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

Abstract

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 250 hPa 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.

Seasonal and regional signatures of ENSO in upper tropospheric jet characteristics from reanalyses

“…Changes in different jet characteristics (latitude, altitude, and wind speed) with ENSO may not show the same relationships in different regions/seasons but may be linked by the relationships between those characteristics. As shown in previous work (e.g., Lorenz and DeWeaver 2007;Manney and Hegglin 2018;Melamed-Turkish et al 2018; also see Fig. S6 in the online supplemental material), the altitude of both subtropical and polar jets nearly always decreases with a poleward shift of that jet.…”

Changing State of the Climate System

“…Despite some regional differences (Woollings et al, 2014;Norris et al, 2016;J. Wang et al, 2017a;Xue and Zhang, 2017;Ma and Zhang, 2018;Melamed-Turkish et al, 2018), overall poleward deflection of storm tracks in boreal winter over both the North Atlantic and the North Pacific was identified during 1979-2010 (Tilinina et al, 2013). Over the SH extra-tropics there is a similarly robust poleward shift in the polar jet since 1979 (Pena-Ortiz et al, 2013;Manney and Hegglin, 2018;WMO, 2018), although after 2000 the December-January-February (DJF) tendency to poleward shift of the SH jet stream position ceased (Banerjee et al, 2020).…”

jsmetrics v0.2.0: a Python package for metrics and algorithms used to identify or characterise atmospheric jet streams

“…However, by isolating lower-level winds, these methods may miss aspects of jet streams whose eddy-driven components do not extend throughout the atmospheric column within the method's given time window. They also do not capture behaviour near the level of maximum wind speed or the presence of multiple jet streams (Melamed-Turkish et al, 2018;Manney et al, 2021).…”