# This file is part of OpenDrift.
#
# OpenDrift is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, version 2
#
# OpenDrift is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with OpenDrift. If not, see <https://www.gnu.org/licenses/>.
#
# Copyright 2016, Knut-Frode Dagestad, MET Norway
import logging; logger = logging.getLogger(__name__)
from datetime import timedelta
import numpy as np
import scipy as sp
import pandas as pd
from math import sqrt
import matplotlib.pyplot as plt
import pyproj
import cmocean
[docs]
def wind_drift_factor_from_trajectory(trajectory_dict, min_period=None):
'''Estimate wind_drift_fator based on wind and current along given trajectory
trajectory_dict: dictionary with arrays of same length of the following variables:
time, lon, lat, x_wind, y_wind, x_sea_water_velocity, y_sea_water_velocity
Returns array of same length minus one of the fitted wind_drift_factor
'''
geod = pyproj.Geod(ellps='WGS84')
time = trajectory_dict['time']
try:
import pandas as pd
time = pd.to_datetime(time)
except:
pass
if min_period is None:
ind = range(len(time))
else:
timestep = time[1] - time[0]
s = np.round(min_period.total_seconds()/(timestep).total_seconds()).astype(int)
ind = np.arange(0, len(time), s).astype(np.int32)
print('Original timestep (%s) multiplied by %i: %s' % (timestep, s, timestep*s))
ind2 = ind.copy()
for i in range(1, s):
ind2 = np.concatenate((ind2, ind+i))
ind = ind2
ind = ind[ind<len(time)]
time = time[ind]
cu = trajectory_dict['x_sea_water_velocity'][ind]
cv = trajectory_dict['y_sea_water_velocity'][ind]
wu = trajectory_dict['x_wind'][ind]
wv = trajectory_dict['y_wind'][ind]
lon = trajectory_dict['lon'][ind]
lat = trajectory_dict['lat'][ind]
current_speed = np.sqrt(cu**2+cv**2)
current_azimuth = np.degrees(np.arctan2(cu, cv))
wind_speed = np.sqrt(wu**2+wv**2)
time_step = (time[1]-time[0]).total_seconds()
# Move forward from each position with current
lonf, latf, back_az = geod.fwd(lon[0:-1], lat[0:-1], current_azimuth[0:-1], current_speed[0:-1]*time_step)
# Find distance and azimuth to next observational position
azimuth_forward, a2, distance = geod.inv(lonf, latf, lon[1:], lat[1:])
# Find the wind_drift_factor needed to give the remaining distance
wind_drift_factor = distance / (time_step*wind_speed[0:-1])
wind_azimuth = np.degrees(np.arctan2(wu, wv))
azimuth_offset = azimuth_forward - wind_azimuth[0:-1] # 0 if downwind drift, positive if rightwards drift is needed towards end position
azimuth_offset = azimuth_offset % 360 # Make sure azimuth angle is between -180 and 180
azimuth_offset = (azimuth_offset + 360) % 360
azimuth_offset[azimuth_offset>180] -= 360
# # New: optimize combined cdf and wdf
# azimuth_north, a2, distance_north = geod.inv(lon[0:-1], lat[0:-1], lon[0:-1], lat[1:])
# azimuth_east, a2, distance_east = geod.inv(lon[0:-1], lat[0:-1], lon[1:], lat[0:-1])
# cu = cu[0:-1]
# cv = cv[0:-1]
# wu = wu[0:-1]
# wv = wv[0:-1]
# su = distance_east / time_step
# sv = distance_north / time_step
# wdf = (sv - su*(cv/cu) ) / (wv - wu*(cv/cu))
# cdf = (sv - su*(wv/wu) ) / (cv - cu*(wv/wu))
return wind_drift_factor, azimuth_offset #, wdf, cdf
[docs]
def plot_wind_drift_factor(wdf, azimuth, wmax_plot=None):
'''Polar plot of array of wind drift factor, with associated azimuthal offset'''
wmax = wdf.max()
wbins = np.arange(0, wmax+.005, .005)
abins = np.linspace(-180, 180, 30)
hist, _, _ = np.histogram2d(azimuth, wdf, bins=(abins, wbins))
A, W = np.meshgrid(abins, wbins)
fig, ax = plt.subplots(subplot_kw=dict(projection='polar'))
ax.set_theta_zero_location('N', offset=0)
ax.set_theta_direction(-1)
pc = ax.pcolormesh(np.radians(A), W, hist.T, cmap=cmocean.cm.dense)
plt.arrow(np.pi, wmax, 0, -wmax, width=.015, facecolor='k', zorder=100,
head_width=.8, lw=2, head_length=.005, length_includes_head=True)
plt.text(np.pi, wmax*.5, ' Wind direction', fontsize=18)
plt.grid()
if wmax_plot is not None:
plt.ylim([0, wmax_plot])
plt.show()
[docs]
def oil_wave_entrainment_rate_li2017(dynamic_viscosity, oil_density, interfacial_tension,
significant_wave_height=None, wave_breaking_fraction=None,
wind_speed=None, sea_water_density=1028.):
# Z. Li, M.L. Spaulding, D. French McCay, J. Mar. Pollut. Bull. (2016):
# An algorithm for modeling entrainment and naturally and chemically dispersed
# oil droplet size distribution under surface breaking wave conditions
if wave_breaking_fraction is None:
if wind_speed is None:
raise ValueError('wave_breaking_fraction or wind_speed must be provided')
wave_breaking_fraction = wave_breaking_fraction_from_wind(wind_speed)
if significant_wave_height is None:
if wind_speed is None:
raise ValueError('significant_wave_height or wind_speed must be provided')
significant_wave_height = significant_wave_height_from_wind_neumann_pierson(wind_speed)
g = 9.81
delta_rho = sea_water_density - oil_density
d_o = 4*np.sqrt(interfacial_tension / (delta_rho*g))
we = sea_water_density*g*significant_wave_height*d_o/interfacial_tension
oh = dynamic_viscosity/np.sqrt(oil_density*interfacial_tension*d_o)
with np.errstate(divide='ignore'):
entrainment_rate = (4.604e-10*we**1.805*oh**-1.023)*wave_breaking_fraction
return entrainment_rate
[docs]
def significant_wave_height_from_wind_neumann_pierson(wind_speed):
# Neumann and Pierson, 1966
# WMO 1998
return 0.0246*np.power(wind_speed, 2)
[docs]
def wave_breaking_fraction_from_wind(wind_speed, wave_period=None):
# TODO: We should also have an option here for
# the case when wave height is given, but no wind
if wave_period is None:
wave_period = wave_period_from_wind(wind_speed)
f = 0.032*(wind_speed - 5)/wave_period
f[f < 0] = 0
return f
[docs]
def wave_period_from_wind(wind_speed):
# Pierson-Moskowitz if period not available from readers
# WMO guide to wave analysis and forecasting pp. 14, WMO (1998)
# fallback value if no wind speed or Hs to avoid division by zero
wind_speed = np.atleast_1d(wind_speed)
omega = 5*np.ones(wind_speed.shape) # Angular frequency
omega[wind_speed>0] = 0.877*9.81/(1.17*wind_speed[wind_speed>0])
return 2*np.pi/omega
[docs]
def verticaldiffusivity_Sundby1983(windspeed, depth, mixedlayerdepth=50, background_diffusivity=0):
''' Vertical diffusivity from Sundby (1983)
S. Sundby (1983): A one-dimensional model for the vertical
distribution of pelagic fish eggs in the mixed layer
Deep Sea Research (30) pp. 645-661
'''
K = 76.1e-4 + 2.26e-4 * windspeed*windspeed * np.ones(np.atleast_1d(depth.shape))
K[depth>mixedlayerdepth-1] = (K[depth>mixedlayerdepth-1]+background_diffusivity)/2 # Transition
K[depth>=mixedlayerdepth] = background_diffusivity # Cutoff below mixed layer
# valid = windspeed_squared < 13**2
return K
[docs]
def verticaldiffusivity_Large1994(windspeed, depth, mixedlayerdepth=50, background_diffusivity=0):
''' Vertical diffusivity from Large et al. (1994)
Depending on windspeed, depth and mixed layer depth (default 50m).'''
# Defining two helper methods:
def stabilityfunction(sigma):
# controls stratification regimes for diffusivity
# a value of 1 represent neutrally buoyant conditions (no stratification)
# a value between 0 and 1 represents stable stratification
return 0.2 # should be depth dependent, too
def G(sigma):
# vertical shape function for eddy diffusivity
a1 = 1.
a2 = -2
a3 = 1
G = a1*sigma + a2*sigma**2 + a3*sigma**3
below = np.where(G>=1)
G[below]=G[below]*0.
return G
depth = np.abs(depth) # Making sure depth is positive value
MLD = mixedlayerdepth # shorthand
rhoa = 1.22 # Air density
cd = 1.25e-3 # Kara et al. 2007
windstress = windspeed*windspeed * cd * rhoa
K = MLD * stabilityfunction(depth/MLD) * 0.4 * G(depth/MLD) * windstress + (depth/MLD)*background_diffusivity
K[depth>=MLD] = background_diffusivity
return K
[docs]
def verticaldiffusivity_stepfunction(depth, MLD=20,
k_above=.1, k_below=.02):
''' eddy diffusivity with discontinuity for testing of mixing scheme'''
depth = np.abs(depth) # Making sure depth is positive value
K = k_above*np.ones(depth.shape)
K[depth>MLD] = k_below
return K
[docs]
def plot_stokes_profile(profiles, view=['vertical', 'birdseye', 'u', 'v'], filename=None):
'''Plot vertical profile of Stokes drift
Args:
list of dictionary with:
u, v: components of Stokes drift vector
z: depth in meters, 0 at surface and negative below (e.g. -5 = 5m depth)
kwargs: forwarded to plot method
view:
- 'vertical': magnitude versus depth
- 'birdseye': viewed from above
- or list of both above with one axis for each case (default)
'''
if len(view)>2:
fig, axs = plt.subplots(2, 2, figsize=(12,12))
axs = axs.ravel()
else:
fig, axs = plt.subplots(1, len(view))
for vi, ax in zip(view, axs):
for p in profiles:
if 'kwargs' in p:
kwargs = p['kwargs']
else:
kwargs=None
u = p['u']
v = p['v']
z = p['z']
if vi == 'vertical':
speed = np.sqrt(u**2 + v**2)
ax.plot(speed, -z, **kwargs)
elif vi == 'birdseye':
ax.plot(u, v, **kwargs)
elif vi == 'u':
ax.plot(u, -z, **kwargs)
elif vi == 'v':
ax.plot(v, -z, **kwargs)
if vi == 'vertical':
ax.invert_yaxis()
ax.set_xlabel('Speed [m/s]')
ax.set_ylabel('Depth [m]')
ax.set_ylim(ax.get_ylim()[0], 0)
elif vi == 'birdseye':
ax.set_xlabel('u [m/s]')
ax.set_ylabel('v [m/s]')
ax.set_aspect('equal')
xlim = np.array(ax.get_xlim())
ylim = np.array(ax.get_ylim())
m = np.maximum(np.abs(xlim).max(), np.abs(ylim).max())
ax.set_xlim(-m, m)
ax.set_ylim(-m, m)
if vi == 'u':
ax.invert_yaxis()
ax.set_xlabel('U-component [m/s]')
ax.set_ylabel('Depth [m]')
ax.set_ylim(ax.get_ylim()[0], 0)
if vi == 'v':
ax.invert_yaxis()
ax.set_xlabel('V-component [m/s]')
ax.set_ylabel('Depth [m]')
ax.set_ylim(ax.get_ylim()[0], 0)
ax.legend()
if filename is None:
plt.show()
else:
plt.savefig(filename)
[docs]
def stokes_transport_monochromatic(mean_wave_period, significant_wave_height):
mean_wave_frequency = 2.*np.pi/mean_wave_period
return mean_wave_frequency * np.power(significant_wave_height, 2) / 16
[docs]
def stokes_drift_profile_monochromatic(stokes_u_surface, stokes_v_surface,
significant_wave_height, mean_wave_period, z):
"""
Vertical Stokes drift profile assuming a single monochromatic wave
Breivik, O., Janssen, P., Bidlot, J., 2014. Approximate stokes drift profiles in deep water.
J. Phys. Oceanogr. 44, 2433-2445. doi:10.1175/JPO-D-14-0020.1.
"""
stokes_surface_speed = np.sqrt(stokes_u_surface**2 +
stokes_v_surface**2)
km = stokes_surface_speed / (
2*stokes_transport_monochromatic(mean_wave_period, significant_wave_height))
stokes_speed = stokes_surface_speed*np.exp(2*km*z)
zeromask = stokes_surface_speed == 0
stokes_u = stokes_speed*stokes_u_surface/stokes_surface_speed
stokes_v = stokes_speed*stokes_v_surface/stokes_surface_speed
stokes_u[zeromask] = 0
stokes_v[zeromask] = 0
return stokes_u, stokes_v, stokes_speed
[docs]
def stokes_drift_profile_exponential(stokes_u_surface, stokes_v_surface,
significant_wave_height, mean_wave_period, z):
"""
Breivik, O., Janssen, P., Bidlot, J., 2014. Approximate stokes drift profiles in deep water.
J. Phys. Oceanogr. 44, 2433-2445. doi:10.1175/JPO-D-14-0020.1.
"""
stokes_surface_speed = np.sqrt(stokes_u_surface**2 +
stokes_v_surface**2)
km = stokes_surface_speed / (
2*stokes_transport_monochromatic(mean_wave_period, significant_wave_height))
ke = km/3
stokes_speed = stokes_surface_speed*np.exp(2*ke*z)/(1-8*ke*z)
zeromask = stokes_surface_speed == 0
stokes_u = stokes_speed*stokes_u_surface/stokes_surface_speed
stokes_v = stokes_speed*stokes_v_surface/stokes_surface_speed
stokes_u[zeromask] = 0
stokes_v[zeromask] = 0
return stokes_u, stokes_v, stokes_speed
[docs]
def stokes_drift_profile_phillips(stokes_u_surface, stokes_v_surface,
significant_wave_height, mean_wave_period, z):
"""
Calculate vertical Stokes drift profile from
Breivik et al. 2016, A Stokes drift approximation based on the Phillips spectrum, Ocean Mod. 100
"""
alpha = 0.0083
stokes_surface_speed = np.sqrt(stokes_u_surface**2 +
stokes_v_surface**2)
beta = 1
km = stokes_surface_speed * (1-2*beta/3)/ (
2*stokes_transport_monochromatic(mean_wave_period, significant_wave_height))
stokes_speed = stokes_surface_speed*(np.exp(2*km*z) -
beta*np.sqrt(2*np.pi*km*np.abs(z))*sp.special.erfc(np.sqrt(2*km*np.abs(z))))
zeromask = stokes_surface_speed == 0
stokes_u = stokes_speed*stokes_u_surface/stokes_surface_speed
stokes_v = stokes_speed*stokes_v_surface/stokes_surface_speed
stokes_u[zeromask] = 0
stokes_v[zeromask] = 0
return stokes_u, stokes_v, stokes_speed
[docs]
def stokes_drift_profile_windsea_swell(stokes_u_surface, stokes_v_surface,
swell_mean_direction_to, swell_mean_period, swell_height,
wind_sea_mean_direction_to, wind_sea_mean_period, wind_sea_height, z):
"""
Calculate vertical Stokes drift profile from
Breivik, O., and K. H. Christensen, 2020: A Combined Stokes Drift Profile under Swell and Wind Sea.
J. Phys. Oceanogr., 50, 2819-2833, https://doi.org/10.1175/JPO-D-20-0087.1.
"""
# NB / TODO: assuming here that u is east and v is north
# Calculate swell Stokes component
th_ws_N = np.cos(np.radians(wind_sea_mean_direction_to)) # unit vector
th_ws_E = np.sin(np.radians(wind_sea_mean_direction_to)) # unit vector
th_sw_N = np.cos(np.radians(swell_mean_direction_to)) # unit vector
th_sw_E = np.sin(np.radians(swell_mean_direction_to)) # unit vector
stokes_swell_surface_speed = (stokes_u_surface*th_ws_N - stokes_v_surface*th_ws_E) / \
(th_sw_E*th_ws_N - th_sw_N*th_ws_E)
stokes_swell_surface_u = stokes_swell_surface_speed*th_sw_E
stokes_swell_surface_v = stokes_swell_surface_speed*th_sw_N
stokes_swell_u, stokes_swell_v, stokes_swell_speed = stokes_drift_profile_monochromatic(
stokes_swell_surface_u, stokes_swell_surface_v,
swell_height, swell_mean_period, z)
# Calculate wind Stokes component, with constraint that
# wind and swell Stokes at surface sums to total
stokes_wind_surface_u = stokes_u_surface - stokes_swell_surface_u
stokes_wind_surface_v = stokes_v_surface - stokes_swell_surface_v
stokes_wind_u, stokes_wind_v, stokes_wind_speed = stokes_drift_profile_phillips(
stokes_wind_surface_u, stokes_wind_surface_v, wind_sea_height, wind_sea_mean_period, z)
stokes_u = stokes_swell_u + stokes_wind_u
stokes_v = stokes_swell_v + stokes_wind_v
stokes_speed = np.sqrt(stokes_u**2+stokes_v**2)
return stokes_u, stokes_v, stokes_speed
[docs]
def ftle(X, Y, delta, duration):
"""Calculate Finite Time Lyapunov Exponents"""
# From Johannes Rohrs
nx = X.shape[0]
ny = X.shape[1]
J = np.empty([nx,ny,2,2], np.float32)
FTLE = np.empty([nx,ny], np.float32)
# gradient
dx = np.gradient(X)
dy = np.gradient(Y)
# Jacobian
J[:,:,0,0] = dx[0] / (2*delta)
J[:,:,1,0] = dy[0] / (2*delta)
J[:,:,0,1] = dx[1] / (2*delta)
J[:,:,1,1] = dy[1] / (2*delta)
for i in range(0,nx):
for j in range(0,ny):
# Green-Cauchy tensor
D = np.dot(np.transpose(J[i,j]), J[i,j])
# its largest eigenvalue
lamda = np.linalg.eigvals(D)
FTLE[i,j] = np.log(np.sqrt(max(lamda)))/np.abs(duration)
return FTLE
__stokes_coefficients__ = None
[docs]
def wave_stokes_drift_parameterised(wind, fetch):
"""
Parameterise stokes drift based on pre calculated tables and fetch.
"""
global __stokes_coefficients__
Wf = {}
Wf['5000'] = (0.0173,0.0160,0.0152,0.0145,0.0139,0.0135,
0.0132,0.0129,0.0126,0.0124,0.0122,0.0121,
0.0119,0.0118,0.0117,0.0116,0.0114,0.0113,
0.0112,0.0112,0.0111,0.0110,0.0109,0.0109,
0.0108,0.0107,0.0106,0.0106,0.0106,0.0105)
Wf['25000'] = (0.0173,0.0197,0.0201,0.0185,0.0181,0.0176,
0.0171,0.0167,0.0164,0.0160,0.0158,0.0155,
0.0153,0.0151,0.0149,0.0147,0.0146,0.0144,
0.0143,0.0142,0.0140,0.0139,0.0138,0.0137,
0.0136,0.0135,0.0135,0.0134,0.0133,0.0132)
Wf['50000'] = (0.0173,0.0197,0.0210,0.0216,0.0201,0.0194,
0.0190,0.0186,0.0183,0.0179,0.0176,0.0173,
0.0171,0.0168,0.0166,0.0164,0.0162,0.0160,
0.0159,0.0157,0.0156,0.0155,0.0153,0.0152,
0.0151,0.0150,0.0149,0.0148,0.0147,0.0146)
n = {'5000': 3, '25000':6, '50000': 6} # Polynom order
if __stokes_coefficients__ is None:
c = {}
for f in ['5000', '25000', '50000']:
c[f] = np.polyfit(
range(len(Wf[f])), Wf[f], n[f])
__stokes_coefficients__ = c
windspeed = np.sqrt(wind[0]**2 + wind[1]**2)
windspeed[windspeed>30] = 30
wf = np.polyval(__stokes_coefficients__[fetch], windspeed)
stokes_drift_x_velocity = wind[0]*wf
stokes_drift_y_velocity = wind[1]*wf
return stokes_drift_x_velocity, stokes_drift_y_velocity
__stokes_hs_coefficients__ = None
[docs]
def wave_significant_height_parameterised(wind, fetch):
"""
Parameterise significant wave height based on pre calculated tables and fetch.
"""
global __stokes_hs_coefficients__
Sw = {}
Sw['5000'] = (0.030,0.077,0.124,0.170,0.216,0.263,
0.311,0.360,0.409,0.459,0.509,0.560,
0.612,0.664,0.716,0.771,0.823,0.876,
0.932,0.987,1.041,1.095,1.152,1.210,
1.265,1.319,1.375,1.434,1.494,1.552)
Sw['25000'] = (0.030,0.122,0.251,0.336,0.442,0.546,
0.650,0.753,0.856,0.959,1.063,1.168,
1.273,1.379,1.486,1.593,1.702,1.811,
1.920,2.030,2.142,2.254,2.366,2.478,
2.592,2.707,2.822,2.936,3.051,3.166)
Sw['50000'] = (0.030,0.122,0.274,0.474,0.591,0.724,
0.873,1.021,1.168,1.314,1.460,1.606,
1.752,1.898,2.045,2.192,2.340,2.489,
2.639,2.789,2.940,3.092,3.244,3.397,
3.551,3.706,3.862,4.017,4.173,4.330)
if __stokes_hs_coefficients__ is None:
c = {}
for f in ['5000', '25000', '50000']:
c[f] = np.polyfit(
range(len(Sw[f])), Sw[f], 1)
__stokes_hs_coefficients__ = c
windspeed = np.sqrt(wind[0]**2 + wind[1]**2)
windspeed[windspeed>30] = 30
wave_significant_height = np.polyval(
__stokes_hs_coefficients__[fetch], windspeed)
return wave_significant_height
[docs]
class PhysicsMethods:
"""Physics methods to be inherited by OpenDriftSimulation class"""
[docs]
@staticmethod
def sea_water_density(T=10., S=35.):
'''The function gives the density of seawater at one atmosphere
pressure as given in :
N.P. Fofonoff and R.C. Millard Jr.,1983,
Unesco technical papers in marine science no. 44.
S = Salinity in promille of the seawater
T = Temperature of the seawater in degrees Celsius
'''
if np.atleast_1d(T).max() > 100:
raise ValueError('Temperature should be in celcius, but is > 100')
R4 = 4.8314E-04
DR350 = 28.106331
# Pure water density at atmospheric pressure
# Bigg P.H. (1967) BR. J. Applied Physics pp.:521-537
R1 = ((((6.536332E-09 * T - 1.120083E-06) * T + 1.001685E-04) *
T - 9.095290E-03) * T + 6.793952E-02) * T - 28.263737
# Seawater density at atmospheric pressure
# coefficients involving salinity :
R2 = (((5.3875E-09 * T - 8.2467E-07) * T + 7.6438E-05) *
T - 4.0899E-03) * T + 8.24493E-01
R3 = (-1.6546E-06*T+1.0227E-04)*T-5.72466E-03
# International one-atmosphere equation of state of seawater :
SIG = R1 + (R4*S + R3*np.sqrt(S) + R2)*S
Dens0 = SIG + DR350 + 1000.
return Dens0
[docs]
def advect_ocean_current(self, factor=1):
cdf = self.elements.current_drift_factor
cdfmin = cdf.min()
cdfmax = cdf.max()
if cdfmin != 1 or cdfmax != 1:
if cdfmin == cdfmax:
logger.debug('Using currrent drift factor of %s' % cdf)
else:
logger.debug('Using currrent drift factor between %s and %s'
% (cdfmin, cdfmax))
factor = factor*cdf
# Runge-Kutta scheme
if self.get_config('drift:advection_scheme')[0:11] == 'runge-kutta':
x_vel = self.environment.x_sea_water_velocity
y_vel = self.environment.y_sea_water_velocity
# Find midpoint
az = np.degrees(np.arctan2(x_vel, y_vel))
speed = np.sqrt(x_vel*x_vel + y_vel*y_vel)
dist = speed*self.time_step.total_seconds()*.5
geod = pyproj.Geod(ellps='WGS84')
mid_lon, mid_lat, dummy = geod.fwd(self.elements.lon,
self.elements.lat,
az, dist, radians=False)
# Find current at midpoint, a half timestep later
logger.debug('Runge-kutta, fetching half time-step later...')
mid_env, profiles, missing = self.env.get_environment(
['x_sea_water_velocity', 'y_sea_water_velocity'],
self.time + self.time_step/2,
mid_lon, mid_lat, self.elements.z, profiles=None)
if self.get_config('drift:advection_scheme') == 'runge-kutta4':
logger.debug('Runge-kutta 4th order...')
x_vel2 = mid_env['x_sea_water_velocity']
y_vel2 = mid_env['y_sea_water_velocity']
az2 = np.degrees(np.arctan2(x_vel2, y_vel2))
speed2 = np.sqrt(x_vel2*x_vel2 + y_vel2*y_vel2)
dist2 = speed2*self.time_step.total_seconds()*.5
lon2, lat2, dummy = \
geod.fwd(self.elements.lon,
self.elements.lat,
az2, dist2, radians=False)
env2, profiles, missing = self.env.get_environment(
['x_sea_water_velocity', 'y_sea_water_velocity'],
self.time + self.time_step/2,
lon2, lat2, self.elements.z, profiles=None)
# Third step
x_vel3 = env2['x_sea_water_velocity']
y_vel3 = env2['y_sea_water_velocity']
az3 = np.degrees(np.arctan2(x_vel3, y_vel3))
speed3 = np.sqrt(x_vel3*x_vel3 + y_vel3*y_vel3)
dist3 = speed3*self.time_step.total_seconds()*.5
lon3, lat3, dummy = \
geod.fwd(self.elements.lon,
self.elements.lat,
az3, dist3, radians=False)
env3, profiles, missing = self.env.get_environment(
['x_sea_water_velocity', 'y_sea_water_velocity'],
self.time + self.time_step,
lon3, lat3, self.elements.z, profiles=None)
# Fourth step
x_vel4 = env3['x_sea_water_velocity']
y_vel4 = env3['y_sea_water_velocity']
u4 = (x_vel + 2*x_vel2 + 2* x_vel3 + x_vel4)/6.0
v4 = (y_vel + 2*y_vel2 + 2* y_vel3 + y_vel4)/6.0
# Move particles using runge-kutta4 velocity
self.update_positions(u4*factor, v4*factor)
else:
# Move particles using runge-kutta velocity
self.update_positions(
factor*mid_env['x_sea_water_velocity'],
factor*mid_env['y_sea_water_velocity'])
elif self.get_config('drift:advection_scheme') == 'euler':
# Euler scheme
self.update_positions(
factor*self.environment.x_sea_water_velocity,
factor*self.environment.y_sea_water_velocity)
else:
raise ValueError('Drift scheme not recognised: ' +
self.get_config('drift:advection_scheme'))
[docs]
def advect_with_sea_ice(self, factor=1):
if hasattr(self.environment, 'sea_ice_x_velocity'):
self.update_positions(
factor*self.environment.sea_ice_x_velocity,
factor*self.environment.sea_ice_y_velocity)
else:
if not hasattr(self.environment, 'x_sea_water_velocity'):
logger.info('No sea ice velocity available')
return
# Sea ice velocity, rule-of-thumb from Nordam,
# doi:10.1016/j.marpolbul.2019.01.019
ice_velocity_x = self.environment.x_sea_water_velocity + \
0.015*self.environment.x_wind
ice_velocity_y = self.environment.y_sea_water_velocity + \
0.015*self.environment.y_wind
self.update_positions(
factor*ice_velocity_x,
factor*ice_velocity_y)
[docs]
def advect_wind(self, factor=1):
# Elements at/near ocean surface (z>wind_drift_depth) are advected with given percentage
# of wind speed. NB: Only basic Euler scheme is implemented
# Make copy to prevent outside value to be modified
wind_drift_factor = self.elements.wind_drift_factor.copy()
# Convert wind_drift_factor to array
if len(np.atleast_1d(wind_drift_factor)) == 1:
wind_drift_factor = wind_drift_factor*np.ones(len(self.elements))
# Convert z to array
if not hasattr(self.elements, 'z'):
z = np.zeros(len(self.elements)) # Assumed on surface, if no z
else:
z = self.elements.z
if len(np.atleast_1d(z)) == 1:
z = z*np.ones(len(self.elements))
try:
wind_drift_depth = self.get_config('drift:wind_drift_depth')
except:
wind_drift_depth = 0
if wind_drift_depth == 0:
surface_only = True
else:
wind_drift_depth = np.abs(wind_drift_depth)*np.ones(len(self.elements))
surface_only = False
surface = self.elements.z >= -wind_drift_depth
if surface.sum() == 0:
if surface_only is True:
logger.debug('All elements are below surface, no wind-induced shear drift')
else:
logger.debug('All elements are below %fm, no wind-induced shear drift' % wind_drift_depth[0])
return
wdf = wind_drift_factor.copy()
wdf_air = wdf.copy()
if surface_only is False:
# linear decrease from surface down to wind_drift_depth
wdf = wdf*(wind_drift_depth+self.elements.z)/wind_drift_depth
# Resetting wdf for elements in air
wdf[self.elements.z>0] = wdf_air[self.elements.z>0]
wdf[~surface] = 0.0
wdfmin = wdf[surface].min()
wdfmax = wdf[surface].max()
x_wind = self.environment.x_wind.copy()
y_wind = self.environment.y_wind.copy()
try:
if self.get_config('drift:relative_wind') is True:
# Use wind relative to (subtracted) ocean current
x_wind = x_wind - self.environment.x_sea_water_velocity
y_wind = y_wind - self.environment.y_sea_water_velocity
except:
pass
speed = np.sqrt(x_wind[surface]*x_wind[surface] + y_wind[surface]*y_wind[surface])
if wdf[surface].max() == 0:
logger.debug('Wind drift factor is 0')
return
if speed.max() == 0:
logger.debug('No wind for wind-sheared ocean drift')
return
speed = speed*wdf[surface]
if surface_only is True:
logger.debug('Advecting %s of %i elements at surface with '
'wind-sheared ocean current (%f m/s - %f m/s)'
% (np.sum(surface), self.num_elements_active(),
speed.min(), speed.max()))
else:
logger.debug('Advecting %s of %i elements above %.3fm with '
'wind-sheared ocean current (%f m/s - %f m/s)'
% (np.sum(surface), self.num_elements_active(),
wind_drift_depth[0],
speed.min(), speed.max()))
self.update_positions(x_wind*wdf*factor, y_wind*wdf*factor)
[docs]
def stokes_drift(self, factor=1):
if self.get_config('drift:stokes_drift') is False:
logger.debug('Stokes drift not activated')
return
if np.max(np.array(
self.environment.sea_surface_wave_stokes_drift_x_velocity+
self.environment.sea_surface_wave_stokes_drift_y_velocity)) \
== 0:
logger.debug('No Stokes drift velocity available')
return
wave_height = self.significant_wave_height()
wave_period = self.wave_period()
if np.max(np.array(wave_height)) == 0:
logger.debug('Stokes drift is available, but not Hs: using Hs=1 for Stokes profile')
wave_height = 1
if np.max(np.array(wave_period)) == 0:
logger.debug('Stokes drift is available, but not Tp: using Tp=8 for Stokes profile')
wave_period = 8
stokes_profile = self.get_config('drift:stokes_drift_profile', default='monochromatic')
if stokes_profile == 'monochromatic':
stokes_u, stokes_v, s = stokes_drift_profile_monochromatic(
self.environment.sea_surface_wave_stokes_drift_x_velocity,
self.environment.sea_surface_wave_stokes_drift_y_velocity,
wave_height, wave_period, self.elements.z)
if stokes_profile == 'exponential':
stokes_u, stokes_v, s = stokes_drift_profile_exponential(
self.environment.sea_surface_wave_stokes_drift_x_velocity,
self.environment.sea_surface_wave_stokes_drift_y_velocity,
wave_height, wave_period, self.elements.z)
if stokes_profile == 'Phillips':
stokes_u, stokes_v, s = stokes_drift_profile_phillips(
self.environment.sea_surface_wave_stokes_drift_x_velocity,
self.environment.sea_surface_wave_stokes_drift_y_velocity,
wave_height, wave_period, self.elements.z)
elif stokes_profile == 'windsea_swell':
stokes_u, stokes_v, s = stokes_drift_profile_windsea_swell(
self.environment.sea_surface_wave_stokes_drift_x_velocity,
self.environment.sea_surface_wave_stokes_drift_y_velocity,
swell_mean_direction_to = self.environment.sea_surface_swell_wave_to_direction,
swell_mean_period = self.environment.sea_surface_swell_wave_peak_period_from_variance_spectral_density,
swell_height = self.environment.sea_surface_swell_wave_significant_height,
wind_sea_mean_direction_to = self.environment.sea_surface_wind_wave_to_direction,
wind_sea_mean_period = self.environment.sea_surface_wind_wave_mean_period,
wind_sea_height = self.environment.sea_surface_wind_wave_significant_height,
z=self.elements.z)
self.update_positions(stokes_u*factor, stokes_v*factor)
if s.min() == s.max():
logger.debug('Advecting with Stokes drift (%s m/s)' % s.min())
else:
logger.debug('Advecting with Stokes drift (%s to %s m/s)' %
(s.min(), s.max()))
[docs]
def resurface_elements(self, minimum_depth):
# Keep surfacing elements in water column as default,
# i.e. no formation of surface slick
surface = np.where(self.elements.z >= 0)[0]
self.elements.z[surface] = minimum_depth
[docs]
def calculate_missing_environment_variables(self):
# Missing significant wave height
if hasattr(self.environment,
'sea_surface_wave_significant_height') and \
self.environment.sea_surface_wave_significant_height.max() == 0:
Hs = self.significant_wave_height()
logger.debug('Calculating Hs from wind, min: %f, mean: %f, max: %f' %
(Hs.min(), Hs.mean(), Hs.max()))
# Missing wave periode
if hasattr(self.environment,
'sea_surface_wave_mean_period_from_variance_spectral_density_second_frequency_moment') and \
self.environment.sea_surface_wave_mean_period_from_variance_spectral_density_second_frequency_moment.max() == 0:
wave_period = self.wave_period()
logger.debug('Calculating wave period from wind, min: %f, mean: %f, max: %f' %
(wave_period.min(), wave_period.mean(), wave_period.max()))
[docs]
def wind_speed(self):
return np.sqrt(self.environment.x_wind**2 +
self.environment.y_wind**2)
[docs]
def current_speed(self):
return np.sqrt(self.environment.x_sea_water_velocity**2 +
self.environment.y_sea_water_velocity**2)
[docs]
def significant_wave_height(self):
# Significant wave height, parameterise from wind if not available
if hasattr(self.environment,
'sea_surface_wave_significant_height') and \
self.environment.sea_surface_wave_significant_height.max() > 0:
Hs = self.environment.sea_surface_wave_significant_height
else:
## Neumann and Pierson, 1966
#return 0.2*np.power(self.wind_speed(), 2)/9.81
# WMO 1998
Hs = 0.0246*np.power(self.wind_speed(), 2)
self.environment.sea_surface_wave_significant_height = Hs
return Hs
[docs]
def _wave_frequency(self):
# Note: this is angular frequency, 2*pi*fp
# Pierson-Moskowitz if period not available from readers
# WMO guide to wave analysis and forecasting pp. 14, WMO (1998)
windspeed = self.wind_speed()
# fallback value if no wind speed or Hs to avoid division by zero
omega = 5*np.ones(windspeed.shape)
omega[windspeed>0] = 0.877*9.81/(1.17*windspeed[windspeed>0])
return omega
[docs]
def wave_period(self):
if hasattr(self.environment, 'sea_surface_wave_mean_period_from_variance_spectral_density_second_frequency_moment'
) and self.environment.sea_surface_wave_mean_period_from_variance_spectral_density_second_frequency_moment.max() > 0:
# prefer using Tm02:
T = self.environment.sea_surface_wave_mean_period_from_variance_spectral_density_second_frequency_moment.copy()
logger.debug('Using mean period Tm02 as wave period')
elif hasattr(self.environment, 'sea_surface_wave_period_at_variance_spectral_density_maximum'
) and self.environment.sea_surface_wave_period_at_variance_spectral_density_maximum.max() > 0:
# alternatively use Tp
T = self.environment.sea_surface_wave_period_at_variance_spectral_density_maximum.copy()
logger.debug('Using peak period Tp as wave period')
else:
# calculate Tp from wind speed:
logger.debug('Calculating wave period Tm02 from wind')
T = (2*np.pi)/self._wave_frequency()
self.environment.sea_surface_wave_mean_period_from_variance_spectral_density_second_frequency_moment = T
#print '\n T %s \n' % str(T.mean())
if T.min() == 0:
logger.warning('Zero wave period found - '
'replacing with mean')
T[T==0] = np.mean(T[T>0])
logger.debug(' min: %f, mean: %f, max: %f' % (T.min(), T.mean(), T.max()))
return T
[docs]
def wave_energy(self):
return 9.81*1028*np.power(self.significant_wave_height(), 2)/16
[docs]
def wave_energy_dissipation(self):
# Delvigne and Sweeney
return 0.0034*self.sea_water_density()*9.81 * \
np.power(self.significant_wave_height(), 2)
[docs]
def wave_damping_coefficient(self):
omega = 2*np.pi / self.wave_period()
return (10E-5)*omega * \
np.power(self.wave_energy(), 0.25)
# def sea_water_density(self):
# return 1027 # kg/m3
[docs]
def sea_surface_wave_breaking_fraction(self):
# TODO: We should also have an option here for
# the case when wave height is given, but no wind
f = 0.032*(self.wind_speed() - 5)/self.wave_period()
f[f < 0] = 0
return f
[docs]
def air_density(self):
return 1.225 # Could calculate from temperature
[docs]
def windspeed_from_stress(self):
wind_stress = np.sqrt(
self.environment.surface_downward_x_stress**2 +
self.environment.surface_downward_y_stress**2)
return windspeed_from_stress_polyfit(wind_stress)
[docs]
def solar_elevation(self):
'''Solar elevation at present time and position of active elements.'''
return solar_elevation(self.time, self.elements.lon, self.elements.lat)
[docs]
def wind_drag_coefficient(windspeed):
'''Large and Pond (1981), J. Phys. Oceanog., 11, 324-336.'''
Cd = 0.0012*np.ones(len(windspeed))
Cd[windspeed > 11] = 0.001*(0.49 + 0.065*windspeed[windspeed > 11])
return Cd
[docs]
def windspeed_from_stress_polyfit(wind_stress):
'''Inverting Large and Pond (1981) using polyfit'''
windspeed = np.linspace(0, 30, 30)
rho_air = 1.225
stress = wind_drag_coefficient(windspeed)*rho_air*(windspeed**2)
z = np.polyfit(stress, windspeed, 3)
p = np.poly1d(z)
return p(wind_stress)
[docs]
def solar_declination(time):
'''Solar declination in degrees.'''
try:
day_of_year = time.timetuple().tm_yday
except:
day_of_year = np.asarray([t.timetuple().tm_yday for t in time])
declination = \
np.arcsin(np.deg2rad(-23.44)*
np.cos(np.radians((360.0/365.24)*(day_of_year + 10) +
(360.0/np.pi)*0.0167*
np.sin(np.radians((360.0/365.24)*
(day_of_year - 2)))
)))
return np.rad2deg(declination)
[docs]
def equation_of_time(time):
'''Equation of time in minutes.'''
time = np.atleast_1d(time)
day_of_year = np.asarray([t.timetuple().tm_yday for t in time])
hour = np.asarray([t.hour for t in time])
gamma = 2*np.pi/365.0*(day_of_year - 1. +
(hour - 12.) / 24.)
eqtime = 229.18 * (0.000075 + 0.001868*np.cos(gamma) -
0.032077*np.sin(gamma) -
0.014615*np.cos(2*gamma) - 0.040849*np.sin(2*gamma))
return eqtime
[docs]
def hour_angle(time, longitude):
'''Solar hour angle in degrees.'''
time = np.atleast_1d(time)
time_offset = equation_of_time(time) + 4*longitude
day_minutes = [t.hour*60.0 + t.minute + t.second/60.0 for t in time]
true_solar_time = day_minutes + time_offset
hour_angle = (true_solar_time/4.0) - 180.0 # degrees
return hour_angle
[docs]
def solar_elevation(time, longitude, latitude):
'''Solar elevation in degrees.'''
d_rad = np.deg2rad(solar_declination(time))
h = hour_angle(time, longitude)
solar_elevation = np.rad2deg(np.arcsin(
np.sin(np.deg2rad(latitude))*np.sin(d_rad) +
np.cos(np.deg2rad(latitude))*np.cos(d_rad)*np.cos(np.deg2rad(h))))
return solar_elevation