@article{TotzTzipermanCoumouetal.2017,
  author    = {Totz, Sonja Juliana and Tziperman, Eli and Coumou, Dim and Pfeiffer, Karl and Cohen, Judah},
  title     = {Winter precipitation forecast in the European and mediterranean regions using cluster analysis},
  series = {Geophysical research letters},
  volume    = {44},
  journal   = {Geophysical research letters},
  publisher = {American Geophysical Union},
  address   = {Washington},
  issn      = {0094-8276},
  doi       = {10.1002/2017GL075674},
  pages     = {12418 -- 12426},
  year      = {2017},
  abstract  = {The European climate is changing under global warming, and especially the Mediterranean region has been identified as a hot spot for climate change with climate models projecting a reduction in winter rainfall and a very pronounced increase in summertime heat waves. These trends are already detectable over the historic period. Hence, it is beneficial to forecast seasonal droughts well in advance so that water managers and stakeholders can prepare to mitigate deleterious impacts. We developed a new cluster-based empirical forecast method to predict precipitation anomalies in winter. This algorithm considers not only the strength but also the pattern of the precursors. We compare our algorithm with dynamic forecast models and a canonical correlation analysis-based prediction method demonstrating that our prediction method performs better in terms of time and pattern correlation in the Mediterranean and European regions.},
  language  = {en}
}
@article{KretschmerCoumouAgeletal.2018,
  author    = {Kretschmer, Marlene and Coumou, Dim and Agel, Laurie and Barlow, Mathew and Tziperman, Eli and Cohen, Judah},
  title     = {More-Persistent weak stratospheric polar vortex states linked to cold extremes},
  series = {Bulletin of the American Meteorological Society},
  volume    = {99},
  journal   = {Bulletin of the American Meteorological Society},
  number    = {1},
  publisher = {American Meteorological Soc.},
  address   = {Boston},
  issn      = {0003-0007},
  doi       = {10.1175/BAMS-D-16-0259.1},
  pages     = {49 -- 60},
  year      = {2018},
  abstract  = {The extratropical stratosphere in boreal winter is characterized by a strong circumpolar westerly jet, confining the coldest temperatures at high latitudes. The jet, referred to as the stratospheric polar vortex, is predominantly zonal and centered around the pole; however, it does exhibit large variability in wind speed and location. Previous studies showed that a weak stratospheric polar vortex can lead to cold-air outbreaks in the midlatitudes, but the exact relationships and mechanisms are unclear. Particularly, it is unclear whether stratospheric variability has contributed to the observed anomalous cooling trends in midlatitude Eurasia. Using hierarchical clustering, we show that over the last 37 years, the frequency of weak vortex states in mid- to late winter (January and February) has increased, which was accompanied by subsequent cold extremes in midlatitude Eurasia. For this region, 60\% of the observed cooling in the era of Arctic amplification, that is, since 1990, can be explained by the increased frequency of weak stratospheric polar vortex states, a number that increases to almost 80\% when El Nino-Southern Oscillation (ENSO) variability is included as well.},
  language  = {en}
}