1 Daily modes of the South Asian monsoon variability and their relation with SST Deepthi Achuthavarier Work done with V. Krishnamurthy Acknowledgments Ben Kirtman, Kathy Pegion, Bohua Huang, Jennifer Adams COLA SAC Presentation April 12, 2010

2 0 1 June30 Sep Intraseasonal oscillations weaker correlation with SST; mainly due to Internal dynamics? Slowly varying climate signals present in daily data or Persistent modes Strong correlation with SST Daily anomalies A conceptual model for monsoon variability Seasonal mean = persistent modes + Intraseasonal oscillations Cartoon based on Krishnamurthy and Shukla 2000; 2007 Flood year Drought year

3 Role of Indian and Pacific SST in ENSO and ISO modes ISO modes –What is the role of Indian Ocean SST and air-sea interaction? –What happens to ISO modes without Pacific SST variability? Persistent modes (mainly ENSO mode) –What is the role of Indian Ocean SST and air-sea interaction? What controls the monsoon variability in the absence of the ENSO? Is there an inherent rainfall-SST variability in the IO? These investigations will help us understand the predictability of the system

4 Analysis methodology Multi-channel singular spectrum analysis (MSSA) Dominant modes in the daily data are obtained using MSSA –Captures spatial structure of maximum variance and its propagation in time –Captures nonlinear oscillations, trends, interannual signals (or repeating sequences in data in their order of variance) –Captures unstable periodic orbits of the system –Data adaptive filtering Intraseasonal scale –Oscillations are obtained without pre-filtering the data –Both the 45 and 28 day modes and their propagation are addressed Interannual scale; why daily data? –Isolates low-frequency climate signals from daily data; Climate signal that is not influenced by ISO can be obtained

5 Methodology Numerical experiments using regional coupling strategy AGCM OGCM SST Heat and momentum fluxes Prescribed SST Atmosphere sees prescribed SST in a certain region; but OGCM produces global SST fields at each time step Impact of SST variability or air-sea interaction over a certain basin can be isolated Blending of prescribed and OGCM-produced SST at the boundaries

6 Regionally coupled simulations using NCEP CFS List of simulations (all 30 year long) ControlFully coupled everywhereNA IO-V(C)SST PO-CSST Prescribed SST regions Atmospheric initial conditions taken from the control; but perturbations introduced

7 Northeastward propagating mode latitude-phase and longitude-phase diagrams of the composites IO-VSST No IO air -sea interaction PO-CSST Pacific climatology, No ENSO Control Fully coupled everywhere Northeastward propagating mode obtained even without IO coupling, but NOT without SST variability in the IO Northeastward propagating mode obtained without ENSO

8 Northeastward propagating mode in IO-CSST Latitude-time and longitude-time diagrams for the 106-day mode

9 Northwestward propagating mode latitude-phase and longitude-phase diagrams of the composites IO-VSST No IO air -sea interaction IO-CSST IO forced with climatology Westward propagation is obtained without IO SST variability SST variability in the WP may have influence on this mode; PO- CSST does not produce this mode Control Fully coupled everywhere

10 Seasonally persistent ENSO mode ( EOF1 of the ENSO mode ) CTL IO-CSST IO-VSST

11 ENSO mode in the control run lead/lag regression between monthly SST, precipitation and wind anomalies and monthly mean of the PC1 of the ENSO mode Precipitation SST and UV at 850hPa

12 ENSO-monsoon relation Lead/lag correlation between the JJAS EIMR and monthly NINO3 Total seasonal anomalies of rainfall

13 Summary and conclusions Intraseasonal variability –Northeastward propagating mode depends on SST variability in the IO –No Pacific SST dependence in this mode –Northwestward propagating mode has no clear dependence on IO SST; but has dependence on West Pacific SST Interannual variability –ENSO-induced rainfall does not reach the Indian subcontinent due to an over- active Indian Ocean. Proper air-sea interaction in IO is important. –Without ENSO, no dominant slowly varying SST-driven rainfall modes were obtained; the dominant (atmospheric) mode produces SST anomalies in the IO. –A weak dipole mode is found in the rainfall even in the absence of the ENSO; its contribution to the EIMR region precipitation is negligible. Results are model dependent Further analysis should explore the ocean dynamics in the IO

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Remaining questions and future work A dipole in SST and rainfall is developed in the absence of ENSO; what triggers it? What is the impact of western Pacific SST on monsoon variability? Why western Indian Ocean appears to cool down fast in the model? –Examine subsurface variables, like thermocline depth Future experiments –Observed SST in the Indian Ocean –Observed SST in the Pacific Why is the period of the ISO mode ~106 days? 15

16 Intraseasonal modes in the NCEP CFS Phase composites of the ISO modes 106-d oscillation30-d oscillation

17 Intraseasonal modes in the NCEP CFS Area-average of the 106-day mode and total daily anomalies over monsoon region

18 Seasonally persistent signal in the NCEP CFS EOF1 of RC1 (ENSO mode) PC1 of ENSO mode (black) and -NINO3 (red) Point correlation between PC1 of ENSO mode and daily SST No additional dipole mode is obtained; but ENSO mode has good correlation with DMI also C = 0.53

19 Contribution of the ISO and persistent modes to seasonal mean JJAS seasonal mean of total anomalies and ISO and ENSO modes for EIMR and IOMR regions Standard deviation of seasonal means of RCs as fraction of the total

20 Northeastward propagating mode in Control run Phase composites of the winds, latent heat flux, shortwave radiation and SST based on the phases of the precipitation

21 Northwestward propagating mode latitude-phase and longitude-phase diagrams of the composites SST composites for 106-day mode

22 ENSO mode in the IO-VSST lead/lag regression between monthly SST, precipitation and wind anomalies and monthly mean of the PC1 of the ENSO mode Precipitation SST and UV at 850hPa

Dipole-like mode in the absence of the ENSO 23

24 Intraseasonal modes in the experiments Is SST variability in IO crucial for the ISO modes? Is air-sea interaction in IO crucial for the ISO modes? What happens to ISO modes in the absence of the ENSO? Run ISO mode IO-VSSTIO-CSSTPO-CSST Northeastward propagation (106d) YesNoYes Northwestward propagation (30d) Yes No

Background: Dominant daily modes in observed OLR 25 Northeastward propagation 45-day ISO mode Persistent, non-oscillatory modes ENSO and Dipole ENSO Dipole Northwestward propagation 28-day ISO mode Krishnamurthy and Shukla 2008

26 Background: Daily modes in observed OLR and relation with SST Seasonal anomalies of the oscillatory modesSeasonal anomalies of the persistent modes Krishnamurthy and Shukla 2008; Krishnamurthy and Kirtman 2009 Contribution to the seasonal anomalies 45-d 28-d ENSO Dipole Correlation with SST: Oscillatory modesCorrelation with SST: Persistent modes Relative roles of the Indian and Pacific Ocean SST variability 45-d 28-d ENSO Dipole