Storms and Storm Surges - Development of the storm climate

How has the storm climate in the Northeast Atlantic developed in the last few decades and last few centuries?

Serious efforts to study changing storminess over the Northeast Atlantic began in the early 1990s, when meteorologists noticed a roughening of storm and wave conditions. Wave observations from light houses and ships (Hogben, 1994; Cardone et al., 1990; Carter and Draper, 1988) described a roughening since the 1950s, and an analysis of deep pressure systems in operational weather maps indicated a steady increase of such lows since the 1930s (Schinke et al. 1992). Unfortunately, these analyses all suffered from the problems described before (see 'How to determine decadal and longer variations in the storm climate?'), namely either an insufficient length of data series or compromised homogeneity. For instance, the skill of describing weather details in weather maps has steadily improved in the course of time, because of more and better data reported to the weather services and improved analysis practices. For the case of global re-analysis the improvement related to the advent of satellite data on Southern Hemisphere is described by Kistler et al. (2001). Another example on the effect of better data coverage is provided by Landsea et al. (2004) for an example of a tropical storm.

The breakthrough came when proxies (see 'How to determine decadal and longer variations in the storm climate?') were introduced, mostly in the EU project WASA (WASA, 1998). Alexandersson et al. (1998, 2000) assembled homogeneous series of air pressure readings from 1880 for a variety of locations covering most of Northern Europe. They calculated 99%iles of geostrophic winds from a number of station triangles. After some normalization and averaging they derived proxy time series for the greater Baltic Sea region and for the greater North Sea region. The time series are shown in Figure 2. According to this proxy, the storm activity intensified indeed between 1960 and 1995, but from the beginning of the record until about 1960 there was a long period of declining storminess, and since about 1995 the storm activity is decreasing again in most areas of the Northeast Atlantic (Weisse et al., 2005).

Figure 2: Storm indicator derived from intra-annual percentiles of geostrophic winds derived form a series of triangles of stations for the greater North Sea (left) and the greater Baltic Sea region (right). [Updated version of diagrams provided by Alexandersson et al. (2000)].

A similar result is obtained when analyzing the record of high waters in Den Helder and Esbjerg, two harbours at the Dutch and Danish North Sea coast (Pfizenmayer, 1997). Figure 3 displays two statistics for each of the two tide gauges, the annual mean high tide and the annual 99%iles of the deviations of the high tide from the annual mean. The former, the annual mean, is influenced by a number of non-storm related processes, in particular water works, geological changes (land sinking) and global mean sea level rise. Both locations exhibit a marked increase in mean high tide, but the rate of increase is different at the two locations, which is likely related to different regional processes related to water works and costal defence measures. The two other curves in Figure 3 display the temporal development of the 99%iles (after subtraction of the annual mean); again, an increase is found for the period 1960 to the 1990s, which is, however, not significant when compared to the development prior to 1960.

Figure 3: Changing intra-annual statistics of high tide water levels at Esbjerg (Denmark) and Den Helder (The Netherlands) since the late 19th century. The lower two curves display the annual means; the upper two curves the 99%iles of intra-annual variations relative to the annual mean. The former reflect the presence of all kind of climatic as well as local effects, while the latter is a proxy for regional storm activity. [After Pfizenmayer (1997)]

The 1960-1995 increase in Northeast Atlantic storminess appears also as non-dramatic, when an even longer time window is considered, namely homogenized local air pressure readings at two locations in Sweden, Lund and Stockholm, which have been recorded since the early 1800s and earlier (Bärring und von Storch, 2004). The number of deep pressure systems as well as the number of pressure falls of 16 hPa and more within 12 hours (not shown) is remarkably stationary since the beginning of the barometer measurements. This is remarkably in view of the marked increase in regional temperatures, e.g., the winter mean temperatures for Denmark.

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References

Alexandersson, H., T. Schmith, K. Iden and H. Tuomenvirta, 1998: Long-term trend variations of the storm climate over NW Europe. The Global Atmos. Oc. System 6, 97-120

Alexandersson, H., T. Schmith, K. Iden and H. Tuomenvirta, 2000: Trends of storms in NW Europe derived from an updated pressure data set. Clim. Res. 14:71-73

Bärring, L. and H. von Storch, 2004: Northern European storminess since about 1800. Geophys. Res. Letters 31, L20202, doi:10.1029/2004GL020441, 1-4

Cardone, V.J., Greenwood, J.G. and M.A. Cane, 1990: On trends in historical marine data. J. Climate 3, 113-127

Carter, D.J.T. and L. Draper, 1988: Has the northeast Atlantic become rougher? Nature 322: 494

Grossmann, I., K. Woth and H. von Storch, 2006: Localization of global climate change: Storm surge scenarios for Hamburg in 2030 and 2085. submitted

Hogben, N, 1994: Increases in wave heights over the North Atlantic: A review of the evidence and some implications for the naval architect. Trans. Roy. Inst. Naval Arch. W5, 93-101

Kistler, R., E. Kalnay, W. Collins, S. Saha, G. White, J. Woollen, M. Chelliah, W. Ebisuzaki, M. Kanamitsu, V. Kousky, H. van den Dool, R. Jenne and M. Fiorino, 2001: The NCEP/NCAR 50-year reanalysis. Bull Amer. Meteor. Soc. 82: 247-267

Landsea, C. W., C. Anderson, N. Charles, G. Clark, J. Dunion, J. Fernandez-Partagas, P. Hungerford, C. Neumann, and M. Zimmer, 2004: The Atlantic hurricane database re-analysis project: Documentation for the1851-1910 alterations and additions to the HURDAT database. In: R. J. Murname and K.-B. Liu (eds): Hurricanes and Typhoons: Past, Present and Future, Eds., Columbia University Press, 177-221

Pfizenmayer, A., 1997: Zusammenhang zwischen der niederfrequenten Variabilität in der grossräumigen atmosphärischen Zirkulation und den Extremwasserständen an der Nordseeküste. Diplomarbeit Institut für Geographie Universität Stuttgart

Schinke, H., 1992: Zum Auftreten von Zyklonen mit niedrigen Kerndrücken im atlantisch-europäischen Raum von 1930 bis 1991. Wiss. Zeitschrift der Humboldt Universität zu Berlin, R. Mathematik/Naturwiss. 41, 17-28

WASA, 1998: Changing waves and storms in the Northeast Atlantic? - Bull. Amer. Met. Soc. 79, 741-760

Weisse, R., H. von Storch and F. Feser, 2005: Northeast Atlantic and North Sea storminess as simulated by a regional climate model 1958-2001 and comparison with observations. J. Climate 18, 465-479