Steven Marple

First tomographic estimate of volume distribution of HF‐pump enhanced airglow emission

This report presents the first estimates of the three-dimensional volume emission rate of enhanced O(1D) 6300 A airglow caused by HF radio wave pumping in the ionosphere. Images of the excitation show how the initially speckled spatial structure of excitation changes to a simpler shape with a smaller region that contains most of the excitation. A region of enhanced airglow was imaged by three stations in the Auroral Large Imaging System (ALIS) in northern Scandinavia. These images allowed for a tomography-like inversion of the volume emission of the airglow. The altitude of maximum emission was found to be around 235 ± 5 km with typical horizontal and vertical scale sizes of 20 km. The shape of the O(1D) excitation rate varied from flatish to elongated along the magnetic field. The altitude of maximum emission is found to be approximately 10 km below the altitude of the enhanced ion line and 15 km above the altitude of maximum electron temperature. Comparisons of the measured altitude and temporal variations of the 6300 A emission with modelled emission caused by O(1D) excitation from the high energy tail of a Maxwellian electron distribution show significant deviations. The 6300 A emission from excitation of the high energy tail is about a factor of 4 too large compared with what is observed. This shows that the source of O(1D) excitation is electrons from a “sub-thermal” distribution function, i.e. the electron distribution is Maxwellian at low energies and at energies above 1.96 eV there is a depletion.

All-sky interferometric riometry

The first implementation of a Fourier-based interferometric riometry technique for measuring electron density induced ionospheric opacity at VHF radio frequencies is presented. Unlike multibeam riometers, which form discrete beams on the sky, the interferometric technique permits all-sky sampling of incoming cosmic radio noise emissions resulting in a spatially-continuous radiogram of the entire sky. The map of the received power at each time may then be compared to the equivalent map from a “quiet day”, allowing the morphology of ionospheric absorption of cosmic radio noise to be ascertained. In this work, the high-latitude Kilpisjarvi Atmospheric Imaging Receiver Array (KAIRA) was used to carry out the first interferometric riometry measurements in late 2013, producing all-sky absorption maps of space weather related ionization in the D region.

Testing AIMOS ionization rates in the middle atmosphere: Comparison with ground based radio wave observations of the ionosphere

There is growing interest in coupling energetic particle precipitation (EPP) into Chemistry-Climate Models. Experimental observations show that EPP from the radiation belts during geomagnetic storms lead to significant ozone decreases in polar latitudes, and couple to polar surface air temperatures. Datasets of satellite-derived EPP-driven ionospheric ionization rates have been created. However, there are reasons to suspect the satellite EPP observations, and the ionization rates need to be tested against experimental reality. In this presentation we will contrast the ionization rates output by one model with experimental observations from ground-based observations, specifically VLF receivers and riometers.

AuroraWatch UK: An Automated Aurora Alert System: AURORAWATCH UK

The AuroraWatch UK aurora alert service uses a network of magnetometers from across the United Kingdom to measure the disturbance in the earths magnetic field caused by the aurora borealis (northern lights). The service has been measuring disturbances in the earths magnetic field from the UK, and issuing auroral visibility alerts to its subscribers, since September 2000. These alerts have four levels, corresponding to the magnitude of disturbance measured, which indicate from where in the UK an auroral display might be seen. In the following, we describe the AuroraWatch UK system in detail and reprocess the historical magnetometer data using the current alert algorithm to compile an activity database. This data set is comprised of over 150,000 hours (99.94% data availability) of magnetic disturbance measurements, including nearly 9,000 hours of enhanced geomagnetic activity.