THE DIURNAL BEHAVIOR OF SUDDEN COMMENCEMENTS OF MAGNETIC STORMS AT AGINCOURT

The diurnal variations in the frequencies of sudden commencements of magnetic storms are examined, using the magnetograms from Agincourt for the period from 1946 to 1953 inclusive. The occurrence frequencies of sudden commencements exhibit an apparent diurnal tendency which has its minimum in the morning hours and maximum in the afternoon. The frequency distributions for several groups classified by their amplitudes, however, show different diurnal variations from one another. In order to confirm such local-time effects, a statistical analysis of the shape of sudden commencements has been made, and each sudden commencement classified according to its shape. Results show the following diurnal characteristics. A pronounced augmentation of the sudden commencement impulse occurs in the afternoon hours. In the morning the initial rise of sudden commencements is usually slight and they are frequently inverted in the H-trace, although some of them are quite clear in the D-trace. The local-time variation of the horizontal magnetic vectors at several stages of the initial phase is also estimated statistically. These results suggest that the diurnal control of the magnetic variation must be due to some additional field produced in the earth's upper atmosphere at the time of sudden commencement, tending to modify the primary cause.

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Seasonal variations in the occurrence of geomagnetic storms

Annales Geophysicae ◽

10.1007/s00585-996-0286-1 ◽

1996 ◽

Vol 14 (3) ◽

pp. 286-289 ◽

Cited By ~ 4

Author(s):

John R. Taylor ◽

Mark Lester ◽

Timothy K. Yeoman

Keyword(s):

Solar Wind ◽

Seasonal Variations ◽

Annual Variation ◽

Geomagnetic Storms ◽

Magnetic Activity ◽

Magnetic Storms ◽

Sudden Commencement ◽

Sudden Commencements ◽

Solar Wind Origin

Abstract. Seasonal variations in the onset of magnetic storms are investigated. For the purposes of this study storms have been defined as events in which Dst falls below –50 nT for at least four consecutive hours. The storms have been classified as either storm sudden commencements (SSCs; storms initiated by a sudden commencement) or as storm gradual commencements (SGCs; all other storms). It is found that the semi-annual variation of magnetic activity is reflected in the occurrence statistics of SGC events only, indicative that the solar wind origin is different for SSCs and SGCs. It is suggested that the heliospheric latitude model of seasonal magnetic activity is relatively ineffective in modulating the previously observed seasonal variations in the occurrence of magnetic storms.

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Extreme geomagnetic activities: a statistical study

Earth Planets and Space ◽

10.1186/s40623-020-01261-8 ◽

2020 ◽

Vol 72 (1) ◽

Author(s):

Ryuho Kataoka

Keyword(s):

Magnetic Storms ◽

Magnetic Observatory ◽

Statistical Distributions ◽

Limited Data ◽

Data Set ◽

Sudden Commencements ◽

The One ◽

Log Normal ◽

Geomagnetic Activities ◽

Log Normal Distribution

Abstract Statistical distributions are investigated for magnetic storms, sudden commencements (SCs), and substorms to identify the possible amplitude of the one in 100-year and 1000-year events from a limited data set of less than 100 years. The lists of magnetic storms and SCs are provided from Kakioka Magnetic Observatory, while the lists of substorms are obtained from SuperMAG. It is found that majorities of events essentially follow the log-normal distribution, as expected from the random output from a complex system. However, it is uncertain that large-amplitude events follow the same log-normal distributions, and rather follow the power-law distributions. Based on the statistical distributions, the probable amplitudes of the 100-year (1000-year) events can be estimated for magnetic storms, SCs, and substorms as approximately 750 nT (1100 nT), 230 nT (450 nT), and 5000 nT (6200 nT), respectively. The possible origin to cause the statistical distributions is also discussed, consulting the other space weather phenomena such as solar flares, coronal mass ejections, and solar energetic particles.

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Corrigendum [to “Hydromagnetic propagation of sudden commencements of magnetic storms” by W. E. Francis, M. I. Green, and A. J. Dessler]

Journal of Geophysical Research Atmospheres ◽

10.1029/jz064i012p02470-02 ◽

1959 ◽

Vol 64 (12) ◽

pp. 2470-2470

Keyword(s):

Magnetic Storms ◽

Sudden Commencements

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GPS detection of the instantaneous response of the global ionosphere to strong magnetic storms with sudden commencement

Annals of Geophysics ◽

10.4401/ag-3490 ◽

2009 ◽

Vol 45 (1) ◽

Author(s):

E. L. Afraimovich ◽

E. A. Kosogorov ◽

L. A. Leonovich ◽

O. S. Lesyuta ◽

I. I. Ushakov

Keyword(s):

Magnetic Storms ◽

Sudden Commencement

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Temperature decadal trends, and their relation to diurnal variations in the lower thermosphere, stratosphere, and mesosphere, based on measurements from SABER on TIMED

Annales Geophysicae ◽

10.5194/angeo-39-327-2021 ◽

2021 ◽

Vol 39 (2) ◽

pp. 327-339

Author(s):

Frank T. Huang ◽

Hans G. Mayr

Keyword(s):

Local Time ◽

Lower Thermosphere ◽

3D Models ◽

Diurnal Variations ◽

Local Times ◽

Temperature Trends ◽

Microwave Sounding Unit ◽

Lidar Measurements ◽

Microwave Sounding ◽

Thermal Tides

Abstract. We have derived the behavior of decadal temperature trends over the 24 h of local time, based on zonal averages of SABER data, for the years 2012 to 2014, from 20 to 100 km, within 48∘ of the Equator. Similar results have not been available previously. We find that the temperature trends, based on zonal mean measurements at a fixed local time, can be different from those based on measurements made at a different fixed local time. The trends can vary significantly in local time, even from hour to hour. This agrees with some findings based on nighttime lidar measurements. This knowledge is relevant because the large majority of temperature measurements, especially in the stratosphere, are made by instruments on sun-synchronous operational satellites which measure at only one or two fixed local times, for the duration of their missions. In these cases, the zonal mean trends derived from various satellite data are tied to the specific local times at which each instrument samples the data, and the trends are then also biased by the local time. Consequently, care is needed in comparing trends based on various measurements with each other, unless the data are all measured at the same local time. Similar caution is needed when comparing with models, since the zonal means from 3D models reflect averages over both longitude and the 24 h of local time. Consideration is also needed in merging data from various sources to produce generic, continuous, longer-term records. Diurnal variations of temperature themselves, in the form of thermal tides, are well known and are due to absorption of solar radiation. We find that at least part of the reason that temperature trends are different for different local times is that the amplitudes and phases of the tides themselves follow trends over the same time span of the data. Many of the past efforts have focused on the temperature values with local time when merging data from various sources and on the effect of unintended satellite orbital drifts, which result in drifting local times at which the temperatures are measured. However, the effect of local time on trends has not been well researched. We also derive estimates of trends by simulating the drift of local time due to drifting orbits. Our comparisons with results found by others (Advanced Microwave Sounding Unit, AMSU; lidar) are favorable and informative. They may explain, at least in part, the bridge between results based on daytime AMSU data and nighttime lidar measurements. However, these examples do not form a pattern, and more comparisons and study are needed.

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Ozone and temperature decadal solar-cycle responses, and their relation to diurnal variations in the stratosphere, mesosphere, and lower thermosphere, based on measurements from SABER on TIMED

Annales Geophysicae ◽

10.5194/angeo-37-471-2019 ◽

2019 ◽

Vol 37 (4) ◽

pp. 471-485 ◽

Cited By ~ 1

Author(s):

Frank T. Huang ◽

Hans G. Mayr

Keyword(s):

Solar Cycle ◽

Local Time ◽

Satellite Data ◽

Diurnal Cycle ◽

Lower Thermosphere ◽

Diurnal Variations ◽

Local Times ◽

Data Set ◽

Orbital Drift ◽

Almost All

Abstract. There is evidence that the ozone and temperature responses to the solar cycle of ∼11 years depend on the local times of measurements. Here we present relevant results based on SABER data over a full diurnal cycle, which were not previously available. In this area, almost all satellite data used are measured at only one or two fixed local times, which can differ among various satellites. Consequently, estimates of responses can be different depending on the specific data set. Furthermore, over years, due to orbital drift, the local times of the measurements of some satellites have also drifted. In contrast, SABER makes measurements at various local times, providing the opportunity to estimate diurnal variations over 24 h. We can then also estimate responses to the solar cycle over both a diurnal cycle and at the fixed local times of specific satellite data for comparison. Responses derived in this study, based on zonal means of SABER measurements, agree favorably with previous studies based on data from the HALOE instrument, which only measured data at sunrise and sunset, thereby supporting the analysis of both studies. We find that for ozone above ∼40 km, zonal means reflecting specific local times (e.g., 6, 12, 18, 24 LST – local solar time) lead to different values of responses, and to different responses based on zonal means that are also averages over the 24 h local time period, as in 3-D models. For temperature, the effects of diurnal variations on the responses are not negligible even at ∼30 km and above. We also considered the consequences of local time variations due to orbital drifts of certain operational satellites, and, for both ozone and temperature, their effects can be significant above ∼30 km. Previous studies based on other satellite data do not describe the treatment, if any, of local times. Some studies also analyzed data merged from different sources, with measurements made at different local times. Generally, the results of these studies do not agree very well among themselves. Although responses are a function of diurnal variations, this is not to say that they are the major reason for the differences, as there are likely other data-related issues. The effects due to satellite orbital drift may explain some unexpected variations in the responses, especially above 40 km.

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