Monthly average residual surface current speed and direction Google Earth

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Regional characterisation: a picture paints a thousand words

When deciding the best vessel configuration for your marine project, how can regional characterisation help you understand the processes controlling the local climate where you want to work?

On land, the geography of different regions, whether temperate forest, tropical jungle, hot desert, polar ice cap, still open plain or windy mountains, results in very different climates. This can vary not only with location, but season-to-season and year-to-year.

The global ocean covers 71% of the Earth’s surface, and has a similarly wide range of regional and local climates. The relative importance of the various meteorological and oceanographic (‘metocean’) factors contributing to the local marine climate can also vary.

This article outlines the importance of regional characterisation to inform early stage decision making, and to support the specification and interpretation of more detailed metocean studies, when seeking to work in new locations that may be outside of the user’s previous experience.

What is regional characterisation?

Regional characterisation provides a simply-worded, summary overview of the key metocean factors in the wider area around a planned marine operation.

The characterisation will describe the relative importance, magnitude and variability of these key metocean factors, typically including various measures of winds, waves, currents, and water levels. More complex high-energy metocean events such as tropical revolving storms, squalls and solitons are also usually considered. Depending on the type of project, other factors might also be relevant, such as temperature, lightning, visibility and sea ice.

A single-climate region is normally sufficient for a cluster of fixed location project(s), but multiple climatic regions might be identified in relation to a moving site of operations (e.g. longer vessel transits).

Regional characterisation does not provide detailed statistics for the region or specific locations within it. The region may therefore encompass a certain range of spatial and temporal variability.

For this reason images, rather than text or tables of numbers, are often used to present a summary of otherwise complex details.

Google Earth monthly average residual surface current speed and direction

Intuitive, interactive tools like Google Earth allow regional characterisation information to be easily visually interpreted. This image shows patterns of monthly average residual surface current speed and direction for February (based on 10 years of data from HYCOM (click to enlarge)

Why is regional characterisation useful?

Regional characterisation provides a depth of understanding about the processes that ultimately control the everyday working conditions and the overall workability in an area.

With an understanding of regional processes, the nature and patterns of variance in the key metocean factors can be interpreted and anticipated with confidence and flexibility.

This is especially important when working in new areas that may not only have a different climate, but potentially entirely new metocean processes to consider, that may be simply outside the previous experience of the reader.

Google Earth monthly P90 exceedance surface wind speed

This image shows patterns of monthly P90 exceedance surface wind speed for February (based on 31 years of data from the NCEP Climate Forecast System Reanalysis) (click to enlarge)

When should regional characterisation be used?

Regional characterisation should be sought at an early stage when considering projects in a geographic area outside of the users’ main experience.

The essential knowledge and understanding gained from a regional characterisation might be very relevant to significant early stage decision making, e.g. bid/no-bid, basic vessel selection, programme management (month of year), and major risk identification.

Regional characterisation information can also be used to inform the specification for local project metocean studies, and aid with interpretation of those studies to inform more refined decision making.

How can regional characterisation be applied?

Regional characterisation is developed for areas similar in terms of the relative importance of the key metocean factors, meaning that a single set of information will be broadly applicable to most locations in the region being described.

Within these larger climatic regions there will be variability in the detail of the local climate statistics, and other local or site-specific metocean studies will be required to support more detailed decision making.

At ABPmer, climatic regions are identified by experienced metocean analysts. The relevant key metocean factors are identified first – the selection may be general in nature, or based on the specific requirements of the client or project.

Our analyst will then use their knowledge and experience, usually in conjunction with large (ocean basin or global) scale maps of key metocean factor statistics, to visually identify and characterise regions with the required degree of similarity.

The maps used may include statistics such as the average surface current speed and direction, or the wave height or wind speed with a certain probability of occurrence.

These statistics are created from much larger databases of historical time-series data, generated using computer model simulations.

Separate statistics are usually created for each month to understand seasonal effects on the spatial patterns. The mapped statistics provide context and information to the analyst that cannot be easily achieved by looking at mapped or point time-series data. The maps also allow the identification and characterisation of climatic regions to be an objective and quantitative process.

Regional characterisation for your project

The metocean specialists at ABPmer are highly experienced in global metocean processes, providing a range of services and support for marine operations around the world.

We have developed a number of regional characterisation products for immediate use, and maintain global maps of key factor statistics to inform our services.

We have all the necessary tools and data sets to robustly inform a range of regional and site specific metocean assessments for any type of marine operation.

Prepared by David Lambkin, Metocean Consultant

For more information about metocean services, visit our SEASTATES microsite.