Impact of terrain complexity on the turbulence drag coefficient: A case study from the Indian Himalayan region |
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| Institution: | 1. Department of Earth Science, Science and Research Branch, Islamic Azad University, Tehran, Iran;2. Space Physics Group, Department of Physics, Faculty of Science, Yazd University, Iran;1. Key Laboratory of Meteorological Disaster, Ministry of Education (KLME)/Joint International Research Laboratory of Climate and Environmental Change (ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science and Technology, Nanjing, 210044, China;2. Joint Innovation Center for Modern Forestry Studies, College of Biology and Environment, Nanjing Forestry University, Nanjing, 210037, China;3. Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, NY, 12222, USA;1. Atmospheric Science and Meteorological Research Center, Tehran, Iran;2. York University, Toronto, Canada;3. Soil Conservation and Watershed Management Research Institute (SCWMRI), Agricultural Research, Education and Extension Organization (AREO), Tehran, Iran |
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| Abstract: | The aerodynamic drag coefficient (CD) is conjectured to change (or remains almost uniform) with the horizontal wind speed (U) over a flexible (or fixed) surface element, which is represented with the surface roughness (z0). This conjecture is tested for the near neutral atmospheric turbulence (i.e. when surface stability z/L is almost equal to 0, where z is the measurement height and L is Obukhov length) of monsoon and winter season at an on-slope and a ridge-top site in the Indian Himalaya, wherein the ridge-top site is associated with a higher degree of sensitivity to the roughness element and terrain attributes. This hypothesis is successfully verified for two conditions, (i) the monsoon period observations of ridge-top site are found to have higher z0 due to vegetative growth than the winter period for flows having similar terrain signature, and (ii) the monsoon and winter period observations of on-slope site are noted to have similar z0 for flows having signature of steep terrain. Subsequently, constants (i.e. a and b) of the power-law relationships between CD and U (i.e. CD = aUb), as a function of z0, are optimized. It is noted that the relationship between CD and U has higher sensitivity towards the terrain slope than the vegetative growth. |
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| Keywords: | Drag coefficient Himalayan terrain Surface roughness |
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