Diagnosing Southern Hemisphere planetary wave activity and its influence on regional climate variability

Diagnosing Southern Hemisphere planetary wave activity and its influence on regional climate variability

This paper was presented at the AMOS National Conference, Brisbane Convention and Exhibition Centre, Brisbane, Queensland.

A more detailed account of the work can be found at Authorea: https://www.authorea.com/users/5641/articles/12197/_show_article

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Damien Irving

July 17, 2015
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  1. Damien Irving & Ian Simmonds AMOS Conference, Brisbane 2015 A

    novel approach to diagnosing Southern Hemisphere planetary wave activity and its influence on regional climate variability
  2. Background: ZW1 and ZW3 van Loon & Jenne. 1972. J

    Geophys Res, 77, 992--1003
  3. Background: Previous studies •  Stationary pattern (grid points, EOF) – 

    Problems: •  Seasonal migration •  Out-of-phase patterns •  Fourier transform –  Idea: represent any signal as sum of sinusoids –  Improvement: not stationary –  Problems: •  Assumes constant amplitude •  Patterns don’t always extend around entire hemisphere…
  4. Take v-wind @ 55°S

  5. Take v-wind @ 55°S

  6. New method: Wave envelope •  Planetary Wave Index (PWI) 1. 

    Take ERA-Interim 500 hPa v-wind •  30-day running mean, 1979-2014 2.  For each data time: •  Calculate spatial wave envelope map •  Take meridional max (40-70S) then zonal median •  Threshold: PWI > 90th percentile –  Vast majority show ZW1/ZW3 pattern •  Wavy hemispheric flow -> mixed ZW1/ZW3 –  Proxy for planetary wave activity
  7. Results: Spatial characteristics streamfunction zonal anomaly streamfunction temporal anomaly Mean

    circulation for data times where PWI > 90th percentile
  8. Results: ZW3 rules Time-mean Fourier line spectrum, 55°S

  9. Results: Temporal characteristics Monthly totals, 1979-2014 Individual seasonal totals Distribution

    of data times where PWI > 90th percentile
  10. Sea ice •  Old news: –  ABS, Weddell Sea • 

    New news: –  King Haakon VII Sea •  Conflicting –  D’Urville Sea Raphael. 2014. Geophys Res Lett, 41, 5037-5045
  11. Precipitation •  General wet/dry ZW3 pattern •  Significant topography: – 

    NZ –  Patagonia –  West Antarctica
  12. Surface temperature •  Widespread Antarctic warmth •  West Antarctic warming:

    PSA or zonal waves?
  13. Conclusions •  Wave envelope is a useful tool for identifying

    quasi-stationary patterns •  Defining feature of highly meridional hemispheric states is an enhancement of the ZW3 component •  May offer new insights into SH climate variability –  Antarctic temperature –  Mid-latitude precipitation
  14. Irving D, Simmonds I (in press). A novel approach to

    diagnosing Southern Hemisphere planetary wave activity and its influence on regional climate variability. Journal of Climate. doi:10.1175/JCLI-D-15-0287.1 Preprint: https://www.authorea.com/users/5641/ articles/12197/_show_article