Urban,Rural and Suburban wind velocity change in the troposphere

Different values are to be expected in different environments, systems such at net temperature rise and fall and factors such as roughness are changed in each environment. Wind is a fluid, although we can’t see it, by looking at how water reacts we can get a brief idea to how wind interacts with cities. In rapids, water has (symbolises a city) lots of turbulence as it bounces off the rocky floor, in an estuary (rural area) the water is generally calm but fast moving because the river bed is very smooth creating little turbulence.

In high velocity conditions, cities have on average lower wind speed (S. Mertens 2006), due to increased friction with buildings creating a loss in energy. Rural areas have smaller structures creating less resistance for wind to flow over therefore increasing wind speed, with suburban areas sitting in the middle of the spectrum. However at high pressure conditions, cities have a higher wind speed on average due to atmospheric instability created by urban heat islands, and increased turbulence due to roughness from buildings, this causes an increase in vertical mixing creating higher wind speeds in urban and suburban areas compared to rural areas (D.O Lee, 1979).

All 3 areas have a contrasting wind standard deviations, standard deviation of wind speed relates to the fluctuation around the average velocity in the given study area. Cities have the greatest standard deviation figure due to the design, size and urban heat island effect, (A. Bharat 2012) collectedly all these factors cause turbulence, channelling of wind and a higher urban roughness area (this is the area that roughness created by buildings have a direct influence on the flow of wind) meaning that there is greater possibility for wind to fluctuate. Rural area have a lower standard deviation due to less verticality, smooth areas and lower temperature average which all creates a more aerodynamic environment and consistent resistance level meaning that wind speeds deviate less from the mean on average compared to cities (R.D. Bornstein, 1977).

Suburban areas fit in the middle of this spectrum, having manmade structures with rough edges and unnatural channels (often roads surrounded by rows of houses) along with the effect of urban heat islands causes standard deviation levels to be much greater than rural areas. However, because suburban areas lack the verticality of cities they have less surface roughness area to create turbulence and therefore have a smaller standard deviation than cities (S.Oikawa. 1995)

References: 

Bharat, A. and Ahmed, A.S., 2012. Effects of high rise building complex on the wind flow patterns on surrounding urban pockets. International Journal of Engineering Research and Development, 4(9), pp.21-26.

Bornstein, R.D. and Johnson, D.S., 1977. Urban-rural wind velocity differences. Atmospheric Environment (1967), 11(7), pp.597-604.

Lee, D.O., 1979. The influence of atmospheric stability and the urban heat island on urban-rural wind speed differences. Atmospheric Environment (1967), 13(8), pp.1175-1180.

Mertens, S., 2006. Wind energy in the built environment: concentrator effects of buildings.

Oikawa, S. and Meng, Y., 1995. Turbulence characteristics and organized motion in a suburban roughness sublayer. Boundary-Layer Meteorology, 74(3), pp.289-312.