The microphysics of clouds over the Antarctic Peninsula – Part 2: modelling aspects within Polar WRF

Abstract

Abstract. The first intercomparisons of cloud microphysics schemes implemented in the Weather Research and Forecasting (WRF) mesoscale atmospheric model (version 3.5.1) are performed on the Antarctic Peninsula using the polar version of WRF (Polar WRF) at 5 km resolution, along with comparisons to the British Antarctic Survey's aircraft measurements (presented in part 1 of this work; Lachlan-Cope et al., 2016). This study follows previous works suggesting the misrepresentation of the cloud thermodynamic phase in order to explain large radiative biases derived at the surface in Polar WRF continent-wide (at 15 km or coarser horizontal resolution) and in the Polar WRF-based operational forecast model Antarctic Mesoscale Prediction System (AMPS) over the Larsen C Ice Shelf at 5 km horizontal resolution. Five cloud microphysics schemes are investigated: the WRF single-moment five-class scheme (WSM5), the WRF doublemoment six-class scheme (WDM6), the Morrison doublemoment scheme, the Thompson scheme, and the MilbrandtYau double-moment seven-class scheme. WSM5 (used in AMPS) and WDM6 (an upgrade version of WSM5) lead to the largest biases in observed supercooled liquid phase and surface radiative biases. The schemes simulating clouds in closest agreement to the observations are the Morrison, Thompson, and Milbrandt schemes for their better average prediction of occurrences of clouds and cloud phase. Interestingly, those three schemes are also the ones allowing for significant reduction of the longwave surface radiative bias over the Larsen C Ice Shelf (eastern side of the peninsula). This is important for surface energy budget consideration with Polar WRF since the cloud radiative effect is more pronounced in the infrared over icy surfaces. Overall, the Morrison scheme compares better to the cloud observation and radiation measurements. The fact that WSM5 and WDM6 are single-moment parameterizations for the ice crystals is responsible for their lesser ability to model the supercooled liquid clouds compared to the other schemes. However, our investigation shows that all the schemes fail at simulating the supercooled liquid mass at some temperatures (altitudes) where observations show evidence of its persistence. An ice nuclei parameterization relying on both temperature and aerosol content like DeMott et al. (2010) (not currently used in WRF cloud schemes) is in best agreement with the observations, at temperatures and aerosol concentration characteristic of the Antarctic Peninsula where the primary ice production occurs (part 1), compared to parameterization only relying on the atmospheric temperature (used by the WRF cloud schemes). Overall, a realistic double-moment ice microphysics implementation is needed for the correct representation of the supercooled liquid phase in Antarctic clouds. Moreover, a more realistic ice-nucleating particle alone is not enough to improve the cloud modelling, and water vapour and temperature biases also need to be further investigated and reduced.

In situ measurements of cloud microphysics and aerosol over coastal Antarctica during the MAC campaign

“…Below −9 • C, where secondary ice production is likely to be less significant, Listowski and Lachlan-Cope (2017) found that the number of INPs predicted by DeMott et al (2010) gave better agreement with observed ice concentrations over the Antarctic Peninsula compared to INP parameterisations that only use the ambient temperature as input. For MAC, each in-cloud data point was compared with the closest (in time) out-of-cloud aerosol measurement (1 min average, RH < 90 %).…”

“…The remote location and harsh conditions cause significant logistical challenges for field projects in this region. As a consequence, there is evidence that clouds and their radiative properties are poorly represented in weather and climate models over Antarctica (Bromwich et al, 2013;King et al, 2015;Listowski and Lachlan-Cope, 2017) and the Southern Ocean .…”

Microphysics of Snowfall Over Coastal East Antarctica Simulated by Polar WRF and Observed by Radar

“…For domains with a resolution greater or equal than 9 km, the Kain‐Fritsch cumulus scheme has been activated. This physical package was set after consideration of previous evaluation studies (Bromwich et al, ; Deb et al, ; Listowski & Lachlan‐Cope, ; Young et al, ) and preliminary sensitivity tests over Adélie Land.…”

“…As our study will focus on regional simulations, we will perform sensitivity tests upon the choice among bulk schemes only. Using recent airborne measurements, Listowski and Lachlan‐Cope () have assessed the performances of five bulk microphysical schemes in Polar WRF to represent clouds over the Antarctic Peninsula. The authors showed that the WRF single‐moment scheme 5—WSM5 (Hong et al, ), used in the Antarctic Mesoscale Prediction System—and the WRF Double moment scheme 6—WDM6 (Lim & Hong, ), an upgrade version of WSM5—showed the largest biases in observed supercooled liquid water.…”

Radiative Effects of Secondary Ice Enhancement in Coastal Antarctic Clouds

“…As an optical array shadow probe, the 2-DS images particles of (nominal) sizes from 10 to 1,280 m and can only skilfully conduct phase separation in mixed-phase clouds at particle sizes >80 m; therefore, we exclusively compare between observations and model data in this size range. The Morrison cloud microphysics scheme (Morrison et al, 2005, hereafter, M05) was used within version 3.6.1 of the PolarWRF model: M05 has been previously shown to perform well in reproducing Antarctic clouds by reducing biases in both the cloud supercooled liquid water and the associated surface radiative fluxes in simulations over the eastern Antarctic Peninsula (Listowski & Lachlan-Cope, 2017). Further details on observational data are included in supporting information S1 (Baumgardner et al, 2001;Glen & Brooks, 2013).…”