Jones (1990)

#!/usr/bin/perl

use strict;
use warnings;

use FindBin qw( $Bin );

use File::Basename;
use File::Spec::Functions qw( catfile );

my @input_files = map { catfile $Bin, $_ }
                qw( ant5790.txt nhem1990.txt shem1990.txt );

for my $file ( @input_files ) {
    eval {
        xform_file( $file );
    };

    warn "$@\n" if $@;
}

sub xform_file {
    my ($file) = @_;

    my ($src) = fileparse( $file, '.txt' );

    print STDERR "Processing '$file' ...\n";

    open my $input, '<', $file
        or die "Cannot open '$file': $!";

    my ($year, $month, $anomaly_section);

    my @lattitudes;

    LINE: while ( my $line = <$input> ) {
        chomp $line;
        
        $line =~ s/\A\s+//;
        $line =~ s/\s+\z//;

        next LINE unless length $line;

        if ( $line =~ m{
                \A
                TEMPERATURE\s+ANOMALY\s+DATA
                \s+
                YEAR\s+=\s+(\d{4})
                \s+
                MONTH\s+=\s+(\d{1,2})
            }x ) {
            ($year, $month) = ($1, $2);
            $anomaly_section = 1;

            print STDERR "$year/$month . " 
                unless (12 * $year + $month ) % 36; 
            
            next LINE;
        }

        $anomaly_section = 0 if $line =~ /\ANUMBER/ or $line =~ /\AMEAN/;

        next LINE unless $anomaly_section;

        if ( $line =~ m{\A(?:\d+(?:N|S)\s+){2,}} ) {
            my @lat_centers = split /\s+/, $line;

            for ( my $i = 0; $i < $#lat_centers; ++ $i ) {
                my ($degree, $hemisphere) 
                    = ( $lat_centers[ $i ] =~ /\A(\d{1,2})(N|S)\z/ );

                if ( $hemisphere eq 'N' ) {
                    $lattitudes[ $i ] = { 
                        south => $degree - 2.5, 
                        north => $degree + 2.5,
                    };
                }
                elsif ( $hemisphere eq 'S' ) {
                    $lattitudes[ $i ] = {
                        south => - ( $degree + 2.5),
                        north => - ( $degree - 2.5),
                    };
                }
                else {
                    warn 'How did I get here?';
                }
            }
            next LINE;
        }

        if ( $line =~ /\A(\d{1,3})(E|W)\s+(.+)\z/ ) {
            my ($degree, $hemisphere, $data) = ($1, $2, $3);
            my $longitude;

            if ( $hemisphere eq 'W' ) {
                $longitude = {
                    west => - ( $degree + 5 ),
                    east => - ( $degree - 5 ),
                };
            }
            elsif ( $hemisphere eq 'E' ) {
                $longitude = {
                    west => $degree - 5,
                    east => $degree + 5,
                };
            }
            else {
                warn 'Wot? I am lost.';
            }

            my @celsius = split /\s+/, $data;

            ANOMALY: for ( my $i = 0; $i < $#celsius; ++ $i ) {
                next ANOMALY if $celsius[ $i ] eq '-9999'; 
                printf(
                    "%4.4d|%2.2d|%.1f|%.1f|%.1f|%.1f|%.2f|%s\n",
                    $year, 
                    $month, 
                    $lattitudes[ $i ]->{south},
                    $longitude->{west},
                    $lattitudes[ $i ]->{north},
                    $longitude->{east},
                    $celsius[$i] / 100,
                    $src,
                );
            }
            next LINE;
        }
    }

    print STDERR "\n'$file' done\n";

    close $input or die "Cannot close '$file': $!";

}
__END__