Spatial structure of solar wind at a time of minimum solar activity

In this work we will show the behavior of the horizontal component H of the Earth Magnetic Field (EMF) along the seasons&#160;during the period of solar cycle 24 lasting from 2009 to 2019. By means of &#160;continuous measurements of geomagnetic components (X, Y) of the EMF, we compute the horizontal component H at the Earth&#8217;s surface. The data are recorded with a time resolution of one minute at Tamanrasset observatory in Algeria at the geographical coordinates of 22.79&#176; North and 5.53&#176; East. These data are available from the INTERMAGNET network. We find that the variation in amplitude of the hourly average of H component at low latitude changes from a season to another and it is greater at the maximum solar activity than at the minimum solar activity.Keywords: Solar cycle 24, Season, Horizontal component H.&#160;

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Long-term cosmic ray/solar activity hysteresis phenomenon and properties of solar wind for the last 200 years

10.1063/1.58706 ◽

1999 ◽

Cited By ~ 1

Author(s):

L. I. Dorman ◽

G. Villoresi ◽

I. V. Dorman ◽

N. Iucci ◽

M. Parisi

Keyword(s):

Solar Wind ◽

Solar Activity ◽

Cosmic Ray ◽

Hysteresis Phenomenon

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Breathing of heliospheric structures triggered by the solar-cycle activity

Annales Geophysicae ◽

10.5194/angeo-21-1303-2003 ◽

2003 ◽

Vol 21 (6) ◽

pp. 1303-1313 ◽

Cited By ~ 35

Author(s):

K. Scherer ◽

H. J. Fahr

Keyword(s):

Solar Wind ◽

Solar Activity ◽

Solar Cycle ◽

Activity Cycle ◽

Periodic Variation ◽

Galactic Cosmic Rays ◽

Activity Period ◽

Solar Cycles ◽

Interplanetary Physics ◽

Ram Pressure

Abstract. Solar wind ram pressure variations occuring within the solar activity cycle are communicated to the outer heliosphere as complicated time-variabilities, but repeating its typical form with the activity period of about 11 years. At outer heliospheric regions, the main surviving solar cycle feature is a periodic variation of the solar wind dynamical pressure or momentum flow, as clearly recognized by observations of the VOYAGER-1/2 space probes. This long-periodic variation of the solar wind dynamical pressure is modeled here through application of appropriately time-dependent inner boundary conditions within our multifluid code to describe the solar wind – interstellar medium interaction. As we can show, it takes several solar cycles until the heliospheric structures adapt to an average location about which they carry out a periodic breathing, however, lagged in phase with respect to the solar cycle. The dynamically active heliosphere behaves differently from a static heliosphere and especially shows a historic hysteresis in the sense that the shock structures move out to larger distances than explained by the average ram pressure. Obviously, additional energies are pumped into the heliosheath by means of density and pressure waves which are excited. These waves travel outwards through the interface from the termination shock towards the bow shock. Depending on longitude, the heliospheric sheath region memorizes 2–3 (upwind) and up to 6–7 (downwind) preceding solar activity cycles, i.e. the cycle-induced waves need corresponding travel times for the passage over the heliosheath. Within our multifluid code we also adequately describe the solar cycle variations in the energy distributions of anomalous and galactic cosmic rays, respectively. According to these results the distribution of these high energetic species cannot be correctly described on the basis of the actually prevailing solar wind conditions.Key words. Interplanetary physics (heliopause and solar wind termination; general or miscellaneous) – Space plasma physics (experimental and mathematical techniques)

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Exploring the role of ionospheric drivers during the extreme solar minimum of 2008

Annales Geophysicae ◽

10.5194/angeo-31-2147-2013 ◽

2013 ◽

Vol 31 (12) ◽

pp. 2147-2156 ◽

Cited By ~ 10

Author(s):

J. Klenzing ◽

A. G. Burrell ◽

R. A. Heelis ◽

J. D. Huba ◽

R. Pfaff ◽

...

Keyword(s):

Solar Activity ◽

Solar Minimum ◽

Wind Model ◽

Ion Density ◽

Density Data ◽

Early Afternoon ◽

Minimum Solar Activity ◽

Forecasting System ◽

Electric Field Instrument

Abstract. During the recent solar minimum, solar activity reached the lowest levels observed during the space age, resulting in a contracted atmosphere. This extremely low solar activity provides an unprecedented opportunity to understand the variability of the Earth's ambient ionosphere. The average E × B drifts measured by the Vector Electric Field Instrument (VEFI) on the Communications/Navigation Outage Forecasting System (C/NOFS) satellite during this period are found to have several differences from the expected climatology based on previous solar minima, including downward drifts in the early afternoon and a weak to non-existent pre-reversal enhancement. Using SAMI2 (Sami2 is Another Model of the Ionosphere) as a computational engine, we investigate the effects of these electrodynamical changes as well as the contraction of the thermosphere and reduced EUV ionization on the ionosphere. The sensitivity of the simulations to wind models is also discussed. These modeled ionospheres are compared to the C/NOFS average topside ion density and composition and Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere, and Climate average NmF2 and hmF2. In all cases, incorporating the VEFI drift data significantly improves the model results when compared to both the C/NOFS density data and the F3/C GOX data. Changing the MSIS and EUVAC models produced changes in magnitude, but not morphology with respect to local time. The choice of wind model modulates the resulting topside density and composition, but only the use of the VEFI E × B drifts produces the observed post-sunset drop in the F peak.

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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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Can an interplanetary magnetic field reach the surface of Venus?

Annales Geophysicae ◽

10.5194/angeo-36-1537-2018 ◽

2018 ◽

Vol 36 (6) ◽

pp. 1537-1543

Author(s):

Yasuhito Narita ◽

Uwe Motschmann

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Activity ◽

Interplanetary Magnetic Field ◽

Field Condition ◽

Diffusion Time ◽

Field Reversal ◽

Magnetic Diffusion ◽

The Magnetic Field ◽

Magnetic Field Condition

Abstract. We address the question of whether there is a possibility of an interplanetary magnetic field reaching Venus' surface by magnetic diffusion across the ionosphere. We present a model calculation, estimate the magnetic diffusion time at Venus, and find out that the typical diffusion timescale is in a range between 12 and 54 h, depending on the solar activity and the ionospheric magnetic field condition. The magnetic field can thus permeate Venus' surface and even its interior when the solar wind is stationary (i.e., no magnetic field reversal) on the timescale of half a day to several days.

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