A Northern Hemispheric Wave Train Associated with Fluctuations in Bermuda High during Boreal Summer

The processes that lead to the spatial and temporal evolution of the Bermuda High during July and August (JA) are investigated using linear regression analysis. The analysis is based on a Bermuda high index (BHI): the difference in normalized sea-level pressure (SLP) between Bermuda (40^oN, 60^oW) and New Orleans (30^oN 90^oW). Negative values of BHI indicate a westward expansion of the Bermuda High relative to its climatological-mean location, while positive values indicate contraction. Linear regression of the 500 hPa geopotential height based on the BHI reveals the existence of a Rossby wave train that extends zonally from the western-north Pacific to the eastern-north Atlantic. The troughs and ridges associated with this wave train are spatially collocated with the climatological-mean jet stream, indicating that the jet serves as their waveguide. The robustness of this pattern is verified through the use of empirical orthogonal teleconnections (EOTs). A leading EOT pattern is identified to be well correlated with the BHI, which is -0.54 and explains 4.1% of the JA 500 hPa height variance. The corresponding spatial pattern is identical to the regression maps based on the BHI and shows an active center over southeastern United States, where the anomalies in SLP associated with the BHI are the strongest. Based on these results, it is hypothesized that the EOT is a mode of natural variability. The pattern may be responsible for fluctuations in the Bermuda High during JA and may explain the occurrence of a midsummer drought in the southeastern US.