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:
- Rn222, which is emitted naturally from soils
- Pb210, which is the primary decay product of Rn222
- 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]):
- Rn222 emission poleward of 70 degrees = 0.0 [atoms/cm2/s]
- For latitudes 70S-60S and 60N-70N (both land & ocean), Rn222 emission = 0.005 [atoms/cm2/s]
- 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
- 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 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
- 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.
- 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.
- Koch, D. J. Geophys. Res, 101, D13, 18651, 1996.
- 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 v9-01-02.
--Bob Y. 11:57, 7 July 2011 (EDT)