Evaluation of polar stratospheric clouds in the global chemistry–climate model SOCOLv3.1 by comparison with CALIPSO spaceborne lidar measurements

Abstract

Abstract. Polar stratospheric clouds (PSCs) contribute to catalytic ozone destruction by providing surfaces for the conversion of inert chlorine species into active forms and by denitrification. The latter describes the removal of HNO3 from the stratosphere by sedimenting PSC particles, which hinders chlorine deactivation by the formation of reservoir species. Therefore, an accurate representation of PSCs in chemistry–climate models (CCMs) is of great importance to correctly simulate polar ozone concentrations. Here, we evaluate PSCs as simulated by the CCM SOCOLv3.1 for the Antarctic winters 2006, 2007 and 2010 by comparison with backscatter measurements by CALIOP on board the CALIPSO satellite. The year 2007 represents a typical Antarctic winter, while 2006 and 2010 are characterized by above- and below-average PSC occurrence. The model considers supercooled ternary solution (STS) droplets, nitric acid trihydrate (NAT) particles, water ice particles and mixtures thereof. PSCs are parameterized in terms of temperature and partial pressures of HNO3 and H2O, assuming equilibrium between the gas and particulate phase. The PSC scheme involves a set of prescribed microphysical parameters, namely ice number density, NAT particle radius and maximum NAT number density. In this study, we test and optimize the parameter settings through several sensitivity simulations. The choice of the value for the ice number density affects simulated optical properties and dehydration, while modifying the NAT parameters impacts stratospheric composition via HNO3 uptake and denitrification. Depending on the NAT parameters, reasonable denitrification can be modeled. However, its impact on ozone loss is minor. The best agreement with the CALIOP optical properties and observed denitrification was for this case study found with the ice number density increased from the hitherto used value of 0.01 to 0.05 cm−3 and the maximum NAT number density from 5×10-4 to 1×10-3 cm−3. The NAT radius was kept at the original value of 5 µm. The new parameterization reflects the higher importance attributed to heterogeneous nucleation of ice and NAT particles following recent new data evaluations of the state-of-the-art CALIOP measurements. A cold temperature bias in the polar lower stratosphere results in an overestimated PSC areal coverage in SOCOLv3.1 by up to 40 %. Offsetting this cold bias by +3 K delays the onset of ozone depletion by about 2 weeks, which improves the agreement with observations. Furthermore, the occurrence of mountain-wave-induced ice, as observed mainly over the Antarctic Peninsula, is continuously underestimated in the model due to the coarse model resolution (T42L39) and the fixed ice number density. Nevertheless, we find overall good temporal and spatial agreement between modeled and observed PSC occurrence and composition. This work confirms previous studies indicating that simplified PSC schemes, which avoid nucleation and growth calculations in sophisticated but time-consuming microphysical process models, may also achieve good approximations of the fundamental properties of PSCs needed in CCMs.

Polar Stratospheric Clouds: Satellite Observations, Processes, and Role in Ozone Depletion

“…SOCOL: In the SOCOL (modeling tools for studies of SOlar Climate Ozone Links) model (Steiner et al, 2021;Stenke et al, 2013), all PSC compositions are parameterized using a modal setup. Steiner et al (2021) recently compared CALIOP PSC observations with SOCOLv3 simulations in specified dynamics mode, focusing on Antarctica (C1, C2, and C3). The simulated denitrification was evaluated by comparison with HNO 3 from MLS (C6).…”

“…SOCOL: In the SOCOL (modeling tools for studies of SOlar Climate Ozone Links) model (Steiner et al., 2021; Stenke et al., 2013), all PSC compositions are parameterized using a modal setup. Steiner et al.…”

“…Steiner et al. (2021) recently compared CALIOP PSC observations with SOCOLv3 simulations in specified dynamics mode, focusing on Antarctica (C1, C2, and C3). The simulated denitrification was evaluated by comparison with HNO 3 from MLS (C6).…”

“…While the vertical and temporal distributions are similar, the EMAC simulated volume densities are a factor of three below the lower limit of the observations. SOCOL: In the SOCOL (modeling tools for studies of SOlar Climate Ozone Links) model (Steiner et al, 2021;Stenke et al, 2013), all PSC compositions are parameterized using a modal setup. Steiner et al (2021) recently compared CALIOP PSC observations with SOCOLv3 simulations in specified dynamics mode, focusing on Antarctica (C1, C2, and C3).…”

Mountain-wave-induced polar stratospheric clouds and their representation in the global chemistry model ICON-ART

“…The Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP; Pitts et al, 2009Pitts et al, , 2018Höpfner et al, 2009) on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) was launched on 28 April 2006 (Winker et al, 2007). In 2008, the satellite flew as part of NASA's A-Train constellation in an orbit with 98 • inclination at an altitude of 705 km (Stephens et al, 2002;Pitts et al, 2018). Its orbit was sun-synchronous with Equator crossings at about 01:30 and 13:30 LT.…”