Introduction to CAUSES: weather and climate models' near-surface temperature errors near ARM's SGP observatory
Morcrette, Cyril Julien — Met Office - UK
Area of research:
Scientists at the Met Office in the UK, along with colleagues at the U.S. Department of Energy (DOE), have organized an international multi-model inter-comparison project, called CAUSES (Clouds Above the United States and Errors at the Surface). The project aims to identify the physical processes that lead to the formation of a warm surface air temperature bias in many weather forecast and climate model simulations over the American Midwest.
This paper introduces a series of papers addressing the physical processes contributing to warm surface air temperature bias in the warm season over the Midwest in a number of weather and climate models. This paper documents all the models taking part and quantifies the warm bias in each model. It also demonstrates a high degree of correlation between the diurnal cycle of the model biases over large portion of the American Midwest and the diurnal cycle of the bias at an instrumented site in the Southern Great Plains (SGP). This suggests that conclusions drawn in this paper and its companions, from detailed evaluation of models using instruments located at SGP, will be representative of errors prevalent over a larger spatial scale.
For each model taking part in the CAUSES inter-comparison project, this paper quantifies the warm surface temperature bias in terms of magnitude, vertical depth, and lateral extent. The biases are also described in terms of their variation throughout the warm season, as a function of lead time and as a function of time of day during the diurnal cycle. Using observational data collected from the U.S. DOE Atmospheric Radiation Measurement (ARM) SGP sites, the models’ warm biases are shown to extend several kilometers into the atmosphere. In most models, the warm bias is shown to vary with time of day; some models have their largest warm biases during the day, while some have it at night.