Storms

 

Understanding Global Warming

Extreme storms are long in coming!

 

A total of 187 storms in Denmark are recorded since 1891 and published by the Danish Meteorological Institute (DMI) – hyperlink. The storms are classified in four categories:

DMI Classification 

Class 4

Class 3

Class 2

Class 1

Wind speed 

>28,5 m/s

>26,5 m/s

>24,5 m/s

>21 m/s

Wind speed squared

>812

>702

>600

>441

DMA Index √Class

2,0

1,7

1,4

1,0

Figure 1. The square of the wind speed is included in the calculation of energy content of storms. The square root of the storm class provides an approximate index that allows summing up of the energy content of the year's storms regardless of their class. A Class 4 storm is thus considered to be twice as strong as a Class 1 storm.

Figure 2. The 19th century ended quite stormy with a record high number of storms in 1898. A total of 12 storms were recorded. Three of them in Class 2, giving the year a DMA-index of 13.2. In the period 1891-2019 we have in average experienced 1½ storm a year.

Accumulated cyclone energy (ACE) used by the National Oceanic and Atmospheric Administration (NOAA) weights cyclones according to their kinetic energy as follows: ACE = 10-4 ∑vmax2; where vmax is estimated sustained wind speed in knots at six-hour intervals – hyperlink.

The Danish storm list does not specify the sustained wind speed and its duration. Inspired by ACE, the Danish Methanol Association (DMA) instead weights the storms with the square root of their class.

In the period 1891-1945 13% out of 88 storms are recorded as regional. In the period 1946-2019 as much as 61% out of 99 storms are recorded as regional. The DMA-index does not reflect this trend towards more regional and fewer nationwide storms. It is not known whether the change is merely a consequence of altered classification guidelines or reflects a milder reality.

IPCC found that no robust trends in annual numbers of tropical storms, hurricanes and major hurricanes counts have been identified over the past 100 years in the North Atlantic basin, AR4 section 16.6.1

Stormy weather in Denmark has certainly not become more frequent or worse.

Figure 4. Wavestar – here in storm mode. The device was installed on 19 September 2009 at Hanstholm, Denmark. The intention is to move it to a new position around 1.3 km from the shore at a depth of 15m where the wave potential is higher.

Understanding Global Warming, Oversigt - LINK



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