ERA5气压层数据驱动WRF的一些问题

感谢Dawn的建议，兰溪之水的WRF教程

参考了一些经验，并结合实际后，成功用ERA5驱动WRF。实际上，用ERA5数据驱动WRF的方法和用ERA-Interim 数据驱动WRF极其类似。

总结几点是，下载的变量要全，水平范围要覆盖，垂直层次设置要匹配

1 需要下载的变量

参考http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Basics/UNGRIB/ungrib_req_fields.php

三维场：

'geopotential','relative_humidity','specific_humidity','temperature','u_component_of_wind','v_component_of_wind'

表面场：

'surface_pressure','mean_sea_level_pressure','10m_u_component_of_wind','10m_v_component_of_wind','2m_temperature','sea_surface_temperature','skin_temperature','2m_dewpoint_temperature','snow_depth','sea_ice_cover','land_sea_mask','soil_type','soil_temperature_level_1','soil_temperature_level_2','soil_temperature_level_3','soil_temperature_level_4','volumetric_soil_water_layer_1','volumetric_soil_water_layer_2','volumetric_soil_water_layer_3','volumetric_soil_water_layer_4'

经过本人测试，ERA-Interim.pl的Vtable可直接使用。

关于ERA5的地形和高度

https://confluence.ecmwf.int/display/CKB/ERA5%3A+surface+elevation+and+orography

2 变量场的水平范围大小

下载的变量场的水平范围要大于模拟区域的水平范围。以下报错均和变量场的水平范围太小有关：

metgrid.exe时候，报错，可能是驱动的物理量场范围太小。

FILE

WARNING: Field PRES has missing values at level 200100 at (i,j)=(1,411)

WARNING: Field GHT has missing values at level 200100 at (i,j)=(1,411)

WARNING: Field PMSL has missing values at level 200100 at (i,j)=(1,411)

WARNING: Field PSFC has missing values at level 200100 at (i,j)=(1,411)

WARNING: Field SOILHGT has missing values at level 200100 at (i,j)=(1,411)

ERROR: Missing values encountered in interpolated fields. Stopping.

Abort(53732176) on node 0 (rank 0 in comm 0): application called MPI_

参考wrfforum的意见(原网址忘了)，下载的地面层使用的是全球区域的网格，能够通过了metgrid。（高空没有用全球网格）（这个论坛有类似问题，http://bbs.06climate.com/forum.php?mod=viewthread&tid=30928）

又一坑！metgrid过了，real又没过，翻遍搜索引擎，还是古狗好用：P

国外有大神早就发现了这个问题：http://www.iup.uni-bremen.de/~hilboll/blog/2018/12/wrf-errors-could-not-find-trapping-x-locations/

更新一下，之前下载的高空数据范围太小。和Dawn讨论了一下，下载的数据范围要稍微大一些，重新下载了地面和高空数据，能通过编译了。保险起见，下载变量场的水平范围，东西和南北方向上至少再扩10度以上。

更好的办法：设置好要模拟的网格后，先用WPS自带的plotgrids.ncl脚本将模拟的区域（WRF Domain）画出来，图形的角点和边界中点的位置可以大致确定模拟区域的水平范围。

WPS网格水平范围说明

3 垂直层次设置的匹配

就是输入数据的垂直层次和namelist的层次设置（num_metgrid_levels）要匹配，

另一个坑 Mismatch between namelist and input file dimensions

WRFDomainwizard里面连接ECMWF的Vtable之后，在namelist.wps生成了model_level pres的字段，将其注释掉，否则会在后面出现报错 d01 2018-06-07_00:00:00 ---- ERROR: Mismatch between namelist and input file dimensions

不对！是把这个字段进行更改！num_metgrid_levels改成输入数据的层次（即输入气压层的层数）

关于 &mod_levs，参考了WRF_User_Guide相关章节

B. mod_levs.exe
The mod_levs.exe program is used to remove levels of data from intermediate format files. The levels which are to be kept are specified in a new namelist record in the namelist.wps file:
&mod_levs

 press_pa = 201300 , 200100 , 100000 ,

             95000 ,  90000 ,

             85000 ,  80000 ,

             75000 ,  70000 ,

             65000 ,  60000 ,

             55000 ,  50000 ,

             45000 ,  40000 ,

             35000 ,  30000 ,

             25000 ,  20000 ,

             15000 ,  10000 ,

              5000 ,   1000

 /
Within thenamelist record, the variable press_pa is used to specify a list of levels to keep; the specified levels should match values of xlvl in the intermediate format files (see the discussion of the WPS intermediate format for more information on the fields of the intermediate files). The mod_levs program takes two command-line arguments as its input. The first argument is the name of the intermediate file to operate on, and the second argument is the name of the output file to be written.

Removing all but a specified subset of levels from meteorological data sets is particularly useful, for example, when one data set is to be used for the model initial conditions and a second data set is to be used for the lateral boundary conditions. This can be done by providing the initial conditions data set at the first time period to be interpolated by metgrid, and the boundary conditions data set for all other times. If the both data sets have the same number of vertical levels, then no work needs to be done; however, when these two data sets have a different number of levels, it will be necessary, at a minimum,
to remove (m – n) levels, where m > n and m and n are the number of levels in each of the two data sets, from the data set with m levels. The necessity of having the same number of vertical levels in all files is due to a limitation in real.exe, which requires a constant number of vertical levels to interpolate from.

The mod_levs utility is something of a temporary solution to the problem of accommodating two or more data sets with differing numbers of vertical levels. Should a user choose to use mod_levs, it should be noted that, although the vertical locations of the levels need not match between data sets, all data sets should have a surface level of data, and, when running real.exe and wrf.exe, the value of p_top must be chosen to be below the lowest top among the data sets.

翻译：

在 &mod_levs 字段中，变量press_pa用于指定要保留的层次列表；指定的级别应与中间格式文件中xlvl的值匹配（有关中间文件记录的详细信息，请参阅对WPS中间格式的讨论）。mod_levs程序接受两个命令行参数作为输入。第一个参数是要操作的中间文件的名称，第二个参数是要写入的输出文件的名称。

从气象数据集中删除（指定的层次外的所有层次）特别有用，例如，当一个数据集用于模型初始条件，而第二个数据集用于横向边界条件时。这可以通过提供由metgrid插值的第一时间段的初始条件数据集和所有其他时间的边界条件数据集来实现。如果两个数据集具有相同数量的垂直层次，则无需执行任何工作；但是，当这两个数据集具有不同数量的层次时，至少需要执行以下操作：
要删除（m–n）层次，其中m>n和m和n是两个数据集中每一个数据集中具有m个层次的数据集中的层次数。所有文件中必须具有相同数量的垂直层次，这是由于real.exe中的一个限制，该限制要求从中插入的垂直层次数量恒定。
mod_levs实用程序是解决容纳两个或多个具有不同垂直层次数目的数据集问题的临时解决方案。如果用户选择使用mod_levs，则应注意，虽然层次的垂直位置不需要在数据集之间匹配，但所有数据集都应具有数据的表面层次，并且，在运行real.exe和wrf.exe时，必须选择p_top的值低于数据集中的最低的顶层。

参考网站

https://dreambooker.site/2019/10/03/Initializing-the-WRF-model-with-ERA5-pressure-level/

http://bbs.06climate.com/forum.php?mod=viewthread&tid=30962&highlight=ECMWF