Professor Leila M V Carvalho University of California Santa Barbara Seventh WMO International Workshop on Monsoons IWM7 ONLINE TRAINING WORKSHOP ON SUBSEASONAL TO SEASONAL S2S PREDICTION OF MONSOONS ID: 1021930
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1. The South Atlantic Convergence ZoneProfessor Leila M. V. CarvalhoUniversity of California, Santa BarbaraSeventh WMO International Workshop on Monsoons (IWM-7) ONLINE TRAINING WORKSHOP ON SUBSEASONAL TO SEASONAL (S2S) PREDICTION OF MONSOONS
2. Outline What is the South Atlantic Convergence Zone? What is the relationship between the SACZ and the South American Monsoon System (SAMS)?How to objectively identify the SACZ in observations and models?Does the SACZ exhibit variations on subseasonal time-scales? What mechanisms may explain this variability?Are these variabilities connected with the variability of the SAMS?
3. OLR, 850hPa winds (arrows) and 200hPa streamlinesNote that there is no wind reversal!Cold Pacific
4. The South America Monsoon System (SAMS): Precipitation and 850hPa (GPCP) wind ANOMALIES4(Oct)
5. 5Sao Paulo State46.65 Million InhabitantsMetropolitan Area: 23,46 Million~7.398 Inh/km2Population Density in South AmericaRio de JaneiroState: 17.5 Million Metropolitan area:~ 6.8 Million~5.265inh/km²
6. The SAMS And The SACZ variability
7. How to objectively characterize the SAMS and the SACZ?1) Metric should capture the main features of the SAMS and the SACZ2) Should capture variations on multiple scales3) Should be applicable to reanalyses and climate models
8. Large Scale Index for South America Monsoon (LISAM) (Silva and Carvalho 2007)SAMS is characterized by seasonal changes in: Circulation anomaliesPrecipitationMoisture TemperatureObjective of this index: Characterize the ONSET, DEMISE, DURATION, AMPLITUDE, BREAKS AND ACTIVE PHASES of the SAMS and the SACZ based in all variables above. 8
9. 9Variables used in this IndexZonal (U850) and meridional (V850) winds, Specific Humidity (Q850) and temperature (T850) at 850hPa.Precipitation (can be from reanalyses or not). To retain the seasonal variability, subtract only long-term mean.Method applied to obtain the INDEX: Combined Empirical Orthogonal Function Use first two independent modes (LISAM1, LISAM2) The Large-Scale Index for the South American Monsoon (LISAM - Silva and Carvalho 2007)
10. 10PrecipitationSpecific humidityZonal windMeridional windAir temperatureFirst CEOF Mode - LISAM10Correlation between LISAM and all variables used in the CEOFWesterliesEasterliesNortherly
11. 1111PrecipitationSpecific humidityZonal windMeridional windAir temperatureSecond CEOF Mode – South Atlantic Convergence Zone (SACZ)WesterliesEasterliesNortherlySoutherlyCorrelation between CEOF-2 and all variables used in the CEOF
12. LISAM (1st EOFc) and SACZ (2nd EOFc) time coefficientsOnsetDemiseDurationAnalysis of SAMS SAMS Onset/demise: smooth LISAM (with 5 days moving average)Average Onset: Second Pentad October (non-stationary)Average demise: Second Pentad April (non-stationary)
13. Spatial Differences: Independent analysis with TRMM Precip. Data, DJFDryWet Dry WetNogues-Paegle and Mo, 1998Liebmann et al., 1999Carvalho et al. 2002; 2004The SACZ associated with a seesaw in precipitation over SE South America with period of ~ 10 days or lessOCEANIC SACZSouth American Monsoon
14. What is the SACZ?Kodama 1992/1993: prominent subtropical convergence/front zone, characterized by strong water vapor convergence, and generation of convective instability. Following conditions (1) The subtropical jet is in the subtropical zone (latitude 30-35 degrees). (2) The lower polar airflow predominates at the western edge of the subtropical anticyclone.
15. Spectral variability30 days60 days -From Silva and Carvalho, 2007South American Monsoon: LISAM
16. Liebmann et al 1999:16, 10, and 8 days
17. 17The SACZ intraseasonal variabilityEnhanced SACZComposites of extreme precipitation intraseasonal anomalies (1979-2002) (Muza et al. 2009)Dry S BrWet S BrWeak SACZAnomalous Geopotential Height 200mb compositesWet SE BrDry SE Br
18. EventFrom Wendell Max PhD DissertationLag Composites intraseasonal anomalies (20-90 days)U,V 850hPa, OLR (shade) SACZ persistence 7 days or longer
19. Can we filter the SACZ index and find out about intreaseasonal variability and regional impacts on precipitation ?METHODOLOGY:Filter the Index on a given bandCreate 2 samples: one with values above 1 standard deviation of the filtered index and the other one with values below one standard deviation of the filtered index.Calculate the precipitation average for each sampleSubtract the positive from the negative average.
20. Intraseasonal variability: 15-25 daysSACZ INDEXLISAM INDEXClear Seesaw in precipitation anomaliesEnhanced precipitation over larger continental areas
21. Intraseasonal variability: 28-62 daysSACZ INDEXLISAM INDEXEnhanced precipitation over larger continental areasSeesaw less evident
22. The Madden-Julian Oscillation influence on Active and break phases of the South American Monsoon
23. Can we use the LISAM and SACZ index to evaluate precipitation deficits in a Season?
24. Example: the 2001-2002 seasonExcessDeficit
25. Example: the 2001-2002 season
26. Take away messages: mechanismsThe SACZ is an important feature of the SAMSConvection over the continent and ocean are driven by distinct mechanisms and have different spectral variabilityThe MJO influences more the continental tropical precipitation. Midlatitude Rossby waves-trains explain the spatial and temporal variability of the oceanic SACZ (these midlatitude wave trains can be triggered by the MJO)Other factors: coupled modes influence the SACZ and SAMS on multiple scales. The South Atlantic Dipole is one of them; the AMO , ENSO, PDO1) Take Away messages: Mechanisms
27. Take away messages: mechanismsThe SACZ and the LISAM index discussed here can be applied to modelsFuture research: use S2S model data (e.g, ECMWF) to determine the subseasonal forecast skills of the SACZ and the SAMS1) Take Away messages: Improving predictability of droughts and wet periods
28. References of interestAlvarez, M.S., Vera, C.S., Kiladis, G.N. and Liebmann, B., 2016. Influence of the Madden Julian Oscillation on precipitation and surface air temperature in South America. Climate Dynamics, 46(1-2), pp.245-262.Barros, V., Gonzalez, M., Liebmann, B. and Camilloni, I., 2000. Influence of the South Atlantic convergence zone and SouthAtlantic Sea surface temperature on interannual summerrainfall variability in Southeastern South America. Theoretical and Applied Climatology, 67(3), pp.123-133.Bombardi, R.J., Carvalho, L.M., Jones, C. and Reboita, M.S., 2014. Precipitation over eastern South America and the South Atlantic Sea surface temperature during neutral ENSO periods. Climate Dynamics, 42(5-6), pp.1553-1568.Carvalho, L.M., Jones, C., Cannon, F. and Norris, J., 2016. Intraseasonal-to-interannual variability of the Indian monsoon identified with the large-scale index for the Indian monsoon system (LIMS). Journal of Climate, 29(8), pp.2941-2962.Carvalho, L.M., Silva, A.E., Jones, C., Liebmann, B., Dias, P.L.S. and Rocha, H.R., 2011. Moisture transport and intraseasonal variability in the South America monsoon system. Climate dynamics, 36(9), pp.1865-1880.Carvalho, L.M., Jones, C. and Liebmann, B., 2004. The South Atlantic convergence zone: Intensity, form, persistence, and relationships with intraseasonal to interannual activity and extreme rainfall. Journal of Climate, 17(1), pp.88-108.Carvalho, L.M., Jones, C. and Liebmann, B., 2002. Extreme precipitation events in southeastern South America and large-scale convective patterns in the South Atlantic convergence zone. Journal of Climate, 15(17), pp.2377-2394.Cunningham, C.A. and Cavalcanti, I.F., 2006. Intraseasonal modes of variability affecting the South Atlantic Convergence Zone. International Journal of Climatology: A Journal of the Royal Meteorological Society, 26(9), pp.1165-1180.Jones, C. and Carvalho, L.M., 2002. Active and break phases in the South American monsoon system. Journal of Climate, 15(8), pp.905-914.Kodama, Y., 1992. Large-scale common features of subtropical precipitation zones (the Baiu frontal zone, the SPCZ, and the SACZ) Part I: Characteristics of subtropical frontal zones. Journal of the Meteorological Society of Japan. Ser. II, 70(4), pp.813-836.Kodama, Y.M., 1993. Large-scale common features of sub-tropical convergence zones (the Baiu Frontal Zone, the SPCZ, and the SACZ) Part II: conditions of the circulations for generating the STCZs. Journal of the Meteorological Society of Japan. Ser. II, 71(5), pp.581-610.Liebmann, B., Kiladis, G.N., Marengo, J., Ambrizzi, T. and Glick, J.D., 1999. Submonthly convective variability over South America and the South Atlantic convergence zone. Journal of Climate, 12(7), pp.1877-1891.Muza, M.N., Carvalho, L.M., Jones, C. and Liebmann, B., 2009. Intraseasonal and interannual variability of extreme dry and wet events over southeastern South America and the subtropical Atlantic during austral summer. Journal of Climate, 22(7), pp.1682-1699.Nogués-Paegle, J. and Mo, K.C., 1997. Alternating wet and dry conditions over South America during summer. Monthly Weather Review, 125(2), pp.279-291.Zilli, M.T., Carvalho, L.M., Liebmann, B. and Silva Dias, M.A., 2017. A comprehensive analysis of trends in extreme precipitation over southeastern coast of Brazil. International Journal of Climatology, 37(5), pp.2269-2279.
29. Coupled modes of variability influencing SAMS and SACZ
30. The South Atlantic Dipole (SAD)(Neutral ENSO) - DJFCold tropics warm extratropicsWarm tropics – cold extratropicsCool tropical South Atlantic: stronger Anticyclonic circulationStronger convergence at the northern flank of the SACZEnhanced precipitation in the SACZ regionOPPOSITE CONDITIONS WITH WARM TROPICAL SOUTH ATLANTICBombardi et al. 2011: Precipitation over eastern South America and the South AtlanticSea surface temperature during neutral ENSO periods. Clim Dyn (2014) 42:1553–1568
31. Changes in Precipitation: SAD Negative vs SAD positiveCool tropical AtlanticWarm tropical AtlanticBombardi et al. 2011: Precipitation over eastern South America and the South AtlanticSea surface temperature during neutral ENSO periods. Clim Dyn (2014) 42:1553–1568