave and absorbs 500 Wm-2 solar and longwave

net radiation of atmosphere

emite 581Wm

absorb 478

radiative equilibrium

surface and atmosphere combined are close to equilibrium

but non radiative flow of energy from surface to atmosphere - latent and sensible heat flux

greenhouse effect

greenhouse gases absorb and then reemite long wave radiation

largest contribution 60% H20

solar radiation varies with latitude

distrubuted over greater surface area at higher latitudes

shallow incident angle - more scattering from clouds

longer path through atmosphere = more absorption

radiation balance

positive net radiation in low latitudes

negative net radiation in high latitudes

poleward horizontal latent and sensible heat flow

advection - horizontal movement of air

single cell model - hadley cell

one per hemisphere

air expands and rises at equator and flows toward the poles

descends

flows back toward the equator near the surface

three cell model

polar cell, ferrel cell and hadley cell

cloudy skies at intertropical convergence zone and polar front

clear sk

Coriolis effect

caused by rotation of Earth

N hemisphere - deflection to right

S hemisphere - deflection to left

strongest delfection at poles

deflects hadley circulation to form trade winds

koppen geiger climate classification

classification based on

K-G CC Tropical

A

constant high temperatures and precipitation

F = rainforest

M = monsoon

W = savanna, dry winter

S = savanna, dry summer

K-G CC Dry

B

dry, evaporation exceeds precipitation

W = arid desert

S = semi arid

h = hot

k = cold

K-G CC Temperate

C

mid latitude / seas

w - dry winter

f - no dry season

s - dry summer

sea breeze

land surfaces heat and coold more quickly than water

day - expanding air over land leads to lower surface pressure and surface breeze from sea to land

night - reverse

percent of surface covered by water

71%

sea - smaller than an ocean, completely or partially enclosed by land

gulf - body of water with a narrow opening into a larger body

strait

narrow passage of water connecting two larger portions

sea surface temperature

varies from high 30s to just below 0

correlated with latitude

seasonal variation

changes slower than air

water temperature at depth

warmer at sirface

surface salinity

varies between 32 and 38 PSU

strong correlation to evaporation

strong correlation to freshwater input

thermocline

temperature

halocline

salinity

pyrocline

density

ocean surface currents

impacted by surface winds

coriolis effect

land boundaries

thermohaline circulation

responsible for large scale transport of heat

takes thousands of years

water freezes at poles, becomes denser and falls

transported to lower latitudes, rising and warmer

transported polewards, becoming colder

global tidal range

water at high tide has to go somewhere, areas of high and low tide move across ocean surfaces daily

bay of fundy has greatest - 16m

snowball earth - albedo feedback

ice accumulates

global albedo increases

less solar energy absorbed

temperature decreases more ice accumlates

runaway global warming - albedo feedback

ice melts

global albedo reduces

more solar absorbed

temperature increases

more ice melts

elements of cryosphere

snow

permafrist

sea ice

glaciers and ice caps

ice sheets and ice shelves

snow cover

seasonal snow on land not otherwise covered by ice

largest single component of cryosphere by area

98% in northern hemisphere

reduction in amount of snow cover = climate amplifier due to soil and vegetation reflecting less than snow and ice

measuring snow cover and change

satellite image provide coverage but impacted by cloud cover

microwave remote sensing

snow cover change and consequences

less snow for less time

albedo effect, positive amplifier

also influence vegetation

boreal vegetation growths

growing seasons longer but reduction in permafrost

enhanced exchange of CO2 between soil and atmosphere

permafrost

ground continually frozen for two or more consequetive years

15% of northern hemisphere

mostly north of 66 degrees N

Arctic permafrost soils contains 1700 Gt of carbon

sea ice

natural cycle

growth in winter

reduction in summer

sea ice in northern hemisphere

measured by satellite microwave remote sensing

seasonal fluctions imply a potential rapid response to climate change

long term trend is revealed by standardized anomalies

consequences of sea ice change

albedo temperature positive feedbacl

ice insulated warm sea from very cold polar air

potential for significantm and difficult to predict, impact on climate 1

ice sheet

body of ice >50,000km3

greenland ice sheet

west antarctic ice sheet WAIS

east antarctic ice sheet EAIS

glacier

single body of ice flowing as one unit a valley

mountain glacier formation

precipitation falls in accumulation zone

ice lost in

mountain glaciers furture change

by 2100, expected reduction in glacier mass and area

50% of glaciers could dissapear

consequences of glacier retreat

1%

ice caps

ice shelves

thick floating platforms of ice that form where an ice sheet flows out to sea

several hundreds metres thick

point where land ice transitions to floating ice is grounding line

larsen B collpase

ice shelf collapsed in 2002

surface melt water ponds are believed to be primary cause

consequences of ice sheet change

greenland ice sheet - 7.5m

WAIS - 5.5m

EAIS - 53m