Monday, 9 October 2017
Dr Mark Clilverd
British Antarctic Survey (NERC)
"Halley Research Base Antarctica: 40 years of climate change in the ionospheric D-region: the end of an era?"
In recent years our measurements at the British Antarctic Survey's Halley Research Station, Antarctica, have been made difficult by disruption to the base, as large cracks have developed in the Brunt Ice Shelf. Despite planning for, and successfully achieving the relocation of the entire base 23 km up-stream, uncertainty continues over the viability of long-term measurements at Halley. A brief summary of the current state of play on the Brunt ice shelf will be given. As an example of the long-term research undertaken at Halley this talk discusses the findings of a recently developed technique that analyses long-distance subionospheric very low frequency radiowave observations of the NAA 24.0 kHz transmitter, Cutler, Maine, made from Halley Station, Antarctica, since 1971. Controversy exists over the potential effects of long-term increases in greenhouse gas concentrations on the ionospheric D-region at 60-90 km altitudes. Techniques involving in-situ rocket measurements, remote optical observations, and radio wave reflection experiments have produced conflicting results. A ~10% reduction in the scale size of the transmitter nighttime interference fringe pattern has been determined from the Halley data, taking into account the quasi-11 year solar cycle. Subionospheric radiowave propagation modelling suggests that the contraction of the interference fringe pattern about the mid-latitude NAA transmitter is due to a 3 km reduction in the effective height of the nighttime ionospheric D-region over the last 45 years. This is consistent with the effect of enhanced infra-red cooling by increasing greenhouse gases. Will it be possible to continue to make this type of measurement at Halley in the future?
WHEN: Monday 9 October 2017
WHERE: Room 314, Science 3 Building
TIME: 3.00 pm–4.00 pm
All interested are welcome to attend
Light refreshments to follow in Common Room