Presentation on theme: "Can Amazon rainfall influence Winter Weather over Europe and North America and North Atlantic Oscillation? Rong Fu Robert Dickinson, Mingxuan Chen, Hui."— Presentation transcript:
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
Namias 1972: Northeast Brazil rainfall is connected to blocking in Newfoundland –Greenland area and subtropical Atlantic High. -0.7 +0.4 -0.4 -0.5 +0.2 700 mb height, (Dec-May, 1947- 70), vs. Quixermobim (5S, 39W)
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
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
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.www.nws.noaa.gov
Methods: –Reconstruct data using SVD: Pacific daily rainfall (40ºS - 40ºN, 120ºE- 90ºW) Lagged daily winds over N. Atlantic (8 days) (0º - 70ºN, 90ºW - 30ºE) SVD Reconstructed daily winds over N. Atlantic Remove first 3 Modes Lagged daily rainrate over S. America (7 days) (5º - 25ºS, 45º - 75ºW ) Reconstructed daily rainrate over S. America Remove first 3 Modes SVD Lagged relation – Use a time-dependent barotropic model to simulate the latitudinal propagation of Rossby wave (Sardeshmukh&Hoskins 1988) Ferranti et al. 1990
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.
Anomalous Ocean Surface Winds lagging the P> Amaz Lagged regression between reconstructed QuikSCAT OSW and TRMM P> Amaz Winds Lead 2 days In phase Winds Lag 3 days Wind forced by Amazon rain (lag 3 days minus Lead 2 days)
Anomalous 200 hPa streamfunction lagging the P> Amaz Lagged regression between reconstructed NCEP reanalysis and TRMM P> Amaz
A linear time dependent barotropic model simulation: Forcing: varying sinuously with a 9- day period Mean flow: Jan. 2000 Observed: Simulated: 3 days after the peak force mimicking positive rainfall anomalies. Latitudinal propagation of Rossby waves can explain the observed shift of circulation pattern following the changes of Amazon rainfall:
-0.5 +0.2 Could the anomalous circulation forced by Amazon rainfall projects on NAO?
Surface wind anomalies of positive NAO resemble Anomalous wind patterns lagged and forced by anomalous Amazon rainfall Wallace and Jiang 1987
Correlation between NAO index and Amaz : 95% significance 99% significance NAO lags Amazon rainfall NAO leads Amazon rainfall Wallace and Jiang 1989 Winter of 1999/2000
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?
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.
200 hPa Streamfunction anomalies of NAO 200 hPa Streamfunction anomalies lag anomalies Amazon rainfall