How does stratospheric polar vortex variability affect surface weather? Mark Baldwin and Tom Clemo

Transcription

1 How does stratospheric polar vortex variability affect surface weather? Mark Baldwin and Tom Clemo Mark P. Baldwin, University of Exeter Imperial College 12 December 2012

2 a Observed Average Surface Pressure Anomalies (hpa) 60 days following weak stratospheric winds 60 days following strong stratospheric winds b -1 Strong Vortex Regimes Text b From Baldwin and Dunkerton., 2001

3 Storm Tracks Red: after weak vortex events Blue: after strong vortex events Text From Baldwin and Dunkerton, 2001

4 4

5 Baldwin and Dunkerton (JGR 1999) suggested that the redistribution of mass in the stratosphere, in response to changes in wave driving, may be sufficient to influence the surface pressure significantly, consistent with the theoretical results of Haynes and Shepherd (1989). 4

6 Baldwin and Dunkerton (JGR 1999) suggested that the redistribution of mass in the stratosphere, in response to changes in wave driving, may be sufficient to influence the surface pressure significantly, consistent with the theoretical results of Haynes and Shepherd (1989). Ambaum and Hoskins (JClim 2002) used PV thinking to explain how stratospheric PV anomalies affect surface pressure. 4

7 FIG. 4.Schematicofthebendingofisentropicsurfaces(labeled 0, 1,and 2 )towardapositivepotentialvorticityanomaly.the arrows represent winds associated with the potential vorticity anomaly, becoming weaker away from the anomaly. Diagram from Ambaum and Hoskins J Climate (2002). 5

8 Index formed directly from PV? FIG. 4.Schematicofthebendingofisentropicsurfaces(labeled 0, 1,and 2 )towardapositivepotentialvorticityanomaly.the arrows represent winds associated with the potential vorticity anomaly, becoming weaker away from the anomaly. Diagram from Ambaum and Hoskins J Climate (2002). 5

9 Index formed directly from PV? Polar Cap PV at 530k, 600k FIG. 4.Schematicofthebendingofisentropicsurfaces(labeled 0, 1,and 2 )towardapositivepotentialvorticityanomaly.the arrows represent winds associated with the potential vorticity anomaly, becoming weaker away from the anomaly. Diagram from Ambaum and Hoskins J Climate (2002). 5

10 10 Correlation: JFM Polar Cap PV600K Index with Tbar K surface hpa PV anom. - PV anom Latitude Correla=on during winter (JFM) between the 600K PV index and zonal-mean temperature. The JFM daily correla=on between PV600 and polar cap tropopause T anomalies is From Baldwin and Birner, in prep

11 10 Correlation: JFM Polar Cap PV600K Index with Tbar K surface hpa hpa PV anom. - PV anom Latitude Correla=on during winter (JFM) between the 600K PV index and zonal-mean temperature. The JFM daily correla=on between PV600 and polar cap tropopause T anomalies is From Baldwin and Birner, in prep

12 A simple model Mass Higher pressure and temperature 7

13 A simple model Mass Higher pressure and temperature Polar cap 7

14 Polar cap pressure anomalies (Z) 8

15 Polar cap pressure anomalies (Z) Tropospheric amplifica=on 8

16 Courtesy Tom Clemo 9

17 Courtesy Tom Clemo 10

18 Observed Average Surface Pressure Anomalies (hpa) Text From Baldwin and Dunkerton., 2001

19 a Observed Average Surface Pressure Anomalies (hpa) 60 days following weak stratospheric winds b -1 Strong Vortex Regimes Text b

20 Conclusions 13

21 Conclusions The stratospheric wave-driven pump creates polar PV anomalies. Equivalently, it moves mass into and out of the polar cap. 13

22 Conclusions The stratospheric wave-driven pump creates polar PV anomalies. Equivalently, it moves mass into and out of the polar cap. Both PV theory (and movement of mass) provides an explanation for the observed NAM signal down to the tropopause. 13

23 Conclusions The stratospheric wave-driven pump creates polar PV anomalies. Equivalently, it moves mass into and out of the polar cap. Both PV theory (and movement of mass) provides an explanation for the observed NAM signal down to the tropopause. The magnitude of the surface NAM signal cannot be explained by PV theory. Tropospheric processes presumably involving baroclinic eddies amplify the signal. 13

24 Conclusions The stratospheric wave-driven pump creates polar PV anomalies. Equivalently, it moves mass into and out of the polar cap. Both PV theory (and movement of mass) provides an explanation for the observed NAM signal down to the tropopause. The magnitude of the surface NAM signal cannot be explained by PV theory. Tropospheric processes presumably involving baroclinic eddies amplify the signal. A simple polar cap pressure diagnostic can be used to evaluate the fidelity of S T coupling in models. 13

25 Conclusions The stratospheric wave-driven pump creates polar PV anomalies. Equivalently, it moves mass into and out of the polar cap. Both PV theory (and movement of mass) provides an explanation for the observed NAM signal down to the tropopause. The magnitude of the surface NAM signal cannot be explained by PV theory. Tropospheric processes presumably involving baroclinic eddies amplify the signal. A simple polar cap pressure diagnostic can be used to evaluate the fidelity of S T coupling in models. Index to measure effects of the stratosphere on the troposphere: Polar cap average T at 100hPa. 13

26 Conclusions The stratospheric wave-driven pump creates polar PV anomalies. Equivalently, it moves mass into and out of the polar cap. Both PV theory (and movement of mass) provides an explanation for the observed NAM signal down to the tropopause. The magnitude of the surface NAM signal cannot be explained by PV theory. Tropospheric processes presumably involving baroclinic eddies amplify the signal. A simple polar cap pressure diagnostic can be used to evaluate the fidelity of S T coupling in models. Index to measure effects of the stratosphere on the troposphere: Polar cap average T at 100hPa. 13

27 Conclusions The stratospheric wave-driven pump creates polar PV anomalies. Equivalently, it moves mass into and out of the polar cap. Both PV theory (and movement of mass) provides an explanation for the observed NAM signal down to the tropopause. The magnitude of the surface NAM signal cannot be explained by PV theory. Tropospheric processes presumably involving baroclinic eddies amplify the signal. A simple polar cap pressure diagnostic can be used to evaluate the fidelity of S T coupling in models. Index to measure effects of the stratosphere on the troposphere: Polar cap average T at 100hPa. 13

28 (From Baldwin and Dunkerton, 2001)

29 Text

30 EOFs Text

31 EOFs NAM Index Text

32 EOFs NAM Index Text

33 EOFs NAM Index Potential Text Vorticity

34 EOFs NAM Index Potential Text Vorticity

35 EOFs NAM Index Potential Text Vorticity Pressure (mass), Temperature

36 EOFs NAM Index Potential Text Vorticity Pressure (mass), Temperature

37 Wave Driven Pump Wave Drag Anomalous wave drag leads to variations in vortex strength

38 17

39 50-hPa Annular Mode

40 Form a daily index of PV, averaged over the polar cap (65º pole) at 600k. Text

41 Composite Anomalous Pressure, 33 Weak Vortex events PV index at 600K Pressure Anomaly, 7 hpa between ticks 330K 320K 315K 310K 305K Lag (days) 20

42 Anomalous Baroclinicity (slope of isentropic surfaces) NAO Correla=on during winter (JFM) between the 600K PV index and zonal-mean temperature. The JFM daily correla=on between PV530 and polar cap tropopause T anomalies is