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.

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1 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

2 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

3 Liebmann and Dallured 2005)

4 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

5 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 ; subtract only long-term mean o Combined Empirical Orthogonal Function o Use first two modes (CEOF1,CEOF2) Extended LISAM All fields from NCEP/NCAR reanalysis (including precipitation) 5

6 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

7 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

8 LISAM and SACZ time coefficients Spectral Density LISAM ~ days Annual cycle removed SACZ Period (pentads) CEOF-2: Winter: extratropical transients (cold fronts) ~15-25 days Period (pentads) 8

lower quartile during summer after removing the annual cycle) Wet

9 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

summer) Wet events=201 Difference Precipitation (Wet Dry) Dry

10 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

11 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

12 SAMS Variability LISAM (NNR) and GPCP COR=0.90 COR=

13 SAMS Variability COR=0.90 =Integral of LISAM positive anomalies 13

14 34 Pentads 40 Pentads ~41 Pentads ~38 Pentads Changing Point Analysis Sequential statistical test Rodionov (2004) GRL 14

15 10-yr Moving Average 15

16 Mean vertically integrated moisture flux during SAMS (kg m -1 s -1 ) (onset-demise) Monthly difference in vertically integrated moisture flux: ( ) minus ( ) 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.

17 Annual flow at the Parana River (m 3 s -1 ) during 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 Hydrological models indicate a changing point in 1972 (IRD paleoclimate group personal communication) 17

18 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

South American monsoon indices

ATMOSPHERIC SCIENCE LETTERS Atmos. Sci. Let. 6: 219 223 (2006) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/asl.119 South American monsoon indices Manoel A. Gan,* Vadlamudi