# Presentation: 905914

## Interdecadal Changes of 30-Year SST

**Interdecadal Changes of 30-Year SST**
** ****Normals during 1871-2000**
_**Yan Xue**_ Climate Prediction Center, NCEP/NWS
**Thomas M. Smith and Richard W. Reynolds**
- National Climatic Data Center, NESDIS
- for the 27th Annual Climate Diagnostics and Prediction Workshop held in Fairfax, Virginia
-  on October 21-25, 2002

## Motivation

- <date/time>

**Motivation**

**A 30-year SST normal includes climatological mean and standard deviation, and is defined in a 30-year base period.**
**30-year SST normals used at CPC:**
- _1951-1979 normal_
- _1961-1990 normal_
- _1971-2000 normal_
**30-year normals recommended by WMO:**
- _1951-1980_, _1961-1990_ and _1971-2000_, ......
**Interdecadal changes of the 30-year normals in the past 130 years (1871-2000).**

## Review

**Interannual variability associated with ENSO is high during 1880-1920 and 1960-1990 and low during 1920-1960 (Kestin et al. 1998; Mestat-Nunez and Enfield 2001).**
**Pacific Decadal Oscillation (PDO) in the **_**North Pacific**_** (Mantua et al. 1997).**
**Decadal and interdecadal variability related to the “North Atlantic Oscillation” in the **_**North Atlantic**_** (Kushnir 1994).**
**Decadal and interdecadal variability in the **_**tropical Atlantic**_**. **
**Decadal and interdecadal variability in the **_**Indian Ocean**_**.**

## Approach

**Calculate climatological mean (CM) and standard deviation (SD) in sliding 30-year windows in the past 130 years.**
**	****(**_**1871-1900**_**, **_**1881-1910**_**, **_**1891-1920**_**, ......)**
**Use two independent SST analyses.**
**Make conclusions based on the consistent results from the two SST analyses.**

## Goals

**Primary goals:**
**Estimate interdecadal variability in the global ocean.**
**Estimate interdecadal changes of interannual variability in the global ocean.**
**Estimate interdecadal changes of seasonal persistence. **
**Secondary goals:**
**Provide justification on why the 30-year SST normal needs to be updated every 10 years.**_ _
**Estimate the uncertainties in the two SST analyses.**

## Data

**Extended Reconstructed Sea Surface Temperature (ERSST) by Smith and Reynolds (2002). **
**Period: 1854-2000; Resolution: 2****O**** x 2****O**
**Fitting COADS in situ observations to a set of EOFs**
**Analyzing low- and high-frequency variations separately.**
**Hadley Centre’s Sea Ice and Sea Surface Temperature (HadISST) by Rayner et al. (2002). **
**Period: 1871-1999; Resolution: 1****O**** x 1****O**
**Combination of global SST and sea ice concentration.**
**Using reduced-space optimal interpolation.**

## Methodology

**Seasonal Climatological Mean (CM)**
**Calculating monthly CM by averaging monthly SST over appropriate 30-year base periods.**
**Averaging monthly CM over appropriate seasons.**
**Seasonal Standard Deviation (SD)**
**Deriving monthly anomalies by subtracting monthly CM from monthly data.**
**Deriving seasonal anomalies by averaging monthly anomalies over appropriate seasons.**
**Deriving seasonal SD from seasonal anomalies.**
**Seasonal Persistence (P) **
**Auto-correlation of seasonal anomalies at a two-season lag over appropriate 30-year base periods.**

## Standard Deviation of the eleven 30-year seasonal CMs in 1871-2000.

## Standard Deviation of CM in SON

**Standard Deviation of CM in SON**

**INDIAN**

**PDO**

**NINO3**

**SATL**

**NAO**

## INDIAN Index (45O-100OE, 10OS-25ON)

- Departures from the seasonal CM averaged over all the 30-year base periods during 1871-2000.

- Differences between HadISST and ERSST

- Years

- Years

- Seasons

## PDO Index (160OE-160OW, 35ON-45ON)

- Departures from the seasonal CM averaged over all the 30-year base periods during 1871-2000.

- Differences between HadISST and ERSST

- Years

- Years

- Seasons

## NAO Index (60OW-20OW, 40ON-60ON)

- Departures from the seasonal CM averaged over all the 30-year base periods during 1871-2000.

- Differences between HadISST and ERSST

- Years

- Years

- Seasons

## SATL Index (35OW-10OE, 22OS-2ON)

- Departures from the seasonal CM averaged over all the 30-year base periods during 1871-2000.

- Differences between HadISST and ERSST

- Years

- Years

- Seasons

## NINO3 Index (150OW-90OW, 5OS-5ON)

- Departures from the seasonal CM averaged over all the 30-year base periods during 1871-2000.

- Differences between HadISST and ERSST

- Years

- Years

- Seasons

## Average season SD

- Average season SD

- HadISST-ERSST

## Seasonal SD of NINO3

- Years

- Seasons

- 1971-2000

- 1961-1990

- 1951-1980

- Average in 1871-2000

- Average in NDJ

- Average in MAM

-  **Variance is largest in NDJ and smallest in MAM.**
** ****Variance is intermediate in 1871-1920, small in 1930-1950 and large in 1960-2000.**
** ****Seasonality of variance is moderate in 1871-1920, weak in 1930-1950 and strong in 1960-2000.**

## Years

- Seasons

- Average in NDJ

- Average in MAM

- 1971-2000

- 1961-1990

- 1951-1980

- Average in 1871-2000

## Seasonal Persistence

## Years

- Seasons

- Average in JJA

- Average in DJF

** ****Persistence is largest in JJA and smallest in DJF.**
** ****Seasonality of persistence is weak in 1871-1910, moderate in 1920-1950, strong in 1955-1975, and moderate in 1975-2000.**
** ****Predictability is high in 1871-1920, low in 1920-1940, and high in 1950-2000.**

- P=0.4

- 1951-1980

## Summary

**The interdecadal changes of seasonal CM are prominent (0.3-0.6****O****C) in the tropical Indian Ocean, the middle latitude North Pacific and North Atlantic, most of the South Atlantic and the Sub-Antarctic Front. **
- The tropical Indian and Atlantic show a warming trend, and the middle latitude North Pacific and North Atlantic show multidecadal oscillations.
**The seasonal SD is prominent (0.5-1.3****O****C) in the eastern equatorial Pacific, the middle latitude North Pacific and North Atlantic. **
- The seasonal SD of NINO3 varies interdecadally, intermediate during 1885-1915, small during 1910-1965 and large during 1965-2000._ _
**The seasonal P is largest in the eastern equatorial Pacific, the tropical Indian and Atlantic. **
- The seasonal P of NINO3 varies interdecadally, high during 1885-1920, low during 1920-1940 and high during 1950-2000.

## Summary

**ERSST appears resolves climate signals better and contains less noise than HadISST does. **
**In the middle latitude North Pacific and North Atlantic, HadISST is biased toward warm in summer and cold in winter relative to ERSST. This difference appears too large to be accounted for by analysis errors and should be examined in the near future.**