Bowen ratio in micrometeorology — choose the correct definition What does the Bowen ratio represent in surface energy balance terms?

Introduction / Context:
In micrometeorology and hydrology, the surface energy balance partitions available energy into sensible heat flux (H) and latent heat flux (LE). The Bowen ratio is widely used to characterize this partitioning over land and water surfaces.

Given Data / Assumptions:

• H denotes sensible heat flux (W/m^2).
• LE denotes latent (vapour) heat flux (W/m^2).
• Bowen ratio is a dimensionless measure relating these fluxes.

Concept / Approach:
By definition, the Bowen ratio B = H / LE. Values > 1 indicate dominance of sensible heat (dry conditions), while values < 1 indicate dominance of latent heat (moist conditions). The ratio is central to Bowen ratio energy balance (BREB) methods which infer fluxes from temperature and humidity gradients.

Step-by-Step Solution:
1) Identify fluxes: sensible heat H and latent (vapour) heat LE.2) Form the ratio B = H / LE to describe partitioning.3) Interpret: B acts as a proportionality relating H to LE for a given surface state.4) Select the option that verbalizes this relationship.

Verification / Alternative check:
In BREB, H = B * LE, confirming B as the proportionality factor between the two fluxes.

Why Other Options Are Wrong:
(a) Refers to the Lewis number (ratio of thermal to mass diffusivity); (c) is the evapotranspiration ratio used in irrigation; (d) resembles the Priestley–Taylor coefficient, not the Bowen ratio.

Common Pitfalls:
Confusing Bowen ratio with bulk transfer coefficients; mixing up sign conventions and directions of fluxes.

Final Answer:
Proportionality constant between vapour heat flux and sensible heat flux.