Bond Dissociation Enthalpy

[AndrewJConley]

We need to include heating due to bond energy changes in the MUSICA system to support WACCM simulations.

In the upper atmosphere, bond dissociation enthalpy contributes to two changes in heating rates. Those heating rates start to become relevant in the upper stratosphere.

1. Absorbed solar flux for O3 and O2 leads to both heating and bond dissociation. If one computes solar heating without removing the bond dissociation, the solar heating is too large.
2. Polar mesospheric heating. A significant portion of the heating rate of upper atmosphere wintertime heating in the poles is due to exothermic reactions

In the CAM-chem system, these computations have been performed in two places. The exothermic heating has been computed as part of the solution of the mechanism. The bond dissociation endothermic heating has been computed as a separate (shortward of 200nm and longward of 200nm) radiative transfer (Beer's Law) computation.

[AndrewJConley]

There are many ways we could include these heating terms.

1. Adding bond dissociation energy to the mechanism
2. Including bond energy for every molecule in the system
3. Continuing with the current CAM-chem approach