On the plausible linkage of thermospheric meridional winds with the equatorial spread F

Devasia, C. V.; Jyoti, N.; Subbarao, K.; Viswanathan, K. S.; Tiwari, Diwakar; Sridharan, R.

doi:10.1016/s1364-6826(01)00089-x

Cited by 69 publications

(70 citation statements)

References 44 publications

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“…Further, Lee et al (2005) have shown the linkage of seasonal ESF variability with EIA asymmetry. Devasia et al (2002) have shown meridional winds to be the physical parameter connecting EIA and ESF. They suggested that the meridional winds were the outcome of the pressure bulges associated with ETWA (Raghavarao et al, 1993).…”

Section: Discussionmentioning

confidence: 99%

“…Only those events for which ESF is triggered before 20:00 IST are considered for this study. As mentioned earlier, the criterion of ESF occurrence irrespective of the polarity of meridional winds is applied to h F to determine the threshold height h F c below which equatorward wind is essential for the triggering of ESF (Devasia et al, 2002;Jyoti et al, 2004). Figure 1a shows the scatter plot of the meridional wind velocities against h F values of each of the ESF events during the summer solstice of solar minimum (left panel) and solar maximum (right panel) periods.…”

Section: Experimental Set Up and Data And Methods Of Analysismentioning

confidence: 99%

“…Above the critical height the polarity did not matter. This threshold height of h F (defined by them) has been found to be ∼300 km for the occurrence of ESF during equinoctial periods and showed a linear solar activity dependence (Devasia et al, 2002;Jyoti et al, 2004). Raghavarao et al (1993) conjectured that such equatorward winds could be produced as a result of the pressure bulges associated with Equatorial Temperature and Wind Anomaly (ETWA).…”

Section: Introductionmentioning

confidence: 96%

“…The increased ion-neutral collision frequency (ν in ) at lower heights causes reduction in the linear growth rate of the R-T mechanism responsible for the generation of ESF irregularities (Maruyama, 1988;Mendillo, 1992). Devasia et al (2002) showed that converging/diverging thermospheric meridional winds become significant with the equatorward wind being present when h F was below a threshold height (h F c ), for the R-T instability to become triggered. Above the critical height the polarity did not matter.…”

Section: Introductionmentioning

confidence: 99%

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On the seasonal variations of the threshold height for the occurrence of equatorial spread F during solar minimum and maximum years

2007

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Abstract.A study has been carried out on the occurrence of bottom side equatorial spread F (ESF) and its dependence on the polarity and magnitude of the thermospheric meridional wind just prior to ESF occurrence during summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995), using ionosonde data of Trivandrum (8.5 • N, 76.5 • E, dip=0.5 • N) and SHAR (13.7 • N, 80.2 • E, dip ∼5.5 • N) in the Indian longitude sector. In this study, we have examined the changes in the threshold height of the base of the F layer for the triggering of ESF, irrespective of the magnitude and polarity of the meridional winds during the above periods. The study indicates that the threshold height above which ESF triggering is entirely controlled only by the collisional R-T instability is least for summer months, with higher values for winter and equinox, during the solar minimum period, whereas for the solar maximum period the threshold height is least for winter, with higher values for summer and equinox. But the range over which the threshold height varies is very narrow (<15 km) for solar minimum in relation to the large range of variation (>50 km) in the solar maximum epoch. Further to this, the study also reveals a clear-cut increase in threshold height with solar activity for all seasons. Clear-cut seasonal variability is also observed in the threshold height, especially for solar maximum. The study quantifies the level of the base of the F layer below which neutral dynamical effects play a decisive role in the triggering of ESF during different seasons and solar epochs.

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Section: Discussionmentioning

confidence: 99%

Section: Experimental Set Up and Data And Methods Of Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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On the seasonal variations of the threshold height for the occurrence of equatorial spread F during solar minimum and maximum years

2007

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“…However, the polarity (equatorward/poleward) and magnitude of the meridional winds have been shown to play a significant role only when the maximum bottom height of the post sunset F-layer (h F ) is below a critical height. Above the critical height, the polarity of the winds was shown to be not having a direct control on the generation of ESF (Devasia et al, 2002).…”

Section: Introductionmentioning

confidence: 95%

Observational evidence for the plausible linkage of Equatorial Electrojet (EEJ) electric field variations with the post sunset F-region electrodynamics

et al. 2009

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Abstract. The paper is based on a detailed observational study of the Equatorial Spread F (ESF) events on geomagnetically quiet (A p ≤ 20) days of the solar maximum (2001), moderate (2004) and minimum (2006) years using the ionograms and magnetograms from the magnetic equatorial location of Trivandrum (8.5 • N; 77 • E; dip lat ∼0.5 • N) in India. The study brings out some interesting aspects of the daytime Equatorial Electrojet (EEJ) related electric field variations and the post sunset F-region electrodynamics governing the nature of seasonal characteristics of the ESF phenomena during these years. The observed results seem to indicate a plausible linkage of daytime EEJ related electric field variations with pre-reversal enhancement which in turn is related to the occurrence of ESF. These electric field variations are shown to be better represented through a parameter, termed as "E", in the context of possible coupling between the Eand F-regions of the ionosphere. The observed similarities in the gross features of the variations in the parameter "E" and the F-region vertical drift (V z ) point towards the potential usage of the EEJ related parameter "E" as an useful index for the assessment of V z prior to the occurrence of ESF.

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Latitudinal GRBR‐TEC estimation in Southeast Asia region based on the two‐station method

et al. 2014

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Total electron content (TEC) is an important parameter for revealing latitudinal ionospheric structures, such as the equatorial ionization anomaly (EIA) in Southeast Asia. Understanding the EIA is beneficial for studying equatorial spread F. To reveal the structures, the absolute TEC as a function of latitude must be accurately determined. In early 2012, we expanded a GNU Radio Beacon Receiver (GRBR) network to provide latitudinal coverage in the Thailand-Indonesia sector. We employed the GRBR network to receive VHF and UHF signals from polar low-Earth-orbit satellites. The TEC offset is an unknown parameter in the absolute TEC estimation process. We propose a new technique based on the two-station method to estimate the offset for the latitudinal TEC estimation, and it works better than the original method for a sparse network. The TEC estimation system requires two iterations to minimize the root-mean-square error (RMSE). Once the RMSE reaches the global minimum, the absolute TECs are estimated simultaneously over five GRBR stations. GPS-TECs from local stations are used as the initial guess of the offset estimation. The height of the ionospheric pierce point is determined from the ionosonde hmF2. As a result, the latitudinal GRBR-TEC was successfully estimated from the polar orbit satellites. The two EIA humps were clearly captured by the GRBR-TEC. The result was well verified with the TEC reconstructed from the C/NOFS density data and the ionosonde bottomside data. This is a significant step showing that the GRBR is a useful tool for the study of low-latitude ionospheric features.

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On the plausible linkage of thermospheric meridional winds with the equatorial spread F

Cited by 69 publications

References 44 publications

On the seasonal variations of the threshold height for the occurrence of equatorial spread F during solar minimum and maximum years

On the seasonal variations of the threshold height for the occurrence of equatorial spread F during solar minimum and maximum years

Observational evidence for the plausible linkage of Equatorial Electrojet (EEJ) electric field variations with the post sunset F-region electrodynamics

Latitudinal GRBR‐TEC estimation in Southeast Asia region based on the two‐station method

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