Winter anomaly of the <Emphasis Type="Italic">E</Emphasis>-layer critical frequency in the nighttime auroral zone

Analysis of the annual variation of the E-layer critical frequency median foE in the nighttime (22?02 LT) auroral zone by the data of several stations of the Northern Hemisphere has shown the median maximum in winter and minimum in summer, even though the summer contribution of solar radiation to foE is greater. Thus, a new phenomenon was discovered—an foE median winter anomaly in the nighttime auroral zone. Its amplitude (ratio of winter to summer foE figures) can reach 10–15%; however, this anomaly was weakly expressed and statistically insignificant at particular stations located in the auroral zone. The winter anomaly is more distinct for foE _avr, the median of the E-layer critical frequency foE caused by the auroral source of atmospheric ionization, i.e., excluding the solar radiation contribution to foE. For foE _avr, the amplitude of the winter anomaly can reach 15–20%. Based on the qualitative analysis, it has been found that foE winter anomaly is stipulated by the winter/summer asymmetry of energy flow of accelerated electrons, which induce discrete aurorae in the nighttime auroral zone.     

Solar Activity Index for the Long-Term Prediction of the F2 Layer Critical Frequency

Geomagnetism and Aeronomy - Based on a comparison of the 12-month moving averages of the solar activity indices with the ionospheric index of solar activity IG12 for the period of 1954–2014,...     

Origination of <Emphasis Type="Italic">G</Emphasis> conditions in the ionospheric <Emphasis Type="Italic">F</Emphasis> region depending on solar and geomagnetic activity

The dependence of the origination of G conditions in the ionospheric F region on solar and geomagnetic activity has been determined based on numerical simulation of the ionosphere over points 50° N, 105° E and 70° N, 105° E for summer conditions at noon. It has been found that the threshold value of the Kp geomagnetic activity index (Kp _S ), beginning from which a G condition can originate, is minimal for a low solar activity level at relatively high latitudes during the recovery phase of a geomagnetic storm. On average, Kp _S increases with increasing solar activity, but G conditions can originate at high solar activity levels and be absent at moderate ones for certain Kp values, which was apparently predicted for the first time. These properties of the origination of G conditions do not contradict the known results of a G-condition statistical analysis performed based on the data from the global network of ionospheric stations.     

Effective Solar-Activity Index for Short-Term Forecasting of the Mean Solar-Activity Index

Geomagnetism and Aeronomy - The F1 and F81 indices, the value of the solar-emission flux at a wavelength of 10.7 cm on a given day, and the value of the flux averaged over 81 days and centered to...     

Geomagnetic activity that corresponds to the median of the <Emphasis Type="Italic">F</Emphasis>2-layer critical frequency at various latitudes

On the basis of the F2-layer critical frequency foF2 for the noon at some European stations for 1958–2005, it is found that the geomagnetic activity corresponding to the foF2 median is systematically lower than that averaged over the month; the difference increases with an increase in latitude. Moreover, the dispersion of geomagnetic activity for the foF2 median at relatively high latitudes is lower than at middle latitudes. These regularities are related to the fact that high geomagnetic activity usually leads to a distinct deviation of foF2 from the typical average value, i.e., from the foF2 median, and such deviation is more substantial at relatively high latitudes. That is why the geomagnetic activity for the foF2 median is lower at relatively high latitudes than at middle latitudes.     

Solar Activity Indices for Ionospheric Parameters in the 23rd and 24th Cycles

Geomagnetism and Aeronomy - Characteristics of changes in the solar activity indices (the flux of the solar radio emission at a wavelength of 10.7 cm F and the new version of the relative sunspot...