Invariability of relationship between the polar cap magnetic activity and geoeffective interplanetary electric field

Abstract. The PC (polar cap) index characterizing the solar wind energy input into the magnetosphere is calculated with use of parameters α, β, and φ, determining the relationship between the interplanetary electric field (EKL) and the value of magnetic activity δF in the polar caps. These parameters were noted as valid for large and small EKL values, and as a result the suggestion was made (Troshichev et al., 2006) that the parameters should remain invariant irrespective of solar activity. To verify this suggestion, the independent sets of calibration parameters α, β, and φ were derived separately for the solar maximum (1998–2001) and solar minimum (1997, 2007–2009) epochs, with a proper choice of a quiet daily variation (QDC) as a level of reference for the polar cap magnetic activity value. The results presented in this paper demonstrate that parameters α, β, and φ, derived under conditions of solar maximum and solar minimum, are indeed in general conformity and provide consistent (within 10 % uncertainty) estimations of the PC index. It means that relationship between the geoeffective solar wind variations and the polar cap magnetic activity responding to these variations remains invariant irrespective of solar activity. The conclusion is made that parameters α, β, and φ derived in AARI#3 version for complete cycle of solar activity (1995–2005) can be regarded as forever valid.

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Solar cycle dependent characteristics of the equatorial blanketing E<sub><i>s</i></sub> layers and associated irregularities

Annales Geophysicae ◽

10.5194/angeo-24-2931-2006 ◽

2006 ◽

Vol 24 (11) ◽

pp. 2931-2947 ◽

Cited By ~ 19

Author(s):

C. V. Devasia ◽

V. Sreeja ◽

S. Ravindran

Keyword(s):

Solar Activity ◽

Solar Cycle ◽

Electric Field ◽

Solar Minimum ◽

Solar Maximum ◽

Dominant Role ◽

Onset Time ◽

Vhf Radar ◽

Cycle Dependent ◽

June July

Abstract. The occurrence of blanketing type Es (Esb) layers and associated E-region irregularities over the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip ~0.5°) during the summer solstitial months of May, June, July and August has been investigated in detail for the period 1986–2000 to bring out the variabilities in their characteristics with the solar cycle changes. The study has been made using the ionosonde and magnetometer data of Trivandrum from 1986–2000 along with the available data from the 54.95 MHz VHF backscatter radar at Trivandrum for the period 1995–2000. The appearance of blanketing Es layers during these months is observed to be mostly in association with the occurrence of afternoon Counter Electrojet (CEJ) events. The physical process leading to the occurrence of a CEJ event is mainly controlled by the nature of the prevailing electro dynamical/neutral dynamical conditions before the event. Hence it is natural that the Esb layer characteristics like the frequency of occurrence, onset time, intensity, nature of gradients in its top and bottom sides etc are also affected by the nature of the background electro dynamical /neutral dynamical processes which in turn are strongly controlled by the solar activity changes. The occurrence of Esb layers during the solstitial months is found to show very strong solar activity dependence with the occurrence frequency being very large during the solar minimum years and very low during solar maximum years. The intensity of the VHF radar backscattered signals from the Esb irregularities is observed to be controlled by the relative roles of the direction and magnitude of the prevailing vertical polarization electric field and the vertical electron density gradient of the prevailing Esb layer depending on the phase of the solar cycle. The gradient of the Esb layer shows a more dominant role in the generation of gradient instabilities during solar minimum periods while it is the electric field that has a more dominant role during solar maximum periods.

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Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission

Annales Geophysicae ◽

10.5194/angeo-33-413-2015 ◽

2015 ◽

Vol 33 (3) ◽

pp. 413-426 ◽

Cited By ~ 20

Author(s):

J. H. Zoennchen ◽

U. Nass ◽

H. J. Fahr

Keyword(s):

Solar Wind ◽

Solar Activity ◽

Solar Minimum ◽

Solar Maximum ◽

Neutral Hydrogen ◽

Line Center ◽

Hydrogen Density ◽

Density Distributions ◽

Stereo Mission ◽

The Earth

Abstract. Circumterrestrial Lyman-α column brightness observations above 3 Earth radii (Re) have been used to derive separate 3-D neutral hydrogen density models of the Earth's exosphere for solar minimum (2008, 2010) and near-solar-maximum (2012) conditions. The data used were measured by Lyman-α detectors (LAD1/2) onboard each of the TWINS satellites from very different orbital positions with respect to the exosphere. Exospheric H atoms resonantly scatter the near-line-center solar Lyman-α flux at 121.6 nm. Assuming optically thin conditions above 3Re along a line of sight (LOS), the scattered LOS-column intensity is proportional to the LOS H-column density. We found significant differences in the density distribution of the terrestrial exosphere under different solar conditions. Under solar maximum conditions we found higher H densities and a larger spatial extension compared to solar minimum. After a continuous, 2-month decrease in (27 day averaged) solar activity, significantly lower densities were found. Differences in shape and orientation of the exosphere under different solar conditions exist. Above 3 Re, independent of solar activity, increased H densities appear on the Earth's nightside shifted towards dawn. With increasing distance (as measured at 8Re) this feature is shifted westward/duskward by between −4 and −5° with respect to midnight. Thus, at larger geocentric distance the exosphere seems to be aligned with the aberrated Earth–solar-wind line, defined by the solar wind velocity and the orbital velocity of the Earth. The results presented in this paper are valid for geocentric distances between 3 and 8Re.

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Dependence of SuperDARN cross polar cap potential upon the solar wind electric field and magnetopause subsolar distance

Journal of Geophysical Research Atmospheres ◽

10.1029/2008ja013107 ◽

2008 ◽

Vol 113 (A9) ◽

pp. n/a-n/a ◽

Cited By ~ 8

Author(s):

G. Ya. Khachikjan ◽

A. V. Koustov ◽

G. J. Sofko

Keyword(s):

Solar Wind ◽

Electric Field ◽

Polar Cap ◽

Cross Polar Cap Potential

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Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving

Journal of Geophysical Research Space Physics ◽

10.1002/2015ja021199 ◽

2015 ◽

Vol 120 (6) ◽

pp. 4684-4699 ◽

Cited By ~ 2

Author(s):

W. A. Bristow ◽

E. Amata ◽

J. Spaleta ◽

M. F. Marcucci

Keyword(s):

Solar Wind ◽

Polar Cap ◽

The Relationship

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Alfvénic fluctuations in "newborn"' polar solar wind

Annales Geophysicae ◽

10.5194/angeo-23-1513-2005 ◽

2005 ◽

Vol 23 (4) ◽

pp. 1513-1520 ◽

Cited By ~ 1

Author(s):

B. Bavassano ◽

E. Pietropaolo ◽

R. Bruno

Keyword(s):

Solar Wind ◽

Solar Activity ◽

Solar Maximum ◽

Activity Cycle ◽

Residual Energy ◽

Mhd Waves ◽

Polar Wind ◽

Interplanetary Physics ◽

Low Latitudes ◽

Comparative Statistical Analysis

Abstract. The 3-D structure of the solar wind is strongly dependent upon the Sun's activity cycle. At low solar activity a bimodal structure is dominant, with a fast and uniform flow at the high latitudes, and slow and variable flows at low latitudes. Around solar maximum, in sharp contrast, variable flows are observed at all latitudes. This last kind of pattern, however, is a relatively short-lived feature, and quite soon after solar maximum the polar wind tends to regain its role. The plasma parameter distributions for these newborn polar flows appear very similar to those typically observed in polar wind at low solar activity. The point addressed here is about polar wind fluctuations. As is well known, the low-solar-activity polar wind is characterized by a strong flow of Alfvénic fluctuations. Does this hold for the new polar flows too? An answer to this question is given here through a comparative statistical analysis on parameters such as total energy, cross helicity, and residual energy, that are of general use to describe the Alfvénic character of fluctuations. Our results indicate that the main features of the Alfvénic fluctuations observed in low-solar-activity polar wind have been quickly recovered in the new polar flows developed shortly after solar maximum. Keywords. Interplanetary physics (MHD waves and turbulence; Sources of the solar wind) – Space plasma physics (Turbulence)

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