SEACOOS CDL v2.0 December 9, 2004 11 6.4 Vertical Variable The vertical variable represents the height or depth of the data measurement. The positive variable attribute provides the direction of positive.  The vertical variable should be described unambiguo usly by providing the additional attribute of axis with a value of Z. The vertical variable may be represented as a coordinate variable (e.g. z(z))or a function of time (e.g. z(time)). float z(z); //or z(time) z: standard_name = "height"; z: units = "m"; z: reference = "mean sea level (MSL)"; z: positive = "up"; z: axis = "Z"; 7. Data Variables Requirements for represent ing winds, water temperature, water level, and ocean currents are described in this section. Each dependent variable must always explicitly include the units and standard_name attributes.    7.1 Winds  Horizontal wind requires two dependent variables to describe the speed and direction of the wind or the eastward and northward components relative to True North.  The variable attribute wdir: reference is used to define the reference direction such as True North or Magnetic North. The variable attribute (wspd: z and wdir: z) gives the height of the wind meter in relation to the description and units used by the vertical variable. The exa mples given are for a platform and sensor where the vertical variable is constant. The first example shows how to represent wind magnitude and direction (wspd and wdir).   float wspd(time);   wspd: standard_name = "wind_speed"; wspd: units = "m s-1"; wspd: z = 45; float wdir(time); wdir: standard_name = "wind_from_direction"; wdir: units = "degrees"; wdir: reference = "clockwise from true north"; wdir: valid_range = 0.,360.; wdir: z = 45; Data for wind gusts are provided with a separate variable (wgust).  Wind direction data and metadata must be provided if not already provided with wind speed.