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

Transcript

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
   

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2. Background: ZW1 and ZW3
   van Loon & Jenne. 1972. J Geophys Res, 77, 992--1003
   

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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…
   

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4. Take v-wind
   @ 55°S
   

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5. Take v-wind
   @ 55°S
   

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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
   

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7. Results: Spatial characteristics
   streamfunction zonal
   anomaly
   streamfunction temporal
   anomaly
   Mean circulation for data times where PWI > 90th percentile
   

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8. Results: ZW3 rules
   Time-mean Fourier line
   spectrum, 55°S
   

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9. Results: Temporal characteristics
   Monthly totals, 1979-2014 Individual seasonal totals
   Distribution of data times where PWI > 90th percentile
   

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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
    

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11. Precipitation
    •  General
    wet/dry
    ZW3 pattern
    •  Significant
    topography:
    –  NZ
    –  Patagonia
    –  West
    Antarctica
    

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12. Surface
    temperature
    •  Widespread
    Antarctic
    warmth
    •  West
    Antarctic
    warming:
    PSA or zonal
    waves?
    

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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
    

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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
    

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