Oliver Gutjahr

Max Planck Institute for Meteorology

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Johann Jungclaus

Max Planck Institute for Meteorology

Günther Heinemann

Universität Trier

Helmuth Haak

Max Planck Institute for Meteorology

Dian Putrasahan

Max Planck Institute for Meteorology

Nils Brüggemann

Max Planck Institute for Meteorology

Jin‐Song von Storch

Hamburg Institut (Germany)

Katja Lohmann

Max Planck Institute for Meteorology

Malcolm Roberts

Met Office

Jochem Marotzke

Max Planck Institute for Meteorology

Carolin Mehlmann

Otto-von-Guericke University Magdeburg

Cooperative Institutions

Max Planck Institute for Meteorology

127

Max Planck Society

Universität Hamburg

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

European Centre for Medium-Range Weather Forecasts

German Climate Computing Centre

Centre National de la Recherche Scientifique

NSF National Center for Atmospheric Research

ETH Zurich

Universitat Politècnica de Catalunya

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Effect of resolving ocean eddies on the transient response of global mean surface temperature to abrupt 4xCO2 forcing

AGU Fall Meeting Abstracts (2020)

Dian Putrasahan Oliver Gutjahr Helmuth Haak Johann Jungclaus Katja Lohmann

Forcing (mathematics)

Eddy

Mean radiant temperature

Transient (computer programming)

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Future projections of wind energy potentials in the arctic for the 21st century under the RCP8.5 scenario from regional climate models (Arctic-CORDEX)

Anthropocene (2023)

Mirseid Akperov А. В. Елисеев Annette Rinke И. И. Мохов В. А. Семенов

10.1016/j.ancene.2023.100402

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Impact of the horizontal resolution on the simulation of extremes in COSMO-CLM

Meteorologische Zeitschrift (2016)

Oliver Gutjahr Lukas Schefczyk Philipp Reiter Günther Heinemann

The simulation of extremes using climate models is still a challenging task.Currently, the model grid horizontal resolution of state-of-the art regional climate models (RCMs) is about 11-25 km, which may still be too coarse to represent local extremes realistically.In this study we use dynamically downscaled ERA-40 reanalysis data of the RCM COSMO-CLM at 18 km resolution, downscale it dynamically further to 4.5 km and finally to 1.3 km to investigate the impact of the horizontal resolution on extremes.Extremes are estimated as return levels for the 2, 5 and 10-year return periods using 'peaks-over-threshold' (POT) models.Daily return levels are calculated for precipitation and maximum 2 m temperature in summer as well as precipitation and 2 m minimum temperature in winter.The results show that CCLM is able to capture the spatial and temporal structure of the observed extremes, except for summer precipitation extremes.Furthermore, the spatial variability of the return levels increases with resolution.This effect is more distinct in case of temperature extremes due to a higher correlation with the better resolved orography.This dependency increases with increasing horizontal resolution.In comparison to observations, the spatial variability of temperature extremes is better simulated at a resolution of 1.3 km, but the return levels are cold-biased in summer and warm-biased in winter.Regarding precipitation, the spatial variability improves as well, although the return levels were slightly overestimated in summer by all CCLM simulations.In summary, the results indicate that an increase of the horizontal resolution of CCLM does have a significant effect on the simulation of extremes and that impact models and assessment studies may benefit from such high-resolution model output.

Horizontal resolution

Climate simulation

10.1127/metz/2016/0638

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The Irminger Sea – air-ice-ocean interactions in a 5 km coupled simulation with ICON-ESM

Oliver Gutjahr Johann Jungclaus Nils Brüggemann Helmuth Haak Jochem Marotzke

<p>Recent observations suggest that deep convection and water mass transformation in the Irminger Sea southeast of Greenland, together with overflows from the Nordic Seas, may be more important for the variability of the Atlantic meridional overturning circulation (AMOC) than the Labrador Sea. The preconditioning for and triggering of deep convection in the Irminger Sea is strongly associated with topography-induced mesoscale wind phenomena, such as Greenland tip jets, katabatic winds and marine cold air outbreaks. However, the resolution of current coupled climate models is too coarse to capture all the properties of these wind systems or to capture them at all. Here we explore the air-ice-ocean interactions induced by mesoscale wind phenomena in the Irminger Sea in a 1-year global coupled 5km simulation with ICON-ESM. The model is able to capture the complex interactions of the wind field and the ocean. We find that strong downward katabatic winds cause substantial heat loss from the Irminger Sea in addition to Greenland tip jets. The outflowing katabatic winds form narrow streaks of cold air that extend across the entire Irminger basin from southeast Greenland to Iceland. In addition, cold air outbreaks from the sea ice lead to the genesis of mesoscale cyclones, which in turn can cause Greenland tip jets before moving off to the east. All these wind phenomena cause substantial heat loss that preconditions the ocean for deep convection. If these wind systems are not resolved, the water mass transformation in the Irminger Sea could be too weak, contributing to why the Labrador Sea dominates AMOC variability in models. We conclude that resolving these mesoscale wind systems in an Earth system model could have significant implications for deep convection and water mass transformation in the Irminger Sea, and thus for AMOC variability.</p>

Katabatic wind

10.5194/egusphere-egu21-11010

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Analysis of projected hydrological behavior of catchments based on signature indices

Hydrology and earth system sciences (2012)

Markus Casper Gayane Grigoryan Oliver Gronz Oliver Gutjahr Günther Heinemann

Abstract. To precisely map the changes in hydrologic response of catchments (e.g. water balance, reactivity or extremes), we need sensitive and interpretable indicators. In this study we defined nine hydrologically meaningful signature indices: five indices were sampled on the flow duration curve, four indices were closely linked to the distribution of event runoff coefficients. We applied these signature indices to the output from a hydrologic catchment model for three different catchments located in the Nahe basin (Western Germany) to detect differences in runoff behavior resulting from different meteorological input data. The models were driven by measured and simulated (COSMO-CLM) meteorological data. It could be shown that the application of signature indices is a very sensitive tool to assess differences in simulated runoff behavior resulting from climatic data sets of different sources. Specifically, the selected signature indices allow assessing changes in water balance, vertical water distribution, reactivity, seasonality and runoff generation. These indices showed that the hydrological model is very sensitive to biases in mean and spatio-temporal distribution of precipitation and temperature because it acts as a filter for the meteorological input. Besides model calibration and model structural deficits, we found that bias correction of temperature fields and further adjustment of bias correction of precipitation fields is absolutely essential. We conclude that signature indices can act as indirect "efficiency measures" or "similarity measures" for output from regional or local climate models.

Water balance

Signature (topology)

10.5194/hess-16-409-2012

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Citations (32)

Comparison of ocean vertical mixing schemes in the Max Plank Institute Earth System Model (MPI-ESM1.2)

Oliver Gutjahr Nils Brüggemann Helmuth Haak Johann Jungclaus Dian Putrasahan

Abstract. We compare the effects of four different ocean vertical mixing schemes on the ocean mean state simulated by the Max Planck Institute Earth System Model (MPI-ESM1.2) in the framework of the Community Vertical Mixing (CVMix) library. Besides the PP and KPP scheme, we implemented the TKE scheme and a recently developed prognostic scheme for internal wave energy and its dissipation (IDEMIX) to replace the often assumed constant background diffusivity in the ocean interior. We analyse in particular the effects of IDEMIX on the ocean mean state, when combined with TKE (TKE+IDEMIX). In general, we find little sensitivity of the ocean surface, but considerable effects for the interior ocean. Overall, we cannot classify any scheme as superior, because they modify biases that vary by region or variable, but produce a similar pattern on the global scale. However, using a more realistic and energetically consistent scheme (TKE+IDEMIX) produces a more heterogeneous pattern of vertical diffusion, with lower diffusivity in deep and flat-bottom basins and elevated turbulence over rough topography. In addition, TKE+IDEMIX improves the circulation in the Nordic Seas and Fram Strait, thus reducing the warm bias of the Atlantic water (AW) layer in the Arctic Ocean to a similar extent as has been demonstrated with eddy-resolving ocean models. We conclude that although shortcomings due to model resolution determine the global-scale bias pattern, the choice of the vertical mixing scheme may play an important role for regional biases.

Ocean observations

Eddy diffusion

10.5194/gmd-2020-202

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Do sub-annual bias corrections improve the quantile mapping results for daily precipitation?

EGU General Assembly Conference Abstracts (2016)

Philipp Reiter Oliver Gutjahr Lukas Schefczyk Günther Heinemann Markus Casper

Quantile

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Spatial Feature Reconstruction of Cloud-Covered Areas in Daily MODIS Composites

Remote Sensing (2015)

Stephan Paul Sascha Willmes Oliver Gutjahr Andreas Preußer Günther Heinemann

The opacity of clouds is the main problem for optical and thermal space-borne sensors, like the Moderate-Resolution Imaging Spectroradiometer (MODIS). Especially during polar nighttime, the low thermal contrast between clouds and the underlying snow/ice results in deficiencies of the MODIS cloud mask and affected products. There are different approaches to retrieve information about frequently cloud-covered areas, which often operate with large amounts of days aggregated into single composites for a long period of time. These approaches are well suited for static-nature, slow changing surface features (e.g., fast-ice extent). However, this is not applicable to fast-changing features, like sea-ice polynyas. Therefore, we developed a spatial feature reconstruction to derive information for cloud-covered sea-ice areas based on the surrounding days weighted directly proportional with their temporal proximity to the initial day of interest. Its performance is tested based on manually-screened and artificially cloud-covered case studies of MODIS-derived polynya area data for the polynya in the Brunt Ice Shelf region of Antarctica. On average, we are able to completely restore the artificially cloud-covered test areas with a spatial correlation of 0.83 and a mean absolute spatial deviation of 21%.

Moderate-resolution imaging spectroradiometer

Cloud top

10.3390/rs70505042

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Citations (19)

Polar Lows and Their Effects on Sea Ice and the Upper Ocean in the Iceland, Greenland, and Labrador Seas

Journal of Geophysical Research Oceans (2024)

Oliver Gutjahr Carolin Mehlmann

Abstract Using two case studies, we analyze the effects of explicitly resolving polar lows in a global climate model (ICON‐Sapphire) with a high resolution of 2.5 km on the upper ocean and sea ice. We aim to understand the mechanism of how polar lows form in a global coupled model and how they interact with the upper ocean and sea ice. When polar lows form at the sea ice edge, they induce marine cold air outbreaks that lead to large heat loss from the ocean. This heat loss contributes to dense water formation in the Iceland and Greenland Seas, which replenishes the climatically important Denmark Strait Overflow Water (DSOW). The high wind speeds of polar lows open leads and polynyas in the sea ice cover, such as the Sirius Water Polynya in northeastern Greenland. Heat loss in polynyas is compensated for by the formation of new ice, and the rejected brine densifies the water on the Greenland shelf. In the Labrador Sea, polar lows intensify cold air outbreaks from the sea ice and rapidly deepen the ocean mixed layer. Resolving polar lows and kinematic features in the sea ice improves the realism of climate models, in particular the surface heat loss and the dense water formation in (sub)polar oceans.

10.1029/2023jc020258

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A case for open communication of bugs in climate models, made with ICON version 2024.01

Ulrike Proske Nils Brüggemann Jan P. Gärtner Oliver Gutjahr Helmuth Haak

Abstract. Climate models are not just numerical representations of scientific knowledge, they are also human-written software programs. As such, they contain coding mistakes, which may look mundane, but can affect the results of interconnected and complex models in unforeseen ways. These bugs are underacknowledged in the climate science community. We describe a sea ice bug in the coupled atmosphere-ocean-sea ice model ICON and its history. The bug was caused by a logical flag that was set incorrectly, such that the ocean did not experience friction from sea ice and thus the surface velocity did not slow down, especially in the presence of ocean eddies. While describing the bug and its effects, we also give an example of visual and concise bug communication. In addition, we conceptualize this bug as representing a novel species of resolution-dependent bugs. These are long-standing bugs that are discovered during the transition to high-resolution climate models due to features that are resolved at the kilometer scale. This case study serves to illustrate the value of open documentation of bugs in climate models and to encourage our community to adopt a similar approach.

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10.5194/egusphere-2024-3493

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