In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 20, No. 15 ( 2020-08-13), p. 9491-9524
Abstract:
Abstract. The effect of observational constraint on the ranges of
uncertain physical and chemical process parameters was explored in a global
aerosol–climate model. The study uses 1 million variants of the Hadley Centre General Environment Model version 3
(HadGEM3) that sample 26 sources of uncertainty, together with over 9000
monthly aggregated grid-box measurements of aerosol optical depth, PM2.5,
particle number concentrations, sulfate and organic mass concentrations.
Despite many compensating effects in the model, the procedure constrains the
probability distributions of parameters related to secondary organic
aerosol, anthropogenic SO2 emissions, residential emissions, sea spray
emissions, dry deposition rates of SO2 and aerosols, new particle
formation, cloud droplet pH and the diameter of primary combustion
particles. Observational constraint rules out nearly 98 % of the model
variants. On constraint, the ±1σ (standard deviation) range
of global annual mean direct radiative forcing (RFari) is reduced by
33 % to −0.14 to −0.26 W m−2, and the 95 % credible interval (CI)
is reduced by 34 % to −0.1 to −0.32 W m−2. For the global annual
mean aerosol–cloud radiative forcing, RFaci, the ±1σ
range is reduced by 7 % to −1.66 to −2.48 W m−2, and the 95 % CI by
6 % to −1.28 to −2.88 W m−2. The tightness of the constraint is
limited by parameter cancellation effects (model equifinality) as well as
the large and poorly defined “representativeness error” associated with
comparing point measurements with a global model. The constraint could also
be narrowed if model structural errors that prevent simultaneous agreement
with different measurement types in multiple locations and seasons could be
improved. For example, constraints using either sulfate or PM2.5
measurements individually result in RFari±1σ ranges
that only just overlap, which shows that emergent constraints based on one
measurement type may be overconfident.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-20-9491-2020
DOI:
10.5194/acp-20-9491-2020-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2020
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
