A Multiscale Approach to Geomagnetic Storm Morphology Analysis Based on DMA Activity Measures

The article is focused on the approach based on the discrete mathematical analysis conception and continues a series of studies related to the application of the previously developed methodology to geophysical data analysis. The main idea of the study is the modification of earlier conceptions regarding the interpreter’s logic that allows introducing a multiscale approach and performing the time series analysis using the activity measure plots, implying the vertical scale. This approach was used to study the morphology of several intense geomagnetic storms at the final stages of the 23rd and 24th solar activity cycles. Geomagnetic observatory data and interplanetary magnetic field parameters as well as the solar wind flux speed and proton density were analyzed for each of the studied storms using the activity measures. The developed methods, applied to geomagnetic storm morphological analysis, displayed good results in revealing the decreases and increases in various durations and intensities during storms, detecting low-amplitude disturbances, and storm sudden commencement recognition. The results provide an opportunity to analyze any physical data using a unified scale and, in particular, to implement this approach to geomagnetic activity studies.

СВЯЗЬ НАПРАВЛЕНИЯ ПРИХОДА ФРОНТА МЕЖПЛАНЕТНОЙ УДАРНОЙ ВОЛНЫ СО ВРЕМЕНЕМ SC ПО АНАЛИЗУ ОТДЕЛЬНЫХ КВМ-СОБЫТИЙ

При взаимодействии межпланетных корональных выбросов массы (КВМ), сопровождающиеся ударными волнами, с земной магнитосферой в магнитном поле Земли могут быть зарегистрированы скачки разной интенсивности, которые в некоторых случаях могут инициировать развитие магнитных бурь, представляя собой ее внезапное начало (Storm Sudden Commencement - SSC). В работе представлен первые результаты оценки зависимости времени появления SSC как функции широты/долготы и мирового времени, с целью дальнейшего исследования связи направления прихода фронта ударной волны со временем появления SSC. Для анализа были выбраны два КВМ с источниками формирования в Северном (21.06.2015, 02:36 UT) и Южном (14.07.2017, 01:25 UT) полушарии Солнца. При подходе к Земле они вызвали SSC 22.06.2015 в 18:33 UT и 16.07.2017 в 05:59 UT с последовавшими за ними магнитными бурями. Время старта SSC определялась по секундным данным, доступным в сети INTERMAGNET (около 40 обсерваторий северного и 20 обсерваторий южного полушарий). Для этих событий выполнена оценка появления SSC как функция геомагнитной широты и долготы от всемирного времени. Показано, что с приходом КВМ к Земле старт SSC на наземных магнитных обсерваториях, расположенных на широтах, от высоких до экваториальных, не является одновременным - время старта SSC на разных широтах отличаются на десятки секунд. Кроме этого, в рассмотренных событиях SSC сначала регистрируется на обсерваториях полушария Земли, освященного Солнцем, и, в среднем, появляется раньше в нижних широтах, чем в высоких.

Do Statistical models capture magnetopause dynamics during sudden magnetospheric compressions?

<p>Under steady-state conditions the magnetopause location is described as a pressure balance between internal magnetic pressures and the external dynamic pressure of the solar wind. The question is, does this approximation hold during more dynamic solar wind features?</p><p>Under more extreme solar wind driving, such as high solar wind pressures or strong southward-directed interplanetary magnetic fields, this boundary is significantly more compressed than in steady-state, playing a significant role in the depletion of magnetospheric plasma from the Van Allen Radiation Belts, via magnetopause shadowing. Large step-changes in solar wind conditions enable the real magnetopause to have a significant time-dependence which empirical models cannot capture.</p><p>We use a database of ~20,000 magnetopause crossings, to determine how the measured magnetopause differs from a statistical model, and under which conditions. We find that observed magnetopause is on average 6% closer to the radiation belts,  with a maximum of 42%, during periods of sudden dynamic pressure enhancement, such as during storm sudden commencement. Our results demonstrate that empirical magnetopause models such as the Shue et al. [1998] model should be used cautiously to interpret energetic electron losses by magnetopause shadowing. </p>

Substorms manifestation at high and mid-latitudes during two large magnetic storm

The dynamics of magnetic substorms at high and middle latitudes during two severe geomagnetic storms: on 17March 2015 and on 22–23 June2015has been analyzed. The storms were rather similar: both storms were a result of the solar wind Sheath impact and both storms were characterized by a strong intensity (SYM/Hmin<–200nT). We studied the magnetic substorms during these storms on the base of the INTERMAGNET and IMAGE networks data. The attendant solar wind and Interplanetary Magnetic Field (IMF) parameters were taken from the OMNI data base. The spatial-temporal dynamics of three substorms was studied in detail: at 17:29 UT and at 22:55 UT during the first storm and at 18:33 UT during the second storm. The substorms on 17.03.2015originated during the main storm phase, and the onset of the substorm on 22.06.2015 followed the storm sudden commencement (SSC) of the second storm. All three substorms were characterized by a sharp poleward expansion of the westward electrojet simultaneously with a slower motion to lower latitudes. They were observed also at middle and low latitudes as positive magnetic bays. The westward electrojet reached ~71°CGMLat during the first two substorms and surpassed 75°CGMLat during the third substorm. Therefore, the first two events were “classical” substorms, and the third one –an “expanded” substorm. We suggested that this behavior is related to the different solar wind conditions: the “classical” substorms developed under magnetic cloud (MC) conditions, and the “expanded” –under the Sheath region effect.

Analysis and interpretation of inner-heliospheric SEP events with the ESA Standard Radiation Environment Monitor (SREM) onboard the INTEGRAL and Rosetta Missions

Using two heliospheric vantage points, we study 22 solar energetic particle (SEP) events, 14 of which were detected at both locations. SEP proton events were detected during the declining phase of solar cycle 23 (November 2003–December 2006) by means of two nearly identical Standard Radiation Environment Monitor (SREM) units in energies ranging between 12.6 MeV and 166.3 MeV. In this work we combine SREM data with diverse solar and interplanetary measurements, aiming to backtrace solar eruptions from their impact in geospace (i.e., from L1 Lagrangian point to Earth’s magnetosphere) to their parent eruptions at the Sun’s low atmosphere. Our SREM SEP data support and complement a consistent inner-heliospheric description of solar eruptions (solar flares and coronal mass ejections [CMEs]) and their magnetospheric impact. In addition, they provide useful information on the understanding of the origin, acceleration, and propagation of SEP events at multi-spacecraft settings. All SEP events in our sample originate from major eruptions consisting of major (>M-class) solar flares and fast (>1800 km/s, on average), overwhelmingly (>78%) halo, CMEs. All but one SEP event studied are unambiguously associated with shock-fronted CMEs, suggesting a CME-driven shock acceleration mechanism. Moreover, a significant correlation is found between the SEP event peak and the onset of the storm sudden commencement, that might help improve prediction of magnetospheric disturbances. In general, SEP events correlate better with interplanetary (i.e., in-situ; L1-based) than with solar eruption features. Our findings support (a) the routine use of cost-effective SREM units, or future improvements thereof, for the detection of SEP events and (b) their implementation in multi-spacecraft settings as a means to improve both the physical understanding of SEP events and their forecasting.