04-EnergyBalance

04-EnergyBalance - 3/25/2008 Components of the energy...

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3/25/2008 1 ESM 236: The Mountain Snowpack 1 Energy and Mass Balance of the Snowpack SWE (mass) and mass balance -2 At a time: (snow density depth) (kg m ) (layers) s d n SWE d zd z d ρ ρρ =≈ Δ 2 ( ) , 0 0 Mass balance: Snowfall - Evaporation - Runoff Water balance: Runoff=Melt Storage s sn n SWE Δ= ±Δ Can’t measure Evaporation or Melt, so calculate via energy balance N RH L G M =+ + + R N Net radiation H Sensible heat exchange L Latent heat exchange (energy used in evaporation) 3 • Dry snow M =0 • Wet snow G =0, because T is uniform G Heat flow into/out of pack, direction Δ T M Energy used in melting E Evaporation = L/( λ v + f ) Q m Melt = M/ f Components of the energy balance ( ) 4 Net radiation: solar and thermal infrared (1 ) (T in K) Sensible: N aph a RS F T H CK T T αε σ =− + = D 4 () Latent: Heat flow into pack: ( down) Energy used in melt: residual av f ws a LK q T q T GK z z M ρλ λ ⎡⎤ ⎣⎦ = Measurement of snowpack energy exchange (Colorado Front Range) 5 University of Colorado (Mark Williams) micrometeorological tower at Niwot Ridge Measurement of snowpack energy exchange (Sierra Nevada) 6
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3/25/2008 2 Relationship between snowpack energy balance and runoff from snowmelt • Bring snowpack to 0°C (remove the “cold content”) • Melt snow (overcome latent heat of fusion) Get the water into and through the 7 • Get the water into and through the snowpack (complicated) • Melt enough that water drains when surface melt occurs (make the pack “ripe”) Energy needed to bring snowpack to 0 ° C and then melt it -3 -1 -1 -2 , Cold content of homogeneous layer density thickness T ( C) specific heat of ice kg m m deg J kg deg J m Cold content of pack si d n is i s n nn dTC CT d zC T d ρ ρρ =− Δ × ° × == =− ≈− Δ 8 0 0 Melt rate ra f M λ = = -2 -2 -1 -1 -1 te energy added
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This note was uploaded on 08/06/2008 for the course ESM 236 taught by Professor Dozier during the Spring '08 term at UCSB.

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04-EnergyBalance - 3/25/2008 Components of the energy...

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