Wind Direction Dependent Vertical Wind Shear and Surface Roughness Parameterization in Two Different Coastal Environments

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International Journal of Geology, Agriculture and Environmental Sciences Volume – 4 Issue – 3 June 2016 Website: www.woarjournals.org/IJGAES ISSN: 2348-0254

Wind Direction Dependent Vertical Wind Shear and Surface Roughness Parameterization in Two different Coastal Environments

A.Bagavathsingh1*, C.V.Srinivas1, P. Sardar Maran2, R.Baskaran1, B.Venkatraman1

1Radiological Safety and Environmental Group, Indira Gandhi Atomic Research Centre, Kalpakkam, 603102 India.

2 Centre for Earth & Atmospheric Sciences, Sathyabama University, Chennai-600119 India.

* Corresponding Author: Email: [email protected]; Phone: 044-27480500 Ext. 23572 Abstract: Analysis Surface Boundary Layer parameters (SBL) of wind direction dependent vertical wind shear, surface roughness lengths and surface layer wind conditions has been carried out at a coastal and an urban coastal site for the different wind flow regime. The analysis is carried out from the profile of meteorological data collected from 50m towers at Satayabhma University and Ediyur, Kalpakkam sites during the year 2013. Vertical exchange of heat, moisture, and momentum at the earth's surface strongly depends on the turbulence generated by surface roughness and topography. The differential response of the near coastal and inland urban site SBL parameters (wind shear, roughness length, etc.) was examined as a function of wind direction. Site specific surface roughness parameter can be estimated; derived experimentally or calculated using measured data for roughness parameterization studies. Keywords: Coastal site, Roughness, Wind Shear, SBL, Parameterization. affect the winds and turbulent characteristics. To examine these 1. Introduction local systems and site specific surface atmospheric parameter estimates, micro scale observational network is needed. In this The lower part of the atmosphere where we live is directly study surface layer wind shear profile and roughness influenced by locally generated turbulence exchange processes parameters are examined as function of wind direction in urban which can develop an individual local climate, different to the coastal site of Sathyabhama University and near coastal site at expected average conditions. Analyzing the interactions Ediyur, Kalpakkam using data from 50m meteorological tower between the environment and the atmosphere on a local scale is measurements. The choice of a representative value of the much more complicated than looking at the same system on a roughness length (z0) is a key aspect to estimate the momentum meso-scale. The sea-land breeze is a meso-scale phenomenon flux in the lower atmosphere layer by means of traditional (Oke2005) specific to coastal environments. Especially in micrometeorological methods. Two types of wind profile laws coastal urban areas the great variety of different surfaces and are frequently used in the atmospheric surface-layer: the sheltering obstacles produces a pattern of distinct microclimate theoretically derived logarithmic profile with corrections for systems. The local vegetation and aerodynamic characteristics non-neutral thermal stratification and the empirically derived on land surface directly affect the transport of energy and power law (J.F.Manevell,2010). The need for the establishment substances between land surface and atmospheric boundary of the variable power law indices α which are site specific and layer. Thus the subject of every kind of process on land surface are critical in wind speed calculations is often emphasized becomes important (Stull, 1988; Weingara 1993; Masao, (Ray, et.al, 2006). This study undertakes an analysis of data 1997). Atmospheric boundary layer parameters and surface from multilevel meteorological instrumentation within the layer parameterizations are important in air pollution dispersion roughness sub layer using ten minutes averaged observational analysis. Many pollution sources and their dispersion occur data collected at the Kalpakkam Ediyur site (near coastline) within the roughness surface layer in the lower atmosphere. A and Satyabhama university campus site (urban, coastal site) better understanding of the flow within the roughness sub layer during summer, south west monsoon (SW) and North East will help in the interpretation of the data obtained from all monsoon synoptic period for the year 2013. levels within the urban, coastal complex environments. Aero dynamic roughness parameter is used to describe the degree of roughness of the earth's surface. The roughness length is 2. Background important in determining wind shears over a surface, and 2.1 The vertical wind speed profile and winds shear influences mechanical turbulence development in the PBL. A high roughness length increases surface friction and this The atmospheric surface layer closest to the earth, whose increases vertical turbulent mixing and wind shear. Roughness height typically ranges from 2-2000 m above the ground is length is strongly dependent on wind direction as upstream influenced by contact with the earth's surface. The lowest 10% topographic features are more relevant to local turbulence and of the ABL, called the surface layer is where turbulence and horizontal winds. In complex terrains, however the topography friction drag from the ground are the most significant effects and the non-uniform land use around the measurement point (Huschke, 1989). The surface layer of the ABL has been

WOAR Journals Page 1 studied extensively due to its accessibility and importance, as where u is the wind speed at any reference height Z and b1 and all human life resides in this layer. Observed characteristics of b2 are fitting coefficients. The term b2 is the power-law these studies were often consistent and were used to form the exponent, which depends on surface roughness and basis of the similarity theory principles that are used today in atmospheric stability. defining the behaviours of vertical wind profiles within in ABL The wind shear exponent is used in connection with the (Stull, 1988). Specific scaling relationships (such as the Monin- assumption of a power-law wind profile: Obukhov similarity theory) were developed for the surface α layer and subsequently proven to be accurate when the winds U(z) = Ur (z/zr) (4) are not calm, and in heights between 10-200 m above ground Where Ur and Zr is the reference wind speeds and (Panofsky et al., 1977). These similarity relationships began to measurement height and n is the power law or wind shear function as the foundation for the scientific study of the most exponent. The power law fits well the diabatic vertical wind significant feature of the surface layer for wind energy speed profile, particularly when Eq. (4) is used locally. In order developers and air quality managers. Two kinds of models are to compute a mean shear profile the function a sequence of most widely used in practice: the logarithmic and the power speed series and a sequence of measurement heights is used. law models. They have been applied in studying the transport Then it computes the mean speed of each series over the and dispersion of air pollutants (Strom 1976; Touma 1977; common time steps and fits a power function using the equation Irwin 1979; King 1982; Panofsky and Dutton 1984; Stern et al. (3) gives exponent b1, the coefficient b2. The number of 1984; Carney and Dodd 1989; Juda-Rezler 1989). common time steps and the computed means at each height and Determination of values for the exponent in the power law compare the fitted power function with observed means model has also been the topic of much research (Sutton 1953; (Hogstrom (1988) method is used to approximate the wind Strom 1976; Irwin 1979; Touma 1977; Simiu and Scanlan profile using a second-order polynomial and fitted parameters 1978). determined by a least-squares method). As the wind shear and

mean speed varies across directions, the wind shear estimated Empirical studies using Monin-Obukhov similarity for each direction sector using the mean shear profile function. relationships revealed that wind speed variation with elevation In order to extrapolate your data from measured height to in the surface stratum of the ABL can often be accurately another height you can apply the corresponding power law identified by a logarithmic decay curve in neutral atmospheric exponent to each speed value. The observed and calculated conditions (Oke,1987). When wind speeds are plotted against reference shears are compared by linear fitting and R is can be the natural logarithm of height, In (z), the profile approximates estimated at the best coefficient of determination. Finally the a straight line. This provides the theoretical basis of the shear extrapolation takes speed, direction, measurement height, logarithmic wind profile, or Prandtl-von Karman equation. The destination height and the exponents for each direction sector logarithmic law is expressed as based on a logarithmic wind and gives the extrapolated speed. profile governed by the terrain surface roughness length z : The 0 equations used by the model to calculate mean wind are those of similarity (Panofsky and Dutton, 1988): 2.2 Roughness Length Over most natural terrain, the surface cover is not uniform

u  z  z  and changes significantly from location to location. While u  ln  m   (1) k z  L  atmospheric pressure gradient forces are the major control of a  0  wind speed and direction in the ABL, winds near the ground are heavily influenced through frictional drag imposed by where, U* is the scale velocity related to mechanical turbulence, Ka the von Karman constant and Zo is the ground surface roughness (Oke,1987). This frictional drag cause’s roughness. Ψm is the stability function ( Ψm =1 for neutral turbulence, giving rise to a sharp decrease in wind speed as the stability). underlying surface is approached. The height at which this frictional drag influence is felt is related to the size and The similarity expression is utilized within the surfer layer. distribution of the underlying surface elements. Theoretically, Alternatively, the wind speed profile can be described by a z0is defined as the height in meters above the ground at which power law expressed as follows (Panofsky and Dutton, 1988): the mean wind speed becomes zero when extrapolating the logarithmic wind speed profile downwards through the surface n layer (Huschke,1989). As z0 is observed to increase with the u  z  average height and spacing of individual elements of the z    (2) u  z  ground cover, such as trees or houses, it is often defined in this 1  1  fashion (Jackson, 1980). An alternative but related definition suggests that z0 is the size of turbulent eddies on the ground where uz and u1 are the mean horizontal wind speeds at surface created when winds are disrupted by items on the heights Z and Z1 respectively and ‘n’ is an exponent that is surface; where larger z0 values indicate larger eddy mixing, related to the intensity of turbulence( Irwin,1979). and likely larger surface objects (Panofsky and Dutton, 1984). The power law function has the following form There are numerous ways for the z0 calculation. There are two classes of these methods: (i) micrometeorological (or anemometric) and morphometric (or geometric) methods. u  b1Z b2 (3) Roughness length has commonly been estimated for local sites from vertical wind profiles and micrometeorological theory. Average wind speed increases as the height increases.

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Frictional forces play an important role when dealing with wind building in far south directions. Inland urban coastal site speed profile. In fact the frictional forces are caused by the located in Satyabhama University (12.23N, 81.102E). The surface layer of earth which is called roughness length. The tower location categorized as a costal urban site. There were common profile to represent wind speed in atmospheric few vegetation cover near the tower site and surrounded by boundary layer profiles is logarithmic profile. The influence of industrial and academic buildings in East and South side. To z0 on the logarithmic wind profile is significant. When z0 is the west and southwest is a residential area. small, the wind profile increases rapidly with height over a short length, and then is relatively stable above that height. When z0 is large, the profile has a slow and smooth increase with height (World Meteorological Organization, 1981). Two methods are considered here: the first requires observations of mean wind speed at multiple levels; the second wind speed (U) and the standard deviation of wind speed at one level (S. B. Grimmond.et.al, 1998). Given the logarithmic wind profile equation, and using the D and slope (u/k) value with the wind speed at one level, z0 and zd can be determined. Since the turbulent fluxes are proportional to the square of ln(z0 ),values of the natural logarithm of the aerodynamic roughness length, Figure 1: An aerial photograph of near-coastline site (Ediyur ln(z0), are used for Zo analysis. Power law derived wind site, Kalpakkam) and Inland urban-coastal site (Sathyabama shear power law component is related to z0 by the Equation University site. (9), An alternative method introduced by Beljaars (1987) can be used to calculate z0 from the standard deviation of the wind Analysis of data from multilevel meteorological speed, as σu/u is directly proportional to the degree of surface instrumentation (50m Meteorological tower) within the roughness in neutral atmospheric stability. This technique is roughness sub layer by looking to estimate Ten minutes often used with hot-wire quick response anemometers (Liu et averaged observational data collected at the Kalpakkam- al., 2003) or sonic anemometers (Martano, 2000). Counihan, Ediyur site (near-coastline) and Sathyabama university campus 1975 presents several roughness characteristic parameters and site (Inland urban-coastal site) during Summer and SW and NE their correlation with the roughness length. Also, the roughness monsoon synoptic period for the year 2013 have been utilized length is an adequate parameter to characterize the intensity of for direction dependent roughness parameter (Zo) and shear turbulence profile. In particular, the longitudinal turbulence analysis. The statistics on the mean wind speed, direction and intensity vertical distribution could be guess in the form with σ shear profile (and their variants) are decomposed into 22.5° the root mean square of the velocity fluctuations. If one knows sectors of the compass. The data are divided into 16 equal, or have estimated α or zo, but still wants to use other directional sections, too, those with their wind direction relationship the formula (10) can be used ,giving deviations of classified as sector 0, 1 and 15. Roughness length by 16 wind only few percentage for standard deviations. A relationship direction sector for the 2, 8,50m layers were determined using between surface roughness and exponent α (Freris, L.L, 1990) a least squares fit to the neutral logarithmic wind profile (e.g. is given by the following equation: Hiyama, et al., 1996, and Beljaars, 1982) and Shear parameters (α) between the layers for the 2,8,50m were also determined Zo =15.25 exp(-1/α) (5) from the power law (Irwin, 1979) wind profile method. Roughness length and wind shear analyzed for different wind This prediction is accurate within a few percentages over the directions. range of roughness lengths of interest. It is important to note that the power law has no theoretical foundations; however, it 3.1 Synoptic wind regimes – Wind rose summary is often used by engineers. Using one or the other form, to find the mean wind speed distribution, one has to solve the task of Wind rose’s summaries the occurrence of winds at a estimating roughness parameters or wind shear coefficient. As location, showing their strength,SATHYABAMA direction UNIVERSITY WIND and ROSE frequency. The the hourly mean wind speeds are themselves strongly joint frequency distribution forN.E. MONSOON wind PERIOD speed @ 50 METERand direction in the dependent on the wind direction and the season of the year. form of wind roses are presented inN Figure 2-4 for various

13.39 Roughness length and wind shear profile for different wind seasons. Wind roses in Figure 2 shows 11.43 9.43 that 19.53the winds at Ediyur directions as being analyzed for different season over the site. (near coastal) and Sathyabama University 6.26 during NE monsoon 9.51 3.87

A number of models were subsequently developed to predict period (Sep-Dec) blow W from 6.31 the northeast 1.82 andE north and EDAIYUR MET TOWER WIND ROSE EDAIYUR MET TOWER WIND ROSE 3.42 1.43 N.E.MONSOON PERIOD @ 32 METER N.E. MONSOON PERIOD @ 02 METER the influence of a change in roughness lengths in the wind 1.94 easterly much of the time. 3.65 2.27 profile over fetch distances, which were then incorporated into N 4.02 1.74 N 15.40 12.38 14.59 19.86 10.24 11.11 19.77 larger meso-scale wind flow models (Jensen, 1978; Taylor, 9.36 S 4.23 3.84 7.96 1970; Walmsley et al., 1986; Yu et al., 2006). 9.31 2.44 4.09 Calms excluded. Rings drawn 2.62 at 5% intervals. 2.30 0.1 1.54 3.09 5.14 8.23 10.8 W E 2.77 2.74 Wind flow is FROM the directions shown. W E Wind Speed (m/s) No observations were missing. 1.68 5.00 2.82 1.91 3.05 3.08 2.56 3.72 4.19 SATHYABAMA UNIVERSITY 2.92 3.94 WIND ROSE 2.84 PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) SATHYABAMA 4.03 UNIVERSITY 3.27 WIND ROSE LOWER BOUND OF CATEGORY N.E. LOWER MONSOON BOUND OF CATEGORY PERIOD @ 02 METER 3. Sites and Measurements DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 N.E. MONSOON PERIOD @ 50 METER N 0.55 1.77 2.47 3.22 1.32 0.10 S 0.11 0.59 0.99 0.05 0.00 0.00 NNE 1.12 4.09 5.78 2.13 0.23 0.03 SSW 0.22 0.97 2.53 0.29 N 0.00 0.00 NE 1.43 9.24 8.39 0.47 0.00 0.00 SW 0.38 1.62 1.42 0.23 0.00 0.00 N ENE 0.77 4.43 3.82 0.48 0.01 0.00 WSW 0.49 1.15 1.61 0.17 0.00 0.00 E 0.10 0.66 0.89 0.17 0.00 0.00 W 0.71 1.41 2.78 S1.41 0.00 0.00 ESE 0.09 0.61 0.58 0.16 0.00 0.00 WNW 0.79 1.09 1.33 0.65 0.01 0.00 S SE 0.12 0.53 1.28 0.01 0.00 0.00 NW 0.88 2.95 1.86 0.54 0.02Calms 0.00 excluded. 24.27 10.98 Rings drawn at 5% intervals. SSE 0.14 0.55 1.47 0.11 0.00 0.00 0.1 1.54NNW 3.09 0.725.14 3.758.23 2.8110.8 3.22 0.88 10.65 0.04 Two types of sites are considered in this analysis –near 13.39 Wind flow is FROM the directions shown. 19.53 TOTAL OBS = 9389 MISSING OBS = 0 Wind Speed (m/s) CALM OBS 8.09= 0 No observations were missing. 11.43 9.43 Calms excluded. Rings drawn at 5% intervals. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. 5.68 Wind Speed (m/s) No observations were missing. 6.26 coastline, and inland coastal urban site are depicted in Figure.1. PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: 7.02 Wind Speed (m/s) 4.49 LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY 9.51 DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 3.87 PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) N 7.21W 3.82 1.31 0.04 6.03 0.00 0.00 S 0.77 1.27 1.29 0.86 0.00 0.00E 0.00 NNE 2.26 4.28 7.01 1.04 0.00 0.00 SSW 2.30 1.33 0.10 0.00 0.00 0.00 LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY The near coastal site Ediyur -Kalpakkam is on the coastline NE 1.89 6.65 10.63 0.69 0.00 0.00 SW 2.15 0.88 0.02 0.00 0.00 0.00 DIR 0.1 1.54 3.09 5.14 6.318.23 10.8 DIR 1.820.1 1.54 3.09 5.14 8.23 10.8 1.92 W E ENE 2.01 3.30 2.60 0.06 0.004.88 0.00 WSW 3.30 1.48 0.20 0.02 0.00 0.00 N 0.61 3.89 5.79 3.95 1.03 0.12 S 0.01 0.15 0.87 2.22 0.02 0.00 E 0.95 1.05 0.29 0.01 0.00 0.00 W 1.36 1.90 0.68 0.05 0.00 0.00 0.00 NNE 0.25 0.58 2.27 6.11 1.603.42 0.29 SSW 1.43 0.08 0.44 1.83 1.68 0.00 0.00 ESE 0.80 0.77 0.11 0.00 0.00 4.48 0.00 WNW 2.01 0.42 0.01 0.00 0.00 0.00 NE 0.13 0.49 5.61 12.55 0.95 0.04 SW 0.35 1.21 2.15 0.46 0.02 0.00 2.53 SE 0.58 1.27 1.23 0.00 0.00 0.00 2.96 3.38NW 3.49 0.70 0.03 0.00 0.00 0.00 (12.23N, 81.102E) and is surrounded by fields and marshland ENE 0.31 1.06 4.98 2.86 0.10 0.01 WSW 1.94 0.48 1.21 0.99 0.11 0.02 0.00 SSE 0.41 1.46 2.07 0.01 0.00 0.00 NNW 8.22 1.65 0.37 0.00 0.00 0.00 3.65 E 0.16 0.77 1.66 0.15 0.01 0.00 2.27W 0.79 1.00 0.74 0.24 0.00 0.00 TOTAL OBS = 12279 MISSING OBS = 0 CALM OBS = 0 ESE 0.07 0.80 0.93 0.11 0.00 0.00 4.02 1.74 WNW 0.76 1.49 1.17 0.65 0.02 0.00 SE 0.03 0.34 1.49 0.69 0.00 0.00 NW 0.64 1.33 1.31 0.52 0.03 0.00 SSE 0.03 0.24 1.33 1.24 0.00 0.00 NNW 0.86 4.85 2.64 0.84 0.16 0.01 in the west and forest field in a NE direction and industrial TOTAL OBS = 12279 MISSING OBS = 0 CALM OBS = 0

S Calms excluded. Rings drawn at 5% intervals. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. WOAR Journals Calms excluded. Wind Speed (m/s) No observations werePage missing. 3 Rings drawn at 5% intervals. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. Wind Speed (m/s) No observations were missing.

PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) N 4.04 3.81 3.06 0.07 0.00 0.00 S 2.87 0.10 0.00 0.00 0.00 0.00 LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY NNE 5.82 4.26 0.58 0.00 0.00 0.00 SSW 2.53 0.00 0.00 0.00 0.00 0.00 DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 NE 12.64 11.11 0.52 0.00 0.00 0.00 SW 4.35 0.14 0.00 0.00 0.00 0.00 N 0.55 1.77 2.47 3.22 1.32 0.10 S 0.11 0.59 0.99 0.05 0.00 0.00 ENE 4.12 2.52 0.37 0.00 0.00 0.00 WSW 3.43 1.33 0.12 0.00 0.00 0.00 NNE 1.12 4.09 5.78 2.13 0.23 0.03 SSW 0.22 0.97 2.53 0.29 0.00 0.00 E 1.07 0.20 0.00 0.00 0.00 0.00 W 3.41 2.12 0.50 0.00 0.00 0.00 NE 1.43 9.24 8.39 0.47 0.00 0.00 SW 0.38 1.62 1.42 0.23 0.00 0.00 ESE 1.57 0.35 0.00 0.00 0.00 0.00 WNW 3.16 1.05 0.28 0.00 0.00 0.00 ENE 0.77 4.43 3.82 0.48 0.01 0.00 WSW 0.49 1.15 1.61 0.17 0.00 0.00 SE 1.28 0.09 0.00 0.00 0.00 0.00 NW 4.45 1.01 0.21 0.00 0.00 0.00 E 0.10 0.66 0.89 0.17 0.00 0.00 W 0.71 1.41 2.78 1.41 0.00 0.00 SSE 2.81 0.55 0.01 0.00 0.00 0.00 NNW 5.34 1.71 1.04 0.00 0.00 0.00 ESE 0.09 0.61 0.58 0.16 0.00 0.00 WNW 0.79 1.09 1.33 0.65 0.01 0.00 TOTAL OBS = 9389 MISSING OBS = 0 CALM OBS = 0 SE 0.12 0.53 1.28 0.01 0.00 0.00 NW 0.88 2.95 1.86 0.54 0.02 0.00 SSE 0.14 0.55 1.47 0.11 0.00 0.00 NNW 0.72 3.75 2.81 3.22 0.88 0.04 TOTAL OBS = 9389 MISSING OBS = 0 CALM OBS = 0 SATHYABAMA UNIVERSITY WIND ROSE N.E. MONSOON PERIOD @ 50 METER

13.39 Figure 2: NE monsoon- Wind 11.43 roses 9.43 for 19.53 different observational 6.26

9.51 heights (50m, 2m) at Ediyur 3.87 (Top panel) and Sathyabama Figure 5: Mean wind shear profile (global shear profile) for a) W 6.31 1.82 E

1.43 (Bottom panel) sites. 3.42 EDAIYUR MET TOWER WIND ROSE SOUTH WEST Sathyabama university (left panel) b) Ediyur site during NE 1.94 3.65 2.27 MONSOON PERIOD 2013 AT 08 METER EDAIYUR MET TOWER WIND ROSE SOUTH WEST 4.02 1.74 MONSOON PERIOD 2013 AT 50 METER N monsoon season period (right panel). N S 2.24 0.96 Calms excluded. 4.58 0.45 Rings drawn at 5% intervals. 0.30 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM 9.87 the directions shown. 2.63 0.97 6.22 0.47 Wind Speed (m/s) No observations were missing. 0.30 12.77 0.23 15.45 0.38 0.26 W E PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) 0.66 16.55 0.32 W E LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 2.06 0.43 N 0.55 1.77 2.47 3.22 1.32 0.10 S 0.11 17.10 0.59 0.99 0.05 0.00 0.00 NNE 1.12 4.09 5.78 2.13 0.23 0.03 SSW 0.22 0.97 2.53 0.29 0.00 0.00 1.29 20.29 NE 1.43 9.24 8.39 0.47 0.00 0.00 SW 0.38 1.62 1.42 0.23 0.00 0.00 5.92 2.92 ENE 0.77 4.43 3.82 0.48 0.01 0.00 WSW 0.49 1.15 1.61 0.17 0.00 0.00 10.62 E 0.10 0.66 0.89 0.17 0.00 0.00 W 0.71 1.41 17.09 2.78 1.41 9.61 0.00 0.00 ESE 0.09 0.61 0.58 0.16 0.00 0.00 WNW 0.79 1.09 1.33 0.65 0.01 0.00 9.63 SE 0.12 0.53 1.28 0.01 0.00 0.00 NW 0.88 2.95 1.86 0.54 0.02 13.02 0.00 14.41 SSE 0.14 0.55 1.47 0.11 0.00 0.00 SATHYABAMANNW 0.72 3.75 UNIVERSITY 2.81 3.22 0.88 0.04MET TOWER WIND ROSE SATHYABAMA UNIVERSITY MET TOWER WIND ROSETOTAL OBS = 9389 MISSING OBS = 0 SOUTH WESTCALM MONSOON OBS = 0 PERIOD 2013 AT 08 METER SOUTH WEST MONSOON PERIOD 2013 AT 50 METER S S N Calms excluded. Rings drawn at 5% intervals. N 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. Calms excluded. Wind Speed (m/s) No observations were missing. Rings drawn at 5% intervals. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. Wind Speed (m/s) No observations were missing.

PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY N 0.42 0.32 0.20 0.03 0.00 1.41 0.00 0.52 0.22 S 0.34 1.32 5.62 5.72 0.02 0.00 DIR 0.1 1.54 3.09 5.14 8.23 10.8 0.58 DIR 0.1 1.54 3.09 5.14 8.23 10.8 1.31 0.32 NNE 0.23 0.12 0.07 0.02 2.61 0.00 0.00 SSW 0.84 2.09 4.59 2.09 0.01 0.00 N 0.19 0.28 0.24 0.21 0.05 0.00 S 0.23 0.51 2.38 6.11 0.40 0.00 NE 0.17 0.07 0.04 0.02 0.00 0.00 0.40SW 3.22 7.17 6.07 0.61 0.01 0.00 2.50 0.23 NNE 0.10 0.13 0.13 0.07 0.01 0.01 SSW 0.44 0.58 2.55 8.38 2.35 0.11 ENE 0.11 0.10 0.08 5.78 0.01 0.00 0.00 WSW 7.23 6.65 3.18 0.04 0.00 0.00 NE 0.06 0.06 0.06 0.04 4.87 0.01 0.00 SW 0.21 0.67 3.71 5.48 0.48 0.06 E 0.12 0.15 0.10 0.00 0.00 0.00 0.70W 7.28 5.89 2.27 0.01 0.00 0.00 ENE 0.06 0.07 0.08 0.04 0.01 0.00 WSW 0.770.74 2.17 8.62 8.40 0.32 0.04 ESE 0.13 0.29 0.23 0.01 0.00 0.00 WNW 2.72 3.81 3.14 0.21 0.00 0.00 E 0.10 0.06 0.13 0.04 0.00 0.00 W 1.40 3.50 8.64 2.76 0.21 0.03 SE 0.18 0.91 0.96 0.02 0.00 0.00 NW 0.91 1.37 1.79 0.51 0.01 0.00 ESE 0.07 0.01 0.29 0.05 0.00 0.00 WNW 1.63 2.21 5.07 3.51 0.32 0.04 W 17.57 1.11 E W 15.23 0.97 E SSE 0.21 1.19 3.83 0.69 0.00 0.00 NNW 0.61 0.61 0.80 0.21 0.00 0.00 Figure 6: Shear rose a) Sathyabama university (left panel) SE 0.10 0.14 0.74 0.31 0.00 0.00 NW 0.54 0.75 1.73 2.45 0.67 0.09 TOTAL OBS = 16325 MISSING OBS = 0 CALM OBS = 0 SSE 0.25 0.22 1.34 1.10 0.00 0.00 NNW 0.32 0.45 0.77 0.81 0.21 0.06 TOTAL OBS = 16325 MISSING OBS = 0 2.59 CALM OBS = 0 5.33

14.43 3.87 17.13 b) Ediyur site during NE monsoon season period (right panel). 5.93 7.92 8.51 7.48 9.00 17.27 18.24 11.83 13.37 Figure 5, and 6 (right panel) shows the NE monsoon Figure 3: SWS monsoon- Wind roses for differentS observational Calms excluded. Calms excluded. seasonal pattern of mean wind shear profile and shear rose Rings drawn at 5% intervals. Rings drawn at 5% intervals. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. Wind Speed (m/s) No observations were missing. Wind Speed (m/s) No observations were missing. heights (50m, 2m) at SATHYABAMA Ediyur UNIVERSITY (Top WIND panel)ROSE and Sathyabama from sataybhama site. Figure 7 shows the direction dependent N.E. MONSOON PERIOD @ 50 METER PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) PERCENTEDAIYUR OCCURRENCE: Wind METSpeed (m/s) TOWERPERCENT WIND OCCURRENCE: ROSE Wind Speed (m/s) EDAIYUR LOWER BOUND OF CATEGORY MET TOWER WIND LOWER BOUND ROSE OF CATEGORY N LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY (DIRSUMMERBottom0.1 1.54 3.09 PERIOD5.14 8.23 panel)10.8 2013DIR AT 0.1 site501.54 METER3.09s5.14. 8.23 10.8 DIR SUMMER0.1 1.54 3.09 5.14PERIOD8.23 10.8 2013DIR AT0.1 081.54 METER3.09 5.14 8.23 10.8 N 0.30 0.11 0.13 0.04 0.00 0.00 S 1.23 2.56 4.01 1.20 0.00 0.00 N 0.35 0.12 0.06 0.00 0.00 0.00 S 2.97 3.14 1.37 0.01 0.00 0.00 wind shear profile. NNE 0.23 0.06 0.03 0.00 0.00 0.00 SSW 1.50 5.84 4.28 0.20 0.00 0.01 NNE 0.19 0.02 0.01 0.00 0.00 0.00 SSW 8.86 4.34 0.17 0.01 0.00 0.00 NE 0.08 0.01 0.13 0.01 0.00 0.00 SW 1.81 6.04 7.76 2.58 0.06 0.00 NE 13.39 0.16 0.16 0.09 0.00 0.00 0.00 SW 7.81 7.13 2.27 0.06 0.00 0.00 ENE 0.07 0.10 0.53 0.06 0.00 0.00 WSW 0.95 3.19 8.04 4.77 0.16 0.02 19.53 N N 11.43 9.43 ENE 0.12 0.20 0.37 0.01 0.00 0.00 WSW 3.55 5.08 5.28 0.51 0.00 0.00 E 0.16 0.24 0.56 0.02 0.00 0.00 W 0.73 1.59 6.27 6.33 0.28 0.03 E 0.42 0.48 0.21 0.00 0.00 0.00 W 2.26 3.71 9.41 2.17 0.03 0.00 ESE 0.30 0.91 1.26 0.12 0.00 0.00 WNW 0.45 1.00 2.13 1.23 0.06 0.01 ESE 1.57 2.73 1.03 0.00 0.00 0.00 WNW 1.02 1.62 2.70 0.43 0.01 0.00 SE 0.94 2.61 2.27 0.11 0.00 0.00 NW 0.40 0.41 1.18 0.49 0.02 0.00 6.26 SE 1.75 1.79 0.33 0.00 0.00 0.00 NW 0.65 0.77 1.11 0.06 0.01 0.00 SSE 0.73 2.56 3.79 1.43 0.00 0.00 NNW 0.28 0.43 0.46 0.13 0.01 0.01 SSE 2.31 3.20 9.51 2.38 0.02 0.00 0.00 NNW 0.72 0.42 0.25 0.01 0.01 0.00 TOTAL OBS = 10902 MISSING OBS = 0 CALM OBS = 0 3.87 TOTAL OBS = 10902 MISSING OBS = 0 CALM OBS = 0 W 6.31 1.82 E 2.07 2.82 3.42 1.43 3.12 0.56 1.53 0.95 1.94 2.32 2.06 3.65 2.06 2.19 1.74 2.27 4.02 2.62 2.75 3.67 2.83 W 3.54 2.44 E W 3.22 2.11 E 3.79 3.09 3.74 6.16 S 6.83 4.28 9.26 10.74 Calms excluded. Rings drawn at 5% intervals. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions 11.14 shown. Wind Speed (m/s) No observations were missing. 12.28 SATHYABAMA UNIVERSITY 14.36 MET TOWER WIND 19.00 PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) 25.40 ROSE SUMMER PERIOD 2013 AT 50 METER LOWER BOUND OF CATEGORY SATHYABAMA LOWER BOUND OF UNIVERSITY CATEGORY MET TOWER WIND DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 27.07 N 0.55 1.77 2.47 3.22 1.32 0.10 S 0.11 0.59 0.99 0.05 0.00 0.00 NNE 1.12 4.09 5.78 2.13 0.23 0.03 ROSESSW 0.22 SUMMER 0.97 2.53 0.29 PERIOD 0.00 S0.00 2013 AT 08 METER SN NE 1.43 9.24 8.39 0.47 0.00 0.00 SW 0.38 1.62 1.42 0.23 0.00 0.00 ENE 0.77 4.43 3.82 0.48 0.01 0.00 WSW 0.49 1.15 1.61 0.17 0.00 0.00 E 0.10 0.66 0.89 0.17 0.00 0.00 W 0.71 1.41 2.78 1.41 0.00 0.00 ESE 0.09 0.61 0.58 0.16 0.00 0.00 WNW 0.79 1.09 1.33 0.65 0.01 N0.00 Calms excluded. SE 0.12 0.53 1.28 0.01 0.00 0.00 NW 0.88 2.95 1.86 0.54 0.02 0.00 Rings drawn at 10% intervals. Calms excluded. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. Rings drawn at 10%SSE intervals. 0.14 0.55 1.47 0.11 0.00 0.00 WindNNW Speed 0.72 (m/s) 3.75 2.81 3.22 0.88 0.04 No observations were missing. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM theTOTAL directions OBS = 9389 MISSINGshown. OBS = 0 CALM OBS = 0 Wind Speed (m/s) No observations were missing. PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) 0.18 LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY PERCENT OCCURRENCE: Wind Speed (m/s) 0.63 0.25 PERCENT OCCURRENCE: Wind Speed (m/s) 0.36 LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY DIR 0.1 1.54 3.09 5.14 8.23 0.6910.8 0.20 DIR 0.1 1.54 3.09 5.14 8.23 10.8 0.98 1.38 N 1.15 0.87 0.04 0.02 0.00 0.00 S 0.14 2.07 7.55 8.93 0.31 0.00 DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 1.01 1.45 N 0.18 1.55 1.07 0.03 0.00 0.00 S 0.55 0.45 3.92 17.31 4.57 0.27 NNE 0.23 0.21 0.07 0.05 0.00 0.00 SSW 0.70 2.68 4.87 2.89 0.02 0.00 1.92 1.89 NNE 0.07 0.29 0.52 0.08 1.86 0.00 0.00 SSW 1.79 0.43 0.64 2.61 6.27 4.07 0.34 NE 0.03 0.33 1.09 0.60 0.00 0.00 SW 2.05 3.07 3.47 0.67 0.00 0.00 NE 0.04 0.04 0.45 1.50 0.15 0.00 SW 0.58 0.52 2.42 5.80 1.37 0.05 ENE 0.11 0.34 1.86 0.44 0.00 0.00 WSW 2.37 1.05 0.36 0.01 0.00 0.00 E 0.50 W 1.02 0.93 0.00 4.65 0.00 0.00 W 3.84 2.78 0.62 0.15 E 0.00 0.00 0.00 ENE W 0.07 0.05 0.71 2.01 4.61 0.00 0.00 WSW 3.890.57 1.24 2.36 1.89 E 0.09 0.00 ESE 0.36 1.38 1.34 0.01 0.00 0.00 WNW 1.81 0.38 0.40 0.03 0.00 0.00 E 0.09 0.39 1.37 0.26 0.00 0.00 W 0.62 1.11 1.06 0.39 0.03 0.00 SE 0.30 2.03 3.96 0.53 0.00 0.00 NW 1.78 0.32 0.21 0.02 0.00 0.00 ESE 0.08 0.73 2.60 0.33 0.00 0.00 WNW 1.08 1.19 0.66 0.57 0.16 0.01 4.89 SSE 0.26 2.59 14.29 8.25 0.00 0.01 NNW 2.54 0.50 0.09 0.00 0.00 0.00 SE 0.05 0.39 2.44 1.39 5.97 0.01 0.00 NW 0.43 6.90 0.97 0.26 0.34 0.07 0.00 TOTAL OBS = 12928 MISSING OBS = 0 CALM OBS = 0 SSE 0.10 0.56 4.02 7.14 0.45 0.01 NNW 0.45 0.68 0.29 0.12 0.00 0.00 21.64 7.47 TOTAL OBS = 12928 MISSING OBS =6.20 0 CALM OBS = 1025 8.17 15.93 13.13 12.77 11.71 10.35 15.96 27.35 S

Calms excluded. Figure4:SummerS season-Wind roses for differentRings drawn observational at 5% intervals. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. Wind Speed (m/s) No observations were missing. Calms excluded. Rings drawn at 10% intervals. 0.1 1.54 3.09 5.14 8.23 10.8 Wind flow is FROM the directions shown. Wind Speed (m/s) No observations were missing. heights (50m, 2m) at Ediyur PERCENT (Top OCCURRENCE: Windpanel) Speed (m/s) andPERCENT OCCURRENCE:Sathyabama Wind Speed (m/s) LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 N 0.32 0.03 0.00 0.00 0.00 0.00 S 2.81 3.81 1.51 0.03 0.00 0.00 NNE 0.14 0.05 0.01 0.00 0.00 0.00 SSW 6.89 5.71 0.53 0.00 0.00 0.00 PERCENT OCCURRENCE: Wind Speed (m/s) PERCENT OCCURRENCE: Wind Speed (m/s) NE 0.21 0.88 0.34 0.01 0.00 0.00 SW 4.96 2.15 0.37 0.00 0.00 0.00 (Bottom panel) sites. ENE 0.32 0.93 0.61 0.03 0.00 0.00 WSW 2.46 1.47 0.85 0.11 0.00 0.00 LOWER BOUND OF CATEGORY LOWER BOUND OF CATEGORY E 1.26 1.53 1.06 0.00 0.00 0.00 W 1.72 0.85 1.15 0.93 0.00 0.00 DIR 0.1 1.54 3.09 5.14 8.23 10.8 DIR 0.1 1.54 3.09 5.14 8.23 10.8 ESE 2.58 6.60 12.34 0.13 0.00 0.00 WNW 1.25 0.34 0.26 0.06 0.00 0.00 N 0.13 0.05 0.01 0.00 0.00 0.00 S 1.48 3.19 4.33 1.35 0.00 0.00 SE 2.66 6.66 6.60 0.01 0.00 0.00 NW 0.68 0.22 0.09 0.01 0.01 0.00 NNE 0.13 0.07 0.05 0.01 0.00 0.00 SSW 1.87 4.17 5.19 0.48 0.00 0.00 SSE 2.58 3.98 5.76 0.45 0.00 0.00 NNW 0.46 0.14 0.09 0.00 0.00 0.00 NE 0.09 0.44 0.78 0.07 0.00 0.00 SW 2.16 2.15 1.62 0.26 0.01 0.00 TOTAL OBS = 8714 MISSING OBS = 0 CALM OBS = 0 ENE 0.18 0.41 1.01 0.17 0.01 0.00 WSW 2.81 0.91 1.47 0.61 0.17 0.00 E 0.61 1.32 1.77 0.20 0.00 0.00 W 1.95 0.78 0.72 1.01 0.15 0.00 ESE 0.90 1.97 3.04 0.99 0.00 0.00 WNW 1.11 0.26 0.37 0.10 0.01 0.00 SE 1.45 4.22 13.06 8.62 0.00 0.00 NW 0.63 0.13 0.16 0.03 0.01 0.01 SSE 1.09 2.63 6.59During 5.65 0.01 0.00 SWNNW 0.34 monsoon 0.11 0.15 0.02 0.00 period 0.00 strong synoptic winds are TOTAL OBS = 8714 MISSING OBS = 0 CALM OBS = 0 primarily observed from south west and westerly directional

sector (Fig.3). Sea breezes are most frequently observed on the

both site during the summer period. Figure 4 shows that the

wind is blows from the south east and southerly direction. Generally winds at 50m and 2m height slightly differ from upper air flow (upper height measurements) due to terrain roughness and represent significant shear at the surface.

4. Results and Discussion It is important to consider seasonal effects on the value of wind shear parameters. It is an indication of how much the surrounding surface roughness elements change seasonally.

4.1 NE Monsoon Season North east monsoon associated with the formation of northeasterly wind regime over the study region. During day time NE synoptic flow merges with sea breeze flow in the eastern directional sector.

Figure 7: Direction dependent shear profile (Top panel- Sathyabama University; Bottom panel-Ediyur site) -Mean wind

WOAR Journals Page 4 speeds produced by power law fit. Average meteorological Figure 8, and 9 (right panel) shows the SW monsoon tower observations are shown with circles and power law fit is seasonal pattern of mean wind shear profile and shear rose shown with lines. from sataybhama site. The same depicted for Ediyur site in Figure 8 and 9 (Right Panel) Traditionally neutral atmosphere associated with 0.14 (1/7 power law), the value higher than 0.14 indicating the stable and value lower than 0.14 indicating unstable conditions. High values of the shear value indicate that the wind speed changes rapidly with height, which is common in stable regimes when the surface layer decoupled from the rest of the boundary layer and vertical momentum transport is limited. In contrast, low values of the shear component indicate that the wind speeds are fairly uniform with height, which is common during unstable regimes with substantial vertical mixing. In locations with a Figure 9: Shear rose a) Sathyabama university (left panel b) large degree of surface heating shear component drastically Ediyur site during NE monsoon season period (right panel) changes. The Shear rose depicted in Figure.6 shows that the shear at urban coastal site–Sathyabama University is high compared to the Ediyur site. Direction dependent shear profile at Sathyabama University (Figure7 Top panel) shows the power law exponent lie in the range of 0.202-0.539. The values range from the largest shear value for sector15 (300-330 Deg) to the smallest sector 3 (30-60 Deg). Overall estimated mean values for Sathyabama were found to be 0.309.

Direction dependent mean wind speed profile for Ediyur site is depicted in Figure 7(Bottom Panel). Directionally-dependent profiles exhibit a strong logarithmic relationship with the sector 3, 4 (30-80 Deg) and 8,9 (140-195 Deg). The wind shear profiles shape in the sector 6, 7 and 13 (100-150 Deg, 130,250- 285 Deg) seems to be influenced by directionally-dependent speed reductions in the 50 m wind speed. However, in the northerly sector (300-260 Deg), the 50m m sensor measurement seems to be fast. The profile exhibits Logarithmic, have comparatively large roughness lengths, which could be caused by displacement height effects. Across all directional sectors the values of power law exponent α lie in the range of 0.138-0.470 are noticed. The values range from the largest shear value for sector 15 (210-245 Deg) to the smallest sector 6 (100-125 Dg). Overall estimated mean values of Ediyur site were found to be 0.278.

4.2 SW Monsoon Season

The SW monsoon is the most significant characteristic of Indian climate. Large scale winds are become stronger and oppose the sea breeze formation during this season (June- September).Diurnal changes in wind is lower in this season compared to others season.

Figure 8: Mean wind shear profile for a)Sathyabama university (left panel) b) Ediyur site during NE monsoon season period (right panel).

Figure 10: Direction dependent shear profile (Top panel-

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Sathyabama University, Bottom panel-Ediyur site) -Mean wind from Ediyur site. The shear rose depicted in Figure.12 (right speeds produced by power law fit. Average meteorological panel) shows that the shear at the near coastal site (Ediyur) tower observations are shown with circles and power law fit is quite different from inland site (Sathyabama University.) The shown with lines. low shear winds in the seaside direction sectors are likely related to the overall sea breeze pattern along the kalpakkam During SW monsoon season the both sites show higher wind (Ediyur) coast. Overall estimated mean values of stayabhma shear in the directional sector SSW-WSW (190-260 Deg) site were found to be 0.307.The mean shear profile is shown direction (Figur.9). Overall estimated mean values of in the Figure.11 (Left panel). Figure 13 (Top panel) shows the sathyabama site were found to be 0.322.The mean shear profile direction dependent wind shear profile for stayabhma is shown in the Figure.8 (Left panel). Direction dependent university site. Wind shear profile in the sector 3-11 (65-220 profile at Sathyabama University exhibits a strong logarithmic degrees) exhibits a strong logarithmic relationship. The clear relationship in majority of the sector (Figure 10 Top panel). exception seen in north and north westerly sectors (0-45 deg, The clear exception seen in sector 2, 3 (10-60 Deg) which has a 290-315 deg), which has a marked departure from a marked departure from a logarithmic trend. Across all logarithmic trend. Across all directional sectors the values of directional sectors the values of power law exponent lie in the power law exponent lie in the range of 0.19-0.498 are noticed. range of 0.152-0.570 are noticed. The values range from the Direction dependent wind shear profile for the near coastal site largest shear value for sector 10 (190-220 Deg) to the smallest (Ediyur) depicted in Figure.13 (Bottom panel). sector 3 (30-60 Deg).The mean shear profile is shown in the Figure.8 (Right panel). Direction dependent wind shear profile for the near coastal site (Ediyur) depicted in Figure.10 (Bottom panel). Across all directional sectors the values of power law exponent lie in the range of 0.19-0.393 are noticed. The values range from the largest shear value for sectors 11, 15 (200-240, 300-330 Deg) to the smallest sector 9 (160-195 Deg). Overall estimated mean values for Ediyur during the SW monsoon season were found to be 0.294. The directionally-dependent profiles at Ediyur site follow a generally logarithmic trend in most of the sectors.

4.3 Summer Season

The study regions predominately influenced by meso-scale sea -land breeze circulation in summer season. The diurnal variations of wind speed are higher than that of other seasons. Figure 11 and 12 (Left panel) shows the summer period seasonal pattern of mean wind shear profile and shear rose for Sathyabama and Ediyur sites.

Figure 11: Mean wind shear profile for a) Sathyabama University (left panel) b) Ediyur site during summer monsoon season period (right panel).

Figure 12: Shear rose a) Sathyabama university (left panel b) Ediyur site during summer monsoon season period (right panel).

Figure 11 and 12 (right panel) shows the summer period seasonal pattern of mean wind shear profile and shear rose

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Figure 13: Direction dependent shear profile (Top panel- Figure 14: Direction dependent surface roughness parameter Sathyabama University, Bottom panel-Ediyur site) -Mean wind for different Season (SU-Sathyabama University site, ED- speeds produced by power law fit. Average meteorological Ediyur site). tower observations are shown with circles and power law fit is shown with lines. Figure 14 shows direction dependent mean value's roughness The values range from the largest shear value for sector10 length derived for the 10 minute period in the summer, South (190-220 Deg) to the smallest sector 4 (50-80 Deg). Overall West and NE monsoon case at Sathyabama and kalpakkam estimated mean values for Ediyur during the summer monsoon (Ediyur) site. Roughness length has obvious seasonal patterns. season were found to be 0.225.The directionally-dependent Low and high values are clearly observed during onshore and profiles at Ediyur site follow a strong logarithmic trend in the offshore flows, respectively, with sharp decrease around 450° - sectors 2-12 (20-190 Deg), which shows distinct unstable well 190°and build-up in starts as nearing to the coast at 220° mixed layer (TIBL) near the coastal site. The variation of mean orientation due to land frictional effect. The aerodynamic wind shear coefficient strongly related to the thermal roughness length is higher on the Sathyabama university site conditions of the region and can be explain on the basis of than on Ediyur site. At Ediyur site for all the season the low zo Thermal Stratification. NE and SW monsoon seasons show estimated in the direction sector (90-200 Deg) corresponds to higher values of the wind shear component, whereas summer the area covered by coastal ocean. The large value observed in season it shows lower values. This behaviour can be justified, the direction sector (220-250 Deg) during NE and SW since during summer the ground temperatures are higher, it monsoon season, whereas in the summer period the high value can cause active expansion of air in the vicinity of the surface lies in the northerly and north-westerly sector. As demonstrated and hence, better merger of the air takes place over the ground, in the figure 14 large zo values for sectors (180-240 deg) which results in low values of the Wind shear components , observed for the sathyabama site. A high value of zo levels while, during the SW and NE monsoon synoptic wind regimes related to the roughness elements around urban area (coastal and winter seasons the ground becomes much cooler than urban -Sathyabama University). While the low zo value for higher air, and hence, higher values of wind shear coefficients north and north westerly site correspond to the open fetches are obtained. During summer period Low and high wind shear and some space building. values are clearly observed during onshore and offshore flows, respectively. At Ediyur sea-coastline orientation lies between 5. Summary 60°–200° sector shows lowest value (during sea breeze) and highest value ( land breeze) shown in the sector the sector In this work, considering a near coastal and urban coastal 220°-45deg. Mean structure of ranges from 0.19 to 0.47 with wind site such as Ediyur and stayabhma university site where respect to wind direction wind shear coefficient has been determined and the effect of wind shear on velocity profile has been analyzed. For near 4.4 Roughness distribution coastal smooth terrain the power law is a good approximation to the real surface layer wind profile. At Kalpakkam coastal An estimate of roughness length is required by some site (Ediyur), a significant influence of land-sea interface shows atmospheric models and is also used to determine surface layer lower wind shear coefficient during sea breeze conditions than wind profile under neutral conditions. The choice of technique in land breeze circulation period. for determining roughness lengths is generally constrained by the available input data. Here, we compare sets of roughness The variation of mean wind shear coefficient strongly related lengths derived by different methods. The simplest method to the thermal conditions of the region and can be explain on using logarithmic profile formula from this ln (zo) values the basis of thermal Stratification. NE and SW monsoon generated from the profile measurements, Alternatively seasons show higher values of the wind shear component, Beljaars (1987) give empirical formulae for determining whereas summer season it shows lower values. The mean shear roughness lengths from wind shear or power law coefficient. coefficient at inland coastal site -Sathyabama University is Aerodynamic roughness length changes with wind direction more than the near coastal site .The variation of wind shear and topography. with different directional sector emphasized the major role played by the topography and land use.

3.0 2.5 SU summer ED summer Roughness length is strongly dependent on wind direction, 2.0 1.5 as upstream topographic features are more relevant to local 1.0 turbulence in horizontal winds, rather than local topographic 0.5 Roughness length(m) Roughness 0.0 features. Low and high values are clearly observed during 0 45 90 135 180 225 270 315 360 Wind direction(deg) 3.0 onshore and offshore flows at a near coastal site Kalpakkam. 2.5 SU NE ED NE The characteristics of roughness length and its variation 2.0 1.5 strongly affected by land-sea interface sectors. 1.0 0.5

Roughness Length(m) Roughness 0.0 Site specific direction dependent roughness and shear 0 45 90 135 180 225 270 315 360 Wind Direction(deg) coefficient estimation studies confirmed that the default power 3.0 2.5 SU SW law coefficient should be used with caution for wind energy ED SW 2.0 and pollutant dispersion analysis in various underlying surface 1.5 1.0 and structure in the atmospheric surface layer. In addition, 0.5

Roughness length(m) Roughness more work still needs to be done to fully investigate the 0.0 0 45 90 135 180 225 270 315 360 variation of α, u and z 0 as for the different thermal Wind Direction(Deg) WOAR Journals Page 7 stability conditions and seasons as well as during rainy, [19] Grimmond, C. S. B. and Oke, T. R.: 1998, cloudy and clear sky conditions. ‘Aerodynamic Properties of Urban Areas Derived from Analysis of Surface Form’, J. Appl. Meteorology 6. Acknowledgements [20] Gryning, S.-E., E. Batchvarova, B. Br• ummer, H. Jrgensen, and S. Larsen, 2007a: On the extension of the The authors are grateful for Dr S.A.V.Satyamurthy, Director, wind prole over homogeneous terrain beyond the surface IGCAR for supporting meteorological measurements programs layer. at RSD, IGCAR, Kalpakkam. Authors also thanked to [21] Boundary Layer Meteorology, 124, 251-268. Sathyabama University and staff members for providing data [22] Gryning, S.-E., H. Jrgensen, S. Larsen, and E. support. 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[74] World Meteorological Organization (1981), Meteor. Soc. 98, 845-854. Meteorological aspects of the utilization of wind as an [53] Pasquill, F. 1972. Some aspects of boundary layer energy source, Technical note no. 175. description. J. Royal Meteorol. Soc., 98: 469-494. [75] Yu, W., Benoit, R., Girard, C., Glazer, A., Lemarquis, [54] Patil, M. (2006), Àerodynamic drag coecient and D., Salmon, J. and Pinard, J.(2006), Wind energy roughness length for three seasons over a tropical simulation toolkit (WEST): A wind mapping system for western Indian station', Atmos. Res. 80(4), 280-293 use by the wind energy Industry, Wind Engineering 30, [55] Petrna, A., 2009: Sensing the wind prole. Tech. Rep. 15-33. Risoe-PhD-45(EN), RisDTU, 80 pp. Corresponding Author Profile [56] Pneumatikos, J. 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