WORLD METEOROLOGICAL ORGANIZATION 

MANUAL ON THE GLOBAL OBSERVING SYSTEM 

VOLUME II 

REGIONAL ASPECTS 

(revised edition 1995) 

WMO-No. 544 
Secretariat of the World Meteorological Organization – Geneva – Switzerland  1995 

4.  REGION IV —  NORTH AND CENTRAL AMERICA 

4.1 	Regional basic synoptic network of surface and upper-air observing stations 
4.1.1 	Composition of the regional basic synoptic network 
4.1.1.1 The  regional  basic  synoptic  network  of  surface  and  upper-air  observing  stations  is  reviewed and revised at each session of the Association. The list of stations constituting the current  regional basic synoptic network is given in the report of the most recent session of the Association.  Changes  are  announced  in  the  monthly  “Operational  Newsletter”  issued  by  the  Secretariat  (see  paragraph 4.1.4 below). 
Manned surface stations included in the regional basic synoptic network shall conform  to the specifications laid down for principal land stations in Volume I of this Manual. 4.l.1.2 
4.1.2 	Surface synoptic observations 
All surface stations included in the regional basic synoptic network should make surface  synoptic  observations  at  the  four  main  standard  times  of  observation,  i.e.  0000,  0600,  1200  and  1800 UTC, and at the four intermediate standard times of observation, i.e. 0300, 0900, 1500 and  2100 UTC. The carrying out of the observations at the main standard times of observation should  be given top priority. 
4.1.3 	Upper-air synoptic observations 
All  upper-air stations included in the regional basic synoptic network should carry out  radiosonde and/or radiowind observations up to the 10 hPa level at 0000 and 1200 UTC. Stations  which  are  unable  to  carry  out  the  full  upper-air observing programme should give priority to the  making of observations at 1200 UTC. 
4.1.4 	Arrangements  and  procedures  for  updating and amending the regional basic synoptic 
network 
Certain minor changes in the regional basic synoptic network of surface and upper-air  synoptic stations which do not affect the data requirements of the Region as a whole are inevitable.  To provide a simple and rapid means of effecting such changes, the following procedure shall be  followed: 
(a) Regional Association IV authorizes the president of the Association to approve, at the  request  of  the  Member  concerned  and  in  consultation  with  the  Secretary-General,  any  required  minor  changes  to  the  regional  basic  synoptic  network  provided  they  do  not  adversely  affect  the  density  criteria  and  the  required  programmes,  it  being  understood  that  any  change  of  substance  affecting the density of the network or proposing a change in observational hours would still require  the formal agreement of Members through the adoption of a resolution by postal ballot; 
(b) The  Secretary-General  shall  notify  all  Members  of  WMO  by  circular  letter  of  changes  agreed with the president of the Association. 
4.2 	Regional arrangements and procedures for observations 
4.2.1 	Pressure-reduction method 
According   to   the   WMO   Technical   Regulations,   Annex   V,   Manual   on   the   Global
Observing  System,  Volume  I,  Part  III,  Regulation  2.10.3.2.5,  the  atmospheric  pressure  at  the
station shall be reduced to mean sea-level. However, 

pending a worldwide decision on a uniform pressure-reduction method, the method being used in 
the  United  States  for  reducing  atmospheric  pressure  to  mean  sea-level  should  be  applied in the  Region. 
4.2.2 	Regional comparison of barometers 
Each Member in the Region should ensure that the calibration of the barometer at each  synoptic  station  in  its  territory  is  traceable  to  a  fixed  national  barometric  standard,  through  an  appropriate series of comparisons at least every two years. 4.2.2.1 
4.2.2.2 National barometric standards should be traceable to an absolute barometric standard  recognized by WMO, within or outside the Region, through an appropriate intercomparison at least  every 10 years. 
The  barometric  standard  at  the  National  Bureau  of  Standards  (NBS),  Gaithersburg,  Maryland (United States) shall be recognized as the absolute standard for Region IV. 4.2.2.3 
4.2.2.4 The  barometric  standards  in  Guatemala  City,  Mexico  D.F.,  Miami,  San  Juan,  Silver  Spring, Maryland and Toronto shall be the sub-regional standard barometers for the Region.  
NOTES:     (1) 	The  term  “barometric  standard”  is  used  rather  than  “standard  barometer”  since  often  the  standard  is  not  a  barometer  (e.g.  a  Dead  Weight Tester is a pressure  standard, but not a barometer). 
(2) 	There   is   no   standard   barometer   in   Washington   D.C.   The   standard
barometer  at  NWS  Headquarters  (Silver  Spring)  is  not  a  national  standard,  but  a
working standard traceable to NBS. 
4.2.3 	Ground weather radar observations 
Meteorological  radars  are  important  for  both  operational  and  research  purposes  in
synoptic  meteorology  and  hydrology,  and  in  improving  the  accuracy  of  short-period  forecasts  (especially those for aviation), while non-meteorological radars, such as aircraft surveillance radars,  may often be used advantageously for meteorological purposes and thus fill any temporary gaps in  the radar network. Members should, therefore, take all practical steps to encourage the installation  of  meteorological radars in their own countries, coordinating, where desirable, with neighbouring  countries,  and  should  also  make  maximum  use  of  non-meteorological  radars  for  meteorological  purposes . 
4.2.4 	Regional Instrument Centres (RICs) 
4.2.4.1 	The  instruments  centres  at  Mt.  Washington,  New  Hampshire  (United  States),  the
Caribbean  Meteorological  Institute  in  Barbados  and  at  the  RMTC  in  San  José  (Costa  Rica)  are  designated as Regional Instrument Centres with the following terms of reference: 
(a) 	To   assist   WMO    in   organizing   regional   training   seminars   or   workshops   in   the
maintenance,  calibration  and  comparison  of  meteorological  instruments,  by  providing  laboratory  space, demonstration equipment and expert advisers; 
(b) 	To   advise   Members   of   their   Region   in   their   inquiries   about   the   performance   of
instruments and the availability of related guidance material; 
(c) 	To maintain a library of texts and periodicals on instrumentation science and practice; 
(d) 	To  maintain  a  set  of  meteorological  standard  instruments  traceable  to  recognized
international  or  national  standards,  and  to  keep  a  continous  record  of  their  performance  and
traceability; 

(e) 	To assist Members of their Region to calibrate or compare their national meteorological 
standard instruments against the standards mentioned under (d) and to keep the Members of the  Region and the WMO Secretariat well informed of the standard instruments available. 
4.2.5 	Regional Radiation Centres (RRCs) 
4.2.5.1 	Considering   the   usefulness   of   the   calibration   of   national   and	regional   standard
pyrheliometers against pyrheliometers of the World Standard Group (WSG) at five-year intervals for  guaranteeing  the  high  quality  of  radiation  data,  and  noting  Resolution  11  (EC-XXX)  —  National,  Regional and World Radiation Centres  —   Regional Radiation Centres should be established with  the following terms of reference: 
To possess and maintain a standard group of radiometers, consisting of either: (i) three  standard radiometers of the Ångström, silver disk or absolute radiometer type;     or (ii) two absolute  radiometers; (a) 
(b) To compare at least once every five years one of the standard radiometers against the  World Standard Group; 
(c) 	To  intercompare,  at  least  once  a  year,  the  standard  radiometers  with  the  aim  of
checking  the  stability  of the individual instruments. If the ratio has changed by more than ± 0.2%  and if the erroneous instruments cannot be identified, a recalibration at the World Radiation Centre  (WRC) has to be performed prior to further use as a standard; 
(d) To make available the necessary facilities and laboratory for checking and maintaining  the accuracy of the auxiliary measuring equipment; 
To  provide  the  necessary  outdoor  facilities  for  simultaneous  comparison  of  national  standard radiometers from the Region; (e) 
(f) 	To   provide   qualified   staff   with   wide   experience   in   radiation   for   continuity   of   the
performance of the RRC; 
(g) 	To  organize  and  carry  out  comparisons  of  national  radiation  standards  within  the
Region  in  close  collaboration  with  the  other  RRCs  and  to  maintain  the  standard  instruments  necessary for this purpose. 
4.2.5.2 	Each  Regional  Radiation  Centre  should  satisfy  the  above  conditions  before  it  is
designated as such and should continue to fulfil them after being designated. 
4.2.5.3  The following National Radiation Centres are designated to serve as Regional Radiation  Centres in RA IV: 
Toronto (Canada), Mexico D.F. (Mexico) and Boulder (United States). 
4.3 	CLIMAT and CLIMAT TEMP reporting stations in the Region 
The  Association  encourages  its  Members  to  designate  as  many  as  possible  of  the  stations  in  the  regional  basic  synoptic  network  as  CLIMAT  and/or    CLIMAT  TEMP  reporting
stations.