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The Copernicus Arctic Regional Reanalysis (CARRA) is a novel regional high-resolution atmospheric reanalysis product that covers a considerable part of the European Arctic including substantial amounts of ice-covered areas. Sea ice in CARRA is modelled by means of a one-dimensional thermodynamic sea ice parameterisation scheme, which also explicitly resolves the evolution of the snow layer over sea ice. In the present study we assess the representation of sea ice cover in the CARRA product and validate it against a wide set of satellite products and observations from ice mass balance buoys. We show that sea ice cover in CARRA adequately represents general interannual trends towards thinner and warmer ice in the Arctic. Compared to ERA5, sea ice in CARRA shows a reduced warm bias in the ice surface temperature. The strongest improvement was observed for winter months over the Central Arctic, and the Greenland and Barents seas where a 4.91 °C median ice surface temperature error of ERA5 is reduced to 1.88 °C in CARRA on average. Over the Baffin Bay, intercomparisons suggest the presence of a cold winter-time ice surface temperature bias in CARRA. No improvement over ERA5 was found in the ice surface albedo with spring-time errors in CARRA being up to 8 % higher on average than those in ERA5 when computed against the CLARA-A2 satellite retrieval product. Summer-time ice surface albedos are comparable in CARRA and ERA5. Sea ice thickness and snow depth in CARRA adequately resolve the annual cycle of sea ice cover in the Arctic and bring added value compared to ERA5. However, limitations of CARRA indicate potential benefits of utilising more advanced approaches for representing sea ice cover in next generation reanalyses.

With the ongoing climate change economic activity in the Arctic steadily increases and it is expected to grow further in the coming years. However, harsh weather conditions of the present-day Arctic place strong demands for accurate and timely weather forecasts, which nowadays are obtained by means of numerical weather prediction. Sea ice covers a considerable part of the Arctic Ocean and numerical weather prediction systems operating in the region require a reliable and computationally-efficient representation of the sea ice cover in the model. Traditionally, simplified one-dimensional parameterisation schemes are applied for this task. However, implications of utilising such schemes in the context of contemporary high-resolution regional operational numerical weather prediction are not well studied. The present work aims to assess these effects through a series of numerical experiments in the operational-like environment. A new one-dimensional parameterisation scheme, allowing for varying level of complexity, implemented in the HARMONIE-AROME numerical weather prediction system, is used as the main research tool. The findings show that applying an over-simplified parameterisation scheme can result in considerable deterioration of the ice surface temperature field in the model. Errors in the modelled ice surface temperature influence the turbulent exchange between the ice surface and the model atmosphere, and, as a result, the near-surface atmospheric variables, such as the screen-level air temperature. Thus, improving the ice surface temperature in the model results in a positive impact on the atmospheric forecast of these parameters. Therefore, a sea ice scheme within an operational numerical weather prediction system should preferably include an explicit representation of the snow layer to accurately represent the surface energy budget of sea ice. Applying a sea ice data assimilation procedure to assimilate a near real time satellite ice surface temperature product in HARMONIE-AROME further reduces the root mean square error of the ice surface temperature and improves the screen-level air temperature forecast over Svalbard and Franz Josef Land archipelagos, however the positive effect in the ice surface temperature is short-lived and greatly reduced already after three hours of model forecast. Spatial resolution of contemporary regional numerical weather prediction systems allows some of the fine-scale features of the sea ice cover to be explicitly represented in the model. Numerical experiments show that introducing irregular structures within the marginal ice zone of the model ice cover results in both local and non-local responses in the atmospheric model. These findings indicate potential benefits of applying high-resolution ice cover in regional numerical weather prediction systems, for example, as a surface perturbation in ensemble prediction systems. Klimatförändringarna gör att ekonomisk aktivitet i Arktis ökar och förväntas öka ytterligare under kommande år. Krävande väderförhållanden ställer stränga krav till pålitliga väderprognoser i god tid. Prognoserna tillhandahålls genom en numerisk vädermodell. En stor del av Norra ishavet är täckt av havsis och vädermodeller för området behöver en pålitlig och beräkningsmässigt effektiv representation av havsisen i modellen. Traditionellt sett har förenklade en-dimensionella parametriseringar använts, men det kan vara mindre lämpligt i moderna modeller med finare upplösning. Denna avhandling undersöker detta i en operationell väderprognosmiljö genom en serie numeriska experiment. En ny en-dimensionell rutin som möjliggör varierande grad av komplexitet är implementerad i en regional vädermodell och utgör huvudverktyget i forskningen. Resultaten visar att införandet av en alltför förenklad representation av havsis kan leda till betydlig försämring av isens yttemperatur i modellen, som också påverkar aspekter av atmosfären nära marknivån, t.ex. lufttemperaturen. Förbättringen av temperaturen på isytan ger således en positiv påverkan i väderprognosen av atmosfären för dessa parametrar. En havsisrutin i en vädermodell bör därför innehålla en explicit representation av snölager för att ge en korrekt beskrivning av havsisens yta. Användning av observationer i havsisrutinen har också en positiv effekt på isytans temperatur och förbättrar lufttemperaturen nära havsnivån över Svalbard och Franz Josefs land, men effekten är störst i början av prognoserna. Den rumsliga upplösningen i nutida regional vädermodellsystem gör det möjligt att representera fler och fler egenskaper hos havisen explicit. Numeriska experiment visar att genom att implementera finskala-struktur i havsismodellen påverkas atmosfären inte bara direkt över havsisen men också på mer avlägsna platser. Dessa resultat visar också potentiella fördelar med högupplöst havsis i regionala vädersystem, till exempel som ytterligare en källa till variabilitet i ensembleprognossystem.

Наведені прості формули, які отримані аналітичним інтегруванням, придатні для побудови ефективних алгоритмів, що виключають накопичення обчислювальної похибки й не залежать від особливостей форми полігонів і просторового розташування граней поверхонь та поліедрів., Приведены простые формулы, которые получены путем аналитического интегрирования, пригодные для построения эффективных алгоритмов, исключающих накопление вычислительной ошибки и не зависящих от особенностей формы полигонов и пространственного расположения граней поверхностей и полиэдров., Simple formulas are given which were obtained through analytical integration. They can be used for developing effective algorithms which exclude accumulation of calculation errors and do not depend on characteristics of polygons shapes and spatial position of surface facets and polyhedrons.

Розглянуто методи визначення гідродинамічних навантажень на гребному гвинті у стаціонарному неоднорідному потоці стосовно задач розрахунку валопроводів морських транспортних суден. Проаналізовано найбільш розповсюджені схеми визначення навантажень, що були реалізовані авторами під час розробки автоматизованої системи розрахунків валопроводів ShaftDesigner. Запропоновано практичні рекомендації щодо призначення величин гідродинамічних навантажень на гвинт у випадках, коли бракує достатньо інформації для виконання розрахунків., Рассмотрены методы определения гидродинамических нагрузок на гребном винте в стационарном неоднородном потоке применительно к задачам расчета валопроводов морских транспортных судов. Проанализированы наиболее распространенные схемы определения нагрузок, реализованные авторами в рамках автоматизированной системы расчетов валопроводов ShaftDesigner. Предложены практические рекомендации по назначению величин гидродинамических нагрузок на винт в случае отсутствия исходной информации для выполнения расчетов., The methods for estimation of propeller hydrodynamic loads in the stationary non-uniform wake flow in relation to calculation of cargo ship propulsion shafting are discussed. Widely used approaches for propeller loads estimation which were implemented by authors in ShaftDesigner software are analyzed. Practical recommendations for setting of propeller hydrodynamic loads in the cases where not enough information for calculation are proposed.