Additional diagnostics

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Additional diagnostics can be obtained by combining the standard GEOS-Chem outputs. This page presents some of them.

Vertical wind

Since dP/dt is a conventional unit in atmospheric chemistry, we can proceed as follows to convert a vertical flux into vertical velocity.

The parameters used are ND45 (mixing ratio), ND26 (upward flux), and ND68 (box height, air mass, air density).

The air density must be converted from [molec/m3] to [Kg/m3]:

   Air_Density [Kg/m3] = Air_Density [molec/m3] * 28.9e3 / Avogadro_Number

To calculate the vertical velocity you must choose one tracer that you included in the ND26 diagnostic. For example, if we use CO (molecular weight 28):

   Air_Mass_Flux [Kg/s] = ND26_Up_Flux(CO) [Kg/s] / ND45_Mixing_Ratio(CO)   *  28.9 / 28

   Vertical_velocity [m/s] = Air_Mass_Flux [Kg/s] * Box_Height [m]/Airmass[Kg]

or in the preferred dP/dt format:

   dP/dt = Air_Mass_Flux [Kg/s] * Box_Height [m]/Airmass[Kg]  *  Air_Density [Kg/m3] * 9.8 [m/s2]  (1)

Note that

   Air_Density [Kg/m3] * Box_Height [m] / Airmass[Kg] = 1 / surface [m2]

so you can get the box surface from the grid description (see ctm_boxsize) and replace (1) with:

   dP/dt = Air_Mass_Flux [Kg/s] * 9.8 [m/s2] / surface [m2]  (2)

By using (2), you do not need ND68 anymore.

--phs 17:19, 15 January 2009 (EST)