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
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