Mechanisms for influence of the stratosphere on the troposphere

Transcription

1 Mechanisms for influence of the stratosphere on the troposphere Radiative Mass transfer/chemical Dynamical Alan Plumb M. I. T. Apr 2003

2 What dynamical effect does the stratosphere have on the troposphere?

3 What dynamical effect does the stratosphere have on the troposphere? What does the question mean?

4 What dynamical effect does the stratosphere have on the troposphere? What does the question mean? o How does the troposphere react to a reasonable change in the stratospheric state?

5 What dynamical effect does the stratosphere have on the troposphere? What does the question mean? o How does the troposphere react to a reasonable change in the stratospheric state? What are the mechanisms?

6 What dynamical effect does the stratosphere have on the troposphere? What does the question mean? o How does the troposphere react to a reasonable change in the stratospheric state? What are the mechanisms? o The stratosphere responds to the upwelling EP flux

7 Stratospheric response to tropospheric wave bursts [1]

8 What dynamical effect does the stratosphere have on the troposphere? What does the question mean? o How does the troposphere react to a reasonable change in the stratospheric state? What are the mechanisms? o The stratosphere responds to the upwelling EP flux What determines the EP flux into the stratosphere?

9 What dynamical effect does the stratosphere have on the troposphere? Is there any unambiguous observational evidence for such an effect and how could it be identified?

10 Possible mechanisms for feedback

11 Lorenz & Hartmann J. Atmos. Sci (2001); J. Clim (2003)

12 Possible mechanisms for feedback

13 Planetary wave reflection

14 Response of tropospheric Rossby waves to a stratospheric wind shift (Courtesy of Michael Ring, MIT)

15 Possible mechanisms for feedback change in upwelling EP flux

16 Possible mechanisms for feedback meridional circulation

17 Remote balanced interaction FIG. 5. As in Fig. 4b but for PV inversions (a) using static stability values representing an average over latitudes from 5 to 90 N, (b) that include the contribution of surface theta anomalies, and (c) that include the contribution of PV anomalies located at high latitudes in the upper troposphere.

18 z orographic forcing EQ POLE

19 drag applied where wave is dissipated z form drag at surface EQ POLE

20 drag applied where wave is dissipated z westerly force applied where wave is generated non-orographic forcing EQ POLE

21 Short-term response z EQ POLE

22 Short-term response z U t 0 EQ POLE

23 v q 0 z q 0 q 0 EQ POLE

24 δu < 0 z q 0 q 0 EQ POLE

25 Long-term steady response δu < 0 z EQ POLE

26 Downward control does not always mean downward control!

27 drag applied where wave is dissipated z form drag at surface EQ POLE

28 Surface mean wind long term balance Long-term QG steady state fv 1 cos p F g p p p 0 p J c p y u v Integrated angular momentum balance S 1 g F p S 1 a cos 2 cos2 u v dp 1 g F p S S surface stress form drag lateral radiation of angular momentum

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30 Surface mean wind long term balance Long-term QG steady state fv 1 cos p F g p p p 0 p J c p y u v Integrated angular momentum balance S 1 g F p S 1 a cos 2 cos2 u v dp 1 g F p S S surface stress form drag lateral radiation of angular momentum

31 Short-term behavior

32 Downward propagation? Baldwin, M.P., and T.J. Dunkerton, 2001: Stratospheric harbingers of anomalous weather regimes. Science,

33 Stratospheric response to tropospheric wave bursts [1]

34 Downward propagation? Baldwin, M.P., and T.J. Dunkerton, 2001: Stratospheric harbingers of anomalous weather regimes. Science,

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41 Response of a truncated b-channel model to periodic wave driving z(km) F (m) t (days) z(km) U anomaly (ms -1 ) t (days) Left: Wave amplitude (m; top) and mean zonal wind in response to periodically modulated tropospheric wave forcing. Right: Composites over one wave period. [Plumb & Semeniuk, 2003]

42 3D model results [Plumb & Semeniuk, 2003]

43 Migration is not (necessarily) information transfer Wave amplitude (m; top) and mean zonal wind in response to periodically modulated tropospheric wave forcing. Left: full response. [Plumb & Semeniuk, 2003]

44 Migration is not (necessarily) information transfer Wave amplitude (m; top) and mean zonal wind in response to periodically modulated tropospheric wave forcing. Left: full response. Right: response suppressed above 25km. [Plumb & Semeniuk, 2003]

45 Downward propagation? Baldwin, M.P., and T.J. Dunkerton, 2001: Stratospheric harbingers of anomalous weather regimes. Science,

46 Relation with upwelling EP flux Composite vs. applied EP flux Time of maximum imposed flux

47 Detecting an effect Is there any unambiguous observational evidence for such an effect and how could it be identified?

48 Detecting an effect Is there any unambiguous observational evidence for such an effect and how could it be identified? Most stratospheric behavior has precursors in the troposphere Need independent stratospheric signals

49 Signals of Stratospheric Origin: QBO

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51 Naito J. Met. Soc. Japan (2002)

52 Short-term (intraseasonal) Conclusions Not clear what effect there is Annular modes appear to be controlled by synoptic scale eddies; any effect on annular modes (unless coincidental) requires an impact on tropospheric eddy, mean flow interaction Even if the stratosphere has little or no causal effect, stratospheric behavior may be useful in forecasting for the troposphere by virtue of the rapid stratospheric response

53 Short-term (intraseasonal) Conclusions Not clear what effect there is Annular modes appear to be controlled by synoptic scale eddies; any effect on annular modes (unless coincidental) requires an impact on tropospheric eddy, mean flow interaction Even if the stratosphere has little or no causal effect, stratospheric behavior may be useful in forecasting for the troposphere by virtue of the rapid stratospheric response Long-term (climate) Tropospheric response to tropospheric wave forcing sensitive to location (in latitude but not altitude) of stratospheric wave dissipation (effect ~1ms -1 ) Tropospheric planetary-scale waves (and EP flux into the stratosphere) have some sensitivity to latitudinal shifts of stratospheric winds What controls the EP flux into the stratosphere? The capacity of the stratosphere to absorb wave activity is finite