Previously unreported optical emissions generated during ionospheric heating

Abstract

Several radio‐induced optical emissions were generated during an ionospheric heating experiment performed at the High Power Auroral Stimulation (HIPAS) facility near Two Rivers, Alaska. The O+ 732–733 nm and O(3Do) 799.0 nm emissions, previously unreported from ionospheric heating experiments, were detected, in addition to the already documented O(3P) 844.6 nm and O(5P) 777.4 nm emissions. Maximum emission intensity was observed in the magnetic zenith, when the heater was transmitting continuous wave O‐mode, at a frequency of 2.85 MHz. A modified Czerny‐Turner grating spectrometer was used to acquire high resolution optical spectra of the induced emissions, which were synchronized to the heater duty cycle. Candidate mechanisms for the production of the radio‐induced emissions, which occurred before the “double resonance” condition, are presented.

Heater‐induced ionization inferred from spectrometric airglow measurements

“…While it was initially believed that the enhancements could be explained in terms of heating and the enhancement of the tail of the thermal electron population [Mantas, 1994;Mantas and Carlson, 1996], the measured ratios of red and green line emissions and the appearance of optical emissions with high-energy thresholds signaled the presence of a nonthermal component of the electron energy distribution [Bernhardt et al, 1989;Gustavsson et al, 2001Gustavsson et al, , 2003Djuth et al, 2005;Gustavsson et al, 2005]. Observations of the O + 732-733 nm emission during heating experiments consistent with electron impact ionization also supported this proposition [Mutiso et al, 2008].…”

Correlation between the Sea Surface Temperature and the frequency of severe storms in the tropical oceans using seven years of AIRS data

“…The correlation between the zonal mean SST and the DCC frequency allows us to use the derived sensitivity to calculate the long term trend in the DCC frequency, +38%/K*0.13K/decade = +5%/decade. This is consistent with the 5%/decade result derived based on the seasonal correlation between SST and DCC [6]. Since DCC are associated with intense thunderstorms over the tropical ocean [3], the frequency of these thunderstorms is expected to increase at the same rate as the DCC.…”

“…We therefore evaluated the anomaly correlation. The anomaly is the difference between the daily points and a fit to the data using a linear combination of low order sine and cosine terms [6]. Figure 4 shows an overlay of the SST anomaly and DCC count anomaly.…”

Artificial ionospheric layers driven by high‐frequency radiowaves: An assessment

“…Its usual manifestations for HF pump waves of ordinary (O) polarization are enhanced plasma and ion lines in the incoherent scatter radar (ISR) spectra [e.g., Stubbe et al, 1992;Cheung et al, 2001], elevated electron temperature T e [e.g., Rietveld et al, 2003;Blagoveshchenskaya et al, 2005], enhanced radioaurora, i.e., HF radar coherent backscatter off enhanced field-aligned irregularities (FAI) n ∥ [e.g., Robinson, 1989;Senior et al, 2004], secondary or stimulated electromagnetic emissions (SEE) [e.g., Thidé et al, 1982;Stubbe et al, 1984;Leyser, 2001] due to coupling of electrostatic HF waves with low-frequency (LF) counterparts and FAI, and enhanced optical emissions (artificial aurora) [e.g., Bernhardt et al, 1989;Kosch et al, 2000Kosch et al, , 2004Pedersen et al, 2003]. Optical emissions with the excitation energies 2-18 eV [e.g., Gustavsson et al, 2002Gustavsson et al, , 2006Mutiso et al, 2008] indicate accelerated suprathermal electrons [Carlson et al, 1982]. It is also worth noting HF-induced ion upflows and density ducts in the topside ionosphere [e.g., Rietveld et al, 2003;Milikh et al, 2010;Kosch et al, 2010].…”