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A29  Cyclone density changes during time of war?
Rev. 05 May2011

  • Jonas Bhend, (Diploma Thesis , 2005):   “North Atlantic and European Cyclones: Their Variability and Change  from 1881 to 2003” at the University of Berne, pages 88, 

A recent diploma thesis by Jonas Bhend established that the cyclone density in the North Atlantic showed remarkable anomalies during the winters of 1916/17, 1939/40, and 1940/41 (p.38), whereas cyclone density steadily decrease in the North Atlantic sector from 70° W to 50° E and 25° N to 70° N during the winter seasons between 1881 and 2003. (Fig. 1). Neither he nor his tutor at the University of Berne ask the inevitable question concerning the two remarkable deviation. Their possible  significance with regard to the two  World Wars is obvious. It seems the tutor did not grasped the scientific importance of this two deviation.           

  Figure 1, Data from J. Bhend, (Fig.5.5): See a different version below.

In a longer discussion (sec. 6.3.4) Bhend wants to shed light on the influence of the ENSO on the NAO because of a claim by Brönnimann et al (see next section) that an  ENSO/El Niño from 1939 to 1942 is to blame for the cold winter 1939-1942. At the end of the discussion (sec. 6.3.4) he seems reluctant to confirm a link, outlining that:

 “there are many ENSO events that do not show this anomaly patter. Hence, the generally weak correlations between the NINO 3.4 Index and cyclone statistics over the North Atlantic and Europe lead to the conclusion that the influence of the ENSO on the North Atlantic and Mediterranean storm track is not dominant”.

But there is a turn around  in his Conclusion when saying:  

“ The influence of the El Niño – Southern Oscillation on the North Atlantic and Mediterranean storm track is weak and no-stationary. However, the strong El Niño event from 1939 to 1942 lead to increased cyclonic activity over North Atlantic south of 50° N and over large parts of western Europe. As a consequence of the inconsistent influence of the ENSO, the correlations between the cyclone statistics and the NINO 3.4 index are weak”.

Here the tutor should have intervened. More in the next section that addresses the Brönniman et al claim.    

Fig.2