Evaluation of the sectional aerosol microphysics module SALSA implementation in ECHAM5-HAM aerosol-climate model 1Finnish Meteorological Institute, Kuopio Unit, Kuopio, Finland
Model description paper
18 Jun 2012
2University of Helsinki, Department of Physics, Helsinki, Finland
3Finnish Meteorological Institute, Climate Change, Helsinki, Finland
4University of Eastern Finland, Department of Applied Physics, Kuopio, Finland
Received: 18 Nov 2011 – Published in Geosci. Model Dev. Discuss.: 14 Dec 2011Abstract. We present the implementation and evaluation of a sectional aerosol
microphysics module SALSA within the aerosol-climate model ECHAM5-HAM. This
aerosol microphysics module has been designed to be flexible and
computationally efficient so that it can be implemented in regional or global
scale models. The computational efficiency has been achieved by minimising
the number of variables needed to describe the size and composition
distribution. The aerosol size distribution is described using 10 size
classes with parallel sections which can have different chemical
compositions. Thus in total, the module tracks 20 size sections which cover
diameters ranging from 3 nm to 10 μm and are divided into three
subranges, each with an optimised selection of processes and compounds.
Revised: 10 May 2012 – Accepted: 12 May 2012 – Published: 18 Jun 2012
The implementation of SALSA into ECHAM5-HAM includes the main aerosol
processes in the atmosphere: emissions, removal, radiative effects,
liquid and gas phase sulphate chemistry, and the aerosol microphysics.
The aerosol compounds treated in the module are sulphate, organic
carbon, sea salt, black carbon, and mineral dust. In its default
configuration, ECHAM5-HAM treats aerosol size distribution using the
modal method. In this implementation, the aerosol processes were
converted to be used in a sectional model framework.
The ability of the module to describe the global aerosol properties was
evaluated by comparing against (1) measured continental and marine size
distributions, (2) observed variability of continental number
concentrations, (3) measured sulphate, organic carbon, black carbon and sea-salt
mass concentrations, (4) observations of aerosol optical depth (AOD)
and other aerosol optical
properties from satellites and AERONET network, (5) global aerosol budgets
and concentrations from previous model studies, and (6) model results using
M7, which is the default aerosol microphysics module in ECHAM5-HAM.
The evaluation shows that the global aerosol properties can be reproduced
reasonably well using a coarse resolution of 10 sections in size
space. The simulated global aerosol budgets are within the range of previous
studies. Surface concentrations of sulphate and carbonaceous
species have an annual mean within a factor of two of the observations.
The simulated sea-salt concentrations reproduce the observations within
a factor of two, apart from the Southern Ocean over which the concentrations
are within a factor of five. Regionally, AOD is in a relatively good
agreement with the observations (within a factor of two). At mid-latitudes
the observed AOD is captured well, while at high-latitudes as well as in some
polluted and dust regions the modelled AOD is significantly lower than
Regarding most of the investigated aerosol properties, the
SALSA and the modal aerosol module M7 perform comparably well against observations.
However, SALSA reproduces the observed number concentrations
and the size distribution of CCN sized particles much more accurately than
M7, and is therefore a good choice for aerosol-cloud interaction studies in
global models. Our study also shows that when activation type
nucleation in the boundary layer is included, the observed concentration of
particles under 50 nm in diameter are reproduced much better compared to
when only binary nucleation in the free troposphere is assumed.
Citation: Bergman, T., Kerminen, V.-M., Korhonen, H., Lehtinen, K. J., Makkonen, R., Arola, A., Mielonen, T., Romakkaniemi, S., Kulmala, M., and Kokkola, H.: Evaluation of the sectional aerosol microphysics module SALSA implementation in ECHAM5-HAM aerosol-climate model, Geosci. Model Dev., 5, 845-868, doi:10.5194/gmd-5-845-2012, 2012.