The upper-atmosphere extension of the ICON general circulation model (version: Ua-icon-1.0)

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. © Author(s) 2019

Valley-wind characteristics in the Alpine Rhine Valley: Measurements with a wind-temperature-profiler and numerical simulations

At the beginning of the MAP intensive measurements phase (Sept. 1999), a late summer high-pressure weather system prevailed for nearly three weeks over the Alps. As a result a pronounced valley wind system developed. By means of a wind-temperature-profiler (WTR), the wind and temperature characteristics were measured continuously in the middle of the Alpine Rhine valley near Rankweil. Numerical simulations have been performed with the MM5 model for one selected day (24h cycle of valley wind system), Model calculation and WTR measurements of wind and temperature are in good agreement

Valley-wind characteristics in the Alpine Rhine Valley: Measurements with a wind-temperature-profiler and numerical simulations

At the beginning of the MAP intensive measurements phase (Sept. 1999), a late summer high-pressure weather system prevailed for nearly three weeks over the Alps. As a result a pronounced valley wind system developed. By means of a wind-temperature-profiler (WTR), the wind and temperature characteristics were measured continuously in the middle of the Alpine Rhine valley near Rankweil. Numerical simulations have been performed with the MM5 model for one selected day (24h cycle of valley wind system), Model calculation and WTR measurements of wind and temperature are in good agreement

Valley-wind characteristics in the Alpine Rhine Valley: Measurements with a wind-temperature-profiler and numerical simulations

At the beginning of the MAP intensive measurements phase (Sept. 1999), a late summer high-pressure weather system prevailed for nearly three weeks over the Alps. As a result a pronounced valley wind system developed. By means of a wind-temperature-profiler (WTR), the wind and temperature characteristics were measured continuously in the middle of the Alpine Rhine valley near Rankweil. Numerical simulations have been performed with the MM5 model for one selected day (24h cycle of valley wind system), Model calculation and WTR measurements of wind and temperature are in good agreement

NUMERICAL SIMULATIONS OF THE ELBE FLOOD CASE: SENSITIVITY TO INITIAL AND BOUNDARY DATA

Numerical experiments with the model chain of the German Weather Service are conducted to find the reasons for the bad performance of the operational precipitation forecast in the case of the Elbe flood in August 2002. The sensitivity to initial and to boundary data as well as to a new precipitation scheme and the horizontal model resolution is inspected. The greatest improvement concerning the amount and location of the predicted precipitation field is achieved by using ECMWF analysis data as initial fields. Also, the implementation of a precipitation scheme that allows the rain to be advected with the wind exhibits a positive effect. Last, the better resolution of the global model improves the rainfall forecast, whereas the better resolution of the regional model produces worse results

Synthesising, using, and correcting for telluric features in high-resolution astronomical spectra

We present a technique to synthesise telluric absorption and emission features both for in-situ wavelength calibration and for their removal from astronomical spectra. While the presented technique is applicable for a wide variety of optical and infrared spectra, we concentrate in this paper on selected high-resolution near-infrared spectra obtained with the CRIRES spectrograph to demonstrate its performance and limitation. We find that synthetic spectra reproduce telluric absorption features to about 2%, even close to saturated line cores. Thus, synthetic telluric spectra could be used to replace the observation of telluric standard stars, saving valuable observing time. This technique also provides a precise in-situ wavelength calibration, especially useful for high-resolution near-infrared spectra in the absence of other calibration sources.Comment: 11 pages, 11 figures, accepted for publication in A&A (updated version

The ICON-1.2 hydrostatic atmospheric dynamical core on triangular grids – Part 1: Formulation and performance of the baseline version

Abstract. As part of a broader effort to develop next-generation models for numerical weather prediction and climate applications, a hydrostatic atmospheric dynamical core is developed as an intermediate step to evaluate a finite-difference discretization of the primitive equations on spherical icosahedral grids. Based on the need for mass-conserving discretizations for multi-resolution modelling as well as scalability and efficiency on massively parallel computing architectures, the dynamical core is built on triangular C-grids using relatively small discretization stencils. This paper presents the formulation and performance of the baseline version of the new dynamical core, focusing on properties of the numerical solutions in the setting of globally uniform resolution. Theoretical analysis reveals that the discrete divergence operator defined on a single triangular cell using the Gauss theorem is only first-order accurate, and introduces grid-scale noise to the discrete model. The noise can be suppressed by fourth-order hyper-diffusion of the horizontal wind field using a time-step and grid-size-dependent diffusion coefficient, at the expense of stronger damping than in the reference spectral model. A series of idealized tests of different complexity are performed. In the deterministic baroclinic wave test, solutions from the new dynamical core show the expected sensitivity to horizontal resolution, and converge to the reference solution at R2B6 (35 km grid spacing). In a dry climate test, the dynamical core correctly reproduces key features of the meridional heat and momentum transport by baroclinic eddies. In the aqua-planet simulations at 140 km resolution, the new model is able to reproduce the same equatorial wave propagation characteristics as in the reference spectral model, including the sensitivity of such characteristics to the meridional sea surface temperature profile. These results suggest that the triangular-C discretization provides a reasonable basis for further development. The main issues that need to be addressed are the grid-scale noise from the divergence operator which requires strong damping, and a phase error of the baroclinic wave at medium and low resolutions

ISSUES IN HIGH-RESOLUTION ATMOSPHERIC MODELING IN COMPLEX TOPOGRAPHY --THE HiRCoT WORKSHOP

During the past years the atmospheric modeling community, both from the application and pure research perspectives, has been facing the challenge of high resolution numerical modeling in places with complex topography. In February 2012, as a result of the collaborative efforts of the Institute of Meteorology of the University of Natural Resources and Life Sciences (BOKUMet), the Arctic Region Supercomputing Center (ARSC), the Institute of Meteorology and Geophysics of the University of Innsbruck (IMG) and the enthusiasm of the scientific community, the HiRCoT workshop was held in Vienna, Austria. HiRCoT objectives were to: 1) Identify the problems encountered with numerical modeling at grid spacing lower than 1 km over complex terrain, that is, understand the key areas that are troublesome and formulate the key questions about them; 2) Map out possibilities on how to address these issues; 3) Allow the researchers to discuss the issues on a shared platform (online through a wikipage and face-to-face). This manuscript presents an overview of the topics and research priorities discussed in the workshop

Interactions between the night time valley-wind system and a developing cold-air pool

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Boundary-Layer Meteorology following peer review. The version of record [Arduini, G., Staquet, C & Chemel, C., ‘Interactions between the night time valley-wind system and a developing cold-air pool’, Boundary-Layer Meteorol (2016) 161:1 (49-72), first published online June 2, 2016, is available at Springer online at doi: 10.1007/s10546-016-0155-8The Weather Research and Forecast (WRF) numerical model is used to characterize the influence of a thermally-driven down-valley flow on a developing cold-air pool in an idealized alpine valley decoupled from the atmosphere above. Results for a three-dimensional (3D) valley, which allows for the formation of a down-valley flow, and for a two-dimensional (2D) valley, where the formation of a down-valley flow is inhibited, are analyzed and compared. A key result is that advection leads to a net cooling in the 2D valley and to a warming in the 3D valley, once the down-valley flow is fully developed. This difference stems from the suppression of the slope-flow induced upward motions over the valley centre in the 3D valley. As a result, the downslope flows develop a cross-valley circulation within the cold-air pool, the growth of the cold-air pool is reduced and the valley atmosphere is generally warmer than in the 2D valley. A quasi-steady state is reached for which the divergence of the down-valley flow along the valley is balanced by the convergence of the downslope flows at the top of the cold-air pool, with no net contribution of subsiding motions far from the slope layer. More precisely, the inflow of air at the top of the cold-air pool is found to be driven by an interplay between the return flow from the plain region and subsidence over the plateaux. Finally, the mechanisms that control the structure of the cold-air pool and its evolution are found to be independent of the valley length as soon as the quasi-steady state is reached and the down-valley flow is fully developed.Peer reviewedFinal Accepted Versio