TransportTracers simulation

This page contains information about the Radon-Lead-Beryllium simulation in GEOS-Chem.

Overview

The Rn-Pb-Be simulation in GEOS-Chem was based on that of the old Harvard/GISS CTM model. The current simulation follows Liu et al [2001].

The standard Rn-Pb-Be simulation uses the following tracers:

1. Rn²²², which is emitted naturally from soils
2. Pb²¹⁰, which is the primary decay product of Rn²²²
3. Be⁷, which is produced by cosmic rays in the stratosphere and upper atmosphere

This simulation is most frequently used to validate the convection and advection processes in GEOS-Chem.

Sources

The source of #Rn²²² is determined as follows (cf. Jacob et al [1997]):

1. Rn²²² emission poleward of 70 degrees = 0.0 [atoms/cm2/s]
2. For latitudes 70S-60S and 60N-70N (both land & ocean), Rn²²² emission = 0.005 [atoms/cm2/s]
3. For latitudes between 60S and 60N:
   • Rn²²² over land = 1 [atoms/cm2/s] over land
   • Rn²²² over land = 0.005 [atoms/cm2/s] over oceans
4. Where the surface temperature is below 0° C, reduce Rn²²² emissions by a factor of 3.

The source of Be⁷ is taken from Lal and Peters [1967].

Sinks

Rn²²² decays into Pb²¹⁰ according to the exponential law: EXP( -ΔT * 2.097d-6 )

Pb²¹⁰ decays according to the exponential law: EXP( -ΔT * 9.725d-10 )

Be⁷ decays according to the exponential law: EXP( -ΔT * 1.506d-7 )

where -ΔT is the emission timestep in seconds.

Validation

See Liu et al [2001].

References

1. Liu, H., D. Jacob, I. Bey, and R.M. Yantosca, Constraints from 210Pb and 7Be on wet deposition and transport in a global three-dimensional chemical tracer model driven by assimilated meteorological fields, J. Geophys. Res, 106, D11, 12,109-12,128, 2001.
2. Jacob et al., Evaluation and intercomparison of global atmospheric transport models using Rn-222 and other short-lived tracers, J. Geophys. Res, 102, 5953-5970, 1997.
3. Koch, D. J. Geophys. Res, 101, D13, 18651, 1996.
4. Lal, D., and B. Peters, Cosmic ray produced radioactivity on the Earth. Handbuch der Physik, 46/2, 551-612, edited by K. Sitte, Springer-Verlag, New York, 1967.

Known issues

Incorrect Rn values caused by bug in convection_mod.f

The bug in convection_mod.f described here can cause incorrect values of Rn in GEOS-Chem v8-03-01 and prior versions.

--Bob Y. 16:17, 19 May 2011 (EDT)

Bug for ND44 diagnostic in diag3.f

In the ND44 diagnostic section of diag3.f, the following lines are present twice (once for drydep fluxes and again for drydep velocities). This is a special-case for some tracers in the Caltech isoprene scheme:

              ! Special case for tracers with several dry dep. tracers
              ! E.g. ISOPN: ISOPND and ISOPNB.
              ! We handle both tracers at the same time so we need to 
              ! skip the second tracer. (ccc, 2/3/10)
              !IF ( MMB /= NN ) CYCLE
              IF ( MMB /= NN                .OR.
    &              DEPNAME( N ) == 'ISOPNB' .OR.
    &              DEPNAME( N ) == 'MVKN'       ) CYCLE

However, these lines will cause the drydep fluxes and velocities for Be7 to be skipped. The fix is to bracket these lines with an IF statement so that they will only execute for a full-chemistry simulation:

           IF ( ITS_A_FULLCHEM_SIM() ) THEN
              ! Special case for tracers with several dry dep. tracers
              ! E.g. ISOPN: ISOPND and ISOPNB.
              ! We handle both tracers at the same time so we need to 
              ! skip the second tracer. (ccc, 2/3/10)
              !IF ( MMB /= NN ) CYCLE
              IF ( MMB /= NN                .OR.
    &              DEPNAME( N ) == 'ISOPNB' .OR.
    &              DEPNAME( N ) == 'MVKN'       ) CYCLE
           ENDIF

We will add this fix into GEOS-Chem v9-01-02.

--Bob Y. 14:09, 20 May 2011 (EDT)