Synoptic variability in the Arctic summer

Recent declines in the extent of perennial sea ice in the Arctic have been widely documented and related to trends in atmospheric conditions. Anticyclonic circulation anomalies over the central Arctic Ocean in summer have been shown be present in recent years, and are thought to influence the ice pack through an enhanced downwelling solar flux from decreased cloudiness, an increase in poleward atmospheric energy transport, and by means of Ekman drift in marginal seas. These circulation trends suggest changes in the nature of the summer maximum in cyclonic activity over the central Arctic Ocean, a principal feature of the northern high latitude annual cycle. Recent Arctic synoptic activity is examined here using the Modern Era Retrospective-analysis for Research and Applications (MERRA). The MERRA collection was made using the Data Assimilation System component of the NASA Goddard Earth Observing System, and covers the modern satellite era from 1979 to the present. Comparison of MERRA sea level pressure values with Arctic station observations indicate close agreement. The one-hourly, high spatial resolution fields from MERRA are used to assess cyclonic and anticyclonic variability using band-pass filtering and a tracking algorithm. The analysis contrasts the time 1979-2000 with the last five years 2005-2009 in which the September ice extent has been at least 17 percent below the average for the earlier period. Some questions of interest addressed by this study are as follows.

• How do MERRA fields compare to other reanalyses in their depictions of Arctic atmospheric variability?
• What are the mean characteristics of Arctic stormtracks over the period 1979-2000?
• How have general characteristics of cyclogenesis, cyclolysis, cyclone frequency, and storm track path changed in the recent five year period, and are these changes consistent with previously described trends in Arctic general circulation?