Presentation on theme: "Indrani Roy & Mat Collins"— Presentation transcript:
1 Indrani Roy & Mat Collins SAPRiSEProjectIdentifying the role of the Sun and the El Niño Southern Oscillation on Indian Summer MonsoonIndrani Roy&Mat Collins25th June, 2013
2 Outline I: Observation Role of Sun and ENSO on ISM BackgroundAnalysesII : CMIP5 Model OutputSome features of ISM, ENSO in CMIP5 modelsISM and ENSO teleconnectionHydrological Cycle in CMIP5 models and ISM
4 Background: General Circulation Walker Cell:Hadley Cell:IndiaHadley Cell: Thermally driven rising air around ITCZ and falling 30 lat.Walker Cell: EW circulation in tropics and changes direction in warm and cold phases of ENSO
5 Background : Indian Summer Monsoon(ISM) SLP: ClimatologyMonsoon means seasonalwind reversals. For ISM, it isfrom NE ly (Jan) to SW ly(July).Associated with movement ofITCZ.Heavy rains in summer (JJAS)due to moisture rich air fromocean.Walker circulation and Hadleycirculation both play role.ISM has changed in last fewdecades (IPCC, 2007)JanuaryJuly
6 Background: Major Modes of Variability Tahiti(Australia)Different regions affected by various modes
7 Why NAO? Anticorrelation between NAO and ISM [Sen Roy, 2011] Positive PhaseNegative PhaseAnticorrelation between NAO and ISM [Sen Roy, 2011]ISM is strongly modulated by the NAO [Liu & Yanai, 2001]Relationship bet. temperature W. Eurasia and ISM is stronger,over same period the rel. between the ENSO, ISM weakened.[Chang et al. 
8 Why Indian Ocean Dipole (IOD) ? Positive PhaseNegative PhaseConnection: ISM- Australia- E. African rainfallIOD and ENSO have complementarily affected ISM during (Ashok et al, 2001)
9 Atmos-Ocean coupling was different during 1950s to 1997 Global warming caused weakening of tropical circulation:more in the Walker cell than the Hadley cellStrong decrease in intensity of Walker circulation after 1950sModest intensification since (Vecchi, et al. 2007)[McPhaden and Zhang, 2004]Could climate change during that period have modified ISM?
10 Solar signal on ISM detected using Solar peak year compositing JJA Max-yrJJA Min-yrAnomalyVan Loon and Meehl (2012) only used solar max-yr compositing on SLP and rainfall and suggested sun enhances ISMIs it true solar signal?
11 Solar Peak years and ENSO Average SSNENSO (DJF)[Roy and Haigh, 2010]Almost all solar peak years are with –ve ENSO indexENSO signal in peak-yr compositing might be mis- interpreted as solarIs any other strong signal also mixed up in compositing method?
12 Solar compositing on SLP Min r.tMax r.tMin r.tMax r.tMax-yr significant signal around Azore High, min-yr Icelandic Low. Unaffect with change of period of anomaly.SH is mostly affected due to climate change signal duringDuring same period, land (+ve)-sea(-ve) SLP contrast favours ISM rainfall
13 ISM in solar compositing covering India Min r.tMax r.tMin r.tMax r.tMax-yr as well as min-yr compositing suggest similarly around Indian subcontinent.Max-yr suggest stronger effect on ITCZ that min-yr compositing.
15 ENSO Signal in JJAENSO captures SO in SLP, but major changes around Australia in later period. Australia (Darwin), one lobe of SO is also coincidentally one end of IOD.-ve NAO pattern observed in later period.Local N-S Hadley circulation, as manifest as NAO in NH and IOD in SH may have played role in modulating ISM in later period.
16 Solar Signal in JJAUsing regression, no significant signal is detected around regions of Indian subcontinent.This is true irrespective of the period considered
17 Some connections between Sun and ISM +ve ENSO index +-ve ENSO index *Rainfall deficit years are usually associated with warm phase of ENSOand vice versa (L.H.S).Some connections, solar cycle and ISM rainfall- different since 1950s.Decadal solar forcing on trade winds (Meehl, et al 2008, Roy & Haigh,2012) that acts alongside inter-annual ENSO may be responsible.
18 Summary ISolar influence on ISM rainfall, using method of solar peak year compositing, may not be robust and can be influenced by factors as ENSO and trends.Compositing suggests SH is mostly affected by climate change signal. Min year detects signal around Icelandic low and max year around Azore high.During 2nd half of last century, the weakened Walker circulation due to climate change seems to be overtaken by local N-S Hadley circulation, as manifest as NAO in NH and IOD in SH.Some connections between solar cycle and monsoon rainfall, which are different since 1950s.
20 Comparison with Observation and another model - last 50 years Observation-CRU : black; Model-all forcing: redTemporalBehaviour(Bollasina, et al2011, Science)5-yr running mean JJAS(relative ) over central-N India (box)Observation-CRUModel (NOAA GFDL CM3) all forcingSpatialBehaviour-ve anomaly in box for both cases.
21 Spatial Pattern (Historical Run) Precipitation Anomaly w.r.t. ( )No consistent pattern – even in box (starting from +ve to –ve shown)
23 Analysis: Historical +rcp (w.r.t 1985-2005) Rainfall (box), 11 year running mean, blue rcp scenario.21Most models rising trend in rcp, some overall no trend (e.g. ),some falling trend in rcp scenario (e.g. ).Similar observation not only in box but also for overall rainfall.12
24 SST(Nino 3.4 in JJAS): rcp (w.r.t 1985-2005) Model with least trend in NinoModel high variable NinoAll models rising trend in rcp, exception123
25 ISM and ENSO Teleconnection ModelCorrelation : Rainfall vs. Nino3.4Whole India BoxI II I II(His) (rcp) (His) (rcp)MIROC-ESM-CHEMNorESM1-MMIROC-ESMInmcm4ACCESS1-0CSIRO-Mk3-6-0IPSL-CM5A-MRMPI-ESM-LRCanESM2-ve correlation - both in historical (I) and rcp (II)- after removing trend.True in the box region as well.
27 Global Hydrological Cycle : CMIP3 (Vecchi and Soden, 2007)Moistening vary model to model, but all models exhibit a nearly linear relationship between column water vapour and surface temperature.The rate of this increase is 7.5% /K, following Clausius Clapron (C-C) equation.
28 Precipitation Time Series:CMIP5 GlobalMonsoonGlobal:annual & JJAS resemble.Uncertainty increases with time.Matches CMIP3 study.Nearterm prediction skill good.Monsoon:large uncertainty throughout.Magnitude-wise much higher.
29 Hydrological cycle and ISM:CMIP5 AnnualAtm water and tempPrecipitation, vert. vel and tempJJASPpt, vert. vel and temp (Globe)Precipitation, vert. vel and temp (India)Although there can be significant regional changes in relative humidity among models, the global-mean behaviour closely resembles that expected from (C–C) arguments also in CMIP5.
30 Questions to answer/future work It is usually said that monsoon increases due toincrease in water vapour offset by weakeningcirculation.Hypothesis: Can this explain variations betweenCMIP5 models?Does global change reflect regional change?Studies using HADCM3/ RM3 with perturbed physicswill be carried to understand monsoon dynamics.Emphasis will be on circulation fields.
31 Summary II ISM - General Features vary model to model in CMIP5. Model FGOALS-g2 does not show any trend in nino3.4 for historical or rcp scenario.ISM and ENSO teleconnection studied. All models suggest -ve correlation in historical as well as rcp scenario.Hydrological Cycle and ISM were analysed using CMIP5 models. Hydrological cycle matches to that of earlier CMIP3 study.Monsoon rainfall suggests large uncertainty in CMIP5.