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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}
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Fine structure in North American summer
The mean annual cycle• Solar forcing: annual + semiannual • Earth response: ditto, + faster “fine structure”
Three fine structures1. May rain onset in Caribbean region2. Southwest monsoon onset3. Midsummer dry spell in central America
Temporal Fourier spectrum of TOA insolation
No forcing:nonlinear dynamics
fine structure
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}
Ex: 1979-1995 OLR, May
Ex: 1979-1995 OLR, E. Cuba
TotalFine structure
Wavelet analysis of fine structure
“Onset”Day 125
significance
Subtropical Atlantic May onsetdate plotted for ‘significant’ peaks
SW-NE bandSW-NE bandMoves NWMoves NW
CMAP rain climatology1979-2001
Significance (repeatability)
Gridpoint comparison with NCAR CSM 20th century climatology
total
fine
Same gridpointCSM rain
CMAP
?Analogous
to east Asiansubtropical monsoon (Mei-yu /
Baiu)?
2. North American monsoon onset
Date of rapid OLR drop (wavelet power peak)
July 1 Jul 20Jun 10
Observed (1979-96 mean OLR) Models: a worthy challenge…
GFDL(POGA-MLM)
CSM(coupled)
CCM3 w/1950-95 SST
3. Mid-summer dry spellMex./CA
(Magaňa et al. 1999)
Fine structureAnomaly map
These days
total
fine
Slight +
Mid-summer dry spell
(coincides with NA
monsoon)
Fine structureAnomaly map
These days
total
fine
Mid-summer
NCEP skin (SST)
(Magaňa hypothesis)
Fine structureAnomaly map
These days
total
fine
Mid-summer dry spell
(coincides w/ WNP
monsoon)
Fine structureAnomaly map
These days
total
fine
Mid-summerSLP:
Atlantic High noses in to IAS
SLP peak isochrone map
total
fine
Conclusions
North American summer has 3 prominent fine structures in its (hydro) climatology:
1. May onset, backing (EW) into Caribbean/Florida. American Mei-Yu?
2. July onset north w. Mexico NAM3. Midsummer tropical rainfall dip in late
July-Aug, Atlantic High surges west. Fundamental/easy? (2 CGCMs have it)
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