Cryospheric sciences寒冷圏 科学

Heinz Blatterpresently: ILTS, Hokkaido University, Sapporo

Special lecture on cryospheric Science

International Antarctic Institute

Graduate School of Environmental Science

Hokkaido University, Sapporo

Program 2013

Fridays, 16.30-18.00

•October 18: Cryosphere and climate •October 25: Land ice and snow •November 1: Sea ice •November 8: Glaciers •November 22: Ice sheets •November 29: Past of the cryosphere •December 6: Future of the cryosphere

ftp://iacftp.ethz.ch/pub_read/blatter/IAI-2013/

ppt and pdf files are available (see subdirectories)

Cryosphere:

κρύος: cold 「さむい」 σφαῖρα: sphere 「球、圏」

glaciers 　「氷河」 , ice sheets 　「氷床」permafrost 　「永久凍土」

sea ice 　「海氷」 , lake ice 　「湖氷」 , river ice　「川氷」

snow 「雪」ice clouds 　「氷の雲」 , hail 　「氷雨」

hoar frost 　「霧氷」

Climate system

• Atmosphere: – thermodynamics, wind, clouds, precipitation

• Hydrosphere (ocean): – heat transport, evaporation, roughness

• Pedosphere (solid Earth surface): – surface fluxes of heat, momentum, water

• Biosphere: – surface fluxes, evapotranspiration

Where is the cryosphere?

Cryosphere

• integral part of the climate system• many different sub-systems• many different processes• strong feedback mechanisms• strong influence to

– atmospheric dynamics and precipitation– ocean surface energy exchange– terrestrial water balance

this lecture presents an individual selection of topics:a physicists view

processes:

• dynamics:– wind, convection, ocean currents

• thermodynamics:– insolation: surface, atmosphere, ocean– thermal radiation: „greenhouse effect“– surface energy flux– meridional energy transport in atmosphere

and ocean

• weather:– clouds and precipitation (rain, snow, hail)

schematic of the climate system

IPCC

Weather vs. Climate

• weather: transient situation, days to weeks

• climate: mean state of the climate system, mostly atmosphere

– averaging time 30 years– high temporal and spatial variability on time

scales of 2, 5-10, 50-1000, 20‘000-400‘000, millions of years and longer

– gap around 30 years

spectrum of periodic variabilities of climate

Solar radiation

Solar „constant“

Mean solar radiative flux at Earth

rs: solar radius

ae: mean distance between Earth and the sun

Bs: radiative energy flux through the surface of the sun

(black body radiation at 5700 K: 6.28 · 107 Wm−2)

Latest corrected value: S = 1362 Wm-2

Global mean solar radiation on the surface of the Earth

A: Albedo (fraction of reflected solar radiation) (Earth: A=0.3)

e: eccentricity of Earth orbit

mean insolation:

Area of circle: r2

Surface area of sphere: 4r2

Global mean energy fluxes

seasonal variation of daily insolation in percent of the solar constant S=1362 W m−2

Radiation laws

Stefan-Boltzmann law:

B = T4 with σ = 5.67×10−8 W m−2 K−4

B=1368 W m−2 T=395 K (122oC)

B/4=342 W m−2 T=279 K (5oC)

0.7*B/4=239 W m−2 T=255 K (-18oC)

Radiation in the planetary system

``solar constant``: S proportional to 1/r 2

Temperature: T proportional to S1/4

T proportional to 1/r1/2

radiation temperature in the planetary system

Venus, Earth, Mars

• Venus: runaway greenhouse, only vapor

• Earth: water in all three phases

• Mars: runawy icehouse, only ice

Ice• solid state of water

• anomalies:– ice floats on water (expansion at freezing)– melting point decreases with pressure

• hexagonal lattice

• phase diagram of ice

ice crystal halos

role of ice in the climate system

• Albedo: most important– albedo: reflectivity of solar spectrum– snow and ice have high albedo– strong positive feedback

• latent heat flux– melt and freezing: snow, sea ice, land ice– sublimation: high altitude– crystallisation: ice clouds

albedo:fraction of reflected sunlight

• rock: 0.1• forest: 0.1-0.2• ocean: 0.05• desert: <0.3• snow: 0.4-0.9• glacier ice: 0.3-0.5

ice albedo feedback氷のアルベドの帰還

• controll circuit– negative feedback: perturbation is damped– positive feedback: perturbation is enhanced

regulator

target va lue

regulatedquantity

sensor

perturbation

ice albedo feedback• example:

– large closed snow cover in Eurasia,

– longer winter

• example:– decrease of sea ice cover

in arctic ocean– more absorption of solar

radiation– warmer in arctic ocean– further decrease of sea ice

cover

• polar climate more sensitive to changes in radiative forcing (greenhouse)

summary

• cryosphere is an important part of the climate system

• snow and ice play an important role in many fundamental processes in the climate system

as Goethe already mentioned 200 years ago:

ice is more important than you think