Modulation of Atmospheric Rivers by the Arctic Stratospheric Polar Vortex

Abstract

Variability in atmospheric river (AR) frequency can drive hydrometeorological extremes with broad societal impacts. Mitigating the impacts of increased or decreased AR frequency requires forewarning weeks to months ahead. A key driver of Northern Hemisphere wintertime mid‐latitude subseasonal‐to‐seasonal climate variability is the stratospheric polar vortex. Here, we quantify AR frequency, landfall, genesis, and termination depending on the strength of the lower stratospheric polar vortex. We find large differences between weak and strong vortex states consistent with a latitudinal shift of the eddy‐driven jet, with the greatest differences over the British Isles, Scandinavia, and Iberia. Significant differences are also found for the Pacific Northwest of North America. Most of the seasonal‐scale stratospheric modulation of precipitation over Europe is explained by modulation of ARs. Our results provide potentially useful statistics for extended‐range prediction, and highlight the importance of ARs in bringing about the precipitation response to anomalous vortex states.

Atmospheric River Variability Over the Last Millennium Driven by Annular Modes

“…Using the LME, we have characterized how ARs have responded to extratropical variability (both natural and anthropogenically forced) over the last millennium. Prior investigations into the relationship between ARs and extratropical variability have focused almost exclusively on the regional role of (a) northern extratropical variability on European and North American ARs (e.g., Brands et al., 2017; Guan et al., 2013; Lavers & Villarini, 2013; Lee et al., 2022; Zavadoff & Kirtman, 2020) and (b) southern extratropical variability on Australian and Antarctic ARs (e.g., Meneghini et al., 2007; Pohl et al., 2021; Reid et al., 2022; Wille et al., 2021). We add to these regional studies by providing new perspective on the global role of the NAM and SAM on ARs: mean north–south displacements in zonal winds induced by the annular modes potentially comprise the primary driver of AR variability, with positive (negative) phases of the annular modes intensifying (weakening) and weakening (intensifying) ARs over the subpolar and subtropical latitudes, respectively.…”

“…The relationship between ARs and extratropical variability, however, requires further understanding, despite ARs being features of the extratropical atmosphere. Although several studies have examined the regional role of (a) northern extratropical variability on ARs over Europe and North America (e.g., Brands et al., 2017; Guan et al., 2013; Lavers & Villarini, 2013; Lee et al., 2022; Zavadoff & Kirtman, 2020) and (b) southern extratropical variability on ARs over Australia and Antarctica (e.g., Meneghini et al., 2007; Pohl et al., 2021; Reid et al., 2022; Wille et al., 2021), respectively, the global relationship between ARs and extratropical variability is not well known. In particular, the global role of the dominant modes of extratropical variability—known as annular modes due to their zonal symmetry—on ARs has not been investigated.…”

Global Application of the Atmospheric River Scale

“…In this regard, interannual variability is most notable with AR 4 and AR 5 in coastal/land areas in the extratropics, where coefficients of variation are around 0.15 and 0.3, respectively (Figures 5d and 5e 2020) could be related to discrepancies between "permissive" and "restrictive" methods, as they also postulated. Besides ENSO, other large-scale conditions in the ocean-atmosphere system, such as the Pacific Decadal Oscillation and stratospheric polar vortex variability, affect AR frequencies (Gershunov et al, 2017;Lee et al, 2022), compounding the relationship between interannual AR activity anomaly and ENSO. Despite the difference in the magnitude of the AR frequency values (a quotient of ∼1.5-2.5 depending on the region and AR rank; third group of numbers near the right of each panel), AR frequencies based on the two methods are temporally highly correlated (r > 0.8 in most cases; second group of numbers near the right of each panel).…”

Influence of Volcanic Activity on Weather and Climate Changes

“…It depends on where the ashes send the emissions into the atmosphere. Emissions can reach the Polar vortex, and the disturbance in the weather will follow all the same latitudes and different longitudes where the vortex went [23].…”