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Forcing of Kelvin Waves over South America

Forcing of Kelvin Waves over South America. Brant Liebmann, George Kiladis, Leila Carvalho, Carolina Vera, Charles Jones, Ileana Bladé, Dave Allured. We wish to thank the following agencies for providing the data sets used in this study: Agência Nacional de Águas (Brasil)

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Forcing of Kelvin Waves over South America

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  1. Forcing of Kelvin Waves over South America Brant Liebmann, George Kiladis, Leila Carvalho, Carolina Vera, Charles Jones, Ileana Bladé, Dave Allured

  2. We wish to thank the following agencies for providing the data sets used in this study: Agência Nacional de Águas (Brasil) Agência Nacional Energia Elétrica (Brasil) British Atmospheric Data Centre - NASA Langley U.T.E. Uruguay C.T.M. Salto Grande NOAA (NESDIS, NCEP) Servicio Meteorologico Nacional (Argentina, Paraguay, Uruguay) FUNCEME (Ceará, Brasil) U.S. National Climatic Data Center IAPAR - SIMEPAR (Paraná, Brasil) DAEE (São Paulo, Brasil) Minesterio del Ambiente y los Recursos Naturales (Venezuela) Meteorogische Dienst Suriname METEO-France ASANA (Bolivia)

  3. Gill 1982 (Matsuno 1966)

  4. Kelvin Filter Wheeler and Kiladis 1999

  5. Variance of Kelvin-filtered OLR March May January - May 1979-2001

  6. Lead and Lag Regressions Base point: Kelvin-filtered OLR at 60W, Eq. Fields: 30-day high-pass filtered OLR, 200 mb winds and stream function

  7. The dates are then separated by additional criteria before compositing: Dates are found with a 1 standard deviation negative OLR anomalies at 60W, Eq. “Pacific” cases: 3 days before key date Kelvin-filtered OLR more than 8 Wm-2 below mean at 95W, 2.5N “South America” cases: 3 days before key date, 30-day high- pass filtered OLR more than 6 Wm-2 below mean at 60W, 20S. 56 Pacific cases 60 South America cases 30 common cases (77 neither)

  8. Pacific events Base point: Kelvin-filtered OLR, 1 STD anomaly (plus constraint at 95W, 2.5N) Fields: 30-day high-pass OLR 200 mb wind and streamfunction Wm-2

  9. Pacific events Base point: Kelvin-filtered OLR, 1 STD anomaly (plus constraint at 95W, 2.5N) Fields: 30-day high-pass OLR 200 mb wind and streamfunction Wm-2

  10. Fields lead key point by 3 days 200 mb and OLR 850 mb and rain Fields: 30-day high-pass 200 Contours and vectors are twice those at 850 Base point: Kelvin-filtered OLR (plus constraint at 95W, 2.5N)

  11. Fields lead key point by 1 day 200 mb and OLR 850 mb and rain Fields: 30-day high-pass 200 Contours and vectors are twice those at 850 Base point: Kelvin-filtered OLR (plus constraint at 95W, 2.5N)

  12. Fields lag key point by 1 day 200 mb and OLR 850 mb and rain Fields: 30-day high-pass 200 Contours and vectors are twice those at 850 Base point: Kelvin-filtered OLR (plus constraint at 95W, 2.5N)

  13. Contrast with “South America” example (note different latitude range) 30-day High-pass OLR, 200 mb wind and stream function

  14. Fields lead base point by 5 days 200 mb Heights and OLR 850 mb Heights and Rain 1000 mb Heights and Unfiltered rain 200 850 1000 Blue contours indicate positive height anomalies

  15. Fields lead base point by 4 days 200 850 1000

  16. Fields lead base point by 3 days 200 850 1000

  17. Fields lead base point by 2 days 200 850 1000

  18. Fields lead base point by 1 day 200 850 1000

  19. Fields simultaneous with base point 200 850 1000

  20. Fields lag base point by 1 day 200 850 1000

  21. Fields lag base by two days Pacific South America

  22. Conclusions • There are at least two mechanisms that force Kelvin waves over South America a) at upper levels from the Pacific b) at lower levels from southern South America (e.g., Garreaud and Wallace 1998; Garreaud 2000) • Not all South American (cold) events force Kelvin waves

  23. Fields lead base point by 3 days Kelvin-filtered base point 30-day high pass base point OLR, 200 mb winds and heights

  24. Fields simultaneous with base point Kelvin-filtered base point 30-day high pass base point OLR, 200 mb winds and heights

  25. Fields lag base point by 1 day Kelvin-filtered base point 30-day high pass base point OLR, 200 mb winds and heights

  26. Fields lag base point by 2 days Kelvin-filtered base point 30-day high pass base point OLR, 200 mb winds and heights

  27. Conclusions • There are at least two mechanisms that force Kelvin waves over South America a) at upper levels from the Pacific b) at lower levels from southern South America (e.g., Garreaud and Wallace 1998; Garreaud 2000) • Not all South American (cold) events force Kelvin waves • Some Kelvin waves may be initiated in-situ

  28. Neither Pacific nor South America - in situ?

  29. Conclusions • There are at least two mechanisms that force Kelvin waves over South America a) at upper levels from the Pacific b) at lower levels from southern South America (e.g., Garreaud and Wallace 1998; Garreaud 2000) • Not all South American (cold) events force Kelvin waves • Some Kelvin waves may be initiated in-situ

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