Spatial correlation of marine wind‐speed observations

Abstract

The spatial characteristics of the wind speeds from ships, drilling platforms, and satellites (SASS and SMMR) were investigated through autocorrelation analysis. Values of the spatial correlation coefficient in minimum separation classes revealed that SASS winds contained the least noise, followed by drilling‐platform and SMMR winds, measured ship winds and estimated ship winds. The variances explained by wind‐speed observations within a 100‐km radius of each other were found to be 86, 72, 62, 48 and 41%, respectively. Ship wind‐speed estimates made during hours of darkness showed significantly higher noise than daytime reports.     

Trends and low frequency variability of extra-tropical cyclone activity in the ensemble of twentieth century reanalysis

An objective cyclone tracking algorithm is applied to twentieth century reanalysis (20CR) 6-hourly mean sea level pressure fields for the period 1871–2010 to infer historical trends and variability in extra-tropical cyclone activity. The tracking algorithm is applied both to the ensemble-mean analyses and to each of the 56 ensemble members individually. The ensemble-mean analyses are found to be unsuitable for accurately determining cyclone statistics. However, pooled cyclone statistics obtained by averaging statistics from individual members generally agree well with statistics from the NCEP-NCAR reanalyses for 1951–2010, although 20CR shows somewhat weaker cyclone activity over land and stronger activity over oceans. Both reanalyses show similar cyclone trend patterns in the northern hemisphere (NH) over 1951–2010. Homogenized pooled cyclone statistics are analyzed for trends and variability. Conclusions account for identified inhomogeneities, which occurred before 1949 in the NH and between 1951 and 1985 in the southern hemisphere (SH). Cyclone activity is estimated to have increased slightly over the period 1871–2010 in the NH. More substantial increases are seen in the SH. Notable regional and seasonal variations in trends are evident, as is profound decadal or longer scale variability. For example, the NH increases occur mainly in the mid-latitude Pacific and high-latitude Atlantic regions. For the North Atlantic-European region and southeast Australia, the 20CR cyclone trends are in agreement with trends in geostrophic wind extremes derived from in-situ surface pressure observations. European trends are also consistent with trends in the mean duration of wet spells derived from rain gauge data in Europe.     

Trends and variability of storminess in the Northeast Atlantic region, 1874–2007

This article builds on the previous studies on storminess conditions in the northeast North Atlantic–European region. The period of surface pressure data analyzed is extended from 1881–1998 to 1874–2007. The seasonality and regional differences of storminess conditions in this region are also explored in more detail. The results show that storminess conditions in this region have undergone substantial decadal or longer time scale fluctuations, with considerable seasonal and regional differences. The most notable differences are seen between winter and summer, and between the North Sea area and other parts of the region. In particular, winter storminess shows an unprecedented maximum in the early 1990s in the North Sea area and a steady upward trend in the northeastern part of the region, while it appears to have declined in the western part of the region. In summer, storminess appears to have declined in most parts of this region. In the transition seasons, the storminess trend is characterized by increases in the northern part of the region and decreases in the southeastern part, with increases in the north being larger in spring. In particular, the results also show that the earliest storminess maximum occurred in summer (around 1880), while the latest storminess maximum occurred in winter (in the early 1990s). Looking at the annual metrics alone (as in previous studies), one would conclude that the latest storminess maximum is at about the same level as the earliest storminess maximum, without realizing that this is comparing the highest winter storminess level with the highest summer storminess level in the period of record analyzed, while winter and summer storminess conditions have undergone very different long-term variability and trends. Also, storminess conditions in the NE Atlantic region are found to be significantly correlated with the simultaneous NAO index in all seasons but autumn. The higher the NAO index, the rougher the NE Atlantic storminess conditions, especially in winter and spring.     

Detection of external influence on trends of atmospheric storminess and northern oceans wave heights

The atmospheric storminess as inferred from geostrophic wind energy and ocean wave heights have increased in boreal winter over the past half century in the high-latitudes of the northern hemisphere (especially the northeast North Atlantic), and have decreased in more southerly northern latitudes. This study shows that these trend patterns contain a detectable response to anthropogenic and natural forcing combined. The effect of external influence is found to be strongest in the winter hemisphere, that is, in the northern hemisphere in January–March and in the southern hemisphere in July–September. However, the simulated response to anthropogenic and natural forcing combined, which was obtained directly from climate models in the case of geostrophic wind energy and indirectly via an empirical downscaling procedure in the case of ocean wave heights, is significantly weaker than the magnitude of the observed changes in these parameters.     

Storm waves in Canadian waters: A major marine hazard

Abstract

In this paper, an overview of storm waves associated with intense weather systems affecting the east and west coasts of Canada is presented. The paper presents the wave climatology of the east and west coasts in terms of the 100‐year significant and maximum wave heights and further analyses the directional distribution of wave heights at selected locations in the Canadian east and west coasts offshore. The paper also analyses wave hazards associated with storm waves in the Beaufort Sea as well as the Canadian Great Lakes region. A section on ocean wave modelling provides a brief history of the development of ocean surface wave models and its present status. The paper further considers the impact of climate change scenarios on wave hazards and finally examines mitigation measures in terms of wave products available from operational wave models and related wave climatology.     

Trends and low-frequency variability of storminess over western Europe, 1878–2007

This study analyzes extremes of geostrophic wind speeds derived from sub-daily surface pressure observations at 13 sites in the European region from the Iberian peninsula to Scandinavia for the period from 1878 or later to 2007. It extends previous studies on storminess conditions in the Northeast (NE) Atlantic-European region. It also briefly discusses the relationship between storminess and the North Atlantic Oscillation (NAO). The results show that storminess conditions in the region from the Northeast Atlantic to western Europe have undergone substantial decadal or longer time scale fluctuations, with considerable seasonal and regional differences (especially between winter and summer, and between the British Isles-North Sea area and other parts of the region). In the North Sea and the Alps areas, there has been a notable increase in the occurrence frequency of strong geostrophic winds from the mid to the late twentieth century. The results also show that, in the cold season (December–March), the NAO-storminess relationship is significantly positive in the north-central part of this region, but negative in the south-southeastern part.     

Quantifying wave measurement differences in historical and present wave buoy systems

Ocean Dynamics - An intra-measurement evaluation was undertaken, deploying a NOMAD buoy equipped with three National Data Buoy Center and two Environment and Climate Change Canada-AXYS...     

The 14th international workshop on wave hindcasting and forecasting and the 5th coastal hazards symposium

Following the 14th International Workshop on Wave Hindcasting and Forecasting and 5th Coastal Hazards Symposium in November 2014 in Key West, Florida, a topical collection has appeared in recent issues of Ocean Dynamics. Here, we give a brief overview of the 16 papers published in this topical collection as well as an overview of the widening scope of the conference in recent years. A general trend in the field has been towards closer integration between the wave and ocean modelling communities. This is also seen in this topical collection, with several papers exploring the interaction between surface waves and mixed layer dynamics and sea ice.