@article{Ibebuchi2023,
  author    = {Ibebuchi, Chibuike Chiedozie},
  title     = {On the representation of atmospheric circulation modes in regional climate models over Western Europe},
  series = {International Journal of Climatology},
  volume    = {43},
  journal   = {International Journal of Climatology},
  number    = {1},
  doi       = {10.1002/joc.7807},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312424},
  pages     = {668 -- 682},
  year      = {2023},
  abstract  = {Atmospheric circulation is a key driver of climate variability, and the representation of atmospheric circulation modes in regional climate models (RCMs) can enhance the credibility of regional climate projections. This study examines the representation of large-scale atmospheric circulation modes in Coupled Model Inter-comparison Project phase 5 RCMs once driven by ERA-Interim, and by two general circulation models (GCMs). The study region is Western Europe and the circulation modes are classified using the Promax rotated T-mode principal component analysis. The results indicate that the RCMs can replicate the classified atmospheric modes as obtained from ERA5 reanalysis, though with biases dependent on the data providing the lateral boundary condition and the choice of RCM. When the boundary condition is provided by ERA-Interim that is more consistent with observations, the simulated map types and the associating time series match well with their counterparts from ERA5. Further, on average, the multi-model ensemble mean of the analysed RCMs, driven by ERA-Interim, indicated a slight improvement in the representation of the modes obtained from ERA5. Conversely, when the RCMs are driven by the GCMs that are models without assimilation of observational data, the representation of the atmospheric modes, as obtained from ERA5, is relatively less accurate compared to when the RCMs are driven by ERA-Interim. This suggests that the biases stem from the GCMs. On average, the representation of the modes was not improved in the multi-model ensemble mean of the five analysed RCMs driven by either of the GCMs. However, when the best-performed RCMs were selected on average the ensemble mean indicated a slight improvement. Moreover, the presence of the North Atlantic Oscillation (NAO) in the simulated modes depends also on the lateral boundary conditions. The relationship between the modes and the NAO was replicated only when the RCMs were driven by reanalysis. The results indicate that the forcing model is the main factor in reproducing the atmospheric circulation.},
  language  = {en}
}
@article{Ibebuchi2022,
  author    = {Ibebuchi, Chibuike Chiedozie},
  title     = {Patterns of atmospheric circulation in Western Europe linked to heavy rainfall in Germany: preliminary analysis into the 2021 heavy rainfall episode},
  series = {Theoretical and Applied Climatology},
  volume    = {148},
  journal   = {Theoretical and Applied Climatology},
  number    = {1-2},
  issn      = {0177-798X},
  doi       = {10.1007/s00704-022-03945-5},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-324100},
  pages     = {269-283},
  year      = {2022},
  abstract  = {The July 2021 heavy rainfall episode in parts of Western Europe caused devastating floods, specifically in Germany. This study examines circulation types (CTs) linked to extreme precipitation in Germany. It was investigated if the classified CTs can highlight the anomaly in synoptic patterns that contributed to the unusual July 2021 heavy rainfall in Germany. The North Atlantic Oscillation was found to be the major climatic mode related to the seasonal and inter-annual variations of most of the classified CTs. On average, wet (dry) conditions in large parts of Germany can be linked to westerly (northerly) moisture fluxes. During spring and summer seasons, the mid-latitude cyclone when located over the North Sea disrupts onshore moisture transport from the North Atlantic Ocean by westerlies driven by the North Atlantic subtropical anticyclone. The CT found to have the highest probability of being associated with above-average rainfall in large part of Germany features (i) enhancement and northward track of the cyclonic system over the Mediterranean; (ii) northward track of the North Atlantic anticyclone, further displacing poleward, the mid-latitude cyclone over the North Sea, enabling band of westerly moisture fluxes to penetrate Germany; (iii) cyclonic system over the Baltic Sea coupled with northeast fluxes of moisture to Germany; (iv) and unstable atmospheric conditions over Germany. In 2021, a spike was detected in the amplitude and frequency of occurrence of the aforementioned wet CT suggesting that in addition to the nearly stationary cut-off low over central Europe, during the July flood episode, anomalies in the CT contributed to the heavy rainfall event.},
  language  = {en}
}