An explicit estimate of terrestrial evaporative fraction based on weather data for a boundary layer at diurnal equilibrium
Abstract
A method for estimating evaporation (ET) from temperature, humidity, pressure, and net solar radiation is proposed. The method is demonstrated with approximately 100,000 site-days of fluxnet data (with one set of parameters) over a range of land cover and climate conditions. The method rests on two approximations: 1) Mixed layer humidity (q) is on average the same at the start and end of boundary layer growth; and 2) The humidity lapse rate is zero except above the lifting condensation level (LCL). The approximations are based on the absence of moisture sinks below the LCL and negligible convergence. With these approximations, a unique value of daily-constant evaporative fraction (EF) yields an equilibrium diurnal cycle of predicted q, for which entrainment of dry air and cloud mass fluxes of humidity balance ET. Enforcing equilibrium with budget terms calculated from weather data estimates EF. Under simplifying conditions, EF depends on two dimensionless variables related to the LCL and maximum mixed layer height, yielding an explicit (algebraic) equation for EF in terms of weather variables. Performance at daily, seasonal, and interannual scales will be presented.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A24D..03S
- Keywords:
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- 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSES;
- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3379 Turbulence;
- ATMOSPHERIC PROCESSES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES