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Fine structure in North American summer

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

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Fine structure in North American summer

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

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

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

  4. Ex: 1979-1995 OLR, May

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

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

  7. Significance (repeatability)

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

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

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

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

  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-summerSLP: Atlantic High noses in to IAS SLP peak isochrone map fine total

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

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