KLIWAS

Seite  27

possible  for  of  easterly  winds  due  to  a  lack  of  satellite  data  and  corresponding
observations  at  this  wind  direction.  In  a  random  selection  of  satellite  observations  the
conditions  regarding  to  the  cloud  state  is  not  defined,  therefore  the  temporal  statistics
is  influenced  by  a  seasonal  dependency  again.
A  further  promising  approach  is  the  selection  of  the  satellite  scenes  on  pixel  level  and
generating  a  uniform  distribution  with  regard  to  the  wind  direction  and  the  number  of
cloud-free  observations.  Due  to  time  and  budget  restrictions  this  approach  could  not
been  realized  in  this  project  phase.  In  Fig.  12  we  present  some  first  results  basing  on
the  uniform  distribution  shown  in  Fig.  11.  The  Figures  are  based  on  AVHRR-sensor
data  of  NOAA  and  MetOp  satellites.

Fig.  8:  Frequency  of  geostrophic  east  (red)  and  west  (blue)  winds  over  the  North  Sea.  Daily
means  for  1990-2011.

Fig.  9:  Relative  monthly  frequency  of  geostrophic  east  (red)  and  west  (red)  winds  wind  direction.
Daily  means  for  1990-2011.  Left:  original  distribution,  right:  after  adjusting  the  seasonal
distribution  of  westerly  winds  to  that  of  easterly  winds.

KLIWAS
Climatology
of  North  Sea
Fronts