High Wind Speed Regime Research Articles

Sources of anisotropy in the Reynolds stress tensor in the stable boundary layer

AbstractData collected by 12 sonic anemometers over the Plaine Morte Glacier (Swiss Alps) during the Snow Horizontal Arrays Turbulence Study are used to investigate sources of anisotropy in the Reynolds stress tensor for stable boundary layers. A coarse‐graining approach is applied to evaluate transfers of kinetic energy across scales, and internal gravity waves (IGWs) are detected with a suitable criterion. Both approaches are combined with a classification of anisotropy based on the barycentric map of 1 min Reynolds stress tensors. A wind‐speed threshold is found that discriminates between regimes with a different dominant topology of the Reynolds stress tensor. One‐component and isotropic states are frequent for low wind speed and strong stratification, whereas two‐component axisymmetric states dominate the high wind speed regime with strong vertical shear. Results suggest that the presence of IGWs is mostly responsible for one‐component states, and additionally influences the relative amount of kinetic and potential energy in the perturbation field. To provide supporting evidence, a complementary analysis of a clean IGW detected during a field campaign in Dumosa (Australia) is presented. This case study highlights how waves contribute to drive the Reynolds stress tensor towards the one‐component limit. Cases are shown where a linear detrending procedure may be effective in filtering out waves and avoid their spurious contributions in turbulence statistics.

A Review of Parameterizations for Enthalpy and Momentum Fluxes from Sea Spray in Tropical Cyclones

AbstractThe intensity of tropical cyclones is sensitive to the air-sea fluxes of enthalpy and momentum. Sea spray plays a critical role in mediating enthalpy and momentum fluxes over the ocean’s surface at high wind speeds, and parameterizing the influence of sea spray is a crucial component of any air-sea interaction scheme used for the high wind regime where sea spray is ubiquitous. Many studies have proposed parameterizations of air-sea flux that incorporate the microphysics of sea spray evaporation and the mechanics of sea spray stress. Unfortunately, there is not yet a consensus on which parameterization best represents air-sea exchange in tropical cyclones, and the different proposed parameterizations can yield substantially different tropical cyclone intensities. This paper seeks to review the developments in parameterizations of the sea spray-mediated enthalpy and momentum fluxes for the high wind speed regime and to synthesize key findings that are common across many investigations.

Tropical Cyclone Wind Speed Estimation From Satellite Altimeter‐Derived Ocean Parameters

AbstractThis study investigates the satellite altimeter‐derived ocean parameters from Joint Altimetry Satellite Oceanography Network (Jason)‐2 and Jason‐3 response to the coincident wind speed at 10 m from sea surface (U10) from Meteorological Operational (MetOp)‐A and MetOp‐B satellite scatterometers inside the tropical cyclone environment. The high wind speed regime and rainy condition inside the tropical cyclone have reduced the U10 accuracy and thus, would benefit from more ocean related parameters to be considered. The altimeter Ku‐band backscatter and significant wave height are commonly used to estimate extreme U10 but still show significant error in rainy tropical cyclone. New U10 models incorporating several Jasons derived ocean parameters (including brightness temperatures and water content) were designed by the multiple linear regression and artificial neural network techniques. Parameter analysis indicated that the C‐band backscatter outperforms the Ku‐band counterpart in relation to U10 inside the tropical cyclone. The proposed models show U10 estimation up to 35 ms−1 with 1 ms−1 accuracy and major improvement inside the tropical cyclone rain and at the high wind speed regime. This too shows the ability of satellite altimeter in estimating U10 in extreme environment with great accuracy.

Effects of the Sea Surface Roughness and Sea Spray‐Induced Flux Parameterization on the Simulations of a Tropical Cyclone

AbstractA tropical cyclone (TC) interacts with the ocean through the interchange of surface fluxes of heat and momentum at the air‐sea interface. The sustainability and intensification of TCs are maintained by the enhancement in the latent heat flux in the high wind speed regime. An accurate calculation of heat fluxes is vital to understand the dynamics of the TC. The sea surface roughness is a crucial parameter that modulates the air‐sea fluxes. A coupled ocean‐atmosphere‐wave model is used to simulate TC Vardah over the Bay of Bengal during 10–15 December 2016. The study focuses on the influence of sea surface roughness on the heat fluxes, track, and intensity of TC Vardah. Four numerical experiments are performed with different parameterization schemes for surface roughness on the basis of (i) frictional velocity (Charnock), (ii) wave age, (iii) wave steepness, and (iv) a combination of wave steepness and wave age. A change in ocean surface roughness results in the modification of the cyclone track and heat fluxes. However, the effect of sea spray on the simulation of wind intensity of TC Vardah is only marginal. Out of the four experiments, the wave age‐based roughness parameterization was found to improve cyclone track, wind, and, hence, the generation of wind waves on the sea surface. In the case study of TC Vardah, the dynamic sea spray reduces surface wind speed up to 1.5 m/s which is within the uncertainty range of the model. An intercomparison of model experiments reveals the impact of surface heat fluxes on the TC Vardha characteristics.

Sensitivity of PBL parameterizations on PM10 and ozone simulation using chemical transport model WRF-Chem over a sub-tropical urban airshed in India

Meteorology plays vital role in predicting air quality parameters in regional chemical transport models. WRF-Chem is one such chemical transport model that includes various physics and chemistry options for simulating ozone and PM10 concentrations. In this study, WRF-Chem model was used to compare the performance of different Planetary Boundary Layer (PBL) parameterization namely, the Yonsei University (YSU) and Asymmetric Convective Model v2 (ACM2) PBL schemes, over the Delhi megacity urban airshed. Surface observations were used for comparisons and evaluating model performance for both meteorological and air quality variables. The ACM2 PBL scheme resulted in better model performance for simulating ozone and PM10 concentrations along with an improvement in temperature and wind speeds due to incorporation of both local and non-local characteristics. The dependency of ozone and PM10 concentrations on meteorological parameters temperature and wind speed were studied. The influence of PBL height and ventilation coefficient on model performance was analysed as dispersion of pollutants strongly depend on these factors. The PBL height was highly over estimated during evening hours which was also reflected in the corresponding ventilation coefficient values. Even though ACM2 PBL scheme was concluded as the best PBL scheme for the study region, it still requires significant improvement for simulating air quality parameters. Further, ozone and PM10 concentrations were scrutinized for varying ranges of temperature and wind speed. Model performance for ozone and PM10 concentrations was good for temperature values below 40 °C and wind speed ≤8 m/s. A poor model performance was observed for regions with high wind speed values. Even though certain limitations were observed in the model evaluation of PBL height and high wind speed values, WRF-Chem model can be effectively employed for simulating ozone and PM10 concentrations giving due considerations to limitations on high temperature and high wind speed regime.

Tropical Cyclone Winds Retrieved From C-Band Cross-Polarized Synthetic Aperture Radar

This paper presents a geophysical model function (GMF) that has been developed to describe the relation of the ocean surface wind with the normalized radar cross section (NRCS) at C-band cross polarization (cross-pol). Synthetic aperture radar (SAR) images have been simultaneously collected at copolarization (co-pol) and cross-pol at moderate to high wind speeds. Using the SAR co-pol retrieved wind fields and an uncertainty estimate of the retrieved wind speeds, the cross-pol dependencies of the NRCS are investigated with respect to wind, incidence angle, and polarization pairs. For wind speeds above 10 m/s, there is a significant dependence of the NRCS on wind speed. However, the SAR cross-pol data are also significantly affected by the noise floor and crosstalk between the channels. Estimates of the noise floor are determined and removed from the NRCS. Three GMFs are developed: the first is for transmission at horizontal (H) polarization and the second at vertical (V) polarization. A third GMF accounts for wind direction dependence. Validation of the GMFs is conducted by comparison with collocated Stepped Frequency Microwave Radiometer (SFMR) data. The resulting bias of -0.7 m/s and standard deviation of 3.7 m/s demonstrate the excellent performance for these GMFs for wind speed retrieval between 10 and 35 m/s. Furthermore, comparisons show that SAR cross-pol retrieved wind speeds are of similar quality as those of SFMR and are significantly better in the moderate to high wind speed regime than SAR co-pol retrieved winds.

Closure to Discussion on “Primary Frequency Regulation by Deloaded Wind Turbines Using Variable Droop”

In this paper, a detailed ancillary service pricing mechanism must be in place to encourage wind farm owners to opt for deloaded operating strategies. The authors do not agree that “over-speeding” de-loading tends to respond poorly in the high wind-speed regime; on the contrary, the WTG response to frequency regulation will be better during high wind speeds due to higher reserve generation available. As demonstrated in this work, it is possible to reduce the stability related issues significantly by carefully selecting the deloading percent and the droop parameter of the wind turbine generator.

Assessment of the ASCAT wind error characteristics by global dropwindsonde observations

This research focuses on assessing the accuracy of the advanced scatterometer (ASCAT) wind vector around tropical cyclones by using data from dropwindsondes deployed by the surveillance and reconnaissance flights during 2007–2010. There are 987 matching samples for the comparisons, with wind speed up to 50 m s−1. The bias and root‐mean‐square differences of wind speed between ASCAT and dropwindsonde data are −1.7 and 5.3 m s−1, respectively. Further analyses also indicate that large wind direction differences occur in the low wind speed regime, while large wind speed differences occur in the high wind speed regime. The accuracy of wind vector in weak wind speed and high wind speed regimes are significantly reduced in saturated regions, implying that the rain contamination issue still affects the accuracy of ASCAT wind retrieval. The wind vector in the medium wind speed regime has much better quality, in good agreement with the satellite's designed specification. The ASCAT wind data obviously contain negative wind speed bias, which grows larger as wind speed increases. A regression fit between ASCAT and dropwindsonde wind speed is adopted to correct the bias of the ASCAT wind speed. The error characteristics are largely determined by the magnitude of wind speed and moisture saturation which are highly variable around the storm. Nevertheless, results from this study suggest that ASCAT wind data of velocities measuring between 12 and 18 m s−1 are more reliable and can be applied to determine the radius of 34 knot winds, a critical parameter in operational tropical cyclone analysis.

풍력발전시스템 출력에 대한 난류강도의 영향 연구

The installed capacity of wind turbines in Korea are growing and enlarging by the central government`s supporting program. But the majority area having the abundant wind energy resources is composed of mountainous and complex district, thus the turbulence intensity of there is so high and belongs to the turbulence characteristic A category of IEC design requirement. This paper presents the effect of the turbulence intensity on the power performance of a wind turbine system. Particularly, the effect of the power curve of the wind turbine system due to the turbulence intensity has analyzed. As a result, the power curve has a high turbulence characteristic shows the lower value than normal one in high wind speed regime and the AEP will be reduced at the relatively high turbulence area.

Meteorological profiles and optical turbulence in the free atmosphere with NCEP/NCAR data at Oukaïmeden - I. Meteorological parameters analysis and tropospheric wind regimes

In this paper, we have used the National Centers for Environmental Prediction (NCEP)/National Centers for Atmospheric Research (NCAR) Reanalysis data base to study, first, a comparison between balloon sounding made at different stations with coinciding model-based meteorological analysis. The comparison allows the assessment of reliability of the analysis in the studied period and to highlight NCEP/NCAR Reanalysis as an interesting data base for site characterization. Using the same system of Reanalysis, we present, secondly, the first complete characterization of main meteorological parameters at Oukaimeden Observatory: wind speed, its direction, temperature and pressure. The statistical treatment of data will cover the years between 1990 and 2009. Monthly, seasonal and annual results are analysed. The comprehensive and reliable statistics of tropospheric wind speeds at Oukaimeden are presented. We found a clear annual periodicity of 200 mbar wind speed. This periodicity could be related to the seasonal dependence of seeing that is affected by the existence of cloud sea during the period around autumn–winter and by high wind speed regimes during spring. The connection of high- to low-altitude tropospheric winds has been explored. We found a high correlation comparable to the ones found at La Silla and La Palma sites. The local parameters in particular topography and stratocumulus formations might affect 700 mbar wind roses. Richardson numbers calculated for each month at Oukaimeden and La Palma are presented. By analysing the values, we found out that the periods and the regions of development of turbulence in relative terms of stability for the two locations are very similar. In addition, we present the first example of a profile estimated from NCEP/NCAR Reanalysis. We found that this profile presents a tendency very similar to the same averaged profile measured by the balloon-born radiosondes.

On the parameterization of turbulent fluxes over the tropical Eastern Pacific

Abstract. We present estimates of turbulent fluxes of heat and momentum derived from low level (~30 m) aircraft measurements over the tropical Eastern Pacific and provide empirical relationships that are valid under high wind speed conditions (up to 25 ms−1). The estimates of total momentum flux and turbulent kinetic energy can be represented very accurately (r2=0.99, when data are binned every 1 ms−1) by empirical fits with a linear and a cubic terms of the average horizontal wind speed. The latent heat flux shows a strong quadratic dependence on the horizontal wind speed and a linear relationship with the difference between the air specific humidity and the saturated specific humidity at the sea surface, explaining 96% of the variance. The estimated values were used to evaluate the performance of three currently used parameterizations of turbulence fluxes, varying in complexity and computational requirements. The comparisons with the two more complex parameterizations show good agreement between the observed and parameterized latent heat fluxes, with less agreement in the sensible heat fluxes, and one of them largely overestimating the momentum fluxes. A third, very simple parameterization shows a surprisingly good agreement of the sensible heat flux, while momentum fluxes are again overestimated and a poor agreement was observed for the latent heat flux (r2=0.62). The performance of all three parameterizations deteriorates significantly in the high wind speed regime (above 10–15 ms−1). The dataset obtained over the tropical Eastern Pacific allows us to derive empirical functions for the turbulent fluxes that are applicable from 1 to 25 ms−1, which can be introduced in meteorological models under high wind conditions.