Climatological Wind Research Articles

Comparison of three reanalysis‐driven regional climate models over New Zealand: Climatology and extreme events

AbstractThree ~12‐km reanalysis‐driven regional climate models (RCMs) are evaluated in terms of capturing climatologies and extremes of precipitation, temperature and surface wind over Aotearoa/New Zealand (NZ). NZ provides an excellent case study for evaluating high‐resolution RCMs due to its coastal and complex terrain and isolated geographical position in the midlatitudes, exposed to both tropical and polar influences. Overall, we find that the RCMs faithfully reproduce the observed climate, with precipitation and temperature climatologies particularly well‐captured. However, the RCMs display significant differences from observations in capturing the surface wind climatology, highlighting a remaining key challenge. The excess “drizzle problem” is apparent to varying degrees, leading to a weaker representation in the length of meteorological drought in some regions. The RCMs also diverge in reproducing diurnal temperature range which appears partly related to cloud cover. Finally, we discuss the important role of observational uncertainty in the context of model evaluation.

The influence of thunderstorm type on extreme near-surface wind speeds: Iowa case study

The derecho of August 10, 2020 that impacted Iowa and neighboring states is the costliest thunderstorm disaster in U.S. history. A derecho, which features prolonged and destructive winds, is a type of thunderstorm which has different near-surface wind generating mechanisms than typically assumed in wind engineering. The derecho event prompted two research questions with respect to wind engineering: (1) should derechos, and more broadly thunderstorm type, be considered separately? and (2) how unique is this particular derecho event?Wind speeds for design in the U.S. are currently estimated using an approach where probability distributions of all thunderstorm winds are analyzed through a mixed distribution. Using Automated Surface Observing System (ASOS) and radar data from the National Weather Service, thunderstorm events with ASOS wind speeds >58 mph (26 m/s) were classified by thunderstorm type: single-cell, multicellular, or supercell thunderstorms in Iowa. An extreme value analysis was done on each thunderstorm type. Multicellular thunderstorms, like the August 2020 derecho, dominate the extreme wind climatology in Iowa. Evaluating the uniqueness of the derecho event required a post-damage assessment. Analysis from failed and unfailed street signs and nearby anemometry was used to estimate peak wind speeds approaching 120 mph (50 m/s).

Development of WACCM With the Non‐Hydrostatic MPAS‐A Dynamical Core

AbstractThe non‐hydrostatic Model for Prediction Across Scales‐Atmosphere (MPAS‐A) dynamical core has recently been adapted for the Specified Chemistry Whole Atmosphere Community Climate Model (SC‐WACCM). In this study, the mean zonal wind and temperature climatology from SC‐WACCM/MPAS‐A is compared with the results from SC‐WACCM using the finite volume and spectral element dynamical cores, as well as the zonal wind and temperature climatology of Upper Atmosphere Research Satellite mission and SABER. The simulations have been performed at horizontal resolutions of ∼100 km. Generally a good agreement is seen between the results from the three dynamical cores, which verifies that the new dynamical core is working with WACCM.

Mesonet-Based Climatology Of Severe Convective Winds in West Texas

Multiple studies have investigated the occurrence of severe convective winds and have increased our understanding of the forces driving severe winds and their spatial and temporal patterns. Some of the data used in studies have come from airport stations maintained by the National Weather Service. Their standardization across the United States makes them ideal for research, but they are limited in their distribution. This study aims to create a climatology of severe convective winds in West Texas using a mesoscale network (“mesonet”). Like their ASOS (Automated Surface Observing System) counterparts, these stations are standardized and well maintained. This study provides a 15-year climatology of severe convective wind gusts measured by the West Texas Mesonet (WTM). After extracting and manually verifying the measured gusts from over 30 WTM stations, both spatial and temporal distributions are presented. While temporal patterns in the gust distribution generally matched previous research, the high spatial resolution of the mesonet elucidated differences across a regional escarpment known as the Caprock. Comparison with regional AWOS / ASOS stations also revealed potential effects of a larger urban area. In addition to gust data, thermodynamic characteristics and rainfall accumulations associated with each gust were also investigated. In doing so, a substantial contribution from dry thunderstorm outflow winds and heat bursts to the production of regional severe wind was documented.

Retaining Short‐Term Variability Reduces Mean State Biases in Wind Stress Overriding Simulations

AbstractPositive feedbacks in climate processes can make it difficult to identify the primary drivers of climate phenomena. Some recent global climate model (GCM) studies address this issue by controlling the wind stress felt by the surface ocean such that the atmosphere and ocean become mechanically decoupled. Most mechanical decoupling studies have chosen to override wind stress with an annual climatology. In this study we introduce an alternative method of interannually varying overriding which maintains higher frequency momentum forcing of the surface ocean. Using a GCM (NCAR CESM1), we then assess the size of the biases associated with these two methods of overriding by comparing with a freely evolving control integration. We find that overriding with a climatology creates sea surface temperature (SST) biases throughout the global oceans on the order of ±1°C. This is substantially larger than the biases introduced by interannually varying overriding, especially in the tropical Pacific. We attribute the climatological overriding SST biases to a lack of synoptic and subseasonal variability, which causes the mixed layer to be too shallow throughout the global surface ocean. This shoaling of the mixed layer reduces the effective heat capacity of the surface ocean such that SST biases excite atmospheric feedbacks. These results have implications for the reinterpretation of past climatological wind stress overriding studies: past climate signals attributed to momentum coupling may in fact be spurious responses to SST biases.

Validation of the wind climatology from the ALARO-0 model at different resolutions over Ethiopia

Validation of the wind climatology from the ALARO-0 model at different resolutions over Ethiopia

The Overall Collection Efficiency of Catching‐Type Precipitation Gauges in Windy Conditions

AbstractThe wind‐induced bias of catching‐type precipitation measurement instruments is quantified using Computational Fluid Dynamics with embedded liquid (raindrops) and solid (snowflakes) particle tracking. The performance of six common commercial gauges having different outer geometry is compared under a range of Precipitation Intensity (PI) and wind speed conditions by means of the numerically calculated catch ratios. Validation of the simulated aerodynamic behavior and its effect on water drop trajectories is provided by previous wind tunnel experiments. The functional dependence of the overall collection efficiency on the PI is derived as a quantitative measure of the instrument performance under a wind climatology with a uniform probability density function. Instruments with aerodynamic design produce a less pronounced diversion of hydrometeor trajectories—at any given size—than those having more traditional geometry. For liquid precipitation measurements, chimney‐shaped instruments rank low, while inverted conical and Nipher shielded instruments are quite performant solutions. The investigated quasi‐cylindrical gauges have intermediate behavior depending on their detailed aerodynamic features. For solid precipitation, all instruments rank low at light to moderate PI, except the Nipher shielded gauge. Results allow selecting the appropriate instrument for the local precipitation climatology at the measurement site and can be used to apply suitable adjustments to the measured precipitation.

The peculiar wind and wave climatology of the Arabian Gulf

Based on a 40-year hindcast, we analyze the climatology and long-term trends of wind and waves in the Arabian Gulf. We identify and characterize four dominant wind systems, and their related mean wave conditions and long-term trends. Focusing on the summer Shamal wind, we observed a mild decrease in the number of Shamal events with time, whereas their intensity shows little to no variation. Further, we revealed a tendency toward an extension of the summer Shamal season from August to September. On a short time scale, the related wind fields show an evident daily oscillation associated with the daily heating of the Arabian Peninsula, with wind speeds peaking at 3:00 p.m. local time (UTC+3) on land and 12 h later on the sea. The long-term analysis conducted herein reveals limited, but significant, trends in surface pressure and related west-to-east pressure gradients in August. In September, the observed increasing number of Shamal storms is associated with an increase of the longitudinal local pressure gradient.

Wind farm power density optimization according to the area size using a novel self-adaptive genetic algorithm

This work studies the power density (PD) optimization in wind farms, and its sensitivity to the available area size. A novel genetic algorithm (PDGA) is introduced, which optimizes PD and the turbine layout, by self-adapting to the PD and to the solutions diversity. PDGA uses the levelized cost of energy (LCOE) as cost function, which in turn employs the EPFL analytical wake model to derive the power output. For the baseline area size, PDGA reduces 2.25% the original LCOE, 2.6 times more than optimizing with constant PD. PDGA-driven solutions provide 11% and 6% LCOE reductions against the default layout for the smallest (6.4 km2) and largest (386 km2) scaled wind farm areas, respectively. Specially relevant for the industry, PDGA solutions depict convex fronts for area vs. LCOE or vs. PD, which allows determining the required area or turbine number given a target LCOE. Unlike default layouts, optimized ones reveal a linear relationship between LCOE and PD. The mean turbine spacing tends to 8-9D for very large areas. The economics-optimized PDs are below the estimated PD available in the atmosphere. This work is limited to a simplified, offshore wind climatology, a specific wind turbine model, and the LCOE specifications used herein.

Climatology and pre-convection environmental conditions of dry and wet thunderstorm high winds over eastern China

Thunderstorm high wind (THW) is defined as a kind of convective weather phenomenon with a maximum wind gust speed not less than 17.2 m·s−1 over China. It is a sudden, damaging, but common convective weather phenomenon during the warm seasons of China. By adopting a kernel density estimation (KDE) for the THWs during warm seasons (March–September) of 2010–2019 over eastern China and the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) dataset, the dry and wet THWs usually with different mechanisms are objectively obtained, and climatology and pre-convection environmental conditions investigated. KDE shows the total precipitable water (TPW) of 38 mm can be used as the threshold for distinguishing dry THWs from wet ones. Dry THWs mainly concentrate in North China and Yunnan province, while wet ones mainly concentrate in South China. West of Hebei province has high frequencies for both dry and wet THWs. A comparison of pre-convection environmental conditions shows dry THWs mainly occur under environmental conditions with lower saturation at both the middle-lower and upper layers, while wet ones usually have relatively lower saturation at the middle-lower layers. The instability of wet THWs can be well characterized by the most unstable lifted index (MULI) and most unstable convective available potential energy (MUCAPE), while dry ones can be well depicted by the lower 500 hPa temperature caused higher temperature difference (DT85) or temperature lapse rate (TLR85) between 850 and 500 hPa. The 0–6-km vertical wind shear (SHR6) can distinguish dry THWs from wet ones better than SHR1. The typical difference can be comprehensively revealed by the representative soundings. The results provide objective references for understanding and forecasting THWs under dry and wet environmental conditions.

Adjustment of 1 min rain gauge time series using co-located drop size distribution and wind speed measurements

Abstract. A procedure to adjust rainfall intensity (RI) measurements to account for the wind-induced measurement bias of traditional catching-type gauges is proposed and demonstrated with an application to a suitable case study. The objective is to demonstrate that adjustment curves derived from numerical simulations and disdrometer measurements allow for a posteriori correction of rainfall time series based on the wind velocity measurements alone. To quantify the impact of wind on long-term records, 1 min RI measurements from a cylindrical tipping-bucket rain gauge installed at the Hong Kong Observatory are adjusted. Catch ratios derived from the instrument's aerodynamic behaviour under varying wind speed and drop size combinations are obtained by fitting computational fluid-dynamic simulation results already available in the literature. Co-located high-resolution wind speed measurements from a cup and vane sensor and drop size distribution measurements from an optical video disdrometer (the 2DVD or two-dimensional video disdrometer) are used to infer the collection efficiency of the gauge as a function of wind speed and RI alone and to adjust raw data from a 4-year dataset (2018–2021) of 1 min RI measurements. Due to the specific local climatology, where strong wind is often associated with intense precipitation, 80 % of the dataset adjustments are limited to 4 % of the observed RI values. This, however, results in a significant amount of available freshwater resources that would be missing from the calculated hydrological and water management budget of the region should the adjustments be neglected. This work raises the need to quantify the impact of the wind-induced bias at other sites where disdrometer data support a characterisation of the relationship between the drop size distribution and the measured RI. Depending on the local rain and wind climatology, the correction may account for a significant portion of the annual rainfall amount.

Wind Simulations over Western Patagonia Using the Weather Research and Forecasting model and Reanalysis

The Chilean Western Patagonia has the highest wind potential resources in South America. Its complex terrain deserves a special attention for wind modeling and assessments. In this work, we have performed a comprehensive meso-scale climate simulation on Weather Research and Forecasting (WRF) in order to provide new insights into the wind climatology in Western Patagonia. Simulations were carried out from 1989 to 2020, and we considered a previous sensitivity analysis for their configuration. In situ data from a wind mast, meteorological information and data from eddy flux stations were used to evaluate the results. Reanalysis data from ERA-5, MERRA-2 and RECON80-17 were also used to perform a comparison of the obtained results with the WRF simulation. The results show that the WRF simulation using ERA-5 presented in this work is slightly different to a mathematical reconstruction using MERRA-2 (RECON80-17), which is widely accepted in Chile for wind resource assessments, presenting a statistical difference of about EMD = 0.8 [m s−1] and RMSE = 0.5. Non-significative differences were found between the WRF simulation and MERRA-2 reanalysis, while ERA-5 with MERRA-2 presented a remarkable statistical difference of about EMD = 1.64 [m s−1] and RMSE = 1.8. In relation to flux comparison, reanalysis and WRF in contrast with in situ observations presented a good performance during the summer season, although a spatial resolution bias was noticed. These results can be used as an input for further research related to WRF simulations in Western Patagonia to provide reliable information on wind energy exploration and extreme climatological phenomena such as heat waves.

On the dynamics and air-quality impact of the exceptional East Asian dust outbreak in mid-March 2021

In mid-March 2021, one of the strongest dust storms of the last decade hit East Asia with adverse impacts on socio-economic activities and loss of life. The aim of this study is to assess the atmospheric dynamics involved in the temporal evolution of the Mongolian extra-tropical cyclone driving the dust event in different dust source regions in East Asia and to quantify to what extent the event was unusual for the first time. To that end, we use observation and model data from different sources. We identify that dust aerosols of the event primarily originated in the Gobi Desert. The anomalously strong dust-emitting winds were here associated with the passage of a cold front and exceeded the 99th percentile of the near-surface wind climatology for March 1992–2021 by far. Over the Loess Plateau, the dust deposition mostly exceeded the regional dust emission, indicative of the region being a net sink for dust aerosols, even during a high-impact event like in mid-March 2021. The formed dust aerosol layer of thousands of kilometers in extent led to sharp decreases in the air quality across China with record-high urban particulate matter concentrations, poor air quality, and low atmospheric visibility. Our results highlight that also the Taklamakan Desert contributed to the dust outbreak in the Western part of China. The dust emissions in the Taklamakan Desert were associated with nocturnal low-level jets that were favored by the cold air intrusion. It provides the first evidence for a link between different dust-emission mechanisms across East Asian Deserts during synoptic-scale dust outbreaks.

Spatial differences in impacts of CO2 effect on China’s meteorological droughts: Analysis from surface resistance perspective

Studying impacts of the CO2 effect on potential evapotranspiration (PET) and offline drought indices from surface resistance perspective is significant for understanding and accessing droughts. This study comprehensively investigated impacts of the CO2 effect on PET and Standardized Precipitation-Evapotranspiration Index (SPEI) over China during 1971–2010 based on two simulations with and without CO2 effect, respectively. We found that the CO2 effect led to decreased PET and increased SPEI, and decreased drought, which showed strong spatial variations with the greatest impact over northern China (excluding westernmost part for PET). Such spatial variations had functional relationships not only with CO2 concentration but also climatological conditions, i.e., climatological wind speed (U) and slope of vapour pressure curve (s) for PET, but climatological U, s and precipitation (P) for SPEI. Further analyses implied that climatological U (climatological U and P) determined the spatial variations in the CO2 effect-induced PET (SPEI) changes over China during 1971–2010.

An investigation of spatial wind direction variability and its consideration in engineering models

Abstract. We propose that considering mesoscale wind direction changes in the computation of wind farm cluster wakes could reduce the uncertainty of engineering wake modeling tools. The relevance of mesoscale wind direction changes is investigated using a wind climatology of the German Bight area covering 30 years, derived from the New European Wind Atlas (NEWA). Furthermore, we present a new solution for engineering modeling tools that accounts for the effect of such changes on the propagation of cluster wakes. The mesoscale wind direction changes relevant to the operation of wind farm clusters in the German Bight are found to exceed 11∘ in 50 % of all cases. Particularly in the lower partial load range, which is associated with strong wake formation, the wind direction changes are the most pronounced, with quartiles reaching up to 20∘. Especially on a horizontal scale of several tens of kilometers to 100 km, wind direction changes are relevant. Both the temporal and spatial scales at which large wind direction changes occur depend on the presence of synoptic pressure systems. Furthermore, atmospheric conditions which promote far-reaching wakes were found to align with a strong turning in 14.6 % of the cases. In order to capture these mesoscale wind direction changes in engineering model tools, a wake propagation model was implemented in the Fraunhofer IWES wind farm and wake modeling software flappy (Farm Layout Program in Python). The propagation model derives streamlines from the horizontal velocity field and forces the single turbine wakes along these streamlines. This model has been qualitatively evaluated by simulating the flow around wind farm clusters in the German Bight with data from the mesoscale atlas of the NEWA and comparing the results to synthetic aperture radar (SAR) measurements for selected situations. The comparison reveals that the flow patterns are in good agreement if the underlying mesoscale data capture the velocity field well. For such cases, the new model provides an improvement compared to the baseline approach of engineering models, which assumes a straight-line propagation of wakes. The streamline and the baseline models have been further compared in terms of their quantitative effect on the energy yield. Simulating two neighboring wind farm clusters over a time period of 10 years, it is found that there are no significant differences across the models when computing the total energy yield of both clusters. However, extracting the wake effect of one cluster on the other, the two models show a difference of about 1 %. Even greater differences are commonly observed when comparing single situations. Therefore, we claim that the model has the potential to reduce uncertainty in applications such as site assessment and short-term power forecasting.

Diurnal Valley Winds in a Deep Alpine Valley: Model Results

Thermally driven local winds are ubiquitous in deep Alpine valleys during fair weather conditions resulting in a unique wind climatology for any given valley. The accurate forecasting of these local wind systems is challenging, as they are the result of complex and multi-scale interactions. Even more so, if the aim is an accurate forecast of the winds from the near-surface to the free atmosphere, which can be considered a prerequisite for the accurate prediction of mountain weather. This study combines the evaluation of the simulated surface winds in several Alpine valleys with a more detailed evaluation of the wind evolution for a particular location in the Swiss Rhone valley, at the town of Sion during the month of September 2016. Four numerical simulations using the COSMO model are evaluated, two using a grid spacing of 1.1 km and two with a grid spacing of 550 m. For each resolution, one simulation is initialised with the soil moisture from the COSMO analysis and one with an increased soil moisture (+30%). In a first part, a comparison with observations from the operational measurement network of MeteoSwiss is used to evaluate the model performance, while, in a second part, data from a wind profiler stationed at Sion airport is used for a more detailed evaluation of the valley atmosphere near the town of Sion. The analysis focuses on 18 valley wind days observed in the Sion region in September 2016. Only the combination of an increased soil moisture and a finer grid spacing resulted in a significant improvement of the simulated flow patterns in the Sion region. This includes a stronger and more homogeneous along-valley wind in the Wallis and a more realistic cross-valley wind and temperature profile near the town of Sion. It is shown that the remaining differences between the observed and simulated near-surface wind are likely due to very local topographic features. Small-scale hills, not resolved on even the finer model grid, result in a constriction of the valley cross section and an acceleration of the observed low-level up-valley wind in the region of Sion.

How do topography and thermal front influence the water transport from the northern Laotieshan Channel to the Bohai Sea interior in summer?

Water renewal through the Bohai Strait largely dominates the water quality of the semi-enclosed Bohai Sea (BS), which connects only to the northern Yellow Sea (NYS) through the strait. Although the peak water transport through the Bohai Strait occurs in summer, the spatially averaged water residence time of the BS shows no significant decrease compared to other periods. A three-dimensional model is applied to unravel the detailed structure and dynamic processes of the summertime NYS water transport from the northern Laotieshan Channel to the BS interior. Model results from both climatological and hindcasting cases show that despite a large amount of the NYS water enters the strait, they are confined to the Laotieshan Channel between the Central Bank and Dalian surrounded by a strong Ω-shaped tidal front and could not move further north into the Liaodong Bay. The strong along-front flow steered by the topography forms a counter-clockwise circulation pattern in the strait zone, resulting in most of water southward movement east of the Central Bank, then join the outflow south of the strait and leave for the NYS. The Central Bank and the topographic sill north of the Laotieshan Channel act as a barrier that significantly reduces the water exchange between the strait zone and the BS interior, in particular the Liaodong Bay. Particle-tracking experiments suggest that less than 10% of particles released in the NYS could finally reach the BS interior, and among of them only a small portion of them could move further north into the Liaodong Bay. Momentum diagnostics suggest that the water transport northwest of the strait is dominated by geostrophic balance in the Ω-shaped frontal region. Sensitivity experiments indicate that tides promote the surface water transport from the NYS to the BS interior. The realistic wind forcing including synoptic events may facilitate the water transport from the strait to the BS interior by modulating the barotropic and baroclinic pressure gradient than that with the climatological wind case.

Channelling flows in the Hunter Valley

The Hunter Valley is well known for the strong westerly winds in winter and elevated fire danger arising from hot and dry north-westerly winds in summer. These hazards are closely related to the valley channelling in the region, and the connection between the two has been an interest to weather forecasters, emergency service personnel, and the aviation industry. In this paper, the climatology of valley winds is constructed to identify the dominant types of channelling in the Hunter Valley and their preferred directions using the 10-year data of Automatic Weather Station observations, upper air sounding and ERA5 reanalysis data between July 2010 and June 2020. Particular attention is given to the conceptual model of pressure-driven channelling of westerlies in winter and its mechanics, as the climatology shows that it is the main cause of wind-warning conditions in the Hunter.

A climatology-based wind speed map for NBR 6123

abstract: Updating the basic wind speed map of NBR 6123 –-Wind loading on buildings – is one of the duties of the committee responsible for the revision of this code. Traditionally such maps are elaborated by means of extreme value wind speed data collected at meteorological stations, use of statistical methods for data characterization, and application of mathematical regression to elaborate the territorial maps. However, the spatial distribution of the atmospheric phenomena responsible for strong winds cannot be disregarded. This work presents a proposal for a new wind speed map for NBR 6123 combining a climatological approach and wind speed data recently compiled from hundreds of meteorological stations. A climatological wind map was first produced considering the phenomena which cause strong winds, and used as a basis to draw the isopleths of the basic wind speed map, considering the measured wind speed data. The resulting map shows basic wind speeds ranging from 30 to 48m/s.

Current and future wind energy resources in the North Sea according to CMIP6

Abstract. We explore the changes in wind energy resources in northern Europe using output from historical to mid-21st century CMIP6 simulations and the high-emission SSP5-8.5 scenario. This study improves upon many assumptions made in the past. First, we interpolate the winds to hub height using model-level raw data; second, we use a large ensemble of CMIP6 models; third, we consider the possible wake effects on the annual energy production of a large wind farm cluster proposed for the North Sea. The common practice of extrapolating 10 m wind speeds to turbine height using the power law with a constant shear exponent is often a poor approximation of the actual turbine-height wind speed. This approximation can exaggerate the future changes in wind resources and ignore possible surface roughness and atmospheric stability changes. The evaluation of the wind climatologies in the CMIP6 models over the North Sea for the historical period shows good correspondence with measurements from tall masts and three reanalysis data points for 16 of the 18 models. Some of the models run at relatively high spatial resolution are as good as the reanalyses at representing the wind climate in this region. Our results show that annual mean wind speed and wind resources in northern Europe are not particularly affected by climate change in 2031–2050 relative to 1995–2014, according to a subset of 16 models in the CMIP6 collection. However, the seasonal distribution of these resources is significantly altered. Most models agree on reductions in the future wind in summer in a band that extends from the British Isles to the Baltic Sea and on increases in winter in the southern Baltic Sea. The energy production calculations show that summer energy production in a planned large wind farm cluster in the North Sea could be reduced by a median of 6.9 % during 2031–2050 when taking into account the wind farm wakes (that accounts for −0.7 %) and the changes in air density (that account for −0.9 %).