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 Investigations of long-term trends in the ionosphere with world-wide ionosonde observations*

2005 ◽  
Vol 2 ◽  
pp. 253-258 ◽  
Author(s):  
J. Bremer
Keyword(s):  
Data Series ◽  
Model Calculations ◽  
Maximum Electron Density ◽  
Model Predictions ◽  
Density Values ◽  
Long Term Trends ◽  
Experimental Values ◽  
The Individual ◽  
Global Mean

Abstract. Basing on model calculations by Roble and Dickinson (1989) for an increasing content of atmospheric greenhouse gases in the Earth’s atmosphere Rishbeth (1990) predicted a lowering of the ionospheric F2- and E-regions. Later Rishbeth and Roble (1992) also predicted characteristic longterm changes of the maximum electron density values of the ionospheric E-, F1-, and F2-layers. Long-term observations at more than 100 ionosonde stations have been analyzed to test these model predictions. In the E- and F1-layers the derived experimental results agree reasonably with the model trends (lowering of h'E and increase of ƒoE and ƒoF1, in the E-layer the experimental values are however markedly stronger than the model data). In the ionospheric F2-region the variability of the trends derived at the different individual stations for hmF2 as well as ƒoF2 values is too large to estimate reasonable global mean trends. The reason of the large differences between the individual trends is not quite clear. Strong dynamical effects may play an important role in the F2-region. But also inhomogeneous data series due to technical changes as well as changes in the evaluation algorithms used during the long observation periods may influence the trend analyses.

scholarly journals Differing pre-industrial cooling trends between tree rings and lower-resolution temperature proxies

2020 ◽  
Vol 16 (2) ◽  
pp. 729-742 ◽  
Author(s):  
Lara Klippel ◽  
Scott St. George ◽  
Ulf Büntgen ◽  
Paul J. Krusic ◽  
Jan Esper
Keyword(s):  
Tree Ring ◽  
Tree Rings ◽  
Ice Core ◽  
Temperature Sensitive ◽  
Global Trends ◽  
Temperature Changes ◽  
Long Term Trends ◽  
Sediment Data ◽  
Common Era

Abstract. The new PAGES2k global compilation of temperature-sensitive proxies offers an unprecedented opportunity to study regional to global trends associated with orbitally driven changes in solar irradiance over the past 2 millennia. Here, we analyze pre-industrial long-term trends from 1 to 1800 CE across the PAGES2k dataset and find that, in contrast to the gradual cooling apparent in ice core, marine, and lake sediment data, tree rings do not exhibit the same decline. To understand why tree-ring proxies lack any evidence of a significant pre-industrial cooling, we divide those data by location (high Northern Hemisphere latitudes vs. midlatitudes), seasonal response (annual vs. summer), detrending method, and temperature sensitivity (high vs. low). We conclude that the ability of tree-ring proxies to detect pre-industrial, millennial-long cooling is not affected by latitude, seasonal sensitivity, or detrending method. Caution is advised when using multi-proxy approaches to reconstruct long-term temperature changes over the entire Common Era.

scholarly journals Ionospheric F1 layer long-term trends and the geomagnetic control concept

2008 ◽  
Vol 26 (12) ◽  
pp. 3793-3803 ◽  
Author(s):  
A. V. Mikhailov
Keyword(s):  
Geomagnetic Activity ◽  
Temperature Changes ◽  
Term Variation ◽  
Control Concept ◽  
E Region ◽  
Long Term Trends ◽  
Long Term Trend ◽  
The Magnetic Field ◽  
Long Term Variations

Abstract. A previous approach to the ionospheric long-term trend analysis has been applied to the foF1 observations from Slough and Rome in order to investigate a possible relationship between the foF1 and the long-term variation of geomagnetic activity. A 40-year period, starting in 1962, has been used for the analysis. According to the results obtained earlier for F2 and E-region trends, geomagnetic control of the long-term variation has also been revealed for the foF1. Thus, it is now possible to speak about the geomagnetic control of the ionospheric trends in the whole ionosphere. This is not surprising as the Earth's ionosphere is a single entity that is strongly controlled, either directly or indirectly, by the magnetic field. As with the F2-region, this geomagnetic control is provided via neutral composition and temperature changes. A very long-term (centennial) increase in geomagnetic activity in the 20th century is seen in the long-term foF1 variations as well. After its removal, the residual foF1 trends are very small and insignificant. In principal, this means that the observed foF1 long-term variations have a natural origin and can be attributed to solar and geomagnetic activity long-term variations. However, the situation in the thermosphere has been changing since 1997 and available foF2 observations at the two stations reveal information about the "break down" of the geomagnetic control in the F2-region. Possible reasons of these changes are discussed.

scholarly journals On the inclusion of data from solar cycle 19 to estimate F2 layer characteristic long term trends

2015 ◽  
Vol 58 (4) ◽  
Author(s):  
Blas F. de Haro Barbas ◽  
Ana G. Elias
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Solar Radio ◽  
Data Series ◽  
Radio Flux ◽  
Solar Radio Flux ◽  
Long Term Trends ◽  
Layer Characteristic ◽  
Dominant Influence

<p>The effect of including solar cycle 19 (1954-1964) in ionospheric trend estimation is assessed using experimental foF2 values. The dominant influence on the F2 layer is solar EUV radiation. In fact, around 90% of inter-annual variance of ionospheric parameters, such as foF2, is explained by solar EUV proxies such as the sunspot number, Rz, and solar radio flux at 10.7 cm, F10.7. This makes necessary to filter out solar activity effects prior to long term trends estimation, which is reduced at most to the remaining 10% variance. In general solar activity is filtered assessing the residuals of a linear regression between foF2 and Rz, or between foF2 and F10.7. Solar cycle 19 is a strong cycle during which Rz and F10.7 exceeded the values beyond which the ionosphere does not respond linearly to a further increase in EUV radiation. This effect, called saturation, implies a break down of the linearity between foF2 and EUV, and results in persistent negative residuals during this period. Since solar cycle 19 is at the beginning of the time series, trends result to be positive, or less negative, than trends without considering this period. In this case the filtering process is generating a “spurious” trend in the filtered data series which may lead to erroneous conclusions. hmF2 that do not present a saturation effect is also analyzed.</p><div> </div>

scholarly journals Long-term in situ measurements of NO<sub>x</sub> and NO<sub>y</sub> at Jungfraujoch 1998–2009: time series analysis and evaluation

2011 ◽  
Vol 11 (8) ◽  
pp. 21835-21875
Author(s):  
S. Pandey Deolal ◽  
D. Brunner ◽  
M. Steinbacher ◽  
U. Weers ◽  
J. Staehelin
Keyword(s):  
Time Series ◽  
Warm Season ◽  
Data Series ◽  
Data Set ◽  
Long Term Trends ◽  
Investigation Period ◽  
Transport And Mixing ◽  
Time Required

Abstract. We present an analysis of the NOy (NOx + other oxidized species) measurements at the high alpine site Jungfraujoch (JFJ, 3580 m a.s.l.) for the period 1998–2009, which is the longest continous NOy data set reported from the lower free troposphere worldwide. Due to stringent emission control regulations, nitrogen oxides (NOx) emissions have been reduced significantly in Europe since the late 1980s as well as during the investigation period. However, the time series of NOy at JFJ does not show a consistent trend but a maximum during 2002 to 2004 and a decreasing tendency thereafter. The seasonal cycle of NOy exhibits a maximum in the warm season and a minimum in the cold months, opposite to measurements in the PBL, reflecting the seasonal changes in vertical transport and mixing. Except for summer, the seasonal mean NOx concentrations at JFJ show a high year-to-year variability which is strongly controlled by short episodic pollution events obscuring any long-term trends. The low variability in mean and median NOx values in summer is quite remarkable indicating rapid photochemical conversion of NOx to higher oxidized species (NOz) of the NOy family on a timescale shorter than the time required to transport polluted air from the boundary layer to JFJ. In order to evaluate the quality of the NOy data series, an in-situ intercomparison with a second collocated NOy analyzer with a separate inlet was performed in 2009–2010 which showed an agreement within 10 % including all uncertainties and errors.

scholarly journals Long-Term Changes in Ionospheric Climate in Terms of foF2

Atmosphere ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 110
Author(s):  
Jan Laštovička
Keyword(s):  
Critical Frequency ◽  
Secular Change ◽  
Main Magnetic Field ◽  
Data Series ◽  
Main Driver ◽  
Important Trend ◽  
Long Term Trends ◽  
Climate Space ◽  
The Impact

There is not only space weather; there is also space climate. Space climate includes the ionospheric climate, which is affected by long-term trends in the ionosphere. One of the most important ionospheric parameters is the critical frequency of the ionospheric F2 layer, foF2, which corresponds to the maximum ionospheric electron density, NmF2. Observational data series of foF2 have been collected at some stations for as long as over 60 years and continents are relatively well covered by a network of ionosondes, instruments that measure, among others, foF2. Trends in foF2 are relatively weak. The main global driver of long-term trends in foF2 is the increasing concentration of greenhouse gases, namely CO2, in the atmosphere. The impact of the other important trend driver, the secular change in the Earth’s main magnetic field, is very regional, being positive in some regions, negative in others, and neither in the rest. There are various sources of uncertainty in foF2 trends. One is the inhomogeneity of long foF2 data series. The main driver of year-to-year changes in foF2 is the quasi-eleven-year solar cycle. The removal of its effect is another source of uncertainty. Different methods might provide somewhat different strengths among trends in foF2. All this is briefly reviewed in the paper.

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 Low-frequency lower E-region wind and reflection height measurements as sensor for climate variability

2008 ◽  
Vol 6 ◽  
pp. 331-335 ◽  
Author(s):  
C. Jacobi
Keyword(s):  
Oblique Incidence ◽  
Lower Thermosphere ◽  
Low Frequency ◽  
Time Interval ◽  
Radio Waves ◽  
Reflection Height ◽  
E Region ◽  
Long Term Trends ◽  
Mlt Region

Abstract. Measurements of reflection heights of low-frequency (LF) radio waves at oblique incidence and estimates of mesosphere/lower thermosphere (MLT) region horizontal winds applying the D1 spaced receiver method on LF field strength registrations are analyzed with respect to possible long-term trends and interdecadal variability in the time interval from ~1980 to date. While no clear signal of mesospheric height trend is registered during the last two decades, significant trends of MLT horizontal winds are found. These trends are non-linear, in particular a change of trends around 1990 is found, which is probably connected with changes in tropospheric and stratospheric conditions at that time.

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