Relationships between Convectively Coupled Kelvin Waves and Extratropical Wave Activity George N. Kiladis Klaus Weickmann Brant Liebmann NOAA, Physical.

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Presentation transcript:

Relationships between Convectively Coupled Kelvin Waves and Extratropical Wave Activity George N. Kiladis Klaus Weickmann Brant Liebmann NOAA, Physical Sciences Division Earth System Research Laboratory CIRES, University of Colorado George N. Kiladis Klaus Weickmann Brant Liebmann NOAA, Physical Sciences Division Earth System Research Laboratory CIRES, University of Colorado

Or: Some (as yet only partially explained) observations of Kelvin Waves and Associated Extratropical Disturbances

Data Sources Cloud Archive User Services (CLAUS) Brightness Temperature 8 times daily,.5  resolution July 1983-September 2005 NCEP-NCAR Reanalysis products 4 times daily, 17 pressure levels, 2.5  resolution

Key Papers: Lindzen, R. D., 1967: Planetary waves on beta-planes. Mon. Wea. Rev. Hoskins, B. J. and T. Ambrizzi 1993: Rossby wave propagation on a realistic longitudinally varying flow. J. Atmos. Sci. Zhang, C. and P. J. Webster, 1989: Effects of zonal flows on equatorially-trapped waves. J. Atmos. Sci. Zhang, C. and P. J. Webster, 1992: Laterally forced equatorial perturbations in a linear model. J. Atmos. Sci. Yang, G. –Y. and B. J. Hoskins 1996: Propagation of Rossby waves of non-zero frequency. J. Atmos. Sci. Hoskins, B. J., and G. –Y. Yang, G. –Y. 2000: The equatorial response to higher latitude forcing. J. Atmos. Sci. Roundy, P. E., 2008: Analysis of convectively coupled Kelvin waves in the Indian Ocean MJO. J. Atmos. Sci. Dias, J. and O. Pauluis, 2009: Convectively coupled Kelvin waves propagating along an ITCZ. J. Atmos. Sci. Ferguson, J., B. Khouider, M. Namazi, 2009: Two-way interactions between equatorially-trapped waves and the barotropic flow. Chinese Ann. Math.

Theoretical Considerations: Effects of Meridional Shear in the Zonal Wind Differential advection leads to straining and deformation: Affects shape and group velocity Wave-guiding: Trapping of Rossby wave energy along jets, extratropical waves are guided towards low latitudes in certain regions Non-Doppler Effect: Meridional shear modifies the  -effect, leading to differences in equivalent depths and equatorial trapping Critical Line: Where the zonal phase speed of a Rossby Wave equals that of the background zonal wind (waves are absorbed or perhaps reflected here).

200 hPa Climatological Zonal Wind, Dec.-Feb Contour interval 5 m s -1

200 hPa Climatological Zonal Wind, June-Aug Contour interval 5 m s -1

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day 0 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue Kiladis, 1998

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day-5 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day-4 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day-3 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day-2 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day-1 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day 0 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day+1 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 10  N, 150  W for Dec.-Feb Day+2 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 7.5  N, 30  W for Dec.-Feb Day-2 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue Kiladis and Weickmann, 1997

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 7.5  N, 30  W for Dec.-Feb Day-1 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 7.5  N, 30  W for Dec.-Feb Day 0 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 7.5  N, 30  W for Dec.-Feb Day+1 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 7.5  N, 30  W for Dec.-Feb Day+2 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OBSERVATIONS OF KELVIN AND INERTIO-GRAVITY WAVES CLAUS Brightness Temperature (2.5S–7.5N), April-May 1987

OBSERVATIONS OF KELVIN AND INERTIO-GRAVITY WAVES CLAUS Brightness Temperature (2.5S–7.5N), April-May m s -1

OLR and 850 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day+1 Geopotential Height (contours.5 m) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue Straub and Kiladis, 1997

Kelvin Wave Theoretical Structure Wind, Pressure (contours), Divergence, blue negative

OLR and 850 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day+1 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day+1 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-6 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-5 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-4 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-3 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-2 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-1 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day 0 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day+1 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day+2 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day+3 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day+4 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-10 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-9 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-8 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-7 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 7.5  N,  W for June-Aug Day-6 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at Eq., 90  E for June-Aug Day 0 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at Eq., 90  E for March-May Day 0 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at Eq., 90  E for Dec.-Jan Day 0 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against <30 day filtered OLR (scaled -20 W m 2 ) at 7.5  N, 30  W for Dec.-Feb Day 0 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 10 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 2.5  N, 0.0  for March-May Day-1 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at 2.5  N, 0.0  for March-May Day+1 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

Mechanisms? Local Dynamic and Thermodynamic fields associated with initial Kelvin wave development are very weak One possibility: “Direct projection” of extratropical forcing onto equatorially- trapped waves, exciting a resonant response

Hoskins and Yang, 2000

1987 CLAUS Brightness Temperature 5ºS-5º N

1998 CLAUS Brightness Temperature 5ºS-5º N

1993 CLAUS Brightness Temperature 5ºS-5º N

1989 CLAUS Brightness Temperature 5ºS-5º N

1999 CLAUS Brightness Temperature 5ºS-5º N

1984 CLAUS Brightness Temperature 5ºS-5º N

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day 0 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day-4 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day-3 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day-2 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day-1 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day 0 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day+1 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day+2 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day+3 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day+4 Streamfunction (contours 5 X 10 5 m 2 s -1 ) Wind (vectors, largest around 5 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue

Geopotential Height (contours 1 m) Wind (vectors, largest around 3 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue OLR and 1000 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day-4

Geopotential Height (contours 1 m) Wind (vectors, largest around 3 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue OLR and 1000 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day-3

Geopotential Height (contours 1 m) Wind (vectors, largest around 3 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue OLR and 1000 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day-2

Geopotential Height (contours 1 m) Wind (vectors, largest around 3 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue OLR and 1000 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day-1

Geopotential Height (contours 1 m) Wind (vectors, largest around 3 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue OLR and 1000 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at eq, 60  W for January-June Day 0

The dates are then separated by additional criteria before compositing: “Pacific” cases: 3 days before key date Kelvin-filtered OLR more than 16 Wm -2 below mean at 95W, 2.5N “South America” cases: 3 days before key date, 30-day high- pass filtered OLR more than 50 Wm -2 below mean at 60W, 20S. 53 Pacific cases 48 South America cases 4 common cases Dates are found with a 1.5 standard deviations negative OLR anomalies at 60W, Eq.

Base point: Kelvin-filtered OLR, 1.5 STD anomaly (plus constraint at 95W, 2.5N) Fields: 30-day high-pass OLR 200 mb wind and streamfunction Wm -2 Pacific events

Base point: Kelvin-filtered OLR, 1.5 STD anomaly (plus constraint at 95W, 2.5N) Fields: 30-day high-pass OLR 200 mb wind and streamfunction Wm -2 Pacific events

Contrast with “South America” example (note different latitude range) 30-day High-pass OLR, 200 mb wind and stream function

Fields lead base point by 5 days Blue contours indicate positive height anomalies 200 mb Heights and OLR 850 mb Heights and Rain 1000 mb Heights and Unfiltered rain

Fields lead base point by 4 days

Fields lead base point by 3 days

Fields lead base point by 2 days

Fields lead base point by 1 day

Fields simultaneous with base point

Fields lag base point by 1 day

Conclusions There are at least two mechanisms that force Kelvin waves over South America a) at upper levels from the Pacific b) at lower levels from southern South America (e.g., Garreaud and Wallace 1998; Garreaud 2000) Not all South American (cold) events force Kelvin waves Some Kelvin waves may be initiated in-situ

Conclusions Convectively coupled Kelvin waves have many “non-Kelvin” features, including off-equatorial gyres presumably forced in part by heating There are strong associations between Kelvin wave activity and extratropical Rossby wave activity In some cases it is clear that Kelvin waves are forced by the extratropics Kelvin convection is associated with subtropical anticyclonic vorticity, unlike other cases of tropical-extratropical interaction Subtropical “pressure surges” are also seen to be involved in forcing of some Kelvin activity over South America These results do not rule out “spontaneous” generation of Kelvin waves by equatorial convection or local dynamical forcing

E Vectors (assumption of quasi-geostrophy) where:is a measure of anisotropy is minus the northward flux of westerly momentum and Approximate direction of group velocity: from Hoskins, James and White (1983)

200 hPa Climatological < 30 Day E Vectors and OLR December-February E Vectors, largest around 200 m -2 s -2 OLR shading starts at 250 W s -2 at 10 W s -2 intervals

Stationary Wavenumber K s where: is the meridional gradient of absolute vorticity K s is the total wavenumber (k 2 +l 2 ) 1/2 at which a barotropic Rossby Wave is stationary in a given background Zonal Flow According to WKB theory, Rossby Wave Energy should be refracted toward higher values of K s see Hoskins and Ambrizzi (1993)

200 hPa Climatological < 30 Day E Vectors and OLR December-February E Vectors, largest around 200 m -2 s -2 OLR shading starts at 250 W s -2 at 10 W s -2 intervals

200 hPa Climatological < 30 Day E Vectors, Ks and OLR December-February E Vectors, largest around 200 m -2 s -2 Ks (contours) by total wavenumber OLR shading starts at 250 W s -2 at 10 W s -2 intervals

Lead and Lag Regressions Base point: Kelvin-filtered OLR at 60W, Eq. Fields: 30-day high-pass filtered OLR, 200 mb winds and stream function

Conclusions There are at least two mechanisms that force Kelvin waves over South America a) at upper levels from the Pacific b) at lower levels from southern South America (e.g., Garreaud and Wallace 1998; Garreaud 2000) Not all South American (cold) events force Kelvin waves

Fields lead base point by 3 days Kelvin-filtered base point30-day high pass base point OLR, 200 mb winds and heights

Fields simultaneous with base point Kelvin-filtered base point30-day high pass base point OLR, 200 mb winds and heights

Fields lag base point by 1 day Kelvin-filtered base point30-day high pass base point OLR, 200 mb winds and heights

Fields lag base point by 2 days Kelvin-filtered base point30-day high pass base point OLR, 200 mb winds and heights

OLR and 200 hPa Flow Regressed against Kelvin-filtered OLR (scaled -20 W m 2 ) at Eq., 90  E for Dec.-Jan Day-2 Streamfunction (contours 2 X 10 5 m 2 s -1 ) Wind (vectors, largest around 2 m s -1 ) OLR (shading starts at +/- 6 W s -2 ), negative blue