On the influence of sea‐ice inhomogeneities onto roll convection in cold‐air outbreaks

Abstract

[1] In this study we use large-eddy simulations (LES) to model roll convection within the convective atmospheric boundary-layer (CBL) during strong cold-air outbreaks (CAO). Previous LES were mostly unsuccessful in reproducing clear signals of roll convection, especially in case of strong surface heating and weak vertical wind shear in the CBL. In nature however, this phenomenon is very robust and roll convection can be observed as cloud streets in satellite pictures of almost any CAO. Previous LES studies assumed homogeneous sea-ice, unlike the current study, where under strong surface heating clear signals of rolls appear only when introducing sea-ice inhomogeneities in the marginal ice zone. For weaker surface heating, rolls also appear without sea-ice inhomogeneities. The results of this study suggest that in case of strong surface heating and weak vertical wind shear surface inhomogeneities increase the chance of roll formation. Citation: Gryschka, M., C. Drüe, D. Etling, and S. Raasch (2008), On the influence of sea-ice inhomogeneities onto roll convection in cold-air outbreaks,

Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

“…Challenges remain in the high sensitivity of winter air temperatures to sea ice concentration (Lüpkes et al, 2008a;Tetzlaff et al, 2013) in the representation of new, thin ice in atmospheric models (Tisler et al, 2008) and in the interaction of convective plumes with capping stable or near-neutral environments (Lüpkes et al, 2008b). In the dynamics of cold air outbreaks over the open ocean, the new results linking the occurrence of roll convection with surface inhomogeneities in upwind sea ice (Liu et al, 2006;Gryschka et al, 2008) are an interesting discovery, although the links are still under discussion. This work also demonstrates the need for close collaboration of atmospheric and sea ice scientists.…”

“…There are, however, still fundamental questions under discussion. Gryschka et al (2008) found in an LES study that in case of strong surface heating and weak wind shear, surface inhomogeneity in the MIZ is an important factor for the generation of convection rolls. This finding also stresses the importance of a close-to-reality treatment of the MIZ processes including the near-surface-fluxes (see Sect.…”

The Parallelized Large-Eddy Simulation Model (PALM) version 4.0 for atmospheric and oceanic flows: model formulation, recent developments, and future perspectives

“…Cloudy boundary layers have been simulated using bulk cloud microphysics for cold-air outbreaks by Gryschka et al (2008) as well as for the analysis of second-order budgets in cloudtopped boundary layers for BOMEX and DYCOMS-II 10 (see Stevens et al, 2005) experiments by Heinze et al (2015). Recently, the embedded LCM has been employed for studying the effect of turbulence on the droplet dynamics and growth (Lee et al, 2014;Riechelmann et al, 2015), and for investigating the entrainment (of aerosols) at the edges of cumulus clouds (Hoffmann et al, 2015(Hoffmann et al, , 2014.…”

“…The early studies used idealized surface heterogeneity, i.e., stripes or checkerboard patterns (Raasch and Harbusch, 2001;Kim et al, 2004;Letzel and Raasch, 2003;Inagaki et al, 2006), whereas recent studies incorporated more complex surface configurations using the irregularly distributed land use classes as observed during the LITFASS-2003 field experiment (see Beyrich and Mengelkamp, 2006;Maronga and Raasch, 2013;Sühring and Raasch, 2013;Maronga et al, 2014;Sühring et al, 2015). Moreover, PALM has been applied to study the flow over Arctic ice leads and during cold-air outbreaks (e.g., Lüpkes et al, 2008;Gryschka et al, 2008Gryschka et al, , 2014. PALM has also been used several times to evaluate in situ measurement systems and strategies, e.g., for acoustic tomography, eddy covariance measurements, airborne flux observations, and scintillometers (e.g., Weinbrecht et al, 2004;Kanda et al, 2004;Sühring and Raasch, 2013;Maronga et al, 2013b).…”

A Case Study of Offshore Advection of Boundary Layer Rolls over a Stably Stratified Sea Surface

“…Boundary layer rolls have been successfully simulated by LES models [1,5,8,[15][16][17] and in a few cases also by numerical weather prediction models [18,19]. The advantage of using weather prediction models is the ability to simulate a longer time period, to obtain the diurnal variations, and to include the large-scale forcing and realistic topography, which gives the horizontal variations over extended areas.…”