Long-term climate change in the D-region.

Area of Science:

• Atmospheric Science
• Geophysics
• Space Physics

Background:

• Conflicting data exists regarding greenhouse gas effects on the ionospheric D-region (60-90 km).
• Previous studies used in-situ rocket measurements, optical observations, and radio wave reflection, yielding inconsistent results.

Purpose of the Study:

• To investigate the long-term effects of greenhouse gases on the ionospheric D-region.
• To introduce and validate a novel technique for analyzing subionospheric radio wave propagation.

Main Methods:

• Analysis of long-distance subionospheric very low frequency (VLF) radio wave observations (NAA 24.0 kHz transmitter from Halley Station, Antarctica, 1971-2016).
• Technique is insensitive to transmitter power changes and compensates for equipment variations.
• Confirmed accuracy of timing systems over the 45-year record.

Main Results:

• A ~10% reduction in the scale size of the nighttime interference fringe pattern was determined, accounting for the solar cycle.
• Subionospheric radiowave propagation modeling indicates a 3 km reduction in the effective height of the nighttime ionospheric D-region.

Conclusions:

• The observed contraction of the interference fringe pattern suggests a lowering of the nighttime ionospheric D-region.
• This finding is consistent with enhanced infrared cooling due to increasing greenhouse gas concentrations.