title: pandas merge with dataframes of different frequency (hourly and daily)
body: <p>I'm trying to merge dataframes that are either daily or hourly. It seems on the first iteration through my loop, I can merge the first daily with hourly values. But the second time around I get this error:</p>
  
  <pre><code>raise Exception('Cannot join tz-naive with tz-aware DatetimeIndex')
  Exception: Cannot join tz-naive with tz-aware DatetimeIndex
  </code></pre>
  
  <p>I can't really provide a good example, but I now that all the dataframes are tz-aware when they are created (e.g. I call <code>df.tz_localize('UTC')</code> on each after it is created.</p>