title: Replace variable in array
body: <p>I have this array of temperature with variable time :</p>
  <p>temperature</p>
  <p>xarray.Variable   <strong>time: 8256</strong></p>
  <pre><code>array([   28.22,    28.35,    28.07, ..., -9999.  , -9999.  , -9999.  ],
        dtype=float32)
  </code></pre>
  <p>I would like to replace this time and put the newtime inside the temperature:</p>
  <p>new time</p>
  <pre><code>array(['2002-07-22', '2004-11-03', '2004-11-04', '2004-12-13',
         '2005-06-07', '2006-07-12', '2006-07-22', '2006-09-10',
         '2006-10-03', '2007-02-19', '2007-03-23', '2008-12-11',
         '2008-12-14', ......., '2009-9-23', '2020-10-03',
         '2020-10-13', '2020-10-23', '2020-11-02', '2020-12-26',
         '2020-12-31', '2021-01-05', '2021-01-15', '2021-01-24',
         '2021-01-25', '2021-01-29', '2021-02-04', '2021-02-08',
         '2021-02-14', '2021-02-26'], dtype=object)
  </code></pre>
  <p>Someone can help me ? Thank You!</p>