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 Ionospheric long-term trends: can the geomagnetic control and the greenhouse hypotheses be reconciled?

2006 ◽  
Vol 24 (10) ◽  
pp. 2533-2541 ◽  
Author(s):  
A. V. Mikhailov
Keyword(s):  
Geomagnetic Activity ◽  
Western Europe ◽  
Temperature Changes ◽  
Neutral Temperature ◽  
Control Concept ◽  
Long Term Trends ◽  
The 1960S ◽  
Strongly Damped ◽  
Long Term Variations

Abstract. The ionospheric F2-layer parameter long-term trends are considered from the geomagnetic control concept and the greenhouse hypothesis points of view. It is stressed that long-term geomagnetic activity variations are crucial for ionosphere long-term trends, as they determine the basic natural pattern of foF2 and hmF2 long-term variations. The geomagnetic activity effects should be removed from the analyzed data to obtain real trends in ionospheric parameters, but this is not usually done. Only a thermosphere cooling, which is accepted as an explanation for the neutral density decrease, cannot be reconciled with negative foF2 trends revealed for the same period. A more pronounced decrease of the O/N2 ratio is required which is not provided by empirical thermospheric models. Thermospheric cooling practically cannot be seen in foF2 trends, due to a weak NmF2 dependence on neutral temperature; therefore, foF2 trends are mainly controlled by geomagnetic activity long-term variations. Long-term hmF2 variations are also controlled by geomagnetic activity variations, as both parameters, NmF2 and hmF2 are related by the F2-layer formation mechanism. But hmF2 is very sensitive to neutral temperature changes, so strongly damped hmF2 long-term variations observed at Slough after 1972 may be considered as a direct manifestation of the thermosphere cooling. Earlier revealed negative hmF2 trends in western Europe, where magnetic declination D<0 and positive trends at the eastern stations (D>0), can be related to westward thermospheric wind whose role has been enhanced due to a competition between the thermosphere cooling (CO2 increase) and its heating under increasing geomagnetic activity after the end of the 1960s.

scholarly journals An interpretation of the <i>ƒo</i>F2 and <i>hm</i>F2 long-term trends in the framework of the geomagnetic control concept

2001 ◽  
Vol 19 (7) ◽  
pp. 733-748 ◽  
Author(s):  
A. V. Mikhailov ◽  
D. Marin
Keyword(s):  
Geomagnetic Activity ◽  
Electron Precipitation ◽  
Ionospheric Disturbances ◽  
Temperature Changes ◽  
Layer Parameter ◽  
Latitudinal Dependence ◽  
Control Concept ◽  
Long Term Trends ◽  
Frame Work

Abstract. Earlier revealed morphological features of the foF2 and hmF2 long-term trends are interpreted in the scope of the geomagnetic control concept based on the contemporary F2-layer storm mechanisms. The F2-layer parameter trends strongly depend on the long-term varying geomagnetic activity whose effects cannot be removed from the trends using conventional indices of geomagnetic activity. Therefore, any interpretation of the foF2 and hmF2 trends should consider the geomagnetic effects as an inalienable part of the trend analysis. Periods with negative and positive foF2 and hmF2 trends correspond to the periods of increasing or decreasing geomagnetic activity with the turning points around 1955, and the end of 1960s and 1980s, where foF2 and hmF2 trends change their signs. Such variations can be explained by neutral composition, as well as temperature and thermospheric wind changes related to geomagnetic activity variations. In particular, for the period of increasing geomagnetic activity (1965–1991) positive at lower latitudes, but negative at middle and high latitudes, foF2 trends may be explained by neutral composition and temperature changes, while soft electron precipitation determines nighttime trends at sub-auroral and auroral latitudes. A pronounced dependence of the foF2 trends on geomagnetic (invariant) latitude and the absence of any latitudinal dependence for the hmF2 trends are due to different dependencies of NmF2 and hmF2 on main aeronomic parameters. All of the revealed latitudinal and diurnal foF2 and hmF2 trend variations may be explained in the frame-work of contemporary F2-region storm mechanisms. The newly proposed geomagnetic storm concept used to explain F2-layer parameter long-term trends proceeds from a natural origin of the trends rather than an artificial one, related to the thermosphere cooling due to the greenhouse effect. Within this concept, instead of cooling, one should expect the thermosphere heating for the period of increasing geomagnetic activity (1965–1991).Key words. Ionosphere (ionosphere-atmosphere interactions; ionospheric disturbances)

Long-term variations in the geomagnetic activity level Part II: Ascending phases of sunspot cycles

1994 ◽  
Vol 12 (10/11) ◽  
pp. 1065-1070 ◽  
Author(s):  
V. Mussino ◽  
O. Borello Filisetti ◽  
M. Storini ◽  
H. Nevanlinna
Keyword(s):  
Correlation Coefficient ◽  
Geomagnetic Activity ◽  
Activity Level ◽  
Activity Levels ◽  
Data Set ◽  
The Past ◽  
Long Term Trends ◽  
A Minor ◽  
Long Term Variations

Abstract. Monthly averages of the Helsinki Ak-values have been reduced to the equivalent aa-indices to extend the aa-data set back to 1844. A periodicity of about five cycles was found for the correlation coefficient (r) between geomagnetic indices and sunspot numbers for the ascending phases of sunspot cycles 9 to 22, confirming previous findings based on a minor number of sunspot cycles. The result is useful to researchers in topics related to solar-terrestrial physics, particularly for the interpretation of long-term trends in geomagnetic activity during the past, and to forecast geomagnetic activity levels in the future.

scholarly journals A revised approach to the ƒ<i>o</i>F2 long-term trends analysis

2002 ◽  
Vol 20 (10) ◽  
pp. 1663-1675 ◽  
Author(s):  
A. V. Mikhailov ◽  
D. Marin ◽  
T. Yu. Leschinskaya ◽  
M. Herraiz
Keyword(s):  
Geomagnetic Activity ◽  
Practical Importance ◽  
Ionospheric Disturbances ◽  
Activity Increase ◽  
New Approach ◽  
Long Term Trends ◽  
Time Periods ◽  
Short Time ◽  
Long Term Variations

Abstract. A new approach to extract foF2 long-term trends, which are free to a great extent from solar and geomagnetic activity effects, has been proposed. These trends are insensitive to the phase (increasing/decreasing) of geomagnetic activity, with long-term variations being small and insignificant for such relatively short time periods. A small but significant residual foF2 trend, with the slope Kr = - 2.2 × 10-4 per year, was obtained over a 55-year period (the longest avail-able) of observations at Slough. Such small trends have no practical importance. On the other hand, negative (although insignificant) residual trends obtained at 10 ionosonde stations for shorter periods (31 years) may be considered as a manifestation of a very long-term geomagnetic activity increase which did take place during the 20th century. All of the revealed foF2 long-term variations (trends) are shown to have a natural origin related to long-term variations in solar and geomagnetic activity. There is no indication of any manmade foF2 trends.  Key words. Ionosphere (ionosphere-atmosphere interactions, ionospheric disturbances)

Investigation of long-term variation of atmospheric oxidation in background areas of China

2020 ◽  
Author(s):  
Junhua Wang ◽  
Baozhu Ge ◽  
Bo Yao ◽  
Weili Lin ◽  
Ying Liu ◽  
...  
Keyword(s):  
Model Simulation ◽  
Atmospheric Oxidation ◽  
Oh Radical ◽  
Quasi Biennial Oscillation ◽  
Direct Observations ◽  
Term Variation ◽  
Long Term Trends ◽  
Low Levels ◽  
Long Term Trend

&lt;p&gt;The atmospheric&amp;#160;oxidizing capacity&amp;#160;(AOC) is closely related to the self-cleaning ability of the atmosphere in which the air pollutants were removed through reacting with oxidations such as OH radical. The level of OH radical is a dominant indicator to the AOC in clean regions characterized as low levels of NO&lt;sub&gt;x&lt;/sub&gt;&amp;#160;which is another factor that influences AOC. Due to a lack of VOCs-related mechanisms in model simulation and high cost of&amp;#160;the direct observations of OH radical, the long-term trend of OH radical in China is still unclear, especially under the circumstance of significant reduction of Chinese emissions in recent years. In this study, three methods based on a proxy gas CH&lt;sub&gt;3&lt;/sub&gt;CCl&lt;sub&gt;3&lt;/sub&gt;&amp;#160;from 5 regional background stations in China have been developed to investigate the long-term&amp;#160;variation of OH radical in China.&amp;#160;The concentration of OH radical in the background area of China is approximately (0.8&amp;#177;0.1)*10&lt;sup&gt;6 &lt;/sup&gt;molecular/cm&lt;sup&gt;3&lt;/sup&gt;, lower than the results in other background regions of the world. This could be explained by the larger depletion of OH radical in China due to the higher concentrations of polluted gases (i.e., NO&lt;sub&gt;x&lt;/sub&gt;, CO and CH&lt;sub&gt;4&lt;/sub&gt;). The different methods showed almost consistent results for the long-term trends of OH radical in China. From 2006 to 2017, the annual averaged OH concentration showed a slow downward but insignificant trend with the anomalous annual changes ranging from -0.1% to 0.15%. However, significant inter-annual fluctuations were also detected concurrently with a period about two years. This is consistent with the 2-3 years Quasi-biennial Oscillation (QBO) in the long-term variation of surface O&lt;sub&gt;3 &lt;/sub&gt;concentrations. These results provide the new insights into the annual variation of OH radical in China, which could help improve our understanding of the long-term characteristics of atmospheric oxidation in background areas of China.&lt;/p&gt;

scholarly journals Long-term trends of <i>f</i>oE and geomagnetic activity variations

2003 ◽  
Vol 21 (3) ◽  
pp. 751-760 ◽  
Author(s):  
A. V. Mikhailov ◽  
B. A. de la Morena
Keyword(s):  
Geomagnetic Activity ◽  
Lower Thermosphere ◽  
Chemical Pollution ◽  
Anthropogenic Activity ◽  
Ionospheric Disturbances ◽  
Time Period ◽  
Long Term Trends ◽  
First Time ◽  
Long Term Variations

Abstract. A relationship between foE trends and geomagnetic activity long-term variations has been revealed for the first time. By analogy with earlier obtained results on the foF2 trends it is possible to speak about the geomagnetic control of the foE long-term trends as well. Periods of increasing geomagnetic activity correspond to negative foE trends, while these trends are positive for the decreasing phase of geomagnetic activity. This "natural" relationship breaks down around 1970 (on some stations later) when pronounced positive foE trends have appeared on most of the stations considered. The dependence of foE trends on geomagnetic activity can be related with nitric oxide variations at the E-layer heights. The positive foE trends that appeared after the "break down" effect may also be explained by the [NO] decrease which is not related to geomagnetic activity variations. But negative trends or irregular foE variations on some stations for the same time period require some different mechanism. Chemical pollution of the lower thermosphere due to the anthropogenic activity may be responsible for such abnormal foE behavior after the end of the 1960s.Key words. Ionosphere (ionosphere-atmosphere interactions; ionospheric disturbances)

scholarly journals Maps, trends, and temperature sensitivities—phenological information from and for decreasing numbers of volunteer observers

2021 ◽  
Author(s):  
Ye Yuan ◽  
Stefan Härer ◽  
Tobias Ottenheym ◽  
Gourav Misra ◽  
Alissa Lüpke ◽  
...  
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Strong Decrease ◽  
Temperature Changes ◽  
Interpolation Accuracy ◽  
Observation Network ◽  
Shiny App ◽  
Long Term Trends ◽  
Autumn And Winter

AbstractPhenology serves as a major indicator of ongoing climate change. Long-term phenological observations are critically important for tracking and communicating these changes. The phenological observation network across Germany is operated by the National Meteorological Service with a major contribution from volunteering activities. However, the number of observers has strongly decreased for the last decades, possibly resulting in increasing uncertainties when extracting reliable phenological information from map interpolation. We studied uncertainties in interpolated maps from decreasing phenological records, by comparing long-term trends based on grid-based interpolated and station-wise observed time series, as well as their correlations with temperature. Interpolated maps in spring were characterized by the largest spatial variabilities across Bavaria, Germany, with respective lowest interpolated uncertainties. Long-term phenological trends for both interpolations and observations exhibited mean advances of −0.2 to −0.3 days year−1 for spring and summer, while late autumn and winter showed a delay of around 0.1 days year−1. Throughout the year, temperature sensitivities were consistently stronger for interpolated time series than observations. Such a better representation of regional phenology by interpolation was equally supported by satellite-derived phenological indices. Nevertheless, simulation of observer numbers indicated that a decline to less than 40% leads to a strong decrease in interpolation accuracy. To better understand the risk of declining phenological observations and to motivate volunteer observers, a Shiny app is proposed to visualize spatial and temporal phenological patterns across Bavaria and their links to climate change–induced temperature changes.

scholarly journals Different long-term trends of the oxygen red 630.0 nm line nightglow intensity as the result of lowering the ionosphere F2 layer

2008 ◽  
Vol 26 (8) ◽  
pp. 2069-2080 ◽  
Author(s):  
N. B. Gudadze ◽  
G. G. Didebulidze ◽  
L. N. Lomidze ◽  
G. Sh. Javakhishvili ◽  
M. A. Marsagishvili ◽  
...  
Keyword(s):  
Electron Density ◽  
Line Intensity ◽  
Peak Height ◽  
Height Distribution ◽  
Theoretical Simulation ◽  
Type Layer ◽  
Long Term Trends ◽  
The Mean ◽  
Long Term Trend

Abstract. Long-term observations of total nightglow intensity of the atomic oxygen red 630.0 nm line at Abastumani (41.75° N, 42.82° E) in 1957–1993 and measurements of the ionosphere F2 layer parameters from the Tbilisi ionosphere station (41.65° N, 44.75° E) in 1963–1986 have been analyzed. It is shown that a decrease in the long-term trend of the mean annual red 630.0 nm line intensity from the pre-midnight value (+0.770±1.045 R/year) to its minimum negative value (−1.080±0.670 R/year) at the midnight/after midnight is a possible result of the observed lowering of the peak height of the ionosphere F2 layer electron density hmF2 (−0.455±0.343 km/year). A theoretical simulation is carried out using a simple Chapman-type layer (damping in time) for the height distribution of the F2 layer electron density. The estimated values of the lowering in the hmF2, the increase in the red line intensity at pre-midnight and its decrease at midnight/after midnight are close to their observational ones, when a negative trend in the total neutral density of the upper atmosphere and an increase in the mean northward wind (or its possible consequence – a decrease in the southward one) are assumed.

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