The aim of this study was to generate hourly mean monthly maximum wind speed return period curves for heights 60 m above the ground using Weather Research and Forecasting modeled data. The ...methodology introduced produces long-term wind speed data in places where the available measured series for such heights are not long enough for a correct extreme value analysis. Climate Forecast System Reanalysis data are used as input for the Weather Research and Forecasting simulations, providing information for the period 1979–2015. The modeled results are compared with wind speed series measured in anemometric towers, available for the period 2008–2015. Weather Research and Forecasting output is then adjusted to model properly the wind speed at the measuring sites. A good representation of the cumulative distribution of monthly maxima was reached after applying a double linear adjustment.
The rain-free normalized radar cross-section (NRCS) measurements from the Ku-band precipitation radars (PRs) aboard the tropical rainfall measuring mission (TRMM) and the global precipitation ...measurement (GPM) mission, along with simultaneous sea surface wind truth from buoy observations, stepped-frequency microwave radiometer (SFMR) measurements, and H*Wind analyses, are used to investigate the abilities of the quasi-specular scattering models, i.e., the physical optics model (PO) and the classical and improved geometrical optics models (GO and GO4), to reproduce the Ku-band NRCS at low incidence angles of 0–18° over the wind speed range of 0–45 m/s. On this basis, the limitations of the quasi-specular scattering theory and the effects of wave breaking are discussed. The results show that the return caused by quasi-specular reflection is affected significantly by the presence of background swell waves at low winds. At moderate wind speeds of 5–15 m/s, the NRCS is still dominated by the quasi-specular reflection, and the wave breaking starts to work but its contribution is very small, thus, the models are found in excellent agreement with the measurements. With wind speed increasing, the impact of wave breaking increases, whereas the role of standard quasi-specular reflection decreases. The wave breaking impact on NRCS is first visible at incidence angles near 18° as wind speed exceeds about 20 m/s, then it becomes dominant when wind speed exceeds about 37 m/s where the NRCS is insensitive to wind speed and depends linearly on incidence angle, which cannot be explained by the standard quasi-specular scattering theory.
The Madeira International Airport (MIA) lies on the island’s south-eastern coast and it is known to be exposed to wind hazards. A link between these adverse winds at MIA and the synoptic-scale ...circulation is established using a weather type (WT) classification. From April to September (summer period), five WTs prevail, cumulatively representing nearly 70% of days. These WTs reflect the presence of well-established Azores high, with some variations on location and strength. Although with a low frequency of occurrence (<5%), this anticyclone occasionally strengthens and extends towards Iberia, inducing anomalously strong NNE/NE up to 3–5 km over Madeira. The most severe and longer-lasting wind conditions at the MIA, with a higher frequency of gusts above 35 kt, are driven by this synoptic-scale pattern and are more common in summer. An episode of adverse winds at the MIA is analysed, illustrating the occurrence of upstream stagnation, flow splitting, and lee wake formation. The upstream conditions include a low-level inversion, strong NNE/NE winds near and above the inversion and a Froude number less than 1. The AROME (Application of Research to Operations at Mesoscale) model predicted the occurrence of downslope winds, in association with a large-amplitude mountain wave. At this time, the strongest wind gusts were registered and one aircraft executed a missed approach. The wind regime in different places of the island suggests that these conditions are relatively frequent, mostly in summer. Finally, objective verification of AROME wind forecast, for a three-year period and from June to August, is discussed.
Morphology and evolution of cold‐frontal misocyclones Smart, D. J.; Browning, K. A.
Quarterly journal of the Royal Meteorological Society,
January 2009 Part B, 2009, 2009-01-00, 20090101, Letnik:
135, Številka:
639
Journal Article
Wind gusts are parameterized in a numerical weather prediction model using a new method based on considerations of turbulence and atmospheric stability in the planetary boundary layer. This method ...was recently introduced by Brasseur and has already been successfully applied to various atmospheric situations, amongst those several in the complex terrain in Iceland. In this study, the method is applied to a large collection of simulations of flow over Iceland. The simulated data is generated with the MM5 numerical model at a high horizontal resolution and using boundary conditions from the ECMWF. The performance of the method is validated by comparison with wind gust observations from a collection of automatic weather stations spread throughout flat and mountainous terrain in Iceland. The accuracy of the method is strongly dependent on the accuracy of the simulated atmospheric fields and for locations where the mean wind speed is well simulated, the predicted wind gusts are found to be in general in acceptable agreement with the observations.
Wind gusts are parameterized in a numerical weather prediction model using a new method based on considerations
of turbulence and atmospheric stability in the planetary boundary layer. This method ...was recently introduced by Brasseur and has already been successfully applied to various atmospheric situations, amongst those several in the complex terrain in Iceland. In this study, the method is applied to a large collection of simulations of flow over Iceland. The simulated data is generated with the MM5 numerical model at a high horizontal resolution and using boundary conditions from the ECMWF. The performance of the method is validated by comparison with wind gust observations from a collection of automatic weather stations spread throughout flat and mountainous terrain in Iceland. The accuracy of the method is strongly dependent on the accuracy of the simulated atmospheric fields and for locations where the mean wind speed is well simulated, the predicted wind gusts are found to be in general in acceptable agreement with the observations.
This paper deals with the application of Smith's (1985) internal hydraulic theory to some special cases of Adriatic bora during ALPEX SOP. ln particular, the case of 15 April 1982 is analysed for ...which the numerical simulation by Klemp and Durran (1987) is available. Their conclusion is that in this case neither inversion nor critical level are important for the bora occurrence, but the low-level wave breaking due to weak flow in the upstream region. While this conclusion seems reasonable, from the present analysis it is argued that these results are valid only for the characteristics of the local bora in Senj and not for the flow across the higher mountains along the northern Adriatic coast.
This conclusion is based on a comparison with the results of the theory application to the stronger bora condition on the previous day and especially to the case of the strongest SOP bora on 6 March 1982 for which the hydraulic theory offered much better results.
Cool season severe wind events may be related to the occurrence of mesoscale convective systems with a bow echo (i.e. arch-shaped band of radar reflectivity). This research provides an insight into ...the spatial and temporal distribution of bow echoes occurring in the cool season (October–March) between January 2007 and March 2019 over Poland and presents atmospheric conditions (synoptic, kinematic, and thermodynamic) associated with such events. The analysis has been performed utilizing SYNOP (surface observations), ESWD (European Severe Weather Database), radar (CMAX, CAPPI), reanalysis (ERA-5) and sounding data. During the period studied, 27 Cool Season Bow Echoes (CSBEs) were identified across Poland. The area most exposed to the occurrence of CSBEs included south-western Poland, while the north-eastern and eastern part of the country was generally free of this phenomenon. Unlike the warm season cases, CSBEs do not indicate a clear diurnal cycle. As our results have shown, a high shear/low CAPE (Convective Available Potential Energy) environment in combination with a triggering mechanism along the cold front (frontal cases) or along the surface trough (post-frontal cases) can be considered as supportive for CSBE. Such cases were always associated with the presence of strong air flow in the low and mid troposphere. The analysis of 500 hPa geopotential height fields revealed that troughs (often with embedded smaller-amplitude dynamic waves) moving over Central Europe were present in 26 out of 27 cases. The median value of vertical wind shear for identified cases exceeded 30 m/s for deep-layer shear (DLS), was well above 20 m/s for mid-level shear (MLS), and higher than 17 m/s for low-level shear (LLS). A recurring finding was also that post-frontal cases formed in an environment with weaker shear, but higher CAPE.
•The spatiotemporal distribution of cool season bow echoes (CSBEs) in Poland.•27 CSBEs have been identified between 2007 and 2019.•CSBEs are strongly affected by the presence of fast flow from mid to upper level.•CSBEs are characterized by weak instability and strong vertical wind shear.
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