How-to-generate-ERA5-data-and-use-it-in-Ash3d.md

 Meteorological ECMWF ERA5 reanalysis data are currently (August 2020) the highest quality reanalysis wind data publicly available.  Ash3d can read those data, but there are multiple ways to get those data and only one particular file format can be read by ash3d.  This this article I explain how to obtain those data and save them in a format that Ash3d can read.
 
-1)  Go to the ECMWF web site and download the data.
+# 1)  Go to the ECMWF web site and download the data.
 The site were data can be obtained is [here](https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-pressure-levels?tab=form).  You will need an account on this web site to download data, but the accounts are free.  Click “login/register” in the upper right to get your own account.  Once you have it, then log in.
 
 You should choose data as follows:
---"Product type":  choose "Reanalysis"
---    "Variable":  choose only one from "Geopotential", "Temperature", "U-component 
+* "Product type":  choose "Reanalysis"
+* "Variable":  choose either "Geopotential", "Temperature", "U-component of wind", "V-component of wind", or "Vertical velocity".  You will ultimately generate five files, each of which contains a single variable from this list.
+* "Pressure level": Choose all pressure levels
+* "Year":  Choose one (and only one)
+* "Month": Choose one (and only one)
+* "Day":  Choose one (and only one)
+* "Time":  Choose all hours in this list
+* "Geographic area":  Choose either "Whole available region", or specify a geographic subregion.  The geographic subregion must include the model domain.
+* "Format":  Choose "NetCDF"
+
+Click "Submit Form".  This will place your job in the queue and generate a download link once the job is done.  Download the file to your computer.
+
+For each date. you will generate five files containing the five variables listed above.  I usually name them using the convention below, using the example for an eruption on May 18, 1980:
+
+Variable                  file name
+Geopotential              1980.05.18_z.nc
+Temperature               1980.05.18_t.nc
+U-component of wind       1980.05.18_u.nc
+V-component of wind       1980.05.18_v.nc
+vertical velocity         1980.05.18_w.nc
+
+# 2.  Convert these files to a format that Ash3d can read
+
+For the conversion, use the fortran program convertERA5_EC2NC.f90, located at xxx, and compiled using the makefile that accompanies it.  You may need to modify lines 16 and 20 to make sure that the variables USGSROOT and NCLIBS point to the locations of the compiled Ash3d program libraries and of the NetCDF fortran libraries respectively.
+
+1. Copy convertERA5_EC2NC.f90 to the directory containing your new wind files.
+2. Copy the makefile to convertERA5_EC2NC.f90
+3. Modify the makefile as needed.
+4. Type "make" to compile
+5. Convert each file using the command
+    ./convertERA5_EC2NC infile
+   where "infile is one of the files above (e.g. 1980.05.18_z.nc)
+
+To convert a series of wind files such as the 1980.05.18_\*.nc files above, it may be easiest to write a shell script.  The conversion of the 1980.05.18_\*.nc files produces new files with the following names:
+
+e5.oper.an.pl.128_129_z.ll025sc.1980051800_1980051823.nc
+e5.oper.an.pl.128_130_t.ll025sc.1980051800_1980051823.nc
+e5.oper.an.pl.128_131_u.ll025uv.1980051800_1980051823.nc
+e5.oper.an.pl.128_135_w.ll025sc.1980051800_1980051823.nc
+
+# 3.  Modify the Ash3d input file to read these files
+
+   a)  Modify block 3, line 1 of the ash3d input file so that iwind=5, iwindFormate=29, as below:
+      5   29              #iwind, iwindFormat
+   b)  Modify block 3, line 5 so that nWindFiles=1
+   c)  Modify Block 5 so that it contains a single line with a path that points to the location of the ERA5 wind files.
+
+
+
+