Book contents
- Frontmatter
- Contents
- Preface
- Part I A grammar of turbulence
- Part II Turbulence in the atmospheric boundary layer
- 8 The equations of atmospheric turbulence
- 9 The atmospheric boundary layer
- 10 The atmospheric surface layer
- 11 The convective boundary layer
- 12 The stable boundary layer
- Part III Statistical representation of turbulence
- Index
11 - The convective boundary layer
from Part II - Turbulence in the atmospheric boundary layer
Published online by Cambridge University Press: 11 April 2011
- Frontmatter
- Contents
- Preface
- Part I A grammar of turbulence
- Part II Turbulence in the atmospheric boundary layer
- 8 The equations of atmospheric turbulence
- 9 The atmospheric boundary layer
- 10 The atmospheric surface layer
- 11 The convective boundary layer
- 12 The stable boundary layer
- Part III Statistical representation of turbulence
- Index
Summary
Introduction
The mean structure of the convective boundary layer (CBL) is sketched in Figure 11.1. The surface layer (the lowest 10%, say) is the most accessible to observation and therefore the best understood. Above it lies the mixed layer (not “mixing” layer; that is the turbulent shear layer between parallel streams of different speeds). Here the turbulent diffusivity tends to be largest and mean gradients of wind and conserved scalars smallest. The interfacial layer buffers the mixed layer from the free atmosphere. Its top at mean height h2 can be thought of as the greatest height reached by the surface-driven convective elements, and its bottom at h1 the deepest penetrations of the nonturbulent free atmosphere. The mean CBL depth zi lies between these two; it is often taken as the height at which the vertical turbulent flux of virtual potential temperature has its negative maximum.
The mixed layer: velocity fields
Mixed-layer similarity
A mimimal set of governing parameters for the quasi-steady mixed layer is the M-O group u*, z, g/θ0, Q0 (the surface flux of virtual temperature), (the surface flux of a conserved scalar) plus the boundary-layer depth zi. The dimensional analysis (Chapter 10) here has m − 1 = 6 governing parameters and n = 4 dimensions, so there are m − n = 3 independent dimensionless quantities. One is the dimensionless dependent variable; it is conventional to take the other two as z/zi and zi/L.
- Type
- Chapter
- Information
- Turbulence in the Atmosphere , pp. 241 - 266Publisher: Cambridge University PressPrint publication year: 2010