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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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A Statistical Analysison theStratosphere-Troposphere Coupled Variabilityby Using Large Samplesobtained from a Mechanistic Circulation Model Yoko NAITO& Shigeo YODEN Dept. of Geophysics, Kyoto Univ.
Outline A statistical analysis with data obtained bya numerical experiment Check the model results with data observed inthe real atmosphere
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)
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
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
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)
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
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
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)
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)
4.2 Composite difference (Westerly minus Easterly) of the zonal-mean temperature (K) 50 hPa Maximal difference; ~4K pressure (hPa) 250 hPa ~2K latitude
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
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
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)
