Strides, steps and stumbles in the march of the seasons

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Strides, steps and stumbles in the march of the
seasons

• Astronomical signal, processed by Earth
• Earthly data sets, processed by computer
• Strides annual, semiannual
• Steps Asian monsoon onset, Americas MSD
• Stumbles (a.k.a. singularities)
• the US January Thaw
• Brazil rain
• Software demo (DVD available - ask)

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High frequency aspects of the mean seasonal cycle

• Brian Mapes
• University of Miami

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Seasonality the forcing
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Astronomical forcing(spherical Earth, circular
orbit)
equinox
equinox
solstice
solstice
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Temporal Fourier spectrum of annual insolation
no forcing, just internal nonlinearitites
sin(4pt/365d) Semiannual
sin(2pt/365d) Annual
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Annual cycle signal processing(by the Earth)
Cloud, albedo
heating
Heat capacity
temperature
gravity
pressure
rotation
web of feedbacks
wind
precip
evaporation, advection
humidity
micro- physics
vertical motion
cloud
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Annual cycle signal processing (by the computer)

• Form mean daily climatologies
• var (365 calendar days lat, lon, level,
  dataset)
• Compute mean, annual semiannual harmonics
  
• ? mean, 2 amplitudes, 2 phases
• Residual is called HF
• HF climatology - annual - semiannual
• Wavelet analysis of HF
• ? dates, periods, amplitudes, significances of
  HF events

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Wavelet example

• Paul wavelet
• Sharp time localization
• ? broad in frequency
• Real part max/min
• Imaginary part rise/fall
• (Torrence and Compo 1998 BAMS)

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Signal processed. Now what??

• Fourier and wavelet coefficients form a
  supplement (index) to climatology.
• This doubles the size of the data set.
• ?? What to do with all this information ??

interactive GUI visualization tool
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Outline of examples

• Annual
• Easy (local, thermal) Tsfc
• Nonlocal Z250 (jet streams)
• Semiannual
• Nonlinear angular momentum and u250
• Statistical 250mb eddy activity
• Ter-annual and beyond
• oceanic subtropical highs, monsoons

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Simplest annual harmonic of surface air T
OBS
GFDL
CSM
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Cold winter ? low tropospheric thickness?annual
harmonic of Z250
OBS
GFDL
CSM
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Temperature ? thickness?Not so simple
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Local Hadley cells?
Annual Harmonic of u at 200 hPa
Jan 1
Apr 1
Annual Harmonic of atmos. heating
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Outline of examples

• Annual
• Easy (local, thermal) Tsfc
• Nonlocal Z250 (jet streams)
• Semiannual
• Nonlinear angular momentum and u250
• Statistical 250mb eddy activity
• Ter-annual and beyond
• oceanic subtropical highs, monsoons

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Semiannual harmonic of 250 hPa zonal
wind(Weickmann Chervin 1988)
Jan min
Jan max
Apr
Apr
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Semiannual harmonic of 250 hPa zonal wind
Apr-Oct
Jan
Apr
Apr
OBS
MayNov
HF
total
Apr
JunDec
CSM
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semiannual harmonic of 250 hPa zonal
windsemiannual u in a forced/damped barotropic
model forced with annual harmonic only of 200mb
div (Huang Sardeshmukh 2000)
Apr-Oct
Jan-Jul
Apr-Oct
total
Apr-Oct
Jan-Jul
Apr-Oct
A nonlinear overtone
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Semiannual eddy (storm) activity

• Midwinter Suppression of Baroclinic Wave Activity
  in the Pacific
• Nakamura 1992
• ABSTRACT
• Seasonal variations in baroclinic wave activity
  and jet stream structure in the Northern
  Hemisphere are investigated based upon over 20
  years of daily data. Baroclinic wave activity at
  each grid point is represented for each day by an
  envelope function, the lowpass-filtered time
  series of the squared highpass-filtered
  geopotential height. Baroclinic wave activity
  over the Atlantic exhibits a single maximum in
  January, whereas in the Pacific it exhibits peaks
  in late autumn and in early spring and a
  significant weakening in midwinter, which is more
  evident at the tropopause level than near the
  surface. This suppression occurs despite the fact
  that the low-level baroclinity and the intensity
  of the jet stream are strongest in midwinter.
  Based on the analysis of 31-day running mean
  fields for individual winters, it is shown that
  over both the oceans baroclinic wave activity is
  positively correlated with the strength of the
  upper-tropospheric jet for wind speeds up to 45
  m s 1. When the strength of the westerlies
  exceeds this optimal value, as it usually does
  over the western Pacific during midwinter, the
  correlation is negative wave amplitude and the
  meridional fluxes of heat and zonal momentum all
  decrease with increasing wind speed. The phase
  speed of the waves increases with wind speed,
  while the steering level drops, which is
  indicative of the increasing effects of the mean
  flow advection and the trapping of the waves near
  the surface.

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midwinter eddy minimumsemiannual amplitude
(color) of a climatology of stdev of 9d sliding
window v250Decently simulated by coupled model
NCEP 1969-96
OctApr maxima of eddy v variance
CSM 1.3
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Outline of examples

• Annual
• Easy (local, thermal) Tsfc
• Nonlocal Z250 (jet streams)
• Semiannual
• Nonlinear angular momentum and u250
• Statistical 250mb eddy activity
• Ter-annual and beyond
• oceanic subtropical highs, monsoons

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Ter-annual variations of sea-level pressure
HF
total
10d
100d
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CSM climate model
HF
total
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Understanding SLP seasonalityZonal mean
total
HF
10d
100d
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Pacific ter-annual SLP schematic
NH Winter High
NH Summer Low
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Outline of examples

• Annual
• Easy (local, thermal) Tsfc
• Nonlocal Z250 (jet streams)
• Semiannual
• Nonlinear angular momentum and u250
• Statistical 250mb eddy activity
• Ter-annual and beyond
• oceanic subtropical highs, monsoons

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Linho and Wang 2002wavelet method
EASM
ISM
WNPM
EASM
ISM
WNPM
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a modeldecentISM onset, but poor at oceanic
systems
EASM
ISM
WNPM
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North America at same time
ENASM?
EASM
NAM
ISM
WNPM
EASM
ISM
WNPM
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June onset in southeast US(from CPC .25deg
1948-98 gauge data set)(mid-summer dip)
Jun 1
Jul 1
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Ter-annual midsummer structure high dry in
tropical Americas
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CMAP 23y mean obs. rain
1
dry
July
Aug
NCEP 27 year (1969-96) SLP Gulf of Mexico area
HF
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Midsummer high in W. Atlantic
21 May- 10 June
wet
3-27 July
dry
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SLP obs G MexicoIPRC/ ECHAM model decent
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Key features of Asian vs. American monsoons a
model experiment

• IPRC / ECHAM model shown to have decent Asian
  onset, American midsummer drought
• Enhance monsoons by allowing each calendar day
  (solar declination) to last 5x24 hours. Summer
  continents get hotter, atm has time to
  equilibrate.
• (SST fixed to obs. for each calendar day)

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April-Sept rainfall, exp-controlS. Asia wetter,
Americas drier

• S. Asia time series shows earlier (May) onset in
  exp
• Stated regarding the control run,
• Land-atm lags delay Asian monsoon onset behind
  its seasonal forcing by 1mo.
• Onset is the main disequilibrium of the Asian
  monsoon wrt seasonal forcing

total
May
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April-Sept rainfall, exp-controlS. Asia wetter,
Americas drier

• Americas time series shows mid-summer drought
  earlier and drier in exp
• Stated regarding the control run,
• Land-atm lags prevent American midsummer drought
  from developing fully
• Midsummer drought is the main disequilibrium of
  the American summer monsoon wrt seasonal forcing

Jun
July
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Outline of examples

• Ter-annual and beyond
• oceanic subtropical highs
• monsoons
• Asian onset
• American midsummer drought
• These things are related

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Chen, Hoerling and Dole 2001
Heating
Eddy Z1000 w/o shear
Eddy Z1000 July u(y,p)
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u300, zonal mean
60N
Westerlies retreat to gt30N in midsummer
lt0
Eq
J F M A M J J A S O N D
easterlies protrude to 30N suddenly in mid summer

• WHY, in terms of u budget?
• Not fv barotropic v(t) wrong
• uv Tilted TUTTs, Tibetan High, Transients?

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Suggested story timing as seen in Key West data
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Winter Wiggles

• Sub-ter-annual time scales real ??
• The January Thaw
• a statistical phantom? (BAMS Jan 2001)
• Brazilian rainfall

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January Thaw lit. of 1919
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Boston, 1872-1965
Entire debate centers on this spike
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Revisit, withmore spatialaveraging
3K

• 1969-96 NCEP reanalysis surface air temperature
• N. America mean
• (think vdT/dy)

HF part
unsmoothed daily T
5K
Jun
Jul
10d
100d
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CPC USprecip1948-98
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Winter Wiggles

• Sub-ter-annual time scales real ??
• The January Thaw
• a statistical phantom? (BAMS Jan 2001)
• Brazilian rainfall

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Where are those boxes? W. subtropical oceans
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TAIWAN 25N

• CMAP rainfall climatologies

May
CUBA 25N
May
SE BRAZIL 25S
Nov.
MADAGASCAR 25S
Nov.
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East Brazil rain gauge data
?
Source CPTEC Web site
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SP Rioclim.
?
Source Hotel inter-continental Web site
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Sub-ter-annual Wiggles

• Brazilian rainfall
• Live software demo
• mapes_at_miami.edu for a DVD copy

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1. Semiannual jets questions

• OK, its a nonlinear overtone driven by the
  annual harmonic of divergence. What and where is
  the nonlinearity?
• Superposition fails of course, but surely one
  could say more than ann div everywhere -gt semiann
  u
• Tropical vs. extratropical divergence?
• Advection of/by divergent vs. rotational wind, u
  vs v?
• Zonal mean vs. longitudinal features (where)?
• Spring/summer/fall/winter?
• (HS2000 is really just a succession of steady
  states)
• Does using obs. divergence presuppose too much?

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East Asia midsummer drought mechanism the Bonin
Highupper level (barotropic)Formation
mechanism of the Bonin High in August(Enomoto,
Hoskins, Matsuda 2003)
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HF anomalies (total - annual - semiannual)
Yes, the Bonin High and 2 other stationary
waves are evident, but also a zonally elongated u
anomaly spanning all Asia-WPAC
u200 HF anomaly plot, July-Aug
Japan
2
0 m/s
-4
-2
time slice
HF
total
Jul Aug
HF wavelet analysis
10d
100d
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Interannual consistency of the Asian HF jet
anomaly 1 Aug
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A hemisphericadjustment?

• SLP 1969-96 from NCEP reanalysis