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C.3  Concluding  Remarks

by  the  birds  of  a  feather  flock  together  rule,  however,  nature  couples  maritime  and
continental  wind  characteristics  according  to  the  complementary  principle  opposites
attract  which  results  in  a  hybrid  wind  climate.
While  within-regime  differences  among  the  seasonal  distributions  are  significant  beyond ­
  doubt,  the  cross-regime  differences  for  the  winter  and  summer  distributions
(Fig.  3-19,  p.  75,  bottom)  were  felt  to  deserve  statistical  confirmation.  To  this  end,  a  2-dimensional ­
  Kolmogorov-Smirnov  test  (Press  et  al.  1992)  was  performed  on  the  unbinned ­
  seasonal  sample  distributions.  The  K-S  test  statistic  >D<  is  the  maximum  difference ­
  in  the  fraction  of  data  within  1  of  4  natural  quadrants  around  the  maximizing  data
point  in  the  velocity/direction  plane  which  is  found  by  ranging  over  both  all  data  points
and  associated  quadrants.  For  the  2  winter  distributions  D  attains  a  maximum  of  19  %
in  the  quadrant  northeast  of  approx.  (8  hPa,  200°).  Similarly,  for  the  summer  samples,
D  =  17  %  again  in  the  quadrant  NE  of  about  (5  hPa,  190°).  Both,  the  wintry  and  the
summery  distributions  turn  out  to  be  significantly  different  at  p-levels  next  to  certainty,
viz.  <  5  x  10" 8  %  and  <  7  x  10" 6  %,  respectively.  The  D-values  are  in  good  agreement
with  cumulative  differences  within  the  ±  0.5  %  contours  of  Fig.  3-19,p.  75  (bottom)  which
amount  to  ±  18  %  for  winter  (JFM)  and  ±  15  %  for  summer  (JAS).  As  an  aside,  the
complementary  difference  patterns  of  Fig.  3-19,  p.  75  imply  that  annual  wind  statistics
would  not  have  produced  any  cross-regime  differences  to  speak  of  due  to  mutual  cancellation ­
  over  the  annual  cycle.
A  quantitative  summary  of  Fig.  3-19,  p.  75  is  supported  by  Table  3-9,  p.  76.  Notably  different ­
  decadal  SST  regimes  (-  A(R 2 )  +  A(R 3 )  «  1  K)  are  sustained  by  hybrid  couples  of
wind  distributions.  The  cold  regime  is  consistent  with  an  intra-annual  shift  from  continental ­
  winds  in  winter  (cold)  to  maritime  winds  in  summer  (cold).  A  regime  shift  in  SST
is  accompanied  by  a  consistent  reversal  of  the  seasonal  wind  climate.
The  most  recent  cold  to  warm  shift  in  the  late  1980s  went  along  in  winter  with  a  61  %
increase  in  strong  maritime  winds  on  the  expense  of  a  40  %  decrease  in  moderate
continental  winds  (»ConWin«  =>  »MarWin«).  Conversely,  strong  maritime  winds
dropped  by  26  %  in  summer  due  to  an  overall  increase  of  continental  winds  by  59  %
(»MarSum«  =>  »ConSum«).  While  changes  in  direction  and  velocity  were  about  balanced ­
  in  winter,  directional  changes  clearly  surpassed  velocity  changes  in  summer.

C.3  Concluding  Remarks
The  bi-stability  of  SST  regimes  casts  doubt  on  the  usefulness  of  standard  CliNo  climatologies ­
  in  climatic  mishmash  regions  such  as  the  North  Sea  where  the  implicit  assumption ­
  of  climatic  stationarity  is  violated.  As  a  consequence,  the  »significant-departure-from-normal
  alert«  is  on  next  to  constantly  (cf.  Fig.  3-18,  p.  72)  because  the  alarm
device  is  not  »aware«  of  a  significant  change  in  normality.  A  solution  might  consist  in
judging  the  significance  of  anomalies  from  mixed  probability  density  functions  that  account ­
  for  the  bi-stability  phenomenon.
The  findings  as  to  hybrid  and  reversed  wind  distributions  during  different  SST  regimes
were  obtained  for  the  cold  period  1978  -  1987  and  the  recent  warm  episode.  The  robustness ­
  of  these  results  should  be  examined  e.  g.  by  way  of  extending  the  analysis
to  the  long  SST  time  series  of  Helgoland  Roads.
Finally,  it  would  appear  useful  to  explore  how  the  changeable  wind  characteristics
across  the  North  Sea  associate  with  large  scale  (anomalous)  features  of  the  general