Team 3694 Page 10 of 37 Mass balance ablate We then model the two parts of ablation, sublimation and melting Sublimation rate(mass flux )is given by M (T TRT where M is the molecular weight of water. This expression can be derived from the ideal gas law and the Maxwell-Boltzmann distribution. Substituting Buck's expression for e sat we obtain 18.678-/34s)r S=6.1121e 2nR(T+273.15) Buck's equation is applicable over a large range of temperatures and pressures, including the environment of Greenland. The approximation fails at extreme temperatures and pressures but is computationally simple(relatively ) To convert mass flux into rate of thickness change of the ice, we divide the mass flux expression by the density of ice Thus we can express rate of height change as follows 6.1121·d 257.14+T Sh 2mR(T+273.15 where d is the deposition factor, given by d=(l-deposition rate)=0.01. This term is needed because sublimation and deposition are in constant equilibrium. with the sublimation rate expression, it is now trivial to find the thickness of the ice sheet after one timestep of the computational model. Indeed, the new thickness due to ablation via given S(1)=h-STeam # 3694 Page 10 of 37 Mass Balance - Ablation We then model the two parts of ablation, sublimation and melting. Sublimation rate (mass flux) is given by: 2 1 0 2 ( )       = RT M S e T w sat π (6) where Mw is the molecular weight of water. This expression can be derived from the ideal gas law and the Maxwell-Boltzmann distribution . Substituting Buck’s expression for esat, we obtain: ( ) 2 1 257.14 234.5 18.678 0 2 ( 273.15) 6.1121         + = ⋅           + − R T M S e w T T T π (7) Buck’s equation is applicable over a large range of temperatures and pressures, including the environment of Greenland. The approximation fails at extreme temperatures and pressures but is computationally simple (relatively). To convert mass flux into rate of thickness change of the ice, we divide the mass flux expression by the density of ice. Thus we can express rate of height change as follows: ( ) 2 1 257.14 234.5 18.678 2 ( 273.15) 6.1121         + ⋅ ⋅ =           + − R T M e d S w T T T ice h ρ π (8) where d is the deposition factor, given by d = (1-deposition rate) = 0.01 . This term is needed because sublimation and deposition are in constant equilibrium. With the sublimation rate expression, it is now trivial to find the thickness of the ice sheet after one timestep of the computational model. Indeed, the new thickness due to ablation via sublimation is given by: S t h S t h ( ) = − ⋅ (9)