| 1. |
- Wen, Yuanqiao, et al.
(författare)
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Green routing design in short seas
- 2017
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Ingår i: International Journal of Shipping and Transport Logistics. - : INDERSCIENCE ENTERPRISES LTD. - 1756-6517 .- 1756-6525. ; 9:3, s. 371-390
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, with the development of shipping industry, the mass of greenhouse gases (GHG) emissions originating from ships is also increasing rapidly. To reduce the GHG emissions from ships, designing the optimised routes with higher energy use efficiency is becoming more important for ships navigating in short seas. Based on the innovative application of energy efficiency operational index (EEOI), a route optimisation model is established. To solve the model, we divide one single voyage into several voyage segments and consider the variable speed across voyage segments. Then the navigation strategy is used to find out the sailing route of the minimum EEOI value, this sailing route is called as the green route. Finally, numerical experimental results show that the EEOI values of the experimental groups which used the optimised navigation method are 4.67%-16.95% lower than that of the control group. The results demonstrate that the green route designed in this paper can effectively improve the energy use efficiency of ships.
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| 2. |
- Zuo, Daxing, et al.
(författare)
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Spatial patterns of short-term extreme precipitation and their causes
- 2024
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Ingår i: Hydrological Processes. ; 38:7
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The spatial distribution of extreme precipitation significantly affects flow-producing processes and flooding. Previous studies on heavy rainfall have mainly emphasized the temporal distribution characteristics, with little emphasis on rainfall spatial patterns. We objectively classified 3-h scale extreme precipitation spatial patterns (EPSPs) in Guangdong Province, China. We calculated the importance of the influencing factors on EPSPs, analysed weather backgrounds corresponding to various EPSPs, and explained the causes of extreme precipitation. We found that the incidence of most EPSPs increased significantly over this 40-year period, and this increase has been particularly pronounced since the beginning of the 21st century. The Pacific Decadal Oscillation (PDO) was found to be the main factor influencing the extreme precipitation events (EPEs) in western Guangdong, and the weakening of the PDO contributed to the occurrence of EPEs in these areas. Urbanization was the main factor contributing to the increase in EPEs in the southern and coastal areas of Guangdong. The EPSPs in central Guangdong were caused by a southwest jet stream and topographic uplift. Extreme precipitation in southern and coastal Guangdong was mainly triggered by the convergent shear of southwesterly winds. The EPSPs over western Guangdong were caused by the low vortex in western Guangdong and the influx of large amounts of water vapour from the southern ocean. This study has provided new ideas for the study of the formation process and mechanism of localized heavy precipitation as well as an important reference for the simulation of runoff in coastal areas.
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| 3. |
- Cai, Yongqing, et al.
(författare)
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Factors Modulating the Variability of Eddy Kinetic Energy in the Southern Ocean from Idealized Simulations
- 2024
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Ingår i: Ocean-Land-Atmosphere Research. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- The Southern Ocean is characterized by high levels of eddy activity, which are crucial for the vertical exchange or transfer of matter, energy, and momentum. Previous studies have shown that the variability of eddy kinetic energy (EKE) in the Southern Ocean is primarily intrinsic. However, the factors that modulate the forced and intrinsic variability of the EKE remain unclear. In this study, we conduct a series of idealized simulations and apply ensemble analysis to investigate the impact of topography and wind-stress perturbations on the forced and intrinsic variability of the EKE and their relative contributions. The results show that while the large wind-stress perturbation obviously increases the forced variability of EKE by enhancing the Ekman response, the topography not only amplifies the forced variability by sharpening isopycnals and energizing the mean flow but also intensifies the intrinsic variability of EKE. However, EKE variabilities in both complex-topographic and flat-bottom cases are dominated by their intrinsic components, even when driven by escalated wind-stress perturbations. These findings deepen our understanding of the eddy field, its ongoing variability in the Southern Ocean, and its potential impact on the balance of heat, carbon, and freshwater.
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| 4. |
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| 5. |
- Cai, Yongqing, et al.
(författare)
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Impact of wave breaking on upper-ocean turbulence
- 2017
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Ingår i: Journal of Geophysical Research - Oceans. - 2169-9275 .- 2169-9291. ; 122:2, s. 1513-1528
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have demonstrated that surface wave breaking can impact upper-ocean turbulence through wave-breaking-induced turbulence kinetic energy (TKE) flux and momentum flux. Wave-breaking-induced momentum flux decays approximately exponentially with depth, and the decay exponent depends on both the wind speed and wave age. With increasing wave age, the decay speed of wave-breaking-induced momentum flux first decreases, reaching a minimum around a wave age of 16, and then increases. In this study, a wave-breaking-induced momentum flux parameterization was proposed based on wave age and wind-speed dependence. The new proposed parameterization was introduced into a one-dimensional (1-D) ocean model along with a wave-age-dependent wave-breaking-induced TKE flux parameterization. The simulation results showed that the wave-breaking impact on the ocean mainly affected the upper-ocean layer. Adding the wave-age impact to the wave-breaking-induced TKE flux and momentum flux improved the 1-D model performance concerning the sea temperature. Moreover, the wave-breaking-induced momentum flux had a larger impact on the simulation results than the wave-breaking-induced TKE flux.
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| 6. |
- Emmanuel, George Victor, et al.
(författare)
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Role of source terms in parameterizing wave decay in the marginal ice zones
- 2022
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Ingår i: Ocean Modelling. - : Elsevier. - 1463-5003 .- 1463-5011. ; 180
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Tidskriftsartikel (refereegranskat)abstract
- Wave decay in the marginal ice zones (MIZ) plays a crucial role in shaping the Arctic Ocean behaviours. Parameterizing wave decay in the MIZ is indispensable in climate models for better capturing the climate change in the Arctic. However, current wave decay parameterizations were developed without considering the influences of wave source terms. This study investigated the role and contributions of different source terms in shaping the MIZ wave decay based on sensitivity simulations. Simulation results show that the ice-induced damping term is the main contributor to MIZ wave decay. The wind input source term also plays an important role in the wave evolution in the MIZ. During high wind speeds (wind speed>10 m/s), wind input was found to increase the wave height by about 10% on average (relative to the wave height decayed by ice), irrespective of the sea ice concentration. Wind input contributes up to 30% in high wind speed areas with low sea ice concentration. Meanwhile, the contributions from wind input term to MIZ wave are more important when winds blow from the open water to MIZ. However, the angle between winds and waves is insignificant in shaping contributions from wind input. Low SIC and high wind speed conditions also favour the enhancement of wave spreading. In general, the contributions from nonlinear wave–wave interactions and dissipation source terms were found to play a minor role in shaping MIZ wave decay. However, the role of nonlinear wave–wave interactions can be important in shaping the wave spectrum. Thus, it is suggested to update the model wave decay parameterizations to accommodate the role played by wind input source term, in particular under high wind speed conditions.
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| 7. |
- Gröger, Matthias, et al.
(författare)
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Coupled regional Earth system modeling in the Baltic Sea region
- 2021
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Ingår i: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 12:3, s. 939-973
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Forskningsöversikt (refereegranskat)abstract
- Nonlinear responses to externally forced climate change are known to dampen or amplify the local climate impact due to complex cross-compartmental feedback loops in the Earth system. These feedbacks are less well represented in the traditional stand-alone atmosphere and ocean models on which many of today's regional climate assessments rely (e.g., EURO-CORDEX, NOSCCA and BACC II). This has promoted the development of regional climate models for the Baltic Sea region by coupling different compartments of the Earth system into more comprehensive models. Coupled models more realistically represent feedback loops than the information imposed on the region by prescribed boundary conditions and, thus, permit more degrees of freedom. In the past, several coupled model systems have been developed for Europe and the Baltic Sea region. This article reviews recent progress on model systems that allow two-way communication between atmosphere and ocean models; models for the land surface, including the terrestrial biosphere; and wave models at the air-sea interface and hydrology models for water cycle closure. However, several processes that have mostly been realized by one-way coupling to date, such as marine biogeochemistry, nutrient cycling and atmospheric chemistry (e.g., aerosols), are not considered here. In contrast to uncoupled stand-alone models, coupled Earth system models can modify mean near-surface air temperatures locally by up to several degrees compared with their stand-alone atmospheric counterparts using prescribed surface boundary conditions. The representation of small-scale oceanic processes, such as vertical mixing and sea-ice dynamics, appears essential to accurately resolve the air-sea heat exchange over the Baltic Sea, and these parameters can only be provided by online coupled high-resolution ocean models. In addition, the coupling of wave models at the ocean-atmosphere interface allows for a more explicit formulation of small-scale to microphysical processes with local feedbacks to water temperature and large-scale processes such as oceanic upwelling. Over land, important climate feedbacks arise from dynamical terrestrial vegetation changes as well as the implementation of land-use scenarios and afforestation/deforestation that further alter surface albedo, roughness length and evapotranspiration. Furthermore, a good representation of surface temperatures and roughness length over open sea and land areas is critical for the representation of climatic extremes such as heavy precipitation, storms, or tropical nights (defined as nights where the daily minimum temperature does not fall below 20gC), and these parameters appear to be sensitive to coupling. For the present-day climate, many coupled atmosphere-ocean and atmosphere-land surface models have demonstrated the added value of single climate variables, in particular when low-quality boundary data were used in the respective stand-alone model. This makes coupled models a prospective tool for downscaling climate change scenarios from global climate models because these models often have large biases on the regional scale. However, the coupling of hydrology models to close the water cycle remains problematic, as the accuracy of precipitation provided by atmosphere models is, in most cases, insufficient to realistically simulate the runoff to the Baltic Sea without bias adjustments. Many regional stand-alone ocean and atmosphere models are tuned to suitably represent present-day climatologies rather than to accurately simulate climate change. Therefore, more research is required into how the regional climate sensitivity (e.g., the models' response to a given change in global mean temperature) is affected by coupling and how the spread is altered in multi-model and multi-scenario ensembles of coupled models compared with uncoupled ones.
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| 8. |
- Huang, Hongxun, et al.
(författare)
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Identification and detection of high NOx emitting inland ships using multi-source shore-based monitoring data
- 2024
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Ingår i: Environmental Research Letters. - : Institute of Physics Publishing (IOPP). - 1748-9326. ; 19:4
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Tidskriftsartikel (refereegranskat)abstract
- In urban areas situated along busy waterways like the Yangtze River, the diesel engines of inland navigation ships emerge as significant contributors to air pollution. Among these vessels, certain high-emission ships exhibit considerably higher levels of nitrogen oxides (NOx) emissions compared to others. To effectively identify such ships, this study employed a cost-effective ship emission monitoring sensor platform, comprising high-precision gas sensors, automatic identification system (AIS) receiver, and sensitive meteorological sensors, along the Yangtze River in Wuhan City. By combining multi-source shore-based monitoring data, we identified ship emission signals and proposed a high-emission ship detection method using inverse modelling. Using this method, we successfully detected inland high-emission ships based on two months of monitoring data. Furthermore, the relationship between different ship types, sizes, speeds, and ship NOx emission rates were investigated. The results of this study are beneficial for strengthening the regulation of high-emission vessels in inland waterways, thereby reducing the adverse impact of ship emissions on the environment and climate. It also encourages the inland shipping industry to adopt more environmentally friendly technologies and fuels, as advocated by the International Maritime Organization.
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| 9. |
- Jeworrek, Julia, et al.
(författare)
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Characteristics of convective snow bands along the Swedish east coast
- 2017
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Ingår i: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 8, s. 163-175
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Tidskriftsartikel (refereegranskat)abstract
- Convective snow bands develop in response to a cold air outbreak from the continent or the frozen sea over the open water surface of lakes or seas. The comparatively warm water body triggers shallow convection due to increased heat and moisture fluxes. Strong winds can align with this convection into wind-parallel cloud bands, which appear stationary as the wind direction remains consistent for the time period of the snow band event, delivering enduring snow precipitation at the approaching coast. The statistical analysis of a dataset from an 11-year high-resolution atmospheric regional climate model (RCA4) indicated 4 to 7 days a year of moderate to highly favourable conditions for the development of convective snow bands in the Baltic Sea region. The heaviest and most frequent lake effect snow was affecting the regions of Gavle and Vastervik (along the Swedish east coast) as well as Gdansk (along the Polish coast). However, the hourly precipitation rate is often higher in le than in the Vtervik region. Two case studies comparing five different RCA4 model setups have shown that the Rossby Centre atmospheric regional climate model RCA4 provides a superior representation of the sea surface with more accurate sea surface temperature (SST) values when coupled to the ice-ocean model NEMO as opposed to the forcing by the ERA-40 reanalysis data. The refinement of the resolution of the atmospheric model component leads, especially in the horizontal direction, to significant improvement in the representation of the mesoscale circulation process as well as the local precipitation rate and area by the model.
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| 10. |
- Li, Huidong, et al.
(författare)
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A sensitivity study of the WRF model in offshore wind modeling over the Baltic Sea
- 2021
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Ingår i: Geoscience Frontiers. - : Elsevier. - 1674-9871. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- Accurate wind modeling is important for wind resources assessment and wind power forecasting. To improve the WRF model configuration for the offshore wind modeling over the Baltic Sea, this study performed a sensitivity study of the WRF model to multiple model configurations, including domain setup, grid resolution, sea surface temperature, land surface data, and atmosphere-wave coupling. The simulated offshore wind was evaluated against LiDAR observations under different wind directions, atmospheric stabilities, and sea status. Generally, the simulated wind profiles matched observations, despite systematic underestimations. Strengthening the forcing from the reanalysis data through reducing the number of nested domains played the largest role in improving wind modeling. Atmosphere-wave coupling further improved the simulated wind, especially under the growing and mature sea conditions. Increasing the vertical resolution, and updating the sea surface temperature and the land surface information only had a slight impact, mainly visible during very stable conditions. Increasing the horizontal resolution also only had a slight impact, most visible during unstable conditions. Our study can help to improve the wind resources assessment and wind power forecasting over the Baltic Sea.
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