title: Why is the NETcdf data I created masked?
body: <p>I create a netcdf file with some data, and when I import the data in another script, it is masked :</p>
  
  <pre><code>    &gt;&gt;&gt; type(Data[:])
      &lt;class 'numpy.ma.core.MaskedArray'&gt;
  </code></pre>
  
  <p>Here is how I create the data :</p>
  
  <pre><code>    # Put in a grid
      print 'Putting the data in a grid...'
      LatRange = range( int(min(Lat)), int(max(Lat)), 1 )
      LonRange = np.arange( int(min(Lon)), int(max(Lon)), 1 )
      dRange = range(0,200,10) + range(200,4000,100)
      dateRange = np.arange( float(min(Dates).year)+min(Dates).month/12., float(max(Dates).year)+max(Dates).month/12., 1./12. )
  
      dataset = Dataset('gridded_data/DataAveraged.nc','w', format='NETCDF4_CLASSIC')
      zD = dataset.createDimension('zD',len(dRange))
      latD = dataset.createDimension('latD',len(LatRange))
      lonD = dataset.createDimension('lonD',len(LonRange))
      timeD = dataset.createDimension('timeD',len(dateRange))
  
      tempAve = dataset.createVariable('tempAve', np.float32, ('zD','latD','lonD','timeD'), fill_value=-9999)
      tempAve.units = 'psu'
      tempAve[:] = Tgrid_ave
  </code></pre>
  
  <p>Where Tgrid_ave is a numpy array.</p>
  
  <p>Then, I import the data this way in another script :</p>
  
  <pre><code>    dataset = Dataset('gridded_data/DataAveraged.nc', 'r')
  
      LatRange = dataset.variables['lat'][:]
      LonRange = dataset.variables['lon'][:-1]
  
      Tgrid_ave = dataset.variables['tempAve']
  </code></pre>
  
  <p>And my Lat and Lon data are not masked, but my Tgrid_ave data is.</p>
  
  <p>How can I avoid this!?</p>