Fine structure in North American summer

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
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)
July 1
Jul 20
Jun 10
Date of rapid OLR drop (wavelet power peak)
11
3. Mid-summer dry spellMex./CA(Magana 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) (Magana 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)