The representation of winds in the lower troposphere in ECMWF forecasts and reanalyses during the EUREC4A field campaign

The characterization of systematic forecast errors in lower-tropospheric winds over the ocean is a primary need for reforming models. Winds are among the drivers of convection, thus an accurate representation of winds is essential for better convective parameterizations. We focus on the temporal variability and vertical distribution of lower-tropospheric wind biases in operational medium-range weather forecasts and ERA5 reanalyses produced with the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). Thanks to several sensitivity experiments and an unprecedented wealth of measurements from the 2020 EUREC4A field campaign, we show that the wind bias varies greatly from day to day, resulting in RSME's up to 2.5 m s−1, with a mean wind speed bias up to −1 m s−1 near and above the trade-inversion in the forecasts and up to −0.5 m s−1 in reanalyses. The modeled zonal and meridional wind exhibit a too strong diurnal cycle, leading to a weak wind speed bias everywhere up to 5 km during daytime, turning into a too strong wind speed bias below 2 km at nighttime. The biases are fairly insensitive to the assimilation of sondes and likely related to remote convection and large scale pressure gradients. Convective momentum transport acts to distribute biases throughout the lowest 1.5 km, whereas at higher levels, other unresolved or dynamical tendencies play a role in setting the bias. Below 1 km, modelled friction due to unresolved physical processes appears too strong, but is (partially) compensated by dynamical tendencies, making this a challenging coupled problem.

A Review on the Building Wind Impact through On-site Monitoring in Haeundae Marine City: 2021 12th Typhoon OMAIS Case Study

Overcrowding of high-rise buildings in urban zones change the airflow pattern in the surrounding areas. This causes building wind, which adversely affects the wind environment. Building wind can generate more serious social damage under extreme weather conditions such as typhoons. In this study, to analyze the wind speed and wind speed ratio quantitatively, we installed five anemometers in Haeundae, where high-rise buildings are dense, and conducted on-site monitoring in the event of typhoon OMAIS to determine the characteristics of wind over skyscraper towers surround the other buildings. At point M-2, where the strongest wind speed was measured, the maximum average wind speed in 1 min was observed to be 28.99 m/s, which was 1.7 times stronger than that at the ocean observatory, of 17.0 m/s, at the same time. Furthermore, when the wind speed at the ocean observatory was 8.2 m/s, a strong wind speed of 24 m/s was blowing at point M-2, and the wind speed ratio compared to that at the ocean observatory was 2.92. It is judged that winds 2–3 times stronger than those at the surrounding areas can be induced under certain conditions due to the building wind effect. To verify the degree of wind speed, we introduced the Beaufort wind scale. The Beaufort numbers of wind speed data for the ocean observatory were mostly distributed from 2 to 6, and the maximum value was 8; however, for the observation point, values from 9 to 11 were observed. Through this study, it was possible to determine the characteristics of the wind environment in the area around high-rise buildings due to the building wind effect.

Assessing the Inter-Relationship between Rural Population Migration and Environmental Change in the Dano Watershed, Burkina Faso

The study analyses the Land Use and Land Cover (LULC) dynamics as an important environmental factor and links it to migration trends towards the study area. The work uses data collected across two (2) villages, both located in the Dano watershed. Three sets of 30-m Landsat images were used to measure the changes in LULC types for the years 1986, 1999 and 2014. Cumulatively focus group discussion and household interview were employed for socio-economic data collection. Census data for the periods 1987, 1996 and 2006 were also collected from the national census reports. LULC analysis revealed that vegetation area was progressively converted into croplands with an annual rate of 0.92% during the period of study. Pearson correlation analysis between population and cropland on one hand and population and vegetation on the second hand revealed a high positive correlation between population size and cropland (r = 0.99), while there was a high negative correlation between population size and vegetation (r = 0.96). The survey of 180 farmers revealed a diversity of questions about environmental change on their livelihood. Most 78% of farmers believe that deforestation is the main driver of environmental change as a result of the decrease of rainfall and strong wind. Many strategies are used by local communities as a response to environmental changes and migration is seen by 31% of the respondents as a common strategy used by the affected communities. These results from the study showed that migration is one of the major local responses to environmental change.

The Effects of Bubble Scattering on Sound Propagation in Shallow Water

As sea waves break, a bubble layer forms beneath the sea surface. The bubble scattering affects sound propagation, thus influencing the accuracy of sound field prediction. This paper aims to investigate the effects of bubble scattering on the statistical characteristics of the sound field, the distribution of transmission loss (TL), and the average scattering attenuation in shallow water. A bubble layer model based on the bubble spectrum and a parallel Parabolic Equation (PE) model are combined to calculate and analyse the sound field in the marine environment with bubbles. The effects of the bubble layer are then compared with those of the fluctuant sea surface. The results show that the bubble scattering causes additional energy loss and random fluctuations of the sound field. The TL distribution properties and the average scattering attenuation are related to the wind speed, range, frequency, and source position relative to the negative gradient sound speed layer in shallow water. The comparison demonstrates that the random variation caused by the fluctuation of the sea surface is more significant than that caused by bubbles, and the energy loss caused by bubble scattering is more significant than the fluctuant sea surface under strong wind conditions.

The characteristics of weather-related wind load parameters and wind 2 power quality over the Dabanchen strong gale area

Analysis of data from cup and ultrasonic anemometers on a 100 m-tall wind mast in the Dabanchen Canyon reveals that the turbulence intensities, gust factors, and peak factors measured by cup anemometers tend to be severely undervalued compared to longitudinal values from an ultrasonic anemometer, and onsite three-dimensional measurement data are preferred for weather-related wind load calculation. This difference is related to the rotating responses of cup anemometers during wind speed acceleration or deceleration and the higher vertical fluctuation speeds driven by dynamic interactions with the sloped canyon terrain. The higher lateral turbulence is key consideration for determining wind turbine classes in Danbanchen strong wind area. The longitudinal gust and peak factors under wind speeds exceeding 25.0 m s−1 are comparable with those of typhoon-prone open, flat regions. The chances of high turbulence and unstable stratification convective processes are very high; thus, wind power collection efficiencies are not high. Except the longitudinal turbulence integral scale, China’s wind-resistance codes are not applicable due to occasional undesirable strong gales with extraordinary turbulence structures. The measured vertical power spectral density of fluctuating wind in the high-frequency domain cannot reflect the rapidly adapting features of the vast terrain under strong gales.

The characteristics of weather-related wind load parameters and wind power quality over the Dabanchen strong gale area

Analysis of data from cup and ultrasonic anemometers on a 100 m-tall wind mast in the Dabanchen Canyon reveals that the turbulence intensities, gust factors, and peak factors measured by cup anemometers tend to be severely undervalued compared to longitudinal values from an ultrasonic anemometer, and onsite three-dimensional measurement data are preferred for weather-related wind load calculation. This difference is related to the rotating responses of cup anemometers during wind speed acceleration or deceleration and the higher vertical fluctuation speeds driven by dynamic interactions with the sloped canyon terrain. The higher lateral turbulence is key consideration for determining wind turbine classes in Danbanchen strong wind area. The longitudinal gust and peak factors under wind speeds exceeding 25.0 m s−1 are comparable with those of typhoon-prone open, flat regions. The chances of high turbulence and unstable stratification convective processes are very high; thus, wind power collection efficiencies are not high. Except the longitudinal turbulence integral scale, China’s wind-resistance codes are not applicable due to occasional undesirable strong gales with extraordinary turbulence structures. The measured vertical power spectral density of fluctuating wind in the high-frequency domain cannot reflect the rapidly adapting features of the vast terrain under strong gales.

Weather extremes and plantation crops in the humid tropics

Monsoon rainfall across the State of Kerala was declining since last 60 years (cyclic trend of 40-60 years is also noticed with annual/monsoon rainfall) while rise in temperature is evident. Of course, rate of increase in temperature was alarming across the High ranges (where cardamom, coffee and tea are grown) due to deforestation. It is also true to some extent along the Coast (low land) due to increase in sea surface air temperature. The decade 1981-90 was the driest and warmest decade. The year 1987 was the warmest year across Kerala. The State as a whole was moving from wetness to dryness within the Humid Climate ((B4-B3 as per the Thornthwaite’s climate classification). Among weather extremes, summer drought, monsoon flood, strong wind (blows in Palghat Gap from November to February, other than cyclonic wind across the State), hailstorms, unusual rains, landslides and warming may adversely affect plantation crops’ production and its quality. Heat wave and cold waves are not relevant with reference to plantation crops under the Humid Tropics. The effect of summer drought on coconut yield was noticed in 1983, 2004 and 2013. In the case of coffee, it appears that crop matures early in recent years due to increase in temperature and climate change. The quality of coffee and black pepper, nut size in coconut and cashew are also influenced due to global warming and climate change. In the case of black pepper, the mortality rate is high in young pepper vines due to prolonged summer drought as noticed in summer 1983, 2004 and 2013. Mixed cropping/integrated farming is suggested to sustain crop income against adverse weather on long run under projected climate change scenario.

Method for holistic wind turbine drivetrain comparison exemplarily applied to geared and direct drive systems

The drivetrain as an important part of wind turbines needs to be improved in order to deal with today’s high development and cost pressure. One important step towards enhanced drivetrains is to identify the most suitable concept for a targeted onshore application in an early design stage. With this purpose, a holistic lifecycle system evaluation approach relying on minimum input information is presented. In order to identify a dominant solution, an additive target system is defined taking cost, ecological sustainability, and supplied energy into account. This multi-criteria decision is aggregated by defining a macrosocial evaluation criterion: “drivetrain specific energy supply effort”. A physics- and empirically-based model is developed to quantify the targets for different onshore drivetrain concepts. The validity of the model results is shown by a comparison to meta-analysis findings. Being utilized on a drivetrain concept comparison between geared and direct drive the approach’s value is showcased. Both concepts score on a comparable level slightly differing in weak and strong wind regimes. An exemplary trade-off between investment- and operational effort shows, that for both concepts the investment effort is higher than the operational. The comparison furthermore shows how robust decision support can be provided by parameter variation and finally it stresses, that the decision maker’s preferences need to be incorporated in the decision. Concluding, this analysis shows that physics- and empirically-based model approaches enable holistic wind turbine drivetrain concept comparisons in an early design stage.