1. Fine structure in North American summer The mean annual cycle Solar forcing: annual + semiannual Earth response: ditto, + faster “fine structure” Three fine structures 1.May rain onset in Caribbean region 2.Southwest monsoon onset 3.Midsummer dry spell in central America

2. Temporal Fourier spectrum of TOA insolation No forcing: nonlinear dynamics  fine structure

3. Annual cycle: data processing 1.Form a mean daily climatology: var (365 calendar days; lat, lon, level, dataset) 2.Remove mean, annual + semiannual harmonics 3.Wavelet analysis of remainder (fine structure) 4.Collect real + imaginary wavelet power peaks {dates, periods, amplitudes, significances}

4. Ex: 1979-1995 OLR, May

5. Ex: 1979-1995 OLR, E. Cuba Total Fine structure Wavelet analysis of fine structure “Onset” Day 125 significance

6. Subtropical Atlantic May onset date plotted for ‘significant’ peaks SW-NE band Moves NW CMAP rain climatology 1979-2001

7. Significance (repeatability)

8. Gridpoint comparison with NCAR CSM 20 th century climatology total fine Same gridpoint CSM rain CMAP

9. ? Analogous to east Asian subtropical monsoon (Mei-yu / Baiu) ?

10. 2. North American monsoon onset Date of rapid OLR drop (wavelet power peak) July 1Jul 20Jun 10 Observed (1979-96 mean OLR) Models: a worthy challenge… GFDL (POGA-MLM) CSM (coupled) CCM3 w/ 1950-95 SST

11. 3. Mid- summer dry spell Mex./CA (Magaňa et al. 1999) Fine structure Anomaly map These days total fine Slight +

12. Mid- summer dry spell (coincides with NA monsoon) Fine structure Anomaly map These days total fine

13. Mid- summer NCEP skin (SST) (Magaňa hypothesis) Fine structure Anomaly map These days total fine

14. Mid- summer dry spell (coincides w/ WNP monsoon) Fine structure Anomaly map These days total fine

15. Mid- summer SLP: Atlantic High noses in to IAS SLP peak isochrone map total fine

16. Conclusions North American summer has 3 prominent fine structures in its (hydro) climatology: 1.May onset, backing (E  W) into Caribbean/Florida. American Mei-Yu? 2.July onset north w. Mexico NAM 3.Midsummer tropical rainfall dip in late July-Aug, Atlantic High surges west. Fundamental/easy? (2 CGCMs have it)