HOW DOES THIS BALANCE BETWEEN INSOLATION AND OUTGOING LONGWAVE RADIATION MANIFEST ITSELF GLOBALLY?
Energy Balance - Portland State UniversityENERGY BALANCE AT 5 ELEVATIONS Pasterzegletscher U5 3225 m...
Transcript of Energy Balance - Portland State UniversityENERGY BALANCE AT 5 ELEVATIONS Pasterzegletscher U5 3225 m...
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Energy Balance
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WaterFlow
Climate
Local Meteorology
Surface MassAnd
Energy Exchange
Net Mass Balance
Dynamic Response
Changes In
GeometryEffect onLandscape
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WaterFlow
Climate
Local Meteorology
Surface MassAnd
Energy Exchange
Net Mass Balance
Dynamic Response
Changes In
GeometryEffect onLandscape
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Accumulation - Ablation = Mass Change
CalvingWind Erosion
SublimationMelt
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Mass
Mass Balance
IN OUT
Analogy for heat balance
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Mass
Surface Energy Balance
Conduction
Radiation
Turbulent (wind) exchange
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Mass
Surface Energy Balance Radiation
Shortwave Longwave
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Mass
Turbulent (wind) exchange
Surface Energy Balance
1. Sensible Heat
2. Latent Heat
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S short-wave incoming radiation fluxa albedo of the surfaceL long-wave incoming radiation fluxL long-wave outgoing radiation fluxQH sensible heat fluxQL latent heat fluxQm phase change
FLUXES: ATMOSPHERE - GLACIER
0 = S ( 1 – ) + L - L + QH + QL + Qm
Greuell, 2003
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S ( 1 – α ) ….net shortwave radiation
Short Wave Radiation
S short-wave incoming radiation flux
α albedo of the surface
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Antarctic Snow
~ 0.8
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~ 0.5Clean Ice
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DIRTY ICE~ 0.2
Pasterzeglet
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Midtalsbreen 2009
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L - L
Long Wave Radiation
L long-wave incoming radiation flux
L long-wave outgoing radiation flux
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SHORT- AND LONG-WAVE RADIATION
Q = T4
Q flux (irradiance) Stefan Boltzmann
constant (5.67.10-8 W m-2 K-4)
temperature
0
0.2
0.4
0.6
0.8
1
0.1 1 10 100
Black body radiation
Nor
mal
ized
irra
dian
ce
Wavelength (µm)
T = 5780 Ksun
T = 290 KEarth
Greuell, 2003
Q = εT4
ε emmisivity
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TURBULENT FLUXES
Vertical transport of properties of the air by eddiesTurbulence is generated by wind shear (du/dz)Turbulent fluxes increase with wind speed
Heat: sensible heat flux, QH
Water vapor: latent heat flux, QL
Greuell, 2003
QH + QL
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SENSIBLE HEAT FLUX (QH)
QH a Cpa 2 u T Ts
ln zz0
mzLob
ln zzT
hzLob
a air densityCpa specific heat capacity of airk von Karman constantu wind speedT air temperature at height zTs surface temperaturez0 momentum roughness lengthzT roughness length for temperaturem, h constantsLob Monin-Obukhov length (depends on u and T-Ts)
calculated with the “bulk method”
Greuell, 2003
z
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QL a Ls 2 u q qs
lnz
z0
mzLob
lnzzq
hzLob
LATENT HEAT FLUX(QL)
a air densityLs latent heat of sublimationk von Karman constantu wind speedq specific humidity at height zqs surface specific humidityz0 roughness length for velocityzq roughness length for water vaporm, h constantsLob Monin-Obukhov length (depends on u and T-Ts)
calculated with the “bulk method”
Greuell, 2003
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INSTRUMENTSmeasure short-wave radiation
with a pyranometer (glass dome)
measure long-wave radiationwith a pyrgeometer (silicon
dome)
measure sensible heat fluxwith a sonic anemometer
Greuell, 2003
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ZERO-DEGREE ASSUMPTION
Assumption: surface temperature = 0˚C
Leads to:Q0 > 0: Q0 is consumed in meltingQ0 ≤ 0: nothing occurs
Assumption okay when melting conditions are frequent
Not okay when positive Q0 causes heating of the snow (spring, early morning, higher elevation)
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Diurnal Variation
site on glacier ice in summer
-400
-200
0
200
400
600
800
1000
0 4 8 12 16 20 24
Ener
gy fl
ux (W
/m2 )
Time
short wave in
short wave out
long wave in
long wave out
sensible heat
latent heat
Greuell, 2003
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NET FLUXES
-100
0
100
200
300
400
500
600
700
0 4 8 12 16 20 24
Ener
gy fl
ux (W
/m2 )
Time
net short wave
net long wave
sensible heat
latent heat
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R = net radiation
S = sensible heat
L = latent heat
G = ground heat flux
M = melt
POSTIVE FLUX IS TOWARDSTHE SURFACE
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ENERGY BALANCE AT 5 ELEVATIONSPasterzegletscher
U53225 m=0.59
T=3.2ÞC
-50
0
50
100
150
200
250
300net shortwavenet longwavesensible heatlatent heat
Ener
gy fl
ux in
W/m
2
A12205 m=0.21
T=6.8ÞC
U22310 m=0.29
T=6.4ÞC
U32420 m=0.25
T=7.1ÞC
U42945 m=0.59
T=3.5ÞCGreuell, 2003
oCoC oC oC oC
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Effect of Solar Radiation
Google Maps Rueters
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0
50
100
150
200
6:00 12:00 18:00 0:00 6:00
Dis
char
ge (l
/s)
Canada Stream0
50
100
150
200
6:00 12:00 18:00 0:00 6:00
Disc
harg
e (l/
s)
Anderson Stream
N
EW
S
Jan 2, 1994Bomblies (2000)
Effect of Solar Radiation
Stream flow Stream flow
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Cliff area accounts for 2% of the ablation zone.
But cliff melt accounts for15-20% of the runoff
Ablation 27.4 cmSublimation 1.8 cmMelt 25.7 cm
Ablation 5.2 cmSublimation 3.5 cmMelt 1.7 cm
Dec-Jan 1996-1997
Lewis et al. (1999)
Effect of Solar Radiation, Turbulent Exchange
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Penitentes are the name of the caps of the nazarenos; literally Neve Penitentes Upper Rio Blanco, Argentina Photo: Arvakithose doing penance for their sins. Photo: Sanbec Wikipedia Wikipedia
1.5m
Effect of Solar Radiation, Turbulent Exchange
Mount Rainier Notice the tilt angle0.5 m tall.
person
Photo: Mark Sanderson Wikipedia
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DEGREE-DAY METHOD
M = Tpdd M: melt: degree-day factor [mm day-1 K-1]Tpdd: sum of positive daily mean temperatures
Why does it work:- net long-wave radiative flux, and sensible and latent heat flux ~
proportional to T- feedback between mass balance and albedo
Advantages:- computationally cheap- input: only temperature needed
Disadvantages:- more tuning to local conditions needed: e.g. b depends on mean
solar zenith angle- only sensitivity to temperature can be calculated
Statistical Model 1 of 2
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REGRESSION MODELS
Mn = c0 + c1Ts + c2Pw
Mn: mean specific mass balance
ci: coefficients determined by regression analysis
Ts: Annual mean summer temperature
Pw: Winter Precipitation
Statistical Model 2 of 2
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End