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Rong Fu Robert Dickinson, Mingxuan Chen, Hui Wang Earth & Atmospheric Sciences

Can Amazon rainfall influence Winter Weather over Europe and North America and North Atlantic Oscillation?. Rong Fu Robert Dickinson, Mingxuan Chen, Hui Wang Earth & Atmospheric Sciences Georgia Institute of Technology Acknowledgement: Walter Robinson, Wenqing Tang, W. Timothy Liu.

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Rong Fu Robert Dickinson, Mingxuan Chen, Hui Wang Earth & Atmospheric Sciences

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  1. Can Amazon rainfall influence Winter Weather over Europe and North America and North Atlantic Oscillation? Rong Fu Robert Dickinson, Mingxuan Chen, Hui Wang Earth & Atmospheric Sciences Georgia Institute of Technology Acknowledgement: Walter Robinson, Wenqing Tang, W. Timothy Liu III LBA Scientific Conference, July 27-29, 2004, Brasilia. Brazil

  2. Namias 1972: Northeast Brazil rainfall is connected to blocking in Newfoundland –Greenland area and subtropical Atlantic High. +0.4 -0.4 -0.7 700 mb height, (Dec-May, 1947-70), vs. Quixermobim (5S, 39W) -0.5 +0.2

  3. Can South American rainfall influence atmosphere over North Atlantic and adjacent continents? • Dickinson, 1971: Convection over Summer hemisphere drives cross-equatorial propagation of Rossby wave over the regions with weak westerly flow. • Grimm and Silva Dias 1995, Gandu, and Silva Dias, 1998: Amazon convection can influence global atmosphere, including atmospheric circulation over North Atlantic and adjacent continents. • Gedney and Valdes, 2000: Change of rainfall caused by Amazon deforestation could influence the atmospheric circulation over the NE Atlantic and Europe. Westerly duct

  4. Can we observe any influence of South America rainfall on atmosphere over North Atlantic? • Issues need to be addressed: • Remove lower frequency surface influences (e.g., Atlantic SSTs) – higher frequency variations with daily resolution • Remote Pacific influences on atmospheric circulation over N. Atlantic and rainfall over South America– reconstruct data using SVD

  5. Data Sets: • QuikSCAT daily ocean surface winds (V21): global, 1.0°1.0°, 12 hrs, but averaged to daily. • TRMM daily precipitation (3B42): global tropics, 1°1°, derived jointly from VSIR and TMI. • NCEP analysis: global, 2.5 °2.5°, 6-hrs averaged to daily. Analysis Period: December-March of 1999/2000 (+NAO), 2000/01(-NAO): 2001/02 (+/-NAO), 2002/03 (~0), 2003/04 (~0). Daily NAO index: www.nws.noaa.gov.

  6. Methods: Ferranti et al. 1990 Lagged daily winds over N. Atlantic (8 days) (0º - 70ºN, 90ºW - 30ºE) Lagged daily rainrate over S. America (7 days) (5º - 25ºS, 45º - 75ºW ) • Reconstruct data using SVD: Pacific daily rainfall (40ºS - 40ºN, 120ºE- 90ºW) SVD SVD Remove first 3 Modes Remove first 3 Modes Reconstructed daily rainrate over S. America Reconstructed daily winds over N. Atlantic Lagged relation • Use a time-dependent barotropic model to simulate the latitudinal propagation of Rossby wave (Sardeshmukh&Hoskins 1988)

  7. Winter of 1999/2000: • Our empirical analysis needs to show: • The anomalous wind patterns over N. Atlantic that lag the South American rainfall are distinctively different from those that lead the the South American rainfall • The correlation coefficient of the former is significantly stronger than that of the latter.

  8. Anomalous Ocean Surface Winds lagging the d<P>Amaz Winds Lead 2 days In phase Wind forced by Amazon rain (lag 3 days minus Lead 2 days) Winds Lag 3 days Lagged regression between reconstructed QuikSCAT OSW and TRMMd<P>Amaz

  9. Anomalous 200 hPa streamfunction lagging the d<P>Amaz Lagged regression between reconstructed NCEP reanalysis and TRMMd<P>Amaz

  10. Latitudinal propagation of Rossby waves can explain the observed shift of circulation pattern following the changes of Amazon rainfall: A linear time dependent barotropic model simulation: Forcing: varying sinuously with a 9-day period Mean flow: Jan. 2000 Simulated: 3 days after the peak force mimicking positive rainfall anomalies. Observed:

  11. Could the anomalous circulation forced by Amazon rainfall projects on NAO? -0.5 +0.2

  12. Surface wind anomalies of positive NAO resemble Anomalous wind patterns lagged and forced by anomalous Amazon rainfall Wallace and Jiang 1987

  13. Correlation between NAO index and d<P>Amaz: Winter of 1999/2000 NAO lags Amazon rainfall 99% significance 95% significance NAO leads Amazon rainfall Wallace and Jiang 1989

  14. However, • The anomalous circulation pattern lagging Amazon rainfall anomalies resembles to that of NAO pattern in winters of 99/00, 00/01, 01/02, but not inwinters of 02/03, 03/04 • Why? • Pattern of anomalous heating? • Grimm and Silva Dias, 1995: the influence is highly sensitive to the pattern of the atmospheric heating • Structure of zonal flow?

  15. Summary • Satellite observations are able to detect the influence of Aamzon rainfall on atmospheric circulation over N. Atlantic and adjacent continents. • Latitudinal propagation of atmospheric waves driven by latent heat of Amazon rainfall appears to contributes to the observed teleconnection. • However, conditions that control such influence, and whether the influence can project on the circulation pattern of NAO remain unclear.

  16. 200 hPa Streamfunction anomalies of NAO 200 hPa Streamfunction anomalies lag anomalies Amazon rainfall

  17. Anomalous Ocean Surface Winds lagging the d<P>Amaz Winds 2 days lead Winds 1 days lead Winds 1 day lag In phase Lagged regression between reconstructed QuikSCAT OSW and TRMMd<P>Amaz

  18. Anomalous 200 hPa streamfunction lagging the d<P>Amaz Lagged regression between reconstructed NCEP reanalysis and TRMMd<P>Amaz

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