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1
Tomaru, Ryota, Chris Done, Ken Ohsuga, Mariko Nomura, and Tadayuki Takahashi. "The thermal-radiative wind in low-mass X-ray binary H1743−322: radiation hydrodynamic simulations." Monthly Notices of the Royal Astronomical Society 490, no. 3 (October 3, 2019): 3098–111. http://dx.doi.org/10.1093/mnras/stz2738.
Анотація:
Abstract Blueshifted absorption lines are seen in high inclination black hole binary systems in their disc-dominated states, showing these power an equatorial disc wind. While some contribution from magnetic winds remain a possibility, thermal and thermal-radiative winds are expected to be present. We show results from radiation hydrodynamic simulations that show that the additional radiation force from atomic features (bound–free and lines) is important along with electron scattering. Together, these increase the wind velocity at high inclinations, so that they quantitatively match the observations in H1743−322, unlike purely thermal winds that are too slow. We highlight the role played by shadowing of the outer disc from the (subgrid) inner disc Compton heated layer, and show that the increase in shadow from the higher Compton temperature after the spectral transition to the hard state leads to strong suppression of the wind. Thermal-radiative winds explain all of the spectral features (and their disappearance) in this simplest wind system and magnetic winds play only a minor role. We speculate that thermal-radiative winds can explain all the spectral features seen in the more complex (larger disc size) binaries, GRO J1655−40 and GRS 1915+105, without requiring magnetic winds.
2
Samelson, R. M., and P. L. Barbour. "Low-Level Jets, Orographic Effects, and Extreme Events in Nares Strait: A Model-Based Mesoscale Climatology." Monthly Weather Review 136, no. 12 (December 1, 2008): 4746–59. http://dx.doi.org/10.1175/2007mwr2326.1.
Анотація:
Abstract A mesoscale atmospheric model, nested in operational global numerical weather prediction fields, is used to estimate low-level winds and surface wind stress through Nares Strait, between Ellesmere Island and Greenland, during 2 yr from August 2003 to July 2005. During most of the year, the model low-level winds are dominated by intense, southward along-strait flow, with monthly-mean southward 10-m winds reaching 10 m s−1 in winter. Summertime flow is weak and distributions of hourly along-strait winds during the 2-yr period are strongly bimodal. The strong southward low-level winds are associated with ageostrophic, orographically channeled flow down the pressure gradient from the Lincoln Sea to Baffin Bay and are highly correlated with the pressure difference along Nares Strait. The 2-yr means and leading EOFs of monthly-mean 10-m winds and wind stress place the strongest winds and stress in the southern parts of Smith Sound and of Kennedy Channel, at the openings to Baffin Bay and Kane Basin, at known sites of polynya formation, including the North Water polynya in Smith Sound, suggesting that the locally intensified winds may cause these persistent polynyas. An intense wind event observed in Nares Strait by a field camp, with surface winds exceeding 30 m s−1, generally follows the typical pattern of these low-level flows. Based on the model correlation of winds and pressure difference, a 51-yr time series of estimated winds in Nares Strait is reconstructed from historical surface pressure measurements at Thule, Greenland, and Alert, Canada. The pressure difference and reconstructed wind time series are correlated with the Arctic Oscillation at annual and longer periods, but not on monthly periods.
3
SURESH, R. "An account of low level wind shear over Chennai airport - Part II : Turbulence and eddy dissipation." MAUSAM 60, no. 3 (November 27, 2021): 325–42. http://dx.doi.org/10.54302/mausam.v60i3.1104.
Анотація:
In-flight reports on Low Level Wind Shear (LLWS) received from aircrafts are used to issue wind shear alerts for all subsequent landing aircrafts as per standing guidelines of International Civil Aviation Organisation (ICAO). In this paper, winds reported by aircrafts at 1000 and 1800 ft. are used to validate the wind estimated from DWR measured radial wind data employing standard algorithms. Turbulence indices and parameters have been computed independently using conventional (RS/RW) upper air data, aircraft measured winds and DWR estimated winds and compared these with wind shear induced turbulence reported by aircrews. Mean power law (wind escalation law) profiles in the boundary layer have been arrived at for unstable and stable atmospheric conditions.
Three dimensional shear (3DS) upto 600 m a.g.l. has been worked out from DWR measured radial velocity data and compared with wind shear computed from RS/RW and aircraft measured winds and DWR estimated winds. It is found that 3DS values of more than 16 * 10-3 s-1 predict well the occurrence of moderate turbulence. Contrary to the general belief that wind shear is a short lived phenomenon which may last for a few minutes only, it has been observed that incidences of LLWS and induced moderate turbulence lasting more than 10 hrs are not at all uncommon over Chennai aircraft.
4
Caton Harrison, Thomas, Stavroula Biri, Thomas J. Bracegirdle, John C. King, Elizabeth C. Kent, Étienne Vignon, and John Turner. "Reanalysis representation of low-level winds in the Antarctic near-coastal region." Weather and Climate Dynamics 3, no. 4 (December 2, 2022): 1415–37. http://dx.doi.org/10.5194/wcd-3-1415-2022.
Анотація:
Abstract. Low-level easterly winds encircling Antarctica help drive coastal currents which modify transport of circumpolar deep water to ice shelves, and the formation and distribution of sea ice. Reanalysis datasets are especially important at high southern latitudes where observations are few. Here, we investigate the representation of the mean state and short-term variability of coastal easterlies in three recent reanalyses, ERA5, MERRA-2 and JRA-55. Reanalysed winds are compared with summertime marine near-surface wind observations from the Advanced Scatterometer (ASCAT) and surface and upper air measurements from coastal stations. Reanalysis coastal easterlies correlate highly with ASCAT (r= 0.91, 0.89 and 0.85 for ERA5, MERRA-2 and JRA-55, respectively) but notable wind speed biases are found close to the coastal margins, especially near complex orography and at high wind speeds. To characterise short-term variability, 12-hourly reanalysis and coastal station winds are composited using self-organising maps (SOMs), which cluster timesteps under similar synoptic and mesoscale influences. Reanalysis performance is sensitive to the flow configuration at stations near steep coastal slopes, where they fail to capture the magnitude of near-surface wind speed variability when synoptic forcing is weak and conditions favour katabatic forcing. ERA5 exhibits the best overall performance, has more realistic orography, and a more realistic jet structure and temperature profile. These results demonstrate the regime behaviour of Antarctica's coastal winds and indicate important features of the coastal winds which are not well characterised by reanalysis datasets.
5
Shimada, Teruhisa. "Structures and Seasonal Variations of Surface Winds Blowing through the Tsushima Strait." Journal of Applied Meteorology and Climatology 49, no. 8 (August 1, 2010): 1714–27. http://dx.doi.org/10.1175/2010jamc2301.1.
Анотація:
Abstract Surface winds blowing through the Tsushima Strait are statistically investigated using satellite wind measurements and atmospheric reanalysis data. This study first presents structures and seasonal variations of the northeasterly and southwesterly along-strait winds by imposing newly proposed conditions for defining them. Although the speeds of the northeasterly along-strait winds are generally high within the entire strait, the maximum wind speeds are located downwind of the two channels. The southwesterly along-strait winds start to accelerate at the west exit within the strait. Weak-wind regions are formed in the lee of Tsushima Island in both cases. The occurrence frequencies of the northeasterly and southwesterly along-strait winds are high (low) in the warm (cool) season. The northeasterly along-strait winds are more often observed than the southwesterly along-strait winds. The frequency of the northeasterly along-strait wind is extraordinarily high in September, but the averaged wind speed is comparable to those in the other months. Most of the southwesterly along-strait wind cases fall within low-Froude-number regimes, suggesting the significant effects of Tsushima Island on the wind in the strait. Synoptic situations favorable for the along-strait winds are investigated. Correlations between the along-strait wind component and sea level pressure (SLP) indicate that the along-strait winds are induced by SLP perturbations primarily over the Japan Sea and secondarily on the south of the strait. In addition, cluster analysis of the SLP fields shows four representative SLP fields favorable for the along-strait winds and their monthly occurrence frequencies.
6
Hughes, Christopher P., and Dana E. Veron. "Characterization of Low-Level Winds of Southern and Coastal Delaware." Journal of Applied Meteorology and Climatology 54, no. 1 (January 2015): 77–93. http://dx.doi.org/10.1175/jamc-d-14-0011.1.
Анотація:
AbstractWinds across the Delaware Peninsula transport pollutants, modify the temperature, and play a critical role within the state’s agricultural and tourism industries. The low-level winds inland and near Delaware’s coastline are characterized using observations from eight meteorological stations operated by the Delaware Environmental Observing System and the National Data Buoy Center from 2005 through 2012. The low-level winds have pronounced dominant directions during the summer (southwest/southeast) and winter (northwest) seasons, with the greatest spatial and temporal variability occurring in the summer. This inhomogeneity was further investigated with a set of simulations of the low-level winds over the Delaware Bay and surrounding landmass using the Weather Research and Forecasting Model for a subset of days from 2006 through 2012. The model was run with three nests, with the inner nest having a 2-km horizontal resolution. The randomly selected days were organized by synoptic type and season. Mesoscale wind events such as the sea-breeze circulation introduce significant variability in the local wind field of coastal Delaware—an effect that is seen in both observed and modeled data. Southerly winds off Delaware’s coast frequently shift counterclockwise up the Delaware Bay in alignment with the bay coastline. Long-term data from station B44009 (1984–2012) indicate a May decrease (0.03 m s−1 yr−1; significance p = 0.026) and an October increase (0.04 m s−1 yr−1; p = 0.006) of the mean wind speed. Results suggest that the local wind regime is multifaceted and contains significant seasonal, diurnal, and spatial variations.
7
Rajaram, R., and S. Gurubaran. "Seasonal variabilities of low-latitude mesospheric winds." Annales Geophysicae 16, no. 2 (February 28, 1998): 197–204. http://dx.doi.org/10.1007/s00585-998-0197-4.
Анотація:
Abstract. Observations of mesospheric winds over a period of four years with the partial reflection radar at Tirunelveli (8.7°N, 77.8°E), India, are presented in this study. The emphasis is on describing seasonal variabilities in mean zonal and meridional winds in the altitude region 70–98 km. The meridional winds exhibit overall transequatorial flow associated with differential heating in the Northern and Southern Hemispheres. At lower altitudes (70–80 km) the mean zonal winds reveal easterly flow during summer and westerly flow during winter, as expected from a circulation driven by solar forcing. In the higher altitude regime (80–98 km) and at all altitudes during equinox periods, the mean zonal flow is subjected to the semi-annual oscillation (SAO). The interannual variability detected in the occurrence of SAO over Tirunelveli has also been observed in the data sets obtained from the recent UARS satellite mission. Harmonic analysis results over a period of two years indicate the presence of long-period oscillations in the mean zonal wind at specific harmonic periods near 240, 150 and 120 days. Results presented in this study are discussed in the context of current understanding of equatorial wave propagation.Key words. Meteorological and atmospheric dynamics · General circulation · Middle atmosphere dynamics · waves and tides.
8
Furevik, Birgitte Rugaard, Harald Schyberg, Gunnar Noer, Frank Tveter, and Johannes Röhrs. "ASAR and ASCAT in Polar Low Situations." Journal of Atmospheric and Oceanic Technology 32, no. 4 (April 2015): 783–92. http://dx.doi.org/10.1175/jtech-d-14-00154.1.
Анотація:
AbstractForecasting and monitoring polar lows are, to a large degree, based on satellite observations from passive radiometers and from scatterometer winds in addition to synoptic observations and numerical models. Synthetic aperture radar (SAR) brings higher resolution compared to other remotely sensed sources of ocean wind, such as scatterometer data and passive microwave wind products. The added information in polar low situations from SAR and the increased-resolution scatterometer wind fields are investigated. Statistically, higher variability in the MetOp Advanced Scatterometer (ASCAT) wind is clearly found during polar low situations compared to all situations. Slightly more variability is also seen in the ASCAT 12.5-km wind product compared to the operational European Centre for Medium-Range Weather Forecasts (ECMWF) model surface winds. In two analyzed polar low cases, Environmental Satellite (Envisat) Advanced SAR (ASAR) images reveal numerous interesting features, such as the sharp fronts and the location and strength of the strongest wind field in the polar low. It is likely that if SAR images are available to operational weather forecasting, that it can in some cases lead to earlier detection of polar lows. However, a reliable wind field from SAR is still needed.
9
Karnauskas, Kristopher B., Antonio J. Busalacchi, and Raghu Murtugudde. "Low-Frequency Variability and Remote Forcing of Gap Winds over the East Pacific Warm Pool." Journal of Climate 21, no. 19 (October 1, 2008): 4901–18. http://dx.doi.org/10.1175/2008jcli1771.1.
Анотація:
Abstract The low-frequency variability of gap winds at the Isthmuses of Tehuantepec and Papagayo is investigated using a 17-yr wind stress dataset merging the remotely sensed observations of Special Sensor Microwave Imager (SSM/I) and Quick Scatterometer (QuikSCAT) satellite sensors. A decadal signal is identified in the Tehuantepec gap winds, which is shown to be related to the Atlantic tripole pattern (ATP). Using linear regression and spectral analysis, it is demonstrated that the low-frequency variability of the Tehuantepec gap winds is remotely forced by the ATP, and the Papagayo gap winds are primarily governed by El Niño–Southern Oscillation (ENSO) with the ATP being of secondary importance. The Tehuantepec (Papagayo) time series of wind stress anomalies can be better reconstructed when the local cross-isthmus pressure difference and large-scale climate information such as the ATP (ENSO) are included, suggesting that there is important information in the large-scale flow that is not transmitted directly through the background sea level pressure gradient. The geostrophic modulation of the easterly trades in the western Caribbean also serve as a remote driver of the Papagayo gap winds, which is itself not fully independent from ENSO. Finally, it is suggested that precipitation variability in the Inter-Americas region is closely related to the same remote forcing as that of the Tehuantepec gap winds, being the ATP and associated large-scale atmospheric circulation.
10
Parsons, Timothy N., Raman K. Prinja, Matheus Bernini-Peron, Alex W. Fullerton, Derck L. Massa, Lidia M. Oskinova, Daniel Pauli, Matthew J. Rickard, and Andreas A. C. Sander. "Optically thick structure in early B-type supergiant stellar winds at low metallicities." Monthly Notices of the Royal Astronomical Society 527, no. 4 (December 23, 2023): 11422–57. http://dx.doi.org/10.1093/mnras/stad3966.
Анотація:
ABSTRACT Accurate determination of mass-loss rates from massive stars is important to understand stellar and galactic evolution and enrichment of the interstellar medium. Large-scale structure and variability in stellar winds have significant effects on mass-loss rates. Time-series observations provide direct quantification of such variability. Observations of this nature are available for some Galactic early supergiant stars but not yet for stars in lower metallicity environments such as the Magellanic Clouds. We utilize ultraviolet spectra from the Hubble Space Telescope ULLYSES program to demonstrate that the presence of structure in stellar winds of supergiant stars at low metallicities may be discerned from single-epoch spectra. We find evidence that, for given stellar luminosities and mean stellar wind optical depths, structure is more prevalent at higher metallicities. We confirm, at Large Magellanic Cloud (0.5 Z⊙), Small Magellanic Cloud (0.2 Z⊙), and lower (0.14–0.1 Z⊙) metallicities, earlier Galactic results that there does not appear to be correlation between the degree of structure in stellar winds of massive stars and stellar effective temperature. Similar lack of correlation is found with regard to terminal velocity of stellar winds. Additional and revised values for radial velocities of stars and terminal velocities of stellar winds are presented. Direct evidence of temporal variability, on time-scales of several days, in stellar wind at low metallicity is found. We illustrate that narrow absorption components in wind-formed profiles of Galactic OB stellar spectra remain common in early B supergiant spectra at low metallicities, providing means for better constraining hot, massive star mass-loss rates.
11
Berkovic, Sigalit, and Pinhas Alpert. "A Synoptic Study of Low Troposphere Wind at the Israeli Coast." Open Atmospheric Science Journal 12, no. 1 (August 13, 2018): 80–106. http://dx.doi.org/10.2174/1874282301812010080.
Анотація:
Objective:This research is dedicated to the study of the feasibility of surface wind downscaling from 925 or 850 hPa winds according to synoptic class, season and hour.Methods:Two aspects are examined: low tropospheric wind veering and wind speed correlation and verification of the ERA-Interim analysis wind by comparison to radiosonde data at Beit Dagan, a station on the Israeli coast.Results:Relatively small (< 60°) cross angles between the 1000 hPa wind vector and the 925 hPa or 850 hPa wind vector at 12Z and high correlation (0.6-0.8) between the wind speed at the two levels were found only under winter lows. Relatively small cross angles and small wind speed correlation were found under highs to the west and Persian troughs.The verification of ERA-Interim analysis in comparison with radiosonde data has shown good prediction of wind direction at 12Z at 1000, 925 and 850 hPa levels (RMSE 20°-60°) and lower prediction quality at 1000 hPa at 0Z (RMSE 60°-90°). The analysis under-predicts the wind speed, especially at 1000 hPa. The wind speed RMSE is 1-2 m/s, except for winter lows with 2-3 m/s RMSE at 0Z, 12Z at all levels.Conclusion:Inference of surface wind may be possible at 12Z from 925 or 825 hPa winds under winter lows. Inference of wind direction from 925 hPa winds may be possible under highs to the west and Persian troughs. Wind speed should be inferred by interpolation, according to historical data of measurements or high resolution model.
12
Gierens, Rosa, Stefan Kneifel, Matthew D. Shupe, Kerstin Ebell, Marion Maturilli, and Ulrich Löhnert. "Low-level mixed-phase clouds in a complex Arctic environment." Atmospheric Chemistry and Physics 20, no. 6 (March 24, 2020): 3459–81. http://dx.doi.org/10.5194/acp-20-3459-2020.
Анотація:
Abstract. Low-level mixed-phase clouds (MPCs) are common in the Arctic. Both local and large-scale phenomena influence the properties and lifetime of MPCs. Arctic fjords are characterized by complex terrain and large variations in surface properties. Yet, not many studies have investigated the impact of local boundary layer dynamics and their relative importance on MPCs in the fjord environment. In this work, we used a combination of ground-based remote sensing instruments, surface meteorological observations, radiosoundings, and reanalysis data to study persistent low-level MPCs at Ny-Ålesund, Svalbard, for a 2.5-year period. Methods to identify the cloud regime, surface coupling, and regional and local wind patterns were developed. We found that persistent low-level MPCs were most common with westerly winds, and the westerly clouds had a higher mean liquid (42 g m−2) and ice water path (16 g m−2) compared to those with easterly winds. The increased height and rarity of persistent MPCs with easterly free-tropospheric winds suggest the island and its orography have an influence on the studied clouds. Seasonal variation in the liquid water path was found to be minimal, although the occurrence of persistent MPCs, their height, and their ice water path all showed notable seasonal dependency. Most of the studied MPCs were decoupled from the surface (63 %–82 % of the time). The coupled clouds had 41 % higher liquid water path than the fully decoupled ones. Local winds in the fjord were related to the frequency of surface coupling, and we propose that katabatic winds from the glaciers in the vicinity of the station may cause clouds to decouple. We concluded that while the regional to large-scale wind direction was important for the persistent MPC occurrence and properties, the local-scale phenomena (local wind patterns in the fjord and surface coupling) also had an influence. Moreover, this suggests that local boundary layer processes should be described in models in order to present low-level MPC properties accurately.
13
Tomaru, Ryota, Chris Done, Ken Ohsuga, Hirokazu Odaka, and Tadayuki Takahashi. "The thermal-radiative wind in low-mass X-ray binary H1743−322 – II. Iron line predictions from Monte Carlo radiation transfer." Monthly Notices of the Royal Astronomical Society 494, no. 3 (April 10, 2020): 3413–21. http://dx.doi.org/10.1093/mnras/staa961.
Анотація:
ABSTRACT We show the best current simulations of the absorption and emission features predicted from thermal-radiative winds produced from X-ray illumination of the outer accretion disc in binary systems. We use the density and velocity structure derived from a radiation hydrodynamic code as input to a Monte Carlo radiation transport calculation. The initial conditions are matched to those of the black hole binary system H1743−322 in its soft, disc dominated state, where wind features are seen in Chandra grating data. Our simulation fits well to the observed line profile, showing that these physical wind models can be the origin of the absorption features seen, rather than requiring a magnetically driven wind. We show how the velocity structure is the key observable discriminator between magnetic and thermal winds. Magnetic winds are faster at smaller radii, whereas thermal winds transition to a static atmosphere at smaller radii. New data from XRISM (due for launch 2022 January) will give an unprecedented view of the physics of the wind launch and acceleration processes, but the existence of static atmospheres in small disc systems already rules out magnetic winds which assume self-similar magnetic fields from the entire disc as the origin of the absorption features seen.
14
Isoguchi, Osamu, Masanobu Shimada, and Hiroshi Kawamura. "Characteristics of Ocean Surface Winds in the Lee of an Isolated Island Observed by Synthetic Aperture Radar." Monthly Weather Review 139, no. 6 (June 1, 2010): 1744–61. http://dx.doi.org/10.1175/2010mwr3564.1.
Анотація:
Abstract Characteristics of ocean surface winds around an isolated island are examined in relation to atmospheric stability using a synthetic aperture radar (SAR) and rawinsonde sounding observations. The SAR-derived winds on 22 May 2009 indicate a low-level jet extending over 30 km behind the island. Around the time of SAR acquisition, winds intensified on the leeward side in association with the stabilization of stratified flows, which suggests the connection of the SAR-derived jet with downslope winds. A number of SAR-derived winds elucidate typical wind patterns and their transitions depending on the nondimensional mountain height . For cases of large (>2), a wake is formed in the lee of the island and low-level jets produce strong wind shear on both sides of the wake. For cases of relatively small (<1.75), although a weak wind region is formed behind the mountain, no wind jets develop. As a transition of the above two cases , a low-level jet develops in the lee of the island, as in the case on 22 May 2009. These wake configurations and their -dependent transitions seem to correspond to major regimes for hydrostatic flow over topography with constant upstream speed and buoyancy frequency: small-amplitude waves , wave breaking , and flow splitting . It is noted that the ocean surface winds behind the island are very sensitive to around the transition point, changing up and down. The occurrence of each wind pattern shows clear seasonal features dependent on atmospheric stability.
15
Zeng, Jie, Wen Yi, Xianghui Xue, Iain Reid, Xiaojing Hao, Na Li, Jinsong Chen, Tingdi Chen, and Xiankang Dou. "Comparison between the Mesospheric Winds Observed by Two Collocated Meteor Radars at Low Latitudes." Remote Sensing 14, no. 10 (May 13, 2022): 2354. http://dx.doi.org/10.3390/rs14102354.
Анотація:
This study compares the hourly mesospheric horizontal winds observed by two collocated and independent low-latitude meteor radars operating at 37.5 MHz and 53.1 MHz in Kunming, China (25.6°N, 103.8°E). Upon analyzing simultaneously detected meteor echoes, we find a fixed angular deviation between the baselines of the two meteor radar antenna arrays within the east–north–up coordinate system. Then, we correct the deviation in the antenna azimuth direction using a novel method and recalculate the horizontal zonal and meridional winds. A comparison of the results before and after the correction shows strong consistency between the winds observed by both meteor radars within the entire detection altitude range. Furthermore, we summarize the performance of different techniques for measuring mesospheric winds. Ultimately, our statistical analysis approach allows the uncertainties associated with meteor radar wind observations to be more precisely estimated.
16
Kalapureddy, M. C. R., D. N. Rao, A. R. Jain, and Y. Ohno. "Wind profiler observations of a monsoon low-level jet over a tropical Indian station." Annales Geophysicae 25, no. 10 (November 6, 2007): 2125–37. http://dx.doi.org/10.5194/angeo-25-2125-2007.
Анотація:
Abstract. Three-year high-resolution wind observations of the wind profiler have been utilized to characterize the diurnal and seasonal features of the monsoon Low-Level Jet (LLJ) over a tropical station, Gadanki (13.5° N, 79.2° E), with a focus on the diurnal variability of low-level winds. The Boreal summer monsoon winds show a conspicuously strong westerly LLJ with average wind speed exceeding 20 m s−1. The L-band wind profiler measurements have shown an advantage of better height and time resolutions over the conventional radiosonde method for diurnal wind measurements. An interesting diurnal oscillation of LLJ core has been observed. It is varying in the height range of 1.8±0.6 km with the maximum and minimum intensity noticed during the early morning and afternoon hours, respectively. The jet core (wind maxima) height is observed to coincide with the inversion height. Strong wind shears are normally located beneath the LLJ core. The sole wind profiler observations are capable of identifying the monsoon phases, such as onset, break and active spells, etc. The mutual influence between the LLJ and the boundary layer has been discussed. One notices that the observed LLJ diurnal structures depend on the local convective activity, wind shears and turbulence activity associated with boundary layer winds. The day-to-day change in the LLJ structure depends on the latitudinal position of the LLJ core.
17
Xue, Lin, Ying Li, and Sen Yao. "A Statistical Analysis of Tropical Cyclone-Induced Low-Level Winds near Taiwan Island." Atmosphere 14, no. 4 (April 14, 2023): 715. http://dx.doi.org/10.3390/atmos14040715.
Анотація:
Using ERA5 reanalysis data and the tropical cyclone (TC) best track datasets from the China Meteorological Administration and Joint Typhoon Warning Center (from 1979 to 2021), TC-induced low-level winds near Taiwan Island are statistically analyzed. This study mainly concerns TC activity, low-level wind fields around Taiwan Island under TCs, and the detailed characteristics of TC wind structure. Results show that on average, 8.3 TCs enter the study region near Taiwan Island every year mainly from May to November, with more frequent and stronger TCs on the eastern and southern sides of Taiwan Island. For TC centers located at different positions around Taiwan Island, positive and negative vertical vorticity belts alternate between Taiwan Island and the TC center. Moreover, stronger and more frequent TC-induced winds mainly occur on the eastern side of Taiwan Island and the north of Taiwan Strait. TCs to the east of Taiwan Island have stronger maximum sustained wind than those on the western side of the island. Radii of the maximum wind (RMW) for TCs around Taiwan Island range from 5 to 90 nautical mile (nm, 9.3 to 116.7 km) with a mean value of 24.7 nm (44.4 km). Moreover, the RMWs of TCs are the largest (smallest) when the TC centers are located to the southwest (east) of the island. In addition, the outer sizes of TC winds vary from 52 to 360 nm (17.2 to 666.7 km) in the study region, with 187.4 nm (347.1 km) on average, and smaller values for TCs on the western side of the island. The average radii of severe winds, including R34, R50, and R64, are largest in the northeast quadrant and smallest in the southwest quadrant of the TC. The higher the specific wind speed is, the smaller the TC radius and the more symmetric its wind circle. These statistical results may provide references for TC gale forecasting and wind-resistant design for offshore engineering to mitigate TC-induced wind hazards.
18
Vidotto, A. A. "Incorporating magnetic field observations in wind models of low-mass stars." ASTRA Proceedings 1 (June 6, 2014): 19–22. http://dx.doi.org/10.5194/ap-1-19-2014.
Анотація:
Abstract. Stellar winds of cool, main-sequence stars are very tenuous and difficult to observe. Despite carrying away only a small amount of the stellar mass, they are important for regulating the rotation of the star and, consequently, its activity and magnetism. As it permeates the interplanetary space, the stellar wind interacts with any exoplanet encountered on its way, until it reaches the interstellar medium (ISM). These interactions can result in complex physical processes that depend on the characteristics of the wind. To better constrain the wind characteristics, more realistic wind models that account for factors such as stellar rotation and the complex/diverse observationally-derived stellar magnetic field configurations of cool stars are required. In this paper, I present a three-dimensional model of the wind of cool stars, which adopt as boundary condition observationally-derived magnetic maps. I also discuss how these studies are relevant for, e.g., the characterisation of the interaction between stellar winds and planets/ISM, and the propagation of cosmic rays.
19
Li, Gang, Juan Cui, Tingshan Liu, Yongqiu Zheng, Congcong Hao, Xiaojian Hao, and Chenyang Xue. "Triboelectric-Electromagnetic Hybrid Wind-Energy Harvester with a Low Startup Wind Speed in Urban Self-Powered Sensing." Micromachines 14, no. 2 (January 23, 2023): 298. http://dx.doi.org/10.3390/mi14020298.
Анотація:
Wind energy as a renewable energy source is easily available and widely distributed in cities. However, current wind-energy harvesters are inadequate at capturing energy from low-speed winds in urban areas, thereby limiting their application in distributed self-powered sensor networks. A triboelectric–electromagnetic hybrid harvester with a low startup wind speed (LSWS-TEH) is proposed that also provides output power within a wide range of wind speeds. An engineering-implementable propeller design method is developed to reduce the startup wind speed of the harvester. A mechanical analysis of the aerodynamics of the rotating propeller is performed, and optimal propeller parameter settings are found that greatly improved its aerodynamic torque. By combining the high-voltage output of the triboelectric nanogenerator under low-speed winds with the high-power output of the electromagnetic generator under high-speed winds, the harvester can maintain direct current output over a wide wind-speed range after rectification. Experiments show that the harvester activates at wind speeds as low as 1.2 m/s, powers a sensor with multiple integrated components in 1.7 m/s wind speeds, and drives a Bluetooth temperature and humidity sensor in 2.7 m/s wind speeds. The proposed small, effective, inexpensive hybrid energy harvester provides a promising way for self-powered requirements in smart city settings.
20
Mears, Carl, Tong Lee, Lucrezia Ricciardulli, Xiaochun Wang, and Frank Wentz. "Improving the Accuracy of the Cross-Calibrated Multi-Platform (CCMP) Ocean Vector Winds." Remote Sensing 14, no. 17 (August 27, 2022): 4230. http://dx.doi.org/10.3390/rs14174230.
Анотація:
The Cross-Calibrated Multi-Platform (CCMP) Ocean vector wind analysis is a level-4 product that uses a variational method to combine satellite retrievals of ocean winds with a background wind field from a numerical weather prediction (NWP) model. The result is a spatially complete estimate of global ocean vector winds on six-hour intervals that are closely tied to satellite measurements. The current versions of CCMP are fairly accurate at low to moderate wind speeds (<15 m/s) but are systematically too low at high winds at locations/times where a collocated satellite measurement is not available. This is mainly because the NWP winds tend to be lower than satellite winds, especially at high wind speed. The current long-term CCMP version, version 2.0, also shows spurious variations on interannual to decadal time scales caused by the interaction of satellite/model bias with the varying amount of satellite measurements available as satellite missions begin and end. To alleviate these issues, here we explore methods to adjust the source datasets to more closely match each other before they are combined. The resultant new CCMP wind analysis agrees better with long-term trend estimates from satellite observations and reanalysis than previous versions.
21
Ricciardulli, Lucrezia, Carl Mears, Andrew Manaster, and Thomas Meissner. "Assessment of CYGNSS Wind Speed Retrievals in Tropical Cyclones." Remote Sensing 13, no. 24 (December 16, 2021): 5110. http://dx.doi.org/10.3390/rs13245110.
Анотація:
The NASA CYGNSS satellite constellation measures ocean surface winds using the existing network of the Global Navigation Satellite System (GNSS) and was designed for measurements in tropical cyclones (TCs). Here, we focus on using a consistent methodology to validate multiple CYGNSS wind data records currently available to the public, some focusing on low to moderate wind speeds, others for high winds, a storm-centric product for TC analyses, and a wind dataset from NOAA that applies a track-wise bias correction. Our goal is to document their differences and provide guidance to users. The assessment of CYGNSS winds (2017–2020) is performed here at global scales and for all wind regimes, with particular focus on TCs, using measurements from radiometers that are specifically developed for high winds: SMAP, WindSat, and AMSR2 TC-winds. The CYGNSS high-wind products display significant biases in TCs and very large uncertainties. Similar biases and large uncertainties were found with the storm-centric wind product. On the other hand, the NOAA winds show promising skill in TCs, approaching a level suitable for tropical meteorology studies. At the global level, the NOAA winds are overall unbiased at wind regimes from 0–30 m/s and were selected for a test assimilation into a global wind analysis, CCMP, also presented here.
22
Carr, James L., Dong L. Wu, Mariel D. Friberg, and Tyler C. Summers. "Multi-LEO Satellite Stereo Winds." Remote Sensing 15, no. 8 (April 19, 2023): 2154. http://dx.doi.org/10.3390/rs15082154.
Анотація:
The stereo-winds method follows trackable atmospheric cloud features from multiple viewing perspectives over multiple times, generally involving multiple satellite platforms. Multi-temporal observations provide information about the wind velocity and the observed parallax between viewing perspectives provides information about the height. The stereo-winds method requires no prior assumptions about the thermal profile of the atmosphere to assign a wind height, since the height of the tracked feature is directly determined from the viewing geometry. The method is well developed for pairs of Geostationary (GEO) satellites and a GEO paired with a Low Earth Orbiting (LEO) satellite. However, neither GEO-GEO nor GEO-LEO configurations provide coverage of the poles. In this paper, we develop the stereo-winds method for multi-LEO configurations, to extend coverage from pole to pole. The most promising multi-LEO constellation studied consists of Terra/MODIS and Sentinel-3/SLSTR. Stereo-wind products are validated using clear-sky terrain measurements, spaceborne LiDAR, and reanalysis winds for winter and summer over both poles. Applications of multi-LEO polar stereo winds range from polar atmospheric circulation to nighttime cloud identification. Low cloud detection during polar nighttime is extremely challenging for satellite remote sensing. The stereo-winds method can improve polar cloud observations in otherwise challenging conditions.
23
Gaffin, David M. "On High Winds and Foehn Warming Associated with Mountain-Wave Events in the Western Foothills of the Southern Appalachian Mountains." Weather and Forecasting 24, no. 1 (February 1, 2009): 53–75. http://dx.doi.org/10.1175/2008waf2007096.1.
Анотація:
Abstract Extremely high winds of 40–49 m s−1 [90–110 miles per hour (mph)] were reported across the western foothills of the southern Appalachian Mountains on 22–23 December 2004, 17 October 2006, 24–25 February 2007, and 1 March 2007. The high winds in all four of these events were determined to be the result of mountain waves, as strong southeast winds became perpendicular to the mountains with a stable boundary layer present below 750 hPa and a veering wind profile that increased with height. Adiabatic warming of the descending southeasterly winds was also observed at the Knoxville airport during all four events (although of varying intensities), with the 850-hPa air mass immediately upwind of the Smoky Mountains determined to be the source region of these foehn winds. An interesting similarity among these four events was the location of the strongest 850-hPa winds northwest of the region, with a rapidly decreasing speed gradient observed over the mountains. These 850-hPa winds northwest of the mountains were also stronger than the 700-hPa winds in the region. It was hypothesized that strong low-level divergence developed in the foothills, as the stronger 850-hPa winds on the western side accelerated away from the mountains while the mountains prevented a rapid return flow from the eastern side. This low-level divergence likely helped to further strengthen the mountain-wave-induced mesolow and high winds in the western foothills. A 12-yr climatology of high wind events induced by mountain waves at Cove Mountain was also constructed. This climatology revealed that these events occurred primarily at night between November and March. Composite maps of mountain-wave events that produced warning-level and advisory-level winds revealed that an axis of stronger 850-hPa winds was typically located west of the mountains (away from the foothills). This finding (using reanalysis data instead of model data) further suggested that low-level divergence normally contributed to the intensity of mountain-wave-induced mesolows and winds in the western foothills of the southern Appalachian Mountains.
24
Carpenter, K. G., and R. D. Robinson. "Winds And Mass-Loss From Evolved, Low-Gravity Cool Stars." Highlights of Astronomy 11, no. 1 (1998): 378. http://dx.doi.org/10.1017/s1539299600021286.
Анотація:
The character of the winds and the amount of mass-loss from stars during the red giant and supergiant stage of evolution are critical to the progression of that evolution. We therefore summarize here the results of a series of programs utilizing the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) to study the winds and mass-loss from the surface of evolved, low-gravity cool stars. We discuss the structure of the chromospheres in which the base of these stellar winds lie, the velocity of the wind and its acceleration with height, and what these spectra tell us about the mass-loss from these stars. Because of its relevance to this Joint Discussion, we will also discuss in some detail what we have learned about real-time variability of these phenomena and the implied somewhat erratic nature of the mass-loss process in at least some of these stars.
25
Shimada, Teruhisa, Masahiro Sawada, Weiming Sha, and Hiroshi Kawamura. "Low-Level Easterly Winds Blowing through the Tsugaru Strait, Japan. Part I: Case Study and Statistical Characteristics Based on Observations." Monthly Weather Review 138, no. 10 (October 1, 2010): 3806–21. http://dx.doi.org/10.1175/2010mwr3354.1.
Анотація:
Abstract This study has investigated structures and diurnal variations of the easterly surface winds blowing throughout the east–west passage comprising the Tsugaru Strait, Mutsu Bay, and circumjacent terrestrial gaps in northern Japan during the summer months. Based on observational and reanalysis data, a representative case study in June 2003 and supplemental statistical analyses are presented. The cool easterly winds accompanied by clouds and fog are blocked by the central mountain range. This condition increases an along-strait sea level pressure (SLP) gradient, which induces strong winds in the west of the strait. The along-strait SLP gradient is enhanced by the developed Okhotsk high and by low pressure systems passing along the southern coast of Japan or over the Japan Sea. Stronger (weaker) and easterly (east-northeasterly) winds are observed during the nighttime (daytime), corresponding to the cool air intrusion from the east (retreat from west). Differences in SLP observed at meteorological observation stations on the east and west can be a good indicator of wind speed in the west of the strait. Meanwhile, the winds over the land also show diurnal variations specific to the times of the prevailing cool easterly winds. The easterly winds over the land are stronger and more divergent across the strait during the daytime than nighttime. This indicates the possibility that the diurnal wind variations are thermally induced. Reduction of diurnal air temperature changes in the east increases east–west thermal contrast. Additionally, the cool air over the strait and the bay can enhance land–sea thermal contrast across the coast.
26
Small, David, Eyad Atallah, and John Gyakum. "Wind Regimes along the Beaufort Sea Coast Favorable for Strong Wind Events at Tuktoyaktuk." Journal of Applied Meteorology and Climatology 50, no. 6 (June 2011): 1291–306. http://dx.doi.org/10.1175/2010jamc2606.1.
Анотація:
AbstractThe community of Tuktoyaktuk (Northwest Territories, Canada) along the Beaufort Sea experiences dramatic shoreline erosion during storm surge events that tend to occur during persistent northwesterly wind events in the late summer months (July–September) when the sea ice coverage of the Beaufort Sea reaches its annual minimum. This study compiles the climatology of hourly surface wind, low-level geostrophic wind, and static stability to investigate the physical mechanisms responsible for the high frequency of northwesterly winds observed at Tuktoyaktuk during the late summer. The results link the prevalence of westerly to northwesterly winds at the surface to the high frequency of northwesterly geostrophic winds and a tendency for low static stability. With an environment that favors strong northwesterly geostrophic wind and suggests lower static stability, the high frequency of strong northwesterlies observed at the surface appears to be associated with momentum mixing by turbulent eddies. A composite analysis indicates that persistently strong northwesterly winds are associated with anomalously low pressure northeast of Tuktoyaktuk and high pressure over the Bering Sea and eastern Siberia. The high pressure anomalies over the Bering Sea also extend well to the east along the northern edge of the Brooks Range. An apparent topographic modification of the sea level pressure (SLP) field by cold air trapped to the north of mountains produces the pressure gradient favorable for strong westerly to northwesterly geostrophic winds at Tuktoyaktuk. The results suggest that cold-air damming contributes to the wind regime at Tuktoyaktuk by altering the pressure gradient along the Beaufort coast.
27
Coleman, Timothy A., and Kevin R. Knupp. "Factors Affecting Surface Wind Speeds in Gravity Waves and Wake Lows." Weather and Forecasting 24, no. 6 (December 1, 2009): 1664–79. http://dx.doi.org/10.1175/2009waf2222248.1.
Анотація:
Abstract Ducted gravity waves and wake lows have been associated with numerous documented cases of “severe” winds (>25 m s−1) and wind damage. These winds are associated with the pressure perturbations and transient mesoscale pressure gradients occurring in many gravity waves and wake lows. However, not all wake lows and gravity waves produce significant winds nor wind damage. In this paper, the factors that affect the surface winds produced by ducted gravity waves and wake lows are reviewed and examined. It is shown theoretically that the factors most conducive to high surface winds include a large-amplitude pressure disturbance, a slow intrinsic speed of propagation, and an ambient wind with the same sign as the pressure perturbation (i.e., a headwind for a pressure trough). Multiple case studies are presented, contrasting gravity waves and wake lows with varying amplitudes, intrinsic speeds, and background winds. In some cases high winds occurred, while in others they did not. In each case, the factor(s) responsible for significant winds, or the lack thereof, are discussed. It is hoped that operational forecasters will be able to, in some cases, compute these factors in real time, to ascertain in more detail the threat of damaging wind from an approaching ducted gravity wave or wake low.
28
Wheatley, Dustan M., Robert J. Trapp, and Nolan T. Atkins. "Radar and Damage Analysis of Severe Bow Echoes Observed during BAMEX." Monthly Weather Review 134, no. 3 (March 1, 2006): 791–806. http://dx.doi.org/10.1175/mwr3100.1.
Анотація:
Abstract This study examines damaging-wind production by bow-shaped convective systems, commonly referred to as bow echoes. Recent idealized numerical simulations suggest that, in addition to descending rear inflow at the bow echo apex, low-level mesovortices within bow echoes can induce damaging straight-line surface winds. In light of these findings, detailed aerial and ground surveys of wind damage were conducted immediately following five bow echo events observed during the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment (BAMEX) field phase. These damage locations were overlaid directly onto Weather Surveillance Radar-1988 Doppler (WSR-88D) images to (i) elucidate where damaging surface winds occurred within the bow-shaped convective system (in proximity to the apex, north of the apex, etc.), and then (ii) explain the existence of these winds in the context of the possible damaging-wind mechanisms. The results of this study provide clear observational evidence that low-level mesovortices within bow echoes can produce damaging straight-line winds at the ground. When present in the BAMEX dataset, mesovortex winds produced the most significant wind damage. Also in the BAMEX dataset, it was observed that smaller-scale bow echoes—those with horizontal scales of tens of kilometers or less—produced more significant wind damage than mature, extensive bow echoes (except when mesovortices were present within the larger-scale systems).
29
Nawri, N., and R. E. Stewart. "Channelling of high-latitude boundary-layer flow." Nonlinear Processes in Geophysics 15, no. 1 (January 31, 2008): 33–52. http://dx.doi.org/10.5194/npg-15-33-2008.
Анотація:
Abstract. Due to the stability of the boundary-layer stratification, high-latitude winds over complex terrain are strongly affected by blocking and channelling effects. Consequently, at many low-lying communities in the Canadian Archipelago, including Cape Dorset and Iqaluit considered in this study, surface winds for the most part are from two diametrically opposed directions, following the orientation of the elevated terrain. Shifts between the two prevailing wind directions can be sudden and are associated with geostrophic wind directions within a well defined narrow range. To quantitatively investigate the role of large-scale pressure gradients and the quasi-geostrophic overlying flow, an idealised dynamical system for the evolution of channelled surface winds is derived from the basic equations of motion, in which stability of stationary along-channel wind directions is described as a function of the geostrophic wind. In comparison with long-term horizontal wind statistics at the two locations it is shown that the climatologically prevailing wind directions can be identified as stationary states of the idealised wind model, and that shifts between prevailing wind directions can be represented as stability transitions between these stationary states. In that sense, the prevailing local wind conditions can be interpreted as attracting states of the actual flow, with observed surface winds adjusting to a new stable direction as determined by the idealised system within 3–9 h. Over these time-scales and longer it is therefore advantageous to determine the relatively slow evolution of the observationally well-resolved large-scale pressure distribution, instead of modelling highly variable surface winds directly. The simplified model also offers a tool for dynamical downscaling of global climate simulations, and for determining future scenarios for local prevailing wind conditions. In particular, it allows an estimation of the sensitivity of local low-level winds to changes in the large-scale atmospheric circulation.
30
Schmidlin, PhD, Thomas W., Barbara O. Hammer, MA, Paul S. King, BS, L. Scott Miller, PhD, Gregory Thumann, MS, and Helene Wetherington, MA. "Determining critical wind speeds for overturning two types of ambulances and a large city bus." Journal of Emergency Management 3, no. 2 (March 1, 2005): 21. http://dx.doi.org/10.5055/jem.2005.0016.
Анотація:
Two types of ambulances and a city bus were modeled in a wind tunnel for the minimum wind speed required to upset the stationary vehicles. The Type I ambulance was vulnerable to upset with wind speeds of 135 to 150 mph on the vehicle over wind angles of 40° to 145°. The Type II ambulance was vulnerable to upset with wind speeds of 140 to 170 mph over wind angles of 30° to 145°. The 40-passenger city bus was vulnerable to upset with wind speeds of 60 to 75 mph over wind angles of 35° to 145°. These results showed ambulances were more stable in high winds than common passenger vehicles, but the city bus was very vulnerable in high winds. Testing showed that moving ambulances can be driven at low speeds in minimal hurricane-force winds without exceeding the upset wind speeds on the vehicles. This information provides guidance for safe operation of these vehicles during high winds including hurricanes, thunderstorms, and extra-tropical cyclones.
31
Holzer, Thomas E. "Theory of winds from cool stars." Symposium - International Astronomical Union 122 (1987): 289–305. http://dx.doi.org/10.1017/s0074180900156591.
Анотація:
The goal of this paper is to provide a framework for thinking about the various physical processes that may play significant roles in driving the massive winds of cool, low-gravity stars. First, some general theoretical considerations involving mass, momentum, and energy balance are discussed. Next, the value of the solar wind as an analog for these late-type stellar winds and for related astrophysical flows is briefly examined. Finally, four specific mass-loss mechanisms are discussed, and the possible importance of each of these mechanisms for massive winds from cool, low-gravity stars is evaluated.
32
McQuinn, Kristen B. W., Liese van Zee, and Evan D. Skillman. "Galactic Winds in Low-mass Galaxies." Astrophysical Journal 886, no. 1 (November 21, 2019): 74. http://dx.doi.org/10.3847/1538-4357/ab4c37.
33
McQuinn, Kristen B. W., Liese van Zee, and Evan D. Skillman. "Galactic Winds in Low-Mass Galaxies." Proceedings of the International Astronomical Union 14, S344 (August 2018): 301–4. http://dx.doi.org/10.1017/s1743921319000085.
Анотація:
AbstractMass-loss via stellar-feedback driven outflows is predicted to play a critical role in the baryon cycle of low-mass galaxies. However, observational constraints on warm winds are limited as outflows are transient, intrinsically low-surface brightness events and, thus, difficult to detect. Here, we search for outflows in a sample of eleven nearby starburst dwarf galaxies which are strong candidates for outflows. Despite deep H? imaging on galaxies, only a fraction of the sample show evidence of winds. The spatial extent of all detected ionized gas is limited and would still be considered part of the ISM by simulations. These new observations indicate that the physical extent of warm phase outflows is modest and most of the mass will be recycled to the galaxy. The sample is part of the panchromatic STARBurst IRegular Dwarf Survey (STARBIRDS) designed to characterize the starburst phenomenon and its impact on the evolution of low-mass galaxies.
34
Anselmo, Evandro M., Courtney Schumacher, and Luiz A. T. Machado. "The Amazonian Low-Level Jet and Its Connection to Convective Cloud Propagation and Evolution." Monthly Weather Review 148, no. 10 (October 1, 2020): 4083–99. http://dx.doi.org/10.1175/mwr-d-19-0414.1.
Анотація:
AbstractWe describe the existence of an Amazonian low-level jet (ALLJ) that can affect the propagation and life cycle of convective systems from the northeast coast of South America into central Amazonia. Horizontal winds from reanalysis were analyzed during March–April–May (MAM) of the two years (2014–15) of the GoAmazon2014/5 field campaign. Convective system tracking was performed using GOES-13 infrared imagery and classified into days with high and weak convective activity. The MAM average winds show a nocturnal enhancement of low-level winds starting near the coast in the early evening and reaching 1600 km inland by late morning. Mean 3-hourly wind speeds maximize at 9–10 m s−1 near 900 hPa, but individual days can have nighttime low-level winds exceeding 12 m s−1. Based on objective low-level wind criteria, the ALLJ is present 10%–40% of the time over the Amazon during MAM depending on the location and time of day. The evolution of the ALLJ across the Amazon impacts the frequency of occurrence of cloud clusters and the intensity of the moisture flux. In addition, the ALLJ is associated with the enhancement of northeasterly flow in the midtroposphere during active convective days, when vertical momentum transport may be occurring in the organized cloud clusters. During the weakly active convective period, the ALLJ is weaker near the coast but stronger across the central Amazon and appears to be linked more directly with the South American low-level jet.
35
Lefort, Jean-Pierre, John Renouf, and Guzel Danukalova. "Transit boosting of trans-Channel katabatic winds by depressions associated with the west European storms tracks: impact on Pleistocene loess deposits." Journal of the Geological Society 179, no. 3 (October 18, 2021): jgs2021–078. http://dx.doi.org/10.1144/jgs2021-078.
Анотація:
Onshore and offshore sedimentological, geochemical, geomorphological, palaeontological and geochronological studies of loess deposits located under and around the English Channel revealed that they were transported by katabatic winds generated by the British–Irish Ice Sheet. Katabatic winds, which are low-altitude wind flows, were able to jump over the low southern British hills but were stopped by the higher Brittany and Normandy hills. This regional topography is interrupted by a north–south corridor linking the northern and southern shores of Brittany where loess propagated down to the mouth of the Loire River. This long transit shows that the total distance travelled by the katabatic wind was around 750 km, which represents an unusual distance for the propagation of this wind under continental conditions. Strong similarities with Antarctica and Greenland, where well documented cases of katabatic winds are known, show that the transit of the trans-Channel katabatic winds were strongly enhanced by the seasonal drift of storms propagating in an eastward direction along the axis of the English Channel. This increasing strength of the north–south katabatic flux was probably at the origin of the transport of loess particles down to the mouth of the Loire River.
36
Rikiishi, Kunio, and Shinya Takatsuji. "On the growth of ice cover in the Sea of Okhotsk with special reference to its negative correlation with that in the Bering Sea." Annals of Glaciology 42 (2005): 380–88. http://dx.doi.org/10.3189/172756405781812619.
Анотація:
AbstractCharacteristic features of the growth of sea-ice extent in the Sea of Okhotsk are discussed statistically in relation to the surface wind and air temperature over the Okhotsk basin. It is shown that cold-air advection from the continent is not the only factor for the growth of ice extent: air-mass transformation with fetch (downwind distance from the coast) is another important factor. Using weekly growth rates of ice extent and objectively analyzed meteorological data, it is shown that the ice cover extends when cold northerly/northwesterly winds blow, whereas the ice cover retreats when warm northeasterly/easterly winds blow. It is concluded that the advance/retreat of the Sea of Okhotsk ice cover is largely determined by the atmospheric circulation, which is in turn controlled by the position and intensity of the Aleutian low. Occasional out-of-phase fluctuations between the Sea of Okhotsk and Bering Sea ice covers are found to occur when an intensified Aleutian low is located in the mid-western part of the Bering Sea and induces cold northwesterly winds to the Okhotsk basin and warm southeasterly winds to the Bering Sea, or when a weakened Aleutian low is displaced eastward and induces cold northeasterly winds to the Bering Sea and warm northeasterly winds to the Okhotsk basin.
37
Bao, J.-W., S. A. Michelson, P. O. G. Persson, I. V. Djalalova, and J. M. Wilczak. "Observed and WRF-Simulated Low-Level Winds in a High-Ozone Episode during the Central California Ozone Study." Journal of Applied Meteorology and Climatology 47, no. 9 (September 1, 2008): 2372–94. http://dx.doi.org/10.1175/2008jamc1822.1.
Анотація:
Abstract A case study is carried out for the 29 July–3 August 2000 episode of the Central California Ozone Study (CCOS), a typical summertime high-ozone event in the Central Valley of California. The focus of the study is on the low-level winds that control the transport and dispersion of pollutants in the Central Valley. An analysis of surface and wind profiler observations from the CCOS field experiment indicates a number of important low-level flows in the Central Valley: 1) the incoming low-level marine airflow through the Carquinez Strait into the Sacramento River delta, 2) the diurnal cycle of upslope–downslope flows, 3) the up- and down-valley flow in the Sacramento Valley, 4) the nocturnal low-level jet in the San Joaquin Valley, and 5) the orographically induced mesoscale eddies (the Fresno and Schultz eddies). A numerical simulation using the advanced research version of the Weather Research and Forecasting Model (WRF) reproduces the overall pattern of the observed low-level flows. The physical reasons behind the quantitative differences between the observed and simulated low-level winds are also analyzed and discussed, although not enough observations are available to diagnose thoroughly the model-error sources. In particular, hodograph analysis is applied to provide physical insight into the impact of the large-scale, upper-level winds on the locally forced low-level winds. It is found that the diurnal rotation of the observed and simulated hodographs of the local winds varies spatially in the Central Valley, resulting from the combining effect of topographically induced local forcing and the interaction between the upper-level winds and the aforementioned low-level flows. The trajectory analysis not only further confirms that WRF reproduces the observed low-level transport processes reasonably well but also shows that the simulated upper-level winds have noticeable errors. The results from this study strongly suggest that the errors in the WRF-simulated low-level winds are related not only to the errors in the model’s surface conditions and atmospheric boundary layer physics but also to the errors in the upper-level forcing mostly prescribed in the model’s lateral boundary conditions.
38
Sivareddy, S., M. Ravichandran, and M. S. Girishkumar. "Evaluation of ASCAT-Based Daily Gridded Winds in the Tropical Indian Ocean*." Journal of Atmospheric and Oceanic Technology 30, no. 7 (July 1, 2013): 1371–81. http://dx.doi.org/10.1175/jtech-d-12-00227.1.
Анотація:
Abstract The quality of daily gridded Advanced Scatterometer (ASCAT; DASCAT) blended winds is examined in the tropical Indian Ocean using 3-day running mean gridded Quick Scatterometer (QuikSCAT; QSCAT) winds and in situ daily winds from the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA). The primary objective of this study is to examine whether DASCAT is a reliable replacement for the widely used QSCAT wind products. Spatial distributions of DASCAT and QSCAT winds show good agreement in speed and direction, except over a few localized regions. The study finds a significant spatial coherence between rainfall and the regions of discrepancy between DASCAT and QSCAT. Comparison of DASCAT and QSCAT wind products with RAMA moorings indicates that DASCAT better captures the overall wind variability compared to QSCAT, especially during rainy and low wind (<5 m s−1) conditions. The root-mean-square of the RAMA–DASCAT (RAMA–QSCAT) difference during rainfall in the zonal and meridional winds is 1.4 and 1.6 m s−1 (2.7 and 2.0 m s−1), respectively. The present study indicates that the DASCAT blended wind product is a reliable alternative to QSCAT in the tropical Indian Ocean.
39
Ham, Yoo-Geun, Jong-Seong Kug, and Mi-Jung Lim. "Rectification Feedback of High-Frequency Atmospheric Variability into Low-Frequency Zonal Flows in the Tropical Pacific." Journal of Climate 25, no. 14 (July 15, 2012): 5088–101. http://dx.doi.org/10.1175/jcli-d-11-00303.1.
Анотація:
Abstract In this study, the rectification process of high-frequency (HF) zonal-wind variability on the low-frequency (LF) zonal wind is investigated through an idealized experiment using an atmospheric general circulation model (AGCM). Through an idealized AGCM experiment with a fixed SST boundary forcing, it is shown that there is positive (negative) correlation between HF (2–90-day period) zonal-wind variance and LF (3-month average) zonal wind where the HF zonal-wind variance is positively (negatively) skewed because the stronger HF westerly (easterly) wind events than HF easterly (westerly) wind events induce a residual westerly (easterly), and it results in an additional rectified LF westerly (easterly) anomaly. This means that, over regions with positively skewed HF zonal winds, LF westerly anomalies are generated due to the residuals of the HF zonal winds. It implies that the LF zonal wind can be generated through internal processes of the atmosphere without external forcing and the interaction between LF and HF is not a one-way process from LF to HF but, rather, a two-way interaction process.
40
Arons, Jonathan. "Acceleration and Dissipation in Relativistic Winds." Symposium - International Astronomical Union 218 (2004): 163–66. http://dx.doi.org/10.1017/s0074180900180866.
Анотація:
I argue that ideal MHD relativistic winds are always limited in practice to asymptotic 4-velocity γ∞ ≍ σ1/30 and asymptotic magnetization σ ∼ σ 2/30 ≫ 1, where σ0 is the wind magnetization with respect to the rest energy density, evaluated at the light cylinder of the rotating, magnetized compact object that drives the flow. This suggests that the observed low value of the asymptotic σ in the equatorial sectors of the winds driving pulsar wind nebulae and the associated high values of the asymptotic 4-velocity are a consequence of magnetic dissipation in the wind zone.
41
Kudritzki, Rolf-Peter. "Line driven winds, ionizing fluxes and UV-spectra of hot stars at extremely low metalIicity." Symposium - International Astronomical Union 212 (2003): 325–33. http://dx.doi.org/10.1017/s0074180900212394.
Анотація:
Wind models of very massive stars with metallicities in a range from 10–4-1.0 Z⊙ are presented using a new treatment of radiation driven winds with depth dependent radiative force multipliers and a comprehensive list of more than two million of spectral lines in non-LTE. The models yield mass-loss rates, wind velocities, wind momenta and wind energies as a function of metallicity and can be used to discuss the influence of stellar winds on the evolution of very massive stars in the early universe and on the interstellar medium in the early phases of galaxy formation. It is shown that the normal scaling laws, which predict stellar mass-loss rates and wind momenta to decrease as a power law with metal abundance break down at a certain threshold. The new wind models are applied to calculate ionizing fluxes and observable UV-spectra of very massive stars as a function of metallicity using the wm-basic code developed by Pauldrach et al. (2001), and the efffects of metallicity are discussed.
42
Greenwell, D. I., N. J. Wood, E. K. L. Bridge, and R. J. Addy. "Aerodynamic characteristics of low-drag bicycle wheels." Aeronautical Journal 99, no. 983 (March 1995): 109–20. http://dx.doi.org/10.1017/s0001924000028281.
Анотація:
AbstractA number of modern “aerodynamic” bicycle wheels were tested at full scale speeds in a windtunnel. The effects of wheel geometry, rotational speed and cross winds on drag force, side force and yawing moment were investigated.Compared with a conventional spoked wheel, all the “aerodynamic” wheels were found to give similar improvements in drag of approximately 25%. In cross wind conditions, aerodynamic characteristics were strongly dependent on wheel geometry, but essentially independent of wheel rotational speed.
43
Pimenta, Felipe M., Edmo José Dias Campos, Jerry L. Miller, and Alberto R. Piola. "A numerical study of the Plata River plume along the southeastern South American continental shelf." Brazilian Journal of Oceanography 53, no. 3-4 (December 2005): 129–46. http://dx.doi.org/10.1590/s1679-87592005000200004.
Анотація:
The Rio de la Plata, one of the largest rivers on Earth, discharges into the ocean waters from basin that covers a large area of South America. Its plume extends along northern Argentina, Uruguay, and southern Brazil shelves strongly influencing the ecosystems. In spite of this, little is known about the mechanisms that control it. Here we report results of simulations with POM carried out to investigate the roles of wind and river discharge in Plata plume dynamics. Different outflows were explored, including an average climatological value and magnitudes representative of La Niña and El Niño. Forcing the model with river discharge the average plume speed was directly related to the outflow intensity. The Plata northward extension varied from 850 to 1550 km and for average discharge a band of low salinity waters formed from the estuary up to 30ºN of South Brazilian Shelf. Upwelling and downwelling winds were applied after 130 days. The distribution of low salinity waters over the shelf was more sensitive to the wind direction than to the river outflow variability. Downwelling winds were very capable of advecting the low salinity signal downshelf. Upwelling winds were efficient in eroding the plume, which was basically detached from the coast by Ekman drift. Abnormal plume intrusions toward low latitudes may be a result of the original plume position coupled with events of persistent strong downwelling favorable winds.
44
Tollinger, Mathias, Rune Graversen, and Harald Johnsen. "High-Resolution Polar Low Winds Obtained from Unsupervised SAR Wind Retrieval." Remote Sensing 13, no. 22 (November 18, 2021): 4655. http://dx.doi.org/10.3390/rs13224655.
Анотація:
High-resolution sea surface observations by spaceborne synthetic aperture radar (SAR) instruments are sorely neglected resources for meteorological applications in polar regions. Such radar observations provide information about wind speed and direction based on wind-induced roughness of the sea surface. The increasing coverage of SAR observations in polar regions calls for the development of SAR-specific applications that make use of the full information content of this valuable resource. Here we provide examples of the potential of SAR observations to provide details of the complex, mesoscale wind structure during polar low events, and examine the performance of two current wind retrieval methods. Furthermore, we suggest a new approach towards accurate wind vector retrieval of complex wind fields from SAR observations that does not require a priori wind direction input that the most common retrieval methods are dependent on. This approach has the potential to be particularly beneficial for numerical forecasting of weather systems with strong wind gradients, such as polar lows.
45
Coffer, Brice E., and Matthew D. Parker. "Is There a “Tipping Point” between Simulated Nontornadic and Tornadic Supercells in VORTEX2 Environments?" Monthly Weather Review 146, no. 8 (August 1, 2018): 2667–93. http://dx.doi.org/10.1175/mwr-d-18-0050.1.
Анотація:
Abstract Previous work has suggested that the lower-tropospheric wind profile may partly determine whether supercells become tornadic. If tornadogenesis within the VORTEX2 composite environments is more sensitive to the lower-tropospheric winds than to either the upper-tropospheric winds or the thermodynamic profile, then systematically varying the lower-tropospheric wind profile might reveal a “tipping point” between nontornadic and tornadic supercells. As a test, simulated supercells are initiated in environments that have been gradually interpolated between the low-level wind profiles of the nontornadic and tornadic VORTEX2 supercell composites while also interchanging the upper-tropospheric winds and thermodynamic profile. Simulated supercells become tornadic when the low-level wind profile incorporates at least 40% of the structure from the tornadic VORTEX2 composite environment. Both the nontornadic and tornadic storms have similar outflow temperatures and availability of surface vertical vorticity near their updrafts. Most distinctly, a robust low-level mesocyclone and updraft immediately overlie the intensifying near-surface circulation in each of the tornadic supercells. The nontornadic supercells have low-level updrafts that are disorganized, with pockets of descent throughout the region where surface vertical vorticity resides. The lower-tropospheric wind profile drives these distinct configurations of the low-level mesocyclone and updraft, regardless of the VORTEX2 composite upper-tropospheric wind profile or thermodynamic profile. This study therefore supports a potentially useful, robust link between the probability of supercell tornadogenesis and the lower-tropospheric wind profile, with tornadogenesis more (less) likely when the orientation of horizontal vorticity in the lowest few hundred meters is streamwise (crosswise).
46
RAMA, G. V., and T. R. SIVARAMAKRISHNAN. "Diurnal wind variation in the planetary boundary layer during southwest monsoon over Sriharikota." MAUSAM 41, no. 4 (February 24, 2022): 125–28. http://dx.doi.org/10.54302/mausam.v41i4.2796.
Анотація:
Three hourly pilot balloon winds collected over SHAR DURING FOUR DAYS OF July 1988 were analysed and existence of a diurnal cycle of variation at low level winds was established, Maximum changes in the wind speed occurred towards midnight. Harmonic analysis was performed for both the meridional and zonal component winds and the results are presented. The results suggest the PBL over SHAR to be about 1000 m thick. The shear and the steadiness factor values have also been evaluated and discussed.
47
Ramachandran, Varsha. "Winds of OB stars: impact of metallicity, rotation and binary interaction." Proceedings of the International Astronomical Union 17, S370 (August 2021): 223–29. http://dx.doi.org/10.1017/s1743921322004720.
Анотація:
AbstractWinds of massive stars are an important ingredient in determining their evolution, final remnant mass, and feedback to the surrounding interstellar medium. We compare empirical results for OB star winds at low metallicity with theoretical predictions. Observations suggest very weak winds at SMC metallicity, but there are exceptions. We identified promising candidates for rotationally enhanced mass-loss rates with two component wind and partially stripped stars hiding among OB stars with slow but dense wind in the SMC. A preliminary analysis of these systems, derived parameters, and their implications are discussed. Finally, we briefly discuss the interaction of OB winds near black holes in X-ray binaries.
48
Pierini, Stefano. "Low-Frequency Variability, Coherence Resonance, and Phase Selection in a Low-Order Model of the Wind-Driven Ocean Circulation." Journal of Physical Oceanography 41, no. 9 (September 1, 2011): 1585–604. http://dx.doi.org/10.1175/jpo-d-10-05018.1.
Анотація:
Abstract In this paper, a low-order spectral quasigeostrophic (QG) model of the wind-driven ocean circulation is derived and used to analyze the low-order character of the intrinsic low-frequency variability of the midlatitude double-gyre ocean circulation and of the related coherence resonance and phase selection phenomena. The model includes an exponential in the basis functions that allows for westward intensification, retains only four modes in the Galerkin projection, is defined in a rectangular domain, and is forced by deterministic and stochastic winds, thus extending previous low-order QG ocean models. The solution under steady forcing is first obtained, and the results are also analyzed in terms of dynamical systems theory. A homoclinic bifurcation (with the wind amplitude chosen as the control parameter) leads to intrinsic decadal relaxation oscillations (ROs) similar in several respects to those obtained with primitive equation models. The system is then forced with an additional red noise wind, and, in a parameter range preceding the global bifurcation, a coherence resonance scenario very similar to the one found with a primitive equation model of the Kuroshio Extension is obtained: this suggests that such a phenomenon is of low-order character. To study the RO excitation mechanism, a method denoted as phase selection is proposed. The system is forced with additional fictitious periodic winds that produce an emergence of ROs yielding strong phase dependence with the periodic forcing. The subsequent analysis reveals the character of the wind forcing that is most likely to excite a RO. All the results are discussed within the general framework of climate dynamics.
49
Sampe, Takeaki, and Shang-Ping Xie. "Mapping High Sea Winds from Space: A Global Climatology." Bulletin of the American Meteorological Society 88, no. 12 (December 1, 2007): 1965–78. http://dx.doi.org/10.1175/bams-88-12-1965.
Анотація:
High winds at sea are feared by sailors, but their distribution is poorly known because ships have avoided them as much as possible. The accumulation of spaceborne scatterometer measurements now allows a global mapping of high winds over the ocean. Seven years of Quick Scatterometer (QuikSCAT) data gathered since July 1999 show that high-wind events, defined as wind speeds greater than 20 m s−1 (“strong gale” and higher on the Beaufort scale), mostly happen in winter. Over coastal regions, land orography is the major cause of high winds, forcing wind jets of various types. Over the open ocean, high winds tend to be collocated with the extratropical storm tracks, along which migratory low and high pressure systems travel eastward. In comparison, tropical cyclones do not leave a strong signature in the climatology of high-wind occurrence except in the western Pacific east of Taiwan. In the extratropics, sea surface temperature (SST) fronts and their meanders significantly change the frequency of high-wind events. For example, high winds occur twice as often (or more) over the warmer than the colder flank of the Gulf Stream, and over the poleward than equatorward meanders of the Antarctic Circumpolar Current. The collocation of frequent high winds and SST frontal zones is not a mere coincidence because SST gradients anchor storm tracks, which in turn sustain the surface westerlies against friction with lateral heat and momentum flux. Both the high mean speed and large variance of wind increase the probability of high winds. Implications for navigation safety and oceanographic and climate research are discussed.
50
Ishida, Yasuyuki, Akihito Yoshida, Shuhei Kamata, Yuta Yamane, and Akashi Mochida. "Wind Tunnel Experiments on Interference Effects of a High-Rise Building on the Surrounding Low-Rise Buildings in an Urban Block." Wind 3, no. 1 (February 21, 2023): 97–114. http://dx.doi.org/10.3390/wind3010007.
Анотація:
High-rise buildings cause accelerated winds around them. However, the interference effects of high-rise buildings on the surrounding low-rise buildings in urban blocks have not been evaluated. This study investigated the wind pressure coefficients on the roofs and walls of low-rise buildings surrounding a high-rise building through wind tunnel experiments. Seventy-two wind directions were considered from 0° to 355° in 5° increments, and the influence of the wind direction on the wind pressure coefficients of surrounding buildings was evaluated. At a 30° wind direction angle, the positive and negative peak wind pressure coefficients occurred in a low-rise building at the leeward side of the high-rise building. The positive peak pressure, approximately 1.4 times that without a nearby high-rise building, occurred at the windward corner on the front wall of a low-rise building. The negative peak value, approximately three times that without a nearby high-rise building, was observed at the windward edge on the roof of a low-rise building. Thus, accelerated winds caused by high-rise buildings may result in unexpected damage to the surrounding low-rise buildings.