Hydroclimatic and circulation anomalies associated with the North Atlantic subtropical high

Hydroclimatic and circulation variability in regions around the Atlantic sector are linked to the intensity, location, and areal extent of the North Atlantic subtropical high (STH). Few analyses focus directly on the influence of the STH on climatic variability. Using sea level pressure (SLP) data from the NCEP/NCAR Reanalysis dataset, a time series of the STH was produced using principal components analysis (PCA) to describe the temporal variability of the STH from January 1948 to December 2001. A simple area average of SLP across the PCA domain is shown to describe the same phenomena (the dominant mode of the STH variability) with r2=0.828. Given the ability of a simple areal-average to reproduce PCA results, the areally-averaged subtropical North Atlantic SLP (STHTS) is used to define STH variability in all of the analyses and is correlated with global moisture and circulation variables. Spectral analyses were performed on STHTS to detect cyclic behavior for all months and for each of the four seasons: winter (DJF), spring (MAM), summer (JJA), and autumn (SON). Results indicate a 4.5 year peak for the all-month STHTS, while the seasonal power spectra indicate significant peaks around 2.6-2.8 years for DJF, 3.6-3.8 years for MAM, 2.8-3.0 and approximately 7 years for JJA, but no significant peaks at the 90 percent confidence level during SON. Three-month seasonal means were calculated from January 1948 to December 2001 using hydroclimatic and circulation variables and correlated with STHTS. Effects of the STH\u27s variability around the Atlantic sector and for specific regions (Brazil, Sahel/Guinea, East Africa, North America, and the Great Plains low-level jet region) are described. Results are generally consistent with published research but with some interesting exceptions and implications. Increased (decreased) precipitation and atmospheric moisture content were found throughout much of the year over Brazil (Sahel/Guinea), and during DJF over East Africa with a more intense STH. Over North America and the Great Plains LLJ region, the large spatial scale for which data were available, the heterogeneity of the terrain and extremes of climate from the warm to cool seasons prevent a consistent analysis, but results for other regions are consistent