Synoptic Climatology of Lake El’gygytgyn
In support of paleoclimate work being done at Lake El'gygytgyn an analysis of the synoptic climatology of Lake El'gygytgyn for the period 1960 to 2009 using a combination of global reanalysis and in-situ observations will be completed. This will result in an improved understanding of the relationship between near surface climate (temperature and precipitation) and changes in synoptic circulation. Analysis of any trends in temperature and precipitation over this period will also be completed, with any significant trends being attributed to changes in the frequency of occurrence of different synoptic patterns or to changes in the mean weather associated with given synoptic patterns.
The method of self-organizing maps (SOMs) described by Kohonen (2001) has proven quite useful in the construction of objective synoptic climatologies (e.g. Hewitson and Crane 2002 Cassano et al. 2006, 2007). For this project we will apply the SOM technique to the 40+ year European Centre for Medium Range Weather Forecasts (ECMWF) reanalysis (ERA40) and the National Center for Environmental Prediction (NCEP) / National Center for Atmospheric Research (NCAR) reanalysis (NNR). The synoptic climatology will be based on sea level pressure from both reanalyses. Using the SOM technique we will identify the primary 35 weather patterns that control the weather and climate of the Lake El'gygytgyn region. The frequency of occurrence of these weather patterns will be determined based on the reanalysis data for seasonal and annual time periods. We will also identify changes in the frequency of these weather patterns over the study period (from 1958-present). Average temperature and precipitation will be calculated for each of the weather patterns, using both the reanalysis data and available in-situ observations (which will be provided by collaborators at the University of Alaska – Fairbanks). Changes in the mean temperature and precipitation for each pattern over the period of analysis will be determined. As shown in Cassano et al. (2007) the combination of information on changes in synoptic weather pattern frequency and changes in mean atmospheric state for each weather pattern will allow for partitioning of the observed trends into dynamics (frequency change) and thermodynamic (changes in mean state) components. The results of this synoptic climatology analysis will provide a summary of the atmospheric circulation controls on Lake El'gygytgyn weather and climate.