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
Fine structure in North American summer The mean annual cycle Solar forcing: annual + semiannual Earth response: ditto, + faster fine structure Three.
Jan 18, 2018
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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