Total Enthalpy of Ice Model?

[citibeth]

I would like to obtain the total state of energy of the PISM ice sheet, and also to understand the inflows and outflows. Some questions, which I think I have answers to but would like verification if possible:

1. Is it really true that an Enthalpy Reference Temperature = 223.15K was chosen by default? I'm curious about the rationale for this.
   T_0 = config.get("enthalpy_converter_reference_temperature");// K
   Are there any limits on what I could set that reference temperature to? Easiest would be to set it to match what ModelE uses.
2. If ModelE and PISM need to use different enthalpy reference temperatures, it looks like I can do so by adding/subtracting a constant. Or alternatively, maybe it's more robust to compute E,p and omega in ModelE space, then call getWaterFraction() (or the reverse, to convert the other direction)?
3. How do I get the pressure of the basal water? It looks like I can just ask for this, via: PISMHydrology::subglacial_water_pressure()
4. How do I compute the enthalpy of the basal "runoff"? In the Null "can" hydrology model, this is water sitting at the bottom of the ice sheet that "disappears." Hence, it is under pressure p (see 2), and in equilibrium with the ice sheet, hence it's at the pressure melting point for p. It seems, then, that I can ask the Enthalpy converter:
   T = getMeltingTemp(p); enthalpy = getEnth(T, 1.0, p);
   or maybe: getEnthalpyInterval(p, junk, enthalpy)
5. How do I compute the total enthalpy of the ice model? I suppose I just use IceModel::Enth3 [J/kg].
6. How can I compute enthalpy in J/m^3? I suppose I just do IceModel::Enth3 / rho_ice.
7. How can I compute enthalpy in J/m^2? This should just be the result of sum_columns() on (5). (sum_columns() was already developed to sum strain_heating).
8. I see there are two enthalpy converters in PISM. Which ones are used when, and what is the default? (See EnthalpyConverter *IceModel::EC. varcEnthalpyConverter is used in case of the use_linear_in_temperature_heat_capacity flag).
9. What is the energy balance of the ice sheet, in J/m^2? I'm assuming we have:
   [Total Enthalpy]_(t+1) = [Total Enthalpy]_t + dt * ([Strain Heating] + [Enthalpy of SMB] - [Enthalpy of basal runoff] + [Geothermal Flux] + [Enthalpy gained/lost through top T boundary condition])

Am I missing anything here?