Apr 19, 2023 1

The Variability of the Martian Thermosphere-Ionosphere

Stephen W. BougherJared M. Bell

(U. of Michigan)

Jim Murphy (NMSU)

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Martian Atmospheric Regions and Processes

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Recent Mars Thermosphere-Ionosphere Datasets (Solar Cycle, Inter-annual, Seasonal, Diurnal)

MGS and Odyssey Accelerometer AB measurements (densities, T): Latitudinal density gradients and inferred temperatures (Keating et al.,

2002). Diurnal variations over ~100-170 km (Withers et al; 2003). Winter polar warming (100-130 km) driven by inter-hemispheric

circulation near solstices (Keating et al;, 2003; Bougher et al., 2005). MGS longitude variations as a function of season, latitude, SLT, and

height in the thermosphere (Forbes et al., 2002; Withers et al., 2003).

MGS/ER derived neutral densities from 170-240 km. Latitudinal density gradients on the nightside near crustal magnetic

field features (Lillis et al., 2005); seasonal variations observed.

MGS/RS electron density profiles (~100-200 km) at SZA >75º: High N. latitudes (LAT> 65N; SLT ~ 3); High S. latitudes (LAT> 65S; SLT ~ 3); Longitude variations obs. in F1-peak heights over 2-Martian years (Bougher et al., 2004)..

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Solar Cycle and Seasonal Sampling of the Martian Thermosphere

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Martian Upper Atmosphere Sampling fromMGS and Odyssey Accelerometers

MGS Accelerometer data over Phase 1 (7-months) and Phase 2 (4.5 months) aerobraking. Measured densities (inferred scale heights and temperatures) over 110-160 km. Nearly ~1200 vertical structures. -- Phase 1 : Ls = 180-300; F10.7-cm = 70-90-- Phase 2: Ls = 30-95; F10.7-cm = 130-150

Odyssey Accelerometer data over 5-months of aerobraking. Measured densities (inferred scale heights and temperatures) over 95-170 km. Nearly ~600 vertical structures . -- Total : Ls = 265-310; F10.7-cm = 175 -- Following summer 2001 dust storm season

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Accelerometer Densities :

RED = MGS2 (D)GRN = MGS2 (N)

BLK = MGS1BLU = ODY (D)GRY = ODY(N)

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Accelerometer Temperatures :

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Summer

Winter

Subsidence

Adiabatic Heating

N

S

Meridional Flow

From Summer H.

To Winter H.

Schematic of Likely MarsWinter Polar Warming Process

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Solar Cycle and Seasonal Variation of Exospheric Temperatures (No Coupling)

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Longitudinal Variability of Thermosphere from MGS-ACC Data (Outbound: 10-20ºN)

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Longitudinal Variability of Thermosphere from MGS-ACC Data

(Normalized Wave Amplitudes at 130 km)

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Longitudinal Variability of Ionosphere from MGS-RS Data:

Height of Primary Electron Density Peak

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Mars Upper Atmosphere Modeling Teams

MGCM-MTGCM (Bougher et al., 01; 04; 05): Coupled/separate models spanning 0-300 km NCAR (TGCM) and NASA Ames (MGCM) heritage. Benchmark (validation) for “whole atmosphere” models. LMD-GCM (Angelat-i-Coll et al; 05; Gonzalez-Galindo et al., 05; ) Ground to exosphere code (0-240 km) LMD/AOPP MGCM heritage; LMD/IAA teaming. ASPEN (Crowley et al. 04; 05) Troposphere to thermosphere (14-300 km) NCAR TIEGCM heritage MM3 (Moudden et al., 04; 05) Ground to thermosphere code (0-160 km) Canadian MET model heritage.

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MTGCM Input Parameters, Fields, and Domain

Domain : ~70-300 km; 33-levels; 5x5 ° resolution Major Fields and Species : T, U, V, W, CO2, CO, O, N2

Minor Species : O2, He, Ar, NO, N(4S)

Ions (PCE) : CO2+, O2+, O+, NO+, CO+, N2+ (<180 km)

Time step : 150 sec Homopause Kzz = 1-2x 107 cm2/sec (at ~125 km) Prescribed Heating efficiencies : EUV and FUV (~22%) Fast NLTE 15-µm cooling and IR heating formulations

from Spanish 1-D NLTE code (Miguel Lopez-Valverde) Simplified ion-neutral chemistry (Fox and Sung, 2001) Empirical Ti and Te from Viking.

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MGCM-MTGCM Simulations: Formulation, Parameters and Inputs:

Separate but coupled NASA Ames MGCM (0-90 km) and NCAR/Michigan MTGCM (70-300 km) codes, linked across an interface at 1.32-microbars on 5x5º grid. Detailed coupling at every grid point and time-step.

Fields passed upward at interface (T, U, V, Z) on 2-min time-step intervals. No downward coupling enabled.

MGCM-MTGCM captures upward propagating migrating and non-migrating tidal oscillations, as well as in-situ driven solar EUV-UV migrating tides in the thermosphere.

Seasonal Simulations: --Odyssey: Ls = 270; F10.7 = 175; τ ~ 1.0 (TES-YR2)-- MGS2 : Ls = 90 ; F10.7 = 130; τ ~ 0.4 (TES-YR1) Conrath parameter scheme used to specify vertical dust distributions (mixed moderately to ~40-50 km). Highly sensitive to vertical dust (Bell et al. 2004).

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Seasonal Variability

Mars thermosphere-ionosphere variations throughout the Mars year are driven by:

Seasonal changes in lower atmosphere dust distributions (both horizontal and vertical);

Seasonal changes in migrating and non-migrating tidal propagation from <100 km;

Solar insolation changes owing to Mars eccentricity (aphelion to perihelion).

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TES Dust Distributions (Ls = 90): MGS2Year #1 (1999-2000)

LAT

LON

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TES Dust Distributions (Ls = 270): ODYYear #2 (2001-2002)

LAT

LON

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MTGCM Aphelion Case (Ls = 90):Temperatures (K) at SLT=15 (MGS2)

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MTGCM Aphelion Case (Ls = 90): Temperatures (K) at SLT=3 (MGS2)

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MTGCM Aphelion Case (Ls = 90): Meridional Winds (m/sec) at SLT=3 (MGS2)

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MTGCM Aphelion Case (Ls = 90): Vertical Winds (m/sec) at SLT=3 (MGS2)

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MTGCM Aphelion Case (Ls = 90): MGS2Dynamical Heating (K/day) : SLT = 3

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MTGCM Odyssey Case (Ls = 270):SLT=17 Temperatures versus Latitude

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MTGCM Odyssey Case (Ls = 270):SLT=3 Temperatures versus Latitude

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MTGCM Aphelion Case (Ls = 270): Meridional Winds (m/sec) at SLT=3 (ODY)

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MTGCM Aphelion Case (Ls = 270): Vertical Winds (m/sec) at SLT=3 (ODY)

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MTGCM Odyssey Case (Ls = 270): Dynamical Heating (K/day) : SLT = 3

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Ls = 90 (top) and Ls = 270 (bottom) : Densities (kg/km3) and Temperatures (K) at 120 km.

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Solar Cycle Variability

Mars thermospheric-ionosphere variations over the solar cycle are driven by:

Solar cycle changes in EUV-UV fluxes; both E10.7 and (F10.7+F10.7A)/2. indices are presently used by aeronomers;

Mars eccentricity changes in solar fluxes must be deconvolved for true solar cycle variability to be quantified;

Solar rotation variations (27-day) must be shifted to Mars solar longitude.

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T+(U,V) near Exobase:Ls = 270; F10.7 = 200

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T+(U,V) near Exobase:Ls = 270; F10.7 = 70

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T+(U,V) near Exobase:Ls = 90; F10.7 = 200

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T+(U,V) near Exobase:Ls = 90; F10.7 = 70

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Solar Cycle and Seasonal Variation of Exospheric Temperatures (Coupling On)

MAX

MIN

MOD

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Electron Density at SLT = 15 and 3 :Ls = 270; F10.7 = 200

SLT = 15 SLT = 3

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Electron Density at SLT = 15 and 3 :Ls = 270; F10.7 = 70

LST = 15 SLT = 3

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Electron Density at SLT = 15 and 3 :Ls = 90; F10.7 = 200

SLT = 15 SLT = 3

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Electron Density at SLT = 15 and 3 :Ls = 90; F10.7 = 70

SLT = 15 SLT = 3

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Longitudinal Variability

Mars thermospheric-ionosphere variations as a function of longitude are driven by:

Upward propagating migrating and non-migrating tides, whose magnitudes/phasing vary with LAT & season (Forbes et al., 02; Withers et al, 03);

Neutral density variations drive corresponding PCE ionosphere variations near the primary ionospheric peak (Bougher et al. 01; 04);

Aphelion season longitudinal variations observed to repeat over 2-Martian years (Bougher et al., 04)

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MGCM-MTGCM Simulation for Ls ~ 90:(a) Lon. Variation of 133 km densities;(b) Lon. Variation of F1-Peak Heights.

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MGCM-MTGCM Simulation for Ls ~ 90:Fractional Density Amp. of σ=2, s=(-1) Tide.

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Inter-annual Variability

Mars thermospheric-ionosphere variations from Martian year-to-year are driven by:

Near perihelion changes in lower atmos. dust distributions (both horizontal and vertical); aphelion changes are minimal;

Dust induced changes in migrating and non-migrating tidal propagation from <100 km;

Solar cycle changes in EUV-UV fluxes.

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% Differences in Temperatures: Ls = 270 vs 90

(LST = 15; TES Year #2 minus TES Year #1)

Ls = 270 Ls = 90

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% Differences in Temperature: Ls = 270 (120 km Constant Height)

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% Differences in Temperature: Ls = 90 (120 km Constant Height)

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Variations in Ionosphere (Ls = 270; SLT = 15): TES Year #1 vs Year #2

TES1 TES2

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Conclusions and Summary

Martian long-term thermosphere-ionosphere variability must be considered before SW-ionosphere/thermosphere interactions can be quantified and understood (solar cycle, inter-annual, seasonal, diurnal).

Episodic variations of the Mars thermosphere-ionosphere. Nightside auroral features, episodic neutral thermospheric heating, and ionospheric irregularities are all manifestations of particle (electron) precipitation in cusp regions linked to the crustal magnetic field centers.

Solar cycle plus seasonal orbital variations must be considered together to account for the changes observed in dayside T∞

Inter-annual variability is significant during perihelion periods, and minor near aphelion (e.g. polar night temperatures and densities; electron density profiles).

Durnal/longitudinal variations are linked to upward propagating migrating and non-migrating tidal oscillations. These tidal effects are strongest during periods when the in-situ solar forcing is weak (e.g. near aphelion, solar minimum conditions).