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Nick Rayner 
Hadley Centre for Climate Prediction and Research, Met Office 
Exeter, U.K. 
The GCOS climate monitoring principles provide a useful check list of requirements 
which  should  be  satisfied  by  any  data  sets  used  to  monitor  climatic  changes.  The  most 
relevant  of  these  requirements  can  be  summarized  in  terms  of:  stability,  homogeneity  and 
continuity.  GCOS  has  recommended  that  high  priority  should  be  given  to  making 
measurements  in  data sparse  or  climatically  sensitive  regions.  In  particular,  the  needs  of 
climate assessments like those of the IPCC should be integrated into the plans from the start. 
In addition, users should be given easy access to data and uncertainties and any biases in the 
data should be quantified and published. 
There  are  a  bewildering  number  of  sea  ice  data  sets  apparently  available  for  climate 
studies.  Many  of  these  data  sets  are  available  from  the  National  Snow  and  Ice  Data  Center 
(NSIDC) in the U.S. They also provide helpful data summaries describing the strengths and 
weaknesses of the most popular data sets. This archive contains different data sets based on 
passive  microwave  retrievals  from  the  ESMR,  SSMR,  SSM/I  and  AMSR E  instruments  on 
various  satellites,  digitized  chart  collections  and  some  field  measurements.  The  passive 
microwave  data  sets  differ  in  the  algorithms  used  to  retrieve  sea  ice  concentration  by 
combination  of  brightness  temperatures  sensed  by  different  frequency  channels  of  the 
instrument.  None  are  universally  applicable  and  most  have  been  validated  over  limited 
regions  or  times.  Fields  of  passive  microwave  retrieved  sea  ice  concentration  are  not 
presented with accompanying error estimates. Digitized chart collections include the Russian 
charts  from  the  Arctic  and  Antarctic  Research  Institute  (AARI),  Chapman  and  Walsh  data, 
plus charts for Alaska, Canadian Arctic and the Bering Sea and other Arctic regions  
Other data sets are also referred to on, but not accessible from, the NSIDC web pages. 
The  Hadley  Centre  SST  and  sea  ice  analysis  (HadISST1)  is  our  attempt  (see  Rayner,  et  al., 
2003)  at  creating  a  more homogeneous  sea  ice  concentration  data  set  by  blending  chart 
derived data from Walsh and Chapman and the National Ice Center with passive microwave 
data.  The  Global  Digital  Sea  Ice  Data  Bank  (GDSIDB)  was  collected  by  JCOMM  and 
comprises  operational  ice  charts  from  various  countries.  An  analysis  of  these  latter  data 
combined  with  data  from  Walsh  and  Chapman  and  climatology  (where  no  actual  data  was 
available) was recently  created by Vasily Smolyanitsky during a visit to the Hadley Centre. 
We hope to incorporate these into the next version of HadISST. Other operational charts have 
not  yet  been  collected  into  the  GDSIDB,  but  there  are  plans  for  expansion.
Historical  Ice  Chart  Archive  contains  historical  sea ice  observations  in  the  Arctic  region 
between 30W and 70E in the form of digitized maps. It was created at the Norwegian Polar 
Institute. The earliest chart dates from 1553, and the most recent is from December 2002. We 
also hope to include these in the next version of HadISST. 
To  improve  sea ice  fields,  it  is  necessary  to  identify  the   best   passive  microwave 
algorithm  (or  combination  of  algorithms)  for  retrieval  of  sea  ice  concentration.  Often 
algorithms  and  brightness  temperature  fields  are  worked  up  into  sea  ice  concentration  data 
sets  for  only  a  limited  period,  but  algorithms  are  simple  enough  to  apply  to  the  whole 

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