# Presentation: 535367

## Forcing of Kelvin Waves over South America

- Brant Liebmann, George Kiladis, Leila Carvalho, Carolina Vera, Charles Jones, Ileana Bladé,
- Dave Allured

- With support from:
- CPPA GC07-042
- CPPA GC07-134

## Slide 2

## Kelvin Filter

- Wheeler and Kiladis 1999

## Variance of Kelvin-filtered OLR

- 1979-2005

- June - October

- November - May

## Correlation of Daily Kelvin variance with Niño 3.4

- November - May (1979/80 - 2005/06)

- June - October (1979 - 2005)

## 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

## Slide 7

## 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.

## Pacific events

- 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

- OLR, 1.5 STD anomaly
- (plus constraint at 95W, 2.5N)

- Fields: 30-day high-pass OLR
-             200 mb wind and
-             streamfunction

- Wm-2

## 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

- 200

- 850

- 1000

- 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

- 200

- 850

- 1000

## Fields lead base point by 3 days

- 200

- 850

- 1000

## Fields lead base point by 2 days

- 200

- 850

- 1000

## Fields lead base point by 1 day

- 200

- 850

- 1000

## Fields simultaneous with base point

- 200

- 850

- 1000

## Fields lag base point by 1 day

- 200

- 850

- 1000

## 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 point

- 30-day high pass base point

- OLR, 200 mb winds and heights

## Fields simultaneous with base point

- Kelvin-filtered base point

- 30-day high pass base point

- OLR, 200 mb winds and heights

## Fields lag base point by 1 day

- Kelvin-filtered base point

- 30-day high pass base point

- OLR, 200 mb winds and heights

## Fields lag base point by 2 days

- Kelvin-filtered base point

- 30-day high pass base point

- OLR, 200 mb winds and heights

## 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