Comments on paper ?the solar wind cycle, the sunspot cycle and the corona? by J. Hirshberg

1974 ◽  
Vol 28 (1) ◽  
pp. L7-L10 ◽  
Author(s):  
L. Diodato ◽  
G. Moreno
Keyword(s):  
Solar Wind ◽  
Sunspot Cycle ◽  
Wind Cycle

scholarly journals Extremely low geomagnetic activity during the recent deep solar cycle minimum

2011 ◽  
Vol 7 (S286) ◽  
pp. 200-209 ◽  
Author(s):  
E. Echer ◽  
B. T. Tsurutani ◽  
W. D. Gonzalez
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Solar Minimum ◽  
Solar Wind Speed ◽  
Sunspot Cycle ◽  
Cycle Minimum ◽  
Current Minimum ◽  
Solar Wind Parameters ◽  
Xix Century

AbstractThe recent solar minimum (2008-2009) was extreme in several aspects: the sunspot number, Rz, interplanetary magnetic field (IMF) magnitude Bo and solar wind speed Vsw were the lowest during the space era. Furthermore, the variance of the IMF southward Bz component was low. As a consequence of these exceedingly low solar wind parameters, there was a minimum in the energy transfer from solar wind to the magnetosphere, and the geomagnetic activity ap index reached extremely low levels. The minimum in geomagnetic activity was delayed in relation to sunspot cycle minimum. We compare the solar wind and geomagnetic activity observed in this recent minimum with previous solar cycle values during the space era (1964-2010). Moreover, the geomagnetic activity conditions during the current minimum are compared with long term variability during the period of available geomagnetic observations. The extremely low geomagnetic activity observed in this solar minimum was previously recorded only at the end of XIX century and at the beginning of the XX century, and this might be related to the Gleissberg (80-100 years) solar cycle.

North-South Asymmetry of the Polar Solar Wind and Some Characteristics of Solar Magnetic Field

1996 ◽  
Vol 154 ◽  
pp. 165-168
Author(s):  
T.E. Girish ◽  
G. Gopkumar
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Wind Speed ◽  
Solar Magnetic Field ◽  
Solar Wind Speed ◽  
Sunspot Cycle ◽  
Coronal Magnetic Field ◽  
Sunspot Activity ◽  
Dipolar Contribution ◽  
South Asymmetry

AbstractWe have found correlated variations of the yearly averaged north-south asymmetry in the polar solar wind speed (Δsol) and the ratio of the zonal quadrupolar to the zonal dipolar contribution in the inferred coronal magnetic field during the declining phase of sunspot cycle 21. A physically meaningful association between Δsol and some polar solar magnetic field proxies is also observed during the low sunspot activity periods of the above cycle.

scholarly journals Quasi-biennial and quasi-triennial oscillations in geomagnetic activity indices

1997 ◽  
Vol 15 (12) ◽  
pp. 1581-1594 ◽  
Author(s):  
R. P. Kane
Keyword(s):  
Solar Wind ◽  
Geomagnetic Activity ◽  
Southern Oscillation ◽  
Activity Index ◽  
Sunspot Cycle ◽  
Low Latitude ◽  
Sunspot Maximum ◽  
Chance Coincidence ◽  
Before And After ◽  
Abstract Data

Abstract. Data for geomagnetic activity index aa for 1868–1994 were subjected to spectral analysis for 12 intervals each of 11 consecutive years. In each interval, QBO and QTO (quasi-biennial and quasi-triennial oscillations) were observed at ~2.00, 2.15, 2.40, 2.70 y and ~3.20, 3.40 y, but not all in all intervals. These fluctuations are absent near (2–3 y before and after) the sunspot minima and are present only as 2 or 3 peaks in aa indices, one near or before the sunspot maximum and the other (one or two, generally the larger ones) in the declining phase of the sunspot cycle. Comparison with the solar wind (1965 onwards) showed a fairly good match, indicating that the aa variations were mostly due to similar variations in the solar wind, which must have their origin in solar physical processes. A few aa variations did not match with solar wind. When compared with terrestrial phenomena, no match was found with stratospheric low-latitude zonal wind QBO; but some QTO in aa matched QTO in ENSO (El Nino/Southern Oscillation). This may or may not be a chance coincidence and needs further exploration.

scholarly journals Latitude dependence of long-term geomagnetic activity and its solar wind drivers

2015 ◽  
Vol 33 (5) ◽  
pp. 573-581 ◽  
Author(s):  
M. Myllys ◽  
N. Partamies ◽  
L. Juusola
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Geomagnetic Activity ◽  
High Speed ◽  
Sunspot Cycle ◽  
Horizontal Magnetic Field ◽  
Geomagnetic Variations ◽  
Latitude Dependence ◽  
Latitude Region ◽  
The Impact

Abstract. To validate the usage of global indices in studies of geomagnetic activity, we have examined the latitude dependence of geomagnetic variations in Fennoscandia and Svalbard from 1994 to 2010. Daily standard deviation (SD) values of the horizontal magnetic field have been used as a measure of the ground magnetic disturbance level. We found that the timing of the geomagnetic minimum depends on the latitude region: corresponding to the minimum of sunspot cycle 22 (in 1996), the geomagnetic minimum occurred between the geomagnetic latitudes 57–61° in 1996 and at the latitudes 64–67° in 1997, which are the average auroral oval latitudes. During sunspot cycle 23, all latitude regions experienced the minimum in 2009, a year after the sunspot minimum. These timing differences are due to the latitude dependence of the 10 s daily SD on the different solar wind drivers. In the latitude region of 64–67°, the impact of the high-speed solar wind streams (HSSs) on the geomagnetic activity is the most pronounced compared to the other latitude groups, while in the latitude region of 57–61°, the importance of the coronal mass ejections (CMEs) dominates. The geomagnetic activity maxima during ascending solar cycle phases are typically caused by CME activity and occur especially in the oval and sub-auroral regions. The strongest geomagnetic activity occurs during the descending solar cycle phases due to a mixture of CME and HSS activity. Closer to the solar minimum, less severe geomagnetic activity is driven by HSSs and mainly visible in the poleward part of the auroral region. According to our study, however, the timing of the geomagnetic activity minima (and maxima) in different latitude bands is different, due to the relative importance of different solar wind drivers at different latitudes.

A survey of coronal holes and their solar wind associations throughout sunspot cycle 20

Solar Physics ◽  
1978 ◽  
Vol 56 (1) ◽  
pp. 161-183 ◽  
Author(s):  
R. M. Broussard ◽  
N. R. Sheeley ◽  
R. Tousey ◽  
J. H. Underwood
Keyword(s):  
Solar Wind ◽  
Coronal Holes ◽  
Sunspot Cycle

scholarly journals On the periodic variations of geomagnetic activity indices Ap and ap

1998 ◽  
Vol 16 (5) ◽  
pp. 510-517 ◽  
Author(s):  
H. Schreiber
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Sunspot Cycle ◽  
Solar Wind Plasma ◽  
Sector Structure ◽  
Interplanetary Physics ◽  
Before And After ◽  
Activity Indices ◽  
The Imf

Abstract. Yearly averages of geomagnetic activity indices Ap for the years 1967–1984 are compared to the respective averages of ν2·Bs, where v is the solar wind velocity and Bs is the southward interplanetary magnetic field (IMF) component. The correlation of both quantities is known to be rather good. Comparing the averages of Ap with ν2 and Bs separately we find that, during the declining phase of the solar cycle, ν2 and during the ascending phase Bs have more influence on Ap. According to this observation (using Fourier spectral analysis) the semiannual and 27 days, Ap variations for the years 1932–1993 were analysed separately for years before and after sunspot minima. Only those time-intervals before sunspot minima with a significant 27-day recurrent period of the IMF sector structure and those intervals after sunspot minima with a significant 28-28.5-day recurrent period of the sector structure were used. The averaged spectra of the two Ap data sets clearly show a period of 27 days before and a period of 28–29 days after sunspot minimum. Moreover, the phase of the average semiannual wave of Ap is significantly different for the two groups of data: the Ap variation maximizes near the equinoxes during the declining phase of the sunspot cycle and near the beginning of April and October during the ascending phase of the sunspot cycle, as predicted by the Russell-McPherron (R-M) mechanism. Analysing the daily variation of ap in an analogue manner, the same equinoctial and R-M mechanisms are seen, suggesting that during phases of the solar cycle, when ap depends more on the IMF-Bs component, the R-M mechanism is predominant, whereas during phases when ap increases as v increases the equinoctial mechanism is more likely to be effective.Key words. Interplanetary physics · Magnetic fields · Solar wind plasma · Solar wind · magnetosphere interaction

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