NuSDaS Data Model

NuSDaS is designed to store grid data in NWP (numerical weather prediction). It classifies various data and stores them into structured directory. Since it is not multi-purpose I/O library (like netCDF or HDF) nor database management system, the interface is specialized for use of NWP.

In NuSDaS, all data consists of records, a two-dimensional array of numbers. The number may be integer or floating-point number ^*1. In most cases, a record corresponds to grids on horizontal plane. They are identified by following dimensions (see description in Reference Manual for detailed computational expression):

Data Type: A 16-character ^*2 string that identifies dataset.
Base Time: Analysis time, initial time of forecast, or map time of observation. Equivalent to "reference time" in GRIB specification.
Member: Member of ensemble forecast.
Valid Time: Time to which forecast or observation is related to. Data for time span (such as average or accumulation) is identified using a pair of valid times.
Plane: Location of two-dimensional grids represented by record. For example, "SURF△△" and "500△△△" denotes surface and 500hPa plane, respectively. In most cases, horizontal grids are identified by vertical coordinate. Data for layer is identified using a pair of plane.
Element: Physical quantity name. For example, "T△△△△△" and "P△△△△△" denotes temperature and pressure, respectively.

The elements of record identifier is called `dimension', since there is a metaphor that associates all accessible data to single huge array. However, storage design based on simple array would be inefficient for these reasons:

the array may be sparse --- the size of dimension depends on the nature of data;
some dimensions (such as data type, member, element) is not suitable for management by number, not by character symbols; and
effective method for query like "on what plane the element RAIN is available?" is required, and round-robin search for whole array is not realistic.

Thus records are designed to be stored in a particular file in a particular directory determined by the data identifier. (The rule is described below.)

^*1see User Data Array Type in Reference Manual for available data types
^*2Pandora data server and some tools uses notation using period (such as _GSMLLPP.FCSV.STD1) for readability