Front Wind Research Articles

Cold-front-induced flushing of the Louisiana Bays

Water level variations were used to calculate cold-front-induced water exchange fluxes for three Louisiana bays. Twenty-nine cold fronts were identified from weather maps between September 2006 and April 2007. Cold front passages cause water to flush out of the bays, with large variability in volume fluxes. Due to the differences in water body area and basin geometry, the Atchafalaya/Vermilion Bays have exchange rates an order of magnitude higher than the Barataria Bay. We identified five largest flushing events which were all associated with migrating extra-tropical cyclones with frontal orientations perpendicular to the coastline, suggesting that wind direction is an important component in determining the flushing rate. Both alongshore and cross-shore winds play important roles in bay-shelf water exchange, and northwest winds appeared to be most effective in flushing the bays. Strong cold fronts may flush more than 40% of the bay waters out onto the continental shelf within a less than 40-hour period. An analytical model is applied for the cold front wind induced flushing process which reveals that the amplitudes of water level variations induced by alongshore and cross-shore winds have the same order of magnitude, indicating that they play almost equally important roles in driving the subtidal water level changes inside the bays.

Acoustic noise from tandem wind rotors of intelligent wind power unit

The authors had invented the unique wind power unit composed of the large-sized front wind rotor, the small-sized rear wind rotor and the peculiar generator with the inner and the outer rotational armatures without the conventional stator. This unit is called “Intelligent Wind Power Unit” by the authors. The front and the rear wind rotors drive the inner and the outer armatures, respectively, while the rotational torque is counter-balanced between both armatures/wind rotors. This paper discusses experimentally the acoustic noise from the front and the rear wind rotors. The acoustic noise, in the counter-rotating operation, is induced mainly from the flow interaction between both rotors, and has the dominant power spectrum density at the frequency of the blade passing interaction. The noise is caused mainly from the turbulent fluctuation due to the flow separation on the blade, when the rear wind rotor stops or rotates in the same direction as the front wind rotor.

Verification of Mesoscale NWP Forecasts of Abrupt Cold Frontal Wind Changes

Abstract During a wildfire, a sharp wind change can lead to an abrupt increase in fire activity and change the rate of spread, endangering firefighters working on what had been the flank of the fire. In southeastern Australia, routine forecast of cold-frontal wind change arrival times is a critical component of the fire weather forecasting service, and mesoscale NWP model predictions are integral to this forecast process. An event-based verification method has been developed in order to verify these mesoscale NWP model forecasts of wind changes. The approach is based on fuzzy-rule techniques and objectively determines the timing of significant (fire weather) wind changes from time series of observations at a single surface station. In this paper these rules are applied to observational and NWP model forecast time series at observation locations over five fire seasons to determine objective “observed wind change times” and “forecast wind change times” for significant frontal wind changes in southeastern Australia. These forecast wind change times are compared with those observed, and also with those determined subjectively by forecasters at the Victorian Regional Forecast Centre. This provides an objective verification of NWP wind change forecasts and a measure of contemporary NWP model skill against which future model improvements may be measured. Case studies of two wind change events at selected stations are also presented to demonstrate some of the strengths, weaknesses, and characteristics of this verification technique.

Characteristics and impact of a gale-force storm field over the Norwegian Sea

A unique data set was sampled by aircraft, ship, drift buoys and satellites in a strong storm event which occurred over the Norwegian Sea in March 2005 during the LOFZY field experiment. The atmospheric characteristics and the impact on the upper ocean are investigated. The storm field with winds up to 27 m s−1 was situated on the west-side of a low-pressure trough along the Norwegian coast and was marked by a sharp wind front. The entire system of trough, front and storm field was about 200 km wide, had a lifetime of 2 d in the area and advanced at 1–3 m s−1 SE-wards. Temperature contrast across the system was small, but wind contrast was remarkable and concentrated in a step-like front with 5–15 m s−1 difference over a distance of 3 km. The entire system was restricted to the lowest 2 km. It was accompanied by wide-spread rain and snow. Precipitation slightly surpassed evaporation (0.22 mm h−1). Surface heat fluxes amounted up to 400 W m−2. However, they cannot account for the observed sea surface temperature changes between −0.8 and +0.1 K within 6 h during the frontal passage. This is attributed to vertical mixing in the ocean caused by the frontal wind impact and superimposed to pre-existing mesoscale eddy circulations. The mixing acted on a temperature stratification in the uppermost 20–100 m which was opposite on both sides of the Norwegian Current

Surface pressure and wind load characteristics on prisms immersed in a simulated transient gust front flow field

Thunderstorm generated gust fronts are responsible for various degrees of structural damage in many areas of the world. However, the resulting impact of gust front winds is not fully understood to such a level that their flow kinematics, dynamics and impact on structures can be quantified with some certainty. Gust front winds are transient in nature and have a flow profile which differs significantly from a typical boundary layer flow field. This study focuses on investigating the effects of this flow profile and its transient nature on the aerodynamics of bluff, prismatic bodies. A gust front type flow field is generated using a multiple fan wind tunnel and the resulting surface pressures are captured on a suite of prismatic models, which vary in size in relationship to the oncoming wind profile. The temporal variations in surface pressures are analyzed using traditional time, frequency and time-frequency domain schemes. Results indicate the changing nature of the surface pressure field in time, highlighting both qualitative and quantitative differences between local and area-averaged pressures under a host of flow profiles.

Intelligent wind turbine unit with tandem rotors (discussion of prototype performances in field tests)

The authors had invented the unique wind turbine unit composed of the large-sized front wind rotor, the small-sized rear wind rotor and the peculiar generator with the inner and the outer rotational armatures. The rotational torques of both armatures/wind rotors are counter-balanced, while the rotational speeds and the directions are adjusted automatically in response to the wind conditions. The prototype unit is composed of the tandem wind rotors, whose front and rear diameters are 2 m and 1.33 m, and the double rotational armatures type synchronous generator. The unit was boarded on a pick-up type vehicle in the field test. The performance of the unit is significantly affected not only by the blade setting angles of both wind rotors, but also by the bulb load. The test results suggest that more improvement is necessary for the blade profiles as tandem wind rotors taking account of the flow interaction between both wind rotors.

Evolution of a new sense for wind in flying phasmids? Afferents and interneurons

The evolution of winged stick insects (phasmids) from secondarily wingless ancestors was proposed in recent studies. We explored the cuticle of flying phasmids for wind sensors that could be involved in their flight control, comparable to those known for locusts. Surprisingly, wind-sensitive hairs (wsH) occur on the palps of mouthparts and on the antennae of the winged phasmid Sipyloidea sipylus which can fly in tethered position only when air currents blow over the mouthparts. The present study describes the morphology and major functional properties of these “new” wsH with soft and bulging hair bases which are different from the beaker-like hair bases of the wsH on the cerci of phasmids and the wsH described in other insects. The most sensitive wsH of antennae and palps respond with phasic-tonic afferents to air currents exceeding 0.2 ms−1. The fields of wsH on one side of the animal respond mainly to ventral, lateral, and frontal wind on the ipsilateral side of the head. Afferent inputs from the wsH converge but also diverge to a group of specific interneurons at their branches in the suboesophageal ganglion and can send their integrated input from wsH fields of the palps and antennae to the thoracic central nervous system. Response types of individual wsH-interneurons are either phasic or phasic-tonic to air puffs or constant air currents and also, the receptive fields of individual interneurons differ. We conclude that the “new” wsH system and its interneurons mainly serve to maintain flight activity in airborne phasmids and also, the “new” wsH must have emerged together with the integrating interneurons during the evolution from wingless to the recent winged forms of phasmids.

Modification of SAR spectra associated with surface wind fields in the sea off the Kii Peninsula: A case study

Using surface wave parameters and a high-resolution surface wind field derived from Synthetic Aperture Radar (SAR) image mode data, we have investigated the spatial modification of SAR spectra. We found a surface wind front, formed by sheltering effect of the Kii Mountains, separating high and low wind-speed regions in a sea area of an European Remote-Sensing Satellite (ERS) SAR image off the Kii Peninsula. A swell system propagating westward dominates in the whole sea area covered by the SAR image. The wavelength retrieved from the SAR spectra in the sheltered (non-sheltered) region is longer (shorter). Since the distributions of surface wave parameters and surface wind speed are so well correlated, it can be considered that the SAR spectra are modified differently by the sheltered/non-sheltered surface winds. In order to examine the phenomena observed on the SAR image we have estimated the wind-wave SAR spectrum using the SAR surface winds, a wind-wave spectrum model and a SAR wave imaging model. We assume that the SAR spectrum related to the swell is homogeneous in the area imaged by SAR, and that the SAR spectrum of the wind-wave components causes the observed SAR spectra modification. Differences between the observed SAR spectra and the estimated SAR spectra in the sheltered and non-sheltered regions agree well with each other. In the present case, it can be concluded that the observed SAR spectra can be regarded as a linear combination of the wind-wave SAR spectra and the swell SAR spectra.

Improved Stability for Wind-Diesel Generator Systems in Wind Gust Condition

With a sudden wind gust, a wind-diesel system with a large wind turbine penetration can suffer from power system instability, even though it may be stable under steady-state conditions at the same wind speeds. This suggests that the wind-diesel system should be investigated for better frequency and power stability. In this paper, a concept has been presented to improve the stability of the wind-diesel system in high wind gust condition, by placing the wind turbines in such a way that the wind turbines experience the wind gust at different times. A 1.25 MVA Caterpillar diesel generator with six NORDEX150 turbines has been modelled using MATLAB, and it has been found that when all the wind turbines experience a sufficiently large wind gust simultaneously, frequency and power control is lost. However, if the turbines are located so that they experience the wind gust at staggered times, the power system is found to remain stable for the same gust conditions. The potential stability benefits of this approach have been demonstrated for an area with a known predominant wind front movement direction.

Dark formation detection using neural networks

Synthetic Aperture Radar (SAR) images are extensively used for dark formation detection in marine environment, as they are not affected by local weather conditions and cloudiness. Dark formations can be caused by man‐made actions (e.g. oil spills) or natural ocean phenomena (e.g. natural slicks and wind front areas). Radar backscatter values for oil spills are very similar to backscatter values for very calm sea areas and other ocean phenomena because they dampen the capillary and short gravity sea waves. Thus, traditionally, dark formation detection is the first stage of the oil‐spill detection procedure and in most studies is performed manually or using a fixed size window in which a threshold value is adopted. In high‐resolution imagery, dark formation detection may fail due to the nonlinear behaviour of the pixel values contained in the dark formation and in the area around it. In this paper, we examine the ability of two feed‐forward neural network families, i.e. Multilayer Perceptron (MLP) and the Radial Basis Function (RBF) networks, to detect dark formations in high‐resolution SAR images. The general objective of this paper is to test the potential of artificial neural networks for dark formation detection using SAR high‐resolution satellite images. Both the type and the architecture of the network are subjects of research. The inputs into the networks are the original SAR images. Each network is called to classify an area of the image as dark area or sea. The group of MLP networks can be recognized as the most suitable group for dark formation detection, as it presents reliable stable results for all the examined accuracies. Nevertheless, in terms of single topology, there is no an MLP topology that performs significantly better than the others.

Development of Intelligent Wind Turbine Unit with Tandem Wind Rotors and Double Rotational Armatures (2nd Report, Characteristics of tandem wind rotors)

The authors have invented the superior wind turbine unit which is composed of the tandem wind rotors and the double rotational armature type generator without the traditional stator. The large-sized front wind rotor and the small-sized rear wind rotor drive the inner and the outer armatures respectively, in keeping the rotational torque counter-balanced. Such operating conditions may be able to make the output higher than the traditional wind turbines, and to keep the output constant in the rated operation mode without the brakes and/or the pitch control mechanism. The unique rotational conditions of the tandem wind rotors and the fundamental characteristics of this unit were presented at the previous paper. Continuously, this paper discusses experimentally the effects of the tandem wind rotor profiles on the characteristics of this unit. The desirable profiles and the main results are as follows. (1)The optimum diameter ratio is DRF (rear wind rotor diameter divided by the front wind rotor diameter) = 0.84, and the axial distance between both wind rotors should be set as short as possible. (2)The output is higher while the relative tip speed ratio increases as compared with the single wind rotor.

Detection and discrimination between oil spills and look-alike phenomena through neural networks

Synthetic Aperture Radar (SAR) images are extensively used for dark formation detection in the marine environment, as their recording is independent of clouds and weather. Dark formations can be caused by man made actions (e.g. oil spill discharging) or natural ocean phenomena (e.g. natural slicks, wind front areas). Radar backscatter values for oil spills are very similar to backscatter values for very calm sea areas and other ocean phenomena because they damp the capillary and short gravity sea waves. The ability of neural networks to detect dark formations in high resolution SAR images and to discriminate oil spills from look-alike phenomena simultaneously was examined. Two different neural networks are used; one to detect dark formations and the second one to perform a classification to oil spills or look-alikes. The proposed method is very promising in detecting dark formations and discriminating oil spills from look-alikes as it detects with an overall accuracy of 94% the dark formations and discriminate correctly 89% of examined cases.

Tornado Generation in a Narrow Cold Frontal Rainband -Fujisawa Tornado on April 20, 2006-

At noon on April 20, 2006, a wind storm occurred in Fujisawa City, Kanagawa Prefecture, Japan with a F0-P1-P1 rank on the Fujita-Pearson-scale (FPP-scale). Damage to over 40 residential buildings was observed. The damage covered an area 2 km by 50 m. The strong winds were accompanied by the passage of a cold front. Eyewitness accounts of a dust column and the recording of a pressure drop (1.5 hPa) indicate the existence of a tornado vortex. A hook-shaped radar echo (5 km in diameter) was observed in the narrow cold frontal rainband, with strong horizontal wind shear above the damage area. The Doppler velocity pattern indicated a misocyclone, which had a diameter of 2 km and a vorticity on the order of 10-2 s-1. The wind storm may have caused the tornado, which formed in the cold frontal wind shear zone.

Development of Intelligent Wind Turbine Generator with Tandem Wind Rotors and Double Rotational Armatures (1st Report, Superior Operation of Tandem Wind Rotors)

This paper proposes the superior wind turbine generator, which is composed of the tandem wind rotors and the double rotational armature type generator without the conventional stator. The large-sized front wind rotor and the small-sized rear wind rotor drive respectively the inner and the outer armatures of the generator, in keeping the rotational torque counter-balanced. Such operating conditions enable to make the output higher than the conventional wind turbine and to keep the output constant in the rated operating mode without using the brake and/or the pitch control mechanisms. Such wonderful advantages in the generating mode are discussed and verified experimentally with the model turbine generator.

Real Front or Baroclinic Trough?

In a recent study, Sanders and Hoffman (2002, hereafter SH) found that only about half of the cold-front segments appearing on surface maps of the National Centers for Environmental Prediction (NCEP) from December 1999 through February 2000 were associated, even loosely, with a moderately strong surface baroclinic zone. In an earlier study (Sanders and Kessler 1999), some extreme examples had been identified in which an abrupt nocturnal temperature rise was analyzed as the passage of a cold front. These features are clearly not the type of structure described by Bjerknes (1918). To enlarge the sample of comparisons between analyzed fronts and baroclinic zones reported by SH, a comparison was made for the period between 7 February and 29 March 2002. The fronts were again taken from analyses prepared by the Hydrometeorological Prediction Center (HPC) of NCEP. The maps of surface potential temperature were prepared at the Department of Atmospheric Science, The University of Arizona, and were manually analyzed without knowledge of the concurrent frontal analysis. As in SH, the times were 0000 and 1200 UTC and the area of analysis was the same. The analysis consisted of isotherms at intervals of 8°C. Areas of moderate or intense gradient, representing an 8°C contrast of potential temperate over distances of no more than 220 or 110 km, respectively, were marked. These distances represent values of the gradient close to those used by SH. Edges of frontal segments occurred where the analyzed notation changed, generally at centers of low pressure, or where indicated in the analyses, or at the edge of the analyzed area. Warm fronts, cold fronts, and stationary fronts were separately considered. A small number of occluded segments occurred but were considered as extended portions of cold or warm fronts, depending on whether the air following the frontal wind shift was colder or warmer than the air ahead. Whereas SH considered each segment as associated or not associated with a baroclinic zone, in this study the total length of each segment was measured, as was the length associated with a baroclinic zone. Association was considered to occur if the analyzed front lay within 220 km of the warm edge of a zone, or was within it. Where the orientations of the front and of the zone differed by nearly 90°, the two were considered associated if the air on the cold side of the front was significantly colder than the air on the warm side, but not otherwise. The length and proportions of frontal segments associated with baroclinic zones are presented in Table 1. In the table the fractional length of segments associated with baroclinic zones was around one-half for both times and for all frontal types. Cold frontal segments were not less associated, as in the study by SH (seen in their Table 3). The lengths of stationary and cold fronts is understated because in many instances the segment was terminated when it reached the limits of the area of analysis of potential temperature, usually over the ocean. If the temperature analysis had extended over the oceanic regions, the association would have likely been weaker because of the lack of prominent contrasts in these regions. Warm fronts were fewer and shorter than other types, representing in many cases stubs ahead of an analyzed cold front with less than compelling indications. In the earlier study a decision was made whether the segment as a whole was or was not associated with a baroclinic zone. The present study may be less subjective. In an attempt to mimic the procedure used in the earlier study, we determined whether each individual frontal segment was or was not associated with a baroclinic zone over at least 50% of its length. The proportions of each frontal type meeting this criterion were 0.53, 0.43, and 0.45 for stationary, cold, and warm segments, respectively. In both studies it is apparent that many analyzed fronts are not assoCorresponding author address: Dr. Frederick Sanders, 9 Flint Street, Marblehead, MA 01945-3716. E-mail: fnmisander@comcast.net AUGUST 2005 F O R E C A S T E R S ’ F O R U M 647

340 インテリジェント風力発電機のタンデム風車ロータを通る流れ(S36-1 自然の流体エネルギー利用技術(1),S36 自然の流体エネルギー利用技術)

The authors invented the superior wind turbine generator, which is composed of the tandem wind rotors and the double rotational armatures type generator without the conventional stator, and have discussed the wonderful advantages in the generating mode. The large-sized front wind rotor and the small-sized rear wind rotor drive respectively the inner and the outer armatures of the generator, in keeping the rotational torque counter-balanced. Such operating conditions enable to make the output higher than one of the conventional turbine and to keep the output constant in the rated operation mode without the brake and/or the pitch control mechanism. Continuously, this paper discusses the flow conditions around the rotors composed of the cambered blades.

OS2-10 タンデムロータ型インテリジェント風力発電機の提案 : 反りを持つブレードによる特性把握(OS2 自然エネルギー)

The authors invented the superior wind turbine generator, which is composed of the tandem wind rotors and the double rotational armatures type generator without the conventional stator, and have discussed the wonderful advantages in the generating mode. The large-sized front wind rotor and the small-sized rear wind rotor drive respectively the inner and the outer armatures of the generator, in keeping the rotational torque counter-balanced. Such operating conditions enable to make the output higher than one of the conventional turbine and to keep the output constant in the rated operation mode without the brake and/or the pitch control mechanism. Continuously, this paper discusses the experimental results using the cambered blades.

Effects of stacked condensers in a high-rise apartment building

The effects of condensers installed in the stacked air-conditioning plant rooms of a high-rise apartment building were studied numerically. The performance of the condensers was evaluated using the coefficient of performance (COP) and condenser group performance indicator (CGPI) parameters. The effects of wind direction, wind velocity, and the arrangement and location of the condensers were investigated. The performance of condensers above the 30th floor was seriously degraded due to the stacking effects. The heat dissipation performance of the condensers in the higher floors dropped significantly when the frontal wind was greater than 4 m/s and the side wind was greater than 8 m/s. The condenser should be arranged in such a manner that the fan of the condenser faces the outside of the building to exhaust the hot air directly to the outside. To prevent the hot air from reentering the air-conditioning plant room and to allow fresh air to enter instead, the condenser considered in this study must be located at the lower left corner of the air-conditioning plant room.

Vertical variations in O3 concentrations before and after a gust front passage

Two consecutive increases in surface ozone, occurring after the cessation of photochemical ozone production, are investigated. A unique suite of instruments, including an ozone profiling lidar, a Doppler lidar, surface chemistry sensors, surface meteorological sensors, and a radar wind profiler, was deployed during the Southern Oxidants Study of 1999 in Nashville, Tennesee. Time series of ozone at 10, 405, and 1035 m above ground level (AGL) on 22 June 1999 showed variations in the vertical gradient of ozone over the course of the afternoon and evening. Analysis of time series of vertical velocity at 8 m AGL and its standard deviation, the variance in Doppler lidar calculated horizontal wind speed from near the surface to 500 m AGL, wind profiles, and meteorological surface station data, revealed mechanisms responsible for these changes in ozone. An early evening rise in surface ozone occurred with the passage of a thunderstorm gust front. Analysis showed that downward mixing of ozone‐rich air from a residual layer (RL) of ozone above 400 m caused a sharp rise in ozone at the surface and a decrease of ozone in the RL. Doppler lidar measurements showed details of the postgust front wind flow, such as the depth of the air mass behind the front, the turbulent wake region, and inferred vertical velocities throughout a layer several hundred meters deep. The second rise in surface ozone was caused by turbulent mixing due to elevated directional wind shear, which mixed ozone‐rich air down to the surface.

Kinematic Characteristics of a Mei-yu Front Detected by the QuikSCAT Oceanic Winds

Abstract Based on conventional surface observations and NASA Quick Scatterometer (QuikSCAT) data, a heavy rainfall event that occurred in the Taiwan mei-yu season was chosen to further study the kinematic characteristics of the accompanying surface front. With the help of the QuikSCAT oceanic surface winds, it was found that the location and propagation of a mei-yu front over the ocean to the east of Taiwan during 10–12 June 2000 are better represented by the frontal wind shift line, which was located approximately on the leading edge of the baroclinic zone. The mesoscale system with cyclonic circulation embedded within the frontal zone was clearly shown in the wind field and kinematic parameters (horizontal divergence and vorticity) as well as satellite clouds and rainfall estimations. The conditional instability of the second kind (CISK) process was suggested to be responsible for the intensification of the mei-yu front and the frontal disturbance over the ocean. Under the influence of island topography...