Modelling the impact of Baltic Sea upwelling on the atmospheric boundary layer

The Loess Plateau is one land-atmosphere coupling hotspot. Soil moisture has an influence on atmospheric boundary layer development under specific early-morning atmospheric thermodynamic structures. This paper investigates the sensitivity of atmospheric convection to soil moisture conditions over the Loess Plateau in China by using the convective triggering potential (CTP)—humidity index (HIlow) framework. The CTP indicates atmospheric stability and the HIlow indicates atmospheric humidity in the low-level atmosphere. By comparing the model outcomes with the observations, the one-dimensional model achieves realistic daily behavior of the radiation and surface heat fluxes and the mixed layer properties with appropriate modifications. New CTP-HIlow thresholds for soil moisture-atmosphere feedbacks are found in the Loess Plateau area. By applying the new thresholds with long-time scales sounding data, we conclude that negative feedback is dominant in the north and west portion of the Loess Plateau; positive feedback is predominant in the south and east portion. In general, this framework has predictive significance for the impact of soil moisture on precipitation. By using this new CTP-HIlow framework, we can determine under what atmospheric conditions soil moisture can affect the triggering of precipitation and under what atmospheric conditions soil moisture has no influence on the triggering of precipitation.

Download Full-text

Evaluation of regional NWP results for sea ice covered Bothnia Bay (Baltic Sea) in winter 2020.

10.5194/egusphere-egu21-14612 ◽

2021 ◽

Author(s):

Marta Wenta ◽

Agnieszka Herman

Keyword(s):

Boundary Layer ◽

Wind Speed ◽

Sea Ice ◽

Surface Temperature ◽

Atmospheric Boundary Layer ◽

Baltic Sea ◽

Polar Regions ◽

Near Surface ◽

Accurate Representation ◽

Complex Processes

The ongoing development of NWP (Numerical Weather Prediction) models and their increasing horizontal resolution have significantly improved forecasting capabilities. However, in the polar regions models struggle with the representation of near-surface atmospheric properties and the vertical structure of the atmospheric boundary layer (ABL) over sea ice. Particularly difficult to resolve are near-surface temperature, wind speed, and humidity, along with diurnal changes of those properties. Many of the complex processes happening at the interface of sea ice and atmosphere, i.e. vertical fluxes, turbulence, atmosphere - surface coupling are poorly parameterized or not represented in the models at all. Limited data coverage and our poor understanding of the complex processes taking place in the polar ABL limit the development of suitable parametrizations. We try to contribute to the ongoing effort to improve the forecast skill in polar regions through the analysis of unmanned aerial vehicles (UAVs) and automatic weather station (AWS) atmospheric measurements from the coastal area of Bothnia Bay (Wenta et. al., 2021), and the application of those datasets for the analysis of regional NWP models' forecasts.&#160;Data collected during HAOS (Hailuoto Atmospheric Observations over Sea ice) campaign (Wenta et. al., 2021) is used for the evaluation of regional NWP models results from AROME (Applications of Research to Operations at Mesoscale) - Arctic, HIRLAM (High Resolution Limited Area Model) and WRF (Weather Research and Forecasting). The presented analysis focuses on 27 Feb. 2020 - 2 Mar. 2020, the time of the HAOS campaign, shortly after the formation of new, thin sea ice off the westernmost point of Hailuoto island.&#160; Throughout the studied period weather conditions changed from very cold (-14&#8451;), dry and cloud-free to warmer (~ -5&#8451;), more humid and opaquely cloudy. We evaluate models&#8217; ability to correctly resolve near-surface temperature, humidity, and wind speed, along with vertical changes of temperature and humidity over the sea ice. It is found that generally, models struggle with an accurate representation of surface-based temperature inversions, vertical variations of humidity, and temporal wind speed changes. Furthermore, a WRF Single Columng Model (SCM) is launched to study whether specific WRF planetary boundary layer parameterizations (MYJ, YSU, MYNN, QNSE), vertical resolution, and more accurate representation of surface conditions increase the WRF model&#8217;s ability to resolve the ABL above sea ice in the Bay of Bothnia. Experiments with WRF SCM are also used to determine the possible reasons behind model&#8217;s biases. Preliminary results show that accurate representation of sea ice conditions, including thickness, surface temperature, albedo, and snow coverage is crucial for increasing the quality of NWP models forecasts. We emphasize the importance of further development of parametrizations focusing on the processes at the sea ice-atmosphere interface.&#160;Reference:Wenta, M., Brus, D., Doulgeris, K., Vakkari, V., and Herman, A.: Winter atmospheric boundary layer observations over sea ice in the coastal zone of the Bay of Bothnia (Baltic Sea), Earth Syst. Sci. Data, 13, 33&#8211;42, https://doi.org/10.5194/essd-13-33-2021, 2021.&#160;

Download Full-text

Unmanned Aerial Systems for Investigating the Polar Atmospheric Boundary Layer—Technical Challenges and Examples of Applications

Atmosphere ◽

10.3390/atmos11040416 ◽

2020 ◽

Vol 11 (4) ◽

pp. 416 ◽

Cited By ~ 2

Author(s):

Astrid Lampert ◽

Barbara Altstädter ◽

Konrad Bärfuss ◽

Lutz Bretschneider ◽

Jesper Sandgaard ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Low Temperatures ◽

Open Water ◽

Future Research ◽

Small Scale ◽

Unmanned Aerial Systems ◽

Research Activities ◽

Aerial Systems ◽

The Impact

Unmanned aerial systems (UAS) fill a gap in high-resolution observations of meteorological parameters on small scales in the atmospheric boundary layer (ABL). Especially in the remote polar areas, there is a strong need for such detailed observations with different research foci. In this study, three systems are presented which have been adapted to the particular needs for operating in harsh polar environments: The fixed-wing aircraft M 2 AV with a mass of 6 kg, the quadrocopter ALICE with a mass of 19 kg, and the fixed-wing aircraft ALADINA with a mass of almost 25 kg. For all three systems, their particular modifications for polar operations are documented, in particular the insulation and heating requirements for low temperatures. Each system has completed meteorological observations under challenging conditions, including take-off and landing on the ice surface, low temperatures (down to −28 ∘ C), icing, and, for the quadrocopter, under the impact of the rotor downwash. The influence on the measured parameters is addressed here in the form of numerical simulations and spectral data analysis. Furthermore, results from several case studies are discussed: With the M 2 AV, low-level flights above leads in Antarctic sea ice were performed to study the impact of areas of open water within ice surfaces on the ABL, and a comparison with simulations was performed. ALICE was used to study the small-scale structure and short-term variability of the ABL during a cruise of RV Polarstern to the 79 ∘ N glacier in Greenland. With ALADINA, aerosol measurements of different size classes were performed in Ny-Ålesund, Svalbard, in highly complex terrain. In particular, very small, freshly formed particles are difficult to monitor and require the active control of temperature inside the instruments. The main aim of the article is to demonstrate the potential of UAS for ABL studies in polar environments, and to provide practical advice for future research activities with similar systems.

Download Full-text

The impact of atmospheric boundary layer, opening configuration and presence of animals on the ventilation of a cattle barn

Journal of Wind Engineering and Industrial Aerodynamics ◽

10.1016/j.jweia.2020.104185 ◽

2020 ◽

Vol 201 ◽

pp. 104185

Author(s):

Štěpán Nosek ◽

Zuzana Kluková ◽

Michala Jakubcová ◽

Qianying Yi ◽

David Janke ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

The Impact

Download Full-text

Microphysics of the air-sea coupling at high winds and its role in the dynamics and thermodynamics of severe sea storms

10.5194/egusphere-egu2020-7149 ◽

2020 ◽

Author(s):

Yuliya Troitskaya ◽

Alexander Kandaurov ◽

Daniil Sergeev ◽

Olga Ermakova ◽

Dmitrii Kozlov ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Water Surface ◽

Synergetic Effect ◽

Ocean Surface ◽

Small Scale ◽

Momentum Exchange ◽

Momentum Fluxes ◽

The Impact ◽

High Winds

Showing the record strengths and growth-rates, a number of recent hurricanes have highlighted needs for improving forecasts of tropical cyclone intensities most sensitive to models of the air-sea coupling. Especially challenging is the nature and effect of the very small-scale phenomena, the sea-spray and foam, supposed to strongly affecting the momentum- and heat- air-sea fluxes at strong winds. This talk will focus on our progress in understanding and describing these "micro-scale" processes, their physical properties, the spray and foam mediated air-sea fluxes and the impact on the development of marine storms.The starting points for this study were two laboratory experiments. The first one was designed for investigation of the spray generation mechanisms at high winds. We found out 3 dominant spray generating mechanisms: stretching liquid ligaments, bursting bubbles, splashing of the falling droplets and "bag-breakup". We investigated the efficiency spray-production mechanisms and developed the empirical statistics of the numbers of the spray generating events of each type. Basing on the "white-cap method" we found out the dependence of the spray-generating events on the wind fetch. The main attention was paid to the "bag-breakup" mechanism. Here we studied in detail the statistics of spray produced from one "bag-breakup" event. Basing on these developments, we estimated heat and momentum fluxes from the spray-generating events of different types and found out the dominant role of the "bag-breakup" mechanism.To estimate the direct heat and momentum fluxes from the ocean surface to the atmosphere, we studied in the special experiment the foam impact on the short-wave part of the surface waves and the heat momentum exchange in the atmospheric boundary layer at high winds. Based on these results, we suggest a simple model for the aerodynamic and temperature roughness and the eddy viscosity in the turbulent boundary layer over a fractionally foam-covered water surface.The synergetic effect of foam at the water surface and spray in the marine atmospheric boundary layer on ocean surface resistance at high winds is estimated so as to be able to explain the observed peculiarities of the air-sea fluxes at stormy conditions. Calculations within the nonhydrostatic axisymmetric model show, that the "microphysics" of the air-sea coupling significantly accelerate development of the ocean storm.This work was supported by RFBR grant 19-05-00249 and RSF grant 19-17-00209.

Download Full-text

The Impact of Wind Turbines on Atmospheric Boundary Layer under Different Topography

International Journal of Energy and Power ◽

10.14355/ijep.2015.04.013 ◽

2015 ◽

Vol 4 (0) ◽

pp. 81

Author(s):

Zhengren Wu ◽

Fei Li ◽

Yunlei Zhai ◽

Mei Liu

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Wind Turbines ◽

The Impact

Download Full-text

New Findings concerning the Structure of the Marine Atmospheric Boundary Layer over the Baltic Sea – Possible Implications for Wind Energy Installations

Wind Engineering ◽

10.1260/030952403773617427 ◽

2003 ◽

Vol 27 (6) ◽

pp. 431-447 ◽

Cited By ~ 1

Author(s):

Ann-Sofi Smedman ◽

Ulf Högström ◽

Hans Bergström ◽

Cecilia Johansson ◽

Anna Sjöblom ◽

...

Keyword(s):

Boundary Layer ◽

Wind Energy ◽

Atmospheric Boundary Layer ◽

Baltic Sea ◽

Marine Atmospheric Boundary Layer ◽

The Baltic Sea ◽

New Findings ◽

The Baltic

Download Full-text

Evaluation of Wind Loads on FPSO Topsides Using a Numerical Wind Tunnel

Volume 2: CFD and VIV ◽

10.1115/omae2016-54346 ◽

2016 ◽

Cited By ~ 1

Author(s):

Daniel Barcarolo ◽

Yann Andrillon ◽

Erwan Jacquin ◽

Alain Ledoux

Keyword(s):

Boundary Layer ◽

Numerical Model ◽

Wind Tunnel ◽

Atmospheric Boundary Layer ◽

Scale Effects ◽

Geometric Model ◽

Wind Tunnel Test ◽

Offshore Structures ◽

Wind Loads ◽

The Impact

The accurate evaluation of wind loads applied on floating offshore structures is extremely important as they are in specific conditions one of the dimensioning criteria for the mooring design. Nowadays these loads are mainly assessed through wind tunnel tests performed at model scale. Estimating realistic wind loads however, remains a big challenge. The complexity and associated simplification level of FPSO topside structures, the scale effects and the establishment of the atmospheric boundary layer imply that many simplifications are to be made. Typically, the FPSO topside is greatly simplified and equivalent blocs of wired frame are used. Today with the evolution of CFD software, and the increase of the meshing capacity, new scopes open to CFD. Aerodynamic simulations on complex FPSO structures are therefore now possible, but need specific developments and validations that are presented in this paper. The main objective of the work presented is to investigate the ability of CFD to evaluate wind loads on complex FPSOs topsides and to provide information on the impact of model simplifications made in wind tunnels. In a first stage, the numerical model was intensively validated by comparing its results to a wind tunnel test case. The numerical model was developed in order to ensure the quality of the results and enable a relevant comparison that was obtained with grids density up to 30 million cells. For this purpose, the geometric model used corresponds to the one used in wind tunnel. The same Atmospheric Boundary Layer was simulated and a thorough effort was performed to ensure the mesh convergence. In a second stage, more physical aspects of the wind tunnel methodology were investigated. Typically the accuracy of the blockage effect correction was evaluated by performing computations with and without blockage, and results were compared with classical corrections applied in wind tunnel. The impacts of the Atmospheric Boundary Layer on wind loads have also been investigated. Finally, the wind load contribution of each component of the FPSO was evaluated.

Download Full-text