# Presentation: 054639

## Slide 1

| Midwinter Suppression of Baroclinic Wave Activity in the Pacific  |
| --- |
| Hisashi Nakamura |
| Journal of the Atmospheric Sciences   Volume 49, Issue 17 (September 1992) pp. 1629–1642  |

## I have calculuated transient eddy kinetic energy and transient eddy

- Poleward heat flux for monthly and seasonal periods.  No filtering
- Has been applied.
- My statistics are calculated from time series of analyses and from
- Time series of certain length forecasts.  Thus I am comparing a series
- Of forecasts of fixed lengths to a series of analyses verifying at
- The same time as the forecasts.
- The following slide shows the transient eddy kinetic energy as a function
- Of pressure averaged over the northern mid-latitudes.  The model decreases
- Eddy activity near the tropopause but increases it slightly in short-range forecasts
- Near 850.
- The results are noisy, but the forecasts tend to increase transient eddy activity
- At low levels over the mid-latitude oceans, easpecially the eastern oceans, by roughly 10-25%.

## September-November 2006

***September-November 2006***

## Slide 4

## Slide 5

## Over the oceans, especially the eastern oceans, transient eddy activity at 850 hPA

- Tends to be stronger in the forecasts than the analyses by 10% or so.

## Slide 7

## 3day

## In both hemispheres there is a tendency for the forecasts to Increase eddy activity over the mid-latitude oceans.

## Slide 10

## Slide 11

## Little increase in transient eddy activity in zonal mean

## Slide 13

## Slide 14

## Forecasts tend to increase transient

- Eddy heat flux in lower troposphere
- But decrease it in upper troposphere.
- Forecasts strengthen baroclinic eddies
- In the lower troposphere, but
- Weaken them in the upper troposphere.

## Slide 16

## Slide 17

## Forecasts tend to increase poleward transient eddy heat flux over midlatitude oceans by 25% or so.

## December 2006

***December 2006***

- Small increase in transient eddies below 400 hPA

## Slide 20

## Slide 21

## Forecasts tend to increase transient

- Eddy kinetic energy over oceans

## ECMWF has slightly

- Less transient eddy
- Eddy activity than GFS

## Slide 24

## Slide 25

## GFS forecasts tend to have more transient eddy activity than ECMWF, especially in northern midlatitudes, but difference is 10% or less.

## November 2006

***November 2006***

- Small decrease

- Small increase

## Slide 28

## Slide 29

## 3day

## Tendency for transient eddy activity

- To increase in forecasts over
- Northern midlatitude oceans

## ECMWF tends to decrease

- Transient eddy activity in
- First 5 days of forecasts
- More than GFS

## Slide 33

## Slide 34

## First 5 forecast days, GFS has more transient eddy activity in northern mid-latitudes than ECMWF

## ECMWF forecasts tend to damp transient eddy activity

- GFS forecasts
- Mixed effect
- On eddy activity

## Slide 37

## GFS tends to weaken eddy activity near jet, strengthen it in lower troposphere, especially over mid-latitude eastern oceans

***GFS increases baroclinic eddies in lower troposphere and weaken them in upper troposphere***
***GFS tends to have stronger transient eddies in forecasts in Northern Hemisphere midlatitude than ECMWF and damps them less in the forecasts.***
***Effect of forecasts on transient eddies 10-25% at most***
***Results noisy, indicating that tendency of forecasts to change eddies fairly weak.***