TransportTracers simulation

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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 information was computed from recent 1-year Rn-Pb-Be benchmark simulations.

GEOS-5 vs. MERRA

Helen Amos ran several 1-year Rn-Pb-Be simulations with to look at how Pb210 wet deposition is affected by GEOS-5 and MERRA meteorology:

  1. GEOS-5 std: Simulation with the standard GEOS-Chem v9-01-02 code, using with GEOS-5 met fields
  2. MERRA std: Simulation with the standard GEOS-Chem v9-01-02 code, using with MERRA met fields
  3. MERRA met GEOS-5 wet dep: Simulation using with MERRA met fields and GEOS-5 wet deposition algorithms
  4. GEOS-5 w/ Wang et al. (2011) aerosol washout: Simulation using with GEOS-5 met fields and Qiaoqiao Wang's updates for aerosol washout (updated snow scavenging and updated scavenging coefficients for liquid precip).

Helen also prepared the following comparison plots from these simulations:

Comparison
GEOS-5 standard simulation (Run 1) vs. MERRA standard simulation (Run 2) January July
GEOS-5 standard simulation (Run 1) vs. MERRA simulation w/ GEOS-5 wetdep algorithms (Run 3) January July
GEOS-5 standard simulation (Run 1) vs. GEOS-5 simulation w/ Wang et al (2011) aerosol washout (Run 4) January July

--Bob Y. 12:46, 29 November 2011 (EST)

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
w/ GEOS-5 		v9-01-01
w/ GEOS-5 		v9-01-02
w/ GEOS-5
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
w/ GEOS-5 		v9-01-01
w/ GEOS-5 		v9-01-02
w/ GEOS-5
Burden (g) 4.31961 4.39407 4.39653
Residence time (days) 33.9930 34.8514 34.8814
Sources (g day-1)
from Stratosphere
 0.0504585 0.0504328 0.0504253
within Troposphere
 0.132552 0.132552 0.132552
Sinks (g day-1)
Dry Deposition
 0.00808056 0.00969345 0.00936374
Wet Deposition
 0.118666 0.116060 0.116350
Stratiform
 0.0846774 0.0767926 0.0769681
Convective
 0.0339885 0.0392671 0.0393817
Radioactive decay
 0.0562636 0.0572312 0.0572633

--Bob Y. 13:58, 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)

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