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START_README.NDP-026E*****2007_Nov*****_*********-*********-*********-*********-
This file contains 227 lines of up to 80 characters.
This file is a brief introduction to the data archive:
*
Carole J. Hahn and Stephen G. Warren, 2007 (updated 2009): A GRIDDED CLIMATOLOGY OF CLOUDS
OVER LAND (1971-96) AND OCEAN (1954-97) FROM SURFACE OBSERVATIONS WORLDWIDE.
NDP-026E, Carbon Dioxide Information Analysis Center,
Oak Ridge National Laboratory, Oak Ridge, TN. (Documentation, 71 pages; plus
a 4-page appendix describing an update of ocean cloud averages for the years
1998-2008.) doi: 10.3334/CDIAC/cli.ndp026e
(Email to authors: sgw@atmos.washington.edu; hahn@atmo.arizona.edu.)
-
NOTE: In August, 2010, this database was updated to contain ocean data
from 1998-2008. See the description of the update at the bottom of the file.

1. General Description of the Cloud Climatology Data Set
This archive provides a gridded climatology of clouds based on surface 
synoptic weather reports which include cloud observations made visually 
from land stations and ships at sea from locations around the globe. Cloud 
averages formed from those observations are given on a 5-degree latitude-
longitude grid (or on a 10-degree grid for some ocean data), with land and 
ocean data processed separately. Averages are given for total cloud cover, 
clear-sky frequency, and nine cloud types from three levels of the troposphere
(high clouds, 3 middle cloud types, and 5 low cloud types). For each grid box,
this archive includes multi-year (1971-96 for land and 1954-97 for ocean) 
annual, seasonal and monthly averages for day and night separately; analyses of
the first harmonic for the annual and diurnal cycles are also given. For the 
ocean, seasonal averages for eight times per day and seasonal and monthly 
averages by year are given for the grid boxes; for land, these latter quantities
were given for each of 5388 individual stations in the companion archive NDP-
026D. Cloud amounts and frequencies are given for all types, non-overlapped 
amounts are provided for middle and high clouds, and mean base heights are 
computed for low cloud types.

This archive supercedes our first climatology in this series (NDP-026). Our 
analysis procedures have been improved and more years of data are used here. 
Nighttime reports are now screened using the illuminance criterion of Hahn et 
al. (1995); we distinguish more cloud types in the middle and low levels (we now
distinguish between As and Ac and between Sc, St and fog); and we imposed more 
selection criteria on the stations and ships contributing. 

These data and full documentation are available from:

Carbon Dioxide Information Analysis Center (CDIAC)
Oak Ridge National Laboratory
Post Office Box 2008
Oak Ridge, TN  37831-6335, U.S.A.
(http://cdiac.esd.ornl.gov/by_new/bynumber.html)

The documentation is also available online via
       www.atmos.washington.edu/CloudMap/. 
-
2. Cloud Averages Contained in the Data Set
The cloud information contained in a synoptic weather report is listed in 
Table 1 below. These quantities, along with the station/ship location and the 
time of the report, are the basic data used to create this climatology.
Table 2 lists the cloud types analyzed for this climatology and provides their
definitions in terms of the synoptic code as defined by the World Meteorological
Organization and as modified in our cloud reports archive (NDP-026C) which was 
the data archive used in the preparation of this climatology. Precipitation 
codes are also given because they are used in our definitions of nimbostratus 
and cumulonimbus cloud types. Note that we group all high clouds together in 
this climatology; this is because preliminary analyses of the various cirriform 
cloud types suggested that the assignment of high clouds among various sub-
species is not globally uniform.

The archive is divided into 52 File Categories; the divisions are based on the 
content of the data. Table 4 (abbreviated from the full documentation), lists
the general contents of the categories. 

These comments and tables provide a guide for the reader as to the makeup of 
this data set. Details of the contents and formats for reading the data are 
given in the full documentation (as well as the list of references cited here 
and definitions of abbreviations used).
-
*********-*********-*********-*********-*********-*********-*********-*********-
       TABLE 1. CLOUD INFORMATION CONTAINED IN SYNOPTIC WEATHER REPORTS         
       ________________________________________________________________         
        Symbol       Meaning                       Codes                        
       ________________________________________________________________         
          N          total cloud cover             0-8 oktas                    
                                                    9= sky obscured             
          Nh         lower cloud amount            0-8 oktas                    
          h          lower cloud base height       0-9                          
          CL         low cloud type                0-9                          
          CM         middle cloud type             0-9                          
          CH         high cloud type               0-9                          
          ww         present weather               00-99                        
          Ix         present weather indicator     1-6                          
       ________________________________________________________________         
-
*********-*********-*********-*********-*********-*********-*********-*********-
TABLE 2.  CLOUD TYPE AND WEATHER TYPE DEFINITIONS USED
________________________________________________________________________________
      Shorthand                                                                 
Level notation   Meaning                 Synoptic codes                         
________________________________________________________________________________
                                                                                
      Tc         total cloud cover        N = 0-9                               
                                                                                
      Cr         completely clear sky     N = 0                                 
                                                                                
      Ppt        precipitation            ww= 50-75,77,79,80-99                 
        D          drizzle                    50-59                             
        R          rain                       60-69                             
        S          snow                       70-75,77,79                       
        Ts         thunderstorm or shower                 80-99                 
                                                                                
Low                                       CL=                                   
      Fo         sky obscured by fog         / with N=9 and                     
                                                    ww=10-12,40-49              
      St         stratus                     6,7                                
      Sc         stratocumulus               4,5,8                              
      Cu         cumulus                     1,2                                
      Cb         cumulonimbus                3,9,                               
                                                  or N=9 with ww=Ts             
      LoL        Fo + St + Sc + Cu + Cb                                         
                                                                                
Mid                                       CM=                                   
      Ns         nimbostratus                2,7, or N=9 with ww=DRS            
                                             /  with ww=DRS and CL=0,7          
                                             /  with ww= RS and CL=4-8          
      As         altostratus                 1; 2 if not DRS                    
      Ac         altocumulus                 3,4,5,6,8,9; 7 if not DRS          
      MiL        Ns + As + Ac                                                   
                                                                                
High                                      CH=                                   
      Hi         cirriform clouds            1-9                                
________________________________________________________________________________
-
*********-*********-*********-*********-*********-*********-*********-*********-
TABLE 4. DATA FILE CATEGORIES CONTAINED IN THE GRIDDED CLOUD ARCHIVE NDP-026E
________________________________________________________________________________
File Category    General Contents
   Number
-------------    ----------------
                 GRID INFORMATION

    1               GRID LAT, LON, LAND-FRACTION
                     & Number of land stations
 -------------------------------------------------------------------------------
         MULTI-YEAR AVERAGES
                 LAND DATA [5c]
    2               Mean Annual  Cloud AMOUNT 
    3               Mean Seasonal Cloud AMOUNT       
    4               Mean Seasonal Cloud FREQUENCY    
    5               Mean Seasonal AMOUNT-WHEN-PRESENT 
    6               Mean Seasonal Mid and Hi Cloud NON-OVERLAPPED AMOUNT 
    7               Mean Seasonal Low Cloud BASE HEIGHT  
    8               Mean Monthly Cloud AMOUNT 
    9               Mean Monthly Cloud FREQUENCY 

   10               Harmonics: ANNUAL; DIURNAL(Seasonally)
 -------------------------------------------------------------------------------
   11           LAND + OCEAN CLOUD AMOUNT [5c], Annual and Seasonal Averages
 -------------------------------------------------------------------------------
                 OCEAN DATA [5c and/or 10r]
   12               Mean Annual  Cloud AMOUNT        
   13               Mean Seasonal Cloud AMOUNT      
   14               Mean Seasonal Cloud FREQUENCY   
   15               Mean Seasonal AMOUNT-WHEN-PRESENT 
   16               Mean Seasonal Mid, Hi Cloud NON-OVERLAPPED AMOUNT
   17               Mean Seasonal Low Cloud BASE HEIGHT 
   18               Mean Monthly  Cloud AMOUNT
   19               Mean Monthly  Cloud FREQUENCY  
 -------------------------------------------------------------------------------
                    by Synoptic Hour*:       
   20                 Mean Seasonal Cloud AMOUNT
   21                 Mean Seasonal Cloud FREQUENCY
   22                 Mean Seasonal Mid, Hi Cloud NON-OVERLAPPED AMOUNT
   23                 Mean Seasonal Low Cloud BASE HEIGHT

   24              Harmonics: ANNUAL; DIURNAL(Seasonally)
 -------------------------------------------------------------------------------
         INDIVIDUAL-YEAR AVERAGES, OCEAN DATA*:

   25               Seasonal Mean Cloud AMT,    DJF
   26               Seasonal Mean Cloud AMT,    MAM
   27               Seasonal Mean Cloud AMT,    JJA
   28               Seasonal Mean Cloud AMT,    SON

   29               Seasonal Mean Cloud FQ,     DJF
   30               Seasonal Mean Cloud FQ,     MAM
   31               Seasonal Mean Cloud FQ,     JJA
   32               Seasonal Mean Cloud FQ,     SON

   33               Seasonal Mean Mid,Hi NOL,   DJF
   34               Seasonal Mean Mid,Hi NOL,   MAM
   35               Seasonal Mean Mid,Hi NOL,   JJA
   36               Seasonal Mean Mid,Hi NOL,   SON

   37               Seasonal Mean Low Base HGT, DJF
   38               Seasonal Mean Low Base HGT, MAM
   39               Seasonal Mean Low Base HGT, JJA
   40               Seasonal Mean Low Base HGT, SON
 -------------------------------------------------------------------------------
   41   OMYD        Monthly Day  AMT, FQ, AWP   JAN
    |                                            |
   52   OMYD        Monthly Day  AMT, FQ, AWP   DEC
________________________________________________________________________________
         INDIVIDUAL-YEAR AVERAGES, OCEAN DATA (update years 1998-2008):

   55               Seasonal Mean Cloud AMT,    DJF
   56               Seasonal Mean Cloud AMT,    MAM
   57               Seasonal Mean Cloud AMT,    JJA
   58               Seasonal Mean Cloud AMT,    SON

   59               Seasonal Mean Cloud FQ,     DJF
   60               Seasonal Mean Cloud FQ,     MAM
   61               Seasonal Mean Cloud FQ,     JJA
   62               Seasonal Mean Cloud FQ,     SON

   63               Seasonal Mean Mid,Hi NOL,   DJF
   64               Seasonal Mean Mid,Hi NOL,   MAM
   65               Seasonal Mean Mid,Hi NOL,   JJA
   66               Seasonal Mean Mid,Hi NOL,   SON

   67               Seasonal Mean Low Base HGT, DJF
   68               Seasonal Mean Low Base HGT, MAM
   69               Seasonal Mean Low Base HGT, JJA
   70               Seasonal Mean Low Base HGT, SON
 -------------------------------------------------------------------------------
   71   OMYD        Monthly Day  AMT, FQ, AWP   JAN
    |                                            |
   72   OMYD        Monthly Day  AMT, FQ, AWP   DEC
________________________________________________________________________________
* For land data see NDP-026D.
*
END__README.NDP-026E_*********-*********-*********-*********-*********-*********