Upward Drifts Research Articles

Ionospheric vertical drift response at a mid-latitude station

Vertical plasma drift data measured at a mid-latitude ionospheric station Pruhonice (50.0°N, 14.6°E) were collected and analysed for the year 2006, a year of low solar and geomagnetic activity. Hence these data provide insight into the drift behaviour during quiet conditions. The following typical diurnal trend is evident: a significant decay to negative values (downward peak) at dawn; generally less pronounced downward peak at dusk hours. Magnitude of the downward drift varies during the year. Typically it reaches values about 20ms-1 at dawn hours and 10ms-1 at dusk hours. Maximum dawn magnitude of about 40ms-1 has been detected in August. During daytime the vertical drifts increases from the initial small downward drifts to zero drift around noon and to small upward drifts in the afternoon. Night-time drift values display large variability around a near zero vertical drift average. There is a significant trend to larger downward drift values near dawn and a less pronounced decrease of the afternoon upward vertical drifts near sunset. Two regular downward peaks of the drift associated with the dawn and dusk are general characteristics of the analysed data throughout the year 2006. Their seasonal course corresponds to the seasonal course of the sunrise and sunset. The duration of prevailing negative drift velocities forming these peaks and thus the influence of the dawn/dusk on the drift velocity is mostly 1.5–3h. The dawn effect on vertical drift tends to be larger than the effect of the dusk. The observed magnitude of the sunrise and sunset peaks show significant annual course. The highest variability of the magnitude is seen during winter. High variability is detected till March equinox and again after September equinox. Around solstice, both peaks reaches lowest values. After that, the magnitudes of the drift velocity increase smoothly till maxima in summer (August). The vertical drift velocity course is smooth between June solstice and September equinox. In general, the detected values of the observed vertical drift are of lower magnitudes compare to low latitudes. Drift data in midlatitudes seems to be more influenced by the atmospheric waves than data in lower latitudes.

The Study on Long-Term Dynamics in China’s Coal Prices Based on Jump- Diffusion Modles

This paper analyzes the evolution process of China’s coal prices formation mechanism and the trend of dynamic weekly data of Datong mix coal in Qinhuangdao market from January 2004 to December 2013. Resorting to the jump diffusion models and cumulants estimation, the empirical study on the phenomenon of coal prices fluctuations is executed. These results show that coal prices dynamics are characterized by high volatility, high intensity jumps, and upward drifts, and are concomitant with underlying fundamentals of coal markets and China’s economy. Furthermore, markets expected coal prices to still remain volatile and jumpy with higher probability and stay in jump for the next couple of years.

Daytime ionospheric equatorial vertical drifts during the 2008–2009 extreme solar minimum

AbstractOne of the most interesting observations made by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite mission was the detection of average equatorial ionospheric vertical drifts that largely differed from model predictions. C/NOFS measurements showed, in particular, downward drifts in the afternoon sector, and upward drifts around local midnight hours during the 2008 and 2009 extreme solar minimum. The unexpected behavior of the drifts has important implications for ionospheric modeling and suggests the necessity for a better understanding of the low‐latitude electrodynamics. We used ground‐based radar measurements to quantify the seasonal and solar flux variability of daytime equatorial drifts at lower altitudes (∼150 km) than those probed by C/NOFS (above ∼400 km). We found that average vertical drifts at 150 km altitude are in good agreement with model predictions of F region drifts and did not show the signatures of an enhanced semidiurnal pattern, as seen by C/NOFS. Comparison of the 150 km echo drifts with model predictions also shows that the increase (decrease) with height of the vertical drifts in the morning (afternoon) hours is a regular feature of the equatorial ionosphere. It occurred in all seasons and solar flux conditions between 2001 and 2011.

Ionospheric response to sudden stratospheric warming events at low and high solar activity

AbstractThe sensitivity of the ionospheric response to a sudden stratospheric warming (SSW) event has been examined under conditions of low and high solar activity through simulations using the whole atmosphere model (WAM) and the global ionosphere plasmasphere model (GIP). During non‐SSW conditions, simulated daytime mean vertical drifts at the magnetic equator show similar solar activity dependence as an empirical model. Model results of ionospheric total electron content (TEC) and equatorial vertical drift for the January 2009 major SSW, which occurred at very low solar activity conditions, show reasonable agreement with observations. The simulations demonstrate that the E region dynamo is capable of creating the semidiurnal variation of vertical drift. WAM and GIP were also run at high solar activity conditions, using the same lower atmosphere conditions as present in the January 2009 SSW event. The simulations indicate that the amplitude and phase of migrating tides in the dynamo region during the event have similar magnitudes for both solar flux conditions. However, comparing the ionospheric responses to a major SSW under low and high solar activity periods, it was found that the changes in the ionospheric vertical drifts and relative changes in TEC decreased with increasing solar activity. The simulations indicate that the F region dynamo becomes more important throughout the daytime and contributes to the upward drift in the afternoon during the event when the solar activity is higher. Our test simulations also confirm that the increase of the ionospheric conductivity associated with increasing solar activity is responsible for the decrease of vertical drift changes during an SSW. In particular, first, the increase in F region conductivity allows the closure of E region currents through the F region, reducing the polarization electric field before noon. Second, the F region dynamo contributes an upward drift postnoon, maintaining upward drifts till after sunset. The direct changes of the thermospheric wind at higher solar activity due to increased dissipation of the tides from the lower atmosphere are relatively minor and do not contribute greatly to the changes of ionospheric responses in the low‐latitude region.

Geomagnetic control of equatorial plasma bubble activity modeled by the TIEGCM with Kp

AbstractDescribing the day‐to‐day variability of Equatorial Plasma Bubble (EPB) occurrence remains a significant challenge. In this study we use the Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIEGCM), driven by solar (F10.7) and geomagnetic (Kp) activity indices, to study daily variations of the linear Rayleigh‐Taylor (R‐T) instability growth rate in relation to the measured scintillation strength at five longitudinally distributed stations. For locations characterized by generally favorable conditions for EPB growth (i.e., within the scintillation season for that location), we find that the TIEGCM is capable of identifying days when EPB development, determined from the calculated R‐T growth rate, is suppressed as a result of geomagnetic activity. Both observed and modeled upward plasma drifts indicate that the prereversal enhancement scales linearly with Kp from several hours prior, from which it is concluded that even small Kp changes cause significant variations in daily EPB growth.

Altitudinal dependence of evening equatorial F region vertical plasma drifts

AbstractWe use Jicamarca incoherent scatter radar measurements to study for the first time the altitudinal variations of late afternoon and early night equatorial F region vertical plasma drifts. We also present the initial vertical drift measurements over the altitudinal range from about 200 to 2000 km. These data show that the afternoon drifts decrease weakly with altitude. Near their evening prereversal enhancements, the vertical drifts generally increase with altitude below about the F layer peak, decrease with height near the F layer peak and above, and are nearly height independent in the (solar flux dependent) topside ionosphere. The transition altitudes from height‐decreasing to height‐independent evening upward drifts decrease with altitude from solar maximum to solar minimum. After their reversal to downward, the vertical drifts do not change much with height. The altitudinal dependence of the evening vertical drifts has large day‐to‐day variability and is closely related to the time dependence of the zonal drifts, as expected from the curl‐free electric field condition.

New aspects of the ionospheric response to the October 2003 superstorms from multiple‐satellite observations

AbstractThe total electron content (TEC) data measured by the Jason, CHAMP, GRACE, and SAC‐C satellites, the in situ electron densities from CHAMP and GRACE, and the vertical E × B drifts from the ROCSAT, have been utilized to examine the ionospheric response to the October 2003 superstorms. The combination of observations from multiple satellites provides a unique global view of ionospheric storm effects, especially over the Pacific Ocean and American regions, which were under sunlit conditions during the main phases of the October 2003 superstorms. The main results of this study are as follows: (1) There were substantial increases in TEC in the daytime at low and middle latitudes during both superstorms. (2) The enhancements were greater during the 30 October superstorm and occurred over a wider range of local times. (3) They also tended to peak at earlier local times during this second event. (4) These TEC enhancement events occurred at the local times when there were enhancements in the upward vertical drift. (5) The strong upward vertical drifts are attributed to penetration electric fields, suggesting that these penetration electric fields played a significant role in the electron density enhancements during these superstorms. Overall, the main contribution of this study is the simultaneous view of the storm time ionospheric response from multiple satellites, and the association of local time differences in ionospheric plasma response with measured vertical drift variations.

Seasonal dependence of the longitudinal variations of nighttime ionospheric electron density and equivalent winds at southern midlatitudes

Abstract. It has been indicated that the observed Weddell Sea anomaly (WSA) appeared to be an extreme manifestation of the longitudinal variations in the Southern Hemisphere, since the WSA is characterized by greater evening electron density than the daytime density in the region near the Weddell Sea. In the present study, the longitudinal variations of the nighttime F2-layer peak electron density at southern midlatitudes are analyzed using the observations of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites between 2006 and 2008. It is found that significant longitudinal difference (> 150%) relative to the minimum density at each local time prevails in all seasons, although the WSA phenomenon is only evident in summer under this solar minimum condition. Another interesting feature is that in summer, the maximum longitudinal differences occur around midnight (~ 23:00–00:00 LT) rather than in the evening (19:00–21:00 LT) in the evening, when the most prominent electron density enhancement occurs for the WSA phenomenon. Thus the seasonal–local time patterns of the electron density longitudinal variations during nighttime at southern midlatitudes cannot be simply explained in terms of the WSA. Meanwhile, the variations of the geomagnetic configuration and the equivalent magnetic meridional winds/upward plasma drifts are analyzed to explore their contributions to the longitudinal variations of the nighttime electron density. The maximum longitudinal differences are associated with the strongest wind-induced vertical plasma drifts after 21:00 LT in the Western Hemisphere. Besides the magnetic declination–zonal wind effects, the geographic meridional winds and the magnetic inclination also have significant effects on the upward plasma drifts and the resultant electron density.

Downbeat nystagmus as the initial manifestation of anti-NMDAR encephalitis

Downbeat nystagmus (DBN) is a rare neurological disorder characterized by slow upward drifts and fast downward phases [1]. In most cases no anatomical lesion is identified, whereas Arnold-Chiari malformation or spinocerebellar degeneration may underlie this condition [1]. AntiNMDAR (N-methyl-D-aspartate receptor) encephalitis rarely causes DBN [2]. Recently, we observed a young lady showing DBN as the sole initial manifestation. A 21-year-old lady presented with the 5-day history of dizziness that worsened gradually. On examination she had spontaneous DBN, which was occasionally overlapped with ocular flutter-like movement. Smooth pursuit was slightly saccadic, and during horizontal gaze horizontal nystagmus overlapped DBN. Eye movements were otherwise intact. She had no intentional tremor or dysmetria on finger-to-nose and heel-to-shin testing. However, her gait was wide-based and mildly unsteady. The remainder of her examination was normal. However, 4 days later, emotional lability and delirium manifested, gradually followed by involuntary movement (crawl swimming-like, myoclonic), mutism, and hyperpnea/apnea that eventually required mechanical ventilation (Fig. 1). Brain magnetic resonance imaging (MRI) on the admission day showed normal findings throughout the course of disease. Single-photon emission computed tomography (SPECT) on the third day showed decrease cerebral perfusion in the medial frontal cortex. An electroencephalography (EEG) was normal. Routine blood studies showed no abnormalities. Cerebrospinal fluid (CSF) analysis showed mildly increased cell count of 35/mm (mononuclear:polymorphonuclear = 32:3) and normal total protein. Viral antigens were all negative. Although survey for malignancies including ovary and paraneoplastic antibodies including anti-Hu, anti-Yo and anti-GAD was negative, she was suspected to have autoimmune encephalitis. Steroid pulse and high-dose intravenous immunoglobulin (IVIG) therapy was of limited benefit. However, anti-NMDAR antibodies in CSF appeared to be increased significantly. From the 37th day she underwent plasmapheresis, which ameliorated significantly her involuntary movement and mildly her level of consciousness. Repeated CT scans of the pelvis showed a 1.5 cm ovarian mass. On the 69th day she underwent tumor resection, which revealed a 14 mm * 13 mm mature teratoma. This surgery brought her to normal consciousness. Previously, DBN has been seldom reported in paraneoplastic encephalitis except for anti-Ma2 antibody encephalitis (one case) [3], anti-glutamate acid decarboxilase (GAD) antibody encephalitis (one case) [4], and anti-NMDAR encephalitis (one case) with upbeat nystagmus at the plateau stage under mechanical ventilation [2]. Our patient was unique in that she presented with DBN and dizziness as the sole initial manifestation. Experimental and functional neuroimaging studies indicated that DBN is caused by dysfunction of the vestibulocerebellum (flocculus, nodulus of cerebellar vermis) and, rarely, bilateral paramedian brainstem [1]. Although brainstem and cerebellum are not commonly Y. Tsuyusaki R. Sakakibara (&) M. Kishi F. Tateno Neurology, Internal Medicine, Sakura Medical Center, Toho University, 564-1 Shimoshizu, Sakura 285-8741, Japan e-mail: sakakibara@sakura.med.toho-u.ac.jp

Spurious AMOC trends in global ocean sea-ice models related to subarctic freshwater forcing

Global ocean sea-ice models with an atmospheric forcing based on bulk formulations of the air-sea fluxes exhibit spurious trends in key flow indices like the Atlantic Meridional Overturning Circulation (AMOC), constraining their use in investigations of multi-decadal ocean variability. To identify the critical model factors affecting the temporal evolution of the AMOC on time scales of up to 60years, a series of experiments with both eddy-permitting (0.25°) and non-eddying (0.5°) ocean-ice models has been performed, focusing on the influence of artificial choices for the freshwater forcing, in particular the restoring of sea surface salinity towards climatological values. The atmospheric forcing builds on the proposal for Coordinated Ocean-ice Reference Experiments (CORE), utilizing the refined atmospheric reanalysis products for 1948–2006 compiled by Large and Yeager. Sensitivity experiments with small variations in precipitation (within the observational uncertainty) and sea surface salinity restoring in the subarctic Atlantic produce a wide range of AMOC transports, between upward drifts to more than 22Sv and nearly-collapsed states with less than 7Sv, reflecting the excessive role of the salinity feedback in such simulations. In all cases the AMOC is tightly related to the density of the Denmark Strait overflow; changes in that density are governed by the salinity in the Nordic Seas; and in turn, that salinity is strongly affected by the properties of the inflowing North Atlantic water.

Observations of quiet time vertical ion drift in the equatorial ionosphere during the solar minimum period of 2009

[1] The extended solar minimum conditions in 2008 and 2009 presented an opportunity to investigate the ionosphere at lower solar activity levels than previously observed. The Coupled Ion Neutral Dynamics Investigation (CINDI) Ion Velocity Meter (IVM) instrument onboard the Communication/Navigation Outage Forecasting System is used to construct the median meridional (vertical) ion drifts, ion densities, and O+ concentrations during periods of low geomagnetic activity for four characteristic seasons each year spanning late 2008 to 2010. The presence of a large semidiurnal component in the ion drift variation at the equator produced significant differences from typical ionospheric conditions. Instead of upward drifts during the day and downward drifts at night, downward drifts in the afternoon and upward drifts near midnight are observed. This semidiurnal component is present in all seasons though it is strongest during the solstice seasons. It is shown that upward drifts at night correspond to regions with a high occurrence of postmidnight irregularities during the December 2008 and June 2009 solstices. A comparison with vertical ion drifts observed by the Jicamarca Radio Observatory supports the methodology used to extract meridional drifts from the IVM.

C/NOFS observations of the equatorial ionospheric electric field response to the 2009 major sudden stratospheric warming event

[1] We present new observations made by the Coupled Ion Neutral Dynamics Investigation (CINDI) Ion Velocity Meter (IVM) instrument onboard the Communication/Navigation Outage Forecasting System (C/NOFS) satellite that show the effects of the January 2009 sudden stratospheric warming (SSW) event on equatorial electric fields. We have used IVM observations to construct composite curves of mean equatorial vertical plasma drifts as a function of local time and longitude sector. These curves show large upward vertical drifts during morning hours and downward drifts during afternoon. Our analysis indicates that this pattern could be observed over the range of longitudes where adequate IVM measurements were available, from approximately 165°E to about 315°E longitude. A clear day-to-day, quasi-deterministic variability in the drifts is also observed, with the transition from upward to downward drifts occurring at increasing local times from 25 to 30 January 2009. The analysis also suggests some level of longitudinal variability in the magnitude of the drifts. These in-situ observations are in good agreement with previous ground-based measurements of the response of equatorial electric fields to SSW events. In particular, we found that IVM drift measurements centered around 285°E depart significantly from climatological values but agree exceptionally well with ground-based measurements of vertical drifts made by the Jicamarca incoherent backscatter radar. Overall, the results agree well with previous studies of SSW events, demonstrate the usefulness of the IVM observations and motivate further studies of the variability of the equatorial ionosphere using C/NOFS.

Forecasting the dynamic and electrodynamic response to the January 2009 sudden stratospheric warming

[1] A whole atmosphere model has been used to simulate the changes in the global atmosphere dynamics and electrodynamics during the January 2009 sudden stratospheric warming (SSW). In a companion paper, it has been demonstrated that the neutral atmosphere response to the 2009 warming can be simulated with high fidelity and can be forecast several days ahead. The 2009 warming was a major event with the polar stratospheric temperature increasing by 70 K. The neutral dynamics from the whole atmosphere model (WAM) was used to drive the response of the electrodynamics. The WAM simulation predicted a substantial increase in the amplitude of the 8-hour terdiurnal tide in the lower thermosphere dynamo region in response to the warming, at the expense of the more typical semidiurnal tides. The increase in the terdiurnal mode had a significant impact on the diurnal variation of the electrodynamics at low latitude. The changes in the winds in the dayside ionospheric E region increased the eastward electric field early in the morning, and drove a westward electric field in the afternoon. The initial large increase in upward drifts gradually moved to later local times, and decreased in magnitude. The change in the amplitude and phase of the electrodynamic response to the SSW is in good agreement with observations from the Jicamarca radar. The agreement with observations serves to validate the whole atmosphere dynamic response. Since WAM can forecast the neutral dynamics several days ahead, the simulations indicate that the electrodynamic response can also be predicted.

Deducing storm timeFregion ionospheric dynamics from 3-D time-varying imaging

[1] The inversion algorithm for Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE) has been created to gain insight into ionospheric dynamics, particularly when direct measurement is unavailable. We extend the capabilities of EMPIRE here, in order to demonstrate its effectiveness on densities obtained from real data. We apply this method to real Ionospheric Data-Assimilation 4-Dimensional (IDA4D) data from storm time measurements, focusing on the midlatitude F2 layer. EMPIRE is used to estimate midlatitude field-aligned and field-perpendicular drifts. The estimated upward drifts from EMPIRE are validated against measurements obtained from the Millstone Hill incoherent scatter radar zenith antenna. The horizontal × drifts are compared to the assimilative mapping of ionospheric electrodynamics (AMIE) model, which estimates drifts from data sources independent of those used in IDA4D. Results show that the direction and magnitude of the × drifts (and therefore the electric fields) may be deduced from imaging based primarily on total electron content data, although altitude variation is not significantly discernible. We also indicate that the initial uplift of the storm-enhanced density may have been more strongly influenced by field-aligned contributions of neutral winds and diffusion than the electric fields.

COSMIC/FORMOSAT‐3 observations of equatorial F region irregularities in the SAA longitude sector

The data of ionospheric electron density and S4 scintillation index from COSMIC/FORMOSAT‐3 GPS occultation soundings are used to study the morphology of the equatorial F region irregularity (EFI) in the longitude sector (0°∼75°W) where the South Atlantic magnetic anomaly (SAA) is located. Launched into low Earth orbits on 14 April 2006, the six‐satellite constellation COSMIC provides daily global measurements of the ionosphere at altitudes below ∼800 km. The large data set enables us a statistically correlative study of electron density depletion and GPS L1 scintillation, which allows the global and altitudinal distributions of irregularity to be examined. Under solar minimum and geomagnetic quiet conditions, postsunset EFI/scintillation events are found to concentrate in the SAA longitude sector during northern winter months (D months), but nearly disappeared in the same longitude sector during the opposite season (J months). The D months’ average pattern of EFI reveals that most of irregularities occurred in the bottom side F region (200–350 km altitude) and at low magnetic latitudes adjacent to the locations of the maximum postsunset Nmax and Hmax. This is consistent with the early postsunset irregularities that are generated in the region where plasma upward drifts have been greatly enhanced. By examining the UT snapshots of the global distributions of electron density and scintillation events, strong spatial correlations are found to exist among the sunset terminator, the westward declined geo‐magnetic field, strong scintillation event, and density depletion in the SAA longitude sector only during D months, where the E region sunset terminator is most possibly parallel to the magnetic field direction at equatorial latitudes. Density depletion structures within this longitude sector were bounded by two postsunset ionization enhancement bands (EIA) that extended over central SAA and its conjugated region, respectively. Such features provide further evidence that the enhanced conductivity gradients due to particle induced ionization in the vicinity of SAA contribute additional electric field enhancements in the equatorial F region. At the walls of the depletion region near the sunset lines, prominent horizontal density gradients exist in both westward and southward directions due to sun setting and SAA ionization enhancement, respectively. The combination of horizontal density gradients with antiparallel (north‐eastward) neutral winds during D months can contribute additional growth rate to the EFI generation. These COSMIC observations not only confirm that the sunset equatorial electrodynamics plays a key role in controlling the seasonal and longitudinal occurrences of the quiet time EFI, but also reveal that seasonally dependent ionospheric responses to the energetic particle precipitation in SAA can affect considerably the morphology of EFI in the SAA longitude sector.

Thermospheric Meridional Wind Control on Equatorial Scintillations and the Role of the Evening F-Region Height Rise, E × B Drift Velocities and F2-Peak Density Gradients

The possible role, on L-band scintillation activity, played by the nighttime magnetic meridional component of the thermospheric horizontal neutral winds, the post-sunset F-layer base height, the electrical field pre-reversal enhancement (PRE) and the latitudinal gradients of the F2-layer peak density is analyzed, considering different cases of scintillation occurrence (and their latitudinal extent) during August and September 2002. The meridional winds were derived over low-latitudes from a modified form of the nonlinear time-dependent servo-model. A chain of two scintillation monitors and three digital ionosondes was operational in Brazil and used to collect, respectively, global positioning system signal amplitude scintillation and ionospheric height (h′F; hpF2) and frequency (foF2) parameters. From the overall behavior in the 2 months analyzed, the results suggest that high near sunset upward vertical plasma drifts are conducive for the generation of spread-F irregularities, whereas large poleward meridional winds tend to suppress the development of plasma bubble irregularities and the occurrence of their associated scintillations. Even when generated, a reduced fountain effect, due to weak electric field PRE, acts for the bubbles to be expanded less effectively to higher latitudes. The results also reveal that high F-layer base and peak heights (at equatorial and off-equatorial latitudes), and intense gradients in the F2-peak density between the dip equator and the equatorial anomaly crests, are favorable conditions for the generation of F-region irregularities and increased scintillation activity. Other distinct features of the controlling factors in the cases of occurrence and non-occurrence of equatorial scintillations are presented and discussed.

C/NOFS observations of deep plasma depletions at dawn

The Communication/Navigation Outage Forecasting System (C/NOFS) satellite was launched in 2008, during solar minimum conditions. An unexpected feature in the C/NOFS plasma density data is the presence of deep plasma depletions observed at sunrise at all satellite altitudes. Ionospheric irregularities are often embedded within these dawn depletions. Their frequencies strongly depend on longitude and season. Dawn depletions are also observed in coincident satellite passes such as DMSP and CHAMP. In one example the depletion extended 50° × 14° in the N‐S and E‐W directions, respectively. These depletions are caused by upward plasma drifts observed in C/NOFS and ground‐based measurements. The reason for these upward drifts is still unresolved. We discuss the roles of dynamo electric fields, over‐shielding, and tidal effects as sources for the reported depletions.

Geographical distribution of long-term changes in the height of the maximum electron density of theFregion: A nonmigrating-tide effect?

[1] The geographical distribution of trends in the height of the maximum electron density of the F2 region (hmF2) seemed to indicate that ionospheric stations showing decreasing (i.e., negative) hmF2 trends are mostly located on or in the vicinity of seashores. In contrast, ionospheric stations in continental areas exhibit generally increasing (i.e., positive) hmF2 trends. On the basis of the present study, it is shown that considering the whole world, the geographical distribution of hmF2 trends is affected essentially by the nonmigrating tidal wind. Moreover, besides the field-aligned drift, the elecrodynamical drift must also be considered in the development of hmF2 trends. Taking into account both the field-aligned and the electrodynamical drift, northward (eastward) tidal winds and southward (westward) tidal winds would create downward and upward drifts, respectively, in the Northern Hemisphere but southward (eastward) and northward (westward) tidal winds in the Southern Hemisphere. An upward drift is accompanied by an increase and a downward drift is accompanied by a decrease of hmF2. It has been suggested that because of the thermal driven origin of the nonmigrating tides, the distribution may also be connected with ocean currents warming or cooling the neighborhood of the coastline. The effect of ocean currents would create downward drift due to cooling at the western coastlines of the continents but upward drift at the eastern coastlines as a result of the warming. This has been shown by comparing the distribution of hmF2 trends with the map of ocean currents. The corresponding hmF2 trends may develop because of changes in the land/sea-warming ratio, where the land-surface air temperature increases faster than the sea-surface air temperature.

Seasonal and longitudinal dependence of equatorial disturbance vertical plasma drifts

We used equatorial measurements from the ROCSAT‐1 satellite to determine the seasonal and longitudinal dependent equatorial F region disturbance vertical plasma drifts. Following sudden increases in geomagnetic activity, the prompt penetration vertical drifts are upward during the day and downward at night, and have strong local time dependence at all seasons. The largest prompt penetration drifts near dusk and dawn occur during June solstice. The daytime disturbance dynamo drifts are small at all seasons. They are downward near dusk with largest (smallest) values during equinox (June solstice); the nighttime drifts are upward with the largest magnitudes in the postmidnight sector during December solstice. During equinox, the downward disturbance dynamo drifts near sunset are largest in the eastern hemisphere, while the late night upward drifts are largest in the western hemisphere. The longitudinal dependence of the disturbance dynamo drifts is in good agreement with results from simulation studies.

The F-Region Equatorial Ionospheric Electrodynamics Drifts

The ionospheric plasma drift is one of the most essential parameters for understanding the dynamics of ionospheric F-region. F-region electromagnetic drifts are calculated for three seasonal conditions from ionosonde observations acquired during quiet period of a typical year of high and low solar activity at Ibadan (7.4oN, 3.9oE, dip 6oS), Nigeria. The vertical plasma drifts derived from h' (f) ionosonde data are compared with vertical drifts obtained by incoherent scatter radar and AE-E satellite measurements during nighttime periods under similar solar and geomagnetic conditions. We find comparable variability among the ionosonde drifts at Ibadan, Jicamarca VHF radar drifts, and AE-E satellite drifts during high solar flux and geomagnetic quiet conditions at equinox and solstices periods. The equinoctial average evening upward drifts enhancements by the three methods are roughly similar and occur at the same local time (19 LT) for all the seasons. Additionally, the evening reversal time from upward daytime to downward nighttime does not vary much except during the winter months; and occurs earliest in summer and equinox, but least during winter period. Also the data indicate asymmetry of evening reversal times about the dip-equator between the Peruvian, Indian, and the African equatorial regions. Our observations are in conformity with some results obtained at other equatorial ionospheric stations Journal of the Nigerian Association of Mathematical Physics Vol. 10 2006: pp. 27-34