Low (web) Quality - BALTEX

238
Numerical modeling of trace species cycles in regional climate model
systems
Bärbel Langmann
Institute of Geophysics, University of Hamburg, Bundesstr. 55, Germany, baerbel.langmann@zmaw.de
1. Introduction
In recent years, numerous atmospheric regional and global
climate models have been extended by modules for transport
and transformation of trace species (Zhang, 2008) to
improve the numerical simulation of atmospheric trace
species cycles, their impact on climate and vice versa. This
is an important step from the chemical and climate point of
view, as the on-line methodology offers several advantages
compared to the off-line methodology, where chemical and
meteorological processes are determined in separate models.
Examples for such regional scale models are GATOR-
GCMM (Jacobson, 2001), REMOTE (Langmann, 2000) and
WRF (Grell et al., 2005).
A further extension towards regional Earth system models is
to couple ocean and atmosphere biogeochemical models on
the regional scale, with the potential to offer new insights
into exchange processes of climate relevant trace species
between the ocean and the atmosphere. Aerosols in the
marine atmosphere influence solar irradiation over the
world’s ocean directly by backscattering incoming solar
radiation and indirectly, by forming cloud condensation
nuclei thereby affecting the cloud albedo. In recent years,
the role of natural organic aerosol (OC) in the marine
environment has received increasing attention.
Measurements indicate that the increase of the marine
biological activity is accompanied by a considerable
increase of the contribution of OC to the submicron marine
aerosol (e.g. O’Dowd et al., 2004) exceeding the mass
fraction of nss sulfate by a factor of more than two. Here the
recent developments of and future plans with the regional
scale climate-chemistry/aerosol model REMOTE are
presented together with selected applications.
2. Model description
The regional scale three-dimensional on-line atmospherechemistry/aerosol
model REMOTE (Regional Model with
Tracer Extension, www.mpimet.mpg.de/en/wissenschaft/
modelle/remote.html) (Langmann, 2000; Langmann et al.,
2008) is one of the few regional climate models that
determines the physical, photochemical and aerosol state of
the atmosphere at every time step thus offering the
possibility to consider trace species effects on climate as
well (e.g. Langmann, 2007). The dynamical part of the
model is based on the former regional weather forecast
system of the German Weather Service (Majewski, 1991)
which is using a hydrostatic assumption for the vertical
pressure gradient. In addition to the German Weather
Service physical parameterisations, those of the global
climate model ECHAM-4 (Roeckner et al., 1996) have been
implemented in REMOTE and are used for most
applications since 2000.
There are different trace species modules available: a
photochemical module, stable water isotopes have been
studied (e.g. Sturm et al., 2005), carbon dioxide (e.g.
Karstens et al., 2006) and recently an aerosol microphysical
module has been implemented in addition to the
photochemical one (Langmann et al., 2008). A study on the
second indirect aerosol effect is described in Langmann
(2007). The model is flexible to be applied all over the
world: many applications focus on Europe, some studies
on Indonesia, South America, Nicaragua and India.
Meanwhile the model is applied in Indonesia, China,
Germany, UK and Ireland, where it is further developed to
study a variety of scientific questions.
3. Selected applications
Recently, O’Dowd et al. (2008) published a novel
approach to develop a combined organic-inorganic submicron
sea-spray source function for inclusion in largescale
models. It requires wind speed and surface ocean
chlorophyll-a concentration as input parameters. The
combined organic-inorganic source function was
implemented in REMOTE and sea-spray fields are
predicted with particular focus on the North East Atlantic.
The model predictions for primary organic carbon (POC)
using the new source functions (Fig. 1, 2) compare well
with observations of total sea-spray mass and organic
carbon fraction in sea-spray aerosol.
Figure 1. REMOTE model results for marine POC
[ug/m 3 ] in surface air during January (left figure)
and June 2003 (right figure).
Figure 2. REMOTE model results for the fraction of
marine POC in accumulation mode sea-spray [%] in
surface air during January (left figure) and June
2003 (right figure).