Description: If unstructured meshes are refined to locally represent eddy dynamics in ocean circulation models, a practical question arises on how to vary the resolution and where to deploy the refinement. We propose to use the observed sea surface height variability as the refinement criterion. We explore the utility of this method (i) in a suite of idealized experiments simulating a wind-driven double gyre flow in a stratified circular basin and (ii) in simulations of global ocean circulation performed with FESOM. Two practical approaches of mesh refinement are compared. In the first approach the uniform refinement is confined within the areas where the observed variability exceeds a given threshold. In the second one the refinement varies linearly following the observed variability. The resolution is fixed in time. For the double gyre case it is shown that the variability obtained in a high-resolution reference run can be well captured on variable-resolution meshes if they are refined where the variability is high and additionally upstream the jet separation point. The second approach of mesh refinement proves to be more beneficial in terms of improvement downstream the midlatitude jet. Similarly, in global ocean simulations the mesh refinement based on the observed variability helps the model to simulate high variability at correct locations. The refinement also leads to a reduced bias in the upper-ocean temperature

Description: A new climate model has been developed that employs a multi-resolution dynamical core for the sea ice-ocean component. In principle, the multi-resolution approach allows one to use enhanced horizontal resolution in dynamically active regions while keeping a coarse-resolution setup otherwise. The coupled model consists of the atmospheric model ECHAM6 and the finite element sea ice-ocean model (FESOM). In this study only moderate refinement of the unstructured ocean grid is applied and the resolution varies from about 25 km in the northern North Atlantic and in the tropics to about 150 km in parts of the open ocean; the results serve as a benchmark upon which future versions that exploit the potential of variable resolution can be built. Details of the formulation of the model are given and its performance in simulating observed aspects of the mean climate is described. Overall, it is found that ECHAM6–FESOM realistically simulates many aspects of the observed climate. More specifically it is found that ECHAM6–FESOM performs at least as well as some of the most sophisticated climate models participating in the fifth phase of the Coupled Model Intercomparison Project. ECHAM6–FESOM shares substantial shortcomings with other climate models when it comes to simulating the North Atlantic circulation.

Description: This contribution focuses on two applications of the FESOM model family. On the one hand, recent runs with the finite volume code FESOM2 on large global meshes with regional focus are presented. FESOM's shallow water branch TsunAWI is the subject of the second part. TsunAWI, still based on finite elements, is used as an operational model in the Indonesia Tsunami Early Warning System (InaTEWS). InaTEWS derives tsunami forecasts in two different ways: from scenarios in a pre-computed database or from an on-the-fly simulation. The pre-computed scenarios are based on TsunAWI simulations with inundation on a triangular mesh with a resolution ranging from 20km in the deep ocean to 300m - 50m in coastal areas. The on-the-fly propagation model EasyWave (Andrey Babeyko, GFZ) solves the linear shallow water equations on a regular finite-difference grid with a resolution of about 1 km and the coast line as a vertical wall. EasyWave is used after a tsunami has been generated in an area not covered by the database or after seismic measurements show an earthquake mechanism not present in the database. As the numerical settings of both models are quite different, variations in the outputs are to be expected; nevertheless, the differences in the warning levels should not be too large for identical sources. In the current study, we systematically compare the warning products like estimated wave height and estimated time of arrival by the two approaches.

Description: Abstract: The Indonesia Tsunami Early Warning System delivers simulated tsunami forecasts in two different ways: either matching scenario(s) from a pre-computed database or running on-the-fly tsunami simulation. Recently, the database has been extended considerably taking into account additional source regions not covered in earlier stages of the system. In this contribution, we present the current status of the data base coverage as well as a study investigating the warning products obtained by the two modeling approaches. The pre-computed tsunami scenarios are based on the finite element model TsunAWI that employs a triangular mesh with resolution ranging from 20km in deep ocean to 300m in coastal areas and to as much as 50m in some highly resolved areas. TsunAWI solves the nonlinear shallow water equations and contains a wetting-drying inundation scheme. The on-the-fly propagation model easyWave solves the linear shallow water equations on a regular finite-difference grid with a resolution of about 1 km and utilizes several simple options to estimate coastal impact. This model is used for forecasting after a tsunami has been generated in an area not covered by the database or after a moment tensor solution shows an earthquake focal mechanism not present in the database. Since warning products like estimated wave height (EWH) and estimated time of arrival (ETA) along the coast are based on modeling results, it is crucial to compare the resulting forecasted warning levels obtained by the two approaches. Resolutions and numerical settings of both models are quite different, therefore variations in the resulting outputs are to be expected; nevertheless, the extent of differences in warning levels should not be too large for identical sources. In the present study, we systematically investigate differences in resulting warning products along InaTEWS forecast points facing the Sunda arc.  Whereas the finite-element mesh of TsunAWI covers the coast up to a terrain height of 50m and warning products have been pre-calculated directly in the forecast points, easyWave offers several options for their approximation including projections from offshore grid points or vertical wall. Differences and potential reasons for variations of warning products like the role of bathymetry resolution as well as the general approach for the assessment of EWH and ETA for different modeling frameworks are discussed.

Description: A new global climate model setup using FESOM2.0 for the sea ice‐ocean component and ECHAM6.3 for the atmosphere and land surface has been developed. Replacing FESOM1.4 by FESOM2.0 promises a higher efficiency of the new climate setup compared to its predecessor. The new setup allows for long‐term climate integrations using a locally eddy‐resolving ocean. Here it is evaluated in terms of (1) the mean state and long‐term drift under preindustrial climate conditions, (2) the fidelity in simulating the historical warming, and (3) differences between coarse and eddy‐resolving ocean configurations. The results show that the realism of the new climate setup is overall within the range of existing models. In terms of oceanic temperatures, the historical warming signal is of smaller amplitude than the model drift in case of a relatively short spin‐up. However, it is argued that the strategy of “de‐drifting” climate runs after the short spin‐up, proposed by the HighResMIP protocol, allows one to isolate the warming signal. Moreover, the eddy‐permitting/resolving ocean setup shows notable improvements regarding the simulation of oceanic surface temperatures, in particular in the Southern Ocean.

Description: Nach dem verheerenden Tsunami im Indischen Ozean 2004 wurde das internationale Kooperationsprojekt ''German-Indonesian Tsunami Early Warning System'' ins Leben gerufen und das Frühwarnzentrum am Amt für Meteorologie, Klimatologie und Geophysik in Jakarta aufgebaut. Auf deutscher Seite wurde das Projekt vom Helholtz-Zentrum Potsdam, Deutsches Geoforschungszentrum geleitet. Die Warnung nach einem starken Erdbeben basiert auf einer Datenbank möglicher Tsunamiszenarien, so dass schnell die Gefährdung der Küsten abgeschätzt werden kann. Im Vorfeld dienen detailiierte Überflutungsrechnungen als Basis für Evakuierungspläne. Der Vortrag stellt den Aufbau des Warnsystems mit einem Schwerpunkt auf der Rolle der Tsunami-Simulation vor. Insbesondere werden die physikalischen und numerischen Grundlagen des Simulationsmodells TsunAWI beleuchtet und am Beispiel einiger Modellrechnungen Möglichkeiten und Grenzen der Simulation aufgezeigt.

Description: A sensitivity study is undertaken to assess the utility of different onshore digital elevation models (DEMs) for simulating the extent of tsunami inundation using case studies from two locations in Indonesia. We compare airborne IFSAR, ASTER, and SRTM against high resolution LiDAR and stereo-camera data in locations with different coastal morphologies. Tsunami inundation extents modeled with airborne IFSAR DEMs are comparable with those modeled with the higher resolution datasets and are also consistent with historical run-up data, where available. Large vertical errors and poor resolution of the coastline in the ASTER and SRTM elevation datasets cause the modeled inundation extent to be much less compared with the other datasets and observations. Therefore, ASTER and SRTM should not be used to underpin tsunami inundation models. A model mesh resolution of 25 m was sufficient for estimating the inundated area when using elevation data with high vertical accuracy in the case studies presented here. Differences in modeled inundation between digital terrain models (DTM) and digital surface models (DSM) for LiDAR and IFSAR are greater than differences between the two data types. Models using DTM may overestimate inundation while those using DSM may underestimate inundation when a constant Manning's roughness value is used. We recommend using DTM for modeling tsunami inundation extent with further work needed to resolve the scale at which surface roughness should be parameterized.

Description: The ultimate goal of establishing InaTEWS is to reduce as much as possible the victims due to tsunami. Since 2008, InaTEWS has been operated by BMKG and has shown its performance, proven by its ability to reliably detect and analyze earthquakes within 5 minutes, produce early warnings, and disseminate the products promptly. One of the important elements in the tsunami early warning is the availability of a pre-calculated tsunami database. The tsunami database provides the information about estimated tsunami arrival times and heights in the affected area. In InaTEWS, the pre-calculated tsunami database is integrated into a decision support system that helps operators to take decisions in issuing tsunami warnings. In 2012, this system has been equipped with a database of tsunami simulations covering the Sunda Zone. Obviously this coverage is not sufficient to account for the Eastern part of Indonesia that is also prone to tsunami. As a result that stage of the tsunami result needs to be extended. A project involving BMKG, Alfred Wegener Institute (AWI) and DMInnovation started in May 2015 to strengthen the decision support system of InaTEWS. Several workshops at BMKG were carried out to expand the scenario database in eastern Indonesia. The basis for tsunami scenario computations is the unstructured mesh finite-element numerical model TsunAWI developed by AWI. It is based on non-linier shallow water theory. The discretization scheme is based on finite elements with the mesh generation (covering the whole Indonesian region) that allows for an accurate local resolution along the coast while keeping coarse resolution in the deep ocean. The discretization of faults as a source for tsunami model was developed by Geoscience Australia / DMInnovation. The tsunami scenarios have been calculated for 13 additional source zones, on total 11949 scenarios in eastern Indonesia. The data products of all these scenarios are integrated to the decision support system TOAST developed by gempa GmbH via the Scenario Database Interface TsunDaBI. The sensitivity of the scenarios database with respect to the epicenter density and magnitude variation needed to be assessed, to test as to whether the current tsunami database is already sufficient or additional simulations are needed. In total the scenario repository was extended from 4580 to more than 16000 simulations. The extended tsunami database is expected to improve the tsunami warning bulletin in East Indonesia considerably.