Evaluation of cloud convection and tracer transport in a three-dimensional chemical transport model 1NCAS, Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UK
22 Jun 2011
2NCAS, Department of Chemistry, University of Cambridge, Cambridge, UK
3Max-Planck-Institut für Meteorologie, Hamburg, Germany
4LSCE/IPSL, CEA-CNRS-UVSQ, France
Received: 02 Sep 2010 – Published in Atmos. Chem. Phys. Discuss.: 06 Oct 2010 Abstract. We investigate the performance of cloud convection and tracer
transport in a global off-line 3-D chemical transport model.
Various model simulations are performed using different
meteorological (re)analyses (ERA-40, ECMWF operational and
ECMWF Interim) to diagnose the updraft mass flux, convective
precipitation and cloud top height.
Revised: 15 Jun 2011 – Accepted: 17 Jun 2011 – Published: 22 Jun 2011
The diagnosed upward mass flux distribution from TOMCAT agrees
quite well with the ECMWF reanalysis data (ERA-40 and
ERA-Interim) below 200 hPa. Inclusion of midlevel convection
improves the agreement at mid-high latitudes. However, the
reanalyses show strong convective transport up to 100 hPa,
well into the tropical tropopause layer (TTL), which is not
captured by TOMCAT. Similarly, the model captures the spatial
and seasonal variation of convective cloud top height although
the mean modelled value is about 2 km lower than observed.
The ERA-Interim reanalyses have smaller archived upward
convective mass fluxes than ERA-40, and smaller convective
precipitation, which is in better agreement with
satellite-based data. TOMCAT captures these relative
differences when diagnosing convection from the large-scale
fields. The model also shows differences in diagnosed
convection with the version of the operational analyses used,
which cautions against using results of the model from one
specific time period as a general evaluation.
We have tested the effect of resolution on the diagnosed
modelled convection with simulations ranging from 5.6° × 5.6° to 1° × 1°. Overall, in the off-line model, the higher model
resolution gives stronger vertical tracer transport,
however, it does not make a large change to the diagnosed
convective updraft mass flux (i.e., the model results
using the convection scheme fail to capture the strong convection
transport up to 100 hPa as seen in the archived convective
mass fluxes). Similarly, the resolution of the
forcing winds in the higher resolution CTM does not make
a large improvement compared to the archived mass fluxes.
Including a radon tracer in the model confirms the importance
of convection for reproducing observed midlatitude
profiles. The model run using archived mass fluxes transports
significantly more radon to the upper troposphere but the
available data does not strongly discriminate between the
different model versions.
Citation: Feng, W., Chipperfield, M. P., Dhomse, S., Monge-Sanz, B. M., Yang, X., Zhang, K., and Ramonet, M.: Evaluation of cloud convection and tracer transport in a three-dimensional chemical transport model, Atmos. Chem. Phys., 11, 5783-5803, doi:10.5194/acp-11-5783-2011, 2011.