Dynamics of the mesosphere during sudden stratospheric warmings

Transcription

1 Dynamics of the mesosphere during sudden stratospheric warmings Christoph Zülicke & Erich Becker (Leibniz Institute of Atmospheric Physics, Kühlungsborn, Germany) in cooperation with Peter Hoffmann & Vivian Matthias (IAP), Hauke Schmidt & Andy Miller (MPI-Met Hamburg), Christoph Renkl (FU Berlin) and the ISSI team 5 on middle atmosphere vertical coupling

2 Motivation Sudden stratospheric warmings classical eample for vertical coupling of the atmosphere (Scherhag s Berliner Phänomen ) Time series of soviet rocket data from Hayes Island, drawn by Dr. Günther Entzain (pers. comm.) Ch. Zülicke: Dynamics of the mesosphere

3 Mesospheric reactions MSU- temperature profiles for ALOMAR in January 009: Stratospheric warming coupled with mesospheric cooling (V. Matthias: pers. comm.) Noted by Quiroz (969), Labitzke (97), Eplained by Holton (983) Simulated cases by Liu & Robel (00) Precise timing still to be resolved! MF-Radar- and ECMWF- zonal wind profiles for Andenes in January 999 (P. Hoffmann: pers. comm.) Ch. Zülicke: Dynamics of the mesosphere 3

4 8.0.0 Ch. Zülicke: Dynamics of the mesosphere 4

5 Aim: Use the Kühlungsborn Mechanistic Climate Model (KMCM) to study the spatio-temporal characteristics of mesospheric dynamics during sudden stratospheric warmings Are there self-generated stratospheric warmings? Are the simulated events realistic in frequency and strength? Are the mesospheric patterns stable? How are they related to stratospheric processes? Statistical evaluation of a long model run Ch. Zülicke: Dynamics of the mesosphere 5

6 570 days permanent January with KMCM T0 L90 KMCM spectral GCM dry; fied SST temperature relaation tropospheric heating (Becker, 009: JAS) T0 Δy ~ 60 km L90 Δz ~ 0.58 km (top) 90 N temperature (30 K bold) (right) 60 N zonal mean zonal wind (0 m/s bold) Identified: MSSW (u 60 (0 hpa) < 0 m/s) 5 wssw (u 60 ( hpa) < 0 m/s) Ch. Zülicke: Dynamics of the mesosphere 6

7 major SSW events wssw event 3 (U60 correlated) 0.0 hpa wssw event 5 (U60 anticorrelated) Geopotential wind maps of (left) event 3 (day 56, correlated winds) and (right) event 5 (day 806, anti correlated winds) at (top) 0.0 hpa and (bottom) 0.0 hpa. The stratospheric wave patterns differ in phase and intensity. 0.0 hpa Ch. Zülicke: Dynamics of the mesosphere 7

8 Benchmark for major SSWs Benchmarks after Charlton & Polvani (007: J. Clim. 0: ) (f: Frequency of MSSWs, i.e. those with zonal wind reversal at 60 N at 0 hpa; ΔT CP : anomaly of polar cap temperature above 60 N; Δu CP : deceleration of zonal wind over 0 days). Actually, MSSW events were sampled (at central days 593 and 806) The KMCM-SSWs appear in realistic order but slightly less frequent and more intense as in the reanalyses Ch. Zülicke: Dynamics of the mesosphere 8

9 Composites of 5 weak SSWs 40 day composites around the central day (60 N zonal wind at hpa below 0 m/s; left: pol temperature; right: zonal wind). Here 5 wssw events entered (days 305, 450, 56, 699 and 806). The warm stratopause and cold mesopehere descend, whereafter the new stratopaues reforms. Descending patterns can also be found in the zonal wind, superimposed with a heightindependent east wind anomaly Ch. Zülicke: Dynamics of the mesosphere 9

10 Diagnosis of the wssw composite zonal mean zonal wind with the zonal wind contours averaged from 60 to 70 N. (top left) residual circulation, (top right) quasigeostrophic Eliassen-Palm flu divergence, (bottom left) GW drag and (bottom right) tendency Ch. Zülicke: Dynamics of the mesosphere 0

11 and zonal mean temperature. superimposed with temperature contours averaged from 70 to 90 N. (top left) residual circulation, (top right) temperature relaation, (bottom left) GW heating, diffusion and dissipation and (bottom right) tendency Ch. Zülicke: Dynamics of the mesosphere

12 Time series at.0 and 0.0 hpa 40 day composites at.0 hpa (solid) and 0.0 hpa (dash dotted) of (left) polar temperature (right) zonal wind. While the opposite sensed temperature changes are obvious, the winds seem not to be correlated Ch. Zülicke: Dynamics of the mesosphere

13 8.0.0 Ch. Zülicke: Dynamics of the mesosphere 3 Variance analysis - Theory The relation between the stratospheric and mesospheric signals ( und ) are quantified with the following receipt: ) Detrending and variance-normalization of signals ) Decomposition into equal-sense (correlated ~ mean) and opposite-sense (anticorrelated ~ difference) parts Corresponding correlated and anti-correlated variances are: ( ) ( ) / / t b a t b a b t a b t a = = = = a c = = =,, s s s s s a c

14 Variance analysis - Results Fraction of correlated (equal sense) signals between the.0 und 0.0 hpa pole temperatures (T90) and 60 N zonal winds (u60) for January (all 570 days), the 40 day composite as well the minimum and maimum of the 5 wssw events. The mesospheric temperatures are 9 % anti-correlated (opposite-sensed) to the stratosphere, while the wind changes are 75 % correlated (equal-sensed). However, the variability from event to event is considerable Ch. Zülicke: Dynamics of the mesosphere 4

15 Summary The KMCM self-generates sudden stratospheric warmings in a permanent January run. They appear nearly realistic, although a bit too seldom and too strong. Mesospheric coolings and wind changes appear as stable patterns in the simulations. Stratospheric and mesospheric temperatures change at 9 % in opposite sense, while winds change at 75 % in the same sense. The event-to-event variability is considerable and shows different wave structures Ch. Zülicke: Dynamics of the mesosphere 5

16 westerlies easterlies cooling warming Numbers (-5) refer to weak SSW events; squares indicate the stratosphere (0.0 hpa), diamonds the mesosphere (0.0 hpa). Bold cross = CP07 values Ch. Zülicke: Dynamics of the mesosphere 6

17 Conclusions KMCM is qualified for climatological studies of mesospheric responses to stratospheric warmings. This middle atmosphere SSW benchmark can also be used for a comparative analysis of other simulations & observations Ch. Zülicke: Dynamics of the mesosphere 7

18 Thanks for attention now questions, please! Ch. Zülicke: Dynamics of the mesosphere 8