Book contents
- Frontmatter
- Dedication
- Contents
- Preface
- 1 Ecosystems and Climate
- Part I The Earth System
- Part II Global Physical Climatology
- Part III Hydrometeorology
- 9 Soil Physics
- 10 Water Balance
- 11 Watershed Hydrology
- 12 Surface Energy Fluxes
- 13 Turbulent Fluxes
- 14 Soil Moisture and the Atmospheric Boundary Layer
- Part IV Biometeorology
- Part V Terrestrial Plant Ecology
- Part VI Terrestrial Forcings and Feedbacks
- Appendix
- Index
- Plate section
- References
14 - Soil Moisture and the Atmospheric Boundary Layer
from Part III - Hydrometeorology
Published online by Cambridge University Press: 05 November 2015
- Frontmatter
- Dedication
- Contents
- Preface
- 1 Ecosystems and Climate
- Part I The Earth System
- Part II Global Physical Climatology
- Part III Hydrometeorology
- 9 Soil Physics
- 10 Water Balance
- 11 Watershed Hydrology
- 12 Surface Energy Fluxes
- 13 Turbulent Fluxes
- 14 Soil Moisture and the Atmospheric Boundary Layer
- Part IV Biometeorology
- Part V Terrestrial Plant Ecology
- Part VI Terrestrial Forcings and Feedbacks
- Appendix
- Index
- Plate section
- References
Summary
Chapter Summary
The atmospheric boundary layer is the layer of the atmosphere directly above Earth's surface. Sensible heat from the surface warms the boundary layer, and evaporated water moistens the boundary layer. The diurnal cycle of surface fluxes imparts a diurnal cycle to the boundary layer. At night, the boundary layer is typically stable with weak turbulent motion. Surface heating during the day warms the boundary layer and it becomes unstable. Soil water influences the boundary layer because of its effect on the partitioning of net radiation into sensible and latent heat. The Bowen ratio is smaller where soil water does not limit evapotranspiration, and the boundary layer is cooler, moister, and shallower than in the absence of evapotranspiration. Dry sites have lower latent heat flux and a warmer, drier, and deeper boundary layer. The changes in surface fluxes and boundary layer characteristics associated with wet soil may create conditions that favor precipitation. Surface heterogeneity in soil moisture can also generate mesoscale atmospheric circulations. A large horizontal contrast in sensible heat flux can produce a circulation similar to a sea breeze in which surface winds flow from cooler wet soil to warmer dry soil while upper winds flow in the opposite direction.
Boundary Layer Characteristics
The atmospheric boundary layer is the layer of the atmosphere above Earth's surface that is directly affected over the course of a day by the surface through heating, cooling, friction, and the emission of atmospheric constituents such as water vapor, CO2, dust, and pollutants. The boundary layer is the region of the atmosphere in which people live and plants grow. Processes in the boundary layer determine the climate near the ground that we experience.
The boundary layer has distinct regions. The surface layer is the layer immediately above the surface where air flow strongly depends on surface characteristics. Vertical variation in surface fluxes is negligible, and the surface layer is also referred to as the constant flux layer. Monin–Obukhov similarity theory describes flux–profile relationships in the constant flux layer (Chapter 13). However, these relationships fail in the layer of flow within and close to the plant canopy, known as the roughness sublayer. The outer layer is the region above the surface layer where flow is not as greatly influenced by the surface.
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- Information
- Ecological ClimatologyConcepts and Applications, pp. 218 - 230Publisher: Cambridge University PressPrint publication year: 2015