Institute of Applied Geophysics

Moscow, Russia

Institute of Applied Geophysics

Moscow, Russia
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Danilov A.D.,Institute of Applied Geophysics | Konstantinova A.V.,Institute of Applied Geophysics
Geomagnetism and Aeronomy | Year: 2013

The trends in the height of the ionospheric F2 layer, hmF2, for the period from the end of the 1990s to the beginning of the 2010s are considered. It is shown that for a majority of the considered situations (time of the day plus season) negative trends are obtained for all stations for which series of initial data satisfying the requirements were found. They vary from -1.2 to -3.1 km per year. The trends in the daytime are slightly higher than in the postsunset period which apparently manifests the influence of the contraction of the upper atmosphere on changes in the hmF2 value. © 2013 Pleiades Publishing, Ltd.


Danilov A.D.,Institute of Applied Geophysics | Konstantinova A.V.,Institute of Applied Geophysics
Journal of Geophysical Research: Atmospheres | Year: 2013

The behavior of the critical frequency foF2 of the ionospheric F2 layer is considered for the period 1990-2010. Various available databanks of ionospheric vertical sounding data are described and compared. The analysis is performed in terms of comparison of the foF2 data for the period 1958-1980 to the data for 1990-2010. Two moments of the day (14:00 LT and the after-sunset moment) and two seasons (winter and summer) are considered for 12 stations for which the necessary data were available. The scatter of the foF2 values (in terms of the standard deviation, SD) relative to the dependence on the solar activity index F10.7 is considered. It is demonstrated that the values of SD for the period 1998-2010 are much higher than for the period 1958-1979. This increase in the SD includes two factors: real increase in the foF2 scatter and systematic decrease (negative trend) in foF2. This systematic decrease makes it possible to provide an independent evaluation of the trend in foF2: -0.03 MHz per year. Analysis of foF2 behavior for each of all 12 stations is performed. The obtained linear trends are negative for all stations, but the trend magnitude varies from one station to another. The trends for two moments of time are found of the same order of magnitude: -0.024 and -0.054 MHz per year for the summer and winter seasons, respectively. Some conclusions on the behavior of the hmF2 trends for the same period are presented. Possible causes of the changes in the trends in the F2 layer parameters are discussed. Key Points Negative trends in critical frequency are derived for 1990-2010. Negative trends in F2-layer height are derived for 1990-2010 It is found that scatter of foF2 and hmF2 increases with time © 2013. American Geophysical Union. All Rights Reserved.


Belyaev A.N.,Institute of Applied Geophysics
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2013

The aim of this work is to develop mathematical foundation of a method which can be used to infer the three-dimensional gravity wave characteristics from multi position airglow observations from space. This work derives a one-dimensional Fredholm integral equation of the first kind, which describes the relations between the gravity wave spectrum and spatial structure of wave perturbations registered by a space-based airglow imager. It is shown that the solution of this equation belongs to the central slice through a three-dimensional gravity wave spectrum, whose plane is perpendicular to the optical axis of the airglow imager. Thus, in order to retrieve the three-dimensional gravity wave characteristics from the airglow observations performed from space, it is needed to obtain the set of images of a local emission layer area from different imager positions. Then this data must be processed using the developed mathematical techniques to obtain a set of the central slices of the three-dimensional gravity wave spectrum. Applying the technique, for a superposition of three individual waves, amplitude and wave vector can be determined. © 2013 Elsevier Ltd.


Danilov A.D.,Institute of Applied Geophysics
Advances in Space Research | Year: 2013

The F2-region reaction to geomagnetic storms usually called as an ionospheric storm is a rather complicated event. It consists of so called positive and negative phases, which have very complicated spatial and temporal behavior. The main morphological features of ionospheric storms and the main processes governing their behavior were understood at the end of the 1900s and described in a series of review papers. During the recent decade there were many publications dedicated to the problem of ionospheric storms. In this paper a concept of ionospheric storm morphology and physics formulated at the end of the 1990s is briefly summarized and the most interesting results obtained in the 2000s are described. It is shown that the main features of the studies of the previous decade were: the use of GPS TEC data for analyzing the ionospheric storm morphology, attraction of sophisticated theoretical models for studying the processes governing ionospheric behavior in disturbed conditions, and accent to analysis of ionospheric behavior during prominent events (very strong and great geomagnetic storms). Also a special attention was paid to the pre-storm enhancements in foF2 and TEC. © 2013 COSPAR. Published by Elsevier Ltd. All rights reserved.


Belyaev A.,Institute of Applied Geophysics
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2016

Model-based investigations of the wave-induced responses of O(1S), O2(b,0-0) and OH(8-3) emissions have been performed. A series of digital experiments performed using the one-dimensional simulation model proposed by Liu and Swenson (2003) demonstrated that, in addition to the variable component, the wave disturbance of airglow emissions has a constant component. This component is the enhancement/depletion of the background emission intensity of an emission layer. To interpret its appearance, the simplest analytical model of airglow disturbance due to a gravity wave has been constructed. This model indicates that enhancement/depletion of the background emission intensity is a nonlinear airglow response to a wave disturbance. Its magnitude depends quadratically on the wave amplitude and can reach a few dozen percent relative to the value of the zenith brightness of the unperturbed OH(8-3)/O(1S) emission layer. © 2016 Elsevier Ltd


Danilov A.D.,Institute of Applied Geophysics
Geomagnetism and Aeronomy | Year: 2012

The current views on long-term changes in parameters (trends) in the upper atmosphere and ionosphere are considered. The concept of cooling and contraction of the middle and upper atmosphere due to the increase in the amount of greenhouse gases in the atmosphere is described. © 2012 Pleiades Publishing, Ltd.


Danilov A.D.,Institute of Applied Geophysics | Konstantinova A.V.,Institute of Applied Geophysics
Geomagnetism and Aeronomy | Year: 2015

The median values of critical frequencies observed at ionospheric stations Slough, Juliusruh, and Rome are analyzed in detail. Long-term trends in foF2 for the period 1985–2010 were found using the method previously described numerous times by the authors. The dependence of the trend value k on local time and month of the year was studied. For all three stations, a similar seasonal and diurnal behavior of k is obtained. The maximum values of the negative trends in foF2 fall on the noontime period of the day (1000–1600 LT). In the seasonal behavior, two maximums of the absolute value of k (in the end of winter-beginning of spring and middle of fall) are observed. The absolute values of the trends are small in the summer months. The conclusion regarding the seasonal behavior of k coincides with the conclusion of the authors in an earlier publication: negative trends in foF2 are better pronounced in winter than in summer. The possible conclusions on the character of trends in the thermospheric parameters, which follow from the obtained conclusions on variations in the foF2 trends, are discussed. © 2015, Pleiades Publishing, Ltd.


Danilov A.D.,Institute of Applied Geophysics
Geomagnetism and Aeronomy | Year: 2011

Changes in the values of the critical frequency of the F2 layer from 1990 to 2005-2007, according to median data, are considered. Eleven stations, for which the necessary data are available, have been found in international databanks. The conclusion of the previous publication by Danilov (2011) that at the end of the 1990s and beginning of the 2000s a negative trend in foF2 was observed both after sunset and in the daytime is confirmed. © 2011 Pleiades Publishing, Ltd.


Danilov A.,Institute of Applied Geophysics
Journal of Geophysical Research A: Space Physics | Year: 2015

Median values of the F2 layer critical frequencies observed at ionospheric stations Slough, Juliusruh, and Rome are analyzed in detail. Long-term trends in foF2, k(fo), for the period 1985-2009 are found using the method described earlier by authors. The dependence of the trend value k(fo) on local time and month of the year is studied. For all three stations, similar seasonal and diurnal behaviors of k(fo) are obtained. The maximum values of the negative trends in foF2 fall on the noon period of the day (1000-1600 LT). In the seasonal behavior, two maxima of the absolute value of k(fo) (at the end of winter and beginning of spring and middle of fall) are observed. The absolute values of the trends are small in the summer months. Possible relation to trends in thermospheric parameters which follow from the obtained conclusions on variations in the foF2 trends are discussed. Arguments are presented in favor of a decrease in the atomic oxygen concentration due to an increase in the eddy diffusion as the main cause of negative foF2 trends. It is shown that a negative trend in the atomic oxygen concentration on the order of 10% per decade is able to explain the negative trend in foF2 in winter. Three possible causes of the difference in foF2 and hmF2 trends obtained by different authors are formulated and discussed. They are the following: the use of the entire series of data and the absence of the allowance for diurnal and seasonal variations in the trends. Key Points Diurnal variations in the foF2 and hmF2 trends Seasonal variations in foF2 and hmF2 trends Need for search of foF2 and hmF2 trends after 1980 ©2015. American Geophysical Union. All Rights Reserved.


Danilov A.D.,Institute of Applied Geophysics
Geomagnetism and Aeronomy | Year: 2011

This article considers sparse available data on variations in the main parameters of the ionospheric F2 layer foF2(ss + 2) and hmF2(ss + 2) at the end of the 1990s and the beginning of 2000s. It is shown that the monotonous behavior of hmF2(ss + 2) obtained in earlier publications for the period after 1980 is violated. The hmF2(ss + 2) behavior obtains a more complicated nature by time with a tendency towards a decrease in hmF2(ss + 2) at the beginning of a new century. A statistically significant relationship between foF2(ss + 2) and hmF2(ss + 2) is discovered confirming the Rishbeth statement that during the first hours after sunset, the critical frequency foF2 is governed by dynamical processes via changes in the F2-layer height. It is found that at the end of the interval in question, there is a tendency towards deviations from the above-mentioned dependence. The latter could be a manifestation of the fact that changes in the aeronomical parameters caused by the general cooling and contraction of the thermosphere begin influencing the foF2 value. It is found that in the summer months, the foF2(ss + 2) value demonstrated a systematic decline tendency from the "boundary date" towards the beginning of the 2000s. © 2011 Pleiades Publishing, Ltd.

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