In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 20, No. 21 ( 2020-11-09), p. 13145-13165
Abstract:
Abstract. Clouds play a potentially important role in Arctic climate change but are poorly represented in current atmospheric models across scales. To
improve the representation of Arctic clouds in models, it is necessary to compare models to observations to consequently reduce this
uncertainty. This study compares aircraft observations from the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD)
campaign around Svalbard, Norway, in May–June 2017 and simulations using the ICON (ICOsahedral Non-hydrostatic) model in its numerical weather
prediction (NWP) setup at 1.2 km horizontal resolution. By comparing measurements of solar and terrestrial irradiances during ACLOUD
flights to the respective properties in ICON, we showed that the model systematically overestimates the transmissivity of the mostly liquid clouds
during the campaign. This model bias is traced back to the way cloud condensation nuclei (CCN) get activated into cloud droplets in the two-moment
bulk microphysical scheme used in this study. This process is parameterized as a function of grid-scale vertical velocity in the microphysical scheme
used, but in-cloud turbulence cannot be sufficiently resolved at 1.2 km horizontal resolution in Arctic clouds. By parameterizing
subgrid-scale vertical motion as a function of turbulent kinetic energy, we are able to achieve a more realistic CCN activation into cloud
droplets. Additionally, we showed that by scaling the presently used CCN activation profile, the hydrometeor number concentration could be modified
to be in better agreement with ACLOUD observations in our revised CCN activation parameterization. This consequently results in an improved
representation of cloud optical properties in our ICON simulations.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-20-13145-2020
DOI:
10.5194/acp-20-13145-2020-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2020
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1