Compilation  of  Summaries

19

and  steady  periods  of  high  W-erly  flow  by  distinctive  wind  shifts.  The  2 nd  of
these  periods  sprang  up  with  a  clustering  of  all  November  gales  (6)  and  maintained ­
  its  stormy  character  beyond  the  turn  of  the  year.  Not  only  did  the  number ­
  of  severe  December  gales  attain  a  new  all-time  high  (6),  the  NAO  index  also
hit  a  never  observed  peak  level  of  2.65,  which  stands  out  in  stark  contrast  to
the  record  low  value  of  -3.56  set  one  year  before.  At  5.9  °C  in  December,  air
temperature  at  Norderney  failed  to  drop  against  the  preceding  month.  Against
previous  year’s  record  amplitude  (21.6  K)  the  descent  in  temperature  since  July
halted  to  10.0  K,  a  range  underrun  but  once  before  (1974).

3  Ocean  Physics
Currents  (Page  Seite  84  et  seq.)
The  near-surface  circulation  of  the  North  Sea  and  volume  transports  through
selected  transects  are  largely  influenced  by  atmospheric  forcing.  During  the
period  under  report  two  outstanding  situations  had  been  observed:  The  accumulation ­
  of  strong  westerly  wind  events  in  November  2009  induced  a  North
Sea  wide  pronounced  cyclonic  circulation  pattern.  This  is  shown  in  the  figures
of  the  monthly  near-surface  circulation  patterns  and  in  the  volume  transports
through  the  Dover  Strait  and  in  the  German  Bight.  This  event  was  followed  by
a  long-lasting  circulation  anomaly  in  the  northern  North  Sea  in  the  winter
2009/2010,  where  a  three-month  outflow  in  the  area  of  the  Norwegian  Trench
was  forced  by  persistent  easterly  winds  during  this  relatively  cold  winter.
The  circulation  statistics  for  the  German  Bight  are  based  on  the  chronological
order  of  the  daily  residual  currents  which  are  assigned  to  nine  typical  circulation ­
  patterns.  The  frequency  distribution  of  the  circulation  patterns  in  the  years
2008  and  2009  is  very  close  to  the  10-year  average.  The  lack  of  longer  phases
of  constant  cyclonic  circulation,  which  had  durations  of  up  to  28  days  in  previous ­
  years,  is  striking  in  2008.  Only  an  11  -day  cyclonic  phase  at  the  beginning
of  September  was  observed  in  2008.  In  November  2009,  a  20-day  cyclonic
phase  occurred  and  was  only  interrupted  by  one  day  with  a  northerly  current.
In  2010,  there  were  significant  deviations  from  the  10-year  average.  The  generally ­
  dominant  cyclonic  pattern  shows  the  lowest  frequency  since  2000,  while
the  anti-cyclonic  pattern  shows  the  greatest  frequency  since  2000.  A  phase  of
constant  anti-cyclonic  circulation  over  8  days  is  also  unusual,  because  in  the
past  longer  p
hases  of  a  constant  circulation  type  had  always  been  formed  by  the  cyclonic
pattern.  In  2011,  the  anti-cyclonic  and  directional  type  show  a  clear  decrease
in  comparison  to  the  10-year  average,  which  was  compensated  by  the  variable
type.  The  variable  type  also  formed  the  longest  phase  of  a  “constant”  current
type  with  11-days  duration.  In  this  case,  however,  it  means  11  days  with  no
directional  preference.

Waves  (Page  Seite  101  et  seq.)
The  wave  climate  during  the  period  2008-2011  was  characterized  by  seasonal
geographic  distribution  of  significant  wave  height,  wind  sea-  and  swell  direc ­