The Madden-Julian Oscillation in a warmer world

Global warming's impact on the Madden-Julian Oscillation (MJO) is assessed using one of the few models capable in reproducing its key features. In a warmer climate predicted for the end of the century, the MJO increases in amplitude (by ~30%) and frequency, showing a more circumglobal propagation tendency. The MJO spatial extent becomes enhanced, deeper, and more zonally extended but meridionally confined. A stronger vertical tilting structure in diabatic heating, moisture, and convergence fields is seen. Our findings indicate that these changes result from an intensification of the frictional wave-conditional instability of the second kind mechanism via the coupling of dynamical and thermodynamic response to the warming. The warming and moistening of the mean state contribute to the enhanced deep convective heating, driving a stronger-forced Kelvin wave-like perturbation. This reinforces the frictional low-level convergence, leading to larger shallow convective heating and therefore to a faster development and enhancement of the deep convection in the MJO

ICON-A: the atmospheric component of the ICON Earth System Model. Part I: Model description

ICON‐A is the new icosahedral non‐hydrostatic (ICON) atmospheric general circulation model in a configuration using the Max Planck Institute (MPI) physics package, which originates from the ECHAM6 general circulation model, and has been adapted to account for the changed dynamical core framework. The coupling scheme between dynamics and physics employs a sequential updating by dynamics and physics, and a fixed sequence of the physical processes similar to ECHAM6. To allow a meaningful initial comparison between ICON‐A and the established ECHAM6‐LR model, a setup with similar, low resolution in terms of number of grid points and levels is chosen. The ICON‐A model is tuned on the base of the AMIP experiment aiming primarily at a well balanced top‐of atmosphere energy budget to make the model suitable for coupled climate and Earth system modeling. The tuning addresses firstly the moisture and cloud distribution to achieve the top‐of‐atmosphere energy balance, followed by the tuning of the parameterized dynamic drag aiming at reduced wind errors in the troposphere. The resulting version of ICON‐A has overall biases which are comparable to those of ECHAM6. Problematic specific biases remain in the vertical distribution of clouds and in the stratospheric circulation, where the winter vortices are too weak. Biases in precipitable water and tropospheric temperature are, however, reduced compared to the ECHAM6. ICON‐A will serve as the basis of further development and as the atmosphere component to the coupled model, ICON‐ESM