Bowen ratio
The Bowen ratio (β) is a crucial climate index that quantifies the relationship between sensible heat flux (D) and latent heat flux (E) at the Earth's surface. Specifically, it is defined as the ratio of D to E (β = D/E). Sensible heat flux refers to energy transfer that results in temperature changes, while latent heat flux involves energy associated with moisture, such as during evaporation. A Bowen ratio greater than 1 indicates that more energy is being transferred as sensible heat, suggesting warmer climate conditions. Conversely, a ratio less than 1 signifies that latent heat flux predominates, often leading to cooler and more humid conditions. The availability of water for evaporation significantly influences the Bowen ratio, as increased water availability tends to enhance latent heat flux. Additionally, the rise in greenhouse gas concentrations can lead to more energy at the surface, which can either increase atmospheric warming or promote evaporation, thus affecting the overall climate dynamics. Understanding the Bowen ratio is vital for comprehending energy transfer processes and their implications for climate change.
Subject Terms
Bowen ratio
Definition
The main process for transporting the daytime energy surplus at Earth’s surface to the atmosphere is convection, which is heat transfer by turbulent air motion. There are two types of convective flows (fluxes), the sensible and latent heat fluxes. If the movement of energy from the surface can be sensed as a rise or fall in temperature, then it is referred to as the sensible heat (D). If the flow of energy involves moisture, as in evaporation or from plants, there will be no change in temperature. In this case, the energy is held dormant in the evaporated moisture for release should the water vapor revert to its liquid state via condensation. This is called the flux (E). Climate is characterized by the apportionment of energy at the Earth’s surface between D and E, the ratio of which is known as Bowen’s ratio (β), so that β = D/E. Negative β values indicate that one and only one of the two fluxes is negative. D is negative when the air is heating the surface. E is negative when (dew) occurs.
Significance for Climate Change
Bowen’s ratio is a climate index. If β is greater than 1, D is greater than E. Since such values indicate that most of the heat being moved into the atmosphere is in sensible form, they also indicate that the climate is warmer than it is when β is less than 1. When β is less than 1, E is greater than D and most of the energy transfer does not contribute directly to warming the air. This transfer may increase atmospheric humidity, however, making the climate cool and humid. The size of Bowen’s ratio is determined chiefly by the availability of water for evaporation. If water is available, the will dominate.
A rise in the concentration of greenhouse gases in the atmosphere means there is more available energy at the Earth’s surface. This additional energy can be used either to heat the atmosphere by way of the (increased warming) or to evaporate water via the latent heat flux. Since 71 percent of the Earth’s surface is water, most of the additional energy would contribute to an enhanced latent heat flux. The resulting warming of the atmosphere would be less in this case than if all the additional available energy was accounted for by the sensible heat flux alone.
Bibliography
"Bowen Ratio." American Meteorological Society, 26 Mar. 2024, glossary.ametsoc.org/wiki/Bowen‗ratio. Accessed 21 Dec. 2024.
Ren, Xueyuan, et al. "Environmental and Biophysical Effects of the Bowen Ratio Over Typical Farmland Ecosystems in the Loess Plateau." Remote Sensing, 14 Apr. 2022, doi.org/10.3390/rs14081897. Accessed 19 Dec. 2024.