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

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strides steps and stumbles in the march of the seasons
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)
temporal fourier spectrum of annual insolation
Temporal Fourier spectrum of annual insolation

no forcing, just

internal

nonlinearitites

sin(4pt/365d)

Semiannual

sin(2pt/365d)

Annual

annual cycle signal processing by the earth
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

annual cycle signal processing by the computer
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}

wavelet example
Wavelet example
  • Paul wavelet
  • Sharp time localization
  •  broad in frequency
  • Real part: max/min
  • Imaginary part: rise/fall
  • (Torrence and Compo 1998 BAMS)
signal processed now what
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

outline of examples
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
slide14
Local Hadley cells?

Annual

Harmonic

of u at

200 hPa

Jan 1

Apr 1

Annual

Harmonic

of atmos.

heating

outline of examples1
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
semiannual harmonic of 250 hpa zonal wind
Apr-Oct

Jan

Apr

Apr-Oct

Semiannual harmonic of 250 hPa zonal wind

Jan

Apr

Apr

OBS

May+Nov

HF

total

Apr

Jun+Dec

CSM

slide18
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

semiannual eddy storm activity
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.

slide20
midwinter eddy minimumsemiannual amplitude (color) of a climatology of stdev of 9d sliding window v250Decently simulated by coupled model

NCEP 1969-96

Oct+Apr maxima

of eddy v variance

CSM 1.3

outline of examples2
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
pacific ter annual slp schematic
Monsoon-related

~100d period high

Oceanic

(Aleutian)

~semiannual low

Pacific ter-annual SLP schematic

NH Winter High

NH Summer Low

outline of examples3
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
linho and wang 2002 wavelet method
Linho and Wang 2002wavelet method

EASM

ISM

WNPM

EASM

ISM

WNPM

north america at same time
North America at same time

ENASM?

EASM

NAM

ISM

WNPM

EASM

ISM

WNPM

ter annual midsummer structure high dry in tropical americas
5Ter-annual midsummer structurehigh & dry in tropical Americas

CMAP 23y mean obs. rain

1

dry

July

Aug

NCEP 27 year (1969-96) SLP

Gulf of Mexico area

HF

midsummer high in w atlantic
Midsummer high in W. Atlantic

21 May-

10 June

wet

3-27

July

dry

key features of asian vs american monsoons a model experiment
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)

april sept rainfall exp control s asia wetter americas drier
April-Sept rainfall, exp-control:S. 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

april sept rainfall exp control s asia wetter americas drier1
April-Sept rainfall, exp-control:S. 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

outline of examples4
Outline of examples
  • Ter-annual and beyond
    • oceanic subtropical highs
    • monsoons
      • Asian onset
      • American midsummer drought
  • These things are related
chen hoerling and dole 2001
Chen, Hoerling and Dole 2001

Heating

Eddy Z1000

w/o shear

Eddy Z1000

July u(y,p)

u300 zonal mean
Jul-Aug time slice

time slice

u300, zonal mean

60N

Westerlies retreat to >30N in midsummer

<0

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 f[v]: ~barotropic; [v](t) wrong
    • [u’v’]: Tilted TUTTs, Tibetan High, Transients?
winter wiggles
Winter Wiggles
  • Sub-ter-annual time scales: real ??
    • ‘The January Thaw’
      • a statistical phantom? (BAMS Jan 2001)
    • Brazilian rainfall
slide42
January Thaw

lit. of 1919

boston 1872 1965
missing thisBoston, 1872-1965

Entire debate centers

on this spike

revisit with more spatial averaging
JanRevisit, withmore spatialaveraging
  • 1969-96 NCEP reanalysis surface air temperature
  • N. America mean
  • (think vdT/dy)

3K

HF part

unsmoothed daily T

5K

Jun

Jul

10d

100d

winter wiggles1
Winter Wiggles
  • Sub-ter-annual time scales: real ??
    • ‘The January Thaw’
      • a statistical phantom? (BAMS Jan 2001)
    • Brazilian rainfall
slide47
High

High

High

High

Where are those boxes? W. subtropical oceans

slide48
TAIWAN 25N

May

CMAP rainfall climatologies:

CUBA 25N

May

SE BRAZIL 25S

Nov.

MADAGASCAR

25S

Nov.

east brazil rain gauge data
East Brazil rain gauge data

?

Source: CPTEC Web site

sp rio clim
SP & Rioclim.

?

Source: Hotel inter-continental Web site

sub ter annual wiggles
Sub-ter-annual Wiggles
  • Brazilian rainfall

Live software demo

[email protected] for a DVD copy

1 semiannual jets questions
1. Semiannual jets: questions
  • OK, it’s 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 -> 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?

slide53
East Asia midsummer drought mechanism: the Bonin Highupper level (barotropic)“Formation mechanism of the Bonin High in August”(Enomoto, Hoskins, & Matsuda 2003)
slide54
u200 HF anomaly plot, July-Aug

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

Japan

2

-4

0 m/s

-2

time

slice

HF

total

Jul Aug

HF wavelet analysis

10d

100d

a hemispheric adjustment
A hemisphericadjustment?
  • SLP 1969-96 from NCEP reanalysis
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