Reanalysis Reveals a Possible Wave Pattern in 250hPa Meridional Wind Anomaly Since 1997

We found unusual transient wave-like patterns in the June-August 250hPa meridional wind anomaly in a band that spans 50-60 degrees north latitude. This pattern is revealed as westward propagation of the meridional wind anomaly from one northern summer to the next, starting around the year 1997. If associated with a real physical phenomenon, this pattern is quite remarkable in that it survives the major change in the basic state flow that occurs due to the seasonal cycle. There is no evidence of the wave prior to 1997, when the anomaly patterns are more stationary. The westward propagation persists to the present. This apparent wave is most prominent in the MERRA reanalysis but it also appears in ERA-interim, CFSR, JRA-55 and surprisingly, even in 20th Century Reanalysis, which is only initialized with observed sea level pressure and sea surface temperature. It is possible that the wave is a random event and tests are currently underway to test the statistical significance of the pattern. We are also in the process of isolating possible lower atmospheric and surface weather links. For example, the wave magnitude occasionally intensifies results in stationary Rossby wave events linked to heat waves (e.g. the 2003 European heat wave and the 2010 Russian heat wave)