<p>The ERA Interim reanalysis is made by ECMWF and the other reanalysis is made by NOAA. Reanalyzes of the past are made by running global climate models and these differ because NOAA and ECMWF use different models and perhaps even slightly different data. The models on the other hand can be very different for example on implementation of data assimilation, parametrization and even grid cell size.</p>

<p>All of these variables are vertically integrated. The ERA variables in the order you mention them contain: </p>

<p><strong>-Total column water:</strong> all water</p>

<p><strong>-Total column rain water:</strong> all liquid and solid water in droplets large enough not to be considered cloud droplets (my guess)</p>

<p><strong>-Total column water vapor:</strong> all gas phase water</p>

<p><strong>-Total column cloud liquid water:</strong> all liquid cloud water</p>

<p>The NOAA variables:</p>

<p><strong>-Cloud water content:</strong> all liquid and solid cloud water</p>

<p><strong>-Precipitable water content</strong> corresponds to <strong>Total column water</strong></p>

<p>From these the <strong>Total column water vapor</strong> corresponds the <strong>Vertically integrated specific moisture</strong>. None of these is the divergence of the total column water vapor phase that you need. Although the paper you are referring approximates precipitation from moisture divergence, you could use just the <strong>Total column rain water</strong> and no approximation is needed (I didn't read the paper so I don't know if this is makes sense).</p>

<p><strong>Edit, added sources:</strong>
The ERA variable list can be found <a href="http://apps.ecmwf.int/codes/grib/param-db" rel="nofollow noreferrer">here</a> and you can search variables there and press them to get the definitions too. For NOAA I couldn't find a source for the definitions of these variables. If someone finds please edit this answer</p>

CC BY-SA 3.0
2017-07-13T20:53:58.460Z
Thank you very much. Could you please add some references to your answer?
ouranos
CC BY-SA 3.0
2017-07-14T09:11:39.827Z
Thank you! I have done some tests and Total Column Rain Water from ERA, from this list, is the variable that best resembles actual precipitation in both space and time (seasonal/interannual scale at least). But apparently there is not such an equivalent from NOAA. Any suggestion?
ouranos
CC BY-SA 3.0
2017-07-14T09:33:52.340Z
I found Precipitation Rate in NOAA variables that might be useful, but it seems to be in units of kg/((m^2)*s) for 3-hourly data, so you will have to change it a bit to make them comparable.
Communisty
CC BY-SA 3.0
2017-08-29T23:25:56.983Z
I noticed that on NCEP 20th Century, daily precipitation rate is availavle as a "forecast" variable, instead of "analysis". This is made very clear in their list of parameters. Any idea of I can use this prate normally? Thanks in advance (hoping to close this thread with this answer)
ouranos
CC BY-SA 3.0
2017-08-30T07:04:24.997Z
IMO you should accept this as an answer as it answers the question and ask another question about the differences of NCEP 'forecast' and 'analysis' parameters.
Communisty
CC BY-SA 4.0
2018-09-25T17:04:06.097Z
thank you for your answer. However, the question on how they are calculated is still open (no proper equations, or any objective method). Also, the list of parameters from ECMWF does not add much as a reference for the calculation, just provides units, basically. The answer is still lacking proper technical references, IMO. I cannot calculate the variables myself from your answer.
ouranos
CC BY-SA 4.0
2018-09-25T17:05:37.127Z
plus, a question on forecast vs. analysis already exists here: https://earthscience.stackexchange.com/questions/12182/difference-between-nceps-20th-century-daily-forecast-and-analysis-variables?noredirect=1&lq=1
ouranos
CC BY-SA 4.0
2018-09-26T06:17:21.093Z
In the ECMWF parameter list you can click on each variable and it will show their description. I'm afraid there probably isn't any place where they would explicitly write down the equations of these parameters. You should be able to write or code the equation of a vertical integral yourself.
Communisty
CC BY-SA 3.0
2017-07-03T13:41:30.660Z
2017-07-14T06:21:16.903Z
2017-07-14T06:21:16.903Z
Communisty
<p>In different reanalysis products (<a href="http://apps.ecmwf.int/datasets/data/era20c-daily/levtype=sfc/type=an/" rel="nofollow noreferrer">ERA 20C</a> and <a href="https://www.esrl.noaa.gov/psd/data/gridded/data.20thC_ReanV2.monolevel.html" rel="nofollow noreferrer">NOAA/OAR/ESRL/PSD 20th Century</a> daily data specifically) one can find the following variables:</p>

<ul>
<li>Total column water (ERA) </li>
<li>Total column rain water (ERA)</li>
<li>Total column water vapor (ERA)</li>
<li>Total column cloud liquid water (ERA)</li>
<li>Cloud water content (NOAA)</li>
<li>Precipitable water content (NOAA)</li>
</ul>

<p><strong>How are they calculated?</strong> What are the differences between them? Could you please cite a reference or book in which this is explained in details?</p>

<p>Which of these may serve as a best approximation to represent large-scale patterns of rainfall (monsoonal cycles)?</p>

<p>Which of these is the vertically integrated specific moisture?</p>

<p>Are any of these equivalent to the vertically integrated moisture flux divergence as an approximation for precipitation, as in <a href="http://www.squallwx.com/papers/MFC2005.pdf" rel="nofollow noreferrer">Banacos and Schultz (2005)</a>?</p>

<meteorology><climate><climate-models><open-data><reanalysis>
Single-layer water content variables
ouranos
# Single-layer water content variables

(Asked by: username_0 on 2017-07-01)

In different reanalysis products ([ERA 20C](http://apps.ecmwf.int/datasets/data/era20c-daily/levtype=sfc/type=an/) and [NOAA/OAR/ESRL/PSD 20th Century](https://www.esrl.noaa.gov/psd/data/gridded/data.20thC_ReanV2.monolevel.html) daily data specifically) one can find the following variables:

* Total column water (ERA)
* Total column rain water (ERA)
* Total column water vapor (ERA)
* Total column cloud liquid water (ERA)
* Cloud water content (NOAA)
* Precipitable water content (NOAA)

**How are they calculated?** What are the differences between them? Could you please cite a reference or book in which this is explained in details?

Which of these may serve as a best approximation to represent large-scale patterns of rainfall (monsoonal cycles)?

Which of these is the vertically integrated specific moisture?

Are any of these equivalent to the vertically integrated moisture flux divergence as an approximation for precipitation, as in [Banacos and Schultz (2005)](http://www.squallwx.com/papers/MFC2005.pdf)?

**Tags:** meteorology, climate, climate-models, open-data, reanalysis


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## 1 answers

### Answer by username_1 on 2017-07-03. Score: 4 | Accepted answer

The ERA Interim reanalysis is made by ECMWF and the other reanalysis is made by NOAA. Reanalyzes of the past are made by running global climate models and these differ because NOAA and ECMWF use different models and perhaps even slightly different data. The models on the other hand can be very different for example on implementation of data assimilation, parametrization and even grid cell size.

All of these variables are vertically integrated. The ERA variables in the order you mention them contain:

**-Total column water:** all water

**-Total column rain water:** all liquid and solid water in droplets large enough not to be considered cloud droplets (my guess)

**-Total column water vapor:** all gas phase water

**-Total column cloud liquid water:** all liquid cloud water

The NOAA variables:

**-Cloud water content:** all liquid and solid cloud water

**-Precipitable water content** corresponds to **Total column water**

From these the **Total column water vapor** corresponds the **Vertically integrated specific moisture**. None of these is the divergence of the total column water vapor phase that you need. Although the paper you are referring approximates precipitation from moisture divergence, you could use just the **Total column rain water** and no approximation is needed (I didn't read the paper so I don't know if this is makes sense).

**Edit, added sources:**
The ERA variable list can be found [here](http://apps.ecmwf.int/codes/grib/param-db) and you can search variables there and press them to get the definitions too. For NOAA I couldn't find a source for the definitions of these variables. If someone finds please edit this answer

> **Comments:**
> **username_0**: Thank you very much. Could you please add some references to your answer?  
> **username_0**: Thank you! I have done some tests and Total Column Rain Water from ERA, from this list, is the variable that best resembles actual precipitation in both space and time (seasonal/interannual scale at least). But apparently there is not such an equivalent from NOAA. Any suggestion?  
> **username_1**: I found Precipitation Rate in NOAA variables that might be useful, but it seems to be in units of kg/((m^2)*s) for 3-hourly data, so you will have to change it a bit to make them comparable.  
> **username_0**: I noticed that on NCEP 20th Century, daily precipitation rate is availavle as a "forecast" variable, instead of "analysis". This is made very clear in their list of parameters. Any idea of I can use this prate normally? Thanks in advance (hoping to close this thread with this answer)  
> **username_1**: IMO you should accept this as an answer as it answers the question and ask another question about the differences of NCEP 'forecast' and 'analysis' parameters.  
> **username_0**: thank you for your answer. However, the question on how they are calculated is still open (no proper equations, or any objective method). Also, the list of parameters from ECMWF does not add much as a reference for the calculation, just provides units, basically. The answer is still lacking proper technical references, IMO. I cannot calculate the variables myself from your answer.  
> **username_0**: plus, a question on forecast vs. analysis already exists here: https://earthscience.stackexchange.com/questions/12182/difference-between-nceps-20th-century-daily-forecast-and-analysis-variables?noredirect=1&lq=1  
> **username_1**: In the ECMWF parameter list you can click on each variable and it will show their description. I'm afraid there probably isn't any place where they would explicitly write down the equations of these parameters. You should be able to write or code the equation of a vertical integral yourself.  

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