Diurnal, Seasonal and Solar Activity Variations of F-Region Parameters.

1994 ◽  
Author(s):  
A K. Paul
Keyword(s):  
Solar Activity ◽  
F Region

scholarly journals Topside equatorial zonal ion velocities measured by C/NOFS during rising solar activity

2014 ◽  
Vol 32 (2) ◽  
pp. 69-75 ◽  
Author(s):  
W. R. Coley ◽  
R. A. Stoneback ◽  
R. A. Heelis ◽  
M. R. Hairston
Keyword(s):  
Solar Activity ◽  
Local Time ◽  
Geomagnetic Field ◽  
General Pattern ◽  
Magnetic Latitude ◽  
Ion Drifts ◽  
F Region ◽  
Westerly Flow ◽  
Solar Local Time ◽  
Ion Velocity

Abstract. The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic Investigation (CINDI) instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of in situ measurements of plasma temperatures, composition, densities, and velocities in the 400–850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to the geomagnetic field) component of plasma motion over the 2009–2012 interval. The general pattern of local time variation of the equatorial zonal ion velocity is well established as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130–150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time. It was found that the zonal ion drifts show longitude dependence with the largest net eastward values in the American sector. The pre-midnight zonal drifts show definite solar activity (F10.7) dependence. The daytime drifts have a lower dependence on F10.7. The apex altitude (magnetic latitude) variations indicate a more westerly flow at higher altitudes. There is often a net topside subrotation at low F10.7 levels, perhaps indicative of a suppressed F region dynamo due to low field line-integrated conductivity and a low F region altitude at solar minimum.

scholarly journals Post midnight spread-F occurrence over Waltair (17.7° N, 83.3° E) during low and ascending phases of solar activity

2003 ◽  
Vol 21 (3) ◽  
pp. 745-750 ◽  
Author(s):  
K. Niranjan ◽  
P. S. Brahmanandam ◽  
P. Ramakrishna Rao ◽  
G. Uma ◽  
D. S. V. V. D. Prasad ◽  
...  
Keyword(s):  
Solar Activity ◽  
Atmospheric Composition ◽  
Activity Period ◽  
Sunspot Activity ◽  
Low Latitude ◽  
F Region ◽  
Composition And Structure ◽  
Spread F ◽  
Solar Activity Period ◽  
Night Airglow

Abstract. A study carried out on the occurrence of post midnight spread-F events at a low-latitude station, Waltair (17.7° N, 83.3° E), India revealed that its occurrence is maximum in the summer solstice months of the low solar activity period and decreases with an increase in the sunspot activity. The F-region virtual height variations show that 80% of these spread-F cases are associated with an increase in the F-region altitude. It is suggested with the support of the night airglow 6300 A zenith intensity data obtained with co-located ground-based night airglow photometer and electron temperature data from the Indian SROSS C2 satellite that the seasonal variation of the occurrence and probable onset times of the post midnight spread-F depend on the characteristics of the highly variable semipermanent equatorial Midnight Temperature Maximum (MTM).Key words. Ionosphere (ionospheric irregularities; ionosphere atmosphere interactions) Atmospheric composition and structure (airglow and Aurora)

scholarly journals On the relation between ionospheric parameters and sunspot number

2020 ◽  
Vol 1 ◽  
Author(s):  
Chris Hall ◽  
Magnar Gullikstad Johnsen
Keyword(s):  
Solar Activity ◽  
Change Point ◽  
Critical Frequency ◽  
Auroral Oval ◽  
Change Points ◽  
Observation Site ◽  
F Region ◽  
Critical Frequency Fof2 ◽  
E Region ◽  
The Relationship

AbstractIn a recent study, mid-latitude ionospheric parameters were compared with solar activity; it was suggested that the relationship between these, earlier assumed stable, might be changing with time (Lastovicka, 2019). Here, the information is extended to higher latitude (69.6°N, 19.2E) and further back in time. For the ionospheric F-region (viz. the critical frequency, FoF2) the same behaviour is seen with a change-point around 1996. For the ionospheric E-region (viz. the critical frequency, foE), change-points are less obvious than in the mid-latitude study, presumably owing to the observation site lying under the auroral oval.

scholarly journals The dependence of plasma density in the topside ionosphere on the solar activity level

2007 ◽  
Vol 25 (6) ◽  
pp. 1337-1343 ◽  
Author(s):  
L. Liu ◽  
W. Wan ◽  
X. Yue ◽  
B. Zhao ◽  
B. Ning ◽  
...  
Keyword(s):  
Solar Activity ◽  
Plasma Density ◽  
Rate Of Change ◽  
Activity Level ◽  
Nonlinear Dependence ◽  
High Solar Activity ◽  
Topside Ionosphere ◽  
Ion Density ◽  
Solar Activity Level ◽  
F Region

Abstract. In this paper, the ten-year (1996–2005) total ion density Ni measurements from the Defense Meteorological Satellite Program (DMSP) spacecraft in the morning and evening (09:30 and 21:30 LT) sectors have been analyzed to explore the dependence of plasma densities in the topside ionosphere at middle and low latitudes on the solar activity level. Results indicate that there is a strong solar activity dependence of DMSP Ni at 848 km altitude, which has latitudinal and seasonal features. The plasma density in the topside ionosphere has an approximately linear dependence on daily F107 and a strongly nonlinear dependence on SEM/SOHO EUV, such that the change rate of Ni becomes greater with increasing solar EUV. This is quite different from the dependence of Ni near the F-Region peak (NmF2), at which the rate of change of NmF2 decreases with increasing solar EUV. The rate of change of Ni at the DMSP altitude is greatest in the latitude range where Ni is greatest during high solar activity. We suggest that this greater rate of change (or amplification effect) of Ni at the DMSP altitude is mainly a consequence of the solar activity variations of the topside scale height. The changes in the height of the F-Region peak (hmF2) and the density NmF2 play a secondary role.

scholarly journals Equatorial ionospheric response to the 10.7 cm radio flux over two sunspot cycles (1969−1991)

1996 ◽  
Vol 14 (7) ◽  
pp. 725-732
Author(s):  
L. A. Hajkowicz
Keyword(s):  
Solar Activity ◽  
Correlation Coefficient ◽  
Geomagnetic Latitude ◽  
Correlation Coefficients ◽  
Radio Flux ◽  
Solar Cycles ◽  
Pronounced Difference ◽  
F Region ◽  
Diurnal Distribution ◽  
10.7 Cm Solar Flux

Abstract. It is evident that fluctuations in a standard ionospheric parameter, the minimum (virtual) height (h´F) of the equatorial F-region in the African (Ouagadougou), Asian (Manila) and American (Huancayo) longitudinal sectors, closely resemble changes in solar activity as deduced from the 10.7 cm solar flux index (S), over two solar cycles (1969–91). The monthly median hourly value of h´F, particularly in the post-sunset period (18–20 LT), are positively correlated with the monthly average S. The value of h´F can be deduced from an empirical formula: h´F=0.68S+218.3, with the correlation coefficient (r) between h´F and S being 0.78. The diurnal distribution of r during daytime (06–14 LT) was radically different for the African and Asian longitudinal sectors during 1980-1991, with the most pronounced difference in the post-noon period (12–14 LT) when the correlation coefficients r for the Asian and African sectors are 0.8 and 0.2, respectively. Thus, the daytime F-region in the African sector responded far less to changes in solar activity than the Asian F-region during this cycle. This longitudinal anomaly was however absent in the preceding cycle (1969–1979) when the African and Asian sectors were both characterised by low daytime and pronounced post-sunset correlation coefficient r. The American sector appears to have a high correlation coefficient r in daytime increasing to a small maximum in the post-sunset interval. The post-sunset enhancement in r is a characteristic feature for equatorial stations only (corrected geomagnetic latitude <10°).

Solar cycle and seasonal variations in F-region vertical drifts over Kodaikanal, India

1995 ◽  
Vol 13 (6) ◽  
pp. 633-640 ◽  
Author(s):  
K. B. Ramesh ◽  
J. H. Sastri
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Seasonal Variations ◽  
Normal Incidence ◽  
Magnetic Activity ◽  
Solar Flux ◽  
Seasonal Trend ◽  
F Region ◽  
Phase Path ◽  
10.7 Cm Solar Flux

Abstract. Measurements of the changes in phase path of F-region reflections at normal incidence at Kodaikanal (77° 28'E, 10° 14'N, dip 3°N) from February 1991 to February 1993 are used to determine the variation of the equatorial evening F-region vertical drifts (V z) with season, solar and magnetic activity. It is found that on average, at Kodaikanal, the post-sunset peak in Vz(Vzp) is higher in equinox and local winter months than in local summer. The day-to-day variability in V zp is highest in summer and lowest in winter. This seasonal trend persists even on magnetically quiet days (Ap \\leq14). Vzp is found to increase with 10.7 cm solar flux in all three seasons but tends to saturate for large flux values (>230 units) during local summer and winter months. Magnetic activity [represented by Ap as well as the time-weighted accumulations of a p and ap (τ)] does not seem to have any statistically significant effect on Vzp , except during equinoctial months of moderate solar activity, when Vzp decreases as magnetic activity increases.

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