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Show melting surface lies to the right of that for a non- melting one. Only this dividing line follows from Equation ( 8); the other lines follow from the later-discussions. 3. The Non- melting Surface In the case of a non- melting surface, ablation is possible only by sublimation. From the water vapor flux n7 W23 W = -~- XL( E- eL) ( 9) pcp it follows that ., W 0,623 M = - = - XL( E- eL). ( 10) P P? cp where p = 1 g cm" 3 is the density of water. The vapor pressure E in Equation ( 10) is the saturation vapor pressure over ice for the corresponding temperature 7> . This, in turn, follows from the energy balance equation at the surface Q + B- XL&- bL)-^^- XL( E- eL)= 0. UD pcp As Equation ( 10) shows, the ablation - M as well as the surface temperature derived from Equation ( 1) used in its calculation depend on five quantities. These are the air temperature oy^ , the vapor pressure e, , the heat input Q+ B, the heat transfer coefficient CL. , and the air pressure p . A two- dimensional representation can embrace the relationships of only three of these quantities. In order to reduce the number of parameters in the illustration, p is held constant. Moreover, ly) "*" ( Q+^ l/ a. is taken as the abscissa, e. as the ordinate and M/ X, |