Work Description

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Date: 8-February-2023
Author: Geoffrey Jenkins
Title: "MAVEN Accelerometer Derived Densities for the
Aerobraking 2019 and Deep Dip 2 Campaigns"

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Analysis Description:
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In early 2019, the Mars Atmosphere and Volatile Evolution (MAVEN) mission underwent an ~2-month aerobraking campaign, during which time the spacecraft periapsis altitude was lowered from its nominal altitude range of 140-160 km to as low as ~123 km. Excluding spacecraft walk-in/out maneuvers, accelerometer measurements were made along 272 orbits with coverage spanning Ls 340-3°, latitudes ~5-54°S, longitudes 0-360°, and Local Solar Time (LST) ~22-17 hours. In this study, we perform a diagnostic analysis of the full aerobraking data set by fitting 4-harmonic waves to mass densities. We then study the variations of these waves as a function of latitude with an emphasis on those observed previously in Mars’ thermosphere by MAVEN and other missions. Additionally, we utilize data collected during the same time period from the Mars Reconnaissance Orbiter’s Mars Climate Sounder to study the vertical propagation of waves originating from the middle atmosphere. Key results indicate that normalized wave amplitudes decrease with latitude, and this is consistent with the latitudinal structure of a diurnal Kelvin mode. We also observe that waves imprinted from the middle atmosphere show normalized amplitude growth with increasing altitude. A complete summary of data sets, analysis methodology, and scientific results is given. The purpose of this study is to add to the body of knowledge surrounding Martian atmospheric wave features and to provide further constraints for future numerical modeling and subsequent tidal mode identification.

Data Methodology:
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Measurements made by the MAVEN spacecraft accelerometer (ACC) instrument provide per-orbit, density profiles set on an irregular (i.e., uneven interval) altitude framework. Our analysis focuses only on those orbits comprising the 2019 aerobraking (AB2019) campaign, and the deep dip 2 (DD2) campaign – walk-in/out orbits not included. Using linear interpolation, we convert profiles to a regular (i.e., even interval) altitude framework and adjust for longitude, latitude, and LST. Next, using a least squares computation, we calculate at-altitude scale heights and hydrostatic mass densities, each with associated sigma values. We then utilize the hydrostatic relationship to calculate temperature values followed by the ideal gas law to calculate pressure values. All of this provides us with MAVEN density profiles on regular altitude intervals along with associate location parameters (longitude, latitude, LST), scale heights, mass densities, temperatures, and pressures – we refer to these as “constant altitude” profiles. This process enables us to analyze density variability as a function of constant altitude.

For our “constant pressure” profiles, we first determine the average value of pressure - calculated on the regular altitude framework – for each of three altitudes (140, 145, and 150 km) across all orbits of the full AB2019/DD2 campaign(s). We then return to the original MAVEN-ACC density profiles and while remaining on the irregular altitude framework, again calculate scale heights, mass densities, temperatures, and pressures. From these new profiles, we then isolate location, altitude, and density parameters closest to the aforementioned average value of pressure from the regular altitude framework. This allows us the analyze altitude variability as a function of constant pressure.

To develop our wave fitting parameters – i.e., to fit waves to these data - we utilize a linear combination of harmonic functions to produce a single composite function which enables us to quantify variability of a given input with longitude. It is a wave-k model calculated to the fourth term (k=4), meaning parameters for four harmonics are calculated. The parameter values include: mean amplitude, raw harmonic amplitude above the mean, normalized (to the mean) harmonic amplitude above the mean, and harmonic phase angle (defined here as the location of the first wave peak east of 0 degrees longitude). Identifying dominant harmonics in a given region allows us to study tides observed during these periods, and it provides a means to compare these to tides previously observed by other mission spacecraft.

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Definition of Acronyms:
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-- LST = Local Solar Time
-- Hs = Scale Height
-- Ls = Solar Longitude

Constant Altitude Profiles (AB2019, DD2):
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COLUMNS 01-10 -- 150 km (inbound),
COLUMNS 11-20 -- 145 km (inbound),
COLUMNS 21-30 -- 140 km (inbound),
COLUMNS 31-40 -- 135 km (inbound),

10 parameters each:
-- Orbit
-- Latitude [deg]
-- Longitude [deg]
-- LST [hrs]
-- Density [kg/km**3]
-- Density Sigma [kg/km**3]
-- Hs [km]
-- Hs Sigma [km]
-- Temperature [K]
-- Pressure [Pa]

Constant Pressure Profiles (AB2019):
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COLUMNS 01-10 -- 9.33E-06 Pa (inbound),
COLUMNS 11-20 -- 1.68E-05 Pa (inbound),
COLUMNS 21-30 -- 2.80E-05 Pa (inbound),

10 parameters each:
-- Orbit
-- Latitude [deg]
-- Longitude [deg]
-- LST [hrs]
-- Altitude [km]
-- Density [kg/km**3]
-- Density Sigma [kg/km**3]
-- Hs [km]
-- Hs Sigma [km]
-- Temperature [K]

Constant Pressure Profiles (MCS):
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COLUMNS 01-10 -- 0.49 Pa (inbound),
COLUMNS 11-20 -- 0.26 Pa (inbound),
COLUMNS 21-30 -- 0.14 Pa (inbound),

10 parameters each:
-- LST [hrs]
-- Latitude [deg]
-- Pressure [Pa]
-- Ls [deg]
-- Longitude [E,deg]
-- Altitude above Areoid [km]
-- Areoid Altitude [km]
-- Temperature [K]
-- Temperature Error [K]
-- Pressure Quality Flag

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Analysis Files in Repository Bundle:
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README.txt
MAVEN_DD2_ConstantAltitude_0-20S.csv
MAVEN_AB2019_ConstantAltitude_0-20S.csv
MAVEN_AB2019_ConstantAltitude_20-40S.csv
MAVEN_AB2019_ConstantAltitude_40-60S.csv
MAVEN_AB2019_ConstantPressure_0-20S.csv
MAVEN_AB2019_ConstantPressure_20-40S.csv
MAVEN_AB2019_ConstantPressure_40-60S.csv
MCS_Dayside_ConstantPressure_0-20S.csv
MCS_Dayside_ConstantPressure_20-40S.csv
MCS_Dayside_ConstantPressure_40-60S.csv

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Citations for Relevant Data Sets:
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-- (MAVEN-ACC)
Tolson, R., & Lugo, R. (2022). MAVEN Accelerometer Data (Version 2,
Revision 1) [Data Set]. NASA Planetary Data System.
https://atmos.nmsu.edu/PDS/data/PDS4/MAVEN/acc bundle/l3/

-- (MRO-MCS)
McCleese, D., & Schofield, J. (2006). MRO MARS CLIMATE SOUNDER LEVEL
4 RDR V1.0 [Data Set] [MRO-M-MCS-4-RDR-V1.0]. NASA Planetary Data
System. https://doi.org/10.17189/p73k-xy37

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