Geomagnetism and Aeronomy最新文献

Variations of weak photospheric magnetic fields with periods on the order of the solar magnetic cycle have been studied. We used synoptic maps of the photospheric magnetic field for the period 1978−2016 (NSO Kitt Peak). To isolate the contribution of weak magnetic fields, the saturation threshold for the synoptic maps was set at 5 G. A time–latitude diagram was constructed from the converted synoptic maps. For further analysis, 18 magnetic field profiles were selected from the diagram. It was found that a 22-year variation in weak magnetic fields is present not only at high, but also at low latitudes. We show that at all latitudes, with the exception of ~26° and ~33° in the Northern Hemisphere and ~−26° in the Southern Hemisphere, weak magnetic fields change cyclically with an average period of 22.3 years. At high latitudes, the magnetic fields of the two hemispheres change approximately out of phase. In contrast, equatorial latitudes are in phase with the high latitude fields of the Northern Hemisphere and out of phase with the Southern Hemisphere. Thus, at low latitudes, the dominant role of the Northern Hemisphere becomes noticeable: the equatorial fields are in phase with the fields of the Northern Hemisphere at high latitudes. The phase of the 22-year variation changes gradually with latitude, but when the 22-year variation is disrupted, phase jumps occur. Before and after the disruption period, the 22-year variation develops in antiphase.

We calculated variations in the cosmic ray geomagnetic cutoff rigidity ΔR_ef during a complex two-stage magnetic storm on November 9–10, 2004, using calculations of particle trajectories in the model magnetic field of the magnetosphere. The response of ΔR_ef to changes in solar wind and magnetosphere parameters reflects the nonsmooth two-stage evolution of this storm. It is found that the curve of changing values that ΔR_ef take as a function of the studied parameters during the main phases of each stage of the storm does not coincide with the curve during the recovery phases, which is a sign of hysteresis. As a result, two hysteresis loops are formed, one for each stage of the storm of November 9–10, 2004. The ambiguous dependence of ΔR_ef values on the studied parameters, which change cyclically during the development of magnetospheric current systems and their subsequent relaxation, is responsible for the formation of the loops. The configuration of two loops similar to those characteristic of dielectric hysteresis seems to be related to the abrupt change from Bz > 0 to Bz < 0, which delimits the stages of the studied storm.

Differences in geomagnetic and ionospheric activity are investigated for the maximum monthly–hourly values of the auroral electrojet AE index, measured on a network of magnetometers above 60° in the Northern hemisphere from 1995 to 2019. The selected extreme AE indices were compared with the time–matched 1-h Apo indices observed in the sub-auroral zone from 1995 to the present. A high correlation of 300 selected values of AE and Apo indices (cc = 0.69) was obtained for the period of their synchronous observations in 1995–2019. For a comparison, variations of the ionospheric zonal dispersion (Net Volume, NT) are considered designating the difference between the positive and negative deviations of TEC from the quiet state in the selected zone. The NT is produced from TEC-based W-index values at the grid in the auroral zones of the Northern and Southern hemispheres for the geomagnetic latitudes exceeding ±60°. The NT values were estimated from JPL maps of the total electron content, GIM–TEC, and the corresponding W-index maps converted from geographic to geomagnetic coordinates. We observed an asymmetry of the ionospheric variability in the Northern and Southern auroral zones with the dominance of the positive (negative) NT values in the local winter (summer). At the same time, the seasonal variation of the geomagnetic AE and Apo indices recorded mainly in the Northern Hemisphere shows changes similar to the ionospheric variations of NT in the Southern Hemisphere with a decrease in the amplitude by the winter solstice. The analytical dependences of NT indices on the day of year in the North and South auroral zones were derived suitable for estimating the ionospheric variability in the operational forecasting models of the ionosphere.

In this work, we studied the formation of a large-scale magnetic field. For this, we used the surface flux transport (SFT) model. We have studied the model’s accuracy and its sensitivity to uncertainties in its key parameters and input data. We also compared the simulated magnetic field with observations of the SDO/HMI and STOP/Kislovodsk magnetic fields. Overall there is good agreement between the simulations and observations. Although the model cannot reproduce fine details of the magnetic field, the long-term evolution of the polar field is very similar in simulations and observations. During even one activity cycle, large-scale field drift waves to high latitudes change polarity. Magnetic field drift waves, the sign of which corresponds to the magnetic polarity of the trailing parts of the active regions, often exist during the decline phase of activity. This does not quite correspond to the idea of mutual compensation of the leading fields of active regions across the equator. We also looked at the magnetic field flux across the equator. We confirmed that the flux across the equator does not show a clear predominance of leading sunspot polarity. The results are discussed to test dynamo models.

The article studies microstreams, increases in solar wind (SW) currents up to several tens of km/s, with a time scale of the order of a day. A comparative analysis of microstreams present in the polar and low-latitude SW at different heliocentric distances has been carried out. The comparison showed that the properties of microstreams in the near-Earth fast SW are qualitatively similar to the properties of microstreams present in the polar SW during periods close to solar activity minima, at heliocentric distances from 2 to 4.5 AU. At the same time, the quantitative parameters of microstreams (amplitudes of variations in radial and tangential velocity, as well as relative variations in temperature, density, and plasma pressure) show a monotonic decrease with increasing heliocentric distance, which can be interpreted as a consequence of the gradual evolution of microstreams with distance from the Sun. However, comparison with SW measurements in the low-latitude region of the heliosphere at distances of about 5 AU shows some significant differences, which indicate a more rapid evolution of microstreams in the inhomogeneous low-latitude SW.

In solar activity, in addition to the 11-year Schwabe cycle, there are also shorter-period oscillations in the range from 27 days to 11 years, which are called mid-term oscillations. In our study, we identify quasi-6-year oscillations in solar activity expressed by the sunspot number SN using wavelet analysis and investigate the characteristics of these variations during 1750–2020. The analysis shows that the ~6-year cycle in SN is a real independent oscillation. A similar quasi-6-year periodicity has been found in the monthly mean records of geomagnetic field components at the Sitka and Honolulu observatories during 1910–2020. It was found that the variations of the geomagnetic field in the range of 5–6-year periods can be caused by the effect of variations in solar activity in the same frequency range. In addition, in the SN series and geomagnetic field variations, a quasi-biennial cycle is well observed, the amplitude of which in some time intervals exceeds the amplitude of the cycle with a period of 5–6 years.

In this article we continue studying the influence of solar activity on the main trajectories of extratropical cyclones (storm tracks) in different parts of the North Atlantic during the cold half of the year (period of intense cyclogenesis). Long-term oscillations in the latitude of storm tracks in the areas located west and east of the Greenwich meridian are compared. It is shown that secular oscillations in latitudes of storm tracks (with periods of ∼80–100 years) are most distinctly pronounced in the western North Atlantic (longitudes 60°–40° W), weaken in the area of the Icelandic Low (30°−10° W), and completely disappear in the eastern part (0°−20° E), where multidecadal oscillations with periods of ∼50–60 years dominate. Bidecadal oscillations in cyclone trajectories (northward shift of trajectories during the declining phase and at the minima of even-numbered solar cycles) have the greatest amplitude in the region of the Icelandic Low and noticeably weaken east of Greenwich. It is shown that the shift of cyclone trajectories to the north in even cycles occurs under increased galactic cosmic ray (GCR) intensity compared to odd cycles. The data providing evidence for the influence of the stratospheric polar vortex on the position of North Atlantic cyclone trajectories are presented. It is suggested that possible reasons for oscillations in the vortex intensity are changes in the chemical composition and temperature regime of the middle polar stratosphere caused by variations in GCR fluxes and geomagnetic activity.

For the first time, several flare events are analyzed based on multifrequency observations using the Radio Solar Telescope Network. The purpose of the analysis is to identify signs of flare preparation. In all considered cases, preflare quasi-periodic fluctuations (QPFs) of radio emission were detected. The duration of preflare wavetrains is 6–20 min. Wavetrains consist of 3–5 pulses. QPFs at lower frequencies (200–600 MHz) begin later than those at high frequencies by 2–6 min. QPFs at frequencies of 2695–8800 MHz occur almost synchronously. The highest amplitude of QPFs is observed at a frequency of 4995 MHz. The observed QPFs can be explained by the force-free magnetic rope model (Solov’ev and Kirichek, 2023).

The study demonstrates the synchronicity of the positive and negative phases of summer irradiation of the Northern Hemisphere in the precession cycle with periods of global climate warming and cooling for the Late Pleistocene and Holocene. The cold phase 50–41.5 ka BP corresponds to the Shestikhinsky cooling in Eastern Europe and the development of glaciation in North America. The warm phase 41–30 ka BP accounts for climate warming in Europe (Bryansk interstadial, Paudorf, Gotwei warming) and in North America (Plum Point Interstadial). The period of maximum development of glaciation in Europe and North America is synchronized with the cold phase 29.5–17.5 ka BP. The warm phase 17–5.5 ka BP is associated with the transition from the cold Pleistocene to the relatively warm Holocene. The Little Ice Age falls on the cold phase 5 ka BP – 5000 CE. It is expected that warming of the climate with respect to the present will correspond to the Warm Epoch 5000–13 000 CE. Changes in solar radiation arriving in the first astronomical half of the year in 5° latitude zones were determined for all astronomical months of the tropical year for climatic precession extrema. This makes it possible to compare spatiotemporal changes in Earth’s solar climate during years of climate precession extrema.

In the recent work by Usoskin et al. (2021) a series of annual sunspot indices for the years 971 to 1899 was reconstructed. Using this series, we study behavior of the “length-amplidude rule” (LAR), according to which the mininum-to-minimum length of a given 11-year solar cycle anticorrelates with the amplitude of the next one. We show that approximately since the 14th century two regimes exist in the series: I) epochs of normal activity, when the LAR is observed; II) epochs of the Maunder, Spörer and Wolf grand minima, when there were no significant links between the amplitudes and lengths of the 11-year cycles. Before the 14th century the LAR and its relation to the level of global activity of the Sun is less pronounced, which, probably, is a consequence of inaccuracies of the 11-year cycle parameters determination in this epoch.