scholarly journals F2-layer parameters long-term trends at the Argentine Islands and Port Stanley stations

2001 ◽  
Vol 19 (3) ◽  
pp. 341-349 ◽  
Author(s):  
A. D. Danilov ◽  
A. V. Mikhailov
Keyword(s):  
Critical Frequency ◽  
Geomagnetic Latitude ◽  
Ionospheric Disturbances ◽  
Ionospheric Storm ◽  
Geomagnetic Index ◽  
Critical Frequency Fof2 ◽  
Long Term Trends ◽  
Atmosphere Interaction ◽  
Ionospheric Sounding

Abstract. The ionospheric sounding data at two southern hemisphere stations, the Argentine Islands and Port Stanley, are analyzed using a method previously developed by the authors. Negative trends of the critical frequency foF2 are found for both stations. The magnitudes of the trends are close to those at the corresponding (close geomagnetic latitude) stations of the northern hemisphere, as considered previously by the authors. The values of the F2 layer height hmF2 absolute trends ΔhmF2 are considered. The effect of ΔhmF2 dependence on hmF2 found by Jarvis et al. (1998) is reproduced. A concept is considered that long-term changes of the geomagnetic activity may be an important (if not the only) cause of all the trends of foF2 and hmF2 derived by several groups of authors. The dependence of both parameters on the geomagnetic index Ap corresponds to a smooth scheme of the ionospheric storm physics and morphology; thus, a principal cause of the foF2 and hmF2 geomagnetic trends is most probably a trend found in several publications in the number and intensity of ionospheric storms.Key words. Ionosphere (ionosphere-atmosphere interaction; ionospheric disturbances)

scholarly journals <i>Letter to the Editor</i>: Spatial and seasonal variations of the <i>fo</i>F2 long-term trends

1999 ◽  
Vol 17 (9) ◽  
pp. 1239-1243 ◽  
Author(s):  
A. D. Danilov ◽  
A. V. Mikhailov
Keyword(s):  
Seasonal Variations ◽  
Critical Frequency ◽  
Geomagnetic Latitude ◽  
Seasonal Effect ◽  
Ionospheric Disturbances ◽  
Trend Magnitude ◽  
Letter To The Editor ◽  
Critical Frequency Fof2 ◽  
Long Term Trends

Abstract. 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.Key words. Ionosphere (ionospheric disturbances; mid-latitude ionosphere)

scholarly journals Long-term trends of <i>fo</i>F2 independent of geomagnetic activity

2003 ◽  
Vol 21 (5) ◽  
pp. 1167-1176 ◽  
Author(s):  
A. D. Danilov
Keyword(s):  
Detailed Analysis ◽  
Local Time ◽  
Geomagnetic Activity ◽  
Geomagnetic Latitude ◽  
Ionospheric Disturbances ◽  
Strong Argument ◽  
Long Term Changes ◽  
Long Term Trends ◽  
The Difference

Abstract. A detailed analysis of the foF2 data at a series of ionospheric stations is performed to reveal long-term trends independent of the long-term changes in geomagnetic activity during the recent decades (nongeomagnetic trends). The method developed by the author and published earlier is used. It is found that the results for 21 out of 23 stations considered agree well and give a relative nongeomagnetic trend of -0.0012 per year (or an absolute nongeomagnetic trend of about -0.012 MHz per year) for the period between 1958 and the mid-nineties. The trends derived show no dependence on geomagnetic latitude or local time, a fact confirming their independence of geomagnetic activity. The consideration of the earlier period (1948–1985) for a few stations for which the corresponding data are available provides significantly lower foF2 trends, the difference between the later and earlier periods being a factor of 1.6. This is a strong argument in favor of an anthropogenic nature of the trends derived.Key words. Ionosphere (ionosphere-atmosphere interactions; ionospheric disturbances; mid-latitude ionosphere)

Long-Term Trends in the Critical Frequency of the E-layer

2018 ◽  
Vol 58 (3) ◽  
pp. 338-347 ◽  
Author(s):  
A. D. Danilov ◽  
A. V. Konstantinova
Keyword(s):  
Critical Frequency ◽  
Long Term Trends

scholarly journals Long-term trends in the relation between daytime and nighttime values of <I>fo</I>F2

2008 ◽  
Vol 26 (5) ◽  
pp. 1199-1206 ◽  
Author(s):  
A. D. Danilov
Keyword(s):  
Solar Activity ◽  
Term Trend ◽  
The World ◽  
Long Term Changes ◽  
Long Term Trends ◽  
Thermospheric Winds ◽  
Long Term Trend ◽  
Ionospheric Sounding ◽  
Limiting Value

Abstract. The data from the vertical ionospheric sounding for 12 stations over the world were analyzed to find the relation between the values of foF2 for 02:00 LT and 14:00 LT of the same day. It is found that, in general, there exists a negative correlation between foF2(02) and foF2(14). The value of the correlation coefficient R(foF2) can be in some cases high enough and reach minus 0.7–0.8. The value of R(foF2) demonstrates a well pronounced seasonal variations, the highest negative values being observed at the equinox periods of the year. It is also found that R(foF2) depends on geomagnetic activity: the magnitude of R(foF2) is the highest for the choice of only magnetically quiet days (Ap<6), decreasing with the increase of the limiting value of Ap. For a fixed limitation on Ap, the value of R(foF2) depends also on solar activity. Apparently, the effects found are related to thermospheric winds. Analysis of long series of the vertical sounding data shows that there is a long-term trend in R(foF2) with a statistically significant increase in the R(foF2) magnitude after about 1980. Similar analysis is performed for the foF2(02)/foF2(14) ratio itself. The ratio also demonstrates a systematic trend after 1980. Both trends are interpreted in terms of long-term changes in thermospheric circulation.

Simultaneous ionosonde investigations of the ionospheric F2 layer critical frequency and peak height at both ends of the geomagnetic tube

2020 ◽  
Vol 1 (1) ◽  
pp. 31-44
Author(s):  
Sergii Panasenko ◽  
Dmytro Kotov ◽  
Taras Zhivolup ◽  
Olexander Koloskov ◽  
Volodymyr Lisachenko
Keyword(s):  
Gravity Waves ◽  
Critical Frequency ◽  
Peak Height ◽  
Ionospheric Disturbances ◽  
Atmospheric Gravity Waves ◽  
Magnetohydrodynamic Waves ◽  
Traveling Ionospheric Disturbances ◽  
Critical Frequency Fof2 ◽  
The Difference ◽  
Atmospheric Gravity

Based on the results of simultaneous ionosonde observations during low solar and weak magnetic activities, a coupling was found between diurnal and quasi-periodic variations in ionospheric parameters over magnetically conjugated regions, where the Ukrainian Antarctic Station (UAS) and Millstone Hill Observatory are located. A significant impact of the summer hemisphere on the nighttime variations of the F2 layer critical frequency foF2 in the magnetically conjugated region in the winter hemisphere was found. The most characteristic manifestation of this impact is the control of foF2 variations over the UAS not by the local sunset (sunrise), but by the sunset (sunrise) over Millstone Hill. It was found that the sunset over Millstone Hill leads to an increase in foF2 over the UAS, while the sunrise leads to a decrease in foF2 with a subsequent sharp increase. Both phenomena are associated with changes in the photoelectron flux from the northern hemisphere, corresponding changes in the electron temperature in the ionosphere above the UAS and the effect of these changes on the compression or rarefaction of the ionospheric plasma and changes in the plasmaspheric fluxes of H + ions. It was shown that the transition from nighttime to daytime conditions over both observation points was characterized by a significant decrease in the F2 layer peak height, and the difference in the values of this ionospheric parameter over Millstone Hill and UAS at night is due to seasonal differences in the thermospheric circulation and the difference in the behavior of the ionospheric parameters in the Northern and Southern hemispheres. Manifestations of atmospheric gravity waves, caused by the passage of local sunrise terminators, as traveling ionospheric disturbances with periods of about 90 and 75 – 120 mins over Millstone Hill and UAS, respectively, were found. These waves were most likely generated in the region located between the ionospheric F1 and F2 layers, where the sharp gradients in the electron and ion densities occur during changes in the intensity of solar radiation. It is confirmed that wave disturbances in atmospheric and ionospheric parameters can be transferred between magnetically conjugated regions by slow magnetohydrodynamic waves generated both at the heights of the ionospheric dynamo region due to the modulation of atmospheric and ionospheric parameters by atmospheric waves and the occurrence of external currents, and at the top of the plasmaspheric tube, where sharp plasma compression and heating or rarefaction and cooling occur during the passage of the solar terminator. Keywords: the ionosphere, F2 region, ionosonde measurements, geomagnetic field tube, magnetoconjugate region coupling, atmospheric gravity waves, traveling ionospheric disturbances, generation of slow magnetohydrodynamic waves

scholarly journals Long-term trends in the ionospheric E and F1 regions

2008 ◽  
Vol 26 (5) ◽  
pp. 1189-1197 ◽  
Author(s):  
J. Bremer
Keyword(s):  
Geomagnetic Latitude ◽  
Data Series ◽  
General Behaviour ◽  
Global Trends ◽  
Evaluation Algorithm ◽  
Ozone Trend ◽  
E Region ◽  
Long Term Trends ◽  
Source Of Information

Abstract. Ground based ionosonde measurements are the most essential source of information about long-term variations in the ionospheric E and F1 regions. Data of such observations have been derived at many different ionospheric stations all over the world some for more than 50 years. The standard parameters foE, h'E, and foF1 are used for trend analyses in this paper. Two main problems have to be considered in these analyses. Firstly, the data series have to be homogeneous, i.e. the observations should not be disturbed by artificial steps due to technical reasons or changes in the evaluation algorithm. Secondly, the strong solar and geomagnetic influences upon the ionospheric data have carefully to be removed by an appropriate regression analysis. Otherwise the small trends in the different ionospheric parameters cannot be detected. The trends derived at individual stations differ markedly, however their dependence on geographic or geomagnetic latitude is only small. Nevertheless, the mean global trends estimated from the trends at the different stations show some general behaviour (positive trends in foE and foF1, negative trend in h'E) which can at least qualitatively be explained by an increasing atmospheric greenhouse effect (increase of CO2 content and other greenhouse gases) and decreasing ozone values. The positive foE trend is also in qualitative agreement with rocket mass spectrometer observations of ion densities in the E region. First indications could be found that the changing ozone trend at mid-latitudes (before about 1979, between 1979 until 1995, and after about 1995) modifies the estimated mean foE trend.

scholarly journals Geomagnetic control of the <i>fo</i>F2 long-term trends

2000 ◽  
Vol 18 (6) ◽  
pp. 653-665 ◽  
Author(s):  
A. V. Mikhailov ◽  
D. Marin
Keyword(s):  
Geomagnetic Activity ◽  
Early Morning ◽  
Lower Latitude ◽  
Ionospheric Disturbances ◽  
Trend Magnitude ◽  
Layer Parameter ◽  
Long Term Trends ◽  
First Time ◽  
Further Development

Abstract. Further development of the method proposed by Danilov and Mikhailov is presented. The method is applied to reveal the foF2 long-term trends on 30 Northern Hemisphere ionosonde stations. Most of them show significant foF2 trends. A pronounced dependence of trend magnitude on geomagnetic (invariant) latitude is confirmed. Periods of negative/positive foF2 trends corresponding to the periods of long-term increasing/decreasing geomagnetic activity are revealed for the first time. Pronounced diurnal variations of the foF2 trend magnitude are found. Strong positive foF2 trends in the post-midnight-early-morning LT sector and strong negative trends during daytime hours are found on the sub-auroral stations for the period with increasing geomagnetic activity. On the contrary middle and lower latitude stations demonstrate negative trends in the early-morning LT sector and small negative or positive trends during daytime hours for the same period. All the morphological features revealed of the foF2 trends may be explained in the framework of contemporary F2-region storm mechanisms. This newly proposed F2-layer geomagnetic storm concept casts serious doubts on the hypothesis relating the F2-layer parameter long-term trends to the thermosphere cooling due to the greenhouse effect.Key words: Ionosphere (ionosphere-atmosphere interactions; ionospheric disturbances)

scholarly journals Simplified Regional Prediction Model of Long-Term Trend for Critical Frequency of Ionospheric F2 Region over East Asia

2019 ◽  
Vol 9 (16) ◽  
pp. 3219 ◽  
Author(s):  
Jian Wang ◽  
Hongmei Bai ◽  
Xiangdong Huang ◽  
Yuebin Cao ◽  
Qiang Chen ◽  
...  
Keyword(s):  
East Asia ◽  
Critical Frequency ◽  
Statistical Characteristics ◽  
Radio Waves ◽  
Distinctive Features ◽  
Ionosphere Model ◽  
Proposed Model ◽  
Regional Prediction ◽  
Critical Frequency Fof2

To improve the accuracy of predictions and simplify the difficulty with the algorithm, a simplified empirical model is proposed in developing a long-term predictive approach in determining the ionosphere’s F2-layer critical frequency (foF2). The main distinctive features introduced in this model are: (1) Its vertical incidence sounding data, which were obtained from 18 ionosonde stations in east Asia between 1949 and 2017, used in reconstructing the model and verification; (2) the use of second-order polynomial and triangle harmonic functions, instead of linear ones, to obtain the relationship between the seasonal vs. solar-cycle variations of foF2 and solar activity parameters; (3) the flux of solar radio waves at 10.7 cm and sunspot number are together introduced in reconstructing the temporal characteristics of foF2; and (4) the use of the geomagnetic dip coordinates rather than geographic coordinates in reconstructing the spatial characteristics of foF2. The statistical results reveal that foF2 values calculated from the proposed model agree well with the trend in the monthly median statistical characteristics obtained from measurements. The results are better than those obtained from the International Reference Ionosphere model using both the CCIR and URSI coefficients. Furthermore, the proposed model has enabled some useful guidelines to be established for a more complete and accurate Asia regional or global model in the future.

THE POLAR RADIO BLACK-OUT OF THE IONOSPHERE OF 7 JULY, 1958

1960 ◽  
Vol 38 (9) ◽  
pp. 1195-1212 ◽  
Author(s):  
John H. Chapman
Keyword(s):  
Geomagnetic Latitude ◽  
Ionospheric Storm ◽  
Polar Cap ◽  
Similar Nature ◽  
First Order ◽  
Ionospheric Absorption ◽  
The Earth ◽  
Severe Event ◽  
Two Stages ◽  
Ionospheric Sounding

Ionospheric sounding station data, particularly f-plots, were used to study the ionospheric storm of 7 July, 1958, which is shown to have consisted clearly of two stages. Polar cap absorption began shortly after an importance 3+ flare was observed at 0039 U.T., and a magnetic storm and auroral absorption event followed at 0749 U.T. on July 8.The polar cap absorption spread towards the geomagnetic equator, but the use of higher than first order magnetic dipole terms was found necessary in order to arrange the data properly in latitude. The absorption began some hours earlier at northern stations than at most southern stations, the main cause of the differences in time of onset being thought to be due to the presence or absence of sunlight.The inference is drawn that ionospheric absorption measured at about 3 Mc/s is caused by ionization at 50- to 80-km heights, in which case the data suggest that electrons first precipitated to the earth above 83° corrected geomagnetic latitude, and then protons and helium ions to lower latitudes. The cutoff latitude was 59°, corresponding to a particle magnetic rigidity of 9.6 × 108 ev/c. This storm was compared with the more severe event of 23 February, 1956, and showed to be of a similar nature.

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