Shigeo Shigeo YODENYODEN, Kosuke ITO, , Kosuke ITO, and Yoko NAITOand Yoko NAITOKyoto Univ., JAPAN Kyoto Univ., JAPAN

AGU Chapman Conference on The Role of the Stratosphere in Climate and Climate Changein Santorini, Greece, on 28th September, 2007

Parameter Sweep ExperimentsParameter Sweep Experimentson the Remote Influences ofon the Remote Influences ofthe Equatorial QBO and Solar the Equatorial QBO and Solar

Heating around the Stratopause Heating around the Stratopause with a Mechanistic Stratospherewith a Mechanistic Stratosphere--

Troposphere Coupled ModelTroposphere Coupled Model

ENSO

possible causes of the interannual variations of the S-T coupled system (Yoden et al., 2002, JMSJ )

remote influence of the equatorial QBO and solar heating around the stratopause to extratropical lower atmosphere

StratosphericSuddenWarmings

Arctic Oscillation

stratosphericsudden warmingis a key processwhich may amplify a (small) externalforcing in high-latitudes

1. Introduction

forcing polarity polar vortex references

ENSOCold eventWarm event

cold and strongwarm and weak

(Labitzke andvan Loon, 1987)

QBOWesterly phaseEasterly phase

cold and strong warm and weak

(Holton and Tan, 1980)1963-1978, n = 18

SUNSolar minSolar max

like QBOopposite to QBO

(Labitzke + van Loon, 1987, 2006)

AOHigh index (+)Low index (-)

cold and strong warm and weak

(Thomson and Baldwin, 2001)

courtesy of Labitzke (2006) + modification

Labitzke (2006)Different forcings influencing the stratospheric polar vortex during the northern winters

OBSERVATIONS

DYNAMICAL MODELSCOMPLEX MEDIUM SIMPLE

EVOLVINGCONCEPTIAL MODELS

A schematic illustration of the optimum situation for meteorological research

“Mechanistic Circulation Model” (MCM)Hoskins (1983; Quart.J.Roy.Meteor.Soc.)

“Dynamical processes in the atmosphere and the use of models”hierarchy of numerical models

THEORIES

NUMERICAL EXPERIMENTS

hierarchy of numerical models of the atmospheresimple Low-Order Model (LOM) of O(100~101) variablesfor conceptual description

ex.: Lorenz (1960,1963)

medium Mechanistic Circulation Model (MCM) of O(104～105) variablesfor understanding mechanisms

ex.: Boville (1984)

complex General Circulation Model (GCM)of O(104～107) variablesfor quantitative arguments

ex.: Phillips (1956), Smagorinsky et al. (1965), ...

Balanced attack with these models is important !

Byron Boville

in this talk, our recent studies in Kyoto with an MCM are summarizedinternal variability is mainly due to SSWs

Taguchi, Yamaga, and Yoden (2001, JAS )Taguchi and Yoden (2002a, 2002b, JAS ; 2002c, JMSJ )Nishizawa and Yoden (2005, JGR )

seasonal variation of histograms of the monthly mean temperature

Berlin data~50 years30 hPaNorth Pole

MCM15,200 years2.6 hPaNorth Pole

courtesy ofDr. Labitzke

an important question:How does the probability density function of mean [T ] change in the winter polar region depending on systematic variations in external forcings ?

effects of the equatorial QBO on winter circulation (stratospheric sudden warmings)

Naito, Taguchi, and Yoden (2003, JAS )Naito and Yoden (2005, SOLA )Naito and Yoden (2006, JAS )

+ solar effectsIto, Naito, and Yoden (2007, in preparation )

2. Effects of the equatorial QBONaito, Taguchi, and Yoden (2003; JAS, 60, 1380-)

3-D global Mechanistic Circulation Model (MCM)GFD Dennou Club AGCM5 (1998)Resolution: T21L42 (surface to the mesopause)Simplified physical processes:

– Newtonian heating/cooling under perpetual-winter condition– Rayleigh friction at the surface– dry atmosphere – idealized surface topography only in NH (winter)

» zonal wavenumber 1, amp.=1000m

“QBO-wind” forcing in the equatorial regioncf. Horinouchi and Yoden (1997)

du/dt = ・・・・・ - αQBO(φ, z){u - UQBO(φ, z)}αQBO (φ, z) = (1/30) γ (φ, z) [1/day]UQBO (φ, z) = 45γ (φ, z) cos{2π(z-zref)/zdep +θ } [m/s]

12,000-day integrations × 9 runs for different UQBO (φ, z) under constant external conditions

testing the difference between two averageslong time integrations with an MCM: N = 10,800 days

frequency distributionsof the polar temperaturein the tropospherein two runs: E1.0 and W1.0

the large sample methoda standard normal variable Z

the probability that Z reaches 40.6 for two samples of the samepopulations is very small (< 10-27)

E1.0 W1.0

~1K

Freq

uenc

y (%

)

Temperature (K)

φ = 86N, p = 449hPa

latitude

pres

sure

(hPa

)

Maximal difference;

~4K

~2K

50 hPa

250 hPa

Naito and Yoden (2005; SOLA, 1, 17-)46-year daily data (DJF) of NCEP/NCAR Reanalysiscomposite difference of [T ] between <W> – <E>

latitude

98.30 %

Most significant;99.9985%

statistical significance (%)of the composite difference

~2K

’

99.9985% significanc

e

90oN, 250hPa

WesterlyEasterly

frequency distribution of polar [T ] in the upper troposphere for Westerly or Easterly phase

highly significantbut heavily overlapped

StrongerPNJ

WeakerPNJ

Naito and Yoden (2006; JAS, 63, 1637-)“QBO-wind” forcing UQBO (φ, z) in a 3-D global MCMrole of planetary waves generated in the troposphere

10,800-day mean fields of [u ] and EP flux

φ = 86N, p = 2.6hPa o : key day of an SSW event

Total 954 events

time variation of [T ] at the polar stratosphere

time variations of [T ] and Fz during SSW events

[T ]86N Fz30-86N

E’liesW’lies

E’lies

W’lies

W’lies

E’lies

-30 0 30 [day] -30 0 30

Correlations between [T ]86N, 12hPa (+1~+6 days)and Fz30-86N at 4 p-levelsfor each run

before SSW events (a) – positive correlation

all in the stratosphereE’lies in the troposphere

– no significant correlationW’lies in the tropospheredue to the variabilityof the equatorward flux

after SSW events (b) – significant positive

correlationW’lies in the stratosphere

– significant negative correlationE’lies in the troposphere

3. Solar effect in the presence of QBOmotivations

Labitzke (1987, 2006)Correlations between 30-hPa heights and the solar flux of 10.7cm1958-2006 (49 years; NCEP/NCAR RA), (20 more years, in blue)

W E

MA W --

MI C --

MA MI

W W C

E -- --

QBO Westerly QBO Easterly

30-h

Pa

pola

r [T

] in

Feb.

influence of the 11-year solar cycleestimated solar irradiance variations in the UV part

Lean et al. (1997)

200 300 400

60

40

20

0

sola

r irr

adia

nce

varia

tions

[%]

wavelength [nm]

NCEP/CPC (1980-1997)

WMO (1999)Lon Hood (2002)

SSU (1979-1997)

+0.8 K

+2.5 K

-1 K

+1 K +0.25 K

observed annual mean solar signal in temperatureMatthes et al. (2003)

Annual mean temperature differences [K]:20-yr mean Max exp. – Min.exp.(Matthes et al., 2003)

GCM results(GRIPS)

Kodera and Kuroda (2002)changes in E-P flux and Brewer-Dobson circulation associated with the sola effect near the stratopause

Matthes et al. (2003)Observed annual mean solar signal in temperature

Experimental designsolar heating

Kodera and Kuroda(2002)

equatorial QBO identical to Naito and Yoden (2006)WWWW and EEEE

??E

??W

MIMA

φc

Results1st trialdifference of the time-mean temperature between Max.-Min.

φc = 5 Nstatistical significance

– dark color: 95% – light color: 80%

red: warmer in Max.blue: cooler in Max.

latitude

pres

sure

W1.2 － Wmin

E1.2 － Emin

MA MI

W W C

E C W

histgrams of the zonal-mean temperature for Max. and Min.

W1.2

E1.2

Wmin

Emin

parameter dependenceφc : latitude of the large meridional gradient of solar heating effects

W2.4 － Wmin

E2.4 － EminE1.2 － Emin

W1.2 － Wmin

Labitzke relationship

----E

CWW

MIMA

Wmax － Wmin

pres

sure

latitude

pres

sure

latitude

Emax － Emin

Labitzke relationship

WCE

CWW

MIMA

Observation: composite difference of [T ] and significance

QBO effects on zonal mean fieldsstatistical significant difference of the composites; [W] - [E]polar vortex (zonal mean u, T )upper troposphere and aboveboth in the model and the real atmospherealthough heavy overlapping in frequency distribution

EP flux diagnosis of SSW eventssystematic dependence on the phase of the QBO

before and after SSWafter effect in the mid-latitude troposphere

smaller upward EP flux in the troposphere in Easterly phase

Solar effect in the presence of QBOconsistent with Labitzke (1987, 2006) although the composite difference is smaller than “QBO” and the PDFs overlap heavily

4. Concluding remarks

Labitzke(1987) MA MI

W W C

E -- --

Uniqueness of our studyparameter sweep for the phase of the QBO and solar forcingsstatistical analysis based on large sample size

Weak points of the experiment on QBO/Solar effectszonal wavenumber 1 forcing only

wavenumber 2 type SSW ?dependence on the height of the solar forcing

resonance ?perpetual winter runs

seasonal march ?Gray et al. (2004)

QBO-West QBO-East

Max.

Min.

Thank you !

Kodera and Kuroda(2002)

a possible mechanism ofthe downward influenceby planetary wave –mean zonal flowinteraction

early winter anomalies

solar Max:larger Ty and Usmaller Fsmaller v* and w*larger T in the equatorial

lower stratosphere

3. Solar effect in the presence of QBOMotivations

Labitzke (1987, 2006)Correlations between 30-hPa heights and the solar flux of 10.7cm1958-2006 (49 years; NCEP/NCAR RA), (20 more years, in blue)

W E

MA W C

MI C W

QBO Westerly QBO Easterly

30-h

Pa

heig

ht [k

m]

MA MI

W W C

E C W