View source: R/spatialBehaviour.R
spatialBehaviour  R Documentation 
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. It also allows to compute three associated summary statistics.
spatialBehaviour(
sts,
product = "MSW",
windThreshold = c(18, 33, 42, 49, 58, 70),
method = "Willoughby",
asymmetry = "Chen",
empiricalRMW = FALSE,
spaceRes = "2.5min",
tempRes = 1,
verbose = 2
)
sts 

product 
character vector. Desired output statistics:

windThreshold 
numeric vector. Minimal wind threshold(s) (in 
method 
character. Model used to compute wind speed and direction. Three different models are implemented:

asymmetry 
character. If

empiricalRMW 
logical. Whether (TRUE) or not (FALSE) to compute
the radius of maximum wind ( 
spaceRes 
character. Spatial resolution. Can be 
tempRes 
numeric. Temporal resolution. Can be 
verbose 
numeric. Whether or not the function should display informations about the process and/or outputs. Can be:

Storm track data sets, such as those extracted from IBRTrACKS (Knapp et
al., 2010), usually provide observation at a 3 or 6hours temporal
resolution. In the spatialBehaviour() function, linear interpolations are
used to reach the temporal resolution specified in the tempRes
argument
(default value = 1 hour). When product = "MSW"
, product = "PDI"
,
or product = "Exposure"
the focal()
function from the terra
R package
is used to smooth the results using moving windows.
The Holland (1980) model, widely used in the literature, is based on the 'gradient wind balance in mature tropical cyclones. The wind speed distribution is computed from the circular air pressure field, which can be derived from the central and environmental pressure and the radius of maximum winds.
v_r = \sqrt{\frac{b}{\rho} \times \left(\frac{R_m}{r}\right)^b \times (p_{oci}  p_c)
\times e^{\left(\frac{R_m}{r}\right)^b} + \left(\frac{r \times f}{2}\right)^2} 
\left(\frac{r \times f}{2}\right)
with,
b = \frac{\rho \times e \times v_m^2}{p_{oci}  p_c}
f = 2 \times 7.29 \times 10^{5} \sin(\phi)
where, v_r
is the tangential wind speed (in m.s^{1}
),
b
is the shape parameter,
\rho
is the air density set to 1.15 kg.m^{3}
,
e
being the base of natural logarithms (~2.718282),
v_m
the maximum sustained wind speed (in m.s^{1}
),
p_{oci}
is the pressure at outermost closed isobar of the storm (in Pa
),
p_c
is the pressure at the centre of the storm (in Pa
),
r
is the distance to the eye of the storm (in km
),
R_m
is the radius of maximum sustained wind speed (in km
),
f
is the Coriolis force (in N.kg^{1}
, and
\phi
being the latitude).
The Willoughby et al. (2006) model is an empirical model fitted to aircraft observations. The model considers two regions: inside the eye and at external radii, for which the wind formulations use different exponents to better match observations. In this model, the wind speed increases as a power function of the radius inside the eye and decays exponentially outside the eye after a smooth polynomial transition across the eyewall.
\left\{\begin{aligned}
v_r &= v_m \times \left(\frac{r}{R_m}\right)^{n} \quad if \quad r < R_m \\
v_r &= v_m \times \left((1A) \times e^{\frac{rR_m}{X1}} +
A \times e^{\frac{rR_m}{X2}}\right) \quad if \quad r \geq R_m \\
\end{aligned}
\right.
with,
n = 2.1340 + 0.0077 \times v_m  0.4522 \times \ln(R_m)  0.0038 \times \phi
X1 = 287.6  1.942 \times v_m + 7.799 \times \ln(R_m) + 1.819 \times \phi
A = 0.5913 + 0.0029 \times v_m  0.1361 \times \ln(R_m)  0.0042 \times \phi
and A\ge0
where, v_r
is the tangential wind speed (in m.s^{1}
),
v_m
is the maximum sustained wind speed (in m.s^{1}
),
r
is the distance to the eye of the storm (in km
),
R_m
is the radius of maximum sustained wind speed (in km
),
\phi
is the latitude of the centre of the storm,
X2 = 25
.
Asymmetry can be added to Holland (1980) and Willoughby et al. (2006) wind fields as follows,
\vec{V} = \vec{V_c} + C \times \vec{V_t}
where, \vec{V}
is the combined asymmetric wind field,
\vec{V_c}
is symmetric wind field,
\vec{V_t}
is the translation speed of the storm, and
C
is function of r
, the distance to the eye of the storm (in km
).
Two formulations of C proposed by Miyazaki et al. (1962) and Chen (1994) are implemented.
Miyazaki et al. (1962)
C = e^{(\frac{r}{500} \times \pi)}
Chen (1994)
C = \frac{3 \times R_m^{\frac{3}{2}} \times r^{\frac{3}{2}}}{R_m^3 +
r^3 +R_m^{\frac{3}{2}} \times r^{\frac{3}{2}}}
where, R_m
is the radius of maximum sustained wind speed (in km
)
The Boose et al. (2004) model, or “HURRECON” model, is a modification of the Holland (1980) model. In addition to adding asymmetry, this model treats of water and land differently, using different surface friction coefficient for each.
v_r = F\left(v_m  S \times (1  \sin(T)) \times \frac{v_h}{2} \right) \times
\sqrt{\left(\frac{R_m}{r}\right)^b \times e^{1  \left(\frac{R_m}{r}\right)^b}}
with,
b = \frac{\rho \times e \times v_m^2}{p_{oci}  p_c}
where, v_r
is the tangential wind speed (in m.s^{1}
),
F
is a scaling parameter for friction (1.0
in water, 0.8
in land),
v_m
is the maximum sustained wind speed (in m.s^{1}
),
S
is a scaling parameter for asymmetry (usually set to 1
),
T
is the oriented angle (clockwise/counter clockwise in Northern/Southern Hemisphere) between
the forward trajectory of the storm and a radial line from the eye of the storm to point $r$
v_h
is the storm velocity (in m.s^{1}
),
R_m
is the radius of maximum sustained wind speed (in km
),
r
is the distance to the eye of the storm (in km
),
b
is the shape parameter,
\rho = 1.15
is the air density (in kg.m^{3}
),
p_{oci}
is the pressure at outermost closed isobar of the storm (in Pa
), and
p_c
is the pressure at the centre of the storm (pressure
in Pa
).
The spatialBehaviour() function returns SpatRaster objects (in WGS84).
The number of layers in the output depends on the number of storms in the inputs,
on the desired product
, as well as the tempRes
argument:
if product = "MSW"
, the function returns one layer for each Storm
.
The names of the layer follow the following terminology, the name of the storm
in capital letters and “MSW” separated by underscores (e.g., "PAM_MSW"),
if product = "PDI"
, the function returns one layer for each Storm
.
The names of the layer follow the following terminology, the name of the storm
in capital letters and “PDI” separated by underscores (e.g., "PAM_PDI"),
if product ="Exposure"
, the function returns one layer for each wind speed values
in the windThreshold
argument and for each Storm
. The names of the layer follow the
following terminology, the name of the storm in capital letters, "Exposure", and the threshold
value separated by underscores (e.g., "PAM_Exposure_18", "PAM_Exposure_33", ...),
if product = "Profiles"
the function returns one layer for wind speed and
one layer for wind direction for each observation or interpolated observation and each Storm
.
The names of the layer follow the following terminology, the name of the storm in capital letters,
"Speed" or "Direction", and the indices of the observation separated by underscores
(e.g., "PAM_Speed_41", "PAM_Direction_41",...).
Boose, E. R., Serrano, M. I., & Foster, D. R. (2004). Landscape and regional impacts of hurricanes in Puerto Rico. Ecological Monographs, 74(2), Article 2. https://doi.org/10.1890/024057
Chen, K.M. (1994). A computation method for typhoon wind field. Tropic Oceanology, 13(2), 41–48.
Holland, G. J. (1980). An Analytic Model of the Wind and Pressure Profiles in Hurricanes. Monthly Weather Review, 108(8), 1212–1218. https://doi.org/10.1175/15200493(1980)108<1212:AAMOTW>2.0.CO;2
Knapp, K. R., Kruk, M. C., Levinson, D. H., Diamond, H. J., & Neumann, C. J. (2010). The International Best Track Archive for Climate Stewardship (IBTrACS). Bulletin of the American Meteorological Society, 91(3), Article 3. https://doi.org/10.1175/2009bams2755.1
Miyazaki, M., Ueno, T., & Unoki, S. (1962). The theoretical investigations of typhoon surges along the Japanese coast (II). Oceanographical Magazine, 13(2), 103–117.
Willoughby, H. E., Darling, R. W. R., & Rahn, M. E. (2006). Parametric Representation of the Primary Hurricane Vortex. Part II: A New Family of Sectionally Continuous Profiles. Monthly Weather Review, 134(4), 1102–1120. https://doi.org/10.1175/MWR3106.1
# Creating a stormsDataset
sds < defStormsDataset()
# Geting storm track data for tropical cyclone Pam (2015) near Vanuatu
pam < defStormsList(sds = sds, loi = "Vanuatu", names = "PAM")
# Computing maximum sustained wind speed generated by Pam (2015) near Vanuatu
# using default settings
msw.pam < spatialBehaviour(pam)
# Computing PDI generated by Pam (2015) near Vanuatu using the Holland model without asymmetry
pdi.pam < spatialBehaviour(pam, method = "Holland", product = "PDI", asymmetry = "None")
# Computing duration of exposure to SaffirSimpson hurricane wind scale threshold values
# during Pam (2015) near Vanuatu using default settings
exp.pam < spatialBehaviour(pam, product = "Exposure")
# Computing wind speed and direction profiles generated by Pam (2015) near Vanuatu
# using Boose model
prof.pam < spatialBehaviour(pam, product = "Profiles", method = "Boose")
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