Variability of Northern Hemisphere terrestrial snow: Self-organizing maps and the Madden-Julian Oscillation

In efforts to understand and quantify the rapidly changing Arctic climate, recent research has focused on the importance of intraseasonal variability of key parameters within this region. For example, Arctic sea ice concentration had been found to vary by phase of the Madden-Julian Oscillation (MJO) in both summer and winter, driven largely by variability in upper- and lower-tropospheric circulation and surface air temperature. Given that Northern Hemisphere terrestrial snow cover extent (SCE) frequently responds to similar atmospheric variables, it seems reasonable to expect that SCE, too, may have an intraseasonal connection to the MJO. In this study, daily changes in SCE, snow depth, snow mass, and snow water equivalent, all taken from cutting-edge reanalysis datasets including the ERA-40 Interim, NASA-MERRA, NCEP/DOE II, and Japanese JAXA reanalyses, were examined for variability by phase of the MJO (as determined by the Wheeler and Hendon Real-time Multivariate MJO index). In addition to defining MJO phase using the Wheeler and Hendon index, Self Organizing Maps (SOMs), trained by outgoing longwave radiation fields, were also utilized to explore the robustness of this tropical-high latitude connection. Composite anomalies of these snow variables by MJO phase were then compared to composite anomalies of mid tropospheric circulation and surface air temperature. Multiple snow variables from multiple reanalysis products were chosen to fully explore variability on the intraseasonal time scale. Furthermore, because snow variables have “memory”, in that snow that falls and accumulates during one MJO phase may remain for several subsequent MJO phases, it was important to examine snow fields from multiple data records. Results of these experiments will be presented at the meeting.