stiltread R package

This package provides tools for interfacing with input and output files used by the Stochastic Time Inverted Lagrangian Transport (STILT) model.

Installation

If R is using the intel fortran compiler, additional compilation flags must be included. Run the following command to check if the ifort compiler is in use, and add PKG_FCFLAGS = -assume byterecl to ~/.R/Makevars if necessary.

R CMD config FC | grep -q ifort && mkdir -p ~/.R && (echo "PKG_FCFLAGS = -assume byterecl" >> ~/.R/Makevars && echo "Modified compiler options at ~/.R/Makevars")
R CMD config FC | grep -q gfortran && mkdir -p ~/.R && (echo "PKG_FCFLAGS = -frecord-marker=8" >> ~/.R/Makevars && echo "Modified compiler options at ~/.R/Makevars")

Package can be installed using devtools.

if (!require('devtools')) install.packages('devtools')
devtools::install_github('uataq/stiltread')

NOTE: the rgdal package was removed from the CRAN repository as of October 2023. To install rgdal nonetheless, it can be installed from source:

url <- "https://cran.r-project.org/src/contrib/Archive/rgdal/rgdal_1.6-7.tar.gz"
install.packages(url, type="source", repos=NULL)

Then, load the package and install the dependencies.

library(stiltread)
install_stiltread()

To read a raster layer from a HRRR data file,

library(stiltread)
shgt <- read_met('/path/to/arl/20150617.00z.hrrra', 
                 var = 'shgt',
                 yy = 15,
                 mm = 6,
                 dd = 17,
                 hh = 3,
                 lvl = 0)
shgt
# class       : RasterLayer 
# dimensions  : 1059, 1799, 1905141  (nrow, ncol, ncell)
# resolution  : 3005.169, 2991.952  (x, y)
# extent      : -2700991, 2705308, -1580359, 1588118  (xmin, xmax, ymin, ymax)
# coord. ref. : +proj=lcc +lon_0=-97.5 +lat_0=38.5 +lat_1=38.5 +lat_2=38.5 +ellps=WGS84 +no_defs
# data source : in memory
# names       : layer 
# values      : -80.036, 4175.964  (min, max)

which returns a raster::RasterLayer containing data, grid coordinates, and projection information using the standard PROJ4 format.

Wind transformations

Since wind is grid relative, use read_met_wind instead of read_met to access wind fields. This is called in the same way as read_met, only no var argument is required. This returns a rasterStack with u and v layers that have been rotated into +proj=longlat.

library(stiltread)
uv <- read_met_wind('/path/to/arl/20150617.00z.hrrra', 
                    yy = 15,
                    mm = 6,
                    dd = 17,
                    hh = 3,
                    lvl = 0)
uv
# class       : RasterStack 
# dimensions  : 72, 78, 5616, 2  (nrow, ncol, ncell, nlayers)
# resolution  : 0.0345, 0.0261  (x, y)
# extent      : -113.4537, -110.7627, 39.81678, 41.69598  (xmin, xmax, ymin, ymax)
# coord. ref. : +proj=longlat +ellps=WGS84 
# names       :          u,          v 
# min values  :  -6.965451, -10.460653 
# max values  :   5.198425,   5.289214

The u and v layers can be accessed by name using

uv$u
# class       : RasterLayer 
# dimensions  : 72, 78, 5616  (nrow, ncol, ncell)
# resolution  : 0.0345, 0.0261  (x, y)
# extent      : -113.4537, -110.7627, 39.81678, 41.69598  (xmin, xmax, ymin, ymax)
# coord. ref. : +proj=longlat +ellps=WGS84 
# data source : in memory
# names       : u 
# values      : -6.965451, 5.198425  (min, max)

Visualizations

Since read_met returns a raster::RasterLayer with projection metadata, we can leverage standard mapping libraries in R.

plot(shgt, main = 'Elevation')

For an interactive leaflet map,

library(leaflet)
leaflet() %>%
  addProviderTiles('CartoDB.Positron') %>%
  addRasterImage(shgt, opacity = 0.5, colors = viridis::viridis(16))

Limitations

1. Returned raster layers are limited to files that use Lambert Conformal Conic for the map projection, which is typical for midlatitudes.
2. Upper levels of pressure variables are often recorded as a difference from the base level. This calculation needs to be performed by the user.