New Deep Cloud Representation Improves Climate Model Simulations during El Niño
Clouds block large amounts of sunlight from reaching the Earth’s surface during El Niño. This shielding effect has largely been missing in the community climate model, CAM3. Scientists in DOE’s Atmospheric Radiation Measurement (ARM) program corrected this long-standing model deficiency by using an improved representation of atmospheric convection based on the ARM observations. The investigators found that the lack of cloud shielding effect in the climate model was caused by poor simulation of low-level cloud cover and water content in the clouds during El Niño. The addition of improved convection representation suppressed what had been overly active deep clouds in the model, making shallow clouds more active, and leading to more low-level clouds than found in the standard model configuration. The improved model also had better representation of water content anomalies in clouds which were higher due to enhanced transport of water vapor by shallow clouds to the lower-middle troposphere. The improvement of the model’s representation of clouds corrected the cloud shielding effect in the community climate model.
Li, G, and GJ Zhang, 2008: Understanding biases in shortwave cloud radiative forcing in the National Center for Atmospheric Research Community Atmosphere Model (CAM3) during El Niño. J. Geophys. Res. 113, D02103, doi:10.1029/2007JD008963.