# Presentation: 605494

## Climate variability in wind waves

**from VOS visual observations**

**Vika Grigorieva & Sergey Gulev, IORAS, Moscow**

** ****Climatology of visually observed wind waves**
** ****Errors and uncertainties**
** ****Centennial-scale changes**
** ****Decadal to interannual variability **
** ****Changes in wave statistics derived from VOS**

_**OUTLINE:**_

***MARCDAT-II Workshop, 2005, Exeter***

## Visual VOS observations: 2 streams (1784-1948) and (1948-2003)

_**Visual VOS observations: 2 streams (1784-1948) and (1948-2003)**_

## Global climatology of wind waves from VOS data:

_**Global climatology of wind waves from VOS data:**_
**http://www.sail.msk.ru/atlas**
** ****monthly**
** ****1958-2002 (updated)**
** ****2-degree resolution**
** ****Separate estimates of**
**  ****sea, swell, SWH **
**Gulev and Grigorieva**
**        ****JGR, 2003**

## All fields are accompanied by:

**Sampling errors**

_**All fields are accompanied by:**_

***See poster of Grigorieva and Gulev for the error analysis***_** **_

## Very long-term changes along the major ship routes 

**65 regions**
**with high sampling**
**during **
**1885-2002**

_**Homogenization:**_
**  ****sub-sampling**
**  ****for 7,15,25,50**
**  ****reports per **
**  ****region per **
**  ****month**

## Homogenized time series

**Buoys: Gower 2002:**

## Very 

_**long-term **_
_**changes: **_
_**linear trends**_
_**Gulev and**_
_**Grigorieva 2004**_

## Trends in sea, swell and SWH: 1958-2002

_**Trends in sea, swell and SWH: 1958-2002**_

**sea**

**swell**

**SWH**

**sea**

**swell**

**SWH**

## Winter (JFM) 1st EOFs of sea, swell and SWH

_**Winter (JFM) 1st EOFs of sea, swell and SWH**_

**sea**

**swell**

**SWH**

**sea**

**swell**

**SWH**

## Atlantic

_**components**__** **_

_**Atlantic**_
**R(H****W****–NAO)=0.68**
**R(H****S****–NAO)=0.48**
**R(SWH–NAO)=0.81**

_**Pacific**_
**R(H****W****–NPI)=0.72**
**R(H****S****–NPI)=0.58**
**R(SWH–NPI)=0.61**

## Canonical  patterns

**Number of cyclones**

**swell**

**SWH**

**scalar**
**wind**

**sea**

**SWH**

## IDM – initial distribution method – methodologically, 

**IDM – initial distribution method – ****methodologically, **
**most relevant for VOS, but does not allow for reliable **
**estimation of extreme waves **
**POT – peak over threshold – ****sensitive to sampling inhomogeneity**

_**Extreme waves from VOS: problem of estimation**_

**100-yr returns in SWH - IDM**

## Estimation of extreme wave heights - POT

## IDM

**1980 - 1970**

**1990 - 1980**

**IDM**

**POT**

****** ****+2 m**

****** ****- 1 m**

****** ****- 1 m**

****** ****+ 2 m**

****** ****+ 2 m**

****** ****- 2 m**

## Conclusions:

***Visual wave data allow for the analysis of centennial-scale variability of ocean wind wave characteristics: linear trends in***
***the North Pacific may amount to 1.2 m per century, being much***
***smaller in the North Atlantic.***

***Interannual variability patterns are different for sea and swell, implying forcing frequency (e.g. cyclones) as a driving mechanism of swell changes with wind speed being responsible for the variations in sea.  ***

***Extreme wave statistics can be evaluated from VOS using IDM and POT methods. POT method shows the higher extreme waves, which are more close to those obtained from the model hindcasts. ***

***However, estimation of decadal changes in extreme waves shows less skills of the POT method, largely influenced by sampling inhomogeneity***

## Sea, swell, SWH 100-years return