Stratospheric aerosol enhancement and decay after Raikoke eruption in July 2019 as observed from Tbilisi, Georgia and Halle, Belgium using ground-based twilight sky brightness spectral measurements.

<p>Twilight sky brightness spectral measurements are an inexpensive and effective way to observe enhancements of stratospheric aerosols. In this work, we present our observations of the volcanic cloud produced by the eruption of Raikoke volcano (Kuril Islands, 48°N, 153°E) above two distinct sites in South Caucasus and Western Europe, respectively: Tbilisi, Georgia (41° 43’ N, 44° 47° E) and Halle, Belgium (50° 44′ N, 4° 14′ E).</p><p>We present our dataset, which describes the evolution of the stratospheric aerosol in the period July 2019-December 2020. Stratospheric aerosol vertical extinction profiles were retrieved at 780 nm from spectral measurements of twilight sky brightness above both sites.</p><p>The first aerosols originating from Raikoke  were observed in the beginning of July above Halle and in August above Georgia. The layer maximum was mostly observed at 17 km above Georgia and at 10-17 km above Belgium until April-May 2020. Later, the volcanic cloud was observed sporadically until the end of 2020.</p>

Properties of the F2-layer maximum density variability over Irkutsk under different levels of the solar and geomagnetic activity

Using hourly data (1958–1992) from Irkutsk ionosonde station, we analyzed properties of variability of the F2-layer maximum density, Nm, under different levels of the solar and geomagnetic activity. The standard deviation s(x) of Nm fluctuations relative to the quiet level (x=(Nm/Nm0–1)·100 %), and the average shift of these fluctuations x-ave were used as characteristics of this variability. For this purpose, the empirical model of the F2-layer maximum density for quiet magnetic conditions, Nm0, was constructed. The Nm variability was found to depend weakly on the solar activity level; in the first approximation, this dependence can be neglected. The Nm variability dependence on geomagnetic activity is among the principal ones, along with the dependences on local time and season. In general, dispersion of Nm fluctuations under quiet conditions is smaller than that during the periods of high geomagnetic activity. During the periods of high geomagnetic activity, however, the dispersion does not increase with the further growth of this activity, while the absolute value of shift x-ave (which is mainly negative under high geomagnetic activity) still increases with growing geomagnetic activity. As a result, if this activity is high enough, the condition |x-ave|>|s(x)| can be fulfilled.