http://www.oasys-research.de A selected list of Frank's publications daily 1 2006-04-27T12:09:21Z http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/KaukerKaminskiEtAl2009 The past two decades saw a steady decrease of summer Arctic sea ice extent. The 2007 value was yet considerably lower than expected from extrapolating the long-term trend. We present a quantitative analysis of this extraordinary event based on the adjoint of a coupled ocean-sea ice model. This new approach allows to efficiently assess the sensitivity of the ice-covered area in September 2007 with respect to any potential influence factor. We can trace back 86\% of the ice area reduction to only four of these factors: May and June wind conditions, September 2-meter temperature, and March ice thickness. Two thirds of the reduction are determined by factors that are already known at the end of June, suggesting a high potential for an early prediction. Citation: Kauker, F., T. Kaminski, M. Karcher, R. Giering, R. Gerdes, and M. Vossbeck (2009), Adjoint analysis of the 2007 all time Arctic sea-ice minimum, Geophys. Res. Lett., 36, L03707, doi: 10.1029/2008GL036323. No publisher reiner 2009-06-03T11:50:26Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/KaukerKoeberleEtAl2008 [1] The ability to simulate the past variability of the sea ice-ocean system is of fundamental interest for the identification of key processes and the evaluation of scenarios of future developments. To achieve this goal atmospheric surface fields are reconstructed by statistical means for the period 1900 to 1997 and applied to a coupled sea ice-ocean model of the North Atlantic/Arctic Ocean. We devised a statistical model using a redundancy analysis to reconstruct the atmospheric fields. Several sets of predictor and predictand fields are used for reconstructions on different time scales. The predictor fields are instrumental records available as gridded or station data sets of sea level pressure and surface air temperature. The predictands are surface fields from the NCAR/NCEP reanalysis. Spatial patterns are selected by maximizing predictand variance during a ``learning'' period. The reliability of these patterns is tested in a validation period. The ensemble of reconstructions is checked for robustness by mutual comparison and an ``optimal'' reconstruction is selected. Results of the simulations with the sea ice-ocean model are compared with historical sea ice extent observations for the Arctic and Nordic Seas. The results obtained with the ``optimal'' reconstruction are shown to be highly consistent with these historical data. An analysis of simulated trends of the ``early 20th century warming'' and the recent warming in the Arctic complete the manuscript. No publisher reiner 2009-03-05T13:08:16Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/inbookreference.2009-03-06.1805133058 No publisher michael 2009-03-06T13:54:18Z Inbook Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/HollowayDupontEtAl2007 As a part of the Arctic Ocean Model Intercomparison Project, results from 10 Arctic ocean/ice models are intercompared over the period 1970 through 1999. Models' monthly mean outputs are laterally integrated over two subdomains (Amerasian and Eurasian basins), then examined as functions of depth and time. Differences in such fields as averaged temperature and salinity arise from models' differences in parameterizations and numerical methods and from different domain sizes, with anomalies that develop at lower latitudes carried into the Arctic. A systematic deficiency is seen as AOMIP models tend to produce thermally stratified upper layers rather than the ``cold halocline'', suggesting missing physics perhaps related to vertical mixing or to shelf-basin exchanges. Flow fields pose a challenge for intercomparison. We introduce topostrophy, the vertical component of V x del D where V is monthly mean velocity and del D is the gradient of total depth, characterizing the tendency to follow topographic slopes. Positive topostrophy expresses a tendency for cyclonic ``rim currents''. Systematic differences of models' circulations are found to depend strongly upon assumed roles of unresolved eddies. No publisher reiner 2009-03-05T13:05:35Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/DornDethloffEtAl2007 [1] A series of sensitivity experiments using a coupled regional atmosphere-ocean-ice model of the Arctic has been conducted in order to identify the requirements needed to reproduce observed sea-ice conditions and to address uncertainties in the description of Arctic processes. The ability of the coupled model to reproduce observed summer ice retreat depends largely on a quasi-realistic ice volume at the beginning of the melting period, determined by the relationship between winter growth and summer decay of ice. While summer ice decay is strongly affected by the parameterization of the sea-ice albedo, winter ice growth depends significantly on the parameterization of lateral freezing. Reciprocal model biases due to uncertainties in the atmospheric energy fluxes can be compensated to a certain extent. However, potential underlying weaknesses of the model cannot be eliminated that way. Since lateral freezing also determines the ice concentration during winter, and thus the heat loss of the ocean and the near-surface air temperature, the model tuning possibilities are limited. A large uncertainty in the model relates to the simulation of long-wave radiation most likely as a result of overestimated cloud cover. The results suggest that uncertainties in the descriptions for Arctic clouds, snow, and sea-ice albedo, and lateral freezing and melting of sea ice, including the treatment of snow, are responsible for large deviations in the simulation of Arctic sea ice in coupled models. Improved descriptions of these processes are needed to reduce model biases and to enhance the credibility of future climate change projections. No publisher reiner 2009-03-05T13:04:19Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/HaekkinenDupontEtAl2007 [1] Observations indicate that the occurrence of dense upper-ocean water masses coincides with periods of intense deep-water formation in the Greenland Sea. This paper focuses on the upper-ocean hydrography of the area and its simulation in models. We analyze properties that reside below the summer mixed layer at 200 m and carry the winter mixing signal. The analysis employs numerical simulations from four different models, all of which are forced as specified by the Arctic Ocean Model Intercomparison Project (AOMIP). The models exhibit varying degrees of success in simulating upper-ocean properties observed in the Greenland Sea, including very dense, saline water masses in the 1950s, 1960s, and 1970s. Two of the models predict the importance of salinity in determining the maximum density in the upper waters of the central gyre. The circulation pattern of Atlantic Water was captured well by two high-resolution models as measured by temperature-salinity-den sity relationships. The simulated temporal variability of Atlantic Water properties was less satisfactory, particularly in the case of salinity. No publisher reiner 2009-03-05T14:21:22Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/articlereference.2007-04-13.9146147495 No publisher michael 2007-07-11T09:23:14Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/bookreference.2007-04-13.4435379672 No publisher michael 2007-04-13T10:56:23Z Book Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/articlereference.2007-04-13.2279724840 No publisher michael 2007-04-13T10:50:14Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/PolyakovBeszczynskaEtAl2005 This study was motivated by a strong warming signal seen in mooring-based and oceanographic survey data collected in 2004 in the Eurasian Basin of the Arctic Ocean. The source of this and earlier Arctic Ocean changes lies in interactions between polar and sub-polar basins. Evidence suggests such changes are abrupt, or pulse-like, taking the form of propagating anomalies that can be traced to higher-latitudes. For example, an anomaly found in 2004 in the eastern Eurasian Basin took ∼1.5 years to propagate from the Norwegian Sea to the Fram Strait region, and additional ∼4.5–5 years to reach the Laptev Sea slope. While the causes of the observed changes will require further investigation, our conclusions are consistent with prevailing ideas suggesting the Arctic Ocean is in transition towards a new, warmer state. No publisher reiner 2006-04-27T12:34:59Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/KaukerGerdesEtAl2005 The impact of North Atlantic Current (NAC) volume, heat, and salt transport variability onto the Nordic Seas and the Arctic Ocean is investigated using numerical hindcast and sensitivity experiments. The ocean-sea ice model reproduces observed propagation pathways and speeds of SST anomalies. Signals reaching the entrance to the Nordic Seas between Iceland and Scotland originate partly in the lower-latitude North Atlantic. Response experiments with different prescribed conditions at 50°N show that changes in the barotropic flow across 50°N have no impact on the seas north of the Greenland-Scotland Ridge because of the strong deformation of the f/H field. A temperature anomaly inserted in the upper 500 m at 50°N, on the other hand, has a widespread effect on the temperature distribution and the circulation in the high-latitude North Atlantic. NAC induced variability in the Nordic Seas and locally induced variability have similar magnitude. The local atmospheric influence and the complexity of North Atlantic-Nordic Seas advection pathways make it unlikely that detection of signal propagation in the NAC could lead to a prediction of oceanic conditions in the Nordic Seas and the Arctic Ocean with several years lead time. No publisher reiner 2006-04-27T21:37:17Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/KarcherGerdesEtAl2005 A large pool of freshwater formed of ice and runoff is hosted by the Arctic Ocean. It exits through the Canadian Archipelago and Fram Strait to enter the North Atlantic deep water production regions. Using a numerical model and observations we trace a strong freshwater release to subpolar waters in the mid-1990s. In contrast to the ice export driven 1970's ‘Great Salinity Anomaly’ its source was a large additional liquid freshwater release from the Arctic Ocean. In fact it was a consequence of a change of the Arctic Ocean's thermohaline structure in response to the very intense North Atlantic Oscillation in the early 1990s. Our results show a strong link of large-scale Arctic Ocean changes with the freshwater flux to subpolar waters. No publisher reiner 2006-04-27T12:34:51Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/GerdesHurkaEtAl2005 No publisher reiner 2006-04-27T21:55:20Z Inbook Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/GooseGerdesEtAl2004 No publisher reiner 2006-04-27T12:34:47Z Article Reference http://www.oasys-research.de/bibliographyfolder.2006-04-27.2205507759/RinkeGerdesEtAl2003 The regional coupled atmosphere-ice-ocean model HIRHAM-MOM has been developed to simulate the Arctic climate. The model has been applied for the year 1990, which was characterized by anomalous ice retreat along the eastern Arctic coasts. Many observed features of the anomalous atmospheric circulation and sea ice concentration pattern during spring to early summer are reproduced by the model. It was even able to generate the extreme summer sea ice conditions in the Eurasian Arctic and the associated high surface air temperatures. The model shows less success in simulating the large ice retreat in the Siberian Arctic in late summer. This is explained mainly by deviations in the simulated atmospheric circulations. Results from an ocean-ice-alone model confirm that the atmospheric forcing dominates the simulated ice retreat. On the other hand, a sensitivity study with the atmosphere-alone model shows the impact of the sea ice conditions on the atmospheric circulation. Only with the accurate satellite-derived sea ice data is the model able to reproduce the anomalous late summer atmospheric pressure patterns. No publisher reiner 2006-04-27T12:34:59Z Article Reference