An Improved Idealized Atmospheric Model for the Study of the Stratosphere-Troposphere System

In their 1994 article in the Bulletin of the American Meteorological Society, Held and Suarez designed an idealized forcing to explore the impact of model numerics on the general circulation of the atmosphere. The forcing, a simple recipe that replaced radiative and convective schemes with Newtonian relaxation towards a prescribed equilibrium temperature profile, took on new life as an idealized model of the atmosphere for research, and has led to discoveries which have increased our understanding of the atmosphere and to improvements of comprehensive models. Polvani and Kushner (2002) extended the “Held-Suarez” forcing upward to create an idealized model of the stratosphere-troposphere system. Recent studies, however, have shown that these adjustments to improve the representation of the stratosphere inadvertently lead to a number of problems: biases in the position of the tropospheric jet streams, the presence of atmospheric flow regimes, and a low tropopause. We trace all of these problems back to bias in the lower stratospheric temperatures, and correct them by fixing the equilibrium temperature profile. The new blend between the “Held-Suarez” and “Polvani-Kushner” forcings preserves the coupling between the troposphere and stratosphere, and further permits one to create a more realistic seasonal cycle of the atmospheric circulation. We strongly recommend that it be used for future idealized studies of the stratosphere-troposphere system.