DMSP Ion Drifts at High Latitudes

Plasma motion measured by the Ion Velocity Meter (IVM) onboard DMSP is natively presented in spacecraft coordinates and does not include any transformations of those directions into published coordinate systems. We present an example on how to plot measured ion drifts at high latitudes using supporting methods in pysatMadrigal.instruments.methods.dmsp().

import datetime as dt
import matplotlib.pyplot as plt
import numpy as np
import numpy.ma as ma

import pysat
import pysatMadrigal as pysat_mad

fdate = dt.datetime(2011, 8, 15)
ivm = pysat.Instrument('dmsp', 'ivm', tag='utd', inst_id='f15')

# Smooth ion drifts to only report the most robust of measurements.
ivm.custom_attach(pysat_mad.instruments.methods.dmsp.smooth_ram_drifts,
                  kwargs={'rpa_flag_key': 'rpa_flag_ut'})

# Add unit vectors relating presumed satellite orientation along
# cartesian and polar directions.
ivm.custom_attach(pysat_mad.instruments.methods.dmsp.add_drift_unit_vectors)

# Express ion drifts measured in the satellite frame along the added
# high latitude unit vectors.
ivm.custom_attach(pysat_mad.instruments.methods.dmsp.add_drifts_polar_cap_x_y,
                  kwargs={'rpa_flag_key': 'rpa_flag_ut'})

# Download data if not already on system
if fdate not in ivm.files.files.index:
    ivm.download(fdate, user='first+lastname', password='myname@email.address')

# Load data
ivm.load(date=fdate)

# Plot multiple orbital passes across polar cap
fig = plt.figure()
ax = fig.add_subplot(111, polar=True)
ax.set_rlim(0, 40.)
ax.set_xticks(np.linspace(0, 2. * np.pi - np.pi / 4., 8))
ax.set_xticklabels(['', 9, 12, 15, 18, 21, 24, 3])
ax.set_xlabel('MLT')
ax.set_yticks([10, 20, 30, 40])
ax.set_yticklabels([80, 70, 60, 50])
ax.text(np.deg2rad(-5.), 41, 'MLAT', rotation=-90.)
ax.grid(True)

# Location of spacecraft in relative polar coords for plotting.
theta = ivm['mlt'] * (np.pi / 12.) - np.pi / 2.0
radius = 90.0- np.abs(ivm['mlat'])

# Calculate magnitude of ion drifts for color values
mag = np.sqrt(ivm['ion_vel_pc_x']**2 + ivm['ion_vel_pc_y']**2)

# Make plot of ion drifts
slice_x = ma.masked_where(np.isnan(ivm['ion_vel_pc_x']), ivm['ion_vel_pc_x'])
slice_y = ma.masked_where(np.isnan(ivm['ion_vel_pc_y']), ivm['ion_vel_pc_y'])
vec_plot = ax.quiver(theta, radius, slice_x, slice_y, mag, scale=10000,
                     clim=[0, 1000.])

# Plot drifts without both an RPA and DM measurement in red.
ipartial, = np.where(ivm['partial'])
ax.quiver(theta[ipartial], radius[ipartial], slice_x[ipartial],
          slice_y[ipartial], color='r', scale=10000)

# Title, colorbar, and save.
plt.title('DMSP Ion Drifts')
label = ''.join(['(', ivm.meta['ion_vel_pc_x', ivm.meta.labels.units], ')'])
label = ''.join(['2D Horizontal Ion Drift ', label])
plt.colorbar(vec_plot, label=label)
plt.tight_layout()
plt.savefig('ex_dmsp_methods.png')
plt.show()