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Yoko NAITO & Shigeo YODEN Dept. of Geophysics, Kyoto Univ.

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.

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Yoko NAITO & Shigeo YODEN Dept. of Geophysics, Kyoto Univ.

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  1. A Statistical Analysison theStratosphere-Troposphere Coupled Variabilityby Using Large Samplesobtained from a Mechanistic Circulation Model Yoko NAITO& Shigeo YODEN Dept. of Geophysics, Kyoto Univ.

  2. Outline  A statistical analysis with data obtained bya numerical experiment  Check the model results with data observed inthe real atmosphere

  3. 1. Introduction 1.1 A statistical analysis by using large samples E1.0 W1.0 Frequency distributions of zonal-mean temperature (86N, 449hPa, 10800 days) in two runs: E1.0 and W1.0 ~1K Frequency (%) Naito, Taguchi and Yoden (2003) A parameter sweep experimenton the effects of the equatorialQBO on stratospheric suddenwarming events [J.Atmos.Sci., 60, 1380— ] Close to Gaussian; Heavily overlapped Temperature (K)

  4. 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 ) [TW] : average of TW [TE] : average of TE sW2 : variance of TW sE2 : variance of TE NW : sample size of TW NE : sample size of TE The difference is very significant

  5. 2. QBO effects on the extratropical stratosphere and troposphere 2.1 The S-T coupled variability and its possible causes (Yoden et al., 2002; JMSJ ) Equatorial Extratropical Stratospheric Sudden Warming (SSW) events Dynamical variability

  6. 32(km) 18 altitude year 1962 1953 1963 1973 1974 1984 1985 1995 1996 2004 2.2 QBO: Quasi-Biennial Oscillation Zonal wind over the Equator in the lower stratosphere (m/s) Easterly Easterly Westerly Westerly (data provided by Naujokat)

  7. 3. Numerical experiments 3.1 Naito, Taguchi and Yoden (2003) Model Simplified 3-D global circulation model Imposed “QBO-wind” forcing du / dt = …… - aQBO ( u - UQBO ) aQBO : relaxation coefficient ; UQBO : basic profile (confined in the equatorial lower stratosphere) Long time integrations • NW = NE = 10800 days • Fixed external conditions

  8. at 90oN, 2.6hPa (K) 300 200 W1.0 (K) 300 200 E1.0 10000 10500 11000 11500 12000 (day) 3.2 The polar temperature and SSW events Obtained time series of the temperature  … key day of a SSW event SSW: Stratospheric Sudden Warming events57 events in the W1.0 run168 events in the E1.0 run cf. observed major warmings in the past 46 years:7 events in the Westerly phase13 events in the Easterly phase

  9. 2. Numerical Experiments Z A key day is defined here 3.3 Composites of the polar temperature during SSWs significance W1.0 ( 57 events) E1.0 (168 events) Temperature (K) • Lower stratosphere - most significant (> 99.99999% at Lag ~ 4 days) • Mid-troposphere - still significant (> 99.9999% at Lag ~ 12 days) Lag (day)

  10. 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 sizeN’  N / t0 t0: an effective sampling time (day) (of the order of months in the stratosphere, of the order of weeks in the troposphere)

  11. 4.2 Composite difference (Westerly minus Easterly) of the zonal-mean temperature (K) 50 hPa Maximal difference; ~4K pressure (hPa) 250 hPa ~2K latitude

  12. 4.3 Statistical significance (%) of the composite difference 50 hPa 98.30 % Maximal difference; ~4K pressure (hPa) Most significant; 99.9985% 250 hPa ~2K latitude latitude

  13. 4.4 Frequency distribution of the polar temperature at the upper troposphere 90oN, 250hPa Westerly ~2K Easterly ’ 99.9985% significance Close to Gaussian; Heavily overlapped

  14. Concluding remarks Proposal of a new experimental framework • Long time integrations can be donewith 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)

  15. That’s all.Thank you for your attention.

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