The correlation between solar and geomagnetic activity – Part 1: Two-term decomposition of geomagnetic activity

Du, Zhanle

doi:10.5194/angeo-29-1331-2011

Cited by 18 publications

(24 citation statements)

References 41 publications

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“…This is consistent with the idea of the more decays for even-numbered cycles than for odd-numbered cycles (Du, 2011a). Therefore, an odd-numbered cycle tends to have a stronger correlation of aa with R z and a shorter lag time of aa to R z than the previous even-numbered cycle (Du, 2011b).…”

Section: Correlations For Even-and Odd-numbered Cyclessupporting

confidence: 88%

The correlation between solar and geomagnetic activity – Part 3: An integral response model

2011

Ann. Geophys.

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Abstract. An integral response model is proposed to describe the relationship between geomagnetic activity (aa index) and solar activity (represented by sunspot number R z ): The aa at a given time t is the integral of R z at past times (t ≤ t) multiplied by an exponential decay factor of the time differences (e −(t−t )/τ ), where τ is the decay time scale (∼ 40 months). The correlation coefficient of aa with the reconstructed series based on this model (r f = 0.85) is much higher than that of aa with R z (r 0 = 0.61). If this model is applied to each solar cycle, the correlation coefficient will be higher (r f = 0.95). This model can naturally explain some phenomena related to aa and R z , such as (i) the significant increase in the aa index (and its baseline) over the twentieth century; (ii) the longer lag times of aa to R z at solar cycle maxima than at minima; and (iii) the variations in the correlations related to solar and Hale cycles. These results demonstrate that aa depends not only on the present R z but also on past values. The profile of aa can be better predicted from R z by this model than by point-point correspondence.

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Section: Correlations For Even-and Odd-numbered Cyclessupporting

confidence: 88%

The correlation between solar and geomagnetic activity – Part 3: An integral response model

2011

Ann. Geophys.

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“…see Fig. 3 in Du, 2011). Moreover, the prolonged minimum of the geomagnetic activity that took place in 1960s-1970s is also present as a period of relatively small peaks of the HT statistics.…”

Section: New Information Provided By the Homogenized Seriesmentioning

confidence: 87%

“…1 do not coincide with the maxima of sunspot numbers, which occurred around 1980, 1990 and 2000 for cycles 21, 22 and 23, respectively. In fact, the strongest events of the geomagnetic activity take place during the declining phase of the solar activity or close to the minimum (Du, 2011). Besides, Love (2011) showed an increase of the mean level of geomagnetic activity over the past 141 yr.…”

Section: Homogeneity Breaksmentioning

confidence: 92%

Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal

2014

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Abstract. The Coimbra Magnetic Observatory (International Association of Geomagnetism and Aeronomy code COI) inPortugal has a long history of observation of the geomagnetic field, spanning almost 150 yr since the first geomagnetic measurements in 1866. These long instrumental geomagnetic records provide very important information about variability of geomagnetic elements and indices, their trends and cycles, and can be used to improve our knowledge on the sources that drive variations of the geomagnetic field: liquid core dynamics (internal) and solar forcing (external).However, during the long life of the Coimbra Observatory, some inevitable changes in station location, instrument's park and electromagnetic environment have taken place. These changes affected the quality of the data collected at COI causing breaks and jumps in the series of geomagnetic field components and local K index. Clearly, these inhomogeneities, typically shift-like (step-like) or trend-like, have to be corrected or, at least, minimized in order for the data to be used in scientific studies or to be submitted to international databases.In this study, the series of local K index and declination of the geomagnetic field are analysed: the former because it allows direct application of standard homogenization methods and the latter because it is the longest continuous series produced at COI. For the homogenization, visual and statistical tests (e.g. standard normal homogeneity test) have been applied directly to the local geomagnetic K index series (from 1951 to 2012). The homogenization of the monthly averages of declination (from 1867 to 2012) has been done using visual analysis and statistical tests applied to the time series of the first differences of declination values, as an approximation to the first time derivative. This allowed not only estimating the level of inhomogeneity of the studied series but also detecting the highly probable homogeneity break points. These points have been cross-checked with the metadata, and the COI series have been compared with reference series from the nearest geomagnetic stations and, in the case of declination series, from the recent geomagnetic field model COV-OBS to set up the required correction factors. As a result, the homogenized series measured in COI are considered to be essentially free of artificial shifts starting from the second half of the 20th century, and ready to be used by the scientific community.

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“…The 2-cycle periodicity in r nm or L nm reflects the asymmetry of the solar cycle, the so-called G-O rule: an oddnumbered cycle tends to be stronger than the previous evennumbered one (Gnevyshev and Ohl, 1948;Wilson, 1988). The stronger correlations for odd-numbered cycles than for even-numbered cycles reflect the G-O rule and the less decays for odd-numbered cycles than for even-numbered cycles (Du, 2011a). Stamper et al (1999) noted that the solar wind speed peaks strongly in the declining phase of evennumbered cycles and can be identified as the chief cause of the phase shift between the sunspot numbers and the aa index.…”

Section: Discussionmentioning

confidence: 99%

The correlation between solar and geomagnetic activity – Part 2: Long-term trends

2011

Ann. Geophys.

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Abstract. Using lag-correlation function analysis, the correlation coefficient at zero lag (r 0 ), the maximum (r m ) and the corresponding lag time (L m ) between solar (R z ) and geomagnetic (aa) activity for a 528-month (44-year) running time window are shown to vary in a declining, declining and rising secular trend, respectively, before 1958. However, these trends changed since 1958 with a rising secular trend in both r 0 and r m and without a significant trend in L m , probably related to a periodicity longer than 140 years. An odd-numbered solar cycle tends to show a higher correlation and a shorter lag time between R z and aa than the previous even-numbered one, suggesting a 2-cycle periodicity superimposed on secular trends. An even-numbered Hale cycle tends to show a higher correlation and a shorter lag time between R z and aa than the previous odd-numbered one, suggesting a 4-cycle periodicity superimposed on secular trends. The variations in the correlations may be related to the nonlinearity between R z and aa, and the decreasing trend in the correlation (r 0 ) is not exclusively caused by the increasing trend in the lag time of aa to R z . These results represent an observational constraint on solar-dynamo models and can help us gain a better understanding of the long-term evolution of solar activities. In applications, therefore, cautions must be taken when using the correlation for molding the dynamical process of the Sun and for predicting solar activities.

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The correlation between solar and geomagnetic activity – Part 1: Two-term decomposition of geomagnetic activity

Cited by 18 publications

References 41 publications

The correlation between solar and geomagnetic activity – Part 3: An integral response model

The correlation between solar and geomagnetic activity – Part 3: An integral response model

Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal

The correlation between solar and geomagnetic activity – Part 2: Long-term trends

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