Relationships between Convectively Coupled Kelvin Waves and Extratropical Wave Activity

1
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

2
OrSome (as yet only partially explained)
observations of Kelvin Waves and Associated
Extratropical Disturbances
3
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

4
(No Transcript)
5
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.

6
Theoretical ConsiderationsEffects 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).

7
200 hPa Climatological Zonal Wind, Dec.-Feb.
1979-2004
Contour interval 5 m s-1
8
200 hPa Climatological Zonal Wind, June-Aug.
1979-2004
Contour interval 5 m s-1
9
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day 0
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
Kiladis, 1998
10
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day-5
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
11
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day-4
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
12
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day-3
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
13
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day-2
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
14
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day-1
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
15
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day 0
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
16
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day1
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
17
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 10?N, 150?W for
Dec.-Feb. 1979-2004
Day2
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
18
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 7.5?N, 30?W for
Dec.-Feb. 1979-2004
Day-2
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
Kiladis and Weickmann, 1997
19
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 7.5?N, 30?W for
Dec.-Feb. 1979-2004
Day-1
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
20
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 7.5?N, 30?W for
Dec.-Feb. 1979-2004
Day 0
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
21
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 7.5?N, 30?W for
Dec.-Feb. 1979-2004
Day1
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
22
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 7.5?N, 30?W for
Dec.-Feb. 1979-2004
Day2
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
23
OBSERVATIONS OF KELVIN AND INERTIO-GRAVITY
WAVES CLAUS Brightness Temperature (2.5S7.5N),
April-May 1987
24
OBSERVATIONS OF KELVIN AND INERTIO-GRAVITY
WAVES CLAUS Brightness Temperature (2.5S7.5N),
April-May 1987
28 m s-1
25
OLR and 850 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day1
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
26
Kelvin Wave Theoretical Structure
Wind, Pressure (contours), Divergence, blue
negative
27
OLR and 850 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day1
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
28
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day1
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
29
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-6
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
30
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-5
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
31
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-4
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
32
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-3
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
33
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-2
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
34
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-1
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
35
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day 0
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
36
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day1
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
37
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day2
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
38
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day3
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
39
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day4
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
40
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-10
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
41
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-9
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
42
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-8
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
43
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-7
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
44
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 7.5?N,
172.5?W for June-Aug. 1983-2005
Day-6
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
45
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at Eq.,
90?E for June-Aug. 1983-2005
Day 0
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
46
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at Eq.,
90?E for March-May 1983-2005
Day 0
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
47
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at Eq.,
90?E for Dec.-Jan. 1983-2005
Day 0
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
48
OLR and 200 hPa Flow Regressed against lt30 day
filtered OLR (scaled -20 W m2) at 7.5?N, 30?W for
Dec.-Feb. 1979-2004
Day 0
Streamfunction (contours 5 X 105 m2 s-1) Wind
(vectors, largest around 10 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
49
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 2.5?N,
0.0? for March-May 1983-2005
Day-1
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
50
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at 2.5?N,
0.0? for March-May 1983-2005
Day1
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue
51
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

52
Hoskins and Yang, 2000
53
1987 CLAUS Brightness Temperature 5ºS-5º N
54
1998 CLAUS Brightness Temperature 5ºS-5º N
55
1993 CLAUS Brightness Temperature 5ºS-5º N
56
1989 CLAUS Brightness Temperature 5ºS-5º N
57
1999 CLAUS Brightness Temperature 5ºS-5º N
58
1984 CLAUS Brightness Temperature 5ºS-5º N
59
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day 0
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
60
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day-4
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
61
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day-3
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
62
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day-2
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
63
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day-1
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
64
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day 0
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
65
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day1
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
66
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day2
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
67
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day3
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
68
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day4
Streamfunction (contours 5 X 105 m2
s-1) Wind (vectors, largest around 5 m s-1) OLR
(shading starts at /- 6 W s-2), negative blue
69
OLR and 1000 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
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
70
OLR and 1000 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
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
71
OLR and 1000 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
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
72
OLR and 1000 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
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
73
OLR and 1000 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at eq, 60?W
for January-June 1979-2004
Day 0
Geopotential Height (contours 1 m) Wind (vectors,
largest around 3 m s-1) OLR (shading starts at
/- 6 W s-2), negative blue
74
The dates are then separated by additional
criteria before compositing
Dates are found with a 1.5 standard
deviations negative OLR anomalies at 60W, Eq.
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
75
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
76
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
77
Contrast with South America example (note
different latitude range)
30-day High-pass OLR, 200 mb wind and stream
function
78
Fields lead base point by 5 days
200 mb Heights and OLR
850 mb Heights and Rain
1000 mb Heights and Unfiltered rain
200
850
1000
Blue contours indicate positive height anomalies
79
Fields lead base point by 4 days
200
850
1000
80
Fields lead base point by 3 days
200
850
1000
81
Fields lead base point by 2 days
200
850
1000
82
Fields lead base point by 1 day
200
850
1000
83
Fields simultaneous with base point
200
850
1000
84
Fields lag base point by 1 day
200
850
1000
85

• 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

86
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

87
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)
88
200 hPa Climatological lt 30 Day E Vectors and OLR
December-February 1979-2004
E Vectors, largest around 200 m-2 s-2 OLR shading
starts at 250 W s-2 at 10 W s-2 intervals
89
Stationary Wavenumber Ks
Ks is the total wavenumber (k2l2)1/2 at which a
barotropic Rossby Wave is stationary in a given
background Zonal Flow
is the meridional gradient of absolute vorticity
where
According to WKB theory, Rossby Wave Energy
should be refracted toward higher values of Ks
see Hoskins and Ambrizzi (1993)
90
200 hPa Climatological lt 30 Day E Vectors and OLR
December-February 1979-2004
E Vectors, largest around 200 m-2 s-2 OLR shading
starts at 250 W s-2 at 10 W s-2 intervals
91
200 hPa Climatological lt 30 Day E Vectors, Ks and
OLR December-February
1979-2004
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
92
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
93
(No Transcript)
94

• 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

95
Fields lead base point by 3 days
Kelvin-filtered base point
30-day high pass base point
OLR, 200 mb winds and heights
96
Fields simultaneous with base point
Kelvin-filtered base point
30-day high pass base point
OLR, 200 mb winds and heights
97
Fields lag base point by 1 day
Kelvin-filtered base point
30-day high pass base point
OLR, 200 mb winds and heights
98
Fields lag base point by 2 days
Kelvin-filtered base point
30-day high pass base point
OLR, 200 mb winds and heights
99
OLR and 200 hPa Flow Regressed against
Kelvin-filtered OLR (scaled -20 W m2) at Eq.,
90?E for Dec.-Jan. 1983-2005
Day-2
Streamfunction (contours 2 X 105 m2 s-1) Wind
(vectors, largest around 2 m s-1) OLR (shading
starts at /- 6 W s-2), negative blue