A study of non-dimensional wind gradient and turbulent intensity, using the Monin-Obukhov similarity theory in a roughness sub-layer of an urban area with complex topography (Tehran)
Message:
Abstract:
Since, the Monin-Obukhov similarity theory (1954) (MOST) has been investigated innumerous studies, especially for the atmospheric surface layer. This theory provides alow-cost method to estimate non-dimensional turbulence intensity and dimensionlesswind gradients that are the bases for the dispersion models. Therefore, this theory hasbeen examined for many surface types, such as water, forest, rural, and urban areas tovalidate the predicted similarity relations.Since the similarity relations were often found for neutral stratification, somemodifications need to be made in order to make them applicable for the other stabilityconditions and, hence, some stability correction functions are applied.The hypothesis of constant surface fluxes with height as a basic assumption of MOST,makes it unpractical for terrains such as forests and urban areas, over which surface fluxesvary horizontally and with regard to height. For these terrains, the local scaling approachwas applied to solve this problem. Similarity functions derived using local scaling wereexamined in numerous experiments and showed good agreement with observationalresults.In this paper, the applicability of MOST was studied over an urban area with complextopography (Tehran) and with a rough sublayer as the lowest part of the surface layer. Forthis, we used data measured by a Sodar (model PA1) located at the Institute ofGeophysics of the University of Tehran for the first 8 months of 2007. Sodar measuredthe speed and direction of wind, standard deviations of three components of the wind, andmomentum fluxes. Also, data from a 100 m tower 150 m away from the Sodar positionwere used. This tower is equipped with four 2D sonic anemometers at 2, 10, 45 and 100m, which measure the speed and direction of wind and the temperature. To validate Sodardata, the u and v components of the wind at 45 m from Sodar were compared with thosefrom the tower at 45 m. The results illustrate good agreement and show similar trends.The first aim of this research was to determine whether the similarity function can befitted to the non-dimensional wind gradient and standard deviations of three componentsof wind. Toward this end, non-dimensional wind gradients and dimensionless turbulentintensities were studied against the stability parameters which were calculated using thelocal similarity approach. Results show that MOST with the local scaling approach can beapplied over this terrain. Therefore, similarity functions for these parameters werecalculated.The second aim of this study was to compare calculated emperical constants for thisterrain with that of previous results that were made over various surface types and fordifferent stability conditions. To achieve an accurate comparison, neutral stratificationswere also studied.The results indicate that emperical constants for the non-dimensional wind gradientand turbulent intensities over Tehran and in the rough sub-layer were larger than those ofother surface types, including those over flat urban areas. This outcome reveals that theknowledge of the effect of Tehran topography, which may have a great influence on airpollution for this city, may be important.Different universal similarity functions and large emperical constants imply thatapplying results from other terrains to predict wind and air pollution over a city as largeand heterogeneous as Tehran may lead to significant errors. The estimated constants forthe empirical universal similarity functions found in this work appear to be necessary forapplications in dispersion studies for Tehran.
Language:
Persian
Published:
Iranian Journal of Geophysics, Volume:5 Issue: 2, 2011
Page:
69
magiran.com/p885781  
دانلود و مطالعه متن این مقاله با یکی از روشهای زیر امکان پذیر است:
اشتراک شخصی
با عضویت و پرداخت آنلاین حق اشتراک یک‌ساله به مبلغ 990,000ريال می‌توانید 70 عنوان مطلب دانلود کنید!
اشتراک سازمانی
به کتابخانه دانشگاه یا محل کار خود پیشنهاد کنید تا اشتراک سازمانی این پایگاه را برای دسترسی نامحدود همه کاربران به متن مطالب تهیه نمایند!
توجه!
  • حق عضویت دریافتی صرف حمایت از نشریات عضو و نگهداری، تکمیل و توسعه مگیران می‌شود.
  • پرداخت حق اشتراک و دانلود مقالات اجازه بازنشر آن در سایر رسانه‌های چاپی و دیجیتال را به کاربر نمی‌دهد.
دسترسی سراسری کاربران دانشگاه پیام نور!
اعضای هیئت علمی و دانشجویان دانشگاه پیام نور در سراسر کشور، در صورت ثبت نام با ایمیل دانشگاهی، تا پایان فروردین ماه 1403 به مقالات سایت دسترسی خواهند داشت!
In order to view content subscription is required

Personal subscription
Subscribe magiran.com for 50 € euros via PayPal and download 70 articles during a year.
Organization subscription
Please contact us to subscribe your university or library for unlimited access!