scholarly journals Secular trends in storm-level geomagnetic activity

2011 ◽  
Vol 29 (2) ◽  
pp. 251-262 ◽  
Author(s):  
J. J. Love
Keyword(s):  
Geomagnetic Activity ◽  
Linear Trend ◽  
Statistical Significance ◽  
Activity Levels ◽  
Future Trends ◽  
Solar Cycles ◽  
Monotonic Trend ◽  
Secular Evolution ◽  
The Past ◽  
K Index

Abstract. Analysis is made of K-index data from groups of ground-based geomagnetic observatories in Germany, Britain, and Australia, 1868.0–2009.0, solar cycles 11–23. Methods include nonparametric measures of trends and statistical significance used by the hydrological and climatological research communities. Among the three observatory groups, German K data systematically record the highest disturbance levels, followed by the British and, then, the Australian data. Signals consistently seen in K data from all three observatory groups can be reasonably interpreted as physically meaninginful: (1) geomagnetic activity has generally increased over the past 141 years. However, the detailed secular evolution of geomagnetic activity is not well characterized by either a linear trend nor, even, a monotonic trend. Therefore, simple, phenomenological extrapolations of past trends in solar and geomagnetic activity levels are unlikely to be useful for making quantitative predictions of future trends lasting longer than a solar cycle or so. (2) The well-known tendency for magnetic storms to occur during the declining phase of a sunspot-solar cycles is clearly seen for cycles 14–23; it is not, however, clearly seen for cycles 11–13. Therefore, in addition to an increase in geomagnetic activity, the nature of solar-terrestrial interaction has also apparently changed over the past 141 years.

scholarly journals Long-term biases in geomagnetic <i>K</i> and <i>aa</i> indices

2011 ◽  
Vol 29 (8) ◽  
pp. 1365-1375 ◽  
Author(s):  
J. J. Love
Keyword(s):  
Geomagnetic Activity ◽  
Estimation Methods ◽  
Activity Levels ◽  
Solar Cycles ◽  
K Value ◽  
K Index ◽  
Medium Level ◽  
Value Estimation ◽  
Aa Index

Abstract. Analysis is made of the geomagnetic-activity aa index and its source K-index data from groups of ground-based observatories in Britain, and Australia, 1868.0–2009.0, solar cycles 11–23. The K data show persistent biases, especially for high (low) K-activity levels at British (Australian) observatories. From examination of multiple subsets of the K data we infer that the biases are not predominantly the result of changes in observatory location, localized induced magnetotelluric currents, changes in magnetometer technology, or the modernization of K-value estimation methods. Instead, the biases appear to be artifacts of the latitude-dependent scaling used to assign K values to particular local levels of geomagnetic activity. The biases are not effectively removed by weighting factors used to estimate aa. We show that long-term averages of the aa index, such as annual averages, are dominated by medium-level geomagnetic activity levels having K values of 3 and 4.

Long-term variations in the geomagnetic activity level Part II: Ascending phases of sunspot cycles

1994 ◽  
Vol 12 (10/11) ◽  
pp. 1065-1070 ◽  
Author(s):  
V. Mussino ◽  
O. Borello Filisetti ◽  
M. Storini ◽  
H. Nevanlinna
Keyword(s):  
Correlation Coefficient ◽  
Geomagnetic Activity ◽  
Activity Level ◽  
Activity Levels ◽  
Data Set ◽  
The Past ◽  
Long Term Trends ◽  
A Minor ◽  
Long Term Variations

Abstract. Monthly averages of the Helsinki Ak-values have been reduced to the equivalent aa-indices to extend the aa-data set back to 1844. A periodicity of about five cycles was found for the correlation coefficient (r) between geomagnetic indices and sunspot numbers for the ascending phases of sunspot cycles 9 to 22, confirming previous findings based on a minor number of sunspot cycles. The result is useful to researchers in topics related to solar-terrestrial physics, particularly for the interpretation of long-term trends in geomagnetic activity during the past, and to forecast geomagnetic activity levels in the future.

scholarly journals Spectrum analysis of short-period <i>K</i> index behaviour at high and mid-latitudes

2015 ◽  
Vol 33 (1) ◽  
pp. 31-37 ◽  
Author(s):  
P. B. Kotzé
Keyword(s):  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Confidence Level ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Coronal Holes ◽  
Activity Levels ◽  
Maximum Phase ◽  
K Index ◽  
Recurrent Activity

Abstract. Geomagnetic activity levels during the declining phase and solar minimum period of the solar cycle are considerably different from those during the solar maximum phase. Previous studies revealed variations in the pattern of recurrent activity from cycle to cycle as well as variations in the average geomagnetic activity levels during a solar cycle. During the declining phase of a solar cycle (and solar minimum), the solar and interplanetary causes of geomagnetic activity are substantially different from those during the solar maximum phase. Co-rotating fast solar wind streams originating from large polar coronal holes, extending towards the Sun's equator, interact with the Earth's magnetosphere, resulting in recurrent geomagnetic activity particularly during solar cycle minimum periods. This is a well-known phenomenon with respect to 27.0- and 13.5-day recurrence geomagnetic activity, and it is well-known to be related to sectorial (non-axial) poloidal magnetic field structure in the Sun. Published results of the recent solar-cycle-23 minimum showed that the presence of 9.0- and 6.7-day recurrent geomagnetic activities can be attributed to the sectorial spherical harmonic structure present in the solar magnetic field. In this study we performed a wavelet and Lomb–Scargle analysis of the geomagnetic activity K index at Lerwick (LER), Hermanus (HER) and Canberra (CNB) for the period between 1960 and 2010, overlapping with solar cycles 20 to 23. Daily mean K indices are used to identify how several harmonics of the 27.0-day recurrent period change during each solar cycle when comparing high and mid-latitude geomagnetic activity, applying a 95% confidence level. In particular the behaviour of the second (13.5-day), third (9.0-day) and fourth (6.7-day) harmonics are investigated by doing a wavelet analysis of each individual year's K indices at each location. Results obtained show that particularly during solar minima the 27.0-day period is no longer detectable above the 95% confidence level, and that geomagnetic activity is in fact dominated by higher harmonics like 13.5-, 9.0- and 6.7-day periods. These findings in fact are in line with previous investigations and confirm the results obtained by researchers using other geomagnetic activity indices like \\textit{aa} and C9. The wavelet-spectrum analysis also reveals that during the downward phase of cycle 23 and the very long minimum of 23–24 between 2002 and 2008, the 27.0-day activity period drops below the 95% confidence level. This is confirmed by Lomb–Scargle analyses of every year's K index activity. Results obtained in this study support evidence by other investigations that this can be attributed to the lack of coronal-mass ejection (CME)-dominated solar activity during solar minima, periods characterized by strong solar dipolar magnetic fields, less sunspot numbers than at solar maxima, and multiple prominent co-rotating solar wind streams present. This analysis further confirms previous studies by other authors that the pattern of recurrent activity is dictated by the configuration of coronal holes which give rise to related high-speed streams during a solar cycle by analysing K indices at both high- and mid-latitude magnetic observatories.

ASSESSMENT OF STATISTICAL SIGNIFICANCE OF HISTORIC DANUBE FLOODS

2020 ◽  
Author(s):  
Stevan Prohaska ◽  
◽  
Aleksandra Ilić ◽  
Pavla Pekarova ◽  
◽  
...  
Keyword(s):  
Middle Ages ◽  
Linear Trend ◽  
Statistical Significance ◽  
Danube River ◽  
Exceedance Probability ◽  
Simultaneous Occurrence ◽  
Flood Wave ◽  
Probability Of Occurrence ◽  
Comprehensive Method ◽  
Flood Hydrograph

Data on historic floods along the Danube River exist since the year 1012. In the Middle Ages, floods were estimated based on historical documents, including original handwritten notes, newspaper articles, chronicles, formal letters, books, maps and photographs. From 1500 until the beginning of organized water regime observations, floods were hydraulically reconstructed based on water marks on old buildings in cities along the Danube (Passau, Melk, Emmersdorf an der Donau, Spilz, Schonbuhen and Bratislava). The paper presents a procedure for assessing the statistical significance of registered historic floods using a comprehensive method for defining theoretical flood hydrographs at hydrological stations. The approach is based on correlation analysis of two basic flood hydrograph parameters – maximum hydrograph ordinate (peak) and flood wave volume. The PROIL model is used to define the probability of simultaneous occurrence of these parameters. It defines the exceedance probability of two random variables, in the specific case two hydrograph parameters of the form: P{Qmax more equal to qmax,p)∩(Wmax more equal to wmax,p)} = P (1) where: Qmax – maximum hydrograph ordinate (peak); qmax,p – maximum discharge of the probability of occurrence p; Wmax – maximum hydrograph volume; wmax,p – maximum flood wave volume of the probability of occurrence p; P – exceedance probability. Spatial positions of the lines of exceedance of two flood hydrograph parameters and the empirical points of the corresponding parameters of the considered historic flood in the correlation field Qmax - Wmax, allow direct assessment of the exceedance probability of a historic flood, or its statistical significance. The proposed procedure was applied in practice to assess the statistical significance of the biggest floods registered along the Danube in the sector from its mouth to the Djerdap 1 Dam. The linear trend in the time-series of maximum annual flows at a representative hydrological station and the frequency of historic floods in the considered sector of the Danube are discussed at the end of the paper.

ANALYSIS OF THE STRUCTURE AND PREDICTION OF HIV INFECTION INCIDENCE IN THE VORONEZH REGION

2020 ◽  
pp. 147-152
Author(s):  
Евгений Николаевич Коровин ◽  
Юлия Викторовна Сиромашенко ◽  
Владимир Николаевич Коровин
Keyword(s):  
Hiv Infection ◽  
Graphical Representation ◽  
Linear Trend ◽  
Risk Groups ◽  
Extrapolation Methods ◽  
The Past ◽  
Voronezh Region ◽  
The Future ◽  
Dynamic Series ◽  
Exponential Smoothing Method

В статье приведены анализ и прогнозирование основных статистических показателей, характеризующих развитие эпидемической ситуации по вирусу иммунодефицита человека (ВИЧ) в Воронежской области, а именно распределение по путям инфицирования. В качестве данных для прогнозирования были использованы показатели заболеваемости прошлых лет. Применяемый метод прогнозирования основан на методах экстраполяции. Все методы экстраполяции объединяет то, что они проецируют на будущее ход событий, сложившийся в прошлом. При этом не устанавливаются никакие причинные связи - принимается, что действующие в прошлом силы без существенных изменений будут действовать и в будущем. При формировании прогнозов с помощью экстраполяции исходят из статистически складывающихся тенденций изменения тех или иных количественных характеристик объекта за определённый период. Прогнозирование заболеваемости ВИЧ осуществляется с помощью метода экспоненциального сглаживания с использованием линейного тренда и выбором оптимальных параметров сглаживания. Трендом называют аналитическое или графическое представление изменения переменной во времени, полученное в результате выделения регулярной (систематической) составляющей динамического ряда. Основной целью анализа и прогнозирования является выявление основных тенденций по распространению ВИЧ-инфекции, определение основных путей инфицирование, а также выделение ключевых групп риска среди населения Воронежской области The article analyzes and predicts the main statistical indicators that characterize the development of the epidemic situation of human immunodeficiency virus (HIV) in the Voronezh region, namely, the distribution by infection pathways. Previous years ' morbidity rates were used as data for forecasting. The applied forecasting method is based on extrapolation methods. What all extrapolation methods have in common is that they project the course of events in the past into the future. At the same time, no causal relationships are established - it is assumed that the forces operating in the past will continue to operate in the future without significant changes. When forming forecasts using extrapolation, they are based on statistically developing trends in changes in certain quantitative characteristics of an object over a certain period. Predicting the incidence of HIV is carried out using the exponential smoothing method using a linear trend and choosing the optimal smoothing parameters. A trend is an analytical or graphical representation of changes in a variable over time, resulting from the allocation of a regular (systematic) component of a dynamic series. The main goal of the analysis and forecasting is to identify the main trends in the spread of HIV infection, identify the main routes of infection, and identify key risk groups among the population of the Voronezh region

scholarly journals Mandatory annuitization and money's worth: evidence from Singapore

2021 ◽  
pp. 1-20
Author(s):  
Joelle H. Fong ◽  
Jackie Li
Keyword(s):  
Expected Value ◽  
Longevity Risk ◽  
Future Trends ◽  
The Past ◽  
The Future ◽  
Population Mortality ◽  
Mortality Improvement ◽  
Life Annuities ◽  
Compulsory Purchase ◽  
The Impact

Abstract This paper examines the impact of uncertainties in the future trends of mortality on annuity values in Singapore's compulsory purchase market. We document persistent population mortality improvement trends over the past few decades, which underscores the importance of longevity risk in this market. Using the money's worth framework, we find that the life annuities delivered expected payouts valued at 1.019–1.185 (0.973–1.170) per dollar of annuity premium for males (females). Even in a low mortality improvement scenario, the annuities provide an expected value exceeding 0.950. This suggests that participants in the national annuity pool have access to attractively priced annuities, regardless of sex, product, and premium invested.

scholarly journals Looking for a proxy of the ionospheric turbulence with Swarm data

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Paola De Michelis ◽  
Giuseppe Consolini ◽  
Alessio Pignalberi ◽  
Roberta Tozzi ◽  
Igino Coco ◽  
...  
Keyword(s):  
Electron Density ◽  
Geomagnetic Activity ◽  
Density Fluctuations ◽  
Rate Of Change ◽  
Topside Ionosphere ◽  
Joint Probability Distribution ◽  
Activity Levels ◽  
Scaling Exponents ◽  
Electron Density Fluctuations ◽  
Scaling Features

AbstractThe present work focuses on the analysis of the scaling features of electron density fluctuations in the mid- and high-latitude topside ionosphere under different conditions of geomagnetic activity. The aim is to understand whether it is possible to identify a proxy that may provide information on the properties of electron density fluctuations and on the possible physical mechanisms at their origin, as for instance, turbulence phenomena. So, we selected about 4 years (April 2014–February 2018) of 1 Hz electron density measurements recorded on-board ESA Swarm A satellite. Using the Auroral Electrojet (AE) index, we identified two different geomagnetic conditions: quiet (AE < 50 nT) and active (AE > 300 nT). For both datasets, we evaluated the first- and second-order scaling exponents and an intermittency coefficient associated with the electron density fluctuations. Then, the joint probability distribution between each of these quantities and the rate of change of electron density index was also evaluated. We identified two families of plasma density fluctuations characterized by different mean values of both the scaling exponents and the considered ionospheric index, suggesting that different mechanisms (instabilities/turbulent processes) can be responsible for the observed scaling features. Furthermore, a clear different localization of the two families in the magnetic latitude—magnetic local time plane is found and its dependence on geomagnetic activity levels is analyzed. These results may well have a bearing about the capability of recognizing the turbulent character of irregularities using a typical ionospheric plasma irregularity index as a proxy.

Solar proton events during the past three solar cycles

1989 ◽  
Vol 26 (6) ◽  
pp. 403-415 ◽  
Author(s):  
D. F. Smart ◽  
M. A. Shea
Keyword(s):  
Solar Proton ◽  
Solar Cycles ◽  
The Past ◽  
Solar Proton Events

Solar-type periodicities in the climate variability of Northern Fennoscandia during the last three centuries: Real influence of solar activity or natural instability in the climate system

The Holocene ◽  
2021 ◽  
pp. 095968362110604
Author(s):  
Maxim Ogurtsov ◽  
Samuli Helama ◽  
Risto Jalkanen ◽  
Högne Jungner ◽  
Markus Lindholm ◽  
...  
Keyword(s):  
Solar Activity ◽  
Climate Variability ◽  
Western Siberia ◽  
Climate System ◽  
Solar Cycles ◽  
Activity Data ◽  
The Past ◽  
Proxy Records ◽  
Northern Fennoscandia ◽  
Solar Type

Fifteen proxy records of summer temperature in Fennoscandia, Northern Europe and in Yamal and Taymir Peninsulas (Western Siberia) were analyzed for the AD 1700–2000 period. Century-long (70–100 year) and quasi bi-decadal periodicities were found from proxy records representing different parts of Fennoscandia. Decadal variation was revealed in a smaller number of records. Statistically significant correlations were revealed between the timescale-dependent components of temperature variability and solar cycles of Schwabe (~11 year), Hale (~22 year), and Gleissberg (сentury-long) as recorded in solar activity data. Combining the results from our correlation analysis with the evidence of solar-climatic linkages over the Northern Fennoscandia obtained over the past 20 years suggest that there are two possible explanations for the obtained solar-proxy relations: (a) the Sun’s activity actually influences the climate variability in Northern Fennoscandia and in some regions of the Northern Hemisphere albeit the mechanism of such solar-climatic linkages are yet to be detailed; (b) the revealed solar-type periodicities result from natural instability of climate system and, in such a case, the correlations may appear purely by chance. Multiple lines of evidence support the first assumption but we note that the second one cannot be yet rejected. Guidelines for further research to elucidate this question are proposed including the Fisher’s combined probability test in the presence of solar signal in multiple proxy records.

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