# Presentation: 725860

## Changes in the Activity of the Madden-Julian Oscillation during 1958-2004

**University of California Santa Barbara**

**Changes in the Activity of the Madden-Julian Oscillation during 1958-2004**

**Case to Case**

**Seasonal  Variations**

**Interannual   Variations**

**Long-term   Behavior**

***Time scales***

**?**

**??**

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**Extensively studied over the years but no comprehensive theory**
**Behavior on time scales longer than interannual  is unknown **

**Notes:**
MJO importance in climate system; little is know about low-frequency behavior of MJO

## This Study

**Are there linear trends in the activity of the MJO? (intensity & number of events)**
**Does the MJO exhibit regimes of high and low activity? **
**Are there significant seasonal differences in the activity of the MJO on time scales longer than **_**interannual**_**? **

***Note: MJO refers to summer and winter events ***

## Identification of MJO events

** ****NCEP/NCAR U200, U850 (1958-2004) ****	****	****20-100 day anomalies**
** ****OLR (1979-2004)****	****	****	****	****20-100 day anomalies**
_**EOF analysis**_
** ****Summer domain: ****south Asian monsoon ****(****Lawrence and Webster 2001) **
** ****Winter domain: Equatorial region ****(Kessler 2001)**

|  | Summer | Winter |
| --- | --- | --- |
| 1979-2004 EOF (OLR)
Covariance matrix | PC1, PC2 (~20%) | RPC1, RPC2 (~43%) |
| 1958-2004 combined EOF (U200, U850)
Correlation matrix | PC1, PC2 (~19%) | PC1, PC2 (~40%) |

** ****Event: ****	****	****amplitude PC1 exceeds ****1 sigma**
**within 20 days PC2 exceeds ****1 sigma**
** ****Events registered at pentads in which PC1 exceed 1 sigma**
** ****1958-2004: ****	****158 events (75 in summer; 83 in winter)****	****(U200,U8500)**
** ****1979-2004:****	**** 90 events (49 summer; 41 winter)****	****(OLR)**

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## 158 events (1958-2004) identified with CEOF (U200, U850) (correlation matrix)

**158 events (1958-2004) identified with CEOF (U200, U850) ****(**_**correlation matrix**_**)**
**Each bar represents an event registered at peak in PC1**
**Amplitude is the variance (15S-15N; all longitudes) of eastward wavenumbers 1-6 20-100 day anomalies (Hendon et al. 1999)**

## Low-Frequency diagram

_**Low-Frequency diagram**_
** ****Consider X****T****, T=1, 3431 pentads, X****T****=1 event, X****T****= 0 no event**

**Define moving window S****K**** and compute percentage of MJO events in S****K:**** P****K,T**** = M****K,T ****/ N where M****K,T**** is number of events and N total number of events**
**Similar for summer: PS****K,T**** = MS****K,T**** / NS where MS****K,T**** is number of summer events and NS total number of summer events**
**Similar for winter: PW****K,T**** = MW****K,T**** / NW where MW****K,T**** is number of winter events and NW total number of winter events**
**S****K**** odd number and varied from ****smallest (1 pentad)**** to ****largest possible (3431 pentads)**

## Low-frequency diagram

**Low-frequency diagram**

**Cone of Influence**

**Cone of Influence**

## Winter & Summer

**Winter & Summer**

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## Mean MJO Low-frequency Variability

**Overall**

**Summer**

**Winter**

**Mean P****K,T**** **
**Mean PS****K,T**** **
**Mean PW****K,T**
**SK = 145 to 657 (1.98 to 9 years) **

## Monte Carlo simulations

_**Monte Carlo simulations**_
_**Summer**_
**X****T****, X****T****=1 summer event, X****T****= 0 no event**
**Randomize seasons 999 times**
**Each batch: **
** ****compute LF diagram**
** ****mean RS****K,T**** (S****K ****=145 to 657 (1.98 to 9 years) **
** ****correlation PS****K,T**** and RS****K,T**** **
**Frequency distribution of correlation > Cr**
**Same for **_**winter**_

## Summary and Conclusions

**MJO exhibits substantial changes in regimes longer than interannual**
**Two regimes of high activity (1974-1978, 1988-1992), and low activity (1981-1986). **
**Markedly different changes in summer and winter activity **
**Summer: ****	****increased from early 1960’s to mid 1970’s and decreased ****	****	****	****steadily until the 1990’s**
**Winter:****	****more regular changes with peaks in 1967, 1976 and 1989 ****	****	****	****and lows in 1971, 1983 and 1997. **
**Changes in summer and winter MJO activity are statistically different from random occurrences**
**There are positive linear trends in (1958-2004): **
** ****U200 **_**amplitudes**_** of summer and winter MJO events**
** **_**Number**_** of summer MJO events**
**Linear trends are not higher than random occurrences (5% level)**
**Trends in U200 amplitudes of the MJO are consistent between EOF metric (this study) and equatorial zonal mean intraseasonal index (Slingo et. 1999)**

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##  Interannual variations in the MJO; NCEP/NCAR 1958-1997

** ****Zonal mean of U 200hPa (10****°S - 10****°N)**
**20-100 day anomalies; square and apply 100 day smoothing**
**40-yr integration of HadAM2a model driven with observed SST reproduced general trends in “MJO activity”**
**Index contains up to 40%***** *****unrelated MJO variability (Hendon et al. 1999)**

**Slingo et al. (1999) Intraseasonal Index ****	****(QJRMS)**

**Notes:**
Motivation for this study; larger amplitudes since mid 1970’s

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