Turbulent heat exchange over polar leads revisited: A large eddy simulation study

Sea ice leads play an important role in energy exchange between the ocean and atmosphere in polar regions, and therefore must be considered in weather and climate models. As sea ice leads are not explicitly resolved in such models, lead-averaged surface heat flux is of considerable interest for the parameterization of energy exchange. Measurements and numerical studies have established that the lead-averaged surface heat flux depends not only on meteorological parameters, but also on lead width. Nonetheless, few studies to date have investigated the dependency of surface heat flux on lead width. Most findings on that dependency are based on observations with lead widths smaller than a few hundred meters, but leads can have widths from a few meters to several kilometers. In this parameter study, we present the results of three series of large-eddy simulations of turbulent exchange processes above leads. We varied the lead width and air temperature, as well as the roughness length. As this study focused on conditions without background wind, ice-breeze circulation occurred, and was the main driver of the adjustment of surface heat flux. A previous large-eddy simulation study with uncommonly large roughness length found that lead-averaged surface heat flux exhibited a distinct maximum at lead widths of about 3 km, while our results show the largest heat fluxes for the smallest leads simulated (lead width of 50 m). At more realistic roughness lengths, we observed monotonously increasing heat fluxes with increasing lead width. Further, new scaling laws for the ice-breeze circulation are proposed

Overview of the PALM model system 6.0

In this paper, we describe the PALM model system 6.0. PALM (formerly an abbreviation for Parallelized Largeeddy Simulation Model and now an independent name) is a Fortran-based code and has been applied for studying a variety of atmospheric and oceanic boundary layers for about 20 years. The model is optimized for use on massively parallel computer architectures. This is a follow-up paper to the PALM 4.0 model description in Maronga et al. (2015). During the last years, PALM has been significantly improved and now offers a variety of new components. In particular, much effort was made to enhance the model with components needed for applications in urban environments, like fully interactive land surface and radiation schemes, chemistry, and an indoor model. This paper serves as an overview paper of the PALM 6.0 model system and we describe its current model core. The individual components for urban applications, case studies, validation runs, and issues with suitable input data are presented and discussed in a series of companion papers in this special issue

The Ferry Lidar Experiment and Benchmark

The presentation consists of two parts: in the first part, the Ferry Lidar Experiment - which is one of the NEWA Experiments, ie a set of unique flow experiments conducted as part of the New European Wind Atlas (NEWA) Project - is introduced. For the Ferry Lidar Experiment a Doppler lidar instrument was placed on a ferry connecting Kiel and Klaipeda in the Southern Baltic Sea from February to June 2017. A comprehensive set of all relevant motions was recorded together with the lidar data and processed in order to obtain and provide corrected wind time series. In the second part of the presentation, first results of a benchmark study are presented which was conducted on the basis of the NEWA Ferry Lidar dataset. In this study a number of different mesoscale model simulations, provided by different participants of the study, are compared with the measurement data

Quantifying variability of Large Eddy Simulations of very large wind farms

Large Eddy Simulations are inherently dynamic as the largest scales are resolved and the smallest scales are modeled temporally. This raises challenges for simulations including very large scales such as atmospheric flows, which require very long simulation times. Simple averages fail at capturing these dynamics and potentially yield misleading interpretations concerning the capabilities of different models when tested in blind tests or in benchmarking exercises such as Wakebench, where results from different flow models are compared. This article will present results from very large wind farm simulations using Actuator Disc (AD) and Line (AL) models for two different turbine spacings with turbulent inflow. The results of each numerical flow model include a certain variability, and it will be examined if different models result in comparable probability distributions