Abstract
The vertical component of the plasma drift, especially the evening-time pre-reversal drift, constitutes an important aspect of the nighttime electrodynamics of the equatorial ionosphere. Over the years, several studies using measurements and models have been performed to understand the characteristics of this process and its implications for the development of the instabilities leading to the plasma bubble formation and ionospheric scintillation. However, the Brazilian region presents some unique features that bring some difficulties for the vertical drift prognosis, which is required for the scintillation forecasting. These features are mainly related to the geomagnetic field lines topology that presents strong differences when compared to those of other equatorial longitudes. In this work, some of the difficulties for the pre-reversal vertical drift modeling and estimation are discussed; also, a dataset containing long-term observation (2001–2009) is compared with a widely used empirical model. The results show an intrinsic trend of underestimation by the model, which seems to be independent of latitude and seasonality thus suggesting an additional contribution arising from sources other than solely the geomagnetic topology. Also, the results indicate that the deviation can vary in the range of 0–40 m/s and the percentage error enhances with increasing values of pre-reversal vertical drift peak and reduces with increasing F10.7 values, thereby, indicating a clear possibility of meridional winds contribution which is not included in the empirical model used and may account for these differences.
Highlights
The vertical component of the plasma drift is the prime mover of the phenomenology of the nighttime ionosphere over the equatorial and low-latitude regions
Abdu et al (1981) using ionosonde data from Fortaleza and Jicamarca showed that the pre-reversal vertical drift magnitude is largely dependent on the magnetic declination angle, which varies with longitude
The results suggest that the SF1999 usually underestimates the pre-reversal vertical drift peak velocity over the Brazilian region in most of the scenarios
Summary
The vertical component of the plasma drift is the prime mover of the phenomenology of the nighttime ionosphere over the equatorial and low-latitude regions. Abdu et al (2009) presented some remarkable results obtained during the Conjugate Point Equatorial Experiment (COPEX) campaign Among their several results one that is noteworthy in the context of the discussion presented here, is that besides the longitudinal asymmetries, the vertical drift over the Brazilian region was found to vary between magnetic conjugate locations. This asymmetry is not due to the topology of the geomagnetic field declination, once both conjugate points present similar declination (À14° and À15.1° over Boa Vista and Campo Grande, respectively). The lack of a more precise model or a large dataset from conjugate points in the Brazilian region brings in some difficulties in the development of adjustments
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