MARS requests for some parameters will also be affected by the migration to GRIB2.

Changes to param keyword

For GRIB1 parameters, the param keyword in the mars request can be set to param=indicatorOfParameter.table2Version. Requests with this structure will not work for GRIB2 as these two keys do not exist in this edition. The paramId must be used for GRIB2 parameters. This is the recommended way of specifying parameters in MARS requests.

...

<pre>
retrieve,
  class=od,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  step=0,
  levtype=sfc,
  <b><font color="red">param=165.128</font></b>,
  target="output_10u.grib1"
<pre>

<pre>
retrieve,
  class=od,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  step=0,
  levtype=sfc,
  <b><font color="red">param=165</font></b>,
  target="output_10u.grib2"
<pre>

Changes for parameters archived with levtype=sol

Parameters on surface levels will be archived with levtype=sol (surface other levels). 

...

<pre>
retrieve,
  class=od,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  step=0,
  <b><font color="red">levtype=sfc</font></b>,
  <b><font color="red">param=141.128</font></b>,
  target="output_sd.grib1"
<pre>

<pre>
retrieve,
  class=od,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  step=0,
  <b><font color="red">levtype=sol</font></b>,
  <b><font color="red">levelist=1/2/3/4/5</font></b>,
  <b><font color="red">param=228141</font></b>,
  target="output_sd.grib2"
<pre>

Changes for parameters archived with levtype=hl

Parameters with typeOfLevel=heightAboveGround and with level set to a value greater than 10m (for example, 100u, 100v, 100si, 200u, 200v, 200si) which were previously archived in MARS with levtype=sfc with will be archived with  levtype=hl  (height levels). Consequently, the paramId (and shortName) for these parameters will also change.

<pre>
retrieve,
  class=od,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  step=0,
  <b><font color="red">levtype=sfc</font></b>,
  <b><font color="red">param=228246/228247/228249</font></b>,      <b><font color="red"># 100u/100v/100wsi</font></b>
  target="output_100m_winds.grib1"
<pre>

<pre>
retrieve,
  class=od,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  step=0,
  <b><font color="red">levtype=hl</font></b>,
  <b><font color="red">levelist=100</font></b>,
  <b><font color="red">param=131/132/10</font></b>,
  target="output_100m_winds.grib2"
<pre>

Addition of new MARS keyword timespan for parameters processed statistically over a time interval

In GRIB1, parameters processed statistically over a time interval, such as maximum or minimum temperature in the last 3 hours or last 6 hours or since previous post-processing, have their own distinct paramIds.  In GRIB2, there will be a single paramId to identify, e.g., maximum 2m temperature and a new MARS keyword, timespan, to specify the period over which the maximum or minium or average, etc, has been taken.  Typically, timespan=1h for "previous hour",  timespan=3h for "previous 3 hours" and timespan=6h for "previous 6 hours", etc.

<pre>
retrieve,
  class=od,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  levtype=sfc,
  <b><font color="red">param=201/202</font></b>,       <b><font color="red"># mx2t/mn2t</font></b>
  step=1/2/3/4/5/6,
  target="output_max_min_2t.grib1"
retrieve,
  <b><font color="red">param=228026/228027</font></b>, <b><font color="red"># mx2t3/mn2t3</font></b>
  step=3/6,
  target="output_max_min_2t.grib1"
retrieve,
  <b><font color="red">param=121/122</font></b>,       <b><font color="red"># mx2t6/mn2t6</font></b>
  step=6,
  target="output_max_min_2t.grib1"

<pre>

<pre>
retrieve,
  class=od,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  levtype=sfc,
  <b><font color="red">param=237167/238167</font></b>, <b><font color="red"># max_2t/min_2t</font></b> 
  <b><font color="red">timespan=1h</font></b>,         <b><font color="red"># last hour</font></b> 
  step=1/2/3/4/5/6,
  target="output_max_min_2t.grib2"
retrieve,
  <b><font color="red">param=237167/238167</font></b>, <b><font color="red"># max_2t/min_2t</font></b>
  <b><font color="red">timespan=3h</font></b>,         <b><font color="red"># last 3 hours</font></b> 
  step=3/6,
  target="output_max_min_2t.grib2"
retrieve,
  <b><font color="red">param=237167/238167</font></b>,  <b><font color="red"># max_2t/min_2t</font></b>
  <b><font color="red">timespan=6h</font></b>,          <b><font color="red"># last 6 hours</font></b>
  step=6,
  target="output_max_min_2t.grib2"
<pre>

Addition of new MARS keyword chem for retrieval of chemical species

Another example are chemical parameters. Besides using the MARS keyword param in the request to specify the parameter type, e.g., mass mixing ratio, an additional MARS keyword chem will be used to specify the chemical substance(s), e.g., nitrogen dioxide.

...

<pre>
retrieve,
  class=mc,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  step=0,
  levtype=ml,
  levelist=1/to/137,
  <b><font color="red">param=210121</font></b>,
  target="output_no2.grib1"
<pre>

<pre>
retrieve,
  class=mc,
  stream=oper,
  expver=1,
  date=-2,
  time=00:00:00,
  type=fc,
  step=0,
  levtype=ml,
  levelist=1/to/137,
  <b><font color="red">param=402000</font></b>,      <b><font color="red"># Mass mixing ratio</font></b>
  <b><font color="red">chem=no2</font></b>,          <b><font color="red"># Nitrogen dioxide</font></b>
  target="output_no2.grib2"
<pre>

Change of

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GRIB packing for GRIB2 parameters retrieved from MARS on a grid

GRIB2 parameters retrieved on a grid will be compressed with CCSDS. To decode these parameter, ecCodes must be linked to libaec. Alternatively, the data can be retrieved in another packing type such as grid_simple packing, which was in use for the model level GRIB2 parameters.

...