The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Q. L. Guo - One of the best experts on this subject based on the ideXlab platform.
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REVISITING THE QUESTION: DOES HIGH-LATITUDE Solar Activity LEAD LOW-LATITUDE Solar Activity IN TIME PHASE?
The Astronomical Journal, 2014Co-Authors: D. F. Kong, Q. L. GuoAbstract:Cross-correlation analysis and wavelet transform methods are used to investigate whether high-latitude Solar Activity leads low-latitude Solar Activity in time phase or not, using the data of the Carte Synoptique Solar filaments archive from 1919 March to 1989 December. From the cross-correlation analysis, high-latitude Solar filaments have a time lead of 12 Carrington Solar rotations with respect to low-latitude ones. Both the cross-wavelet transform and wavelet coherence indicate that high-latitude Solar filaments lead low-latitude ones in time phase. Furthermore, low-latitude Solar Activity is better correlated with high-latitude Solar Activity of the previous cycle than with that of the following cycle, which is statistically significant. Thus, the present study confirms that high-latitude Solar Activity in the polar regions is indeed better correlated with the low-latitude Solar Activity of the following cycle than with that of the previous cycle, namely, leading in time phase.
Jiong Qiu - One of the best experts on this subject based on the ideXlab platform.
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Does High-Latitude Solar Activity Lead Low-Latitude Solar Activity in Time Phase?
The Astrophysical Journal, 2006Co-Authors: Peng-xin Gao, Jiong QiuAbstract:Using data from the Carte Synoptique Solar filaments archive, we investigate whether there is a time lag between high-latitude Solar Activity and low-latitude Solar Activity. The cross-correlation analysis of the number of high-latitude filaments per Carrington rotation (NHF) and that of low-latitude filaments per Carrington rotation (NLF) shows, although inconclusively, that NLF possibly lags behind NHF. The periodic characteristics of both NHF and NLF clearly indicate that the Activity of high-latitude filaments is evidently leading the Activity of low-latitude filaments. Thus, the present study suggests that high-latitude Solar Activity leads low-latitude Solar Activity in time phase.
D. F. Kong - One of the best experts on this subject based on the ideXlab platform.
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REVISITING THE QUESTION: DOES HIGH-LATITUDE Solar Activity LEAD LOW-LATITUDE Solar Activity IN TIME PHASE?
The Astronomical Journal, 2014Co-Authors: D. F. Kong, Q. L. GuoAbstract:Cross-correlation analysis and wavelet transform methods are used to investigate whether high-latitude Solar Activity leads low-latitude Solar Activity in time phase or not, using the data of the Carte Synoptique Solar filaments archive from 1919 March to 1989 December. From the cross-correlation analysis, high-latitude Solar filaments have a time lead of 12 Carrington Solar rotations with respect to low-latitude ones. Both the cross-wavelet transform and wavelet coherence indicate that high-latitude Solar filaments lead low-latitude ones in time phase. Furthermore, low-latitude Solar Activity is better correlated with high-latitude Solar Activity of the previous cycle than with that of the following cycle, which is statistically significant. Thus, the present study confirms that high-latitude Solar Activity in the polar regions is indeed better correlated with the low-latitude Solar Activity of the following cycle than with that of the previous cycle, namely, leading in time phase.
Peng-xin Gao - One of the best experts on this subject based on the ideXlab platform.
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Does High-Latitude Solar Activity Lead Low-Latitude Solar Activity in Time Phase?
The Astrophysical Journal, 2006Co-Authors: Peng-xin Gao, Jiong QiuAbstract:Using data from the Carte Synoptique Solar filaments archive, we investigate whether there is a time lag between high-latitude Solar Activity and low-latitude Solar Activity. The cross-correlation analysis of the number of high-latitude filaments per Carrington rotation (NHF) and that of low-latitude filaments per Carrington rotation (NLF) shows, although inconclusively, that NLF possibly lags behind NHF. The periodic characteristics of both NHF and NLF clearly indicate that the Activity of high-latitude filaments is evidently leading the Activity of low-latitude filaments. Thus, the present study suggests that high-latitude Solar Activity leads low-latitude Solar Activity in time phase.
Ilya Usoskin - One of the best experts on this subject based on the ideXlab platform.
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Evidence for distinct modes of Solar Activity
Astronomy & Astrophysics, 2014Co-Authors: Ilya Usoskin, Gauthier Hulot, Yves Gallet, Raphael Roth, Alexis Licht, Fortunat Joos, Gennady A. Kovaltsov, Erwan Thébault, A. KhokhlovAbstract:Aims. The Sun shows strong variability in its magnetic Activity, from Grand minima to Grand maxima, but the nature of the variability is not fully understood, mostly because of the insufficient length of the directly observed Solar Activity records and of uncertainties related to long-term reconstructions. Here we present a new adjustment-free reconstruction of Solar Activity over three millennia and study its different modes. Methods. We present a new adjustment-free, physical reconstruction of Solar Activity over the past three millennia, using the latest verified carbon cycle, 14 C production, and archeomagnetic field models. This great improvement allowed us to study different modes of Solar Activity at an unprecedented level of details. Results. The distribution of Solar Activity is clearly bi-modal, implying the existence of distinct modes of Activity. The main regular Activity mode corresponds to moderate Activity that varies in a relatively narrow band between sunspot numbers 20 and 67. The existence of a separate Grand minimum mode with reduced Solar Activity, which cannot be explained by random fluctuations of the regular mode, is confirmed at a high confidence level. The possible existence of a separate Grand maximum mode is also suggested, but the statistics is too low to reach a confident conclusion. Conclusions. The Sun is shown to operate in distinct modes – a main general mode, a Grand minimum mode corresponding to an inactive Sun, and a possible Grand maximum mode corresponding to an unusually active Sun. These results provide important constraints for both dynamo models of Sun-like stars and investigations of possible Solar influence on Earth’s climate.
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LONG-TERM Solar Activity: DIRECT AND INDIRECT STUDY
Solar Physics, 2004Co-Authors: Ilya Usoskin, G. A. KovaltsovAbstract:The series of directly observed sunspot numbers is nearly 400 years long. We stress that the recently compiled group sunspot number series is an upgrade of the old Wolf series and should always be used before 1850. The behavior of Solar Activity on longer time scales can be studied only using indirect proxies. Such proxies as aurorae occurrence or naked-eye sunspot observations are qualitative indicators of Solar Activity but can be hardly quantitatively interpreted. Cosmogenic isotope records provide a basis for quantitative estimate of the past Solar Activity. Here we overview the main methods of the long-term Solar Activity reconstruction on the centennial to multimillennia time scale. We discuss that regression-based reconstructions of Solar Activity lead to very uncertain results, while recently developed physics-based models raise Solar Activity reconstruction to a new level and allow studying its behavior on a multimillennia time scale. In particular, the reconstructions show that the recent episode of high Solar Activity is quite unusual in the multimillennia time scale.
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ON THE CLAIMED 5.5-YEAR PERIODICITY IN Solar Activity
Solar Physics, 1997Co-Authors: Kalevi Mursula, Ilya Usoskin, Bertalan ZiegerAbstract:Recently, Djurovic and Pâquet (1996) claimed to have found an oscillation with a period of about 5.5 years in several Solar and Solar-terrestrial parameters, in particular in Solar Activity as indicated by sunspot numbers. Since the temporal evolution of the Solar Activity and Solar-terrestrial environment is of great interest in many fields, we have examined their claim in detail. We show here that their conclusion is based on an artefact due a questionable method applied, and due to the asymmetric form of the Solar cycle. Accordingly, there is no reasonable evidence for the existence of a fundamental 5.5-year periodicity in Solar Activity.
