# Presentation: 515518

## Opposite phases of the Antarctic Oscillation and Relationships with Intraseasonal to Interannual Activity in the Tropics during the Austral Summer 

**(*****submitted to J. Climate*****)**
**Leila M. V. Carvalho****1,2****,Charles Jones****1****, and Tercio Ambrizzi****2**
**1****ICESS, University of California, Santa Barbara**
**2****Dept. Atmospheric Science, Universidade de São Paulo**

## MOTIVATION:

**The ****Antarctic Oscillation (AAO)**** is known as the leading mode of variability of extratropical circulation in the Southern Hemisphere **
**This mode of variability is characterized by ****deep and zonally symmetric or “annular” structures**** (*****Thompson and Wallace 2000*****) with opposite geopotential height perturbations over the pole and approximately in a zonal ring with center around 45****o**** S.**** **
**The annular and zonally symmetric structure involves ****exchanges of mass**** between mid and high latitudes.**
** **

## FOCUS:

**FOCUS:**
**Observational investigation of the variability of the AAO during the austral summer (DJF) **
**ADDRESSED ISSUES**** ****:**
**Are distinct AAO phases related to the variability of convection and circulation in the tropics such as El Niño/La Niña? **
**Similarly, given the depth of the annular mode, can phases of the Quasi Biennial Oscillation (QBO) be related to phases of AAO? **
**3)  On intraseasonal timescales, do tropical anomalies such as the Madden-Julian Oscillation modulate the phases of the AAO?**
** ****4)  What are the key teleconnection mechanisms linking the tropical activity to extratropics and, therefore, AAO? **

## The Daily AAO Index1979-2000

**The daily AAO index**** is computed as the leading mode of the  EOF analysis of daily anomalies of the 700hPa geopotential height (H700) from Reanalysis (20-90 S).**
** **
**Positive (negative) phases of the AAO**** : defined when the time coefficient of the first EOF is greater (less) than 1 standard deviation of the DJF time series.****   **

**POSITIVE PHASE**

## POSITIVE AAO PHASES: 349 DAYS IN 70 INDEPENDENT EVENTS 

** ****NEGATIVE AAO PHASES: 326 DAYS IN 40 INDEPENDENT EVENTS. PERIOD: DJF 1979-2000**

**     ****PERSISTENCE:**
**     ****Number of consecutive days during positive (negative) phases**

## 2. The Role of  Low-Frequency Anomalies

- ENSO
- 	Several previous studies have shown the impacts of ENSO in modifying convection and the circulation patterns from tropics to extratropics

- QBO
- 	Other studies have suggested the existence of links between QBO and ENSO (e.g. Gray et al. 1992)
-     Easterly phases -> El Nino
-     Westerly phases -> La Nina

***Are AAO phases related to both low-frequency forcing ?***
***How?***

## Composites of SST and 200 hPa zonal wind (U200LF):Low-Frequency ( Retained Periods: above 365 days)

**Negative AAO Phase**

**Positive AAO Phase**

** ****U200****LF**

**U200****LF**

**SST****LF**

**SST****LF**

## The Lower Stratosphere : Composites for Low-Frequency Zonal Winds in 50hPa (U50LF) 

**Negative **
**AAO**

**Positive **
**AAO**

**EASTERLY**
**QBO PHASE**

**WESTERLY**
**QBO PHASE**

## Relationships between ENSO patterns and AAO for DJF : Combined EOF was computed with: H700, U200 (daily anomalies)  and OLR low frequency (OLRLF)

**H700**

**OLR****LF**

**U200**

## Intraseasonal Activity and AAO Phases

**Tropical intraseasonal convective anomalies (TICA) such as MJO are known as playing an important role in modulating convection patterns in the tropics and circulation patterns in both  tropics and extratropics ****(e.g. Hendon and Salby 1994)****.**
**Some previous works have suggested that MJO may interact with El Nino episodes**
**Nonetheless, there is significant interannual variability in the frequency of TICA (e.g. Jones et al. 2003)**
**Therefore  TICA events may be an important intraseasonal forcing for circulation in the tropics and extratropics : ****IMPORTANCE FOR AAO PHASES **

## Lag composites (Days) OLR anomalies (20-70 days)

**Lag composites (Days) OLR anomalies (20-70 days****)**

**NEGATIVE AAO**

**POSITIVE AAO**

**LAG 0**

**LAG +5**

**LAG +10**

**LAG +15**

**LAG +20**

**LAG +25**

**LAG 0**

**LAG +5**

**LAG +10**

**LAG +15**

**LAG +20**

**LAG +25**

## AAO AND TELECONECTIONS WITH THE TROPICS

**    *****Teleconnection patterns were examined by applying the Wallace and Gutzler(1981) methodology:***
**Variable investigated : ****Zonal Wind 200hPa**** (daily anomalies ) **
**Positive**** and ****negative**** AAO events were analyzed ****separately**
**A correlation matrix ********C**** is obtained by calculating the temporal (simultaneous) correlation coefficients between anomalies at any given point *****ui***** (**_**from 90S to 40S and all longitudes-**_** annular modes have large amplitudes) and anomalies at every gridpoint ****uj**** (**_**from 90S to 90N and all longitudes**_**).**
**The element *****c******ij***** of the matrix is the correlation of anomalies at a gridpoint *****u******i***** with anomalies at the gridpoint *****u******j*****. The teleconnectivity *****T******i***** ****of the gridpoint *****u******i***** ****is defined as the strongest negative element *****c******ij***** ****of the matrix ****C****, for all gridpoints *****u******j*****: **
*** ******	******T******i*****= minimum [c****ij****] for all u****j**

## Teleconnection Patterns obtained for U200 (40oS-90oS)

**Teleconnection Patterns obtained for U200 (40****o****S-90****o****S)**

**NEGATIVE**

**POSITIVE **

**DIFFERENCE **

**Equatward shift of the  Subtropical Jet**
**Weakening Polar Jet**

** ****Strengthening **
**   ****of the Polar Jet**
** ****Poleward shift subtropical jet**

**Westerly jets can act as Rossby waveguides for propagation from tropics to midlatitudes**

## CONCLUSIONS:

****** ****QBO**

****** ****Deep Tropical Convection               ******** sea level pressure**** **

****** ****Equatorial west wind anomalies**
****** ****Kelvin waves**
****** ****MJO **

**Possible warm pool build up**

****** ****SST =>**
****** ****ENSO**

**Intensification and Equatorward shift of the subtropical Jet**

**Poleward shift of the subtropical Jet**
**Intensification of the Polar jet**

-    **Cold SST**

**Warm SST**

**Dominant Negative AAO**

**Dominant Positive AAO**

**Gray et al (1992)**
**Mechanism**

**CONCLUSIONS:**

## Extratropical Cyclones properties – Murray and Simmonds (1991)

**Extratropical Cyclones properties – Murray and Simmonds (1991)**
**tracking scheme**