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S K Solanki - One of the best experts on this subject based on the ideXlab platform.
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sunspot areas and tilt angles for Solar Cycles 7 10
Astronomy and Astrophysics, 2015Co-Authors: Senthamizh V Pavai, Natalie A Krivova, Rainer Arlt, M Dasiespuig, S K SolankiAbstract:Aims. Extending the knowledge about the properties of Solar Cycles into the past is essential for understanding the Solar dynamo. This paper aims to estimate areas of sunspots observed by Schwabe in 1825−1867 and to calculate the tilt angles of sunspot groups. Methods. The sunspot sizes in Schwabe’s drawings are not to scale and need to be converted into physical sunspot areas. We employed a statistical approach assuming that the area distribution of sunspots was the same in the 19th century as it was in the 20th century. Results. Umbral areas for about 130 000 sunspots observed by Schwabe were obtained, as well as the tilt angles of sunspot groups assuming them to be bipolar. There is, of course, no polarity information in the observations. The annually averaged sunspot areas correlate reasonably with sunspot number. We derived an average tilt angle by attempting to exclude unipolar groups with a minimum separation of the two alleged polarities and an outlier rejection method which follows the evolution of each group and detects the moment it turns unipolar at its decay. As a result, the tilt angles, although displaying considerable scatter, average to 5. ◦ 85 ± 0. 25, with the leading polarity located closer to the equator, in good agreement with tilt angles obtained from 20th century data sets. Sources of uncertainties in the tilt angle determination are discussed and need to be addressed whenever different data sets are combined. The sunspot area and tilt angle data are provided at the CDS.
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sunspot areas and tilt angles for Solar Cycles 7 10
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Senthamizh V Pavai, Natalie A Krivova, Rainer Arlt, M Dasiespuig, S K SolankiAbstract:Extending the knowledge about the properties of Solar Cycles into the past is essential for understanding the Solar dynamo. This paper aims at estimating areas of sunspots observed by Schwabe in 1825-1867 and at calculating the tilt angles of sunspot groups. The sunspot sizes in Schwabe's drawings are not to scale and need to be converted into physical sunspot areas. We employed a statistical approach assuming that the area distribution of sunspots was the same in the 19th century as it was in the 20th century. Umbral areas for about 130,000 sunspots observed by Schwabe were obtained, as well as the tilt angles of sunspot groups assuming them to be bipolar. There is, of course, no polarity information in the observations. The annually averaged sunspot areas correlate reasonably with sunspot number. We derived an average tilt angle by attempting to exclude unipolar groups with a minimum separation of the two alleged polarities and an outlier rejection method which follows the evolution of each group and detects the moment it turns unipolar at its decay. As a result, the tilt angles, although displaying considerable scatter, place the leading polarity on average 5.85+-0.25 closer to the equator, in good agreement with tilt angles obtained from 20th-century data sets. Sources of uncertainties in the tilt angle determination are discussed and need to be addressed whenever different data sets are combined. The sunspot area and tilt angle data are provided online.
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a new satire s spectral Solar irradiance reconstruction for Solar Cycles 21 23 and its implications for stratospheric ozone
Journal of the Atmospheric Sciences, 2014Co-Authors: William T Ball, Natalie A Krivova, Y C Unruh, Joanna D Haigh, S K SolankiAbstract:AbstractThe authors present a revised and extended total and spectral Solar irradiance (SSI) reconstruction, which includes a wavelength-dependent uncertainty estimate, spanning the last three Solar Cycles using the Spectral and Total Irradiance Reconstruction—Satellite era (SATIRE-S) model. The SSI reconstruction covers wavelengths between 115 and 160 000 nm and all dates between August 1974 and October 2009. This represents the first full-wavelength SATIRE-S reconstruction to cover the last three Solar Cycles without data gaps and with an uncertainty estimate. SATIRE-S is compared with the Naval Research Laboratory Spectral Solar Irradiance (NRLSSI) model and ultraviolet (UV) observations from the Solar Radiation and Climate Experiment (SORCE) Solar Stellar Irradiance Comparison Experiment (SOLSTICE). SATIRE-S displays similar cycle behavior to NRLSSI for wavelengths below 242 nm and almost twice the variability between 242 and 310 nm. During the decline of the last Solar cycle, between 2003 and 2008, t...
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a new satire s spectral Solar irradiance reconstruction for Solar Cycles 21 23 and its implications for stratospheric ozone
arXiv: Atmospheric and Oceanic Physics, 2014Co-Authors: William T Ball, Natalie A Krivova, Y C Unruh, Joanna D Haigh, S K SolankiAbstract:We present a revised and extended total and spectral Solar irradiance (SSI) reconstruction, which includes a wavelength-dependent uncertainty estimate, spanning the last three Solar Cycles using the SATIRE-S model. The SSI reconstruction covers wavelengths between 115 and 160,000 nm and all dates between August 1974 and October 2009. This represents the first full-wavelength SATIRE-S reconstruction to cover the last three Solar Cycles without data gaps and with an uncertainty estimate. SATIRE-S is compared with the NRLSSI model and SORCE/SOLSTICE ultraviolet (UV) observations. SATIRE-S displays similar cycle behaviour to NRLSSI for wavelengths below 242 nm and almost twice the variability between 242 and 310 nm. During the decline of last Solar cycle, between 2003 and 2008, SSI from SORCE/SOLSTICE version 12 and 10 typically displays more than three times the variability of SATIRE-S between 200 and 300 nm. All three datasets are used to model changes in stratospheric ozone within a 2D atmospheric model for a decline from high Solar activity to Solar minimum. The different flux changes result in different modelled ozone trends. Using NRLSSI leads to a decline in mesospheric ozone, while SATIRE-S and SORCE/SOLSTICE result in an increase. Recent publications have highlighted increases in mesospheric ozone when considering version 10 SORCE/SOLSTICE irradiances. The recalibrated SORCE/SOLSTICE version 12 irradiances result in a much smaller mesospheric ozone response than when using version 10 and now similar in magnitude to SATIRE-S. This shows that current knowledge of variations in spectral irradiance is not sufficient to warrant robust conclusions concerning the impact of Solar variability on the atmosphere and climate.
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analyzing Solar Cycles
Science, 2011Co-Authors: S K Solanki, Natalie A KrivovaAbstract:Since observational records began about 300 years ago, and very likely for millions of years before that, the Sun has displayed cyclically varying magnetic activity ( 1 ). Approximately every 11 years, a maximum of activity is reached, with a large number of sunspots (see the figure, panel A) present on the Solar surface, strong x-ray emission from the corona, and a peak in the number of flares and coronal mass ejections. The latter cause mid- and low-latitude aurorae, disrupt radio communications, perturb navigation systems and radars, produce electric power outages, and can pose radiation hazards for astronauts and aircraft crew.
K Fujiki - One of the best experts on this subject based on the ideXlab platform.
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global Solar magnetic field and interplanetary scintillations during the past four Solar Cycles
Solar Physics, 2019Co-Authors: Madhusudan Ingale, P Janardhan, K Fujiki, Susanta Kumar Bisoi, Sasikumar K Raja, Prasad Subramanian, M MaksimovicAbstract:The extended minimum of Solar Cycle 23, the extremely quiet Solar-wind conditions prevailing and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in Solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in Solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/Solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975 – 2018. Furthermore, we have measured the normalized scintillation index [ $m$ ] using the IPS observations carried out at the Institute of Space–Earth Environment Research (ISEE), Japan during 1983 – 2017. From these observations, we have found that, since the mid-1990s, the magnetic field over different latitudes at $2.5~\mathrm{R}_{\odot}$ and $10~\mathrm{R}_{\odot}$ (extrapolated using the PFSS method) has decreased by ${\approx}\,11.3\,\mbox{--}\,22.2\%$ . In phase with the declining magnetic fields, the quantity $m$ also declined by ${\approx}\, 23.6\%$ . These observations emphasize the inter-relationship among the global magnetic field and various turbulence parameters in the Solar corona and Solar-wind.
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global Solar magnetic field and interplanetary scintillations during the past four Solar Cycles
arXiv: Solar and Stellar Astrophysics, 2019Co-Authors: Madhusudan Ingale, P Janardhan, K Fujiki, Susanta Kumar Bisoi, Sasikumar K Raja, Prasad Subramanian, M MaksimovicAbstract:The extended minimum of Solar Cycle 23, the extremely quiet Solar-wind conditions prevailing, and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in Solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in Solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/Solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic-fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975-2018. Furthermore, we have measured the normalized scintillation index [m] using the IPS observations carried out at the Institute of Space Earth Environment Research (ISEE), Japan during 1983-2017. From these observations, we have found that, since the mid-1990s, the magnetic-field over different latitudes at 2.5 $\rm R_{\odot}$ and 10 $\rm R_{\odot}$(extrapolated using PFSS method) has decreased by $\approx 11.3-22.2 \%$. In phase with the declining magnetic-fields, the quantity m also declined by $\approx 23.6 \%$. These observations emphasize the inter-relationship between the global magnetic-field and various turbulence parameters in the Solar corona and Solar wind.
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the response of the terrestrial bow shock and magnetopause of the long term decline in Solar polar fields
arXiv: Space Physics, 2017Co-Authors: Madhusudan Ingale, P Janardhan, K Fujiki, Susanta Kumar Bisoi, Diptiranjan RoutAbstract:The location of the terrestrial magnetopause (MP) and it's subSolar stand-off distance depends not only on the Solar wind dynamic pressure and the interplanetary magnetic field (IMF), both of which play a crucial role in determining it's shape, but also on the nature of the processes involved in the interaction between the Solar wind and the magnetosphere. The stand-off distance of the earth's MP and bow shock (BS) also define the extent of terrestrial magnetic fields into near-earth space on the sunward side and have important consequences for space weather. However, asymmetries due to the direction of the IMF are hard to account for, making it nearly impossible to favour any specific model over the other in estimating the extent of the MP or BS. Thus, both numerical and empirical models have been used and compared to estimate the BS and MP stand-off distances as well as the MP shape, in the period Jan. 1975-Dec. 2016, covering Solar Cycles 21-24. The computed MP and BS stand-off distances have been found to be increasing steadily over the past two decades, since ~1995, spanning Solar Cycles 23 and 24. The increasing trend is consistent with earlier reported studies of a long term and steady decline in Solar polar magnetic fields and Solar wind micro-turbulence levels. The present study, thus, highlights the response of the terrestrial magnetosphere to the long term global changes in both Solar and Solar wind activity, through a detailed study of the extent and shape of the terrestrial MP and BS over the past four Solar Cycles, a period spanning the last four decades.
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the prelude to the deep minimum between Solar Cycles 23 and 24 interplanetary scintillation signatures in the inner heliosphere
Geophysical Research Letters, 2011Co-Authors: P Janardhan, Susanta Kumar Bisoi, S Ananthakrishnan, M Tokumaru, K FujikiAbstract:Abstract Extensive interplanetary scintillation (IPS) observations at 327 MHz obtained between 1983 and2009 clearly show a steady and significant drop in the turbule nce levels in the entire inner heliospherestarting from around ∼1995. We believe that this large-scale IPS signature, in theinner heliosphere,coupledwith thefact thatSolarpolarfields have alsobeen de cliningsince∼1995, providea consistentresult showing that the buildup to the deepest minimum in 100 years actually began more than adecade earlier. Introduction The sunspot minimum at the end of Cycle 23, has been one of the deepest we have experienced inthe past 100 years with the first spots of the new cycle 24 appea ring only in March 2010 instead ofDecember 2008 as was expected. Also, the number of spotless days experienced in 2008 and 2009was over 70%. Apart from this, Cycle 23 has shown a slower than average field reversal, a slowerrise to maximum than other odd numbered Cycles, and a second maximum during the declining phasethat is unusual for odd-numbered Cycles. Though these deviations from “normal” behaviour couldbe significant in understanding the evolution of magnetic fie lds on the Sun, they do not yield anydirect insights into the onset of the deep minimum experienced at the end of cycle 23. This is becausepredictions of the strength of Solar Cycles and the nature of their minima are strongly dictated by boththe strength of the ongoing cycle [Dikpati et al. (2006); Choudhuri et al. (2007)] and changes in theflow rates of the meridional circulation [ Nandy et al. (2011)].1
Hiroko Miyahara - One of the best experts on this subject based on the ideXlab platform.
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Gradual onset of the Maunder Minimum revealed by high-precision carbon-14 analyses
Scientific Reports, 2021Co-Authors: Hiroko Miyahara, Fuyuki Tokanai, Toru Moriya, Mirei Takeyama, Hirohisa Sakurai, Kazuho Horiuchi, Hideyuki HottaAbstract:The Sun exhibits centennial-scale activity variations and sometimes encounters grand Solar minimum when Solar activity becomes extremely weak and sunspots disappear for several decades. Such an extreme weakening of Solar activity could cause severe climate, causing massive reductions in crop yields in some regions. During the past decade, the Sun’s activity has tended to decline, raising concerns that the Sun might be heading for the next grand minimum. However, we still have an underdeveloped understanding of Solar dynamo mechanisms and hence precise prediction of near-future Solar activity is not attained. Here we show that the 11-year Solar Cycles were significantly lengthened before the onset of the Maunder Minimum (1645–1715 CE) based on unprecedentedly high-precision data of carbon-14 content in tree rings. It implies that flow speed in the convection zone is an essential parameter to determine long-term Solar activity variations. We find that a 16 year-long cycle had occurred three Solar Cycles before the onset of prolonged sunspot disappearance, suggesting a longer-than-expected preparatory period for the grand minimum. As the Sun has shown a tendency of cycle lengthening since Solar Cycle 23 (1996–2008 CE), the behavior of Solar Cycle 25 can be critically important to the later Solar activity.
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influence of the schwabe hale Solar Cycles on climate change during the maunder minimum
Proceedings of the International Astronomical Union, 2009Co-Authors: Hiroko Miyahara, Yusuke Yokoyama, Yasuhiko T. YamaguchiAbstract:We have examined the variation of carbon-14 content in annual tree rings, and investigated the transitions of the characteristics of the Schwabe/Hale (11-year/22-year) Solar and cosmic-ray Cycles during the last 1200 years, focusing mainly on the Maunder and Spoerer minima and the early Medieval Maximum Period. It has been revealed that the mean length of the Schwabe/Hale Cycles changes associated with the centennial-scale variation of Solar activity level. The mean length of Schwabe cycle had been ~14 years during the Maunder Minimum, while it was ~9 years during the early Medieval Maximum Period. We have also found that climate proxy record shows cyclic variations similar to stretching/shortening Schwabe/Hale Solar Cycles in time, suggesting that both Schwabe and Hale Solar Cycles are playing important role in climate change. In this paper, we review the nature of Schwabe and Hale Cycles of Solar activity and cosmic-ray flux during the Maunder Minimum and their possible influence on climate change. We suggest that the Hale cycle of cosmic rays are amplified during the grand Solar minima and thus the influence of cosmic rays on climate change is prominently recognizable during such periods.
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possible link between multi decadal climate Cycles and periodic reversals of Solar magnetic field polarity
Earth and Planetary Science Letters, 2008Co-Authors: Hiroko Miyahara, Yusuke Yokoyama, K. MasudaAbstract:Abstract The linkage between multi-decadal climate variability and activity of the sun has been long debated based upon observational evidence from a large number of instrumental and proxy records. It is difficult to evaluate the exact role of each of Solar parameters on climate change since instrumentally measured Solar related parameters such as Total Solar irradiance (TSI), Ultra Violet (UV), Solar wind and Galactic Cosmic Rays (GCRs) fluxes are more or less synchronized and only extend back for several decades. Here we report tree-ring carbon-14 based record of 11-year/22-year Solar Cycles during the Maunder Minimum (17th century) and the early Medieval Maximum Period (9–10th century) to reconstruct the state of the sun and the flux of incoming GCRs. The result strongly indicates that the influence of Solar Cycles on climate is persistent beyond the period after instrumental observations were initiated. We find that the actual lengths of Solar Cycles vary depending on the status of long-term Solar activity, and that periodicity of the surface air temperatures are also changing synchronously. Temperature variations over the 22-year Cycles seem, in general, to be more significant than those associated with the 11-year Cycles and in particular around the grand Solar minima such as the Maunder Minimum (1645–1715 AD). The polarity dependence of cooling events found in this study suggests that the GCRs can not be excluded from the possible drivers of decadal to multi-decadal climate change.
Sasikumar K Raja - One of the best experts on this subject based on the ideXlab platform.
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global Solar magnetic field and interplanetary scintillations during the past four Solar Cycles
Solar Physics, 2019Co-Authors: Madhusudan Ingale, P Janardhan, K Fujiki, Susanta Kumar Bisoi, Sasikumar K Raja, Prasad Subramanian, M MaksimovicAbstract:The extended minimum of Solar Cycle 23, the extremely quiet Solar-wind conditions prevailing and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in Solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in Solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/Solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975 – 2018. Furthermore, we have measured the normalized scintillation index [ $m$ ] using the IPS observations carried out at the Institute of Space–Earth Environment Research (ISEE), Japan during 1983 – 2017. From these observations, we have found that, since the mid-1990s, the magnetic field over different latitudes at $2.5~\mathrm{R}_{\odot}$ and $10~\mathrm{R}_{\odot}$ (extrapolated using the PFSS method) has decreased by ${\approx}\,11.3\,\mbox{--}\,22.2\%$ . In phase with the declining magnetic fields, the quantity $m$ also declined by ${\approx}\, 23.6\%$ . These observations emphasize the inter-relationship among the global magnetic field and various turbulence parameters in the Solar corona and Solar-wind.
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global Solar magnetic field and interplanetary scintillations during the past four Solar Cycles
arXiv: Solar and Stellar Astrophysics, 2019Co-Authors: Madhusudan Ingale, P Janardhan, K Fujiki, Susanta Kumar Bisoi, Sasikumar K Raja, Prasad Subramanian, M MaksimovicAbstract:The extended minimum of Solar Cycle 23, the extremely quiet Solar-wind conditions prevailing, and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in Solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in Solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/Solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic-fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975-2018. Furthermore, we have measured the normalized scintillation index [m] using the IPS observations carried out at the Institute of Space Earth Environment Research (ISEE), Japan during 1983-2017. From these observations, we have found that, since the mid-1990s, the magnetic-field over different latitudes at 2.5 $\rm R_{\odot}$ and 10 $\rm R_{\odot}$(extrapolated using PFSS method) has decreased by $\approx 11.3-22.2 \%$. In phase with the declining magnetic-fields, the quantity m also declined by $\approx 23.6 \%$. These observations emphasize the inter-relationship between the global magnetic-field and various turbulence parameters in the Solar corona and Solar wind.
P Janardhan - One of the best experts on this subject based on the ideXlab platform.
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global Solar magnetic field and interplanetary scintillations during the past four Solar Cycles
Solar Physics, 2019Co-Authors: Madhusudan Ingale, P Janardhan, K Fujiki, Susanta Kumar Bisoi, Sasikumar K Raja, Prasad Subramanian, M MaksimovicAbstract:The extended minimum of Solar Cycle 23, the extremely quiet Solar-wind conditions prevailing and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in Solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in Solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/Solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975 – 2018. Furthermore, we have measured the normalized scintillation index [ $m$ ] using the IPS observations carried out at the Institute of Space–Earth Environment Research (ISEE), Japan during 1983 – 2017. From these observations, we have found that, since the mid-1990s, the magnetic field over different latitudes at $2.5~\mathrm{R}_{\odot}$ and $10~\mathrm{R}_{\odot}$ (extrapolated using the PFSS method) has decreased by ${\approx}\,11.3\,\mbox{--}\,22.2\%$ . In phase with the declining magnetic fields, the quantity $m$ also declined by ${\approx}\, 23.6\%$ . These observations emphasize the inter-relationship among the global magnetic field and various turbulence parameters in the Solar corona and Solar-wind.
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global Solar magnetic field and interplanetary scintillations during the past four Solar Cycles
arXiv: Solar and Stellar Astrophysics, 2019Co-Authors: Madhusudan Ingale, P Janardhan, K Fujiki, Susanta Kumar Bisoi, Sasikumar K Raja, Prasad Subramanian, M MaksimovicAbstract:The extended minimum of Solar Cycle 23, the extremely quiet Solar-wind conditions prevailing, and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in Solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in Solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/Solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic-fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975-2018. Furthermore, we have measured the normalized scintillation index [m] using the IPS observations carried out at the Institute of Space Earth Environment Research (ISEE), Japan during 1983-2017. From these observations, we have found that, since the mid-1990s, the magnetic-field over different latitudes at 2.5 $\rm R_{\odot}$ and 10 $\rm R_{\odot}$(extrapolated using PFSS method) has decreased by $\approx 11.3-22.2 \%$. In phase with the declining magnetic-fields, the quantity m also declined by $\approx 23.6 \%$. These observations emphasize the inter-relationship between the global magnetic-field and various turbulence parameters in the Solar corona and Solar wind.
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the response of the terrestrial bow shock and magnetopause of the long term decline in Solar polar fields
arXiv: Space Physics, 2017Co-Authors: Madhusudan Ingale, P Janardhan, K Fujiki, Susanta Kumar Bisoi, Diptiranjan RoutAbstract:The location of the terrestrial magnetopause (MP) and it's subSolar stand-off distance depends not only on the Solar wind dynamic pressure and the interplanetary magnetic field (IMF), both of which play a crucial role in determining it's shape, but also on the nature of the processes involved in the interaction between the Solar wind and the magnetosphere. The stand-off distance of the earth's MP and bow shock (BS) also define the extent of terrestrial magnetic fields into near-earth space on the sunward side and have important consequences for space weather. However, asymmetries due to the direction of the IMF are hard to account for, making it nearly impossible to favour any specific model over the other in estimating the extent of the MP or BS. Thus, both numerical and empirical models have been used and compared to estimate the BS and MP stand-off distances as well as the MP shape, in the period Jan. 1975-Dec. 2016, covering Solar Cycles 21-24. The computed MP and BS stand-off distances have been found to be increasing steadily over the past two decades, since ~1995, spanning Solar Cycles 23 and 24. The increasing trend is consistent with earlier reported studies of a long term and steady decline in Solar polar magnetic fields and Solar wind micro-turbulence levels. The present study, thus, highlights the response of the terrestrial magnetosphere to the long term global changes in both Solar and Solar wind activity, through a detailed study of the extent and shape of the terrestrial MP and BS over the past four Solar Cycles, a period spanning the last four decades.
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the prelude to the deep minimum between Solar Cycles 23 and 24 interplanetary scintillation signatures in the inner heliosphere
Geophysical Research Letters, 2011Co-Authors: P Janardhan, Susanta Kumar Bisoi, S Ananthakrishnan, M Tokumaru, K FujikiAbstract:Abstract Extensive interplanetary scintillation (IPS) observations at 327 MHz obtained between 1983 and2009 clearly show a steady and significant drop in the turbule nce levels in the entire inner heliospherestarting from around ∼1995. We believe that this large-scale IPS signature, in theinner heliosphere,coupledwith thefact thatSolarpolarfields have alsobeen de cliningsince∼1995, providea consistentresult showing that the buildup to the deepest minimum in 100 years actually began more than adecade earlier. Introduction The sunspot minimum at the end of Cycle 23, has been one of the deepest we have experienced inthe past 100 years with the first spots of the new cycle 24 appea ring only in March 2010 instead ofDecember 2008 as was expected. Also, the number of spotless days experienced in 2008 and 2009was over 70%. Apart from this, Cycle 23 has shown a slower than average field reversal, a slowerrise to maximum than other odd numbered Cycles, and a second maximum during the declining phasethat is unusual for odd-numbered Cycles. Though these deviations from “normal” behaviour couldbe significant in understanding the evolution of magnetic fie lds on the Sun, they do not yield anydirect insights into the onset of the deep minimum experienced at the end of cycle 23. This is becausepredictions of the strength of Solar Cycles and the nature of their minima are strongly dictated by boththe strength of the ongoing cycle [Dikpati et al. (2006); Choudhuri et al. (2007)] and changes in theflow rates of the meridional circulation [ Nandy et al. (2011)].1