Скачать или смотреть Is the Sky falling? - Calibrating estimates of long-term ionospheric change

The height of the ionosphere (the electrified fraction of the earth's upper atmosphere), is predicted to decrease as a result of increased levels of tropospheric greenhouse gasses. Sufficiently long sequences of ionospheric data exist to investigate this long-term change, recorded by a global network of ionosondes. However, a direct measurement of ionospheric layer height with these instruments is not possible. As a result, most estimates rely on empirical formulae based on parameters routinely scaled from ionospheric data. Estimates of trends using these formulae show no global consensus.

When heights estimated from ionosonde data are compared with direct measurements of ionospheric heights from an Incoherent Scatter Radar, our results reveal that the empirical formula introduces diurnal, seasonal and long-term biases into the estimates of ionospheric height. We demonstrate that these are strongly controlled by changes in geomagnetic activity. We conclude that localised changes geomagnetic activity cause changes to thermospheric composition which modulates the underlying ionisation, leading to differences in ionospheric height trends.

In a further study, we present a re-analysis of the estimates of ionospheric height over Stanley in the Falkland Islands, in which data with a known bias are removed, and investigate ways to test how the sensitivity to geomagnetic activity at Stanley has changed over time.