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| Titel |
Representation of nucleation mode microphysics in a global aerosol model with sectional microphysics |
| VerfasserIn |
Y. H. Lee, J. R. Pierce, P. J. Adams |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 6, no. 4 ; Nr. 6, no. 4 (2013-08-13), S.1221-1232 |
| Datensatznummer |
250084973
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| Publikation (Nr.) |
 copernicus.org/gmd-6-1221-2013.pdf |
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| Zusammenfassung |
| In models, nucleation mode (1 nm < Dp < 10 nm) particle
microphysics can be represented explicitly with aerosol microphysical
processes or can be parameterized to obtain the growth and survival of
nuclei to the model's lower size boundary. This study investigates how the
representation of nucleation mode microphysics impacts aerosol number
predictions in the TwO-Moment Aerosol Sectional (TOMAS) aerosol microphysics
model running with the GISS GCM II-prime by varying its lowest diameter
boundary: 1 nm, 3 nm, and 10 nm. The model with the 1 nm boundary simulates
the nucleation mode particles with fully resolved microphysical processes,
while the model with the 10 nm and 3 nm boundaries uses a nucleation mode
dynamics parameterization to account for the growth of nucleated particles
to 10 nm and 3 nm, respectively. We also investigate the impact of the time
step for aerosol microphysical processes (a 10 min versus a 1 h time
step) to aerosol number predictions in the TOMAS models with explicit
dynamics for the nucleation mode particles (i.e., 3 nm and 1 nm boundary).
The model with the explicit microphysics (i.e., 1 nm boundary) with the
10 min time step is used as a numerical benchmark simulation to estimate
biases caused by varying the lower size cutoff and the time step. Different
representations of the nucleation mode have a significant effect on the
formation rate of particles larger than 10 nm from nucleated particles
(J10) and the burdens and lifetimes of ultrafine-mode (10 nm ≤ Dp ≤ 70 nm) particles but have less impact on the burdens and
lifetimes of CCN-sized particles. The models using parameterized
microphysics (i.e., 10 nm and 3 nm boundaries) result in higher J10 and
shorter coagulation lifetimes of ultrafine-mode particles than the model
with explicit dynamics (i.e., 1 nm boundary). The spatial distributions of
CN10 (Dp ≥ 10 nm) and CCN(0.2%) (i.e., CCN concentrations
at 0.2% supersaturation) are moderately affected, especially CN10
predictions above ~ 700 hPa where nucleation contributes most
strongly to CN10 concentrations. The lowermost-layer CN10 is substantially
improved with the 3 nm boundary (compared to 10 nm) in most areas. The
overprediction in CN10 with the 3 nm and 10 nm boundaries can be explained
by the overprediction of J10 or J3 with the parameterized
microphysics, possibly due to the instantaneous growth rate assumption in the
survival and growth parameterization. The errors in CN10 predictions are
sensitive to the choice of the lower size boundary but not to the choice of
the time step applied to the microphysical processes. The spatial
distribution of CCN(0.2%) with the 3 nm boundary is almost identical to
that with the 1 nm boundary, but that with the 10 nm boundary can differ
more than 10–40% in some areas. We found that the deviation in the 10 nm
simulations is partly due to the longer time step (i.e., 1 h time step
used in the 10 nm simulations compared to 10 min time step used in the
benchmark simulations), but, even with the same time step, the 10 nm cutoff
showed noticeably higher errors than the 3 nm cutoff. In conclusion, we
generally recommend using a lower diameter boundary of 3 nm for studies
focused on aerosol indirect effects but down to 1 nm boundary for studies
focused on CN10 predictions or nucleation. |
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