
150 Principles of Sustainable Energy Systems
© 2008 Taylor & Francis Group, LLC
Of course, the most critical part of the atmosphere for a WT is relatively close to the
ground. The atmospheric boundary layer (ABL) is the lowest part of the atmosphere and
varies from the ground up to 500–2000 m in height depending on the time of day, tem-
perature, and pressure. In the ABL, the mean wind speed varies from zero at or near the
ground up to the free stream velocity of the atmosphere at the top of the ABL. In addition,
the velocity eld exhibits turbulent uctuations. In other words, each of the three velocity
components for an air particle has a mea ...