yoko naito & shigeo yoden dept. of geophysics, kyoto univ
DESCRIPTION
A Statistical Analysis on the Stratosphere-Troposphere Coupled Variability by Using Large Samples obtained from a Mechanistic Circulation Model. Yoko NAITO & Shigeo YODEN Dept. of Geophysics, Kyoto Univ. Outline. A statistical analysis with data obtained by a numerical experiment. - PowerPoint PPT PresentationTRANSCRIPT
A Statistical Analysis on the
Stratosphere-Troposphere Coupled Variability
by Using Large Samplesobtained from a Mechanistic Circulation
Model
Yoko NAITO & Shigeo YODEN
Dept. of Geophysics, Kyoto Univ.
Outline
Check the model results with data observed in
the real atmosphere
A statistical analysis with data obtained by
a numerical experiment
1.1 A statistical analysis by using large samples
E1.0 W1.0
1. Introduction
Frequency distributions of zonal-mean temperature (86N, 449hPa, 10800 days) in two runs: E1.0 and W1.0
~1K
Frequ
en
cy (
%)
Naito, Taguchi and Yoden (2003)
A parameter sweep experiment
on the effects of the equatorial
QBO on stratospheric suddenwarming events
[J.Atmos.Sci., 60, 1380— ]
Temperature (K)
Close to Gaussian;Heavily overlapped
1.2 Testing the difference between two averages The large sample method A standard normal variable Z : The probability that Z reaches 40.6 for two
samples of the same populations is very small ( < 10-27 )
2 2
2 2
226.8 225.840.6
1.87 1.75
10800 10800
W E
W E
W E
T TZ
N N
[TW] : average of TW
[TE] : average of TE
W2 : variance of TW
E2 : variance of TE
NW : sample size of TW
NE : sample size of TE
The difference is very significant
2. QBO effects on the extratropical stratosphere and troposphere
(Yoden et al., 2002; JMSJ )2.1 The S-T coupled variability and its possible causes
EquatorialEquatorial ExtratropicalExtratropicalDynamical variability StratosphericStratospheric
Sudden WarmingSudden Warming(SSW) events(SSW) events
1953
1963
1974
1985
1996 2004
1962
1973
1984
1995
yearalt
itu
de
32(km)
18
Westerly
Easterly
Westerly
Easterly
2.2 QBO: Quasi-Biennial Oscillation
(data provided by Naujokat)
Zonal wind over the Equator in the lower stratosphere (m/s)
3. Numerical experiments3.1 Naito, Taguchi and Yoden (2003)
Model Simplified 3-D global circulation model
Imposed “QBO-wind” forcing
du dt ……QBOuUQBO
QBO : relaxation coefficient ; UQBO : basic
profile
(confined in the equatorial lower stratosphere)
Long time integrations • NW = NE = 10800 days
• Fixed external conditions
at 90oN, 2.6hPa
W1.0
E1.0
(K)300
200
(K)300
20010000 11000 120001150010500
(day)
3.2 The polar temperature and SSW events
… key day of a SSW event
Obtained time series of the temperature
SSW: Stratospheric Sudden Warming events 57 events in the W1.0 run 168 events in the E1.0 run cf. observed major warmings in the past 46 years: 7 events in the Westerly phase 13 events in the Easterly phase
2. Numerical Experiments
Tem
pera
ture
(K
)
Lag (day)
3.3 Composites of the polar temperature during SSWs
A key day isdefined here
Zsignificance
• Lower stratosphere - most significant (> 99.99999% at Lag ~ 4 days)• Mid-troposphere - still significant (> 99.9999% at Lag ~ 12 days)
W1.0 ( 57 events) E1.0 (168 events)
4. Real atmosphere
4.1 Data and method of the analysis
NCEP/NCAR Reanalysis Data
- Winter months (Dec,Jan,Feb) during 1958—2003
2316 days in the Westerly, 1834 days in the Easterly
Independence of the serial data
- N is replaced by an effective sample size N’ N /
0
0 : an effective sampling time (day)
(of the order of months in the stratosphere,
of the order of weeks in the troposphere)
4.2 Composite difference (Westerly minus Easterly) of the zonal-mean temperature (K)
pre
ssu
re (
hPa)
Maximal differenc
e;
~4K
~2K
latitude
50 hPa
250 hPa
4.3 Statistical significance (%) of the composite difference
latitudelatitude
98.30 %
Most significant;
99.9985%
pre
ssu
re (
hPa)
Maximal differenc
e;
~4K
~2K
50 hPa
250 hPa
~2K
’
Close to Gaussian; Heavily overlapped
99.9985% significan
ce
4.4 Frequency distribution of the polar temperature at the upper troposphere90oN, 250hPa
Westerly
Easterly
Concluding remarksProposal of a new experimental framework • Long time integrations can be done
with a 3-D global circulation modelby changing a key external parameter.
• Statistical significance of the QBO effectson the extratropical variability is testedby the large sample method.
Possible application of this statistical method
• Effects of the other external causescan be tested by this statistical method.(ex. 11-year solar cycle, volcanic aerosols, El Nino/Southern Oscillation, and so on)
That’s all.Thank you for your attention.