Orography filtering – in #8: General Questions

in #8: General Questions

<p> Dear All, </p> <p> These days I am about to set up a <span class="caps"> CCLM </span> simulation over some mountaineous domain at 0.1° horizontal resolution. Doing so I started to wonder about the orography filtering. Reading <span class="caps"> COSMO </span> Newsletter 1 (2001) by Almut Grassmann I understood that the latter is useful if not even mandatory. Yet I am still puzzled about the meaning of the different namelist parameters and the effects different values would have on the simulated climate. </p> <p> I checked http://cosmo-model.org/content/tasks/operational/ and tried the INT2LM namelist setups <span class="caps"> DWD </span> uses for <span class="caps"> COSMO </span> -EU with </p> lfilter_oro T lxso_first F l_topo_z F norder_filter 5 eps_filter 0.1000 ilow_pass_oro 1 numfilt_oro 1 ilow_pass_xso 0 numfilt_xso 1 rxso_mask 0.0000 rfill_valley 0.0000 ifill_valley 0 <p> and the setup Meteo Swiss uses for <span class="caps"> COSMO </span> -7 and <span class="caps"> COSMO </span> -2 with </p> lfilter_oro T lxso_first F l_topo_z F norder_filter 5 eps_filter 0.1000 ilow_pass_oro 4 numfilt_oro 1 ilow_pass_xso 5 numfilt_xso 1 rxso_mask 750.0000 rfill_valley 0.0000 ifill_valley 7 <p> The orography produced with the latter setup is much smoother than that produced with the former. </p> <p> I also saw that the <span class="caps"> COSMO </span> -DE setup equals that of <span class="caps"> COSMO </span> -7 and <span class="caps"> COSMO </span> -2 except rxso_mask = 625.0000 and ifill_valley = 0. As my resolution is slightly coarser than those of <span class="caps"> COSMO </span> -EU and <span class="caps"> COSMO </span> -7 I thought I should choose between the two setups listed above but since the respective resulting orographies differ so much I don’t know what to do. Any suggestions? </p> <p> I’d like to know why there are all those different filtering setups in use and what kind of differences I can expect between the simulated weathers/climates with differently smoothed orographies. Also I wondered if one should filter differently for climate simulations than for weather forecasts… </p> <p> With many thanks in advance, <br/> Stefan </p>

  @redc_migration in #485a7dc

<p> Dear All, </p> <p> These days I am about to set up a <span class="caps"> CCLM </span> simulation over some mountaineous domain at 0.1° horizontal resolution. Doing so I started to wonder about the orography filtering. Reading <span class="caps"> COSMO </span> Newsletter 1 (2001) by Almut Grassmann I understood that the latter is useful if not even mandatory. Yet I am still puzzled about the meaning of the different namelist parameters and the effects different values would have on the simulated climate. </p> <p> I checked http://cosmo-model.org/content/tasks/operational/ and tried the INT2LM namelist setups <span class="caps"> DWD </span> uses for <span class="caps"> COSMO </span> -EU with </p> lfilter_oro T lxso_first F l_topo_z F norder_filter 5 eps_filter 0.1000 ilow_pass_oro 1 numfilt_oro 1 ilow_pass_xso 0 numfilt_xso 1 rxso_mask 0.0000 rfill_valley 0.0000 ifill_valley 0 <p> and the setup Meteo Swiss uses for <span class="caps"> COSMO </span> -7 and <span class="caps"> COSMO </span> -2 with </p> lfilter_oro T lxso_first F l_topo_z F norder_filter 5 eps_filter 0.1000 ilow_pass_oro 4 numfilt_oro 1 ilow_pass_xso 5 numfilt_xso 1 rxso_mask 750.0000 rfill_valley 0.0000 ifill_valley 7 <p> The orography produced with the latter setup is much smoother than that produced with the former. </p> <p> I also saw that the <span class="caps"> COSMO </span> -DE setup equals that of <span class="caps"> COSMO </span> -7 and <span class="caps"> COSMO </span> -2 except rxso_mask = 625.0000 and ifill_valley = 0. As my resolution is slightly coarser than those of <span class="caps"> COSMO </span> -EU and <span class="caps"> COSMO </span> -7 I thought I should choose between the two setups listed above but since the respective resulting orographies differ so much I don’t know what to do. Any suggestions? </p> <p> I’d like to know why there are all those different filtering setups in use and what kind of differences I can expect between the simulated weathers/climates with differently smoothed orographies. Also I wondered if one should filter differently for climate simulations than for weather forecasts… </p> <p> With many thanks in advance, <br/> Stefan </p>

Orography filtering

re wrote

Dear All,

These days I am about to set up a CCLM simulation over some mountaineous domain at 0.1° horizontal resolution. Doing so I started to wonder about the orography filtering. Reading COSMO Newsletter 1 (2001) by Almut Grassmann I understood that the latter is useful if not even mandatory. Yet I am still puzzled about the meaning of the different namelist parameters and the effects different values would have on the simulated climate.

I checked http://cosmo-model.org/content/tasks/operational/ and tried the INT2LM namelist setups DWD uses for COSMO -EU with

lfilter_oro T lxso_first F l_topo_z F norder_filter 5 eps_filter 0.1000 ilow_pass_oro 1 numfilt_oro 1 ilow_pass_xso 0 numfilt_xso 1 rxso_mask 0.0000 rfill_valley 0.0000 ifill_valley 0

and the setup Meteo Swiss uses for COSMO -7 and COSMO -2 with

lfilter_oro T lxso_first F l_topo_z F norder_filter 5 eps_filter 0.1000 ilow_pass_oro 4 numfilt_oro 1 ilow_pass_xso 5 numfilt_xso 1 rxso_mask 750.0000 rfill_valley 0.0000 ifill_valley 7

The orography produced with the latter setup is much smoother than that produced with the former.

I also saw that the COSMO -DE setup equals that of COSMO -7 and COSMO -2 except rxso_mask = 625.0000 and ifill_valley = 0. As my resolution is slightly coarser than those of COSMO -EU and COSMO -7 I thought I should choose between the two setups listed above but since the respective resulting orographies differ so much I don’t know what to do. Any suggestions?

I’d like to know why there are all those different filtering setups in use and what kind of differences I can expect between the simulated weathers/climates with differently smoothed orographies. Also I wondered if one should filter differently for climate simulations than for weather forecasts…

With many thanks in advance,
Stefan

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