spatialBehaviour
The spatialBehaviour() function allows
computing wind speed and direction for each cell of a regular grid
(i.e., a raster) for a given tropical cyclone or set of tropical
cyclones. The product="Profiles" argument allows producing
2D wind fields during the lifespan of the cyclone at a temporal
resolution of up to 15 minutes. The spatialBehaviour()
function also allows to compute three associated summary statistics: the
maximum sustained wind speed (product="MSW"), the power
dissipation index (product="PDI") and the duration of
exposure to winds reaching defined speed thresholds along the life span
of the cyclones (product="Exposure"). Then the
plotBehaviour() and the writeRast() functions
can be used to visualise and export the output. In the following example
we use the test_dataset provided with the package to
illustrate how cyclone track data can be used to compute, plot, and
export 2D wind field profiles or summary statistics.
Computing and plotting spatialBehaviour products
We can compute the behaviour of winds generated by the topical cyclone Pam (2015) near Vanuatu. First, track data are extracted as follows:
## Warning: No basin argument specified. StormR will work as expected
## but cannot use basin filtering for speed-up when collecting data## === Loading data ===
## Open database... /tmp/RtmpXubJ9P/Rinstdbe2cf9d1fb/StormR/extdata/test_dataset.nc opened
## Collecting data ...
## === DONE ===
Wind profiles
Using track data and the spatialBehaviour() function
with the product="Profiles argument we can generate 2D wind
fields at any time as follows:
## class : SpatRaster
## size : 304, 219, 114 (nrow, ncol, nlyr)
## resolution : 0.04166667, 0.04166667 (x, y)
## extent : 163.7083, 172.8333, -23, -10.33333 (xmin, xmax, ymin, ymax)
## coord. ref. : lon/lat WGS 84 (CRS84) (OGC:CRS84)
## source(s) : memory
## names : PAM_Speed_28, PAM_S~28.33, PAM_S~28.67, PAM_Speed_29, PAM_S~29.33, PAM_S~29.67, ...
## min values : 5.927, 2.302, 3.807, 3.087, 0.848, 2.971, ...
## max values : 61.110001, 63.419998, 64.483002, 63.610001, 64.752998, 65.016998, ...
## time : 2015-03-11 21:00:00 to 2015-03-14 05:00:00 (57 steps)The function returns a SpatRaster object with two
rasters, one for the wind speed and one for the wind direction, for each
observation or interpolated observation. Rasters’ names follow the
following terminology, the name of the storm in capital letters, “Speed”
or “Direction”, and the index of the observation, separated by
underscores. Note that actual observations have entire indices (e.g.,
41, 42, …) while interpolated observation have decimals (e.g., 41.1,
41.2, …). Most tropical cyclone track data sets are based on
observations gathered every 3 or 6 hours. Therefore, to be able to
compute wind fields every 1 hour, the observations are interpolated.
Wind direction follows the meteorological convention : it indicates
where the wind is blowing from, with 0° at North and increasing
clockwise.
Wind speed and direction profiles at the 41th observation can be plotted as follows:
Summary statisics
The spatialBehaviour() function can compute the
different products (i.e., "Profiles",
"MSW", "PDI", "Exposure") either
separately or together. Here, we compute all three summary statistics
together as follows:
## class : SpatRaster
## size : 304, 219, 8 (nrow, ncol, nlyr)
## resolution : 0.04166667, 0.04166667 (x, y)
## extent : 163.7083, 172.8333, -23, -10.33333 (xmin, xmax, ymin, ymax)
## coord. ref. : lon/lat WGS 84 (CRS84) (OGC:CRS84)
## source(s) : memory
## names : PAM_MSW, PAM_PDI, PAM_E~re_18, PAM_E~re_33, PAM_E~re_42, PAM_E~re_49, ...
## min values : 13.787, 18868.693359, 1, 1, 1, 1, ...
## max values : 73.904463, 16893412.032754, 30.900826, 14.702479, 9.446281, 6.826446, ...
## time : 2015-03-11 15:00:00zUTCThe spatialBehaviour() function returns a
SpatRaster object with eight rasters: one for the maximum
sustained wind speed ("MSW"), one for the power dissipation
index ("PDI"), and one for each of the six defaults wind
thresholds values set for the duration of exposure
("Exposure").
## [1] "PAM_MSW" "PAM_PDI" "PAM_Exposure_18" "PAM_Exposure_33"
## [5] "PAM_Exposure_42" "PAM_Exposure_49" "PAM_Exposure_58" "PAM_Exposure_70"By default, the function returns the duration of exposure (in hours)
to wind speeds above the thresholds used by the Saffir-Simpson hurricane
wind scale (i.e., 18, 33, 42, 49, 58, and 70 \(m.s^{-1}\)). This can be change using the
wind_threshold argument.
The maximum sustained wind speed can be plotted as follows:
The power dissipation index can be plotted as follows:
The duration of exposure to wind stronger than 58 \(m.s^{-1}\) (i.e., Saffir-Simpson’s categories 4 and 5) can be plotted as follows:
Spatio-temporal resolution
As in the WorldClim database (https://worldclim.org/data/worldclim21.html) four
spatial resolutions are available. By default the spatial resolution is
set to 2.5 min (~4.5 km at the equator), but a finer spatial resolution
of 30 s (~1 km at the equator) and coarser spatial resolutions of 5 min
(~9 km at the equator) or 10 min (~18.6 km at the equator) can be set
using the spaceRes argument. The temporal resolution is set
to 1 hour by default but finer spatial resolution of 0.75, 0.50, or 0.25
hour can be set using the tempRes argument. Maximum
sustained wind speed can be computed at a 10 min spatial resolution and
a 30 min temporal resolution as follows:
ss <- spatialBehaviour(st, product = c("MSW"), verbose = 0, spaceRes = "10min", tempRes = 30)
plotBehaviour(st, ss$PAM_MSW)
#### Dynamic plot plotBehaviour function also provide (See
ExtractStorms vignette) a dynamic plot. Here is an example based on the
same parameters as above.
Exporting spatialBehaviour products
The spatialBehaviour() function returns rasters stored
in a SpatRaster object than can be exported either in
“.tiff” or “.nc” (NetCDF) formats using the writeRast()
function. Here, we export the maximum sustained wind speed in the
working directory as follows: