Upper‐level winds over eastern North America: A regional jet stream climatology

Although it is well known that jet streams play a vital role in everyday weather and long-term climate variability, very few regional climatological studies on jet streams exist to date. Using the high-resolution North American Regional Reanalysis (NARR), this study aims to create a preliminary jet stream, and more specifically a jet core, database for a relatively narrow region in eastern North America covering the period 1979 through 2016 inclusive. We use regional maxima in the smoothed horizontal wind field to locate both the latitudinal and vertical (pressure) location of jet cores along specific meridians. Results show that the median pressure level of all jet cores in the region of interest is 250hPa and that two is the most likely number of distinct jet cores to occur along a given meridian at any given time. The jet cores are categorized into three bins based on their latitude in an attempt to capture the characteristics of the different tropopause-level jet types. However, as the vertical and horizontal extents of the jet streams were not analysed, we cannot conclude for certain that each of the geographical bins corresponds to specific jet types. Statistically significant negative trends in the seasonal and overall mean pressure of the jet cores, implying an increased height, supports the findings of previous studies. Our analysis of NARR winds shows that jet core wind speeds increased in the region studied. This may be related to the increased height of jet cores through the thermal wind equation as well as increased baroclinicity across sections of the region studied. Jet core latitude and meridional circulation index (MCI) trends were generally negligible and not statistically significant. An absence of significant increases in |MCI| diverges from expectations and some theories of what to expect with Arctic amplification in a warming world.