Interannual Variability of the South American Monsoon in Large - PowerPoint PPT Presentation

Interannual Variability of the South American Monsoon in Large Ensemble simulations Ana Claudia Thome Sena Gudrun Magnusdottir Department of Earth System Sciences University of California, Irvine January 2019 Ana Sena (UCI) South American Monsoon January 2019 1 / 18

South America Precipitation Ana Sena (UCI) South American Monsoon January 2019 2 / 18

Methodology Onset: First day when: ◮ Rainfall greater or equal to 4mm/day over Amazon ◮ Zonal Wind at 850 hPa is from East over central Brazil ◮ Conditions remain for at least 40 days ◮ Both rainfall and wind were smoothed using 5-day moving averages Retreat: When those conditions are no longer met. Ana Sena (UCI) South American Monsoon January 2019 3 / 18

Objectives Determine the differences between the large-scale circulation associated with early and late onset/retreat of the South American Monsoon System in a large ensemble of simulation ◮ Are the South American Monsoon features reproduced by the CESM Large Ensemble Simulations (LENS)? ◮ What are the differences between early and late onset in LENS? ◮ What are the differences between early and late retreat in LENS? Ana Sena (UCI) South American Monsoon January 2019 4 / 18

Why use Large Ensemble Simulations? Large Ensemble Simulations: Reanalysis models: Community Earth System Model version 1 (CESM1) Model Period 40 ensemble members ERA interim 1979 - present 1 o spatial resolution MERRA-2 1983 - present NCEP/NCAR 1948 - present Daily JRA-55 1958 - present 1920 - 2005 (historical) ERA20c 1901 - 2010 2006 - 2100 (RCP8.5) Period analyzed: 1920 - 2016 Ana Sena (UCI) South American Monsoon January 2019 5 / 18

SAMS Onset/Retreat Dates in Observations Figure: Onset and retreat date of the SAMS - CHIRPS precipitation and ERA interim wind Ana Sena (UCI) South American Monsoon January 2019 6 / 18

SAMS Onset/Retreat Dates in LENS Figure: SAMS Onset (a) and Retreat (b) dates - LENS Ana Sena (UCI) South American Monsoon January 2019 7 / 18

SAMS Onset/Retreat Dates Observations LENS ◮ Early Onset: 13-Sep (10 cases) ◮ Early Onset: 05-Oct (1053 cases) ◮ Late Onset: 30-Sep (10 cases) ◮ Late Onset: 20-Oct (1037 cases) ◮ Early Retreat: 8-May (10 cases) ◮ Early Retreat: 20-Apr (1046 cases) ◮ Late Retreat: 24-May (10 cases) ◮ Late Retreat: 30-Apr (991 cases) Ana Sena (UCI) South American Monsoon January 2019 8 / 18

SAMS variability in LENS and observations Figure: Value of one standard deviation of onset date, retreat date and length of the SAMS, for each dataset considered. Ana Sena (UCI) South American Monsoon January 2019 9 / 18

Early and Late Onset - LENS Ana Sena (UCI) South American Monsoon January 2019 10 / 18

Early and Late Onset - LENS Ana Sena (UCI) South American Monsoon January 2019 11 / 18

Early and Late Onset - LENS Ana Sena (UCI) South American Monsoon January 2019 12 / 18

Early and Late Onset - LENS Ana Sena (UCI) South American Monsoon January 2019 13 / 18

Early and Late Retreat - LENS Figure: 850 hPa Wind Anomalies and Climatology Ana Sena (UCI) South American Monsoon January 2019 14 / 18

Early and Late Retreat - LENS Ana Sena (UCI) South American Monsoon January 2019 15 / 18

Early and Late Retreat - LENS Ana Sena (UCI) South American Monsoon January 2019 16 / 18

Conclusions General wet season dates and features are reproduced in LENS ◮ Later onset and earlier retreat in LENS ◮ Wet season interannual variability is greater in observations Onset ◮ Early onset is related to early development of the Bolivian High ◮ Rainfall dipole between Northern and Southern Brazil. Retreat ◮ ITCZ southward position is related to a later SAMS retreat ◮ Stronger (weaker) trade winds in late (early) Retreat ◮ South Atlantic Low Level Jet resists longer during late retreat ◮ Moisture incursion from South Atlantic Ocean in Southeastern Brazil during early retreat Ana Sena (UCI) South American Monsoon January 2019 17 / 18

Future Work Determine the mechanisms for interannual variation of SAMS wet season length in LENS Local and remote influences Modes of Climate variability Ana Sena (UCI) South American Monsoon January 2019 18 / 18