24 research outputs found
LARGE-SCALE-FLOW INTERACTIONS WITH THE ALPS AND THEIR IMPACT ON THE LOW-LEVEL TEMPERATURE FIELD IN THE NORTHERN FORELAND
Numerical simulations are presented to examine the sensitivity of the temperature field in the northern Alpine foreland on the large-scale wind direction. The simulations are set up such that changing the wind direction does not create any large-scale systematic temperature advection, thereby isolating the effects of the flow interaction with the Alps. The results show indeed an appreciable impact. In the afternoon, temperatures tend to be higher for southerly flow directions than for northerly ones, as might be expected from the fact that subsidence in the lee of the Alps causes warming while upslope flow is related to cooling. In the morning, however, the lowest temperatures are found for easterly directions while northwesterly flow shows the highest temperatures, followed by westerly flow. The primary reasons for this behaviour are the asymmetry of the flow around the Alpine massif as a whole and the interaction of the friction-induced ageostrophic wind component with the Alps
THE IMPACT OF LEE-SIDE STATIC STABILITY ON THE DISTRIBUTION OF OROGRAPHIC PRECIPITATION
Numerical simulations are presented to examine the effect of the lee-side static stability on the spillover of orographic precipitation. The results show that the presence a cold-air pool in the lee of a mountain ridge greatly increases the precipitation spillover because the cold pool suppresses the lee-side downslope air motion that otherwise leads to a rapid evaporation of the precipitation. The enhancement of the lee-side precipitation reaches up to two orders of magnitude in a nonconvective environment and ranges around one order of magnitude in convective cases. However, the largest absolute spillover is found for a convectively unstable environment because convective cells decay more slowly than
stratiform precipitation
THE IMPACT OF LEE-SIDE STATIC STABILITY ON THE DISTRIBUTION OF OROGRAPHIC PRECIPITATION
Numerical simulations are presented to examine the effect of the lee-side static stability on the spillover of orographic precipitation. The results show that the presence a cold-air pool in the lee of a mountain ridge greatly increases the precipitation spillover because the cold pool suppresses the lee-side downslope air motion that otherwise leads to a rapid evaporation of the precipitation. The enhancement of the lee-side precipitation reaches up to two orders of magnitude in a nonconvective environment and ranges around one order of magnitude in convective cases. However, the largest absolute spillover is found for a convectively unstable environment because convective cells decay more slowly than
stratiform precipitation
MS-GWaM: A 3-dimensional transient gravity wave parametrization for atmospheric models
Parametrizations for internal gravity waves in atmospheric models are
traditionally subject to a number of simplifications. Most notably, they rely
on both neglecting wave propagation and advection in the horizontal direction
(single-column assumption) and an instantaneous balance in the vertical
direction (steady-state assumption). While these simplifications are well
justified to cover some essential dynamic effects and keep the computational
effort small it has been shown that both mechanisms are potentially
significant. In particular, the recently introduced Multiscale Gravity Wave
Model (MS-GWaM) successfully applied ray-tracing methods in a novel type of
transient but columnar internal gravity wave parameterization (MS-GWaM-1D). We
extend this concept to a three-dimensional version of the parameterization
(MS-GWaM-3D) to simulate subgrid-scale non-orographic internal gravity waves.
The resulting global wave model -- implemented into the weather-forecast and
climate code ICON -- contains three-dimensional transient propagation with
accurate flux calculations, a latitude-dependent background source, and
convectively generated waves. MS-GWaM-3D helps reproducing expected temperature
and wind patterns in the mesopause region in the climatological zonal mean
state and thus proves a viable IGW parameterization. Analyzing the global wave
action budget, we find that horizontal wave propagation is as important as
vertical wave propagation. The corresponding wave refraction includes
previously missing but well-known effects such as wave refraction into the
polar jet streams. On a global scale, three-dimensional wave refraction leads
to a horizontal flow-dependent redistribution of waves such that the structures
of the zonal mean wave drag and consequently the zonal mean winds are modified.Comment: 39 pages, 9 figures; This Work has been submitted to the Journal of
Atmospheric Sciences. Copyright in this Work may be transferred without
further notic
Recommended from our members
GGDML: icosahedral models language extensions
The optimization opportunities of a code base are not completely exploited by compilers. In fact, there are optimizations that must be done within the source code. Hence, if the code developers skip some details, some performance is lost. Thus, the use of a general-purpose language to develop a performance-demanding software -e.g. climate models- needs more care from the developers. They should take into account hardware details of the target machine.
Besides, writing a high-performance code for one machine will have a lower performance on another one. The developers usually write multiple optimized sections or even code versions for the different target machines. Such codes are complex and hard to maintain.
In this article we introduce a higher-level code development approach, where we develop a set of extensions to the language that is used to write a model’s code. Our extensions form a domain-specific language (DSL) that abstracts domain concepts and leaves the lower level details to a configurable source-to-source translation process.
The purpose of the developed extensions is to support the icosahedral climate/atmospheric model development. We have started with the three icosahedral models: DYNAMICO, ICON, and NICAM. The collaboration with the scientists from the weather/climate sciences enabled agreed-upon extensions. When we have suggested an extension we kept in mind that it represents a higher-level domain-based concept, and that it carries no lower-level details.
The introduced DSL (GGDML- General Grid Definition and Manipulation Language) hides optimization details like memory layout. It reduces code size of a model to less than one third its original size in terms of lines of code. The development costs of a model with GGDML are therefore reduced significantly
ICON in Climate Limited-area Mode (ICON release version 2.6.1): a new regional climate model
For the first time, the Limited-Area Mode of the new ICON (Icosahedral Nonhydrostatic) weather and climate model has been used for a continuous long-term regional climate simulation over Europe. Built upon the Limited-Area Mode of ICON (ICON-LAM), ICON-CLM (ICON in Climate Limited-area Mode, hereafter ICON-CLM, available in ICON release version 2.6.1) is an adaptation for climate applications. A first version of ICON-CLM is now available and has already been integrated into a starter package (ICON-CLM_SP_betal). The starter package provides users with a technical infrastructure that facilitates long-term simulations as well as model evaluation and test routines. ICON-CLM and ICON-CLM_SP were successfully installed and tested on two different computing systems. Tests with different domain decompositions showed bit-identical results, and no systematic outstanding differences were found in the results with different model time steps. ICON-CLM was also able to reproduce the large-scale atmospheric information from the global driving model. Comparison was done between ICON-CLM and the COnsortium for Small-scale MOdeling (COSMO)-CLM (the recommended model configuration by the CLM-Community) performance. For that, an evaluation run of ICON-CLM with ERA-Interim boundary conditions was carried out with the setup similar to the COSMO-CLM recommended optimal setup. ICON-CLM results showed biases in the same range as those of COSMO-CLM for all evaluated surface variables. While this COSMO-CLM simulation was carried out with the latest model version which has been developed and was carefully tuned for climate simulations on the European domain, ICON-CLM was not tuned yet. Nevertheless, ICON-CLM showed a better performance for air temperature and its daily extremes, and slightly better performance for total cloud cover. For precipitation and mean sea level pressure, COSMO-CLM was closer to observations than ICON-CLM. However, as ICON-CLM is still in the early stage of development, there is still much room for improvement
The Community Foehn Classification Experiment
Strong winds crossing elevated terrain and descending to its lee occur over mountainous areas worldwide. Winds fulfilling these two criteria are called “foehn” in this paper although different names exist depending on region, sign of temperature change at onset, and depth of overflowing layer. They affect local weather and climate and impact society. Classification is difficult because other wind systems might be superimposed on them or share some characteristics. Additionally, no unanimously agreed-upon name, definition nor indications for such winds exist. The most trusted classifications have been performed by human experts. A classification experiment for different foehn locations in the Alps and different classifier groups addressed hitherto unanswered questions about the uncertainty of these classifications, their reproducibility and dependence on the level of expertise. One group consisted of mountain meteorology experts, the other two of Masters degree students who had taken mountain meteorology courses, and a further two of objective algorithms. Sixty periods of 48 hours were classified for foehn/no foehn at five Alpine foehn locations. The intra-human-classifier detection varies by about 10 percentage points (interquartile range). Experts and students are nearly indistinguishable. The algorithms are in the range of human classifications. One difficult case appeared twice in order to examine reproducibility of classified foehn duration, which turned out to be 50% or less. The classification dataset can now serve as a testbed for automatic classification algorithms, which - if successful - eliminate the drawbacks of manual classifications: lack of scalability and reproducibility
Large eddy simulation using the general circulation model ICON
ICON (ICOsahedral Nonhydrostatic) is a unified modeling system for global numerical weather prediction (NWP) and climate studies. Validation of its dynamical core against a test suite for numerical weather forecasting has been recently published by Zängl et al. (2014). In the present work, an extension of ICON is presented that enables it to perform as a large eddy simulation (LES) model. The details of the implementation of the LES turbulence scheme in ICON are explained and test cases are performed to validate it against two standard LES models. Despite the limitations that ICON inherits from being a unified modeling system, it performs well in capturing the mean flow characteristics and the turbulent statistics of two simulated flow configurations - one being a dry convective boundary layer and the other a cumulus-topped planetary boundary layer.BMBF/01LK1202