In:
Geoscientific Model Development, Copernicus GmbH, Vol. 14, No. 6 ( 2021-06-04), p. 3335-3359
Abstract:
Abstract. Aerosol–cloud interactions contribute to a large portion of the spread in
estimates of climate forcing, climate sensitivity and future projections. An
important part of this uncertainty is how much new particle formation (NPF)
contributes to cloud condensation nuclei (CCN) and, furthermore, how this
changes with changes in anthropogenic emissions. Incorporating NPF and early
growth in Earth system models (ESMs) is, however, challenging due to
uncertain parameters (e.g. participating vapours), structural issues
(numerical description of growth from ∼1 to ∼100 nm) and
the large scale of an ESM grid compared to the NPF scale. A common approach in
ESMs is to represent the particle size distribution by a certain number of
log-normal modes. Sectional schemes, on the other hand, in which the size
distribution is represented by bins, are considered closer to first principles
because they do not make an a priori assumption about the size distribution. In order to improve the representation of early growth, we have implemented a
sectional scheme for the smallest particles (5–39.6 nm diameter) in
the Norwegian Earth System Model (NorESM), feeding particles into the original
aerosol scheme. This is, to our knowledge, the first time such an approach
has been tried. We find that including the sectional scheme for early growth
improves the aerosol number concentration in the model when comparing against
observations, particularly in the 50–100 nm diameter range.
Furthermore, we find that the model with the sectional scheme produces much
fewer particles than the original scheme in polluted regions, while it produces
more in remote regions and the free troposphere, indicating a potential impact
on the estimated aerosol forcing. Finally, we analyse the effect on
cloud–aerosol interactions and find that the effect of changes in NPF
efficiency on clouds is highly heterogeneous in space. While in remote
regions, more efficient NPF leads to higher cloud droplet number concentration
(CDNC), in polluted regions the opposite is in fact the case.
Type of Medium:
Online Resource
ISSN:
1991-9603
DOI:
10.5194/gmd-14-3335-2021
DOI:
10.5194/gmd-14-3335-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2456725-5
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