def plot(self, ax):
# Get global u/v wind data
ug, vg = self.chart.get_data(self.gfs_vars, apply_domain=False)
# Get level coordinates for U/V wind components
ug_lv_coord = gfs_utils.get_level_coord(ug, self.level_units)
vg_lv_coord = gfs_utils.get_level_coord(vg, self.level_units)
# Constrain to specified level(s)
ugc = gfs_utils.get_coord_constraint(ug_lv_coord.name(), self.level)
ug = ug.extract(ugc)
vgc = gfs_utils.get_coord_constraint(vg_lv_coord.name(), self.level)
vg = vg.extract(vgc)
# Apply smoothing
ug_data = wrf_smooth2d(ug.data, 6)
ug.data = ug_data.data
vg_data = wrf_smooth2d(vg.data, 6)
vg.data = vg_data.data
# Set up windspharm wind vector object
w = VectorWind(ug, vg)
# Get nondivergent component of wind
upsi, vpsi = w.nondivergentcomponent()
Vpsi = VectorWind(upsi, vpsi)
# Partition streamfunction vorticity into curvature and shear
# components
# Bell and Keyser 1993 Appendix equation A.3b
# Relative curvature vorticity:
# V dalpha/ds = 1/V^2[u^2 dv/dx - v^2 du/dy - uv(du/dx - dv/dy)]
dupsi_dx, dupsi_dy = Vpsi.gradient(upsi)
dvpsi_dx, dvpsi_dy = Vpsi.gradient(vpsi)
ws = Vpsi.magnitude()
vrt = (upsi**2 * dvpsi_dx - vpsi**2 * dupsi_dy - upsi * vpsi *
(dupsi_dx - dvpsi_dy)) / ws**2
# Calculate advection of non-divergent curvature vorticity
dvrt_dx, dvrt_dy = Vpsi.gradient(vrt)
advec = -1 * (upsi * dvrt_dx + vpsi * dvrt_dy)
# Second order advection term needed for masking
dadv_dx, dadv_dy = Vpsi.gradient(advec)
advec2 = upsi * dadv_dx + vpsi * dadv_dy
# Apply domain constraint
domain_constraint = gfs_utils.get_domain_constraint(self.chart.domain)
upsi = upsi.extract(domain_constraint)
vrt = vrt.extract(domain_constraint)
advec = advec.extract(domain_constraint)
advec2 = advec2.extract(domain_constraint)
# Masking rules from Berry & Thorncroft 2007, Table 1
# A1. Mask streamfunction curvature vorticity to exclude AEW
# ridges axes or weak systems (BT2007: K1T = 0.5 * 10^-5 s^-1)
K1T = 1.5 * 10**-5 # s^-1
m1t = vrt.data <= K1T # mask for troughs
m1r = vrt.data >= -K1T # mask for ridges
# A2. Remove "pseudoridge" axes in nondivergent flow that is
# highly cyclonically curved
K2T = 0 # m s^-3
m2 = advec2.data <= K2T
# A3. Removes trough axes in westerly flow
K3T = 0 # m s^-1
m3 = upsi.data >= K3T
trough_mask = m1t | m2 | m3
ridge_mask = m1r | ~m2 | m3
troughs = self.apply_size_mask(trough_mask, advec.data)
ridges = self.apply_size_mask(ridge_mask, advec.data)
# Plot troughs and ridges
ax.contour(self.lon, self.lat, troughs, levels=0, **self.options)
ax.contour(self.lon,
self.lat,
ridges,
levels=0,
**self.options,
linestyles="dotted")
