Surface Energy Exchange or Surface Heat Balance Background

Surface Energy Exchange or Surface Heat Balance

Background “…The Arctic is considered to be particularly sensitive to climate change…” (Arrhenius, 1896) The complex interactions between the surface and the overlying atmosphere are important aspects of the surface heat budget

Meteorological Measurements Weather stations Research vessels/icebreakers Drifting stations Drifting buoys Satellite measurements Meteorological forecast models and re-analyses

NABOS Summer School 2006 Kapitan Dranitsyn © University of Miami, RSMAS

NABOS Summer School 2006

NABOS Summer School 2006 Kapitan Dranitsyn © University of Miami, RSMAS

Surface heat budget The surface heat budget has two components: Radiative fluxes: Short wave insolation (summer, only), dependent on solar geometry (sun above horizon) and state of the atmosphere (moisture, aerosols and clouds); Long wave emission from the atmosphere (year round) dependent on the state of the atmosphere (moisture, aerosols and clouds). Turbulent fluxes: Sensible heat flux – dependent on air sea temperature difference, wind speed, surface roughness; Latent heat flux – dependent on humidity of the atmospheric surface, wind speed, surface roughness.

Surface and radiative exchanges The fraction of sunlight (both direct and diffuse) that a surface reflects is called its albedo. Snow have very high albedos; open ground has a low albedo. Transitions can be on time and spatial scales. The albedo is also a spectrally varying quantity

What more important? For the summer season, turbulent fluxes are secondary to radiative fluxes, in terms of heat budget. For the winter season (polar night), long-wave radiation and turbulent fluxes are dominates

Radiative fluxes generally more important than sensible fluxes Minnett, 1995 Summertime conditions. Large standard deviation in SW is caused by diurnal range of solar zenith angle. Turbulent fluxes ≈ 0 Minnett, 1995

Mathematical description of heat balance (HB) HB – defined by equation, consist of Σ(+) and Σ(-): incoming and out going heat and radiation fluxes (surface, layer…) HB equation – private form of energy saving law t=t1 t=t2 Σ (Qsw + Qlw+ Qshf + Qlhf) = ∆Qa-s (=0, ҂0) ∆Qa-s = срρV(T2 – T1) – changes of heat content of V=1 during ∆t=1

Physical meaning Radiation Balance (RB) RB – difference between incoming (↓) and out going (↑) radiation If RB = 0, SAT (ST) does not change! Radiation equilibrium!

Definition_1 RB = 0 : ↓ = ↑ !!! Typically for Earth as a planet on average per year Heat/Radiation Budget - ↓ ≠ ↑ Heat Content (HC) – heat enclosed in the test column of ground (snow, ice, water)

Definition_2 Heat Storage (HS) – difference between the moment (current) heat content and a smallest (minimum) heat content during year ±∆Q Layer

Составляющие радиационного баланса подстилающей поверхности Q=(1-α)Rs – солнечная радиация Тs4- излучение Земли RT - противоизлучение атмосферы Eэф = RT – εgσTs4 - эффективное излучение Rп – радиационный баланс подстилающей поверхности

Definiton_3 Reflection of solar radiation. Albedo α β Backscattering Q R1 R2 Albedo = (R1+R2)/Q

Mirror albedo Frenel formula (“mirror” surface, no backscattering) A = 0.5[sin2(f-r)/sin2(f+r) + tg2(f-r)/tg2(f+r)] f – incidence angle; r - refraction angle, sin(f) = 1.34 sin(r)