Channelling of high-latitude boundary-layer flow

In the complex terrain where local wind systems are formed, accurate understanding of regional wind variability is required for wind resource assessment. In this paper, cluster analysis based on the similarity of time-series wind vector was applied to classify wind regions with similar wind characteristics and the meteorological validity of regionalization method was evaluated. Wind regions in Jeju Island and Busan were classified using the wind resource map of Korea created by a mesoscale numerical weather prediction modeling. The evaluation was performed by comparing wind speed, wind direction, and wind variability of each wind region. Wind characteristics, such as mean wind speed and prevailing wind direction, in the same wind region were similar and wind characteristics in different wind regions were meteor-statistically distinct. It was able to identify a singular wind region at the top area of Mt. Halla using the inconsistency of wind direction variability. Furthermore, it was found that the regionalization results correspond with the topographic features of Jeju Island and Busan, showing the validity.

Using a high‐resolution boundary‐layer model, effects of heterogeneity over a mesoscale flat domain are investigated through a series of idealised model simulations. In these simulations two different land surface types (bare soil and vegetation) are arranged in two different patterns. It is found that the effect of heterogeneity remains significant with geostrophic winds of 10 m s−1. However, when the geostrophic wind direction is perpendicular to the alignment of the surface heterogeneities (with alignment here defined as the direction along the edges of a sequence of surface patches), higher winds tend to weaken the coherent circulations caused by the surface heterogeneities. The vertical winds generated by the mesoscale circulations associated with the surface heterogeneities are on the order of 0.5 cm s−1. When the geostrophic wind direction is perpendicular to the alignment of the surface heterogeneities over a three‐strip surface type, the mesoscale pattern in horizontal velocity is also pronounced, with significant fluctuations at the interfaces between two different surface patches. The heights at which the heterogeneity effects on potential temperature and winds vanish are well above the convective boundary layer top and reach at least 3.3Ziunder light winds, but depend on the wind speed and directions as well as the orientation of surface heterogeneities.Finally, the implications of the surface heterogeneity for initiation of deep convection have been explored for a surface consisting of two‐dimensional strips of alternating soil and vegetated surfaces aligned in the north–south direction. For this surface pattern, the interaction between westerly background winds and the secondary circulation sets up conditions which favour the initiation of deep convection at the eastern, downwind edge of the soil strip. Copyright © 2010 Royal Meteorological Society

The author analysed the results of previous studies and her own investigations on the prevailing wind direction estimated by wind-shaped trees (Abies Mariesii, A. Veitchii) in the 16 mountainous regions in the subalpine zone in Central and Northern Honshu, Japan. She studied, at first, the relationship between local wind directions and the running directions of mountain ridges which are classified into N-S, NW-SE, NE-SW and W-E. She also compared the wind directions estimated by wind-shaped trees with the data obtained from the instrumental observations at the climatological station near by. The results obtained are summarized as follows: (1) The prevailing wind directions are different regionally in accordance with the directions of mountain ridges. (2) According to the cluster analysis on the combination of wind directions by each direction of mountain ridges in the 16 regions, we can recognize some difinite wind systems with similar characteristics. (3) The regional division was made by these results as shown in Pig. 4. (4) On the basis of the results mentioned above, three climatological regions can be recognized in Central and Northeastern Japan, i.e., (i) The region where the mountain climate of Japan Sea side type prevails (Mt. HachimantaiIwate, Mt. Zao, Mt. Azuma-Adatara-Pandai, Happo-one, Mt. Renge-Eboshi-Mitsudake, Mt. Hakusan, Mt. Kusatsu-shirane). (ii) The region where the mountain climate belonging to the Pacific side type prevails (Ozegahara-nanryo, Mt. tsumata-KumonodairaTaro, Mt. Norikura, Mt. Neko-Azuma, Mt. Kisokoma). (iii) The region where the mountain climates of both types are mixed (Mts. Oku-nikko, Mt. Shiomi-Arakawa, Mts. Okuchichibu. Mt. Yatsu, Mt. Oomine). (5) Roughly speaking, the wind direction distribution estimated by wind-shaped trees on the Japan Sea side of Honshu is similar to the NW flow type of the surface wind system over lowlands. On the other hand, the wind direction distribution estimated by wind-shaped trees on the Pacific side of Honshu is similar to the SW flow type. (6) In addition, the author discussed the results with a few related phenomena: The regional division by climates presented here coincides well with that of the Suzuki's (1962), which was based on the distribution of precipitation in winter. It is, therefore, clear that the wind conditions over the mountainous regions have close relations to precipitation under the influence of winter monsoon. (7) Shimagare phenomena (stripes of needle trees standing dead on the mountain slopes in the subalpine zone) are distributed on the slopes facing south, southwest and southeast in the subalpine zone in Chubu, . Kanto and Kinki Districts of Honshu. It is noteworthy that all of these areas belong to the mountain climate type on the Pacific side of Japan.

Question: Do shrubs influence the spatial pattern of soil seed banks in herbaceous vegetation and are these effects influenced by wind direction, sampling position (windward vs leeward sides of the shrub) and distance from the shrub?Location: Horqin desert in eastern Inner Mongolia, China.Methods: A pioneer shrub, Artemisia halodendron, occurring in a mobile sandy habitat was used as a case study. Species composition and abundance of the seed bank and established herbaceous vegetation around six target shrubs were sampled along transects aligned to the four main wind directions and at 0.5, 1, 2, 3, 4.5 and 6 m from the shrub base on both windward and leeward sides of a transect.Results: The presence of shrubs significantly modified the spatial pattern of seed deposition, but effects varied with wind direction, sampling position and distance from the shrub. More seeds were deposited on the leeward side than on the windward sides in all four transects, especially on transects with the most prevailing wind directions. Shrubs also caused a marked variation in seed deposition across sampling locations; this effect was more pronounced on the leeward side of transects with the most prevailing wind directions, suggesting the mean range of the shrub's influence is within ca. 2 m.Conclusions: The study shows clear evidence of shrubs as a source of spatial heterogeneity in seed availability in the herbaceous layer. Shrub presence effects were strongly influenced by complex interactions between wind direction, sampling position, and distance from the shrub.

The reliance of a developing nation like Nigeria on hydro-electricity over time has led to power shortage which has hampered her economic and technological advancement because of its seasonal variation. The use of fossil fuel will not also be a better alternative since it is not environmental friendly. However, wind energy is free, clean, cheap and does not contribute to acid rain or global warming. The aim of this research is to carry out an assessment of wind potential in Minna, Niger State, Nigeria for power generation. The characteristics of the wind speed and energy potential in Minna, were examined using daily wind speed and direction data of 2 years, obtained using a metrological instrument; Davis 6162 Wireless Vantage Pro2 positioned at 100 m height. The collected data was analysed statistically and summarised in a simple and concise manner. The results show that the most probable wind speed was 0.4 ms -1 with extractable energy density of 25.04 Whm -2 while the wind speed corresponding to the maximum energy was 10.70 ms -1 delivering 45.96 kWh of energy. The average of the annual wind speed was 10.35 ms -1 which produced energy of 38.03 kWh. Though the average wind speed value revealed that the wind is suitable for wind-electric generation but has a low frequency, hence the power generation will do well for irrigation purposes. The prevailing wind direction was in the North-East direction with 14.84 % of the wind direction frequency. So a wind station will be more efficient if it is stationed in this predominant North-East direction. Keywords: Wind speed, wind direction, energy density, power, electricity DOI : 10.7176/APTA/76-01 Publication date :March 31 st 2019

High carbon dioxide (CO2) emissions in cities are a consequence of high energy consumption by a dense population. Fossil fuel related emissions from urban areas contribute to the increase in average atmospheric concentrations of CO2. Typically, the size of the emissions has been estimated through indirect approaches on the base of energy consumption data, but the number of direct atmospheric measurements of the effective CO2 exchange over cities is increasing since about a decade. Results so far show a lot of uncertainties concerning the processes that control the exchange rates to the atmosphere, i.e. the vertical CO2 flux (FC). The wide range of FC reported for cities reflects the variety and complexity of urban areas. It shows that the urban structure around an observational site has a great influence on the measured flux and that additional controlling factors need to be taken into account when addressing urban flux patterns. In this thesis, the main controlling factors for the variability of FC on different scales in time and space are identified. Long term CO2 concentrations and fluxes are observed at two urban observational sites to account for spatial differences within a city. Micro to local scale exchange processes and spatial distribution patterns between individual urban structure elements are addressed by additional measurements inside a street canyon. The key factors that control FC in heterogeneous urban areas are the major emitters of CO2 and their typical cycles on different time scales. Traffic emissions account for average diurnal courses of measured fluxes, while heating related emissions explain seasonality. Sink effects related to photosynthesis are found to be negligible in most cases. The spatial proximity of major roads at both sites is of greater importance than the source area extent and traffic induced FC is estimated to account on average for 70% of the total flux at one of the sites. Wind direction is - in combination with the spatial distribution of sources - the third and most crucial controlling factor due to its typical cycles and its occasional variability. Diurnal patterns interact with the course of traffic and seasonal characteristics with heating emissions. Both account for typical site specific FC patterns, whereas deviations from usually prevailing wind directions can lead to flux variance of noticeable size. Wind directions are also responsible for micro scale distribution and exchange patterns in and above the street canyon. High horizontal concentration differences inside the canyon are a result of in-canyon flows in the form of a helical vortex. Depending on the prevailing wind direction, vertical exchange of CO2 with the layers above is restricted or enhanced. Annual carbon exchange rate is a typical unit used for comparisons between sites and cities. The spatial heterogeneity of emissions induces a bias into these exchange rates that is related to an unequal reflection by wind direction frequencies. Up-scaling of spatially segregated fluxes leads to a comprehensive and more representative total carbon exchange rate of the average source area than FC does. The identified controlling factors explain the patterns of measured FC and the presented results improve the understanding of the variability of carbon dioxide exchange rates in urban areas. City scale differences and the strong relation on the interdependency of the controlling factors and their typical cycles suggest that the reasons for varying FC in cities worldwide are related to similarly complex local effects.

The relationship between the surface and synoptic wind direction is examined climatologically in a complex terrain region. Surface winds were observed over a 1-yr period during the MISTRAL project in the Basel, Switzerland, area. The measurement sites were located in various topographical settings, namely, in broad and narrow valleys, on slopes, at hilltops, on passes, and at mountaintops. The synoptic winds above the MISTRAL area are approximated by upper-level winds from routine rawinsonde observations. The relationship between this synoptic wind and the surface wind at each site was compared to a conceptual model. According to the conceptual model used, there are four mechanisms for the forcing of near-surface winds by synoptic winds. Three of the four forcing mechanisms leading to channeled flow are identified in the MISTRAL area. In this region with its complex terrain, different channeling mechanisms act at different locations as well as different mechanisms may occur at the same location. The study shows that the type of channeling depends on the topography surrounding the observation site. The combination of several channeling mechanisms with the multitude of valley orientations in a complex terrain setting explains the variety of observed flow patterns. One mechanism, the thermal forcing of valley winds. is examined in more detail. Two minima in the averaged diurnal cycle of the wind speed are found. Both minima occur at the time when the direction of the thermally forced wind reverses - one in the morning and one in the evening. The daytime upvalley flow is. on average, stronger than the nighttime downvalley flow. In the MISTRAL region, the frequency of days with thermally driven flow does not have a significant annual cycle.

A preliminary geophysical model function, relating the sea surface brightness temperatures to ocean surface wind speed and direction, was developed using the data acquired at 45/spl deg/, 55/spl deg/, and 65/spl deg/ incidence angles by Jet Propulsion Laboratory's (JPL) aircraft 19- and 37-GHz polarimetric radiometers in 1994 and 1995. Radiometric temperatures from all polarization channels under cloud-free conditions showed clear dependence on surface wind direction. When there were stratus or scattered clouds, T/sub /spl nu// and T/sub h/ were significantly influenced by the radiation from cloud water, but the polarimetric channel U was found to be insensitive to clouds. The Fourier harmonic coefficients of the wind direction signals were derived from experimental data and related to the wind speed and direction, incidence angle and frequency. In general, all harmonic coefficients increase from low to moderate wind speeds, except the sin 2/spl phi/ component of U at 65/spl deg/ incidence, which peaked at low winds with a peak-to-peak amplitude of 0.6 to 1 Kelvin at about 3 m/s winds. At moderate wind speeds, 45/spl deg/ incidence angle exhibits larger second harmonic signals, but smaller first harmonic signals, than higher incidence angles. Wind direction signals were similar in 19 and 37 GHz channels, but the 37 GHz channel showed a slightly stronger wind direction sensitivity than the 19 GHz channel. The results suggest promising applications of passive microwave radiometers to ocean wind vector measurements.

Calculations of the wind-driven ocean circulation are frequently based on atmospheric pressure observations. Geostrophic winds are computed from the pressure field at sea level and then rotated and reduced in magnitude to approximate the 'surface* winds at some nominal height (10-15 meters) above the sea surface. The rotation is usually assumed to be 15°-20° and the reduction in magnitude about 30-40% [Montgomery, 1936; Fofonoff, 1960; Blackford and Tsang, 1964]. Significant departures from some assumed value of the ratio between surface and geostrophic wind speeds have considerable effect on computed wind-driven transports in the ocean, since the field of wind stress at the sea surface depends approximately on the square of the surface wind speed.

A three-dimensional mesoscale numerical model is utilized to investigate the climatological wind field over the Baltic Sea. To cover all synoptic and boundary layer conditions, a large number of model runs have to be made. Since this type of model consumes a rather large amount of computer time, the factors primarily affecting the wind field have been identified to limit the number of model runs. To get accurate results, it was necessary to make simulations representing the four seasons, eight wind directions, and three values of the geostrophic wind speed. The model was run for these 96 conditions with the monthly mean daily temperature variation at screen height over land to include the effects of the thermal stratification. The simulated wind fields were then weighted together using climatological data of the geostrophic wind speed and direction. The model results have been compared with measurements from two lighthouses outside the Swedish coast, as well as with an interpolation of ship measu...

<strong class="journal-contentHeaderColor">Abstract.</strong> Aerosol particle optical, physical and chemical properties have been previously studied in the United Arab Emirates (UAE), but there is still a gap in the knowledge of particle sources, and in the horizontal and vertical transport of aerosol particles and their precursors in the area. To investigate how aerosol particle and SO₂ concentrations at the surface responded to changes in horizontal and vertical transport, we used data from a one-year measurement campaign at a background site where local sources of SO₂ where expected to be minimal. The measurement campaign provided a combination of in-situ measurements at the surface, and the boundary layer evolution from vertical and horizontal wind profiles measured by a Doppler lidar. The diurnal structure of the boundary layer in the UAE was very similar from day to day, with deep well-mixed boundary layer during the day transitioning to a shallow nocturnal layer, with the maximum boundary layer height usually being reached around 1400 local time. Both SO₂ and nucleation mode aerosol particle concentrations were elevated for surface winds coming from the east or western sectors. We attribute this to oil refineries located on the eastern and western coasts of the UAE. The concentrations of larger cloud condensation nuclei (CCN) sized particles and their activation fraction did not show any clear dependence on wind direction, but the CCN number concentration showed some dependence on wind speed, with higher concentrations coinciding with the weakest surface winds. Peaks in SO₂ concentrations were also observed despite low surface wind speeds and wind directions unfavourable for transport. However, winds aloft were much stronger, with wind speeds of 10 m s^-1 at 1 km common at night, and with wind directions favourable for transport, and surface-measured concentrations increased rapidly once these particular layers started to be entrained into the growing boundary layer, even if the surface wind direction was from a clean sector. These conditions also displayed higher nucleation mode aerosol particle concentrations, i.e. new particle formation events occurring due to the increase in the gaseous precursor.

This study compares the performance of different models used to assess the local wind near‐surface conditions at an agricultural site in Scania, southern Sweden. The methods are: (a) the WASP model (Wind Analysis and Application Program), (b) separate linear regressions of the two wind vector components, (c) a regression model based on vector correlation, and (d) linear regression of scalar wind. Each method was tested with three different data sets over nine months: wind measurements from the nearby Sturup airport SYNOP station, 10 m surface wind and surface geostrophic wind produced by the operational Swedish Mesoscale Analysis system (Mesan). The wind climate estimations were compared with observed winds at the field site, with respect to mean wind speed, wind direction, wind speed frequency distribution and the relative frequency of winds above 6 m s−1. All models performed reasonably well with data from Sturup and Mesan surface wind, but gave less reliable results with the Mesan geostrophic data. The estimated frequency of winds above 6 m s−1 was in general lower than the observed frequency. Overall, best results were obtained with WASP in combination with measurements from Sturup. Copyright © 2002 Royal Meteorological Society

In the context of climate change and extreme weather, urban heat island (UHI) phenomenon is exacerbated, affecting people's quality of life and environmental comfort. In the hot and humid climate of Asia, urban ventilation and heat dissipation play a crucial role in improving the thermal environment and reducing heat-related risks. Previous studies have mostly focused on urban wind corridor planning, lacking sufficient evidence of the ventilation benefits of such corridors. This study aims to fill this gap by using Tainan City as a case study to demonstrate the ventilation benefits of urban wind corridors through corridor identification and long-term measurements.Utilizing the 2-kilometer resolution historical climate reconstruction grid data (TReAD) built by the Taiwan Climate Change Projection and Information Platform (TCCIP) of the National Science and Technology Center for Disaster Reduction (NCDR), the heat island phenomenon in Tainan City is examined, and prevailing wind directions are summarized. Geographic information software is employed to calculate the roughness length and formulate urban wind corridors. Mobile observations are conducted to select and evaluate measurement points for assessing the ventilation efficiency of the corridors, followed by long-term observations to obtain high-density data and confirm the ventilation benefits of urban wind corridors.The analysis of corridor formulation and observation yields the following research findings (1) Large open spaces in urban areas significantly increase wind speeds. For instance, at the elementary school near Tainan Park, the hourly average wind speed reaches 1.8 m/s compared to a decrease of 0.9 m/s at points without nearby open spaces, such as roads with a width of 23 meters on both sides. (2) The alignment of road traffic direction with wind direction is the primary factor affecting ventilation efficiency, followed by road width. For example, on Road A with a width of 3 meters and aligned with the wind direction, the hourly average wind speed is 0.7 m/s, compared to an increase of 0.4 m/s at Road B with a width of 21 meters but misaligned with the wind direction. (3) Wind speeds are more stable in crossroad areas. For instance, at the intersection of two road, where dual-directional ventilation occurs, the hourly average wind speed is 0.9 m/s, falling between the efficiency levels of a second-level corridor (1.2 m/s) and a third-level corridor (0.8 m/s).The results of this study can serve as a basis for future urban wind corridor planning, effectively guiding the implementation of strategies to cool urban areas and mitigate the urban heat island effect.

The simulation of Arctic sea ice and surface winds changes significantly when Community Climate System Model version 3 (CCSM3) resolution is increased from T42 (∼2.8°) to T85 (∼1.4°). At T42 resolution, Arctic sea ice is too thick off the Siberian coast and too thin along the Canadian coast. Both of these biases are reduced at T85 resolution. The most prominent surface wind difference is the erroneous North Polar summer anticyclone, present at T42 but absent at T85. An offline sea ice model is used to study the effect of the surface winds on sea ice thickness. In this model, the surface wind stress is prescribed alternately from reanalysis and the T42 and T85 simulations. In the offline model, CCSM3 surface wind biases have a dramatic effect on sea ice distribution: with reanalysis surface winds annual-mean ice thickness is greatest along the Canadian coast, but with CCSM3 winds thickness is greater on the Siberian side. A significant difference between the two CCSM3-forced offline simulations is the thickness of the ice along the Canadian archipelago, where the T85 winds produce thicker ice than their T42 counterparts. Seasonal forcing experiments, with CCSM3 winds during spring and summer and reanalysis winds in fall and winter, relate the Canadian thickness difference to spring and summer surface wind differences. These experiments also show that the ice buildup on the Siberian coast at both resolutions is related to the fall and winter surface winds. The Arctic atmospheric circulation is examined further through comparisons of the winter sea level pressure (SLP) and eddy geopotential height. At both resolutions the simulated Beaufort high is quite weak, weaker at higher resolution. Eddy heights show that the wintertime Beaufort high in reanalysis has a barotropic vertical structure. In contrast, high CCSM3 SLP in Arctic winter is found in association with cold lower-tropospheric temperatures and a baroclinic vertical structure. In reanalysis, the summertime Arctic surface circulation is dominated by a polar cyclone, which is accompanied by surface inflow and a deep Ferrel cell north of the traditional polar cell. The Arctic Ferrel cell is accompanied by a northward flux of zonal momentum and a polar lobe of the zonal-mean jet. These features do not appear in the CCSM3 simulations at either resolution.

Theoretically, in the natural condition the wind is main energy induce wave and sea surface current. The measurements related to the wind patterns may indirectly reflect the condition of waves and the sea surface current. Other theory stated that in some cases, sea surface current has different direction depending on the bathimetry condition or other local factors. This research aimed to discover the correlation between wind and sea surface current direction in Kendal Coastal Area, focussing on nearshore zone nearby Bodri Rivermouth. The research was conducted by a simple measuring instrument for detecting sea surface current direction. The background of this research was the occurrences of the lost people drowned in the research area and being related to the mystical phenomena by the coastal community. The results showed that the correlation values of the wind and sea surface direction up to 0.40 and 0.09, each for point 1 and point 2, respectively. Those differences between wind and sea surface current direction imply that the results against the first wind direction theory. However, the results revealed that the existence of river mouth is the main factor that influences the different pattern of the sea surface current and wind direction. It is proof that the outlet current exists in the research area.