Doctoral dissertation explaining mechanisms of high latitude climate variability

Dr. Svetlana Anatolievna Sorokina has Annual SAT anomalies for 2000 to 2009 compared to the norm for that region from 1951 to 1980. Credit: NASA, image by R. Simmon, based on GISS surface temperature analysis data including ship and buoy data from the Hadley Centre, http://earthobservatory.nasa.gov.Annual SAT anomalies for 2000 to 2009 compared to the norm for that region from 1951 to 1980. Credit: NASA, image by R. Simmon, based on GISS surface temperature analysis data including ship and buoy data from the Hadley Centre, http://earthobservatory.nasa.gov.defended her degree of philosophiae doctor (PhD) entitled “Certain aspects of high-latitude climate variability at the University of Bergen. Her doctoral study has been completed at the Nansen Centre under research projects supported by the Research Council of Norway and Centre for Climate Dynamics (SKD).

Significant changes in the climate have occurred during the twentieth century worldwide, but the largest changes have been observed at northern high latitudes (ACIA 2005, Serreze and Francis 2006, IPCC 2007). An enhanced high-latitude near-surface warming (up to 2.5 °C per decade) of the dubbed as “Arctic amplification”, has been particularly evident during the most recent decades (IPCC 2007, ACIA 2005), and possibly unprecedented during the last 2000 years (Kaufman et al. 2010). The mechanisms behind the occurring changes are still a matter of debates.

 

The doctoral study aims to gain a more detailed knowledge on principal processes that determine the high-latitude region’s climate and addresses uncertainty issues in available observational data. The study constrains of four papers:

  1. The first paper investigates the meridional energy transport between the middle and high latitudes, which is one of the most important factors for Arctic climate formation. Dr. Sorokina shows a relatively good agreement between the estimations of the meridional energy transport from “clean” observational data and reanalysis product. The author concludes however, that reanalysis data are, by construction, more suitable for the estimation of the meridional energy exchange.
  2. The second paper is dedicated to the climatological aspects of the near-surface energy exchange processes, which have been suggested as particularly important factors for the increased Arctic surface warming (ACIA 2005), but relatively little highlighted in the climatological studies. The paper provides an observational reference for potential evaluation of parametrizations of the near-surface energy exchange processes in climate models.
  3. The third paper investigates the robustness of the temperature trends throughout the Arctic atmosphere, which has been a controversial topic. The study concludes that changes in the quality and quantity of observations introduce a potential challenge in long-term trend detection and attribution of the possible responsible mechanisms.
  4. The fourth paper is focused on the understanding of the observed Arctic/mid-latitude linkages, which has been one of the most debatable questions in the scientific community. Namely, the paper investigates the nature of the recent cold Eurasian winters that have been presumed to be a resultant response to the diminishing Arctic sea ice cover. The study highlights a complex two-way interaction that includes significant contribution from the internal atmospheric variability. Dr. Sorokina concludes that the nature of the recent cold Eurasian winters is likely more complicated than a pure atmospheric response to the reduced Arctic sea ice.

The doctoral evaluation committee was lead by the 1st opponent Professor Dr. Paul Kushner, University of Toronto, Canada, the 2nd opponent Dr. Jørn Kristiansen, Meteorological Institute, Oslo, and the committee member Associate professor Dr. Jan Asle Olseth, Geophysical Institute, University of Bergen. The dissertation took place at the Nansen Center on Friday 13. June and was lead by Professor Truls Johannessen, University of Bergen.

 

The PhD thesis Certain aspects of high-latitude climate variability is based on the following three published and one submitted publications:

Paper I: Sorokina, S.A. and I.N. Esau, 2011: Meridional energy flux in the Arctic from data of the IGRA. Izvestiya, Atmospheric and Oceanic Physics, 47 (5), 572–583, doi:10.1134/S0001433811050112.

Paper II: Esau, I.N. and S.A. Sorokina, 2010: Climatology of the Arctic planetary boundary layer. Atmospheric turbulence, meteorological modeling and aerodynamics. Lang, P.R. and F.S. Lombargo (eds.), Nova Science Publishers, pp. 3–58.

Paper III: Alexeev, V.A., I.N. Esau, I.V Polyakov, S.J. Byam, and S.A. Sorokina, 2012: Vertical structure of recent Arctic warming from observed data and reanalysis products. Climatic Change, 111 (2), 215–239, doi:10.1007/s10584-011-0192-8.

Paper IV: Sorokina S.A, J.J. Wettstein, C. Li , and N.G. Kvamstø, 2014: Two-way coupling between the Barents Sea ice and anomalous Eurasian winters. Manuscript (in prep. for submission to J. Climate).

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