Causes of the mid-latitude NmF2 winter anomaly at solar maximum

Павлов, А. В.; Павлова, Н. М.

doi:10.1016/j.jastp.2005.02.009

Cited by 45 publications

(36 citation statements)

References 46 publications

(88 reference statements)

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“…To reach approximately the same level of the solar activity for summer and winter days, the difference between the winter and summer daily F10.7 solar activity indexes is taken to be less or equal to 20 in the statistical analysis. On the other hand, the value of NmF2 is a function of production and loss rate of unexcited and electronically excited O + ions (see, e.g., Pavlov and Pavlova, 2005). As a result, the F2-layer peak electron density depends on the neutral temperature and densities whose values are functions of F10.7 solar activity index for a previous day (Hedin, 1987).…”

Section: Statistical Study Of the Nmf2 Winter Anomaly: Results And DImentioning

confidence: 99%

“…The daytime mid-latitude electron density of the F2-region is decreased up to a factor of 2-3 due to vibrationally excited N 2 and O 2 (Pavlov, 1998;Pavlov et al, 1999;Pavlov and Foster, 2001;Prolss and Werner, 2002). As a result, a part of the mid-latitude F2-layer winter anomaly can be attributed to the seasonal difference of the increase in the loss rate of O + ( 4 S) ions due to vibrationally excited N 2 and O 2 (Torr et al, 1980;Pavlov and Pavlova, 2005;Pavlov et al, 2008a, b).…”

Section: Statistical Study Of the Nmf2 Winter Anomaly: Results And DImentioning

confidence: 99%

“…These electronically excited oxygen ions are converted to N + 2 and O + 2 ions, and O + ( 4 S) ions in chemical reactions constituting a large daytime source, P ex , of O + ( 4 S) ions through chemical reactions (see, e.g., Pavlov and Pavlova, 2005). Neglect of electronically excited oxygen ions in model simulations, leads to inaccurate values of NmF2 while a difference between seasonal variations of P EUV +P ex and P EUV can lead to disagreements between values of r (see Eq.…”

Section: Statistical Study Of the Nmf2 Winter Anomaly: Results And DImentioning

confidence: 99%

“…The model simulations (Torr et al, 1980;Pavlov and Pavlova, 2005;Pavlov et al, 2008a, b) (Pavlov et al, 2008a, b). This decrease in the relative role of these two sources of the NmF2 winter anomaly can be responsible for the decrease of Q(R>1) with decreasing solar activity over the Argentine Islands (see Table 2).…”

Section: Statistical Study Of the Nmf2 Winter Anomaly: Results And DImentioning

confidence: 99%

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Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

Павлов

Павлова

2009

Ann. Geophys.

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Abstract. We present a statistical study of variations in the F2-layer peak electron density, NmF2, and altitude, hmF2, over the Argentine Islands ionosonde. The critical frequencies, foF2, and, foE, of the F2 and E-layers, and the propagation factor, M(3000)F2, measured by the ionosonde during the 1957-1959 and 1962-1995 time periods were used in the statistical analysis to determine the values of NmF2 and hmF2. The probabilities to observe maximum and minimum values of NmF2 and hmF2 in a diurnal variation of the electron density are calculated. Our study shows that the main part of the maximum diurnal values of NmF2 is observed in a time sector close to midnight in November, December, January, and February exhibiting the anomalous diurnal variations of NmF2. Another anomalous feature of the diurnal variations of NmF2 exhibited during November, December, and January when the minimum diurnal value of NmF2 is mainly located close to the noon sector. These anomalous diurnal variations of NmF2 are found to be during both geomagnetically quiet and disturbed conditions. Anomalous features are not found in the diurnal variations of hmF2. The statistical study of the NmF2 winter anomaly phenomena over the Argentine Islands ionosonde was carried out. The variations in a maximum daytime value, R, of a ratio of a geomagnetically quiet daytime winter NmF2 to a geomagnetically quiet daytime summer NmF2 taken at a given UT and for approximately the same level of solar activity were studied. The conditional probability of the occurrence of R in an interval of R, the most frequent value of R, the mean expected value of R, and the conditional probability to observe the F2-region winter anomaly during a daytime period were calculated for low, moderate, and high solar activity. The calCorrespondence to: A. V. Pavlov (pavlov@izmiran.ru) culations show that the mean expected value of R and the occurrence frequency of the F2-region winter anomaly increase with increasing solar activity.

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Section: Statistical Study Of the Nmf2 Winter Anomaly: Results And DImentioning

confidence: 99%

Section: Statistical Study Of the Nmf2 Winter Anomaly: Results And DImentioning

confidence: 99%

Section: Statistical Study Of the Nmf2 Winter Anomaly: Results And DImentioning

confidence: 99%

Section: Statistical Study Of the Nmf2 Winter Anomaly: Results And DImentioning

confidence: 99%

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Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

Павлов

Павлова

2009

Ann. Geophys.

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“…[2] Seasonal and December anomalies in N m F 2 variations have been studied since the beginning of ionospheric observations [Appleton and Naismith, 1935;Seaton and Berkner, 1939;Yonezawa and Arima, 1959]; however, the mechanisms of their formation are still discussed in publications [Richards et al, 1994c;Rishbeth et al, 2000;Richards, 2001;Kawamura et al, 2002;Yu et al, 2004;Pavlov and Pavlova, 2005;Rishbeth and Müller-Wodarg, 2006;Zhao et al, 2007]. Among different explanations proposed during the decades of the problem analysis [see Rishbeth, 1998], the suggestion by Rishbeth and Setty [1961] that F 2 layer seasonal anomaly is due to neutral composition variation may be considered as generally accepted [Rishbeth et al, 2000].…”

Section: Introductionmentioning

confidence: 99%

On the mechanism of seasonal and solar cycleN_mF₂variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations

Mikhailov

Perrone

2011

J. Geophys. Res.

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[1] Seasonal (winter/summer) and solar cycle N m F 2 variations as well as summer saturation effect in N m F 2 have been analyzed using Millstone Hill incoherent scatter radar (ISR) daytime observations. A self-consistent approach to the Ne(h) modeling has been applied to extract from ISR observations a consistent set of main aeronomic parameters and to estimate their quantitative contribution to the observed N m F 2 variations. The retrieved aeronomic parameters are independent of uncertainties in thermosphere and solar EUV empirical models, and this is a distinguishing feature of the present consideration. Different temperatures in winter and in summer in the course of solar cycle overlapped on the O + + N 2 reaction rate coefficient temperature dependence result in different N m F 2 dependences on solar activity: a steep practically linear increase with a tendency to turn up in January (contrary to international reference ionosphere prediction) and a slow increase with a tendency to saturate at high solar activity in July despite increasing solar EUV irradiation. In winter the EUV flux and thermospheric parameters provide approximately equal contributions to the N m F 2 increase, while in summer the contribution of thermospheric parameters is small. Both in winter and in summer the variations of atomic oxygen [O] are small at the F 2 layer peak, and its contribution is small compared to linear loss coefficient, b. It is shown that the summer saturation effect in N m F 2 under high solar activity is not just reduced to O/N 2 or EUV flux solar cycle variations but is determined by b via the g 1 temperature dependence. A new mechanism (qualitative) to explain the December anomaly in N m F 2 is proposed. It is based on the idea that the areas of atomic oxygen production and its loss are spatially separated and that time is required to transfer [O] from one area to the other where [O] associates in a three-body collision. Therefore, under a 7% increase in the O 2 dissociation rate due to the Sun-Earth distance decrease in December-January compared to June-July, an accumulation of atomic oxygen should take place in the thermosphere in the vicinity of the December solstice resulting in a 21% N m F 2 increase, which is close to the observed global December effect.Citation: Mikhailov, A. V., and L. Perrone (2011), On the mechanism of seasonal and solar cycle N m F 2 variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations,

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EOF analysis and modeling of GPS TEC climatology over North America

et al. 2015

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An empirical ionospheric model of the total electron content (TEC) over North America (20°-60°N, 40°-140°W) is constructed using the GPS TEC data collected by Massachusetts Institute of Technology (MIT) Haystack Observatory during the years 2001-2012. This model is based on an analysis of quiet time monthly averages using the empirical orthogonal function (EOF) decomposition technique, allowing for separation of spatial and temporal variations. The importance of different types of spatial-temporal variations to the overall TEC variability can be well represented by the characteristics of EOF basis functions and associated principal components coefficients, with various modes. The mode one EOF decomposition constitutes 97.5% of the total variance and therefore represents the essential feature of North America spatial and diurnal variation of the TEC. The mode two EOF, as reported in an earlier study, reveals a large and significant symmetric longitudinal variation of the ionosphere, organized with respect to magnetic declination. The mode three EOF decomposition shows midlatitude latitudinal structure that varies with season in a manner very similar to the so-called winter anomaly. Because of the quick convergence of EOF decomposition modes, the first four EOF modes are utilized for constructing a TEC empirical model. For each of the EOF modes, the temporal variations are expressed analytically in terms of local time, season, and solar activity, and the spatial variations by cubic-spline functions. An analysis of accuracy and quality indicates that this regional empirical TEC model can reflect the majority of the quiet time monthly means, and represent characteristic temporal-spatial variations in the North America.

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Causes of the mid-latitude NmF2 winter anomaly at solar maximum

Cited by 45 publications

References 46 publications

Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

On the mechanism of seasonal and solar cycleN_mF₂variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations

EOF analysis and modeling of GPS TEC climatology over North America

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Causes of the mid-latitude NmF2 winter anomaly at solar maximum

Cited by 45 publications

References 46 publications

Anomalous variations of &lt;I&gt;Nm&lt;/I&gt;F2 over the Argentine Islands: a statistical study

Anomalous variations of &lt;I&gt;Nm&lt;/I&gt;F2 over the Argentine Islands: a statistical study

On the mechanism of seasonal and solar cycleNmF2variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations

EOF analysis and modeling of GPS TEC climatology over North America

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Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

On the mechanism of seasonal and solar cycleN_mF₂variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations