Model  output  statistics  MOS

9

4.  Wind  surge:  wind  components  of  295  ±10  degrees  and  exponent  1,  1.5  or  2  derived  from  GFS
model  (KALNAY  et  al.,  1990).  Correlations  from  0.8  to  0.7.
5.  Basic  set  of  other  GFS  predictors  and  derived  variables  (about  150  potential  predictors)  with  best
correlations  from  0.75  to  0.65  for  U  components  of  (geostrophic)  wind  between  950  hPa  and  10  m
above  mean  sea  level.
6.  Wind  surge  observations  at  Aberdeen  in  its  double  function  as  a  signal  provider  for  external  surges
coming  in  from  the  Atlantic  Ocean  (CORKAN,  1950)  and  provider  of  general  information  about  the
North  Sea's  current  water  volume,  with  correlations  from  0.6  to  0.5.  External  surges  are  measurable
at  the  Cuxhaven  gauge  after  about  12  hours.
7.  Pers2D_korr:  this  is  the  most  important  predictor  in  the  system:  the  correction  of  the  last  known
initialisation  error  of  the  2D  model.  Correlation  of  predictor  and  predictand  is  low,  but  correlation  of
the  predictor  with  the  residuum  (error)  of  the  1-predictor  MOS  equations  with  the  initialisation  error
of  DMO  of  the  last  corresponding  surge  event  in  some  cases  is  greater  than  0.6.

In  the  discussion  of  MOS  equations  below,  the  symbiosis  of  physics  (2Dv4  model  and  GFS  model),
synoptics  (in  the  selection  and  transformation  of  predictors),  and  statistics  (multiple  linear  screening
regression)  has  been  described  exemplarily.  The  standard  MSWR  regression  table  format  used  for  this
purpose  has  only  been  explained  to  the  extent  required  to  understand  the  explanatory  texts.  A  more
detailed  description  of  the  table  outputs  is  provided  in  KNUPFFER  (1996)  and  HOFFMANN  (2008).

3.2  Predictands
The  following  predictands  are  forecast:

Surge
SurgeH
SurgeL
Surge+
Surge-StH+

StH-StL+

StL-Kombi


unclassified  predictand
high  water  surge  classified  by  HW/LW

classified  by  HW/LW
classified  by  surge+/surgeclassified
  by  surge+/surgeclassified
  by  StH+/StH-/StN+/StNclassified
  by  StH+/StH-/StN+/StNclassified
  by  StH+/StH-/StN+/StNclassified
  by  StH+/StH-/StN+/StN-Suitable
  combination  of  the  latter  four  predictands  if  ABS(surge  -  4  cm)
>  2*Abs_Err_surge,  otherwise  Kombi=surge.  Abs_Err_surge  is  the
MOS-computed  absolute  error  of  the  MOS  prediction  of  the  surge  predictand.

low  water  surge
positive  surge
negative  surge
surge+  at  HW
surge-  at  HW
surge+  at  LW
surge-  at  LW