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

Transcription

1 AGU Chapman Conference on The Role of the Stratosphere in Climate and Climate Change in Santorini, Greece, on 28th September, 2007 Parameter Sweep Experiments on the Remote Influences of the Equatorial QBO and Solar Heating around the Stratopause with a Mechanistic Stratosphere- Troposphere Coupled Model Shigeo YODEN,, Kosuke ITO, and Yoko NAITO Kyoto Univ., JAPAN

2 1. Introduction 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 ENSO Stratospheric Sudden Warmings Arctic Oscillation stratospheric sudden warming is a key process which may amplify a (small) external forcing in highlatitudes

3 Labitzke (2006) Different forcings influencing the stratospheric polar vortex during the northern winters forcing polarity polar vortex references ENSO Cold event Warm event cold and strong warm and weak (Labitzke andvan Loon, 1987) QBO SUN AO Westerly phase Easterly phase Solar min Solar max High index (+) Low index (-) cold and strong warm and weak like QBO opposite to QBO cold and strong warm and weak (Holton and Tan, 1980) , n = 18 (Labitzke + van Loon, 1987, 2006) (Thomson and Baldwin, 2001) courtesy of Labitzke (2006) + modification

4 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 OBSERVATIONS EVOLVING THEORIES CONCEPTIAL MODELS NUMERICAL DYNAMICAL EXPERIMENTS MODELS COMPLEX MEDIUM SIMPLE A schematic illustration of the optimum situation for meteorological research

5 hierarchy of numerical models of the atmosphere simple Low-Order Model (LOM) of O(10 0 ~10 1 ) variables for conceptual description ex.: Lorenz (1960,1963) medium Mechanistic Circulation Model (MCM) of O(10 4 ~10 5 ) variables for understanding mechanisms ex.: Boville (1984) complex General Circulation Model (GCM) of O(10 4 ~10 7 ) variables for quantitative arguments ex.: Phillips (1956), Smagorinsky et al. (1965),... Byron Boville Balanced attack with these models is important!

6 in this talk, our recent studies in Kyoto with an MCM are summarized internal 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 years 30 hpa North Pole MCM 15,200 years 2.6 hpa North Pole courtesy of Dr. Labitzke

7 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 effects Ito, Naito, and Yoden (2007, in preparation )

8 2. Effects of the equatorial QBO Naito, 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 region cf. Horinouchi and Yoden (1997) du/dt = - α QBO (φ, z){u - U QBO (φ, z)} α QBO (φ, z) = (1/30) γ (φ, z) [1/day] U QBO (φ, z) = 45γ (φ, z) cos{2π(z-z ref )/z dep +θ } [m/s] 12,000-day integrations 9 runs for different U QBO (φ, z) under constant external conditions

9 testing the difference between two averages long time integrations with an MCM: N = 10,800 days frequency distributions of the polar temperature in the troposphere in two runs: E1.0 and W1.0 the large sample method a standard normal variable Z Frequency (%) φ = 86N, p = 449hPa E1.0 W1.0 ~1K the probability that Z reaches 40.6 for two samples of the same populations is very small (< ) Temperature (K)

10 Naito and Yoden (2005; SOLA, 1, 17-) 46-year daily data (DJF) of NCEP/NCAR Reanalysis composite difference of [T ] between <W> <E> statistical significance (%) of the composite difference 50 hpa pressure (hpa) % Most significant ; % Maximal difference; ~4K 250 hpa ~2K latitude latitude

11 frequency distribution of polar [T ] in the upper troposphere for Westerly or Easterly phase highly significant but heavily overlapped 90 o N, 250hPa Westerly ~2K Easterly % significanc e

12 Naito and Yoden (2006; JAS, 63, 1637-) QBO-wind forcing U QBO (φ, z) in a 3-D global MCM role of planetary waves generated in the troposphere 10,800-day mean fields of [u ] and EP flux Stronger PNJ Weaker PNJ

13 time variation of [T ] at the polar stratosphere φ = 86N, p = 2.6hPa o : key day of an SSW event Total 954 events

14 time variations of [T ] and Fz during SSW events [T ] 86N Fz 30-86N E lies W lies E lies W lies W lies E lies [day]

15 Correlations between [T ] 86N, 12hPa (+1~+6 days) and Fz 30-86N at 4 p-levels for each run before SSW events (a) positive correlation all in the stratosphere E lies in the troposphere no significant correlation W lies in the troposphere due to the variability of the equatorward flux after SSW events (b) significant positive correlation W lies in the stratosphere significant negative correlation E lies in the troposphere

16 3. Solar effect in the presence of QBO motivations Labitzke (1987, 2006) Correlations between 30-hPa heights and the solar flux of 10.7cm (49 years; NCEP/NCAR RA), (20 more years, in blue) 30-hPa polar [T ] in Feb. QBO Westerly QBO Easterly W E MA W -- MI C -- MA MI W W C E -- --

17 influence of the 11-year solar cycle estimated solar irradiance variations in the UV part solar irradiance variations [%] Lean et al. (1997) wavelength [nm]

18 observed annual mean solar signal in temperature Matthes et al. (2003) NCEP/CPC ( ) SSU ( ) +2.5 K +0.8 K -1 K +1 K K Lon Hood (2002) WMO (1999)

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

20 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

21 Experimental design solar heating Kodera and Kuroda(2002) equatorial QBO identical to Naito and Yoden (2006) WWWW and EEEE MA MI W?? φ c E??

22 Results 1st trial difference of the timemean temperature between Max.-Min. φ c = 5 N statistical significance dark color: 95% light color: 80% red: warmer in Max. blue: cooler in Max. W1.2 - Wmin E1.2 - Emin MA MI W W C E C W pressure latitude

23 histgrams of the zonal-mean temperature for Max. and Min. W1.2 Wmin E1.2 Emin

24 parameter dependence φ c : latitude of the large meridional gradient of solar heating effects W1.2 - Wmin W2.4 - Wmin E1.2 - Emin Labitzke relationship E2.4 - Emin W E MA W -- MI C --

25 Observation: composite difference of [T ] and significance Wmax - Wmin pressure pressure Labitzke relationship W E MA W C MI C Emax W - Emin latitude latitude

26 4. Concluding remarks QBO effects on zonal mean fields statistical significant difference of the composites; [W] - [E] polar vortex (zonal mean u, T ) upper troposphere and above both in the model and the real atmosphere although heavy overlapping in frequency distribution EP flux diagnosis of SSW events systematic dependence on the phase of the QBO before and after SSW after effect in the mid-latitude troposphere smaller upward EP flux in the troposphere in Easterly phase Solar effect in the presence of QBO consistent with Labitzke (1987, 2006) although the composite difference is smaller than QBO and the PDFs overlap heavily Labitzke (1987) MA MI W W C E -- --

27 Uniqueness of our study parameter sweep for the phase of the QBO and solar forcings statistical analysis based on large sample size Weak points of the experiment on QBO/Solar effects zonal 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) Max. QBO-West QBO-East Min.

28 Thank you!

29 Kodera and Kuroda (2002) early winter anomalies a possible mechanism of the downward influence by planetary wave mean zonal flow interaction solar Max: larger Ty and U smaller F smaller v* and w* larger T in the equatorial lower stratosphere

30 3. Solar effect in the presence of QBO Motivations Labitzke (1987, 2006) Correlations between 30-hPa heights and the solar flux of 10.7cm (49 years; NCEP/NCAR RA), (20 more years, in blue) 30-hPa height [km] QBO Westerly QBO Easterly W E MA W C MI C W MA MI W W C E C W