scholarly journals Effect of the IMF <i>B<sub>y</sub></i> component on the ionospheric flow overhead at EISCAT: observations and theory

2000 ◽  
Vol 18 (12) ◽  
pp. 1503-1522 ◽  
Author(s):  
H. Khan ◽  
S. W. H. Cowley
Keyword(s):  
Magnetic Field ◽  
Local Times ◽  
Plasma Convection ◽  
Flow Perturbation ◽  
The North ◽  
Ionosphere Plasma ◽  
Uncertainty Estimates ◽  
Magnetic Model ◽  
Order Of Magnitude ◽  
The Imf

Abstract. We have analysed a database of ∼300 h of tristatic ionospheric velocity measurements obtained overhead at Tromsø (66.3° magnetic latitude) by the EISCAT UHF radar system, for the presence of flow effects associated with the y-component of the IMF. Since it is already known that the flow depends upon IMF Bz, a least-squares multivariate analysis has been used to determine the flow dependence on both IMF By and Bz simultaneously. It is found that significant flow variations with IMF By occur, predominantly in the midnight sector (∼2100–0300 MLT), but also pre-dusk (∼1600–1700 MLT), which are directed eastward for IMF By positive and westward for IMF By negative. The flows are of magnitude 20–30 m s–1 nT–1 in the midnight sector, and smaller, 10–20 m s–1 nT–1, pre-dusk, and are thus associated with significant changes of flow of order a few hundred m s–1 over the usual range of IMF By of about ±5 nT. At other local times the IMF By-related perturbation flows are much smaller, less than ∼5 m s–1 nT–1, and consistent with zero within the uncertainty estimates. We have investigated whether these IMF By-dependent flows can be accounted for quantitatively by a theoretical model in which the equatorial flow in the inner magnetosphere is independent of IMF By, but where distortions of the magnetospheric magnetic field associated with a "penetrating" component of the IMF By field changes the mapping of the field to the ionosphere, and hence the ionospheric flow. We find that the principal flow perturbation produced by this effect is an east-west flow whose sense is determined by the north-south component of the unperturbed flow. Perturbations in the north-south flow are typically smaller by more than an order of magnitude, and generally negligible in terms of observations. Using equatorial flows which are determined from EISCAT data for zero IMF By, to which the corotation flow has been added, the theory predicts the presence of zonal perturbation flows which are generally directed eastward in the Northern Hemisphere for IMF By positive and westward for IMF By negative at all local times. However, although the day and night effects are therefore similar in principle, the model perturbation flows are much larger on the nightside than on the dayside, as observed, due to the day-night asymmetry in the unperturbed magnetospheric magnetic field. Overall, the model results are found to account well for the observed IMF By-related flow perturbations in the midnight sector, in terms of the sense and direction of the flow, the local time of their occurrence, as well as the magnitude of the flows (provided the magnetic model employed is not too distorted from dipolar form). At other local times the model predicts much smaller IMF By-related flow perturbations, and thus does not account for the effects observed in the pre-dusk sector.Key words: Magnetospheric physics (magnetosphere · ionosphere interactions) – Ionosphere (plasma convection; auroral ionosphere)

scholarly journals Polar cap influx

2005 ◽  
Vol 23 (5) ◽  
pp. 1755-1761
Author(s):  
J. MacDougall ◽  
P. T. Jayachandran
Keyword(s):  
Magnetic Field ◽  
Magnetospheric Physics ◽  
Plasma Convection ◽  
Polar Cap ◽  
Cusp Region ◽  
Ionosphere Plasma ◽  
Latitude Station ◽  
The Imf

Abstract. This study uses digital ionosonde data from a cusp latitude station (Cambridge Bay, 77° CGM lat.) to study the convection into the polar cap. Days when the IMF magnetic field was relatively steady were used. On many days it was possible to distinguish an interval near noon MLT when the ionosonde data had a different character from that at earlier and later times. Based on our data, and other published measurements, we used the interval 10:00-13:00 MLT as the cusp interval and calculated the convection into the polar cap in this interval. The integrated convection accounted for only ~1/3 of the open polar cap flux. If the convection through the prenoon/postnoon regions on either side of the cusp was calculated the remaining 2/3 of the flux could be accounted for. The characteristics of the prenoon/postnoon regions were different from the cusp region, and we attribute this to transient flank merging versus more steady frontside merging for the cusp. Keywords. Ionosphere (Plasma convection) Magnetospheric physics (Polar cap phenomenon)

scholarly journals Central polar cap convection response to short duration southward Interplanetary Magnetic Field

2000 ◽  
Vol 18 (8) ◽  
pp. 887-896 ◽  
Author(s):  
P. T. Jayachandran ◽  
J. W. MacDougall
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Short Duration ◽  
Initial Response ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionosphere Plasma ◽  
Rapid Transition ◽  
Convection Speed ◽  
A Chain

Abstract. Central polar cap convection changes associated with southward turnings of the Interplanetary Magnetic Field (IMF) are studied using a chain of Canadian Advanced Digital Ionosondes (CADI) in the northern polar cap. A study of 32 short duration (~1 h) southward IMF transition events found a three stage response: (1) initial response to a southward transition is near simultaneous for the entire polar cap; (2) the peak of the convection speed (attributed to the maximum merging electric field) propagates poleward from the ionospheric footprint of the merging region; and (3) if the change in IMF is rapid enough, then a step in convection appears to start at the cusp and then propagates antisunward over the polar cap with the velocity of the maximum convection. On the nightside, a substorm onset is observed at about the time when the step increase in convection (associated with the rapid transition of IMF) arrives at the polar cap boundary.Key words: Ionosphere (plasma convection; polar ionosphere) - Magnetospheric physics (solar wind - magnetosphere interaction)

scholarly journals An unusual geometry of the ionospheric signature of the cusp: implications for magnetopause merging sites

2002 ◽  
Vol 20 (1) ◽  
pp. 29-40 ◽  
Author(s):  
G. Chisham ◽  
M. Pinnock ◽  
I. J. Coleman ◽  
M. R. Hairston ◽  
A. D. M. Walker
Keyword(s):  
Magnetic Field ◽  
Travel Time ◽  
Spectral Width ◽  
Hf Radar ◽  
Small Scale ◽  
Convection Flow ◽  
Closed Field ◽  
Plasma Convection ◽  
Ionosphere Plasma ◽  
Local Noon

Abstract. The HF radar Doppler spectral width boundary (SWB) in the cusp represents a very good proxy for the equatorward edge of cusp ion precipitation in the dayside ionosphere. For intervals where the Interplanetary Magnetic Field (IMF) has a southward component (Bz < 0), the SWB is typically displaced poleward of the actual location of the open-closed field line boundary (or polar cap boundary, PCB). This is due to the poleward motion of newly-reconnected magnetic field lines during the cusp ion travel time from the reconnection X-line to the ionosphere. This paper presents observations of the dayside ionosphere from SuperDARN HF radars in Antarctica during an extended interval ( ~ 12 h) of quasi-steady IMF conditions (By ~ Bz < 0). The observations show a quasi-stationary feature in the SWB in the morning sector close to magnetic local noon which takes the form of a 2° poleward distortion of the boundary. We suggest that two separate reconnection sites exist on the magnetopause at this time, as predicted by the anti-parallel merging hypothesis for these IMF conditions. The observed cusp geometry is a consequence of different ion travel times from the reconnection X-lines to the southern ionosphere on either side of magnetic local noon. These observations provide strong evidence to support the anti-parallel merging hypothesis. This work also shows that mesoscale and small-scale structure in the SWB cannot always be interpreted as reflecting structure in the dayside PCB. Localised variations in the convection flow across the merging gap, or in the ion travel time from the reconnection X-line to the ionosphere, can lead to localised variations in the offset of the SWB from the PCB. These caveats should also be considered when working with other proxies for the dayside PCB which are associated with cusp particle precipitation, such as the 630 nm cusp auroral emission.Key words. Ionosphere (plasma convection) – Magnetospheric physics (magnetopause, cusp, and boundary layers) – Space plasma physics (magnetic reconnection)

scholarly journals Transient plasma injections in the dayside magnetosphere: one-to-one correlated observations by Cluster and SuperDARN

2004 ◽  
Vol 22 (1) ◽  
pp. 141-158 ◽  
Author(s):  
A. Marchaudon ◽  
J.-C. Cerisier ◽  
J.-M. Bosqued ◽  
M. W. Dunlop ◽  
J. A. Wild ◽  
...  
Keyword(s):  
High Altitude ◽  
Drift Velocity ◽  
Plasma Convection ◽  
Flux Tubes ◽  
Flux Transfer Events ◽  
The North ◽  
Ionosphere Plasma ◽  
Short Period ◽  
One To One ◽  
Transient Plasma

Abstract. Conjunctions in the cusp between the four Cluster spacecraft and SuperDARN ground-based radars offer unique opportunities to compare the signatures of transient plasma injections simultaneously in the high-altitude dayside magnetosphere and in the ionosphere. We report here on such observations on 17 March 2001, when the IMF initially northward and duskward, turns southward and dawnward for a short period. The changes in the convection direction at Cluster are well correlated with the interplanetary magnetic field (IMF) By variations. Moreover, the changes in the ionosphere follow those in the magnetosphere, with a 2–3min delay. When mapped into the ionosphere, the convection velocity at Cluster is about 1.5 times larger than measured by SuperDARN. In the high-altitude cusp, field and particle observations by Cluster display the characteristic signatures of plasma injections into the magnetosphere suggestive of Flux Transfer Events (FTEs). Simultaneous impulsive and localized convection plasma flows are observed in the ionospheric cusp by the HF radars. A clear one-to-one correlation is observed for three successive injections, with a 2–3min delay between the magnetospheric and ionospheric observations. For each event, the drift velocity of reconnected flux tubes (phase velocity) has been compared in the magnetosphere and in the ionosphere. The drift velocity measured at Cluster is of the order of 400–600ms–1 when mapped into the ionosphere, in qualitative agreement with SuperDARN observations. Finally, the reconnected flux tubes are elongated in the north-south direction, with an east-west dimension of 30–60km in the ionosphere from mapped Cluster observations, which is consistent with SuperDARN observations, although slightly smaller. Key words. Ionosphere (plasma convection) – Magnetospheric physics (magnetopause, cusp, and boundary layers; magnetosphere-ionosphere interactions)

scholarly journals Interhemispheric observations of the ionospheric signature of tail reconnection during IMF-northward non-substorm intervals

2005 ◽  
Vol 23 (5) ◽  
pp. 1763-1770 ◽  
Author(s):  
A. Grocott ◽  
T. K. Yeoman ◽  
S. E. Milan ◽  
S. W. H. Cowley
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Field Data ◽  
Plasma Convection ◽  
Field Orientation ◽  
Magnetic Field Data ◽  
Ionospheric Response ◽  
Ionosphere Plasma ◽  
Dayside Magnetopause ◽  
Geosynchronous Satellites

Abstract. This paper presents the first interhemispheric radar observations interpreted as the ionospheric response to tail reconnection during IMF-northward non-substorm intervals. SuperDARN measurements of plasma convection in the nightside ionospheres of both hemispheres, taken on 21–22 February and 26–27 April 2000, show bursts of flow in the midnight sector which are understood to be characteristic of such phenomena. Upstream interplanetary magnetic field data confirm that the field orientation at the dayside magnetopause was northwards, but with a significant IMF By component (negative during the first interval, positive during the second), for many hours prior to the bursts being observed. During the By-negative interval the bursts were directed westwards in the Northern Hemisphere and eastwards in the Southern Hemisphere; during the By-positive interval their directions were reversed. These two asymmetries between the different orientations of IMF By and between the two hemispheres are key to our understanding of the magnetospheric phenomenon responsible for generating the bursts. They provide further evidence in support of the idea that the bursts are a result of reconnection in an asymmetric tail under the prolonged influence of IMF By. Concurrent data from ground magnetometers and geosynchronous satellites confirm that the bursts have no associated substorm characteristics, consistent with previous studies. Keywords. Ionosphere (Plasma convection; Ionospheremagnetosphere interactions) – Magnetospheric Physics (Magnetotail)

scholarly journals Response of ionospheric electric fields to variations in the interplanetary magnetic field

1996 ◽  
Vol 14 (8) ◽  
pp. 794-802 ◽  
Author(s):  
S. P. Mishra ◽  
E. Nielsen
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Interplanetary Magnetic Field ◽  
Electric Fields ◽  
Solar Wind Speed ◽  
Auroral Oval ◽  
Local Times ◽  
Residual Effects ◽  
Magnetospheric Substorms ◽  
The Imf

Abstract. The STARE system (Scandinavian Twin Auroral Radar Experiment) provides estimates of electron drift velocities, and hence also of the electric field in the high-latitude E-region ionosphere between 65 and 70 degrees latitude. The occurrence of drift velocities larger than about 400 m/s (equivalent to an electric field of 20 mV/m) have been correlated with the magnitude of the Interplanetary Magnetic Field (IMF) components Bz and By at all local times. Observation days have been considered during which both southward (Bz<0) and northward (Bz>0) IMF occurred. The occurrence of electric fields larger than 20 mV/m increases with increases in Bz magnitudes when Bz<0. It is found that the effects of southward IMF continue for some time following the northward turnings of the IMF. In order to eliminate such residual effects for Bz<0, we have, in the second part of the study, considered those days which were characterized by a pure northward IMF. The occurrence is considerably lower during times when Bz>0, than during those when Bz is negative. These results are related to the expansion and contraction of the auroral oval. The different percentage occurrences of large electric field for By>0 and By<0 components of the IMF during times when Bz>0, clearly display a dawn-dusk asymmetry of plasma flow in the ionosphere. The effects of the time-varying solar-wind speed, density, IMF fluctuations, and magnetospheric substorms on the occurrence of auroral-backscatter observations are also discussed.

scholarly journals The influence of IMF By on the nature of the nightside high-latitude ionospheric flow during intervals of positive IMF Bz

2004 ◽  
Vol 22 (5) ◽  
pp. 1755-1764 ◽  
Author(s):  
A. Grocott ◽  
S. V. Badman ◽  
S. W. H. Cowley ◽  
T. K. Yeoman ◽  
P. J. Cripps
Keyword(s):  
Convective Transport ◽  
Magnetic Data ◽  
Plasma Convection ◽  
Ionosphere Plasma ◽  
Tail Analysis ◽  
Ground Magnetic ◽  
Open Flux ◽  
East West ◽  
Imf Clock Angle ◽  
The Imf

Abstract. This paper further addresses the issue of nightside flow bursts which occur during intervals of northward but strongly BY-influenced IMF. Recent discussions of such bursts concerned intervals during which the IMF BY component was negative. The present study concerns an interval of BY-positive IMF which occurred on 20 March 2002 (01:00-12:00UT). During the interval BY increased steadily from ~2 to 12nT, whilst the BZ component decreased steadily from ~10 to 0nT. There was thus a ~6-h sub-interval during which the IMF clock angle remained between 30° and 60°, such that moderate dayside reconnection and open flux production was maintained. It is found that flow bursts of a similar size and speed to those observed under BY negative (~1000m s-1, spanning 2-3h of MLT in the midnight sector) also occur when BY is positive. However, the direction of east-west flow is reversed, indicating that they are driven by processes in the magnetosphere which are directly related to the orientation of the IMF. It is suggested that they are caused by a reconfiguration of an asymmetric tail resulting from prolonged dayside reconnection with a BY-dominated IMF. This is consistent with previous suggestions that they are associated with convective transport following reconnection in the more distant tail. Analysis of ground magnetic data, auroral images and geosynchronous particle data also show associated features, but indicate that the flow bursts are not directly associated with substorms.Key words. Ionosphere (plasma convection; ionospheremagnetosphere interactions) – Magnetospheric Physics (magnetotail)

scholarly journals Measuring the dayside reconnection rate during an interval of due northward interplanetary magnetic field

2004 ◽  
Vol 22 (12) ◽  
pp. 4243-4258 ◽  
Author(s):  
G. Chisham ◽  
M. P. Freeman ◽  
I. J. Coleman ◽  
M. Pinnock ◽  
M. R. Hairston ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Interplanetary Magnetic Field ◽  
Line Length ◽  
Hf Radar ◽  
Plasma Convection ◽  
Ionosphere Plasma ◽  
Reconnection Region ◽  
Field Lines ◽  
First Time

Abstract. This study presents, for the first time, detailed spatiotemporal measurements of the reconnection electric field in the Northern Hemisphere ionosphere during an extended interval of northward interplanetary magnetic field. Global convection mapping using the SuperDARN HF radar network provides global estimates of the convection electric field in the northern polar ionosphere. These are combined with measurements of the ionospheric footprint of the reconnection X-line to determine the spatiotemporal variation of the reconnection electric field along the whole X-line. The shape of the spatial variation is stable throughout the interval, although its magnitude does change with time. Consequently, the total reconnection potential along the X-line is temporally variable but its typical magnitude is consistent with the cross-polar cap potential measured by low-altitude satellite overpasses. The reconnection measurements are mapped out from the ionosphere along Tsyganenko model magnetic field lines to determine the most likely reconnection location on the lobe magnetopause. The X-line length on the lobe magnetopause is estimated to be ~6–11 RE in extent, depending on the assumptions made when determining the length of the ionospheric X-line. The reconnection electric field on the lobe magnetopause is estimated to be ~0.2mV/m in the peak reconnection region. Key words. Space plasma physics (Magnetic reconnection) – Magnetospheric physics (Magnetopause, cusp and boundary layers) – Ionosphere (Plasma convection)

scholarly journals Variations in the polar cap area during two substorm cycles

2003 ◽  
Vol 21 (5) ◽  
pp. 1121-1140 ◽  
Author(s):  
S. E. Milan ◽  
M. Lester ◽  
S. W. H. Cowley ◽  
K. Oksavik ◽  
M. Brittnacher ◽  
...  
Keyword(s):  
Hf Radar ◽  
Local Times ◽  
Convection Flow ◽  
Closed Field ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionosphere Plasma ◽  
Dayside Magnetopause ◽  
Magnetospheric Configuration And Dynamics ◽  
Open Flux

Abstract. This study employs observations from several sources to determine the location of the polar cap boundary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified. These data sources include global auroral images from the Ultraviolet Imager (UVI) instrument on board the Polar spacecraft, SuperDARN HF radar measurements of the convection flow, and low altitude particle measurements from Defense Meteorological Satellite Program (DMSP) and National Oceanographic and Atmospheric Administration (NOAA) satellites, and the Fast Auroral SnapshoT (FAST) spacecraft. Changes in the open flux content of the magnetosphere are related to the rate of magnetic reconnection occurring at the magnetopause and in the magnetotail, allowing us to estimate the day- and nightside reconnection voltages during two substorm cycles. Specifically, increases in the polar cap area are found to be consistent with open flux being created when the IMF is oriented southwards and low-latitude magnetopause reconnection is ongoing, and decreases in area correspond to open flux being destroyed at substorm breakup. The polar cap area can continue to decrease for 100 min following the onset of substorm breakup, continuing even after substorm-associated auroral features have died away. An estimate of the dayside reconnection voltage, determined from plasma drift measurements in the ionosphere, indicates that reconnection can take place at all local times along the dayside portion of the polar cap boundary, and hence presumably across the majority of the dayside magnetopause. The observation of ionospheric signatures of bursty reconnection over a wide extent of local times supports this finding.Key words. Ionosphere (plasma convection; polar ionosphere) – Magnetospheric physics (magnetospheric configuration and dynamics)

scholarly journals Anomaly in the earth magnetic field at north provinces of Najaf city

2019 ◽  
Vol 12 (23) ◽  
pp. 1-5
Author(s):  
Arif S. Baron
Keyword(s):  
Magnetic Field ◽  
Numerical Simulation ◽  
Spherical Harmonic ◽  
Kriging Method ◽  
Rich Region ◽  
The North ◽  
The Earth ◽  
Earth Magnetic Field ◽  
Magnetic Model ◽  
East Component

This paper investigated in the numerical simulation model to calculate the Earth magnetic field components at north provinces of Najaf city (Longitude 44.316 o -44.3592o E and Latitude 32.0508o - 32.0256o N). The components of the Earth magnetic field (total intensity (F), horizontal intensity (H), declination (D), inclination (I), the north component(X), the east component(Y), and Down component(Z)) were found by using spherical harmonic world magnetic model (WMM2010). A great deal of anomaly has been discovered in all components of the Earth magnetic field at the selected region (Long. 44.345o-44.335o E, Lat.32.042o-32.032o N) using Kriging method. This anomaly can be attributed either to oil rich region or cracking in the Earth crust.

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