Picture (above): Misty morning. Credit: Icon0 (Pexels).
This paper details a new approach to evaluating the performance of land surface models, the component of climate and weather models that simulates land surface processes. It focuses on the cycle of solar radiation during daylight hours and how the energy from the sun is exchanged between the land surface and lower atmosphere.
The researchers drilled down into this exchange by examining the timing differences between model simulations of evaporation and atmospheric heating by the land surface throughout the course of a day across a wide range of environments and seasons. They then compared this model output to real-world observational data from 20 sites around the world.
The researchers found the evaporative processes under cloud-free conditions were poorly represented across the 13 models they examined, with the best-performing model only producing appropriate timing of evaporation and heating in 33% of cases examined across the sites. This had a direct impact on the timing of heat exchange with the atmosphere these models.
Investigating further, the researchers concluded the poor performance of the daily cycle of turbulent heat exchange appears to be linked to how models solve for the surface energy balance and redistribute heat into the subsurface.
Understanding and responding to these model biases opens up new opportunities for improving land surface models, with the potential to impact the simulation of drought, heat waves and storm formation.
- Paper: Renner, M., A. Kleidon, M. Clark, B. Nijssen, M. Heidkamp, M. Best, and G. Abramowitz, How well can land-surface models represent the diurnal cycle of turbulent heat fluxes?. J. Hydrometeor., doi: https://doi.org/10.1175/JHM-D-20-0034.1.