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.

Note: The current version of the Rn-Pb-Be simulation (v9-01-02) is not compatible with non-local PBL mixing. You must use the TURBDAY PBL mixing scheme. (Helen Amos, 21 Nov 2011 9:02 PM EST)

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

The following budget information were computed from recent 1-year Rn-Pb-Be benchmark simulations.

Budget of Pb210

In this table we plot the budgets of Pb²¹⁰ obtained from 1-year benchmark simulations done with various GEOS-Chem versions. (Computed by Hongyu Liu)

Quantity	v8-03-02	v9-01-01	v9-01-02
Burden (g)	298.318	316.253	317.884
Residence time (days)	9.01288	9.55568	9.60957
Sources (g day-1)
from Stratosphere	0.129642	0.129852	0.121441
within Troposphere	32.9831	32.9831	32.9831
Sinks (g day-1)
Dry Deposition	3.21013	3.66397	3.49208
Wet Deposition	29.8775	29.4223	29.5857
Stratiform	21.3283	19.4090	19.5148
Convective	8.54923	10.0134	10.0709
Radioactive decay	0.0266710	0.0251665	0.0268078

--Bob Y. 13:49, 28 November 2011 (EST)

Budget of Be7

In this table we plot the budgets of Be⁷ obtained from 1-year benchmark simulations done with various GEOS-Chem versions. (Computed by Hongyu Liu)

Quantity	v8-03-02	v9-01-01	v9-01-02
Burden (g)
Residence time (days)
Sources (g day-1)
from Stratosphere
within Troposphere
Sinks (g day-1)
Dry Deposition
Wet Deposition
Stratiform
Convective
Radioactive decay

--Bob Y. 13:53, 28 November 2011 (EST)

Budget from v9-01-02

The following table (prepared by Hongyu Liu) identifies the sources & sinks of Pb²¹⁰ and Be⁷, derived from a 1-year simulation (with 4 years of spinup) done with GEOS-Chem v9-01-02.

                             210Pb         7Be
 Burden, g                   317.884      4.39653
 Residence time, days        9.60957      34.8814
 Sources, g d-1              
   from stratosphere        0.121441    0.0504253
   within troposphere        32.9831     0.132552
 Sinks, g d-1               
   dry deposition            3.49208   0.00936374
   wet deposition            29.5857     0.116350
     stratiform              19.5148    0.0769681
     convective              10.0709    0.0393817
   radioactive decay       0.0268078    0.0572633

Budget from v9-01-01

The following table (prepared by Hongyu Liu) identifies the sources & sinks of Pb²¹⁰ and Be⁷, derived from a 1-year simulation (with 4 years of spinup) done with GEOS-Chem v9-01-01.

                             210Pb         7Be
 Burden, g                   316.253      4.39407
 Residence time, days        9.55568      34.8514
 Sources, g d-1              
   from stratosphere        0.129852    0.0504328
   within troposphere        32.9831     0.132552
 Sinks, g d-1                
   dry deposition            3.66397   0.00969345
   wet deposition            29.4223     0.116060
     stratiform              19.4090    0.0767926
     convective              10.0134    0.0392671
   radioactive decay       0.0266710    0.0572312

Budget from v8-03-02

The following table (prepared by Hongyu Liu) identifies the sources & sinks of Pb²¹⁰ and Be⁷, derived from a 1-year simulation (with 4 years of spinup) done with GEOS-Chem v8-03-02.

                              210Pb         7Be
 Burden, g                   298.318      4.31961
 Residence time, days        9.01288      33.9930
 Sources, g d-1              
   from stratosphere        0.129642    0.0504585
   within troposphere        32.9831     0.132552
 Sinks, g d-1                
   dry deposition            3.21013   0.00808056
   wet deposition            29.8775     0.118666
     stratiform              21.3283    0.0846774
     convective              8.54923    0.0339885
   radioactive decay       0.0251665    0.0562636

--Bob Y. 10:48, 28 November 2011 (EST)

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.

Previous issues that are now resolved

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. This was fixed in GEOS-Chem v8-03-02.

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

Bug for ND44 diagnostic in diag3.f

NOTE: This bug was issued as a post-release patch ("v9-01-01-Patch-diags") in GEOS-Chem v9-01-01 and was approved on 07 Jun 2011.

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

--Bob Y. 11:57, 7 July 2011 (EDT)

Out-of-bounds errors in ND01, ND02 diagnostics

This issue was fixed in GEOS-Chem v9-01-02, just prior to its release.

In RnPbBe_mod.F, the ND01 (Source of Rn, Pb, Be) and ND02 (Decay of Rn, Pb, Be) diagnostics had array-out-of-bounds errors if you requested less than 47 levels.

For example, if you specified these settings in your input.geos file (assuming a GEOS-5 or MERRA simulation w/ 47 levels):

ND01: Rn/Pb/Be source   : 47   all
ND02: Rn/Pb/Be decay    : 47   all

then your run would work just fine. However, if you tried this:

ND01: Rn/Pb/Be source   :  1   all
ND02: Rn/Pb/Be decay    :  1   all

then your run would crash. In some instances, the error masked itself as an I/O error (i.e. "file not found"). This is because an out-of-bounds was probably corrupting the variables that were used to check if all of the data had been read from a particular met field file.

To prevent this from happening, we now test whether the L index is smaller or equal to LD01 (the vertical extent of the AD01 array) or LD02 (the vertical extent of the AD02 array). We have now modified all of the IF statements where the ND01 or ND02 diagnostics are invoked.

For example, we took the existing block of code:

     ! ND01 diag: 7Be emission [kg/s]
     IF ( ND01 > 0 ) THEN
        AD01(I,J,L,3) = AD01(I,J,L,3) + ( ADD_Be / DTSRCE )
     ENDIF

and add an additional test on L:

     ! ND01 diag: 7Be emission [kg/s]
     IF ( ND01 > 0 .and. L <= LD01 ) THEN
        AD01(I,J,L,3) = AD01(I,J,L,3) + ( ADD_Be / DTSRCE )
     ENDIF

etc.

We will add this fix into GEOS-Chem v9-01-02, since it does not affect the full-chemistry simulation.

--Bob Y. 11:08, 28 November 2011 (EST)

Outstanding issues

Missing drydep diagnostics caused by tracer name error

Please use the following tracer names in input.geos when setting up a Rn-Pb-Be simulation:

%%% TRACER MENU %%%     : 
Type of simulation      : 1
Number of Tracers       : 3                      
Tracer Entries -------> : TR#   Name  g/mole   Tracer Members; () = emitted 
Tracer #1               :   1   Rn     222.0  
Tracer #2               :   2   Pb     210.0
Tracer #3               :   3   Be7      7.0

If you use alternate spellings for the Rn and Pb tracers, such as:

Tracer #1               :   1   Rn222  222.0  
Tracer #2               :   2   Pb210  210.0

Then this may cause the dry deposition fluxes and frequencies for Pb²¹⁰ not to be printed out.

A fix is forthcoming in GEOS-Chem v9-01-03.

--Bob Y. 11:57, 7 July 2011 (EDT)