关于WRFDA读取LITTLE_R格式问题

汀汀GRE

大家好，小弟初学WRFDA，有一疑问

http://www2.mmm.ucar.edu/wrf/users/wrfda/OnlineTutorial/Help/littler.html#format
http://www2.mmm.ucar.edu/wrf/users/docs/user_guide_V3/users_guide_chap7.htm#format

如果我没理解错的话，按照以上两个网页上的描述，WRFDA在读取LITTLE_R格式文件中每条记录的header（即地面观测）部分时，只读取一些例如经纬度，测站海拔，时间之类的变量，而其他的一些例如地面气温、气压、降水之类的变量是被丢弃不读取的。

那是否意味着我们无法将地面观测的资料同化进WRF初始场？

谢谢大家！

汀汀GRE

抱歉我来晚了……

本人最近的工作不接触WRFDA了，就把我与wrfhelp的邮件往来po上来吧

Hi WRFDA group,

I am new to data assimilation techniques and I have a question concerning how the WRFDA program processes the LITTLE_R format file.

As you mentioned in your user guide, it seems that, when your program is trying to read the "header" part (i.e. the ground observation) of one LITTLE_R record, it only reads variables such as lat, lon, altitude, time and simply DISCARDS other "substantial" ground observation data such as ground temp, pressure, precipitation and so on.

So how do we assimilate ground observations into first guess fields?

Regards,

回复：

I believe you are reading Chapter 7 of the users guide (http://www2.mmm.ucar.edu/wrf/users/docs/user_guide_V3/users_guide_chap7.htm#format); this is geared towards observation nudging which is a separate capability and uses LITTLE_R observations in a slightly different way. For WRFDA this page is a better reference: http://www2.mmm.ucar.edu/wrf/users/docs/user_guide_V3/users_guide_chap7.htm#format

The header record information which is used by WRFDA is lat/lon, elevation, FM code (observation type), date, and surface pressure (as well as a few more optional fields).

WRFDA does not have the capability to read *ground* temperature (soil temperature), but "surface" temperature (2-meter temperature) can be assimilated just fine. This data should be stored in the data records rather than the header record.

Precipitation observations can also be assimilated, but in a separate format (and for 4DVAR only): http://www2.mmm.ucar.edu/wrf/users/docs/user_guide_V3/users_guide_chap6.htm#_Precipitation_Data_Assimilation

Let us know if you have further questions.

对邮件内容简单总结一下（本人没有进行技术实现）：

1. LITTLE_R中的一条数据记录包含一条header record和若干条data record，WRFDA只会从data record中读取气象要素，从header record中读取经纬度、观测类型等信息。所以，要同化地面(surface)观测数据，应将其写入data record。WRFDA无法同化土壤(ground)数据。
2. 同化降水数据需要通过其他方法，而不是从LITTLE_R文件中获取，且仅能在4DVAR中实现。

xiaogao

我也是新手，在研究同化，但是因为没有地面观察资料，只是研究，么有自己处理过，只是表达下自己的想法哈。
地面温度、露点温度、气压、风速、风向这些变量，不是在data records里么，虽然官网给的高空数据little_r格式文件，title的地面气温等是缺失值，但如果这些数据自己有的话，就可以写上去？比如降水。因为降水没有在data record里面。

sutengye

楼主弄明白了吗？我也有类似的问题，求教啊

m337872010

楼主还在吗？想请教一下，Little_r格式需要用MM5里面的LIttle_r转吗

任性小王子

汀汀GRE 发表于 2017-11-6 12:44
抱歉我来晚了……

本人最近的工作不接触WRFDA了，就把我与wrfhelp的邮件往来po上来吧

非常感谢楼主分享经验，不错的帖子，收藏了。

低头前行

感谢楼主，收藏了