The South American monsoon system and the 1970s climate transition L. M. V. Carvalho 1, C. Jones 1, B. Liebmann 2, A. Silva 3, P. L. Silva Dias 3 1 University of California Santa Barbara 2 CIRES, NOAA, Boulder 3 University of Sao Paulo, Brazil 1
Outline: Discuss a new metric to characterize onset/demise and amplitude of SAMS as a large-scale feature and not local wet seasons Discuss how it captures active and break phases of SAMS Characterize long-term changes in SAMS Show regime shifts in SAMS duration and amplitude 2
1948 1970 2000 3 Liebmann and Dallured 2005)
LISAM: Large-scale Index of SAMS (Silva and Carvalho 2007, Atmos. Sci. Letters) Index capable to characterize large-scale aspects of SAMS Precipitation, circulation and Thermodynamics Characterization of SAMS and SACZ as separate modes Represent intraseasonal variability of SAMS and SACZ Continuous and applicable in real-time 4 4
LISAM (Silva and Carvalho 2007) o Precipitation: Global Precipitation Climatology Project - GPCP (2.5 o resolution) o U850, V850, Q850, T850 NCEP/NCAR reanalysis o Pentads 1979-2007; subtract only long-term mean o Combined Empirical Orthogonal Function o Use first two modes (CEOF1,CEOF2) Extended LISAM 1948-2007 All fields from NCEP/NCAR reanalysis (including precipitation) 5
First CEOF Mode - LISAM Correlation between LISAM and all variables used in the CEOF Precipitation Specific humidity Zonal wind Westerlies Easterlies Meridional wind Air temperature Northerly 6 6
Second CEOF Mode South Atlantic Convergence Zone (SACZ) Correlation between CEOF-2 and all variables used in the CEOF Precipitation Specific humidity Zonal wind Westerlies Easterlies Meridional wind Air temperature Northerly Southerly 7 7
LISAM and SACZ time coefficients Spectral Density LISAM ~ 30-80 days Annual cycle removed SACZ Period (pentads) CEOF-2: Winter: extratropical transients (cold fronts) ~15-25 days Period (pentads) 8
Does LISAM capture active and break phases of SAMS? Differences wet and dry events (defined as indices upper quartile lower quartile during summer after removing the annual cycle) Wet events=123 Difference Precipitation (Wet Dry) Dry events=94 Difference U850 (Wet Dry) 9
Enhanced and Suppressed SACZ Differences wet and dry events (defined as indices upper quartile lower quartile during summer) Wet events=201 Difference Precipitation (Wet Dry) Dry events=213 Difference 850hPa wind(wet Dry) Cyclonic Cyclonic Anti-Cyclonic 10
Example Onset and Demise using LISAM o Smooth LISAM1 o 15 passes 3 pts m. a. o Onset/Demise: pentads of zero crossing Sometimes: significant intraseasonal variations Sometimes: abrupt onset (2005 Amazon drougth) 11
SAMS Variability 1948-2008 LISAM (NNR) and GPCP COR=0.90 COR=0.87 12
SAMS Variability 1948-2007 COR=0.90 =Integral of LISAM positive anomalies 13
34 Pentads 40 Pentads ~41 Pentads ~38 Pentads Changing Point Analysis Sequential statistical test Rodionov (2004) GRL 14
10-yr Moving Average 15
Mean vertically integrated moisture flux during SAMS (kg m -1 s -1 ) (onset-demise) 1948-08 Monthly difference in vertically integrated moisture flux: (1982-08) minus (1948-71) OCT DJF APR 16
Annual flow at the Parana River (m 3 s -1 ) during 1905-2006. Vertical dashed line indicates a changepoint in the series statistically significant at 5% level. Data are from Dai et al. (2009) Lake-level for Laguna mar Chiquita (Argentina) AD 1890-1967 Hydrological models indicate a changing point in 1972 (IRD paleoclimate group personal communication) 17
o LISAM Summary Represents coupling between precipitation, circulation and thermodynamics Retains intraseasonal and interannual variations (LISAM) Captures oceanic part of SACZ (CEOF2) o SAMS duration and amplitude determined with LISAM (NCEP/NCAR) indicates regime shift in duration/amplitude ~early 1970s Somewhat consistent with shifts in Amazon precipitation (Marengo 2004) Consistent with river flow and lake sediment records influenced by SAMS regime 18