F-region Drift Research Articles

F-region drift current and magnetic perturbation distribution by the X-wave heating ionosphere

Abstract. We present a theoretical and numerical study of the drift current and magnetic perturbation model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change in electron temperature ΔTe is about 570 K, and the ratio is ΔTe/Te ∼ 48 %. The maximum drift current density is 8×10-10 A m−2, and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency was strongest when the X wave is heating along the magnetic dip angle, as reported in recent observations by Kotik et al. (2013). We calculate the magnetic field variation in the heating region based on the MHD theory: the results show that the maximum magnetic field perturbation in the heating area is 48 pT.

The role of the F-region vertical drift on the onset time of the equatorial spread F over Ilorin, Nigeria

The equatorial ionosphere often shows the occurrence of plasma-density irregularities and velocity fluctuations with a broad range of scale sizes and amplitudes. These irregularities in the F-region are commonly referred to as the equatorial spread F (ESF) and they are predominantly a night-time phenomenon. The vertical drift of ionisation to higher altitudes post-sunset hours has been suggested to be responsible for the occurrence of these irregularities. We have therefore used all the available ionograms at Ilorin, Nigeria ( $$\hbox {latitude} = 8.48^{\circ }\hbox {N}$$ , $$\hbox {longitude}= 4.67^{\circ }\hbox {W}$$ and $$\hbox {dip}= 4.1^{\circ }\hbox {S}$$ ) to study the occurrence of ESF and the effect of the F-region drift on the occurrence of ESF. The available data at Ilorin, though not continuous, cover a period of 6 yrs (i.e., 2002, 2005, 2006, 2007, 2008 and 2010). The F-region vertical drift velocity was estimated starting from around local sunset until the onset of ESF, and the maximum value for a night ( $$V_{Z,\mathrm{max}})$$ is used to represent the strength of the $$E\times B$$ drift for that night. Results obtained showed that the percentage occurrence of ESF increases with the increase in solar activities. A seasonal trend is also observed in the occurrence frequency; occurrence seems to be more frequent during and around the equinox periods. The onset time or the time of commencement (TOC) of ESF was observed to vary from day to day. Also, $$V_{Z,\mathrm{max}} $$ seems to increase with the increase in solar activities, which in turn influences the TOC of ESF. It was found that the higher the $$V_{Z,\mathrm{max}} $$ , the closer the TOC was found to be to the local time $$V_{Z,\mathrm{max}}$$ . In a few cases, there was no noticeable movement of ionisation prior to the commencement of the ESF, and this might be pointing to the fact that the drifting of ionisation to a higher altitude is not the only condition for the occurrence of ESF. Other conditions that have been identified to play a role in ESF occurrence are thermospheric neutral dynamics, equatorial thermodynamic meridional winds and the post-sunset base height of the F-layer ( $$h^{\prime }F)$$ .

F-region vertical drift measurements at Ebro, Spain

Eighteen months values of vertical drift velocity measured with a Digisonde 256 at the mid-latitude station of Ebro Observatory (40.5°N, 0.5°E) have been analyzed in order to establish the typical daily variations. The daily pattern of the vertical drift velocity can easily be represented by the main daily harmonics. The summer and winter patterns are quite different. The diurnal component is most prominent for each month, with a practically constant phase and larger equinoctial amplitudes. The semidiurnal component displays the same seasonal amplitude variation as the diurnal one, but its phase is sun-synchronous. The terdiurnal component displays a constant phase and it plays a role during the summer half year, with amplitudes larger than those of the semidiurnal component. The variability is larger at nighttime than at daytime, and in general winter shows a larger variability. The usefulness of monitoring the vertical F-region drift motions with Digisonde drift measurements is discussed.

Multistation digisonde observations of equatorial spread F in South America

Abstract. Directional ionogram and F-region drift observations were conducted at seven digisonde stations in South America during the COPEX campaign from October to December 2002. Five stations in Brazil, one in Argentina, and one in Peru, monitored the ionosphere across the continent to study the onset and development of F-region density depletions that cause equatorial spread F (ESF). New ionosonde techniques quantitatively describe the prereversal uplifting of the F layer at the magnetic equator and the eastward motion of the depletions over the stations. Three of the Brazilian stations were located along a field line with a 350-km apex over the equator to investigate the relation of the occurrence of ESF and the presence of sporadic E-layers at the two E-region intersections of the field line. No simple correlation was found.

Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

Abstract. During summer months at solar cycle minimum, F-region lacuna and slant-Es conditions (SEC) are common features of daytime ionograms recorded around local magnetic noon at Casey, Antarctica. Digisonde measurements of drift velocity height profiles show that the occurrence of lacuna prevents the determination of F-region drift velocities and also affects E-region drift velocity measurements. Unique E-region spectral features revealed as intervals of Bragg scatter superimposed on typical background E-region reflection were observed in Digisonde Doppler spectra during intense lacuna conditions. Daytime E-region Doppler spectra recorded at carrier frequencies from 1.5 to 2.7MHz, below the E-region critical frequency foE, have two side-peaks corresponding to Bragg scatter at approximately ±1-2Hz symmetrically located on each side of a central-peak corresponding to near-zenith total reflections. Angle-of-arrival information and ray-tracing simulations show that echo returns are coming from oblique directions most likely resulting from direct backscatter from just below the total reflection height for each sounding frequency. The Bragg backscatter events are shown to manifest during polar lacuna conditions, and to affect the determination of E-region background drift velocities, and as such must be considered when using standard Doppler-sorted interferometry (DSI) techniques to estimate ionospheric drift velocities. Given the Doppler and spatial separation of the echoes determined from high-resolution Doppler measurements, we are able to estimate the Bragg scatter phase velocity independently from the bulk E-region motion. The phase velocity coincides with the ExB direction derived from in situ fluxgate magnetometer records. When ionospheric refraction is considered, the phase velocity amplitudes deduced from DSI are comparable to the ion-acoustic speed expected in the E-region. We briefly consider the plausibility that these previously unreported polar cap E-region Bragg scatter Doppler spectral signatures, observed at Casey in December 1996 during SEC/lacuna conditions may be linked to ionosphere irregularities. These irregularities may possibly be generated by primary plasma waves triggered by current-driven instabilities, that is to say, a hybrid of the "modified two-stream" and "gradient drift" instability mechanisms.

A comparison of polar cap ionospheric velocity determined from a digital ionosonde model and the DICM and IZMEM/DMSP electric potential models

Digisonde Portable Sounder 4 (DPS-4) ionospheric F-region drift measurements at the polar cap station Casey (110.5°E, 66.3°S geographic, 80.8°S corrected geomagnetic), Antarctica were used to derive the Casey 1997 (C97) regression model of Smith [Ionospheric F-region plasma convection at Casey – a southern polar cap station. PhD Thesis. La Trobe University, Australia, 1998]. F-region ionospheric convection velocities derived from C97 are compared with convection velocities derived from the application of E × B /B 2 at the geomagnetic latitude of Casey to the relatively new DICM and IZMEM/DMSP fully parameterized electric potential convection models of Papitashvili and Rich [J. Geophys. Res. 107 (A8) 1198, 2002]. Where the DICM model was constructed from satellite F-region ion drift observations from DMSP satellite data at 840 km, and the IZMEM/DMSP model was constructed using ground-magnetometer measurements and calibrated against DMSP ion data. A comparison between C97 and the new DICM and IZMEM/DMSP models was undertaken as a function of dipole tilt angle or season and for a range of IMF parameters. The initial results of the comparison between these experimental models for estimating F-region ionospheric convection drift velocities will be presented.

Plasma drift estimates from the Dynasonde: comparison with EISCAT measurements

Abstract. Modern ionosondes make almost simultaneous measurements of the time rate of change of phase path in different directions and at different heights. By combining these 'Doppler' measurements and angles of arrival of many such radar echoes it is possible to derive reliable estimates of plasma drift velocity for a defined scattering volume. Results from both multifrequency and kinesonde-mode soundings at 3-min resolution show that the Dynasonde-derived F-region drift velocity is in good agreement with EISCAT, despite data loss during intervals of 'blanketing' by intense E-region ionisation. It is clear that the Tromsø Dynasonde, employing standard operating modes, gives a reliable indication of overall convection patterns during quiet to moderately active conditions.Key words. Auroral ionosphere · Plasma convection · Instruments and techniques

Plasma drift estimates from the Dynasonde: comparison with EISCAT measurements

Modern ionosondes make almost simultaneous measurements of the time rate of change of phase path in different directions and at different heights. By combining these 'Doppler' measurements and angles of arrival of many such radar echoes it is possible to derive reliable estimates of plasma drift velocity for a defined scattering volume. Results from both multifrequency and kinesonde-mode soundings at 3-min resolution show that the Dynasonde-derived F-region drift velocity is in good agreement with EISCAT, despite data loss during intervals of 'blanketing' by intense E-region ionisation. It is clear that the Tromsø Dynasonde, employing standard operating modes, gives a reliable indication of overall convection patterns during quiet to moderately active conditions.Key words. Auroral ionosphere · Plasma convection · Instruments and techniques

Some evidence of ground power enhancements at frequencies of global magnetospheric modes at low latitude

Abstract. A statistical analysis of the power spectra of the geomagnetic field components H and D for periods ranging between 3 min and 1 h was conducted at a low-latitude observatory (L'Aquila, L=1.6) at the minimum and maximum of the solar cycle. For both components, during daytime intervals, we found evidence of power enhancements at frequencies predicted for global modes of the Earth\\'s magnetosphere and occasionally observed at auroral latitudes in the F-region drift velocities (approximately at 1.3, 1.9, 2.6, and 3.4 mHz). Nighttime observations reveal a relative low frequency H enhancement associated with the bay occurrence together with a peak in the H/D power ratio which sharply emerges at 1.2 mHz in the premidnight sector. The strong similarity between solar minimum and maximum suggests that these modes can be considered permanent magnetospheric features. A separate analysis on a two-month interval shows that the observed spectral characteristics are amplified by conditions of high-velocity solar wind.

Some evidence of ground power enhancements at frequencies of global magnetospheric modes at low latitude

A statistical analysis of the power spectra of the geomagnetic field components H and D for periods ranging between 3 min and 1 h was conducted at a low-latitude observatory (L'Aquila, L=1.6) at the minimum and maximum of the solar cycle. For both components, during daytime intervals, we found evidence of power enhancements at frequencies predicted for global modes of the Earth\'s magnetosphere and occasionally observed at auroral latitudes in the F-region drift velocities (approximately at 1.3, 1.9, 2.6, and 3.4 mHz). Nighttime observations reveal a relative low frequency H enhancement associated with the bay occurrence together with a peak in the H/D power ratio which sharply emerges at 1.2 mHz in the premidnight sector. The strong similarity between solar minimum and maximum suggests that these modes can be considered permanent magnetospheric features. A separate analysis on a two-month interval shows that the observed spectral characteristics are amplified by conditions of high-velocity solar wind.

F-region drift velocities in the dusk sector mid-latitude trough

Analysis of 6 months of ground-based ionosonde data from mid/high-latitude Digisonde stations at Millstone Hill, Argentina and Goose Bay, shows the relation between the formation of the mid-latitude trough in the dusk sector and the measured F-region drift velocities. The observed westward drift velocities in the trough are comparable in magnitude with the velocity of the Earth's rotation as required by the stagnation theory of trough formation. Using the Digisonde database of 15 min samples of electron density profiles and F-region drifts, a new trough detection algorithm automatically identifies the occurrence of the trough at any of the three stations. Correlating trough occurrence with the measured drift velocities indicates that troughs develop due to an increase in the horizontal westward velocity component. The extent of the trough formation relates to the magnitude of the horizontal velocity.

Magnetometer and radar observations of magnetohydrodynamic cavity modes in the Earth's magnetosphere

Night and early morning data from the Johns Hopkins University, Applied Physics Laboratory HF radar at Goose Bay and from the magnetometers in the Canadian CANOPUS array often show structured spectra with distinct spectral peaks at 1.3, 1.9, and 2.6 mHz. These frequencies are very stable and vary by less than ±5% for the 6 days of data we have analysed. The radar measurements of the F-region drift velocities indicate that these spectral peaks are often associated with field line resonances of the shear Alfvén wave, and that the resonances are seen at lower latitudes as the frequency increases. The magnetometer data indicate that the magnetohydrodynamic (MHD) waves have westward phase velocities. We shall show that these observations are compatible with the formation of MHD cavity modes in the early morning and nightside magnetosphere, between the magnetopause, at approximately 14.5 RE, and turning points in the dipolar magnetosphere, outside the plasmasphere. Likely sources of energy are compressional pulses from the solar wind or Kelvin–Helmholtz instabilities in the low-latitude boundary layer.

The equatorial ionospheric electric fields. A review

The equatorial electric fields have been extensively studied over the last decade using radio, radar and rocket observations. Radar measurements of vertical and east-west F-region drift velocities at Jicamarca have determined the seasonal and solar cycle variations of the F-region east-west and vertical electric fields, respectively. Rocket observations during twilight indicate the existence of a shear in the east-west drifts with eastward velocities near and above the F-region density peak and westward velocities in the lower F-region where incoherent scatter radar observations are not effective. The vertical drift (i.e. east-west electric field) changes considerably with magnetic activity, but the F-region east-west drift (vertical electric field) is not affected. During magnetically disturbed periods the zonal equatorial electric field shows frequent and large fluctuations indicating the penetration of magnetospheric electric fields into the low-latitude ionosphere. The coupling processes are not yet totally clear. Considerable progress has been made recently in the understanding of these quiet-time and disturbed equatorial electric fields.

Atmospheric solar tides and their electrodynamic effects—III. The polarization electric field

In this final part of our three-part study, we consider the polarization electric field generated by E-region dynamo action, and establish its consistency with presently available experimental measurements. This serves as an independent check on some of the results and conclusions described in Parts I and II. Incoherent scatter measurements of ionospheric drifts are reviewed from the point of view of determining the origin of the polarization electric field in the quiet-time ionosphere, and are compared with the theoretical dynamo electric fields which drive the current systems in Parts I and II. The analysis indicates that the polarization fields originating from E-region dynamo action are consistent with daytime F-region drift measurements, But are in poor agreement at night. This supports previous suggestions that electric fields generated by the plasmaspheric and F-region dynamos are short-circuited by the high E-region conductivity during the day, but contribute strongly to the night-time electric field.

Interpretation of single-site scintillation measurements to estimate F-region drift velocities

A method of estimating ionospheric drift velocities using single-site scintillation measurements is applied to determine a correlation coefficient of 0.55 between magnetic activity and F-region drift velocity near the auroral ionosphere. This method is based on the relationship between the drift velocity and the scintillation spectral breakpoint.

Dispersive Motions in the F-Region of the Equatorial Ionosphere

Some results of “dispersion” analysis of F-region drift data obtained at Ibadan (dip 6°S) are presented. On a number of occasions marked dispersion involving a velocity variation of about 60 msec-1 or more from low to high fading frequencies has been found. The results suggest that in the “correlation” analysis the “apparent” velocity probably measures the motion better than the “true” velocity, whether or not dispersion is present. It is also found that the motions occurring at this latitude are not always in the east-west direction. Occasionally, two independent motions corresponding to different fading frequency ranges and moving at right angles to each other may be involved.

Studies of the Horizontal Drifts in the F-Region of the Ionosphere at Ahmedabad

The paper describes the results of F-region drift measurements at Ahmedabad during different periods between 1957 and 1966, and compliments the results of E-region drifts published in an earlier paper (Rastogi 1969). During any of the season and epoch the mean drift speed is almost the same for the E or the F-region at Ahmedabad. The F-region drift speeds are found to be slightly greater during the night than during the day-time. The day-time speeds (F) are greater in winter than in summer while no consistent seasonal variation is evident for the night-time speed. The most probable direction changes from N-W to S-E direction seasonally from winter to summer or with the decrease of solar activity. The diurnal wave of E-W component for E or F-region drift are similar at Ahmedabad- Waltair or Delhi, but the diurnal wave of N-S components at Ahmedabad is opposite in phase to that in Waltair or Delhi. Ahmedabad seems to lie close to the region of transition of low and high latitude ionospheric wind system.

On the control of the F-region drift velocity by the E-region electric field: experimental evidence

Experimental evidence is presented which shows a good correlation between velocity variations of (1) the vertical motions of the F-region electrons in the equatorial ionosphere, and (2) the horizontal motions of electrons in the underlying E-region.

Effect of Sunspot Activity on F-region Drift Speed at Waltair

BRIGGS1 has reported the variation of the night-time north–south component of F-region drift at Cambridge (52° N., 0° E.) from a southward direction during a sunspot maximum to the northward direction during a minimum. This result highlights the importance of a study of long-term variations of drift parameters with a view to studying the effect of solar activity and verifying existing theories. Morriss and Lyon2 at Ibadan (7° N., 4° E.) reported a general decrease in wind speed with decreasing solar activity and showed that there was no marked change from the International Geophysical Year (IGY) to the International Year of the Quiet Sun (IQSY) in the diurnal variation of the east–west component. Results from Waltair show a decrease in the wind speed with decreasing solar activity. All the investigations mentioned were carried out using similar fades analysis.

Horizontal Drifts in the F-Region of the Ionosphere over Ahmedabad

The results of F-region drift measurements by the method of closely spaced receivers using a wave frequency of 7·0 Mc/s. for a period of November 1959 to February 1962 are described. The histograms showing the annual mean and seasonal variation in drift speed and direction are presented. Diagrams showing the mean hourly variation in drift speed and direction are also presented. An attempt has been made to study the relation between the drift speed, magnetic activity and the daily sunspot-number. It is found that the drift speed does not show any significant relation with magnetic activity or the sunspot number.