scholarly journals IMF effect on sporadic-E layers at two northern polar cap sites: Part I – Statistical study

2006 ◽  
Vol 24 (3) ◽  
pp. 887-900 ◽  
Author(s):  
M. Voiculescu ◽  
A. T. Aikio ◽  
T. Nygrén ◽  
J. M. Ruohoniemi
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Statistical Study ◽  
Polar Cap ◽  
Sporadic E Layers ◽  
Convection Model ◽  
Sporadic E ◽  
The Relationship ◽  
Electric Field Mechanism ◽  
The Imf

Abstract. In this paper we investigate the relationship between polar cap sporadic-E layers and the direction of the interplanetary magnetic field (IMF) using a 2-year database from Longyearbyen (75.2 CGM Lat, Svalbard) and Thule (85.4 CGM Lat, Greenland). It is found that the MLT distributions of sporadic-E occurrence are different at the two stations, but both are related to the IMF orientation. This relationship, however, changes from the centre of the polar cap to its border. Layers are more frequent during positive By at both stations. This effect is particularly strong in the central polar cap at Thule, where a weak effect associated with Bz is also observed, with positive Bz correlating with a higher occurrence of Es. Close to the polar cap boundary, at Longyearbyen, the By effect is weaker than at Thule. On the other hand, Bz plays there an equally important role as By, with negative Bz correlating with the Es occurrence. Since Es layers can be created by electric fields at high latitudes, a possible explanation for the observations is that the layers are produced by the polar cap electric field controlled by the IMF. Using electric field estimates calculated by means of the statistical APL convection model from IMF observations, we find that the diurnal distributions of sporadic-E occurrence can generally be explained in terms of the electric field mechanism. However, other factors must be considered to explain why more layers occur during positive than during negative By and why the Bz dependence of layer occurrence in the central polar cap is different from that at the polar cap boundary.

scholarly journals IMF effect on sporadic-E layers at two northern polar cap sites: Part II – Electric field

2006 ◽  
Vol 24 (3) ◽  
pp. 901-913 ◽  
Author(s):  
T. Nygrén ◽  
A. T. Aikio ◽  
M. Voiculescu ◽  
J. M. Ruohoniemi
Keyword(s):  
Electric Field ◽  
Diurnal Variations ◽  
Field Direction ◽  
Convection Pattern ◽  
Polar Cap ◽  
Model Calculations ◽  
Sporadic E Layers ◽  
Electric Field Direction ◽  
Sporadic E ◽  
The Imf

Abstract. This paper is the second in a series on a study of the link between IMF and sporadic-E layers within the polar cap. In Paper I (Voiculescu et al., 2006), an analysis of the sporadic-E data from Thule and Longyearbyen was presented. Here we concentrate on the electric field mechanism of sporadic-E generation. By means of model calculations we show that the mechanism is effective even at Thule, where the direction of the geomagnetic field departs from vertical only by 4. The model calculations also lead to a revision of the electric field theory. Previously, a thin layer was assumed to grow at a convergent null in the vertical ion velocity, which is formed when the electric field points in the NW sector. Our calculations indicate that in the dynamic process of vertical plasma compression, a layer is generated at altitudes of high vertical convergence rather than at a null. Consequently, the layer generation is less sensitive than previously assumed to fluctuations of the electric field direction within the NW sector. The observed diurnal variations of sporadic-E occurrence at Longyearbyen and Thule are compared with the diurnal variations of the electric field, calculated using a representative range of IMF values by means of the statistical APL model. The results indicate that the main features of Es occurrence can be explained by the convection pattern controlled by the IMF. Electric fields calculated from the IMF observations are also used for producing distributions of sporadic-E occurrence as a function of electric field direction at the two sites. A marked difference between the distributions at Thule and Longyearbyen is found. A model estimate of the occurrence probability as a function of electric field direction is developed and a reasonable agreement between the model and the experimental occurrence is found. The calculation explains the differences between the distributions at the two sites in terms of the polar cap convection pattern. The conclusion is that the electric field is the major cause for sporadic-E generation and, consequently, IMF has a clear control on the occurrence of sporadic E within the polar cap.

scholarly journals The relationship between electric fields, conductances and currents in the high-latitude ionosphere: a statistical study using EISCAT data

1999 ◽  
Vol 17 (1) ◽  
pp. 43-52 ◽  
Author(s):  
J. A. Davies ◽  
M. Lester
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
High Latitude ◽  
Statistical Study ◽  
Field Vector ◽  
Relative Contribution ◽  
High Latitude Ionosphere ◽  
The Times ◽  
The Relationship ◽  
Uhf Radar

Abstract. The relationship between electric fields, height-integrated conductivities and electric currents in the high-latitude nightside electrojet region is known to be complex. The tristatic nature of the EISCAT UHF radar facility provides an excellent means of exploring this interrelationship as it enables simultaneous estimates to be made of the full electric field vector and the ionospheric Hall and Pedersen conductances, further allowing the determination of both field-perpendicular electric current components. Over 1300 h of common programme observations by the UHF radar system provide the basis of a statistical study of electric fields, conductances and currents in the high-latitude ionosphere, from which preliminary results are presented. Times at which there is significant solar contribution to the ionospheric conductances have been excluded by limiting the observations according to solar zenith angle. Initial results indicate that, in general, the times of peak conductance, identified from the entire set of EISCAT observations, do not correspond to the times of the largest electric field values; the relative contribution of ionospheric conductance and electric field to the electrojet currents therefore depends critically on local time, a conclusion which corroborates work by previous authors. Simultaneous measurements confirm a tendency for a decrease in both Hall and Pedersen conductances to be accompanied by an increase in the electric field, at least for moderate and large electric field value, a tendency which is also identified to some extent in the ratio of the conductances, which acts as an indicator of the energy of precipitating particles.Key words. Ionosphere (auroral ionosphere; electric fields and currents)

scholarly journals The role of electric field and neutral wind in the generation of polar cap sporadic E

2008 ◽  
Vol 26 (12) ◽  
pp. 3757-3763 ◽  
Author(s):  
T. Nygrén ◽  
M. Voiculescu ◽  
A. T. Aikio
Keyword(s):  
Electric Field ◽  
Driving Forces ◽  
Neutral Wind ◽  
Polar Cap ◽  
Sporadic E Layers ◽  
Sporadic E ◽  
In The Beginning ◽  
Model Formation ◽  
Good Agreement

Abstract. This paper investigates the roles of electric field and neutral wind in the generation of sporadic-E layers within the polar cap. Two Es layers above Svalbard, observed by the EISCAT Svalbard Radar (ESR), were chosen for investigation. The radar experiment contains four beam directions, and this was used for determining the electric field. The neutral wind was obtained from the HWM93 model. Formation of Es layers was calculated by integrating the continuity equation under the action of driving forces due to neutral wind and electric field. A flat height profile of metal ions was assumed in the beginning. The calculation gives the time variation of the layer, which can be compared with observations. In one case the electric field was shown to be the main driving agent in layer generation. In the other case the electric field was weak and the layer was produced mainly by the neutral wind, but the electric field had influence on the height of the layer. A fairly good agreement between the variations of the observed and calculated layer altitudes was obtained and some agreement between the intensity variations was also found.

Formation of sporadic E-layers by magnetospheric electric fields in the southern polar cap ionosphere

2001 ◽  
Vol 27 (8) ◽  
pp. 1399-1402
Author(s):  
M.L. Parkinson ◽  
P.L. Dyson ◽  
D.P. Monselesan ◽  
R.J. Morris
Keyword(s):  
Electric Fields ◽  
Polar Cap ◽  
Sporadic E Layers ◽  
Sporadic E

scholarly journals Long term trends in sporadic E layers and electric fields over Fortaleza, Brazil

1996 ◽  
Vol 23 (7) ◽  
pp. 757-760 ◽  
Author(s):  
M. A. Abdu ◽  
I. S. Batista ◽  
P. Muralikrishna ◽  
J. H. A Sobral
Keyword(s):  
Electric Fields ◽  
Sporadic E Layers ◽  
Long Term Trends ◽  
Sporadic E

Electric Field Effects on the Stability of Vapor Microlayers: Enhancement of Heat Transfer

Materials ◽  
2003 ◽  
Author(s):  
Subramanian Sankaran ◽  
Jeffrey S. Allen ◽  
Leonard Gumennik
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Heat Fluxes ◽  
Enhancement Of Heat Transfer ◽  
Electric Field Effects ◽  
Heater Wire ◽  
Experimental Parameters ◽  
Flux Level ◽  
The Stability ◽  
The Relationship

The effect of dc electric fields on destabilization of a vapor microlayer formed during film boiling at various subcooling levels is investigated. High voltage electric fields up to 2000 volts were applied between a 127 μm heater wire and a screen electrode that is concentrically placed at a radius of 25 mm. The qmax and qmin heat fluxes were also measured for the various subcooling and electric field strengths. Up to 50% increase in the qmax and the qmin heat fluxes were observed when using the electric fields in this range of experimental parameters. The relationship among subcooling level for a given fluid, the heat flux level, and the electric field strength required to reach the qmin condition is of interest. The preliminary experimental results and the bubble departure and transition boiling patterns resulting from destabilization of the vapor microlayer are discussed.

scholarly journals A statistical study of intense electric fields at 4−7 R<sub><i>E</i></sub> geocentric distance using Cluster

2005 ◽  
Vol 23 (7) ◽  
pp. 2579-2588 ◽  
Author(s):  
T. Johansson ◽  
T. Karlsson ◽  
G. Marklund ◽  
S. Figueiredo ◽  
P.-A. Lindqvist ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Time Distribution ◽  
Statistical Study ◽  
Auroral Oval ◽  
Field Structure ◽  
Geocentric Distance ◽  
Using Data ◽  
Auroral Phenomena ◽  
Current Systems

Abstract. Intense high-latitude electric fields (>150 mV/m mapped to ionospheric altitude) at 4–7 RE geocentric distance have been investigated in a statistical study, using data from the Cluster satellites. The orbit of the Cluster satellites limits the data collection at these altitudes to high latitudes, including the poleward part of the auroral oval. The occurrence and distribution of the selected events have been used to characterize the intense electric fields and to investigate their dependance on parameters such as MLT, CGLat, altitude, and also Kp. Peaks in the local time distribution are found in the evening to morning sectors but also in the noon sector, corresponding to cusp events. The electric field intensities decrease with increasing latitude in the region investigated (above 60 CGLat). A dependence on geomagnetic activity is indicated since the probability of finding an event increases up to Kp=5–6. The scales sizes are in the range up to 10 km (mapped to ionospheric altitude) with a maximum around 4–5km, consistent with earlier findings at lower altitudes and Cluster event studies. The magnitudes of the electric fields are inversely proportional to the scale sizes. The type of electric field structure (convergent or divergent) is consistent with the FAC direction for a subset of events with electric field intensities in the range 500–1000 mV/m and with clear bipolar signatures. The FAC directions are also consistent with the Region 1 and NBZ current systems, the latter of which prevail only during northward IMF conditions. For scale sizes less than 2 km the majority of the events were divergent electric field structures. Both converging and diverging electric fields were found throughout the investigated altitude range (4–7 RE geocentric distance). Keywords. Magnetospheric physics (Electric fields; Auroral phenomena; Magnetosphere-ionosphere interactions)

scholarly journals IMF <i>B</i><sub><i>y</i></sub> effects in the plasma flow at the polar cap boundary

2011 ◽  
Vol 29 (7) ◽  
pp. 1305-1315 ◽  
Author(s):  
R. Lukianova ◽  
A. Kozlovsky
Keyword(s):  
Solar Wind ◽  
Electric Fields ◽  
Plasma Flow ◽  
Relative Reduction ◽  
Polar Cap ◽  
Azimuthal Component ◽  
Ionospheric Convection ◽  
Quantitative Characteristics ◽  
Night Side ◽  
The Imf

Abstract. We used the dataset obtained from the EISCAT Svalbard Radar during 2000–2008 to study statistically the ionospheric convection in a vicinity of the polar cap boundary as related to IMF By conditions separately for northward and southward IMF. The effect of IMF By is manifested in the intensity and direction of the azimuthal component of ionospheric flow. The most significant effect is observed on the day and night sides whereas on dawn and dusk the effect is essentially less prominent. However, there is an asymmetry with respect to the noon-midnight meridian. On the day side the intensity of By-related azimuthal flow is maximal exactly at noon, whereas on the night side the maximum is shifted toward the post-midnight hours (~03:00 MLT). On the dusk side the relative reduction of the azimuthal flow is much larger than that on the dawn side. Overall, the magnetospheric response to IMF By seems to be stronger in the 00:00–12:00 MLT sector compared to the 12:00–24:00 MLTs. Quantitative characteristics of the IMF By effect are presented and partly explained by the magnetospheric electric fields generated due to the solar wind and also by the position of open-closed boundary for different IMF orientation.

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