daily 12-hourly 6-hourly
<br>
<br>
00Z 06Z 12Z 18Z
<br>
<br>
daily 12-hourly 6-hourly
<br>
<br>
00Z 06Z 12Z 18Z
<br>
<br>
Each platform has its own beginning and ending dates.  See:
<a href="http://dss.ucar.edu/datasets/ds353.4/docs/more.summary.html#POR" >this.</a>
<br>
<br>
Also see <a href="http://dss.ucar.edu/datasets/ds353.4/docs/more.summary.html#D-T">this</a>
<br>
<br>
ds353.4_periods.