INTAS ≠ 01-2206 ≥A new generation ocean wave statistics

and wave based sea-air interaction≤

This is a 3 year project (July 2002 - July 2005) supported by INTAS, co-ordinated by SOC with the participation of KNMI (de Bilt, Netherlands), P.P. Shirshov Institute of Oceanology (Moscow, Russia) and Main Geophysical Observatory (St Petersburg, Russia)

 

In September/October 2004 the regular meeting of this group also incorporated a one day workshop on "Extremes of Ocean Waves", for which we invited experts in the estimation of statistical extremes and representatives of "end users". A report on this meeting is given below.

 

Report on the project meeting and project seminar

(SOC, Southampton, 30 September-1 October 2004)

 

 

 

Meeting participants

 

Clive Anderson, University of Sheffield, Sheffield, UK

Roman Bortkovski, Main Geophysical Observatory, St. Petersburg, Russia

Adam Butler, Lancaster University, Lancaster, UK

David Carter, Satellite Observing Systems, Godalming, UK

Peter Challenor, SOC, Southampton, UK

Sofia Caires, KNMI, De Bilt, Netherlands

Sergey Gulev, P.P.Shirshov Institute of Oceanology, Moscow, Russia

Jian-Guo Li, Met Office, UK

Nadia Kovaleva, P.P.Shirshov Institute of Oceanology, Moscow, Russia

Andreas Sterl, KNMI, De Bilt, Netherlands

David Woolf, SOC, Southampton, UK

 

Agenda

 

Thursday, 30 Sep, morning and afternoon sessions

 

Project seminar special programme

 

∑        Welcome and introduction by David Woolf and Peter Challenor

∑        Sofia Caires and Andreas Sterl, KNMI. Estimation and projection of return values of significant wave height using the ERA-40 data

∑        Sergey Gulev and Vika Grigorieva, IORAS. Climate changes in ocean wave extremes from VOS data

∑        Peter Challenor and David Woolf, SOC. Estimation of extreme wave height from altimetry.

∑        Adam Butler, Lancaster University. Extreme value methods for synthetic storm surge data.

∑        Clive Anderson, Problem Areas & Possible Approaches in Ocean Wave Extremes

∑        Discussion, led by David Woolf (participants David Carter, Andreas Sterl, Sergey Gulev, Roman Bortkovsky, Peter Challenor, Clive Anderson)

 

 

Friday, 1 Oct, morning session

Activities report from IORAS (Gulev)

Activities report from SOC (Woolf)

Activities report from KNMI (Sterl)

Scientific presentation

Roman Bortkovski, Boris Egorov and Natalia Tolstobrova, MGO. Recent evaluations of CO2 and O2 air-sea mean exchange in the key ocean areas

 

Friday, 1 Oct, afternoon session

Discussion of project tasks and hot issues:

∑      Assessment of the project results for the two year period (Woolf, Gulev ≠ leaders).

∑      Application of the Peak Over Threshold (POT) method to the VOS data (Sterl, Gulev ≠ leaders)

∑      Further analysis of sea-air interaction parameters, linked to the ocean surface roughness (Woolf, Bortkovsky ≠ leaders)

Project status assessment

Publication strategy

Project report

Next meeting

 

Executive summary

 

The meeting started with welcoming remarks by David Woolf and Peter Challenor at 10:00 01.30.2004 at the meeting room at Southampton Oceanography Centre, Southampton. After the introduction of the participants, a special scientific seminar on the methods of estimation of extreme ocean waves was launched.

 

Sofia Caires in her presentation reviewed the state of the art of the estimation of extreme wave heights from the model hindcasts and presented global fields of extreme significant wave height derived from the recent ERA40-WAM hindcast. Homogeneous sampling in the model data allows for the use of the Peaks Over Threshold (POT) method with no specific limitations. However, model fields themselves require corrections of the impact of the inhomogeneous data assimilation inputs. Methods for appropriate correction procedures were suggested.

Caires and Sterl Presentation

 

Sergey Gulev presented the results of the estimation of extreme wave height form the VOS data and their decadal to centennial variability. VOS data have some limitations for the proper application of the POT methods. Comparisons of the results obtained using initial value distribution method (IDM) with those derived from WAM model data show underestimation of the extreme significant wave height in VOS data. Nevertheless, the variability patterns in the Atlantic and Pacific Oceans are quite comparable in both data sets.

VOS Ocean Wave Statistics

 

Peter Challenor presented a technique enabling application of POT method to altimeter data, which suffer from undersampling as the VOS data do. The results were quite reliable, which implies good prospects on the application of this methodology to VOS data. Connections between interannual variability of the extreme wave height in the Atlantic with the North Atlantic Oscillation were discussed.

Challenor Presentation

 

Adam Butler presented an analysis of extreme surge levels in the North Sea based on the use of hydrodynamic model and observations data. He strongly advocated methods, based on the analysis of extreme tails, which allow ≥them to speak for themselves≤. Dynamical evolution of several extreme surges in the North Sea was presented.

Butler Presentation

 

In the talk of Clive Anderson a general overview of the application of extreme value statistics to the different data types was given. Major issues addressed were the use of combined data, based on different data sources, a combined analysis of the spatial and temporal variability for estimation of extremes and the methods of the analysis of special statistical distributions. It was pointed out that the choice of methods should be strongly constrained by the data types and the research task.

Anderson Presentation

 

During the discussion participants agreed that despite considerable uncertainties in the estimation of the extreme wave heights over the Global Ocean, the project developed considerable progress in the quantitative estimation of the sea roughness extremes. Further directions of the development of extreme wave height estimates based on different data types were suggested.

 

During the executive session (1 October 2004) project participants discussed the major administrative and organizational issues of the project as well as scientific topics, lying beyond the extreme waves. In particular, Roman Bortkovsky presented the analysis of the carbon dioxide sea-air fluxes. The actual gas fluxes in chosen oceanic areas were found as sums of bubble and diffusive transfers with consideration of dissolved gas content changes which are caused by high winds. Mean climatic fluxes are estimated using wind speed probability distribution. The estimates obtained were compared with fluxes, calculated by traditional procedures in which no bubble transfer is considered and the undersurface gas concentration is assumed independent of wind speed. Analysis has shown that the vertical distribution of dissolved gas content in the upper ocean layer significantly influences transfer processes under high winds. It has been found that there is strong variability of the upper ocean layer structure in the Kuroshio and Gulfstream zones and this variability makes the physical description of the air-sea climatic gas exchange very complicated. New estimates of the bubble transfer contributions for climatological fluxes of the oxygen and of the carbon dioxide were found to be compatible with previously obtained results.

Bortkovsky Presentation

 

It has been decided to draft by May-June 2005 a review paper about the project results and to submit it to BAMS or EOS. Such a publication along with more narrow articles under the project will give an excellent overview of the project achievements. It has been decided to run the next project meeting in Moscow in Spring-Summer 2005.

 

Report by Sergey Gulev, edited by David Woolf