IPDP geomagnetic pulsations and their relation to coronal holes and high speed solar wind streams

La frecuencia de ocurrencia de intervalos de pulsaciones de periodo decreciente (IPDP) muestra una correlación inversa con el número de manchas solares, contrariamente a lo que ocurre con la actividad geomagnética en general. En este trabajo tomamos la frecuencia anual de ocurrencia de IPDPs en la estación de Sodankyla para los años 1974-1985 (un ciclo solar) y encontramos que los IPDP tienen una correlación positiva con el área de los hoyos coronales solares, con un coeficiente de correlación de 0.77. Esto sugiere una correlación física entre este tipo de pulsaciones y las corrientes de viento solar rápido (HSSs) que se originan en los hoyos coronales. Comparamos la ocurrencia anual de IPDPs en el periodo 1974-1982 con el m1mero anual de HSSs asociados a hoyos coronales, con velocidades mayores o iguales que 550 km/s en esos años y encontramos una buena correlación alrededor del máximo y en la parte descendente del ciclo. Sin embargo, durante el mínimo y la fase ascendente del ciclo, los IPDPs fueron mas frecuentes que los HSSs. Concluimos que la ocurrencia de los IPDPs parece estar relacionada con cierta propiedades del viento solar de alta velocidad y discutimos una posible causa de las diferencias cerca del mínimo. doi: https://doi.org/10.22201/igeof.00167169p.1998.37.1.215

Preliminary analysis of the geomagnetic pulsations observed at Teoloyucan, Mexico

Desde febrero de 1993, se han estado registrando casi en forma continua micropulsaciones en el Observatorio Magnetico de Teoloyucan, Edo. de México, en la banda de frecuencias de 0.01 a 0.20 Hz, que corresponde a periodos entre 5 y 100 segundos. En este trabajo presentamos un análisis preliminar de los datos en el que se muestra la distribución de la frecuencia de ocurrencia de todos los eventos con respecto al tiempo local y a lo largo del año. Encontramos un máximo de ocurrencia alrededor del mediodía y un mínimo de ocurrencia cerca de la medianoche. Parece haber también una variación estacional que muestra dos máximos, en marzo y en diciembre, y un mínimo en julio

The spatial relationship between active regions and coronal holes and the occurrence of intense geomagnetic storms throughout the solar activity cycle

We study the annual frequency of occurrence of intense geomagnetic storms (Dst < –100 nT) throughout the solar activity cycle for the last three cycles and find that it shows different structures. In cycles 20 and 22 it peaks during the ascending phase, near sunspot maximum. During cycle 21, however, there is one peak in the ascending phase and a second, higher, peak in the descending phase separated by a minimum of storm occurrence during 1980, the sunspot maximum. We compare the solar cycle distribution of storms with the corresponding evolution of coronal mass ejections and flares. We find that, as the frequency of occurrence of coronal mass ejections seems to follow very closely the evolution of the sunspot number, it does not reproduce the storm profiles. The temporal distribution of flares varies from that of sunspots and is more in agreement with the distribution of intense geomagnetic storms, but flares show a maximum at every sunspot maximum and cannot then explain the small number of intense storms in 1980. In a previous study we demonstrated that, in most cases, the occurrence of intense geomagnetic storms is associated with a flaring event in an active region located near a coronal hole. In this work we study the spatial relationship between active regions and coronal holes for solar cycles 21 and 22 and find that it also shows different temporal evolution in each cycle in accordance with the occurrence of strong geomagnetic storms; although there were many active regions during 1980, most of the time they were far from coronal holes. We analyse in detail the situation for the intense geomagnetic storms in 1980 and show that, in every case, they were associated with a flare in one of the few active regions adjacent to a coronal hole

DWT-based methodology for detection of seismic precursors on electric field signals in Mexico

This paper presents an analysis of atmospheric electric field signals which were taken on an important seismic activity period from 2012 to 2015 to study its relationship with seismic events. For this purpose, several measurements were acquired every second by using a triaxial electric field monitoring system. Furthermore, the discrete wavelet transform (DWT) was applied to electric field signals with seismic events of magnitudes greater than Mw > 5.5, which occurred in Mexico with different focal mechanisms. The analysed epochs consist of 24 h of observations for a data-set corresponding to 55 different earthquakes (EQs). The time series were processed 12 h before and 12 h after each seismic event. The proposed methodology proves to be an efficient tool to detect signals with relations between electric field and seismic activity. The methodology presented herein shows important anomalies on different time instants according to the focal mechanism. Finally, a statistical post-processing algorithm was performed in order to quantify the data dispersion as a measure of seismic activity. It is found that the variance increases before, during, and after the seismic event about the coefficients D1 to D7 obtained using the DWT