A. Kozlovsky

Ionospheric effects of the missile destruction on 9 December 2009

We report on ionosonde and meteor radar observations made in Sodankyla Geophysical Observatory (SGO, 67°22′N, 26°38′E, Finland) on 9 December 2009, during a test launch of the Russian solid propellant military missile. Due to a technical problem, the missile was self-destroyed around 07 UT at an ionospheric height (near 200 km altitude) over the Kola Peninsula (Russia), at a distance about 500 km to east from the observatory. Products of the explosion were spread into a large area and reached the region of SGO meteor radar observations in about 2 h (around 09 UT). After about 3 h (around 10 UT), a sporadic E layer presumably composed of the remains including long-lived metallic (aluminum and its oxides) ions, was observed near the zenith of the SGO ionosonde. We discuss possible mechanisms accounting for transport of the remains. (1) Since the event occurred during a long-lasting period of extremely low solar and magnetic activity, the ionospheric electric field was unlikely to play a substantial role in the transport of the remains and sporadic E layer formation. (2) The horizontal transport of the remains cannot be explained by the neutral winds based on empirical models. (3) Theoretical estimations suggest that the observed transport could be due to thermospheric turbulence.

Ionospheric convection in the postnoon auroral oval: Super Dual Auroral Radar Network (SuperDARN) and polar ultraviolet imager (UVI) observations

Received 14 January 2002; revised 22 July 2002; accepted 9 August 2002; published 11 December 2002. [1] Super Dual Auroral Radar Network (SuperDARN) observations, ultraviolet imaging from the Polar satellite (ultraviolet imager [UVI]), and particle precipitation data from Defense Meteorological Satellite Program (DMSP) satellites have been used to investigate the electrodynamics of the postnoon auroral oval in the Northern hemisphere. We show that: (1) For negative interplanetary magnetic field (IMF) By, the convection reversal (CR) was colocated with the maximum of auroral luminosity, but during positive IMF By, the convection reversal was poleward of the auroral oval up to several degrees in latitude. (2) Postnoon auroral oval was associated with a large-scale upward field-aligned current (FAC) of the order of 6 � 10 � 7 Am � 2 in magnitude (the FAC was inferred from the SuperDARN and UVI data). For negative IMF By, the maximum of the auroral intensity coincides in latitude with the maximum of the upward FAC. However, for positive IMF By, the maximum of the upward FAC was shifted to the poleward edge of the auroral oval. (3) In response to the IMF By turning from positive to negative, the maximum of the auroral luminosity did not change its position noticeably, but the position of the CR changed considerably from 80� –81� to about 76� magnetic latitude (MLAT), and the maximum of FAC moved from 77� –78� to about 76� MLAT. Thus, after the IMF By turns negative, both the FAC maximum and CR tend to coincide with the auroral maximum. (4) The IMF Bz positive deflection was followed by a decrease in both FAC intensity and auroral luminosity. However, the decrease in the auroral luminosity lags behind the FAC decrease by about 12 min. Firstly, these observations allow us to suggest that the IMF By-related electric field can penetrate into the closed magnetosphere and produce convection and FAC changes in the region of the postnoon auroral oval. Secondly, we suggest that the interchange instability is a promising mechanism for the postnoon auroras. INDEX TERMS: 2463 Ionosphere: Plasma convection; 2407 Ionosphere: Auroral ionosphere (2704); 2708 Magnetospheric Physics: Current systems (2409); 2784 Magnetospheric Physics: Solar wind/ magnetosphere interactions; KEYWORDS: postnoon aurora, ionospheric convection, field-aligned currents, IMF changes, boundary plasma sheet

Thermal and dynamical perturbations in the winter polar mesosphere‐lower thermosphere region associated with sudden stratospheric warmings under conditions of low solar activity

The upper mesospheric neutral winds and temperatures have been derived from continuous meteor radar (MR) measurements over Sodankyla, Finland, in 2008–2014. Under conditions of low solar activity pronounced sudden mesospheric coolings linked to the major stratospheric warming (SSW) in 2009 and a medium SSW in 2010 are observed while there is no observed thermal signature of the major SSW in 2013 occurred during the solar maximum. Mesosphere-ionosphere anomalies observed simultaneously by the MR, the Aura satellite, and the rapid-run ionosonde during a period of major SSW include the following features. The mesospheric temperature minimum occurs 1 day ahead of the stratospheric maximum, and the mesospheric cooling is almost of the same value as the stratospheric warming (~50 K), the former decay faster than the latter. In the course of SSW, a strong mesospheric wind shear of ~70 m/s/km occurs. The wind turns clockwise (anticlockwise) from north-eastward (south-eastward) to south-westward (north-westward) above (below) 90 km. As the mesospheric temperature reaches its minimum, the gravity waves (GW) in the ionosphere with periods of 10–60 min decay abruptly while the GWs with longer periods are not affected. The effect is explained by selective filtering and/or increased turbulence near the mesopause.

Mesospheric temperature estimation from meteor decay times during Geminids meteor shower

Meteor radar observations at the Sodankylä Geophysical Observatory (67° 22′N, 26° 38′E, Finland) indicate that the mesospheric temperature derived from meteor decay times is systematically underestimated by 20–50K during the Geminidsmeteor shower which has peak on 13 December. A very good coincidence of the minimum of routinely calculated temperature and maximum of meteor flux (the number of meteors detected per day) was observed regularly on that day in December 2008–2014. These observations are for a specific height-lifetime distribution of the Geminids meteor trails and indicate a larger percentage of overdense trails compared to that for sporadic meteors. A consequence of this is that the routine estimates of mesospheric temperature during the Geminids are in fact underestimates. The observations do, however, indicate unusual properties (e.g., mass, speed, or chemical composition) of the Geminids meteoroids. Similar properties were found also for Quadrantids in January 2009–2015, which like the Geminids has as a parent body an asteroid, but not for other meteor showers.

On the VHF radar echoes in the region of midnight aurora: Signs of ground echoes modulated by the ionosphere

We present all-sky interferometric meteor radar (MR), VHF (36.9 MHz), observations from Sodankyla Geophysical Observatory and report on the unusual echoes, which were detected at low elevation on the northern horizon, typically during substorms. These echoes have a near-zero Doppler shift, relatively low power, but with a sharp rise to the power peak, short lifetime (less than 2 s), and nonexponential decay (NED). We suggest that such auroral NED echoes are in fact ground backscatter of the MR waves which have been refracted in the ionosphere, passing through the ionosphere in the substorm region, where pulsating aurora (at a frequency higher than 1.7 Hz) occurs and causes quasiperiodic modulation of the wave propagation conditions, which leads to corresponding modulation of the amplitude of return. The MR treats such oscillating signal as meteor trails.

Response of the quiet auroral arc motion to ionospheric convection variations

Equatorward motion of quiet auroral arcs was studied together with the F region ionospheric plasma drift observed by the European Incoherent Scatter radar in Tromso. Variations in the arc velocity lagged behind corresponding variations in the ionospheric convection velocity by 5–9 min. The same result was obtained from comparison of the arc velocity with variations in the eastward component of ground magnetic field. The variations in the arc and plasma drift velocities followed interplanetary magnetic field Bz variations. The observations indicate that the dawn-dusk electric potential difference arises at the open polar cap magnetic field lines due to the solar wind - magnetosphere interaction and then propagates to the closed magnetotail field lines through the ionosphere.

Asymmetric structures of field-aligned currents and convection of ionospheric plasma controlled by the IMF azimuthal component and season of year

We present the results of using the statistical model of field-aligned currents (FACs) based on satellite data and the numerical model of the electric potential distribution in order to detect the asymmetric part in FAC structures and ionospheric plasma convection controlled by the IMF azimuthal (By) component at different seasons of the year. These structures can be identified by plotting diagrams, which represent differences in corresponding maps for opposite signs of IMF By. Circular near-pole current symmetric about the noon meridian and corresponding convection vortices around the pole have been obtained for the summer and equinox periods. It is difficult to detect distinct structures under winter conditions, and the current is most intense on the morning side. A two-cell convection system with the foci in the afternoon and postmid-night sectors is created in the electric potential difference diagrams. Thus, qualitatively different FAC and convection patterns exist during the solstice in opposite hemispheres. The value of the electric potential originating in the near-pole region under the action of the By component and a change in the potential under the action of additional factors have been estimated.

IPIM Modeling of the Ionospheric F2 Layer Depletion at High Latitudes During a High‐Speed Stream Event

Our aim is to understand the effect of high-speed stream events on the high-latitude ionosphere and more specifically the decrease of the foF2 frequency during the entire day following the impact. First, we have selected one summertime event, for which a large data set was available: Super Dual Auroral Radar Network (SuperDARN) and European Incoherent SCATter (EISCAT) radars, Tromsø and Sodankylä ionosondes, and the CHAllenging Minisatellite Payload (CHAMP) satellite. We modeled with the IPIM model (IRAP Plasmasphere Ionosphere Model) the dynamics of the ionosphere at Tromsø and Sodankylä using inputs derived from the data. The simulations nicely match the measurements made by the EISCAT radar and the ionosondes, and we showed that the decrease of foF2 is associated with a transition from F2 to F1 layer resulting from a decrease of neutral atomic oxygen concentration. Modeling showed that electrodynamics can explain short-term behavior on the scale of a few hours, but long-term behavior on the scale of a few days results from the perturbation induced in the atmosphere. Enhancement of convection is responsible for a sharp increase of the ion temperature by Joule heating, leading through chemistry to an immediate reduction of the F2 layer. Then, ion drag on neutrals is responsible for a rapid heating and expansion of the thermosphere. This expansion affects atomic oxygen through nonthermal upward flow, which results in a decrease of its concentration and amplifies the decrease of [O]/[N2] ratio. This thermospheric change explains long-term extinction of the F2 layer.

High-latitude E and F region coupling signature: A case study results from rapid-run ionosonde

Rapid-run ionosonde installed in the high-latitude Sodankyla Geophysical Observatory enables us to observe for the first time extraordinary details of E-F region coupling process in high-latitude ionosphere during geomagnetically quiet period. We present an example on 15 August 2009 when a dense, patchy sporadic E layer was detected. Associated with this unstable sporadic E layer, exhibiting in addition an unusual enhancement with a vertical extent of about 10 km, the highly structured F layer plasma was observed with apparent plasma depletions. We examine this event taking into account the presence of mesoscale traveling ionospheric disturbances which can initiate coupling between these two regions and compare the data with current theories.