# Presentation: 054637

## Preferred Modes of Variability and 

**Their Relationship with Climate Change**

- The Pennsylvania State University
- Department of Meteorology

- Seok-Woo Son and Sukyoung Lee

## Annular Mode

**Annular Mode**

**SH**

**NH**

- [u]

- SLP

- Thompson et al. 2000

- Leading EOF of SLP

- Zonally symmetric

- Quasi-barotropic

- Useful for understanding internal variability

- Useful for understanding climate change (?)

## Thompson et al. 2000

- Kushner et al. 2001

## To what extent annular mode is capable of predicting zonal-mean climate change?

- “Spatial pattern” of annular mode ≈ recent trend in the observed and simulated zonal-mean circulation

**To what extent annular mode is capable of predicting zonal-mean climate change?**

## Purpose and Approaches

- Evaluate the predictability of zonal-mean climate change by annular mode in terms of their spatial structures.

## Numerical Model

- A dynamic core of GFDL GCM (symmetric boundary cond.)

- Driven by relaxing T toward Te with timescale of 30 days

- R30L10 but zonal wave number 15

- Dissipated by linear friction and 8th order hyperdiffusion

## Numerical Model (Cont.)

- Statistics are derived from the last 4500 days of each 5000-day integration. Data of both hemispheres are used.

- Total 49 realizations

**C** (0.00, 0.17, 0.33, 0.50, 0.67, 0.88, 1.00) K/day
**H** (0.00, 0.33, 0.67, 1.00, 1.33, 1.67, 2.00) K/day

## SJ

- Strong C & weak H → Double Jet

- H ≥ 1.00K/day → Single Jet

**SJ**

**WJ**

**DJ**

## Internal variability of the jets

**Internal variability of the jets**

- Transition

**WJ**

- Poleward Propagation

**DJ**

- Zonal-index (Jet Meander)

**SJ**

- [u] & EOFs

## WJ

- Correlation PC1 vs. PC2

- Transition

- Poleward Propagation

- Zonal-index (Jet Meander)

**WJ**

**DJ**

**SJ**

- Poleward Propagation:   i. Correlation between PC1 & PC2 is very high                                ii. Var(EOF2) is comparable to Var(EOF1)

## Slide 11

## Annular mode & Climate change in the modeI

- Annular mode : EOF1 of [u]

-   [u] is regressed against PC1 time series, unit of m/s.

## Predictability of Climate change by Annular mode

**Predictability of Climate change by Annular mode**

- Predictability is always poor in a poleward propagation regime.

- Shading
- correlation ≥ 0.8

##  Increase of H → enhances subtropical baroclinicity and

-  Increase of H → enhances subtropical baroclinicity and
-                               intensifies Hadley circulation

-  Increase of C → enhances extratropical baroclinicity

## Summary

## Application to the Southern Hemisphere

-             Both poleward propagation and zonal index (e.g., Feldstein 1998;
-             Hartmann and Lo 1998) with γ ≈ 0.5 and χ ≈ 0.3 (Son and Lee 2005b).

**Application to the Southern Hemisphere**

**Applied to the SH climate change at equinoctial condition**
-            Global warming at SH → ENSO-like tropical heating & enhanced
-             extratropical baroclinicity (Son and Lee 2005a) → increase of H and C.

**Structure of the jet**
-             Wide range of interannual variability from single- to double-jet states

## Application to the Southern Hemisphere (Cont.)

**Predictability is marginally good in the SH-like parameter regime.**

**Annular mode may not be useful for understanding paleoclimate change.**

- Slight climate drift to the poleward propagation regime
- → poor predictability.

## Any comment and suggestion are welcome. Thank you!

- Contact information
- Seok-Woo Son:  sus141@psu.edu

## Dependency of internal variability to the mean flow

**Dependency of internal variability to the mean flow**

- The meridional radiation of the waves is prohibited if the PV gradient of the ambient flow is sufficiently sharp (e.g., Hoskins and Ambrizzi 1993)

- Poleward propagation of westerly anomalies may occur only when the PV gradient is relatively weak and broad.

## Prediction of Climate-change ‘Direction’ by Annular mode?

- Climate change direction (positive or negative phase of annular mode) is determined not by the annular mode but by the nature of external forcing.

- Climate change associated with C increase (broadening of extratropical baroclinic zone) →** **positive phase of annular mode (in phase).

- Climate change associated with H increase (warming at tropics) →** **negative phase of annular mode (out of phase).

**+**

**-**

## Prediction of Climate-change ‘Direction’ ? (Cont.)

- Climate change in SH: tropical warming & enhanced extratropical baroclinicity (Son and Lee 2005a) → increase of H and C.

## Predictability of Climate change by Annular mode

-   measured at both
-           subtropics and extratropics

**Predictability of Climate change by Annular mode**

##  Weak latitudinal dependency of 

- Shading δφ ≤ 2 ̊

-  Weak latitudinal dependency of
-     δ[u]C prediction by annular mode.

** **Poor predictability of δ[u]H** **in a
-     zonal-index regime is due to
-     the mid-latitudes.

** **Predictability is generally good
-     when γ ≤ 0.5 or
-           Var(EOF1) ≥ 2•Var(EOF2)

## Prediction of Climate-change ‘Amplitude’ by Annular mode?

**Prediction of Climate-change ‘Amplitude’ by Annular mode?**

## Prediction of Climate-change ‘Amplitude’ by Annular mode?