0. Introduction

The 10° and 2° box systems used in most of these data are defined and then illustrated on maps. The Marsden Square system and the approximate 2° landlocked file are also described. Refer to supp. H for a description of software tools available for use with 10° and 2° boxes, plus details on a machine-readable copy of the landlocked file and a program to read it.

1. 10° Boxes and Marsden Squares

The 10° box (BOX10) numbering system starts with the lower-left (SW) corner of BOX10-1 at 80°N, 30°E and proceeds east, spiraling down through each zone of latitude as follows (see also Figure G1-1):

       BOX10                1     2   ...    36    37   ...   648
SW corner lat ° (+N,-S)    80    80   ...    80    70   ...   -90
  SW corner lon ° (+E)     30    40   ...    20    30   ...    20

The 30° division was chosen to avoid splitting any ocean; therefore, the BOX10s in a 10° latitude zone across any ocean are sequential. (The transformation k = 36 * (j - 1) + i can be used to convert the indices (i, j) of a matrix spanning longitude and latitude, e.g., the FORTRAN array dimensioned BOX10 (36, 18), into a 10° box number k ranging from 1 through 648 as described above.)

Conventions a) and b) are the same as for Marsden Squares.

a) The convention for inclusion of data that fall on the boundary of a BOX10 is dependent on the quadrant: the two inclusive boundaries are those that form the corner nearest the intersection of the equator and the prime meridian (0°N/0°E).

b) However, when the observation falls along the equator or the great circle through the prime meridian (0°E or 180°E), the choice is made by the observer.

Conventions a') and b') are necessary to complete the system.

a') Data at 90°N or 90°S exactly are assigned by convention to BOX10-1 or -648, respectively, and 1° Marsden Square 99 in both cases.

b') In the event the observer's choice is not available, the BOX10 chosen (whether the choice is between two or four BOX10s) is that with the highest number.

Each 10° Marsden Square can be further subdivided into 100 1° sub-squares, numbered 00 through 99 (1° box is synonymous with this 1° sub-square). After the global latitude and longitude are normalized such that -90° ≤ Yy ≤ 90°N and -180° ≤ XXx ≤ 180°E, the sub-square number is yx, i.e., concatenation of the units position of latitude and longitude. Exceptions are at 180°E, where yx must be set to y9, and 90°N or 90°S, where both the 10° and 1° Marsden Square are undefined.

2. 2° Boxes and Landlocked File

The 2° box (BOX2) numbering system starts with BOX2-1 at the North Pole and proceeds east from the prime meridian down through each zone of latitude to 16202 as given by the following:

BOX2-1 is reserved for data at 90°N exactly; thereafter,

        BOX2                2     3   ...   181   182   ... 16201
SW corner lat ° (+N,-S)    88    88   ...    88    86   ...   -90
  SW corner lon ° (+E)      0     2   ...   358     0   ...   358

BOX2-16202 is reserved for data at 90°S exactly.

(The transformation k = 180 * (j - 1) + i + 1 can be used to convert the indices (i,j) of a matrix spanning longitude and latitude, e.g., the FORTRAN array dimensioned BOX2(180, 90), into a 2° box number k ranging from 2 through 16,201 as described above, exclusive of the two polar boxes.)

The convention for inclusion of data that fall on the boundary of a BOX2 is the same as that for a 10° box. Whether the choice of BOX10 for a report was made by the observer or assigned under convention b'), as discussed in sec. 1, it was given the number of the BOX2 enclosed by that BOX10.

Table G2-1 gives in 18 pages the latitude and longitude at the lower-left (SW) corner of each BOX2. The first nine of these (computer generated) pages cover the Northern Hemisphere working eastward from 0°E, and the last nine pages cover the Southern Hemisphere working eastward from 0°E. Each group of 25 (or in the two polar cases 26) BOX2s is delimited as a BOX10, and the BOX10 and MSQ numbers are given at its top. In addition, approximate land boundaries are marked with hand-drawn lines. The names of major land masses have also been marked.

These land boundaries were drawn using values derived from a modified version of the NCDC landlocked file, called LLN2F1, which is available in machine-readable form (see supp. H). The space following each BOX2 shows the specific value associated with it: a period <.> for land, an asterisk <*> for coastal (i.e., any mixture of land and sea), or a space < > for sea. In general, rivers and lakes are shown as land; thus all land <.> boxes form the group referred to as "landlocked" that was automatically trimmed.

Figure G1-1. 10° boxes (larger numerals) over Marsden Squares (smaller numerals).


Table G2-1
BOX2