1. ENSO IN THE Parallel Climate Model Question: What are the processes modulating ENSO Tool: use PCM as a test bed for this study Outline: 1. Description of ENSO in the PCM: NINO3.4 analog (EOF to justify the box) seasonal synchronization composites of summer and winter ENSO dynamical interpretation: multi-variate composite relationship of summer and winter ENSO. 2. Low frequency modulation of the El Ninos

2. PCM's ENSO index - ENSO index is defined as first PC of SST in the area from 5N to 5S across the equatorial Pacific -This index closely corresponds will with NINO3.4-equivalent index in the PCM -Spatial pattern of PC1 is reflects the displaced cold tongue in the model Color bar??, numbers??

3. -ENSO index has a peak in variability at periods from 2-4 years, with amplitude 1-2 degrees C.

4. -Both indices display two peaks in variability: a strong peak in summer and a weaker peak in winter

5. Spectrum and variance as a function of season/month for observations

6. -SST variance is largest during summer and centered over the cold-tongue -Winter variance is not restricted to the cold tongue region, along equator check continuous seasonal cycle from dec to jan

7. SST Seasonal Cylce -The PCM's split ITCZ is most pronounced during May/June and Nov/Dec -The Cold Tongue is displaced farthest westward during May and June

8. Discussion of seasonal cycle in equatorial Pacific (PCM) and in observations. Colorbar in all plots hovmoeller of annual cycle of SST along equator (lon vers tme along equator). Same plots for observations obs should show annual cycle model likely shows semiannual signal compare/discuss pcm annual cycle vis a vis literature show variance versus annual cycle, seasonal sst in contour, variance in color overplot

9. -We define: Summer El Nino: Index value greater than 1.5 STD (about 1.5 degree C) that occurs in July Winter El Nino: Index value greater than 1.5 STD that occurs in January

10. Identify winter/summer la ninas

11. Summer vs Winter ENSO Dynamics: -Response of SST appears to be static in summer and displays propagation during winter -SST signal propagates at 1 m/s (coupled wave?) composite average

12. Composite: include slope consisitent with RW Kelvin waves significance test on composite average compare composite average with that expected that from a randomly chosen sample of same size sensitivity to threshold for composite interpretation: is the evolution consistent with simple models of ENSO? Recharge osc., relationship of sst, thermocline depth and winds, taux on equator, curl off equator WES/evaporation feedback,, does it play a role? Interaction with annual cycle, dynamics of annual cycle in PCM Composite along equator, along a longitude, maps

13. Summer vs Winter ENSO Dynamics: -The model displays large latent heat flux variance during both winter and summer, but there is only a precipitation response during winter

14. Conclusions: -The seasonal synchronization of ENSO within the PCM is not realistic -One can separate the ENSO signal in the PCM into a winter and summer ENSO -The two PCM ENSOs appear to be the result of separate dynamics(?), with the winter ENSO resembling our understanding of ENSO within the natural system -If desired, it is possible to separate this two signals to aid in the analysis of ENSO within the PCM NEEDS MORE MEAT

15. Modulation basic description difference between summer and winter regular/irregular Dynamics of modulation change in background state noise induced multiplicative noise (hard)