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Showing papers on "Wind shear published in 2021"


Journal ArticleDOI
01 Jan 2021-Energy
TL;DR: In this article, the effects of three atmospheric factors (atmospheric stability, turbulence intensity, and wind shear exponent) on the power performance and annual energy production of wind turbines were analyzed.

36 citations


Book ChapterDOI
01 Jan 2021
TL;DR: In this paper, Rossby waves, jets, and waveguides affect atmospheric eddies, such as anticyclonic blocks, and can create prolonged weather conditions that lead to extreme weather impacts.
Abstract: Strong rivers of westerly winds, known as jet streams, are driven primarily by temperature differences between low and high latitudes as well as the rotation of the Earth. The jet streams create and impact weather systems and steer them in the midlatitudes of both hemispheres. Often, these jet streams do not flow directly from west to east, but rather meander north and south in a wave pattern of alternating high- and low-pressure regions. These meanders are Rossby waves, which influence the jet streams via baroclinic instability caused by temperature gradients. Depending on their wavelength, latitude, and the background wind speed, these waves can move to the east or to the west and under certain conditions also be (quasi)stationary. Jet streams can locally increase the gradient of vorticity (atmospheric spin), so that atmospheric wave guides may be formed. These waveguides affect the propagation pathways of Rossby waves, often leading to more zonal propagation, and potentially amplification of waves. Rossby waves, jets, and waveguides affect atmospheric eddies, such as anticyclonic blocks, and can create prolonged weather conditions that lead to extreme weather impacts. Anthropogenic climate change is weakening the north–south temperature gradient. The rapid warming of the Arctic, known as Arctic amplification, is one factor affecting the poleward temperature gradient. It has been hypothesized that a weakened jet stream tends to be “wavier,” which may increase the probability of atmospheric blocking. On the other hand, anthropogenic climate change also cools the polar lower stratosphere and warms the tropical upper troposphere, which should act to strengthen the jet. Jet streams may therefore be experiencing a “tug-of-war” between these effects with opposing signs. Together, these changes tend to increase the vertical wind shear in midlatitudes, leading to increases in turbulence at the cruising altitude of aircraft. It is not yet clear which of these two effects of amplified warming will be dominant, nor how this will depend on season, region, and background state, but changes in the jet would have potential implications for the frequency of extreme weather in a future, warmer climate.

34 citations


Journal ArticleDOI
TL;DR: The development of a more advanced three-dimensional wake model for wind power generation is presented based on a multivariate Gaussian distribution that is capable of predicting the wake distribution of a single wind turbine reasonably well and will benefit the power output of wind farms.

32 citations


Journal ArticleDOI
11 Jun 2021
TL;DR: In this article, the authors show that according to ERA5 convective available potential energy (CAPE) and convective precipitation (CP) have decreased over the tropics and subtropics with simultaneous increases in 0-6 km wind shear (BS06), whereas rawinsonde observations paint a different picture across the mid-latitudes with increasing CAPE and significant decreases to BS06.
Abstract: Globally, thunderstorms are responsible for a significant fraction of rainfall, and in the mid-latitudes often produce extreme weather, including large hail, tornadoes and damaging winds. Despite this importance, how the global frequency of thunderstorms and their accompanying hazards has changed over the past 4 decades remains unclear. Large-scale diagnostics applied to global climate models have suggested that the frequency of thunderstorms and their intensity is likely to increase in the future. Here, we show that according to ERA5 convective available potential energy (CAPE) and convective precipitation (CP) have decreased over the tropics and subtropics with simultaneous increases in 0–6 km wind shear (BS06). Conversely, rawinsonde observations paint a different picture across the mid-latitudes with increasing CAPE and significant decreases to BS06. Differing trends and disagreement between ERA5 and rawinsondes observed over some regions suggest that results should be interpreted with caution, especially for CAPE and CP across tropics where uncertainty is the highest and reliable long-term rawinsonde observations are missing.

25 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate how midlevel dry air and vertical wind shear (VWS) can modulate tropical cyclone (TC) development via radial ventilation and demonstrate the modulating effects of radial ventilation on TC development are the inward transport of low-equivalent potential temperature air, as well as low-level radial outflow upshear.
Abstract: This study demonstrates how midlevel dry air and vertical wind shear (VWS) can modulate tropical cyclone (TC) development via radial ventilation. A suite of experiments was conducted with different combinations of initial midlevel moisture and VWS environments. Two radial ventilation structures are documented. The first structure is positioned in a similar region as rainband activity and downdraft ventilation (documented in Part I) between heights of 0 and 3 km. Parcels associated with this first structure transport low–equivalent potential temperature air inward and downward left of shear and upshear to suppress convection. The second structure is associated with the vertical tilt of the vortex and storm-relative flow between heights of 5 and 9 km. Parcels associated with this second structure transport low–relative humidity air inward upshear and right of shear to suppress convection. Altogether, the modulating effects of radial ventilation on TC development are the inward transport of low–equivalent potential temperature air, as well as low-level radial outflow upshear, which aid in reducing the areal extent of strong upward motions, thereby reducing the vertical mass flux in the inner core, and stunting TC development.

23 citations


Journal ArticleDOI
TL;DR: In this paper, a physics-informed deep learning model is developed to achieve the reconstruction of the 3D spatio-temporal wind field in front of a wind turbine, by combining the 3-D Navier-Stokes equations and the scanning LIDAR measurements.

20 citations


Journal ArticleDOI
TL;DR: Li et al. as discussed by the authors applied a network of Doppler light detection and ranging (LiDAR) as well as back trajectory analysis to comprehensively analyze the effect of a weak Typhoon (Danas) occurring during 16-19 July 2019 on different variations in surface PM and O3 concentration.

18 citations


Journal ArticleDOI
TL;DR: In this article, large-eddy simulations are performed to elucidate the effects of wind shear coefficients (WSCs) and upstream turbulence intensities (TIs) on the complex wind flow fields over the simplified 3-D hills.

18 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the precipitation symmetrization preceding rapid intensification of tropical cyclones experiencing vertical wind shear by analyzing numerical simulations of Typhoon Mujigae (2015) with warm (CTL) and relatively cool (S1) sea surface temperatures (SSTs).
Abstract: This study investigates the precipitation symmetrization preceding rapid intensification (RI) of tropical cyclones (TCs) experiencing vertical wind shear by analyzing numerical simulations of Typhoon Mujigae (2015) with warm (CTL) and relatively cool (S1) sea surface temperatures (SSTs). A novel finding is that precipitation symmetrization is maintained by the continuous development of deep convection along the inward flank of a convective precipitation shield (CPS), especially in the downwind part. Beneath the CPS, downdrafts flush the boundary layer with low-entropy parcels. These low-entropy parcels do not necessarily weaken the TCs; instead, they are “recycled” in the TC circulation, gradually recovered by positive enthalpy fluxes, and develop into convection during their propagation toward a downshear convergence zone. Along-trajectory vertical momentum budget analyses reveal the predominant role of buoyancy acceleration in the convective development in both experiments. The boundary layer recovery is more efficient for warmer SST, and the stronger buoyancy acceleration accounts for the higher probability of these parcels developing into deep convection in the downwind part of the CPS, which helps maintain the precipitation symmetrization in CTL. In contrast, less efficient boundary layer recovery and less upshear deep convection hinder the precipitation symmetrization in S1. These findings highlight the key role of boundary layer recovery in regulating the precipitation symmetrization and upshear deep convection, which further accounts for an earlier RI onset timing of the CTL TC. The inward rebuilding pathway also illuminates why deep convection is preferentially located inside the radius of maximum wind of sheared TCs undergoing RI.

17 citations


Journal ArticleDOI
TL;DR: In this paper, the authors developed a new model for wind shear coefficient, α, which is able to capture hourly variability across a range of geographic/topographic features and demonstrate implications for wind energy estimates over a large geographical area.

17 citations


Journal ArticleDOI
TL;DR: In this article, an analysis of synoptic patterns and mesoscale precursors is produced for Italian tornadoes for the period 2000-2018, based on the ERA-5 reanalysis.

Journal ArticleDOI
15 Jan 2021
TL;DR: In this article, the authors used self-organizing maps to classify polar lows in the north-eastern Atlantic, which were obtained by matching mesoscale cyclones from the ERA-5 reanalysis to polar lows registered in the STARS dataset.
Abstract: . Polar lows are intense mesoscale cyclones that develop in polar marine air masses. Motivated by the large variety of their proposed intensification mechanisms, cloud structure, and ambient sub-synoptic environment, we use self-organising maps to classify polar lows. The method is applied to 370 polar lows in the north-eastern Atlantic, which were obtained by matching mesoscale cyclones from the ERA-5 reanalysis to polar lows registered in the STARS dataset by the Norwegian Meteorological Institute. ERA-5 reproduces most of the STARS polar lows. We identify five different polar-low configurations which are characterised by the vertical wind shear vector, the change in the horizontal-wind vector with height, relative to the propagation direction. Four categories feature a strong shear with different orientations of the shear vector, whereas the fifth category contains conditions with weak shear. This confirms the relevance of a previously identified categorisation into forward- and reverse-shear polar lows. We expand the categorisation with right- and left-shear polar lows that propagate towards colder and warmer environments, respectively. For the strong-shear categories, the shear vector organises the moist-baroclinic dynamics of the systems. This is apparent in the low-pressure anomaly tilting with height against the shear vector and the main updrafts occurring along the warm front located in the forward-left direction relative to the shear vector. These main updrafts contribute to the intensification through latent heat release and are typically associated with comma-shaped clouds. Polar-low situations with a weak shear, which often feature spirali-form clouds, occur mainly at decaying stages of the development. We thus find no evidence for hurricane-like intensification of polar lows and propose instead that spirali-form clouds are associated with a warm seclusion process.

Posted ContentDOI
TL;DR: In this paper, the effects of horizontal resolution on the simulation of tropical cyclones were studied using the Chinese Academy of Sciences (CAS) FGOALS-f3 model.
Abstract: . The effects of horizontal resolution on the simulation of tropical cyclones were studied using the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System Finite-Volume version 3 (FGOALS-f3) climate system model from the High-Resolution Model Intercomparison Project (HighResMIP) for the Coupled Model Intercomparison Project phase 6 (CMIP6). Both the low-resolution (about 100 km resolution) FGOALS-f3 model (FGOALS-f3-L) and the high-resolution (about 25 km resolution) FGOALS-f3 (FGOALS-f3-H) models were used to achieve the standard Tier 1 experiment required by HighResMIP. FGOALS-f3-L and FGOALS-f3-H have the same model parameterizations with the exactly the same parameters. The only differences between the two models are the horizontal resolution and the time step. The performance of FGOALS-f3-H and FGOALS-f3-L in simulating tropical cyclones was evaluated using observations. FGOALS-f3-H (25 km resolution) simulated more realistic distributions of the formation, movement and intensity of the climatology of tropical cyclones than FGOALS-f3-L at 100 km resolution. Although the number of tropical cyclones increased by about 50 % at the higher resolution and better matched the observed values in the peak month, both FGOALS-f3-L and FGOALS-f3-H appear to replicate the timing of the seasonal cycle of tropical cyclones. The simulated average and interannual variabilities of the number of tropical cyclones and the accumulated cyclone energy were both significantly improved from FGOALS-f3-L to FGOALS-f3-H over most of the ocean basins. The characteristics of tropical cyclones (e.g., the average lifetime, the wind–pressure relationship and the horizontal structure) were more realistic in the simulation using the high-resolution model. The possible physical linkage between the performance of the tropical cyclone simulation and the horizontal resolution were revealed by further analyses. The improvement in the response between the El Nino–Southern Oscillation and the number of tropical cyclones and the accumulated cyclone energy in FGOALS-f3 contributed to the realistic simulation of tropical cyclones. The genesis potential index and the vorticity, relative humidity, maximum potential intensity and the wind shear terms were used to diagnose the effects of resolution. We discuss the current insufficiencies and future directions of improvement for the simulation of tropical cyclones and the potential applications of the FGOALS-f3-H model in the subseasonal to seasonal prediction of tropical cyclones.

Journal ArticleDOI
10 Aug 2021
TL;DR: In this paper, the authors leverage a year of these lidar data to quantify and characterize the frequent occurrence of high-wind-shear and low-level-jet events, both of which will have a considerable impact on turbine operation.
Abstract: . As the offshore wind industry emerges on the US East Coast, a comprehensive understanding of the wind resource – particularly extreme events – is vital to the industry's success. Such understanding has been hindered by a lack of publicly available wind profile observations in offshore wind energy areas. However, the New York State Energy Research and Development Authority recently funded the deployment of two floating lidars within two current lease areas off the coast of New Jersey. These floating lidars provide publicly available wind speed data from 20 to 200 m height with a 20 m vertical resolution. In this study, we leverage a year of these lidar data to quantify and characterize the frequent occurrence of high-wind-shear and low-level-jet events, both of which will have a considerable impact on turbine operation. In designing a detection algorithm for these events, we find that the typical, non-dimensional power-law-based wind shear exponent is insufficient to identify many of these extreme, high-wind-speed events. Rather, we find that the simple vertical gradient of wind speed better captures the events. Based on this detection method, we find that almost 100 independent events occur throughout the year with mean wind speed at 100 m height and wind speed gradient of 16 m s −1 and 0.05 s −1 , respectively. The events have strong seasonal variability, with the highest number of events in summer and the lowest in winter. A detailed analysis reveals that these events are enabled by an induced stable stratification when warmer air from the south flows over the colder mid-Atlantic waters, leading to a positive air–sea temperature difference.

Journal ArticleDOI
Xiaoyan Wang1, Renhe Zhang1, Yanke Tan1, Wei Yu1, Wei Yu2 
TL;DR: In this paper, the authors investigated the mechanisms by which synoptic patterns negatively affect the decay processes of pollution episodes in 28 pollution channel cities of the Beijing region and found that PM2.5 concentrations after the decay process show a significantly decreasing trend from 2014 to 2020, reflecting successful emissions mitigation.
Abstract: . The variation in the concentrations of ambient PM2.5 (particles with an aerodynamic diameter less than 2.5 µm ) generally forms a continuous sawtooth cycle with a recurring smooth increase followed by a sharp decrease. The episode of abrupt decay of pollution is mostly meteorological in origin and is controlled by the passage of synoptic systems. One affordable and effective measure for quickly reducing PM2.5 concentrations in northern China is to wait for a strong wind to arrive. However, it is still unclear how strong the wind needs to be and exactly what kind of synoptic system most effectively results in the rapid decay of air pollution episodes. PM2.5 variations over the 28 pollution channel cities of the Beijing region are investigated to determine the mechanisms by which synoptic patterns affect the decay processes of pollution episodes. This work shows more obvious day-to-day variations in PM2.5 concentration in winter than in summer, which implies that wintertime PM2.5 variations are more sensitive to meteorological factors. There were 365 decay processes from January 2014 to March 2020, and 97 of them were related to the effective wet deposition. In total, 26 % – 43 % of PM2.5 pollutant is removed by the wet deposition in different seasons. Two dominant circulation patterns are identified in summer. All the other three seasons have three circulation types (CTs), respectively. The three CTs in spring show the same patterns as those in autumn and winter. The circulation patterns beneficial to the decay processes all exhibit a higher-than-normal surface wind speed, a negative relative humidity anomaly and net outflow of PM2.5 from the domain. In addition, CT1 in spring, autumn and winter is controlled by northeasterly wind and features the most significant horizontal net outflow of air pollutants and effective upward spread of air pollutants to the free atmosphere. CT2 is the most frequent CT in autumn and winter, with the highest wind speed from the northwest, highest boundary layer height (BLH) and lowest relative humidity among the three CTs, all of which are favorable for the reduction of PM2.5 concentrations. In CT3, strong vertical wind shear within the boundary layer enhances the mixing of surface air pollutants, which is the extra cleaning mechanism besides dry and clean air mass inflow. PM2.5 concentrations show significant decreases of more than 37 %, 41 % and 27 % after the passage of CT1, CT2 and CT3, respectively. A dry airflow with a positive BLH anomaly and the effective horizontal outflow of air pollutants are the main reasons for the abrupt decay phase in summer. PM2.5 concentrations after the decay process show a significant decreasing trend from 2014 to 2020, reflecting successful emission mitigation. Emission reductions have led to a 4.3–5.7 µ g m - 3 yr - 1 decrease in PM2.5 concentrations in the 28 pollution channel cities of the Beijing region.

Journal ArticleDOI
TL;DR: In this article, ten-year hourly recorded wind meteorological data at six sites along the coastline of Pakistan at two heights (10 and 50)m) were extrapolated to two higher heights (80 and 100m).
Abstract: Ten-year hourly recorded wind meteorological data at six sites along the coastline of Pakistan at two heights (10 and 50 m) were extrapolated to two higher heights (80 and 100 m). Monthly and seaso...

Journal ArticleDOI
TL;DR: In this article, the authors examined the effects of environmental vertical wind shear and storm motion on TC rainfall asymmetry over the North Indian Ocean (NIO): the Bay of Bengal (BoB) and the Arabian Sea (AS).

Journal ArticleDOI
TL;DR: In this article, the authors identify the source of a gravity wave (GW) observed over Greenland during the POLSTRACC (POLar STRAtosphere in a Changing Climate) aircraft campaign.
Abstract: . To better understand the impact of gravity waves (GWs) on the middle atmosphere in the current and future climate, it is essential to understand their excitation mechanisms and to quantify their basic properties. Here a new process for GW excitation by orography–jet interaction is discussed. In a case study, we identify the source of a GW observed over Greenland on 10 March 2016 during the POLSTRACC (POLar STRAtosphere in a Changing Climate) aircraft campaign. Measurements were taken with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) instrument deployed on the High Altitude Long Range (HALO) German research aircraft. The measured infrared limb radiances are converted into a 3D observational temperature field through the use of inverse modelling and limited-angle tomography. We observe GWs along a transect through Greenland where the GW packet covers ≈ 1 / 3 of the Greenland mainland. GLORIA observations indicate GWs between 10 and 13 km of altitude with a horizontal wavelength of 330 km , a vertical wavelength of 2 km and a large temperature amplitude of 4.5 K . Slanted phase fronts indicate intrinsic propagation against the wind, while the ground-based propagation is with the wind. The GWs are arrested below a critical layer above the tropospheric jet. Compared to its intrinsic horizontal group velocity (25–72 m s−1 ) the GW packet has a slow vertical group velocity of 0.05–0.2 m s−1 . This causes the GW packet to propagate long distances while spreading over a large area and remaining constrained to a narrow vertical layer. A plausible source is not only orography, but also out-of-balance winds in a jet exit region and wind shear. To identify the GW source, 3D GLORIA observations are combined with a gravity wave ray tracer, ERA5 reanalysis and high-resolution numerical experiments. In a numerical experiment with a smoothed orography, GW activity is quite weak, indicating that the GWs in the realistic orography experiment are due to orography. However, analysis shows that these GWs are not mountain waves. A favourable area for spontaneous GW emission is identified in the jet by the cross-stream ageostrophic wind, which indicates when the flow is out of geostrophic balance. Backwards ray-tracing experiments trace into the jet and regions where the Coriolis and the pressure gradient forces are out of balance. The difference between the full and a smooth-orography experiment is investigated to reveal the missing connection between orography and the out-of-balance jet. We find that this is flow over a broad area of elevated terrain which causes compression of air above Greenland. The orography modifies the wind flow over large horizontal and vertical scales, resulting in out-of-balance geostrophic components. The out-of-balance jet then excites GWs in order to bring the flow back into balance. This is the first observational evidence of GW generation by such an orography–jet mechanism.

Journal ArticleDOI
TL;DR: In this paper, a techno-economic assessment of wind energy potential for four passes of Tamil Nadu (Aralvaimozhi, Shencottah, Palghat, and Cumbum) with uncertainty factors is presented.
Abstract: This work demonstrates a techno-economical assessment of wind energy potential for four passes of Tamil Nadu (Aralvaimozhi, Shencottah, Palghat, and Cumbum) with uncertainty factors. First, a potential assessment was carried out with time-series data, and the Weibull parameters, such as c (scale) and k (shape), were determined using the modern-era retrospective analysis for research and applications (MEERA) data set. Using these parameters, the mean speed, most probable speed, power density, maximum energy-carrying speed of wind power were determined. From the analysis, it was observed that all four passes had better wind parameters; notably, the Aralvaimozhi pass attained a better range of about 6.563 m/s (mean wind speed), 226 W/m2 (wind power density), 6.403 m/s (most probable wind speed), and 8.699 m/s (max wind speed). Further, uncertainty factors, such as the probability of exceedance (PoE), wind shear co-efficient (WSC), surface roughness, and wake loss effect (WLE), were evaluated. The value of PoE was found to be within the bound for all the locations, i.e., below 15%. In addition, the ranged of WSC showed a good trend between 0.05 and 0.5. Moreover, the surface length of the passes was evaluated and recorded to be 0.0024 m with a 73% energy index. Further, output power, annual energy production (AEP), capacity factor (CF), and cost of wind energy of all four passes were computed using different wind turbine ratings in two cases, i.e., with and without WLE. It was observed that there was a huge profit in loss from all the four locations due to WLE that was estimated to be Rupees (Rs.) 10.07 crores without considering interest components and Rs. 13.66 crores with interest component at a 10% annual rate of interest.

Journal ArticleDOI
TL;DR: In this article, a suite of high-resolution idealized numerical model simulations of squall lines were run in various vertical wind shear (hereafter “shear”) environments to study the effects of shear on entrainment in deep convective updrafts.
Abstract: The influence of vertical wind shear on updraft entrainment in squall lines is not well understood. To address this knowledge gap, a suite of high-resolution idealized numerical model simulations of squall lines were run in various vertical wind shear (hereafter “shear”) environments to study the effects of shear on entrainment in deep convective updrafts. Low-level horizontal mass flux into the leading edge of the cold pool was strongest in the simulations with the strongest low-level shear. These simulations consequently displayed wider updrafts, less entrainment-driven dilution, and larger buoyancy than the simulations with comparatively weak low-level shear. An analysis of vertical accelerations along trajectories that passed through updrafts showed larger net accelerations from buoyancy in the simulations with stronger low-level shear, which demonstrates how less entrainment-driven dilution equated to stronger updrafts. The effects of upper-level shear on entrainment and updraft vertical velocities were generally less pronounced than the effects of low-level shear. We argue that in addition to the outflow boundary-shear interactions and their effect on updraft tilt established by previous authors, decreased entrainment-driven dilution is yet another beneficial effect of strong low-level shear on squall line updraft intensity.

Journal ArticleDOI
Abstract: We present new results of our studies of zonal and meridional winds in both hemispheres of Venus, using ground- and space-based coordinated observations. The results obtained from telescope observations were retrieved with a Doppler velocimetry method. The wind velocities retrieved from space used an improved cloud-tracked technique based on the phase correlation between images. We present evidence that the altitude level sensed by our Doppler velocimetry method is approximately four kilometres higher (~4 km) than that using ground-tracked winds (using 380 or 365 nm). Since we often take advantage of coordinated space and ground observations simultaneously, this altitude difference will be very relevant in order to estimate the vertical wind shear at the related heights in future observation campaigns. We also explored a previous coordinated campaign using Akatsuki observations and its Ultraviolet Imager (UVI) at 283 and 365 nm filters, which showed that cloud-tracked winds showed a difference of about 10–15 ms−1, as in the case of the comparison between the Doppler velocimetry winds and the 365 nm cloudtracked winds. The results’ comparison also strongly suggested that the cloud-tracked winds based on the 283 nm filter’s images were sensing at about the same atmospheric altitude level as the Doppler winds. The observational results were compared with the ground-to-thermosphere 3D model developed at the Laboratoire de Meteorologie Dynamique (IPSL-Venus General Circulation Model (VGCM)) and AFES-Venus General Circulation Model (GCM), at several pressure levels (and related heights). The analysis and results showed the following: (1) additional confirmation of the coherence and complementarity in the results provided by these techniques on both the spatial and temporal time scales of the two methods; (2) we noticed in the following that the results from the two different Akatsuki/UVI filters (283 and 365 nm) showed an average difference of about 10–15 ± 5 ms−1, and we suggest this may be related to SO2 atmospheric fluctuations and the particular conditions in the coordinated observing time window; (3) we present evidence indicating that, in the context of our observations, visible Doppler methods (highly self-consistent) seem to sense wind speeds at a vertical level closer to or within the range sensed by the UVI 283 nm filter images (again, in the context of our observations); (4) modelling predicted wind profiles suggests that the layers of the atmosphere of Venus sensed by the methods referred to in Point 3 differ by approximately four km in altitude (~4 ± 2 km) regarding the cloud-tracked winds retrieved using 365 or 380 nm images.

Journal ArticleDOI
02 Feb 2021
TL;DR: In this article, the authors analyzed the characteristics of embedded convection in the WCB of cyclone Sanchez based on WCB online trajectories from a convection-permitting simulation and airborne radar observations during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) field campaign (intense observation periods, IOPs, 10 and 11).
Abstract: . Warm conveyor belts (WCBs) are dynamically important, strongly ascending and mostly stratiform cloud-forming airstreams in extratropical cyclones. Despite the predominantly stratiform character of the WCB's large-scale cloud band, convective clouds can be embedded in it. This embedded convection leads to a heterogeneously structured cloud band with locally enhanced hydrometeor content, intense surface precipitation and substantial amounts of graupel in the middle troposphere. Recent studies showed that embedded convection forms dynamically relevant quasi-horizontal potential vorticity (PV) dipoles in the upper troposphere. Thereby one pole can reach strongly negative PV values associated with inertial or symmetric instability near the upper-level PV waveguide, where it can interact with and modify the upper-level jet. This study analyzes the characteristics of embedded convection in the WCB of cyclone Sanchez based on WCB online trajectories from a convection-permitting simulation and airborne radar observations during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) field campaign (intense observation periods, IOPs, 10 and 11). In the first part, we present the radar reflectivity structure of the WCB and corroborate its heterogeneous cloud structure and the occurrence of embedded convection. Radar observations in three different sub-regions of the WCB cloud band reveal the differing intensity of its embedded convection, which is qualitatively confirmed by the ascent rates of the online WCB trajectories. The detailed ascent behavior of the WCB trajectories reveals that very intense convection with ascent rates of 600 hPa in 30–60 min occurs, in addition to comparatively moderate convection with slower ascent velocities as reported in previous case studies. In the second part of this study, a systematic Lagrangian composite analysis based on online trajectories for two sub-categories of WCB-embedded convection – moderate and intense convection – is performed. Composites of the cloud and precipitation structure confirm the large influence of embedded convection: intense convection produces very intense local surface precipitation with peak values exceeding 6 mm in 15 min and large amounts of graupel of up to 2.8 g kg −1 in the middle troposphere (compared to 3.9 mm and 1.0 g kg −1 for the moderate convective WCB sub-category). In the upper troposphere, both convective WCB trajectory sub-categories form a small-scale and weak PV dipole, with one pole reaching weakly negative PV values. However, for this WCB case study – in contrast to previous case studies reporting convective PV dipoles in the WCB ascent region with the negative PV pole near the upper-level jet – the negative PV pole is located east of the convective ascent region, i.e., away from the upper-level jet. Moreover, the PV dipole formed by the intense convective WCB trajectories is weaker and has a smaller horizontal and vertical extent compared to a previous NAWDEX case study of WCB-embedded convection, despite faster ascent rates in this case. The absence of a strong upper-level jet and the weak vertical shear of the ambient wind in cyclone Sanchez are accountable for the weak diabatic PV modification in the upper troposphere. This implies that the strength of embedded convection alone is not a reliable measure for the effect of embedded convection on upper-level PV modification and its impact on the upper-level jet. Instead, the profile of vertical wind shear and the alignment of embedded convection with a strong upper-level jet play a key role for the formation of coherent negative PV features near the jet. Finally, these results highlight the large case-to-case variability of embedded convection not only in terms of frequency and intensity of embedded convection in WCBs but also in terms of its dynamical implications.

Journal ArticleDOI
TL;DR: In this article, a high resolution (25 km) atmospheric model is used to study changes in tropical cyclones across the PETM boundary, showing that greenhouse forcing leads to a poleward shift in TCs, much like projected future scenarios and in simulations of other warm periods in Earth history.

Journal ArticleDOI
TL;DR: In this article, the authors reveal that the genesis location for post-monsoon cyclones is statistically significant against the genesis potential index (GPI) difference, especially for the intense cyclone categories (> 48kt).
Abstract: Intense cyclones have become more frequent over the North Indian Ocean (NIO) region causing significant risk and vulnerability to the coastal regions. Analysis clearly revealed an increasing trend (~ 16.75%) in the intensity of severe cyclonic storms that formed over the NIO during the past 4 decades. Power dissipation index (PDI) showed a correlation of 0.58 with severe cyclonic storms during the study period (1979–2019). Study reveals that the genesis location for post-monsoon cyclones is statistically significant against the genesis potential index (GPI) difference, especially for the intense cyclone categories (> 48 kt). During the La Nina years, increased tropospheric water vapor content initiates over prominent locations in the Andaman Sea and the North China Sea. Also, La Nina periods showed positional shift in the average genesis location of intense tropical cyclones compared to El Nino periods. Cyclogenesis shift is more concentrated towards the west-equatorward directions over the Bay of Bengal basin. Strong mid-level relative humidity (RH600), positive low-level relative vorticity (RV850), weak vertical wind shear (VWS), warm sea surface temperature (SST), and suppressed outgoing longwave radiation (OLR500) are the responsible factors leading to increased tropical cyclone activity in the NIO. Study signifies that RH600, RV850, and OLR500 are distinct during pre-monsoon seasons of the La Nina epoch, favoring the genesis of severe cyclones over this region. Variables such as SST, wind streamlines (W200, W850), vertical velocity (VV500), and specific humidity (SH500) exhibit comparable contributions towards cyclogenesis during both El Nino and La Nina phases.

Journal ArticleDOI
01 Dec 2021-Energy
TL;DR: It is indicated that by optimization of WT parameters, LCOE can be reduced effectively and also provide maximization of the profit generated by the wind power plant within its life-span.

Journal ArticleDOI
07 May 2021
TL;DR: In this article, the authors investigate the ability of the Weather Research and Forecasting model to perform large-eddy simulation of canonical flows and find that the resolved fields from the simulations appear to have the characteristics of the three stability regimes.
Abstract: . We investigate the ability of the Weather Research and Forecasting model to perform large-eddy simulation of canonical flows. This is achieved through comparison of the simulation outputs with measurements from sonic anemometers on a 250 m meteorological mast located at Osterild, in northern Denmark. Osterild is on a flat and rough area, and for the predominant wind directions, the atmospheric flow can be considered to be close to homogeneous. The idealized simulated flows aim at representing atmospheric boundary layer turbulence under unstable, neutral, and stable stability conditions at the surface, which are statistically significant conditions observed at Osterild. We found that the resolved fields from the simulations appear to have the characteristics of the three stability regimes. Vertical profiles of observed mean wind speeds and direction are well reproduced by the simulations, with the largest differences under near-neutral conditions, where the effect of the subgrid-scale model is evident on the vertical wind shear close to the surface. Vertical profiles of observed eddy fluxes are also well reproduced by the simulations, with the largest differences for the three velocity component variances under stable stability conditions, although nearly always within the observed variability. With regards to turbulent kinetic energy, we find good agreement between observations and simulations at all vertical levels. Simulated and observed velocity spectra match very well and show very similar behavior with height and with atmospheric stability within the low-frequency interval; at the effective resolution, the simulated spectra show the typical drop-off of finite differences. Our findings demonstrate that these idealized simulations reproduce the characteristics of atmospheric stability regimes often observed at a high turbulent and flat site within a direction sector, where the air flows over nearly homogeneous land.

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TL;DR: The results show that the advection transport and turbulent diffusion have a synergistic effect on the change of pollutant in the CS of three HPEs, which will help to build a certain foundation for the emission reduction work in the future.


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TL;DR: The proposed algorithm presents a cost-effective alternative to track the wake movement, which is particularly valuable for numerous applications, for example, closed-loop wake steering control.

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TL;DR: In this paper, an experimental study of the impact of typical window geometries on SS1 NV flows driven by wind shear parallel to the building facade is presented. But the results of the experiments were performed in two complementary setups, a wind tunnel test of a reduced-scale SS1 and a full-scale room subjected to artificial wind-shear.