Behavior of <Emphasis Type="Italic">foF</Emphasis>2 and <Emphasis Type="Italic">hmF</Emphasis>2 after sunset

The time behavior of the foF2 and hmF2 values at the time moment T(ss + 2 h) 2 h after sunset is considered. It is assumed that at this moment, the horizontal winds in the thermosphere in the strongest way influence hmF2 and, therefore, foF2. It is found that a fairly well pronounced and statistically significant change (trend) is observed for the foF2(ss + 2)/foF2(14) ratio, the sign of the change being different for different stations and even different seasons at the same station. A similar picture is obtained for the value of hmF2(ss + 2). It is shown that a positive correlation between the trends of these two values is observed. This confirms the initial concept of the paper that the foF2 and hmF2 trends are caused by long-term trends in the thermospheric dynamics.     

Letter to the editor

Using a method suggested by the authors earlier, the long-term trends of the F2-layer critical frequency, foF2 are derived for a set of ionospheric stations with a wide latitudinal and longitudinal coverage. All the trends are found to be negative. A pronounced dependence on geomagnetic latitude is found, the trend magnitude increasing with the latter. No globe scale longitudinal effect in trends is detected. For the majority of the stations there is also a pronounced seasonal effect, the trend magnitude being higher in summer than in winter.     

Reduction of the atomic oxygen content in the upper atmosphere

It is theorized that the discovered negative trends in the critical frequency of the F2 layer are caused by the reduction (a negative trend) of the atomic oxygen concentration in the thermosphere. Such a reduction may be caused by intensification of the turbulence in the region of the turbopause (100–120 km). Arguments are presented in favor of an increase in the turbulence taking place caused by the increase in penetration of internal waves to the turbopause heights.     

Equilibrium phase-space density distribution in numerical dynamical models of open clusters

In dynamical models for open clusters, virial equilibrium is not achieved over the violent relaxation time scale τ_vr. The stars form an equilibrium distribution in (?, ?_ζ, l) space, where ? and l are the energy and angular momentum per unit stellar mass in the combined field of the Galaxy and cluster and ?_ζ is the energy of motion perpendicular to the Galactic plane per unit mass of cluster stars in the gravitational field of the Galaxy. This distribution of stars changes little when t>τ_vr. The stellar phase-space distribution corresponding to this type of equilibrium and the regular cluster potential vary periodically (or quasi-periodically) with time. This phase-space equilibrium is probably possible due to an approximate balance in the stellar transitions between phase-space cells over times equal to the oscillation period for the regular cluster field.     

The structure of the Lomonosov volcanic pipe in the Arkhangel’sk diamond province from anomalies of the microseismic field

This paper presents results from a study of the Lomonosov volcanic pipe as derived from anomalies of the microseismic field. Microseismic sounding revealed that this volcanic pipe is a cone-shaped body with a small gradient of microseismic intensity motion (2 to 5 dB). Discontinuities generally show greater contrasts compared with the variations of microseismic motion in the pipe body. Comparison of the results of this microseismic sounding with other geological and geophysical data showed that the intensities of the microseismic field along lines that traversed the pipe reflect realistic structures of a kimberlite pipe and the host rocks. The method of microseismic sounding was used to reconstruct the deeper structure of the volcanic pipe and the host rocks down to depths greater than 2 km. We estimated the velocity contrast and the errors involved in the identification of vertical boundaries of the pipe. The volcanic pipe has a shape that is consistent with a nearly vertical source situated at a depth of a few hundred meters. This is hypothesized to be a typical occurrence for other diamond-bearing pipes as well.     

Long-term changes in the relation between <Emphasis Type="Italic">foF</Emphasis>2 and <Emphasis Type="Italic">hmF</Emphasis>2

The change in the dependence of the F2-layer critical frequency on its height hmF2 is considered based on two sources of initial data used earlier by the authors. It is found that the slope k of the foF2 dependence on hmF2 systematically decreases from the earlier (“etalon”) period, 1958–1980, to the later periods of 1988–2010, 1998–2010, and 1998–2014. Since the foF2 value depends on the atomic oxygen concentration in the F region much more strongly than hmF2, the found decrease in k confirms the concept of a decrease in the atomic oxygen concentration in the thermosphere with time previously formulated by the authors.     

Discussion of the Problem of Ionospheric Precursors of Magnetic Storms

Geomagnetism and Aeronomy - The problem of disturbances of the parameters of the F2 layer and the upper ionosphere during the days preceding the beginning of a magnetic storm has already been known...     

Changes in the climate and sea ice of the Northern Hemisphere in the 20th and 21st centuries from data of observations and modeling

The shrinking of the area occupied by sea ice in the Northern Hemisphere accelerated at the end of the 1990s, when the record minima of the summer area were successively noted, and its absolute minimum was observed in September 2007. Such a radical decrease is ahead of the projections of global models and provokes interest in the reliability of model calculations of the future of Arctic sea ice. The results of an analysis of the relation between the warming in the Arctic and the ice extent shrinkage from data of observations and modeling by an ensemble of global climate models are presented.     

Polar meteorology: The results of Russian research in 2003–2006

This publication is a review of the results of Russian polar studies performed in 2003–2006. It is based on material prepared by the Commission on Polar Meteorology of the National Geophysical Committee, Russian Academy of Sciences, and included in the National Report on Meteorology and Atmospheric Sciences to the XXIV General Assembly of the International Union of Geodesy and Geophysics, Perugia, Italy, July 2–13, 2007.