Molecular Nitrogen (N2) Density Derived from
Optical Measurements During Ionospheric Heating Experiment (or an
Alternative Hypothesis for the O(1D) Quenching
Coefficient Adjustment).
Christiano
Garnett Marques Brum, Michael Sulzer,
Pedrina
Terra,
Sukanta
Sau,
Selvaraj
Dharmalingam
High frequency (HF) experiments inducing intensification of airglow
emissions at 6300 Å; and 5577 Å (red and green lines, respectively) from
the two lowest excited states of oxygen O(1D) and
O(1S) has been studied since the early 1970s.
The last generation Arecibo HF facility was commissioned in November
2015, and since then several campaigns have been conducted at AO. The
current system consists of six transmitters, each connected to one of
six dipole elements, and each capable of continuous wave (CW) operation
at a nominal power of ~100 kW. Before the AO platform
collapse on December 1, 2020, the HF transmitter system has two
available frequencies, 5.125 MHz and 8.175 MHz, with 130 kHz and 100 kHz
bandwidths, respectively. In this work we are analyzing the excitation
of the red line airglow emission (3600 Å) by high-power radio waves at
~5.125MHz of 28 HF pulses of 5 minutes intercalated by 5
minutes of no HF interaction. The chosen periods were the pre-sunrise
and post-sunset periods of June 5, 2016 (Figure 1 ).
Coincidentally, a small geomagnetic storm occurred during these
observations. The first experiment started along the initial phase of
this disturbance and the second experiment at the end of the main phase
(Figure 2 ). Up to now, our main findings are listed below:
1. Assuming that the modified red line comes from a narrow
height range in the vicinity of the reflection height to a first
approximation and considering that all of the excess emission comes from
a single height (equation 1) (which corresponds to the height where the
plasma frequency equals the transmitted frequency), it was detected that
the lifetime of the O(1D) varies with altitude which a
peak close to the red line emission altitudes (Figure 3 ).
\(\Theta_{r}=\frac{1}{(T1+T2+T3+T4)}\) (1)
Where T1 is the total Einstein transition probability of the
O(1D) state, T2 is the N2concentration at the altitude of reflection times its respective
quenching coefficient
(Q ~5,0.10-11cm3s-1)
as well as T3 the O2 concentration times its respective
quenching coefficient
(R ~7,4.10-11cm3s-1).
2. Assuming a fixed lifetime for all altitudes, we detected
variation of the N2 quenching coefficient
O(1D) also varying with altitude. Such variation could
be a miss determination of the N2 neutral concentration
from the NRLMSISE-00 Atmosphere Model (Figure 4 ) (equation 1).
3. As a practical outcome, our study shows that the 5 minutes
off is not sufficient for the excited region to return to the previous
quiet condition. Our computations show that pulses of 3 minutes
intercalated by 6 minutes off are the ones more appropriate
(Figure 5 ).