Work Description

Date: 15 January, 2021

Dataset Title: Mars Dayside Closed Crustal Field Electron Pitch Angle Distributions Data and Ephemeris Info

Dataset Creator: Shane, Alexander

Dataset Contact: adshane@umich.edu

Research Overview

This data set was created with the purpose to study the electron pitch angle distributions on
dayside closed crustal fields at Mars. The studies using this data set were conducted by
Alexander Shane in the Climate and Space Sciences and Engineering Department at the University
of Michigan. This research was supported by the National Aeronautics and Space
Administration (NASA) Grant NNX16AQ04G to the University of Michigan.

Methods

The data was downloaded and filtered using publicly available software located at
https://lasp.colorado.edu/maven/sdc/public/pages/software.html. The time range spanned by the dataset
is from 12/01/2014 - 12/31/2016. Data from the Magnetometer, Solar Wind Electron Analyzer,
and Langmuir Probes and Waves instruments are used.

Filters applied to data:

Altitude between 200 and 1000 kilometers. Above the photoelectron exobase. Not many crustal
fields extend past 1000 km.

Solar zenith angle less than 90 degrees. Ensures dayside observation.

Spacecraft potential between -1 and 3 volts.

Shape parameter (see Xu et al., 2017 for a description) is less than 1 in the towards and
away directions. This implies photoelectrons are streaming and the measurement can be
considered a closed crustal magnetic field

Magnetic field greater than 20 nanotesla. To ensure measurement is crustal and not deeply draped field.

File Inventory

marsDayClosedCrustalFields.pickle - This file contains a single Python dictionary object holding
all of the relevant data.

Definition of Terms and Variables

List of dictionary keys and description:

One dimensional time series:
time - timestamp for each measurement. Unix time (number of seconds since 1970)
altitude - altitude [kilometers]
latitude - geographic latitude [deg]
longitude - geographic east longitude [deg]
localTime - local time [hours], 12 = noon, 0/24 = midnight, 6 = dawn terminator, 18 = dusk terminator
solarZenithAngle - angle between the sun's rays and local vertical [deg]
xMSO - x-coordinate of spacecraft in MSO system [units of Mars radii]
yMSO - y-coordinate of spacecraft in MSO system [units of Mars radii]
zMSO - z-coordinate of spacecraft in MSO system [units of Mars radii]
orbitNumber - Orbit number. MAVEN defines new orbits at periapsis. This orbit number is shifted by +0.5
so that new orbits begin at apoapsis. A full periapsis pass now has the same integer orbit number.
scPotential - spacecraft potential (composite) [volts]
electronDensity - thermal electron density from Langmuir Probes and Waves [cm^-3]
Bx - x-component of the local magnetic field in MSO coordinates [nT]
By - y-component of the local magnetic field in MSO coordinates [nT]
Bz - z-component of the local magnetic field in MSO coordinates [nT]
B - magnetic field magnitude [nT]
magElevAngle - magnetic elevation angle [deg], 0 = locally horizontal, -90 = locally vertical directed
toward planet, +90 = locally vertical directed away from planet

"Grid" variables:
pitchAngle - pitch angle grid for flux array [deg]
energy - energy grid for flux array [eV]

Multi-dimensional time series:
flux - differential number flux of electrons [eV^-1 s^-1 sr^-1 cm^-2], array dims = [time, pitch angle, energy]
fluxError - error in each flux measurement [eV^-1 s^-1 sr^-1 cm^-2], array dims = [time, pitch angle, energy]
shapeParameter - shape parameter as detailed in Xu et al., 2017, array dims = [time, direction]
direction indices = [away, toward, trapped]

Use and Access

To import the data, open Python and enter:
>> import pickle
>> data = pickle.load(open('marsDayClosedCrustalFields.pickle', 'rb'))

To access a specific variable, use the keys given in Definition of Terms and Variables.
>> variable = data[key]
For example to access the altitude array:
>> alt = data['altitude']