Ralf Weisse

Marine Climate and Climate Change

Marine Climate and Climate Change Storms, Wind Waves and Storm Surges Marine environmental conditions such as storms, storm surges and wave heigths are directly experienced by, for example, off-shore operations or coastal populations. The authors review and bring together the state-of-the-art and present day knowledge about historical changes, recent trends and concepts on how marine environmental conditions may change in the future. Consequences and implications for future off-shore operations and coastal defence are covered.

Regional storm climate and related marine hazards in the Northeast Atlantic

Storms represent a major environmental threat. They are associated with abundant rainfall and excessive wind force. Wind storms cause different types of damages on land and on sea; on land, houses and other constructions may be damaged; also trees may break in larger numbers in forests. In the sea, wind pushes water masses towards the coasts, where the water levels may become dangerously high, overwhelm coastal defense and inundate low-lying coastal areas; also the surface of the sea is affected – wind waves are created, which eventually transform into swell. Obviously, ocean waves represent a major threat for shipping, off-shore activities and coastal defense.

Past and future changes in wind, wave, and storm surge climates

In this chapter we review present knowledge about past and potential future changes and variability of marine weather phenomena. The review provides a snapshot of knowledge as of early 2009 when this chapter was completed. Conclusions, numbers, and interpretations may change when new observational evidence becomes available or when some of the identified shortcomings have been addressed.

How to determine long-term changes in marine climate

So far we have reviewed the dynamics of the global climate system, the marine weather phenomena this book is about—in particular, storms, wind waves, and storm surges—and how to mathematically describe these phenomena. In this chapter, we address the question on how to determine long-term changes in the statistics of marine weather phenomena.

Models for the marine environment

Models are widely used in environmental sciences. However, the word model covers a much broader range than usually recognized by the user. In different areas of science, different meanings prevail and are considered to be correct. These differences can cause much confusion and problems for interdisciplinary cooperation. What a model or even a good model constitutes is a matter of social or cultural agreements within a wider or broader scientific field.1 When referring to models a large variety of different concepts is generally meant, ranging from simple analogs like maps, to idealizations, conceptualizations, huge miniaturizations and, particularly in climate science, to a mathematically constructed substitute reality (von Storch, 2001).

Marine weather phenomena

In this chapter we introduce and describe some of the marine weather phenomena that may cause high impacts at sea or in coastal areas. Naturally, high wind speeds play a crucial role and they are associated with all the phenomena discussed. We start with a description of mid-latitude cyclones and storm tracks (Section 2.2). Mid-latitude cyclones form along the polar front in both hemispheres and preferably propagate eastward. The regions that, on average, experience high mid-latitude cyclone activity are referred to as storm tracks. Mid-latitude or extra-tropical cyclones are to be distinguished from tropical cyclones that preferably form over the tropical oceans within a latitude band ranging from about 5° to 20° in both hemispheres (Section 2.3). Both mid-latitude and tropical cyclones are associated with high wind speeds that are responsible for high-impact variations of sea surface height. The latter comprise wind-generated waves at the sea surface (Section 2.4) and storm surges (Section 2.5). Changes in mean sea level and tides are also addressed in Section 2.5. Although they are not related to high wind speeds, their effects may add to wind-induced variations of sea surface height and thus may significantly enhance the risk of flooding in coastal areas.