Bibliography

Local Geomagnetic Indices and the Prediction of Auroral Power

The aurora has been related to magnetometer observations for centuries, and to geomagnetic indices for decades. As the number of stations and data processing power increases, just how auroral power (AP) relates to geomagnetic observations becomes a more tractable question. This paper compares Polar UVI AP observations during 1997 with a variety of indices. Local time (LT) versions of the SuperMAG auroral electrojet (SME) are introduced and examined, along with the corresponding upper and lower envelopes (SMU and SML). Also, the East\textendashwest component, B_E, is investigated. We also consider whether using any of the local indices is actually better at predicting local AP than a single global index. Each index is separated into 24 LT indices with a sliding 3-h MLT window. The ability to predict AP varies greatly with LT, peaking at 1900 MLT, where about 75\% of the variance (r²) is predicted at 1-min cadence. The aurora is fairly predictable from 1700 MLT \textendash 0400 MLT, roughly the region in which substorms occur. AP is poorly predicted from auroral electrojet indices from 0500 MLT \textendash 1500 MLT, with the minimum at 1000\textendash1300 MLT. In the region of high predictability, the local index which works best is B_E (East\textendashwest), in contrast to long-standing expectations. However using global SME is better than any local index. AP is best predicted by combining global SME with a local index: B_E from 1500\textendash0300 MLT, and either SMU or SML from 0300\textendash1500 MLT. In the region of the diffuse aurora, it is better to use a 30 min average than the cotemporaneous 1-min SME value, while from 1500\textendash0200 MLT the cotemporaneous 1-min SME works best, suggesting a more direct physical relationship with the auroral circuit. These results suggest a significant role for discrete auroral currents closing locally with Pedersen currents.

Newell, P.; Gjerloev, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2014

YEAR: 2014     DOI: 10.1002/2014JA020524

AURORA; auroral electrojet; indices; Pedersen current; Prediction

GPS derived TEC and foF2 variability at an equatorial station and the performance of IRI-model

The ionosphere induces a time delay in transionospheric radio signals such as the Global Positioning System (GPS) signal. The Total Electron Content (TEC) is a key parameter in the mitigation of ionospheric effects on transionospheric signals. The delay in GPS signal induced by the ionosphere is proportional to TEC along the path from the GPS satellite to a receiver. The diurnal monthly and seasonal variations of ionospheric electron content were studied during the year 2010, a year of extreme solar minimum (F10.7\ =\ 81 solar flux unit), with data from the GPS receiver and the Digisonde Portable Sounder (DPS) collocated at Ilorin (Geog. Lat. 8.50\textdegreeN, Long. 4.50\textdegreeE, dip -7.9\textdegree). The diurnal monthly variation shows steady increases in TEC and F2-layer critical frequency (foF2) from pre-dawn minimum to afternoon maximum and then decreases after sunset. TEC show significant seasonal variation during the daytime between 0900 and 1900\ UT (LT\ =\ UT\ +\ 1\ h) with a maximum during the March equinox (about 35 TECU) and minimum during the June solstice (about 24 TECU). The GPS-TEC and foF2 values reveal a weak seasonal anomaly and equinoctial asymmetry during the daytime. The variations observed find their explanations in the amount of solar radiation and neutral gas composition. The measured TEC and foF2 values were compared with last two versions of the International Reference Ionosphere (IRI-2007 and IRI-2012) model predictions using the NeQuick and CCIR (International Radio Consultative Committee) options respectively in the model. In general, the two models give foF2 close to the experimental values, whereas significant discrepancies are found in the predictions of TEC from the models especially during the daytime. The error in height dependent thickness parameter, daytime underestimation of equatorial drift and contributions of electrons from altitudes above 2000\ km have been suggested as the possible causes.

Adebiyi, S.J.; Odeyemi, O.O.; Adimula, I.A.; Oladipo, O.A.; Ikubanni, S.O.; Adebesin, B.O.; Joshua, B.W.;

Published by: Advances in Space Research      Published on: 08/2014

YEAR: 2014     DOI: 10.1016/j.asr.2014.03.026

Equator; IRI-model; NmF2; Prediction; TEC