Description

To improve the treatment of stratospheric water vapor in the global model, NCEP implemented a parameterization of photochemical production and loss (P-L) of water vapor through methane oxidation and photolysis of H2O in the upper mesosphere due to solar Lyman alpha absorption is implemented in GFS.

The Navy Research Laboratory (NRL) linearized parameterization of stratospheric and mesospheric water vapor photochemistry (McCormack at al. (2008) [135]) applies a linearized photochemical tendency to specific humidity q in the form

\[ \frac{dq}{dt}=(P-L)_{0}+\frac{\partial (P-L)}{\partial q}\mid_{0}(q-q_{0}) \]

The second term on the right-hand side quantifies the linearized sensitivity to local changes in \(q\), and yields photochemical relaxation to an equilibrium specific humidity \(q_{0}\)

\[ -[\frac{\partial (P-L)}{\partial q}]_{0}=\tau_*^{-1} \]

The \((P-L)_{0}\) and \(\tau_*\) values were computed from perturbation experiments with the NRL two-dimensional photochemical model (CHEM2D). The equilibrium profile \(q_{0}\) is specified using a climatology based on a combination of reanalysis and satellite observations.

Intraphysics Communication

Argument Table

General Algorithm

GFS H2O Physics Scheme General Algorithm