scholarly journals Longitudinal (UT) effect in the onset of auroral disturbances over two solar cycles as deduced from the AE-index

1998 ◽  
Vol 16 (12) ◽  
pp. 1573-1579 ◽  
Author(s):  
L. A. Hajkowicz
Keyword(s):  
Time Interval ◽  
Solar Cycles ◽  
Field Orientation ◽  
Auroral Activity ◽  
Ae Index ◽  
Auroral Substorm ◽  
Northern Winter ◽  
Diurnal Effect ◽  
Auroral Phenomena ◽  
Substorm Onsets

Abstract. Statistical study on the universal time variations in the mean hourly auroral electrojet index (AE-index) has been undertaken for a 21 y period over two solar cycles (1957–1968 and 1978–1986). The analysis, applied to isolated auroral substorm onsets (inferred from rapid variations in the AE-index) and to the bulk of the AE data, indicates that the maximum in auroral activity is largely confined to 09–18 UT, with a distinct minimum at 03–06 UT. The diurnal effect was clearly present throughout all seasons in the first cycle but was mainly limited to northern winter in the second cycle. Severe storms (AE > 1000 nT) tended to occur between 9–18 UT irrespective of the seasons whereas all larger magnetic disturbances (AE > 500 nT) tended to occur in this time interval mostly in winter. On the whole the diurnal trend was strong in winter, intermediate at equinox and weak in summer. The implication of this study is that Eastern Siberia, Japan and Australia are mostly at night, during the period of maximum auroral activity whereas Europe and Eastern America are then mostly at daytime. The minimum of auroral activity coincides with near-midnight conditions in Eastern America. It appears that the diurnal UT distribution in the AE-index reflects a diurnal change between interplanetary magnetic field orientation and the Earth's magnetic dipole inclination.Key words. Ionosphere (auroral ionosphere) · Magnetospheric physics (auroral phenomena; storms and substorms).

The Auroral Substorm

1996 ◽  
Author(s):  
Charles F. Kennel
Keyword(s):  
Electric Fields ◽  
Large Scale ◽  
Time Development ◽  
Local Times ◽  
Space Resolution ◽  
Auroral Activity ◽  
Auroral Substorm ◽  
The Many ◽  
The One ◽  
Cosmic Noise

Around the time the steady convection model was being developed, Akasofu (1964) was arranging ground-based magnetometer and all-sky camera observations of the complex time dependence of nightside auroral activity into the central phenomenological conception of tune-dependent magnetospheric physics—the auroral substorm. In this chapter, we assemble a description of a substorm from modern observations. We will see that observations of electric fields, auroral X rays, cosmic noise absorption, ionospheric density, and geomagnetic micropulsations have also been successfully ordered by the substorm paradigm. At the same time, it will become clear that each individual substorm has its own irreducible individuality, and that our summary description is really a list of effects that anyone thinking about substorms ought to consider. No real substorm will look exactly like the one described here. Spacecraft observations of auroral light, precipitation, currents, and fields from polar orbit have held out high promise for unified understanding of the development of the auroral substorm around the entire oval. Without truly global auroral observations, it would be difficult to establish decisive contact with observations of large-scale convection and the associated changes in magnetospheric configuration. Despite the high promise and the many other successes of spacecraft observations of the aurora, synthetic understanding of the time development of the auroral substorm at all local times, dayside and nightside, evening and dawn, has been slow in emerging, perhaps because a stringent combination of field of view, sensitivity, space and time resolution, and multispectral capability is required. One needs images of the whole oval with sufficient space resolution to identify important arc structures (50-100 km or better) in a temporal sequence that can articulate the evolution of activity on better than the 10-minute time scale on which polar cap convection develops. Only recently has it been possible to observe auroral activity at all local tunes around the auroral oval simultaneously and follow its time development from the beginning of the growth phase until well into the expansion phase. This amplification of the original paradigm is the subject of Sections 12.2 and 12.3.

scholarly journals A new southern high-latitude index

1998 ◽  
Vol 16 (12) ◽  
pp. 1589-1598 ◽  
Author(s):  
P. Ballatore ◽  
C. G. Maclennan ◽  
M. J. Engebretson ◽  
M. Candidi ◽  
J. Bitterly ◽  
...  
Keyword(s):  
High Latitude ◽  
Activity Level ◽  
Polar Cap ◽  
Geomagnetic Index ◽  
Level Indicator ◽  
Ae Index ◽  
Average Activity ◽  
Using Data ◽  
Auroral Phenomena ◽  
Southern High Latitude

Abstract. We have developed and examined a new regional geomagnetic index AES-80, defined similarly to the classical auroral electrojet AE index, using data from five Antarctic stations located at corrected geomagnetic latitudes about 80 °S. Because only sparse ground-based information can be derived from auroral latitudes in the Southern Hemisphere, and because no index comparable to AE can be constructed from locations in the south, the possibility of using AES-80 as a measure of high latitudes and polar cap activity is investigated. As a global average activity level indicator, it is found that in general AES-80 gives results rather similar to the classical AE index. However AES-80 provides a more robust measure of the occurrence of high-latitude geomagnetic activity.Key words. Magnetospheric physics (auroral phenomena; polar cap phenomena).

scholarly journals Dayside auroral activity as a possible precursor of substorm onsets: A survey using Polar ultraviolet imagery

1997 ◽  
Vol 102 (A9) ◽  
pp. 19835-19843 ◽  
Author(s):  
K. Liou ◽  
P. T. Newell ◽  
C.-I. Meng ◽  
A. T. Y. Lui ◽  
M. Brittnacher ◽  
...  
Keyword(s):  
Auroral Activity ◽  
Substorm Onsets

scholarly journals Electron cross talk and asymmetric electron distributions near the Earth's bowshock

2012 ◽  
Vol 30 (3) ◽  
pp. 503-513 ◽  
Author(s):  
J. J. Mitchell ◽  
S. J. Schwartz ◽  
U. Auster
Keyword(s):  
Cross Talk ◽  
Plasma Electron ◽  
Distribution Functions ◽  
Local Magnetic Field ◽  
Time Interval ◽  
Ion Heating ◽  
Field Orientation ◽  
Electron Distributions ◽  
Relative Electron ◽  
Non Local

Abstract. Electron distributions in the magnetosheath display a number of far from equilibrium features. It has been suggested that one factor influencing these distributions may be the large distances separating locations at which electrons with different energies and pitch angles must cross the bowshock in order to reach a given point in the magnetosheath. The overall heating requirements at these distant locations depends strongly on the shock geometry. In the absence of collisions or other isotropization processes this suggests that the convolution of electrons arriving from different locations should give rise to asymmetries in the distribution functions. Moreover, such cross-talk could influence the relative electron to ion heating, rendering the shock heating problem intrinsically non-local in contrast to classic shock physics. Here, we study electron distributions measured simultaneously by the Plasma Electron and Current Experiment (PEACE) on board the Cluster spacecraft and the Electrostatic Analyser (ESA) on board THEMIS b during a time interval in which both the Cluster spacecraft and THEMIS b are in the magnetosheath, close to the bowshock, and during which the local magnetic field orientation makes it likely that electron trajectories may connect both spacecraft. We find that the relevant portions of the velocity distributions of such electrons measured by each spacecraft display remarkable similarities. We map trajectories of electrons arriving at each spacecraft back to the locations at which they crossed the bowshock, as a function of pitch angle and energy. We then use the Rankine-Hugoniot relations to estimate the heating of electrons and compare this with temperature asymmetries actually observed. We conclude that the electron distributions and temperatures in the magnetosheath depend heavily on non-local shock properties.

scholarly journals A new reconstruction of the <i>D<sub>st</sub></i> index for 1932-2002

2005 ◽  
Vol 23 (2) ◽  
pp. 475-485 ◽  
Author(s):  
A. Karinen ◽  
K. Mursula
Keyword(s):  
High Speed ◽  
Early Period ◽  
Extended Period ◽  
Recovery Phase ◽  
Time Interval ◽  
Solar Cycles ◽  
Annual Average ◽  
Dst Index ◽  
Using Data ◽  
Original Index

Abstract. We have reconstructed a new, homogeneous geomagnetic Dst index for 1932-2002, thus extending the original Dst index by 25 years, i.e. by more than one full solar magnetic cycle. The extension was done by using data from the original set of four low-latitude stations for 1941-1956, and by using the nearby CTO station as a predecessor of the HER station for 1932-1940. Despite some open questions related to the composition of the original Dst index, the reconstructed index is quite similar to the original one during the overlapping time interval (1957-2002). However, the reconstructed Dst index corrects for some known errors in the original Dst index, such as the erroneously large daily UT variation in 1971. Also, despite the overall agreement, the reconstructed index deviates from the original index even on the level of annual averages for several years. For instance, all annual averages of the reconstructed index are negative, and for 1962-1966 they are systematically lower (more stormy) than those of the original index. Accordingly, we disagree with the uniquely positive annual average of the original index in 1965, which most likely is erroneous. We also find somewhat higher (less stormy) values than in the original Dst index for the three lowest annual averages in 1960, 1989 and 1991, out of which the lowest annual average is found in 1989 rather than in 1991. The annual averages of the geomagnetic Ap index and the reconstructed Dst index correlate very well over this time interval, except in the beginning of the series in 1932-1940 and in the declining phase of solar cycles 18, 20 and 21, where high speed solar wind streams cause enhanced geomagnetic activity. Using the superposed epoch method we also find that, on average, the storms in the early extended period (1932-1956) are less intense but tend to have a longer recovery phase, suggesting that there are more HILDCAA-type medium activity intervals during the early period than more recently. We also study the annually averaged storm structure over the 71-year time interval and find that the most stormy years occur during the declining phase of solar cycles 17 and 21 and around the solar maxima of cycles 19 and 22.

scholarly journals A Topological Model of the Solar Magnetic Field Reversals

1991 ◽  
Vol 130 ◽  
pp. 234-236
Author(s):  
E.E. Benevolenskaya
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
High Frequency ◽  
Low Frequency ◽  
Frequency Component ◽  
High Frequency Component ◽  
Time Interval ◽  
Solar Cycles ◽  
Polarity Reversals ◽  
Odd Cycles

The phenomenon of a three-fold reversal of the solar polar magnetic field in both hemispheres has not been observed during the last 115 years. Such three-fold reversals took place in the southern hemisphere alone in the even cycles Nos 12 (1885.8), 14 (1908.4) and in the northern hemisphere alone in solar cycles Nos 16 (1928.5), 18 (1949.0), 20 (1970.6). The single reversal took place in the odd cycles, the only exception is the solar cycle No 19 (Fig. 1).There are periods of 1.7-2.5 years in the variation of background magnetic fields (Makarov et al., 1985). It determines the quasi-period of the high-frequency component and corresponds to a time interval between the zones of alternating polarity of the magnetic field. This enables us to show topologically that single and three-fold polarity reversals of the solar magnetic fields can result from interaction of two types of magnetic fields: a low-frequency component with period of the order of 20 years and a high frequency component with period of order of 1.7-2.5 years (Benevolenskaya and Makarov, 1990).

scholarly journals A global climatological model of extreme geomagnetic field fluctuations

2020 ◽  
Vol 10 ◽  
pp. 5 ◽  
Author(s):  
Neil C. Rogers ◽  
James A. Wild ◽  
Emma F. Eastoe ◽  
Jesper W. Gjerloev ◽  
Alan W. P. Thomson
Keyword(s):  
Geomagnetic Field ◽  
Geomagnetic Latitude ◽  
Model Parameters ◽  
Geomagnetically Induced Currents ◽  
Ionospheric Currents ◽  
Polar Cusp ◽  
Auroral Substorm ◽  
Field Fluctuations ◽  
Substorm Onsets ◽  
Gp Model

This paper presents a multi-parameter global statistical model of extreme horizontal geomagnetic field fluctuations (dBH/dt), which are a useful input to models assessing the risk of geomagnetically induced currents in ground infrastructure. Generalised Pareto (GP) distributions were fitted to 1-min measurements of |dBH/dt| from 125 magnetometers (with an average of 28 years of data per site) and return levels (RL) predicted for return periods (RP) between 5 and 500 years. Analytical functions characterise the profiles of maximum-likelihood GP model parameters and the derived RLs as a function of corrected geomagnetic latitude, λ. A sharp peak in both the GP shape parameter and the RLs is observed at |λ| = 53° in both hemispheres, indicating a sharp equatorward limit of the auroral electrojet region. RLs also increase strongly in the dayside region poleward of the polar cusp (|λ| > 75°) for RPs > 100 years. We describe how the GP model may be further refined by modelling the probability of occurrences of |dBH/dt| exceeding the 99.97th percentile as a function of month, magnetic local time, and the direction of the field fluctuation, dBH, and demonstrate that these patterns of occurrence align closely to known patterns of auroral substorm onsets, ULF Pc5 wave activity, and (storm) sudden commencement impacts. Changes in the occurrence probability profiles with the interplanetary magnetic field (IMF) orientation reveal further details of the nature of the ionospheric currents driving extreme |dBH/dt| fluctuations, such as the changing location of the polar cusp and seasonal variations explained by the Russell-McPherron effect.

scholarly journals Decadal and Bi-Decadal Periodicities in Temperature of Southern Scandinavia: Manifestations of Natural Variability or Climatic Response to Solar Cycles?

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 676
Author(s):  
Maxim Ogurtsov
Keyword(s):  
Solar Cycle ◽  
Time Shift ◽  
Time Interval ◽  
Solar Cycles ◽  
Proxy Records ◽  
Documentary Sources ◽  
Southern Scandinavia ◽  
Winter Temperatures ◽  
Spring Temperatures ◽  
The Mean

Nine proxies of temperature over the last 225–300 years in Southern Fennoscandia (55–63° N) were analyzed. Seven reconstructions of the mean growing season temperatures were obtained by dendroclimatological methods. Reconstructions of spring temperatures in Stockholm and winter temperatures in Tallinn were based on historical documentary sources. It was found that significant decadal (10–13 years) and bi-decadal (22–25 years) periodicities were present in many of these series during the entire time interval. Four proxy records correlated significantly with the quasi 22-year solar cycle of Hale. Three time series correlated significantly with the quasi 11-year solar cycle of Schwabe. This can be considered as evidence of a link between decadal and bi-decadal changes in solar activity and climate in Southern Fennoscandia. On the other hand, signs of correlation differed, as well as the time shift between the solar and temperature cycles. It is difficult to explain such an intricate relationship and, thus, the physical mechanism of solar−climatic linkages remains unclear. That is why assumptions about the purely occasional appearance of correlations cannot yet be rejected. Guidelines for further research are suggested.

scholarly journals Long-term correlations in solar proxies and solar wind parameters

2021 ◽  
Author(s):  
Luca Giovannelli ◽  
Raffaele Reda ◽  
Tommaso Alberti ◽  
Francesco Berrilli ◽  
Matteo Cantoresi ◽  
...  
Keyword(s):  
Solar Wind ◽  
Time Lag ◽  
Magnetic Activity ◽  
Time Shift ◽  
Time Interval ◽  
Solar Cycles ◽  
K Index ◽  
The Earth ◽  
Solar Wind Parameters

&lt;p&gt;The long-term behaviour of the Solar wind and its impact on the Earth are of paramount importance to understand the framework of the strong transient perturbations (CMEs, SIRs). Solar variability related to its magnetic activity can be quantified by using synthetic indices (e.g. sunspots number) or physical ones (e.g. chromospheric proxies). In order to connect the long-term solar activity variations to solar wind properties, we use Ca II K index and solar wind OMNI data in the time interval between 1965 and 2019, which almost entirely cover the last 5 solar cycles. A time lag in the correlation between the parameters is found. This time shift seems to show a temporal evolution over the different solar cycles.&lt;/p&gt;&lt;div&gt;&amp;#160;&lt;/div&gt;

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