Parameter: yearday_GMT

day of year for a specified year; file dependent; year may be reported in the date parameter. This number may be a floating point value in which case, the fraction of the value represents the time within the day. We are tentatively defining the year day with the following attributes, although this is subject to change: Time, if specified by the fraction is in GMT (aka UTC); convention is that a value of 1.5 means January 1 at 1200 hours (noon time).