Plotting plasma waves with GOES-R MAG hires data

@author: alessandra.pacini

Import packages

import os, datetime
import netCDF4 as nc
from netCDF4 import Dataset
import cftime
import numpy as np
import datetime
import matplotlib
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
from scipy import signal
import requests

Define functions

def j2000_sec_to_datetime( unix_ms ):
    dt0 = datetime.datetime( 2000, 1, 1,12)
    dt = np.array( [ dt0 + datetime.timedelta(seconds=unix_ms[i] ) \
                        for i in np.arange( len( unix_ms ) ) ] )
    return( dt )

def datetime_to_day( dt ):
    n_times = len( dt )
    t_diff = ( dt - dt[0])
    unix = np.array( [ ( (t_diff[i].microseconds \
                            + (t_diff[i].seconds \
                            + t_diff[i].days * 86400.) * 10.**6) / 10.**6 ) \
                        for i in np.arange( n_times ) ] )
    return unix

def timeTicks(x, pos):
    d = datetime.timedelta(seconds=x)
    hours, remainder = divmod(d.seconds, 3600)
    minutes, seconds = divmod(remainder, 60)
    duration_formatted = '{:d}:{:02d}:{:02d}'.format(hours, minutes,seconds)
    return duration_formatted

def format_time_axis(ax):
    locator = mdates.HourLocator(interval=1)
    ax.xaxis.set_major_locator(locator)
    ax.xaxis.set_minor_locator(mdates.HourLocator())
    ax.xaxis.set_major_formatter(mdates.ConciseDateFormatter(locator))

def butter_highpass(cutoff, fs, order):
    nyq = 0.5 * fs
    normal_cutoff = cutoff / nyq
    b, a = signal.butter(order, normal_cutoff, btype='high', analog=False)
    return b, a

def butter_highpass_filter(data,cutoff,fs,order=5):
    b,a = butter_highpass(cutoff,fs,order=order)
    data_filt = signal.lfilter(b,a,data)
    return data_filt

Download a day of GOES-16 10 Hz data

dataurl = 'https://data.ngdc.noaa.gov/platforms/solar-space-observing-satellites/goes/goes16/l2/data/magn-l2-hires'
subdir = '/2022/04/'
filename = "dn_magn-l2-hires_g16_d20220427_v1-0-1.nc"
if not os.path.exists(filename):
    with open(filename, "wb") as f:
        url_path = dataurl+subdir+filename
        print(url_path)
        r = requests.get(url_path)
        print(r)
        f.write(r.content)

Read MAG L2 hires data (in VDH), filtering and creating spectrograms

g16a = nc.Dataset(filename)

g16a.variables.keys()
VDH=g16a.variables['b_vdh'] #reading the B in VDH coordinates

TIME_UNITS = "seconds since 2000-01-01 12:00:00"

time=g16a.variables['time']
time=j2000_sec_to_datetime(time[:])
dt= datetime_to_day(time)
dts = cftime.num2pydate(g16a.variables['time'][:],g16a.variables['time'].units)

fs = 10 #sampling frequncy, Hz, usually 10 Hz for mag
cutoff=0.01 #cut off frequency
N = 1 #filter order
btype = 'high' #high or low pass filter
NFFT = 1024 #len of each fft segment
freqlim=1 # requency limit for plotting
db_min,db_max =-15, 20  #power level for plotting
str_plt, end_plt = 0, 1066 #start and end indexes for plotting, 0 and 1123 for full day

befilteredV=butter_highpass_filter(VDH[:,0], cutoff, fs, order=5)

Plot the original data, filtered data, and spectrogram

f,axs = plt.subplots(2,1,figsize=(8,8),dpi=200)

axs[0].set_title('27/04/2022')
axs[0].plot(dts,VDH[:,0],'b-')
axs[0].set_ylabel('B Field Strength VDH - V [nT]')
axs[0].set_xlim(dts[576000],dts[-1])
format_time_axis(axs[0])

axs[1].plot(dts, befilteredV)
axs[1].set_ylabel("V filtered (nT)")
axs[1].set_ylim([-4,4])
axs[1].set_xlim(dts[576000],dts[-1])
format_time_axis(axs[1])

plt.show()

plt.subplots(1,1,figsize=(8,4),dpi=200)
plt.title('27/04/2022')
cmap =  plt.get_cmap('jet')
f, t, Sxx = signal.spectrogram(befilteredV, fs,
                                noverlap = NFFT / 4,
                                nperseg=NFFT,
                                detrend='linear')
sg_db = 10 * np.log10(Sxx)
plt.pcolormesh(t,f,sg_db, cmap=cmap, vmin=db_min, vmax=db_max)
plt.colorbar(orientation='horizontal',label='Power [dB]')
plt.ylim([0, freqlim])
plt.xlim(57600,86399)
plt.ylabel("Frequency (Hz)")
plt.xlabel("Time")
formatter = matplotlib.ticker.FuncFormatter(timeTicks)
plt.gca().xaxis.set_major_formatter(formatter)
plt.show()

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