Abstract
Abstract. How the upper-atmosphere branch of the circulation contributes to and interacts with the circulation of the middle and lower atmosphere is a research area with many open questions. Inertia–gravity waves, for instance, have moved in the focus of research as they are suspected to be key features in driving and shaping the circulation. Numerical atmospheric models are an important pillar for this research. We use the ICOsahedral Non-hydrostatic (ICON) general circulation model, which is a joint development of the Max Planck Institute for Meteorology (MPI-M) and the German Weather Service (DWD), and provides, e.g., local mass conservation, a flexible grid nesting option, and a non-hydrostatic dynamical core formulated on an icosahedral–triangular grid. We extended ICON to the upper atmosphere and present here the two main components of this new configuration named UA-ICON: an extension of the dynamical core from shallow- to deep-atmosphere dynamics and the implementation of an upper-atmosphere physics package. A series of idealized test cases and climatological simulations is performed in order to evaluate the upper-atmosphere extension of ICON.
Highlights
In climate simulations and numerical weather prediction (NWP), there are ongoing efforts to raise the upper model lid, acknowledging possible influences of middle- and upperatmosphere dynamics on tropospheric weather and climate (e.g., Thompson et al, 2002; Scaife et al, 2012; CharltonPerez et al, 2013)
An upper-atmosphere extension of the ICOsahedral Non-hydrostatic (ICON) general circulation model has been presented. This includes the extension of the dynamical core from a shallow-atmosphere to a deepatmosphere formulation in order to account for the spherical shape of the atmosphere and the gravitational field as well as to account for the non-traditional part of the Coriolis acceleration
The physics parameterizations have been complemented by processes which become relevant in the rarified air of the upper mesosphere and lower thermosphere
Summary
In climate simulations and numerical weather prediction (NWP), there are ongoing efforts to raise the upper model lid, acknowledging possible influences of middle- and upperatmosphere dynamics on tropospheric weather and climate (e.g., Thompson et al, 2002; Scaife et al, 2012; CharltonPerez et al, 2013). We mention the middle atmosphere GCM developed by Watanabe et al (2008) and later complemented by physics parameterizations that allow for simulations covering the lower thermosphere up to about 150 km (the Japanese Atmospheric general circulation model for Upper Atmosphere Research (JAGUAR); Watanabe and Miyahara, 2009) It has been employed, for instance, to study the interaction of resolved gravity waves with thermal tides by global simulations of a horizontal, triangularly truncated spectral resolution of T213 and a vertical layer spacing of 500 m throughout the middle atmosphere (Watanabe and Miyahara, 2009).
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