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1.
The monthly means of the ionospheric F2 peak parameters (foF2 and hmF2) over three stations in South Africa (Grahamstown, 33.3°S, 26.5°E, Madimbo, 22.4°S, 26.5°E, and Louisvale, 28.5°S, 21.2°E) were analyzed and compared with IRI-2001, using CCIR (Comité Consultatif International des Radio communications) and URSI (Union Radio-Scientifique Internationale coefficients) options. The analysis covers a few selected quiet and disturbed days during various seasons represented by the months of January, April, July and October 2003. IRI-2001 generally overestimates hmF2 for both quiet and disturbed days and it overestimates and underestimates foF2 at different times for all the stations. In general, foF2 is predicted more accurately by IRI-2001 than hmF2, and on average, the CCIR option performed better than the URSI option when predicting both foF2 and hmF2.In general, the model generates good results, although some improvements are still necessary to be implemented in order to obtain better predictions. There are no significant differences in the model predictions of hmF2 and foF2 for quiet and disturbed days.  相似文献   

2.
Using ionosonde made observations at Concepción (36.8°S; 73.0°W) for the 1958–1994 interval, long-term trends of critical frequency (foF2) and peak height (hmF2) of the ionospheric F2-layer are analysed. The trends found for different times-of-day and all seasons are consistent with an increasing diurnal-variation amplitude of both foF2 and hmF2. An increasing hmF2 trend of up to 1.5 km/year found between midnight and dawn during winter has no precedent. It is suggested that these long-term amplitude changes may be associated with changes in the prevailing thermospheric meridional neutral winds.  相似文献   

3.
The monthly median values of the height of peak electron density of the F2-layer (hmF2) derived from ionosonde measurements at three high latitude stations, namely Narssarssuaq (NAR) (61.2 °N, 314.6 °E), Sondrestrom (SON) (67°N, 309.1°E) and College (COL) (69.9°N, 212.2°E) were analyzed and compared with the International Reference Ionosphere (IRI-2001) model, using Comité Consultatif International des Radio communications) (CCIR and Union Radio-Scientifique Internationale (URSI) options. The analysis covers hmF2 values for March Equinox (February, March, April), June Solstice (May, June, July), September Equinox (August, September, October), and December Solstice (November, December, January), during periods of high (2000–2001), medium (2004–2005) and low (2007–2008) solar activity. Generally, the IRI-2001 prediction follow fairly well the diurnal and seasonal variation patterns of the observed values of hmF2 at all the stations. However, IRI-2001 overestimates and underestimates hmF2 at different times of the day for all solar activity periods and in all the seasons considered. The percentage deviation never exceeded 20%, except during DEC SOLS at COL and SON and during MARCH EQUI at SON during low solar activity period. For all solar activity periods considered, both the URSI and CCIR options of the IRI-2001 model give hmF2 values close to the ones measured, but the URSI option performed better than the CCIR option.  相似文献   

4.
The variability of foF2 in different phases of solar cycle 23   总被引：1，自引：0，他引：1  
In this paper we examined the variations of the foF2 with solar activity for different local time and different seasons. Beside this we evaluated International Reference Ionosphere (IRI) models at different phases of solar cycle 23, different latitudes and different local time. We studied F2 layer critical frequency (foF2) of the ionosphere by using the flare index calculated by the Kandilli Observatory. For this purpose, we identified the months similar with high flare activity during the solar cycle 23. We chose 6 months which represented the different phases (ascending branch, maximum and descending branch) of the solar cycle. We also took into account the fact that these months were in different seasons. The hourly monthly means of observed foF2 data from four ionosonde stations for 6 months were calculated. On the other hand, the identical foF2 values of the same months were calculated for the year 1996, which is the minimum year of the previous solar activity cycle. We subtracted the foF2 values of 1996 from the values of the selected months of the last solar cycle to obtain the residuals, Δ(foF2). Then the magnitude of the residuals is compared through the cycle. We used IRI-2007 as well as IRI-2001 models to see the degree of deviation of the observed results from the predicted ones. We found that the predicted values of the ΔfoF2, which are calculated by the IRI-2007, fitted well with the observed Δ(foF2) and showed that the Δ(foF2) are dependent on the solar cycle variations in general.  相似文献   

5.
Variations of the upper boundary of the ionosphere (UBI) are investigated based on three sources of information: (i) ionosonde-derived parameters: critical frequency foF2, propagation factor M3000F2, and sub-peak thickness of the bottomside electron density profile; (ii) total electron content (TEC) observations from signals of the Global Positioning System (GPS) satellites; (iii) model electron densities of the International Reference Ionosphere (IRI*) extended towards the plasmasphere. The ionospheric slab thickness is calculated as ratio of TEC to the F2 layer peak electron density, NmF2, representing a measure of thickness of electron density profile in the bottomside and topside ionosphere eliminating the plasmaspheric slab thickness of GPS-TEC with the IRI* code. The ratio of slab thickness to the real thickness in the topside ionosphere is deduced making use of a similar ratio in the bottomside ionosphere with a weight Rw. Model weight Rw is represented as a superposition of the base-functions of local time, geomagnetic latitude, solar and magnetic activity. The time-space variations of domain of convergence of the ionosphere and plasmasphere differ from an average value of UBI at ∼1000 km over the earth. Analysis for quiet monthly average conditions and during the storms (September 2002, October–November 2003, November 2004) has shown shrinking UBI altitude at daytime to 400 km. The upper ionosphere height is increased by night with an ‘ionospheric tail’ which expands from 1000 km to more than 2000 km over the earth under quiet and disturbed space weather. These effects are interposed on a trend of increasing UBI height with solar activity when both the critical frequency foF2 and the peak height hmF2 are growing during the solar cycle.  相似文献   

6.
Using digital ionosonde observations at low-latitude station, Delhi (28.6 N, 77.2 E, mag. dip 42.4 N), the diurnal and seasonal variations of the critical frequency of F2 layer (foF2) are analyzed from August 2000 to July 2001 during a high solar activity period. Also, noontime bottomside electron density (Ne-h) profiles, below the F2-peak, are derived from ionogram, using the POLAN (Report UAG-93, WDC-A, for Solar Terrestrial Physics, Boulder, Co.) program during the same period, and these profiles are then normalized to the peak height and density (hmF2, NmF2) of the F2-region. These observations are used to assess the predictability of the International Reference Ionosphere, IRI-2000 model (Radio Sc. 36(2) (2001) 261). Results show in general, a large variability, (1σ, σ is standard deviation), in foF2 during nighttime than daytime during winter and equinox, the variability of foF2 about the mean is about ±25% by night and ±15% by day. The IRI model shows a fairly good agreement with foF2 observations during daytime, however during nighttime, the discrepancies between the two exist. Comparative studies of the normalized observed profiles with those obtained with the IRI model (Bilitza, 2001) using both the options namely: Gulyaeva's (Adv. Space Res. 7 (1987) 39) model and B0-Table (Adv. Space Res. 25(1) (2000) 89), show that during all the seasons, in general, the B0-Tab option, reveals a better agreement with the observations, while the IRI model using Gulyaeva's option, overestimates the electron density distribution during summer and equinox, however, during winter, the model is close to the observations. The comparisons of average profile shape parameters (B0,B1) derived from noontime observed profiles, with those obtained, using B0-Tab option, in the IRI model, show a good agreement during all the seasons. However, B0, B1 obtained, using Gulyaeva's option in the IRI model, show a disagreement with the derived B0, B1 values during all the seasons, except during winter, for B0 parameter.  相似文献   

7.
We analyze Jicamarca ionograms to study the quiet-condition variations in the peak electron density (NmF2), its height (hmF2), and F2-layer thickness parameter (B0) of the equatorial F2 layer during solar minimum. The sunrise peak is found in hmF2 and B0 for all months. During daytime and nighttime, the variation in the hmF2 value is mainly responsible for that in NmF2 and B0. The sunset peaks of hmF2 and B0 exist in the equinoctial months, but not in the winter months. Moreover, the observed values of hmF2, NmF2, and B0 are generally similar to the modeled values of IRI-2001.  相似文献   

8.
Geomagnetism and Aeronomy - The article analyzes the errors in estimating the parameters of the main ionospheric maximum, plasma frequency foF2 and its height hmF2, by automated systems for...  相似文献   

9.
NeQuick ionospheric electron density model produces the full electron density profile in the ionosphere using the F2 layer peak values (foF2 and hmF2) as anchor points. Each part of the profile is modeled using Epstein layer formalism. Simple empirical relations are used to compute the thicknesses of each semi-Epstein layer. It has been observed that when NeQuick model is used to estimate total electron content at low latitudes the modeled values tend to underestimate the observed ones. Beside the F2 peak values, the most important profile parameter is the thickness of the F2 layer bottomside. The present study focuses on NeQuick model behavior at low latitudes comparing modeled profiles parameters with the ones extracted from experimental data mostly from African and Indian sector at different levels of solar activity and different time of the day. Possible model improvements are discussed.  相似文献   

10.
A new single-station model (SSM) for monthly median values of the ionospheric parameters foF2 and M(3000)F2 has been developed. Fourier analysis provides a tool for decomposing the time-varying ionospheric parameters. The 12–month smoothed sunspot number R 12 was used as an external solar characteristic because of its availability and predictability. However, for the first time, the solar activity is described not only by R 12 , but also by the linear coefficient K R representing the tendency of the change of solar activity. A general non-linear approximation of the influence of the solar-cycle characteristics R 12 and K R and ionospheric parameters foF2 and M(3000)F2 was accepted. The new SSM is applied to several European stations and its statistical evaluation shows better results than the other two SSMs used in the paper. The approach described in the paper does not contradict the use of different synthetic ionospheric indices (as the T-index, MF2–index); the basic aim is to show only that using one additional new characteristic of the solar-cycle variations, such as K R , improves the monthly median model.  相似文献   

11.
We have modelled the effects of changes in the Earth's magnetic field on the ionosphere as have occurred from 1957 to 1997 using the NCAR Thermosphere–Ionosphere–Electrodynamics General Circulation Model. Previous studies that attempted to quantify these effects used a constant wind field, so that any electro-dynamical coupling processes could not be accounted for. Using TIE-GCM we can account for these processes. We find substantial changes in the F2 layer peak height hmF2 (up to ±20 km) and critical frequency foF2 (up to ±0.5 MHz) over the Atlantic Ocean and South America, purely due to changes in the Earth's magnetic field (i.e. unrelated to greenhouse gas cooling effects, which are often held responsible for long-term trends in hmf2 and fof2). These would make up a significant contribution to observed long-term trends in these areas and therefore must be taken into account in their interpretation. Modelled trends of hmF2 and foF2 exhibit a strong seasonal and diurnal variation, highlighting the importance of separating data with respect to season and local time. Most of the modelled changes in hmF2 and foF2 can be related to changes in plasma transport up or down magnetic field lines driven by neutral winds, changes, which are mostly caused by changes in the inclination of the field, though changes in declination and neutral wind also play a role. Changes in the vertical component of the E×B drift seem to have little effect on hmF2 and foF2.  相似文献   

12.
This paper deals with the diurnal and seasonal variations of height of the peak electron density of the F2-layer (hmF2) derived from digital ionosonde measurements at a low–middle-latitude station, New Delhi (28.6°N, 77.2°E, dip 42.4°N). Diurnal and seasonal variations of hmF2 are examined and comparisons of the observations are made with the predictions of the International Reference Ionosphere (IRI-2001) model. Our study shows that during both the moderate and low solar activity periods, the diurnal pattern of median hmF2 reveals a more or less similar trend during all the seasons with pre-sunrise and daytime peaks during winter and equinox except during summer, where the pre-sunrise peak is absent. Comparison of observed median hmF2 values with the IRI during moderate and low solar activity periods, in general, reveals an IRI overestimation in hmF2 during all the seasons for local times from about 06 LT till midnight hours except during summer for low solar activity, while outside this time period, the observed hmF2 values are close to the IRI predictions. The hmF2 representation in the IRI model does not reproduce pre-sunrise peaks occurring at about 05 LT during winter and equinox as seen in the observations during both the solar activity periods. The noontime observed median hmF2 values increase by about 10–25% from low (2004–2005) to high solar activity (2001–2002) during winter and equinox, while the IRI in the same time period and seasons shows an increase of about 10–20%. During summer, however, the observed noontime median hmF2 values show a little increase with the solar activity, as compared to the IRI with an increase of about 12%.  相似文献   

13.
We use the measurements of the Jicamarca digisonde to examine the variations in F2 layer peak electron density (NmF2), its height (hmF2), and the F2 layer thickness parameter (B0) near the dip equator. The hourly ionograms during geomagnetic quiet-conditions for a 12-month period close to the maximum solar activity, April 1999–March 2000, are used to calculate the monthly averages of these parameters, for each month. The averages are compared with the International Reference Ionosphere (IRI)-2001 model values. The results show that the higher hmF2 values during daytime, associated with the upward velocity, are mainly responsible for the greater values of NmF2 and B0; while the nighttime lower hmF2, related to the downward velocity, are responsible for the smaller NmF2 and B0. For daytime, hmF2 and NmF2 are correlated with the solar activity in the equinoctial and summer months. The hmF2 and B0 peaks at sunset with an associated sharp decrease in NmF2 are presented in the equinoctial and summer months, but not in the winter months. Comparison of the measured hmF2 values with the International Radio Consultative Committee (CCIR) maps used in IRI-2001 (IRI-CCIR) reveals an IRI overestimate in hmF2 during daytime. The most significant discrepancy is that the IRI-CCIR does not model the post-sunset peak in hmF2. For the NmF2 comparison, the values obtained from both the CCIR and URSI maps are generally close to the observed values. For the B0 comparison, the highest discrepancy between the observation and the Gulyaeva option (IRI-Gulyaeva) is the location of the annual maximum for the daytime values, also the winter daytime predictions are too low. Additionally, the significant negative difference between the observation and the B0-table option (IRI-B0-table) provides a slightly better prediction, except for 0400–1000 LT when the model significantly overestimates. The post-sunset peak in B0 at some months is predicted by neither the IRI-Gulyaeva nor the IRI-B0-table options.  相似文献   

14.
Timoçin  E.  Ünal  İ.  Göker  Ü. D. 《Geomagnetism and Aeronomy》2018,58(7):846-856
Geomagnetism and Aeronomy - This study investigates the impacts of geomagnetic storms on the performance of the International Reference Ionosphere 2016 (IRI-2016) foF2 predictions at different...  相似文献   

15.
A comparison of the diurnal and seasonal variations in the ionospheric equivalent slab thickness (τ) and bottomside slab thickness (B0) is presented based on the observation during high solar activities at a mid-latitude station—Wuhan (114.4°E, 30.6°N). The investigated data include foF2, hmF2, B0, B1, and TEC, and are derived from the measured ionogram and GPS receiver over Wuhan from April 1999 to March 2000. The results show that τ and B0 are highly/weakly correlated during the day/night, respectively. Furthermore, a comprehensive discussion of the relation between τ, B0, and hmF2 for geomagnetic storm events is provided in this paper.  相似文献   

16.
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17.
The Earth's magnetic field presents long-term variations with changes in strength and orientation. Particularly, changes in the dip angle (I) and, consequently, in the sin(I)cos(I) factor, affect the thermospheric neutral winds that move the conducting plasma of the ionosphere. In this way, a lowering or lifting of the F2-peak (hmF2) is induced together with changes in foF2, depending on season, time and location. A simple theoretical approximation, developed in a previous work, is extended to a worldwide latitude–longitude grid to assess hmF2 and foF2 trends due to Earth's magnetic field secular variations. Compared to the greenhouse gases effects over the ionosphere, the Earth's magnetic field may be able to produce stronger trends which vary with season, time and location. However, to elucidate the origin of F2-region trends, long-term variations in the three possible known mechanisms should be considered altogether—greenhouse gases, geomagnetic activity and Earth's magnetic field.  相似文献   

18.
Variations with time during recent decades of three parameters are considered. R(foF2) is the correlation coefficient between the nighttime and daytime values of foF2 within the same day. Stable trends are found for minimal (R(foF2)(min)) and maximal (R(foF2)(max)) values of R(foF2) over the year. The foF2(day)/foF2(night) ratio demonstrates both negative and positive trends; the sign of the trend being governed by the inclination I and declination D of the magnetic field. The correlation coefficient r(h,fo) between foF2 and the 100-hPa level in the stratosphere demonstrates a decrease (both, for the years of maximum and minimum solar activity) from the 1980s to the 1990s. The trends in all three groups of data are considered in the scope of an assumption that there is a long-term change in the circulation in the upper atmosphere. The data considered in the paper provide an indirect confirmation of the existence of this change and show the possibility that further studies of the thermospheric dynamics can be undertaken using ground-based ionospheric observations.  相似文献   

19.
使用COSMIC掩星和垂测仪,探测2011—2012年北京地区电离层临界频率数据,比较不同探测手段获取的电离层特征参量随地方时和地磁季节相关性的变化。研究表明:2组数据具有较好的相关性;标准偏差随地方时变化,日出时6:00 LT开始增大,日落时16:00LT到次高值,19:00LT达最大值后开始下降;标准偏差随地磁季节变化,夏季最小,冬季最大。分析认为,电子密度在垂直和水平方向上的梯度变化,造成掩星反演误差增大,可能导致了数据相关性在不同地磁季节和地方时刻的相应变化。  相似文献   

20.
Arecibo (18.4 N, 66.7 W) incoherent scatter (IS) observations of electron density N(h) are compared with the International Reference Ionosphere (IRI-95) during midday (10/14 h), for summer, winter and equinox, at solar maximum (1981). The N(h) profiles below the F2 peak, are normalized to the peak density NmF2 of the F region and are then compared with the IRI-95 model using both the standard B0 (old option) and the Gulyaeva-B0 thickness (new option). The thickness parameter B0 is obtained from the observed electron density profiles and compared with those obtained from the IRI-95 using both the options. Our studies indicate that during summer and equinox, in general, the values of electron densities at all the heights given by the IRI model (new option), are generally larger than those obtained from IS measurements. However, during winter, the agreement between the IRI and the observed values is reasonably good in the bottom part of the F2 layer but IRI underestimates electron density at F1 layer heights. The IRI profiles obtained with the old option gives much better results than those generated with the new option. Compared to the observations, the IRI profiles are found to be much thicker using Gulyaeva-B0 option than using standard B0.  相似文献   

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