EGU2020-3762
https://doi.org/10.5194/egusphere-egu2020-3762
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Intraseasonal Transitions of the Wintertime Pacific Jet Stream

Maria Madsen and Jonathan Martin
Maria Madsen and Jonathan Martin
  • University of Wisconsin-Madison, Atmospheric and Oceanic Sciences, United States of America (mmmadsen@wisc.edu)

The deficiency in predictability at subseasonal-to-seasonal timescales, as compared to prediction at conventional weather prediction timescales, is significant. Intraseasonal variability of atmospheric features like the jet stream, occurring within this gap, lead to extreme weather events that present considerable hazards to society. As jets are an important feature at the interface of the large-scale general circulation and the life cycle of individual weather systems, there is strong incentive to more comprehensively understand their variability.

The wintertime Pacific jet manifests its intraseasonal variability in two predominant modes: a zonal extension or retraction and a meridional shift by as much as 20° of the jet exit region. These two leading modes are associated with basin-scale anomalies in the Pacific that directly impact weather in Hawaii and continental North America. Although recent work has demonstrated the impact intramodal changes of the Pacific jet have on large-scale structure, sensible weather phenomena, and forecast skill in and around the vast North Pacific Basin, the transitions between the leading modes have hardly been considered and, therefore, are poorly understood. Consequently, this work examines the nature and predictability of transitions between modes of wintertime Pacific jet variability as well as their associated synoptic environments.

We apply two distinct but complementary statistical analyses to 70 cold seasons (NDJFM 1948/49-2017/18) of daily 250-hPa zonal winds from the NCEP/NCAR Reanalysis to investigate such transitions. Empirical orthogonal analysis (EOF)/principal component (PC) analysis is used to depict the state of the daily Pacific jet as a point in a two dimensional phase space defined by the two leading modes.  Supporting this technique is a self-organizing maps (SOMs) analysis that identifies non-orthogonal, synoptically recurring patterns of the Pacific jet. Together, these analyses show that there are, in fact, preferred transitions between these leading modes of variability. Composite and individual case analyses of preferred transition evolutions provides new insight into the synoptic-scale environments that drive Pacific jet variability.

How to cite: Madsen, M. and Martin, J.: Intraseasonal Transitions of the Wintertime Pacific Jet Stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3762, https://doi.org/10.5194/egusphere-egu2020-3762, 2020

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Presentation version 1 – uploaded on 06 May 2020
  • CC1: Comment on EGU2020-3762, Erica Madonna, 07 May 2020

    Dear Maria,

    very interesting work and results.

    I was wondering if you have also looked at the persistence of your 12 North Pacific jet configurations. Are some of them more persistent than others?

    Thanks a lot,
    Erica

    • AC1: Reply to CC1, Maria Madsen, 28 May 2020

      Dear Erica,

      I have breifly looked at the persistence of the 12 regimes, and there are differences between them. Node 4 (extension) is the most persistent, and nodes 9 and 10 (retraction/poleward deflection) are also slightly more persistent than the others. Som node 12 was the least persistent of the nodes. 

      Thank you,

      Maria