Solar Wind Control of the Polar-Cap Voltage

Reiff, P. H.; Luhmann, J. G.

doi:10.1007/978-94-009-4722-1_33

Cited by 186 publications

(107 citation statements)

References 61 publications

Supporting

Mentioning

101

Contrasting

Order By: Relevance

“…Baker et al, 1983;Reiff and Luhmann, 1986;Eriksson et al, 2000). This is again evident in comparing the correlation coefficients for IMF B z and E r with pc in Fig.…”

Section: Resultssupporting

confidence: 55%

“…Here, v is the solar wind bulk velocity in x gsm direction, B t is the projection of the IMF onto the GSM y − z plane, and θ is the clock angle between B t and the positive z gsm direction. These solar wind parameters have been shown to correlate well with the crosspolar potential drop (Reiff and Luhmann, 1986;Eriksson et al, 2000, and references therein). Figure 2 shows the time shifted IMF B z and E r versus time lag t for two cases plotted next to each other.…”

Section: Magnetospheric Response To the Solar Windmentioning

confidence: 85%

See 1 more Smart Citation

Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field

et al. 2001

View full text Add to dashboard Cite

Abstract.The cross-polar potential drop pc and the lowlatitude asymmetric geomagnetic disturbance field, as indicated by the mid-latitude ASY-H magnetic index, are used to study the average magnetospheric response to the solar wind forcing for southward interplanetary magnetic field conditions. The state of the solar wind is monitored by the ACE spacecraft and the ionospheric convection is measured by the double probe electric field instrument on the Astrid-2 satellite. The solar wind-magnetosphere coupling is examined for 77 cases in February and from mid-May to mid-June 1999 by using the interplanetary magnetic field B z component and the reconnection electric field. Our results show that the maximum correlation between pc and the reconnection electric field is obtained approximately 25 min after the solar wind has reached a distance of 11 R E from the Earth, which is the assumed average position of the magnetopause. The corresponding correlation for ASY-H shows two separate responses to the reconnection electric field, delayed by about 35 and 65 min, respectively. We suggest that the combination of the occurrence of a large magnetic storm on 18 February 1999 and the enhanced level of geomagnetic activity which peaks at Kp = 7 − may explain the fast direct response of ASY-H to the solar wind at 35 min, as well as the lack of any clear secondary responses of pc to the driving solar wind at time delays longer than 25 min.

show abstract

“…Baker et al, 1983;Reiff and Luhmann, 1986;Eriksson et al, 2000). This is again evident in comparing the correlation coefficients for IMF B z and E r with pc in Fig.…”

Section: Resultssupporting

confidence: 55%

Section: Magnetospheric Response To the Solar Windmentioning

confidence: 85%

Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field

et al. 2001

View full text Add to dashboard Cite

show abstract

“…What saturation means is that the cross -polar cap potential in the ionosphere is less than expected for a given strength of the solar wind driver [e.g., Wygant et al, 1983;Reiff and Luhmann, 1986;Weimer et al, 1990].…”

Section: Introductionmentioning

confidence: 99%

Polar cap potential saturation, dayside reconnection, and changes to the magnetosphere

2009

View full text Add to dashboard Cite

[1] Global MHD simulations of the Earth's magnetosphere using the Block-AdaptiveTree Solarwind Roe Upwind Scheme code at the Community Coordinated Modeling Center are run with a high-resolution dayside magnetopause and variable-resolution nearEarth regions to study the phenomena of polar cap saturation. In the simulations a resistive spot is maintained on the moving magnetopause to ensure that the correct dayside reconnection rate is obtained. The solar wind parameters are held fixed, and the ionospheric Pedersen conductivity is varied. Strong reduction of the cross-polar cap potential is observed, with modest increases in the cross-polar cap current, and no changes in the local and global reconnection rates. Changes in the magnetosphere associated with the saturation of the polar cap are explored: these include a weakening of the dayside magnetic field strength, an equatorward shift of the cusps, a flattening in Z of the closed field line region of the dayside magnetosphere, and a taillike stretching of the dipole field lines at the terminator. Measurements of the currents and voltages of the polar cap indicate that the solar wind acts like a current-limited voltage generator. A simple circuit model is analyzed using measurements from the MHD simulations, and physically reasonable values for the circuit elements are obtained. Nine models for polar cap saturation are assessed against the findings of the present study.

show abstract

“…Many features of the Earth's magnetosphere and high-latitude ionosphere are known to depend on B z in a reference frame which allows for the orientation of the Earth's magnetic axis (such as the GSM frame). These include the cross polar cap potential (the ionospheric signature of the voltage across the magnetosphere) (Reiff et al, 1981;Doyle and Burke, 1983;Wygant et al, 1983;Cowley, 1984;Reiff and Luhmann, 1986); the patterns of the associated high-latitude F-region ionospheric flows (Heelis, 1984;Heppner and Maynard, 1987;Etemadi et al, 1988) and E-region currents (Nishida, 1968;Friis-Christiansen et al, 1985); field aligned currents (Iijima et al, 1978); the average size of the polar cap (Holzworth and Meng, 1984), the occurrence of global geomagnetic activity (e.g. Schatten and Wilcox, 1967;Arnoldy, 1971;Berthelier, 1976;Baker et al, 1981Baker et al, , 1983Clauer et al, 1981;Bargatze et al, 1985;Scurry and Russell, 1991), including magnetospheric substorms (Rostoker and Falthammer, 1967;Caan et al, 1977;Meloni et al, 1982;Samson and Young, 1986); the occurrence of reconnection signatures such as flux transfer events (Berchem and Russell, 1984) and high speed flow streams at the magnetopause (Scurry et al, 1994); the energy deposition into the high-latitude ionosphere and thermosphere (Akasofu, 1981;Bargatze et al, 1986;Weiss et al, 1992); and the global pattern of winds in the neutral thermosphere (Killeen et al, 1985).…”

Section: Introductionmentioning

confidence: 99%

Ionospheric and geomagnetic responses to changes in IMF <i>B<sub>Z</sub></i>: a superposed epoch study

et al. 1997

View full text Add to dashboard Cite

Abstract. Superposed epoch studies have been carried out in order to determine the ionospheric response at mid-latitudes to southward turnings of the interplanetary magnetic field (IMF). This is compared with the geomagnetic response, as seen in the indices K p , AE and Dst. The solar wind, IMF and geomagnetic data used were hourly averages from the years 1967-1989 and thus cover a full 22-year cycle in the solar magnetic field. These data were divided into subsets, determined by the magnitudes of the southward turnings and the concomitant increase in solar wind pressure. The superposed epoch studies were carried out using the time of the southward turning as time zero. The response of the mid-latitude ionosphere is studied by looking at the F-layer critical frequencies, f o F2, from hourly soundings by the Slough ionosonde and their deviation from the monthly median values, f o F2. For the southward turnings with a change in B z of B z > 11:5 nT accompanied by a solar wind dynamic pressure P exceeding 5 nPa, the F region critical frequency, f o F2, shows a marked decrease, reaching a minimum value about 20 h after the southward turning. This recovers to pre-event values over the subsequent 24 h, on average. The Dst index shows the classic storm-time decrease to about )60 nT. Four days later, the index has still to fully recover and is at about )25 nT. Both the K p and AE indices show rises before the southward turnings, when the IMF is strongly northward but the solar wind dynamic pressure is enhanced. The average AE index does register a clear isolated pulse (averaging 650 nT for 2 h, compared with a background peak level of near 450 nT at these times) showing enhanced energy deposition at high latitudes in substorms but, like K p , remains somewhat enhanced for several days, even after the average IMF has returned to zero after 1 day. This AE background decays away over several days as the Dst index recovers, indicating that there is some contamination of the currents observed at the AE stations by the continuing enhanced equatorial ring current. For data averaged over all seasons, the critical frequencies are depressed at Slough by 1.3 MHz, which is close to the lower decile of the overall distribution of f o F2 values. Taking 30-day periods around summer and winter solstice, the largest depression is 1.6 and 1.2 MHz, respectively. This seasonal dependence is confirmed by a similar study for a Southern Hemisphere station, Argentine Island, giving peak depressions of 1.8 MHz and 0.5 MHz for summer and winter. For the subset of turnings where B z > 11:5 nT and P 5 nPa, the response of the geomagnetic indices is similar but smaller, while the change in f o F2 has all but disappeared. This confirms that the energy deposited at high latitudes, which leads to the geomagnetic and ionospheric disturbances following a southward turning of the IMF, increases with the energy density (dynamic pressure) of the solar wind flow. The magnitude of all responses are shown to depend on B z . At Slough, the peak depression alwa...

show abstract

Solar Wind Control of the Polar-Cap Voltage

Cited by 186 publications

References 61 publications

Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field

Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field

Polar cap potential saturation, dayside reconnection, and changes to the magnetosphere

Ionospheric and geomagnetic responses to changes in IMF <i>B<sub>Z</sub></i>: a superposed epoch study

Contact Info

Product

Resources

About

Solar Wind Control of the Polar-Cap Voltage

Cited by 186 publications

References 61 publications

Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field

Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field

Polar cap potential saturation, dayside reconnection, and changes to the magnetosphere

Ionospheric and geomagnetic responses to changes in IMF &lt;i&gt;B&lt;sub&gt;Z&lt;/sub&gt;&lt;/i&gt;: a superposed epoch study

Contact Info

Product

Resources

About

Ionospheric and geomagnetic responses to changes in IMF <i>B<sub>Z</sub></i>: a superposed epoch study