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Studies of the Lower Ionosphere at NRL. David Siskind Space Science Division Naval Research Laboratory Washington DC, USA with M. Friedrich, Graz University of Technology, Austria Jorg Gumbel, Stockholm University. OASIS: Originally Austrian Study of the IonoSphere .

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Studies of the lower ionosphere at nrl
Studies of the Lower Ionosphere at NRL

David Siskind

Space Science Division

Naval Research Laboratory

Washington DC, USA

with

M. Friedrich, Graz University of Technology, Austria

Jorg Gumbel, Stockholm University

OASIS: Originally Austrian Study of the IonoSphere.

1. New interest in the D region:

HF communications (e.g. Eccles et al., Radio Sci, 2005)

2. History at NRL, OASIS (Gumbel et al., 2003)

3. New data to constrain D region models  emphasis on lowermost altitudes (below 70 km)

Work at NRL sponsored by the Office of Naval Research


New interest in hf absorption
New interest in HF absorption

Eccles et al, Space Weather, 2005

Absorption coefficient scales as product of [e-] and e-n collision frequency (which

in turn, scales as the neutral density)

Implication: although [e-] decreases with decreasing altitude, ne can increase.

Which wins out?


Hf absorption empirical model pederick and cervera radio sci 2014
HF Absorption: Empirical Model(Pederick and Cervera, Radio Sci 2014)

Error in labeling, unclear

which is FIRI or stnd IRI.

But, evidence for 2ndary

peak in HF absorption

below 70 km.


D region studies

OASIS: Originally Austrian Study of the IonoSphere.

Frederich and Torkar (1983), brought to NRL by Jorge Gumbel in 2002

Inputs: neutral atmosphere (including NO),

Ly A, EUV, Xray, GCR, energetic particle fluxes

Outputs: positive ions, negative ions, hydrated ions, electrons

Options for aerosol-ion interaction

(so-called [e-] biteouts seen in polar summer mesosphere)

D region studies

SABER: Sounding of the Atmosphere with Broadband Emission Radiometry

on NASA/TIMED satellite

Measures IR emission from ozone, CO2(temperature), OH airglow etc.



Below 80 km negative ions
Below 80 km: Negative Ions

Starts with: e- + O2 + O2  O2- + O2


Role of atomic oxygen
Role of Atomic Oxygen

Controls the partitioning between negative ions and electrons

O2- + O  e- + O + O2

or

O2- + X  X- + O2

X can be CO2 or NO2


Summary of d region
Summary of D region

Overview of D region, different regimes, different ionization sources vs. alt.

Negative ions: extending OASIS below 80 km. How it handles negative ions.

Basic processes

O2+ attach to H2O,

NO+ attaches to N2 and CO2 and eventually (H2O)n

 Proton hydrates dominate below 80 or 85 km (dep upon T and H2O)

My initial interest is when free electrons attach to neutrals (below 70 -75 km)

e- + O2 + M  O2- + M

Three things happen to O2-

Photodetachment (fast): O2- + hn  e- + O2

reaction with O to neutralize: O2- + O  e- + O + O2

charge exchange to produce heavier ions: O2- + X  X- + O2

(X- have much slower photodetachments)

X can be several species; OASIS bundles it all into X (seems to work)


Historically o not well studied below 80 km
Historically, O not well studied below 80 km

From Barabash’s paper

SABER O: Inferred from ozone measurements.

O/O3 = JO3/(k [O2][M])

Above 80 km, validated w/ Meinel Band (OH(v’)) technique

(Smith et al., 2010; Mlynczak et al 2014)


A saber o climatology vs sza
A SABER O climatology vs SZA

Variability is generally small except w.r.t. SZA. 70 km behavior is interesting

Equator 45oN


Saber vs local time
SABER vs. Local Time

Equator 45N

70 km

70 km


Some results validation
Some results/validation

I_total

I_NO

[e-]

PH+

O2-

I_GCR

X-

Ann Geo., 2012


New data from kwajalein sep 20 2004
New data from Kwajalein, Sep 20, 2004

This new data suggests that [e-] densities between 60-65 km greater than 100-400 cm-3

are a robust feature. This is 4-10 times greater than the model (which is probably

already biased high due to the high O)


Overview of rocket data hf mf radio absorption
Overview of Rocket Data: HF/MF radio absorption

Kwajalein Atoll

Or Indian Ocean

Wallops Is., VA, USA

About 30-40 useful low/mid-latitude measurements since WWII




Equatorial electron densities
Equatorial Electron Densities

Hints of big disagreement

between theory and

empirical model


Data Taken by Friedrich et al., 2 MHz absorption, Sep 19, 2004


Variations with latitude model vs firi
Variations with latitude: model vs FIRI

Model shows increasing [e-] latitude  tracks cosmic ray flux

FIRI shows equatorial peak; harder to understand


Conclusions
Conclusions

OASIS works and is validated down to 60km. Some cleaning up of higher altitudes

needed (photoelectrons from X rays)

Tested with a variety of atomic oxygen profiles (not shown)

SABER O can be a valuable constraint on model inputs that is underappreciated.

Evidence for large [e-] below 70 km which suggests:

a) a problem with the models and

b) confirms significant HF absorption between 60-70 km


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