This paper presents a study of the St Patrick's Day storm of 2015, with its ionospheric response at middle and low latitudes. The effects of the storm in each longitudinal sector (Asian, African, American, and Pacific) are characterized using global and regional electron content. At the beginning of the storm, one or two ionospheric positive storm effects are observed depending on the longitudinal zones. After the main phase of the storm, a strong decrease in ionization is observed at all longitudes, lasting several days. The American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed. At low latitudes, using spectral analysis, we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field (PPEF) and of the disturbance dynamo electric field (DDEF) on the basis of ground magnetic data. Concerning the PPEF, Earth's magnetic field oscillations occur simultaneously in the Asian, African, and American sectors, during southward magnetization of the Bz component of the interplanetary magnetic field. Concerning the DDEF, diurnal magnetic oscillations in the horizontal component H of the Earth's magnetic field exhibit a behavior that is opposed to the regular one. These diurnal oscillations are recognized to last several days in all longitudinal sectors. The observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models.

[1] During magnetic storms, wind disturbances produced by auroral phenomena can affect the whole thermospheric circulation and associated ionospheric dynamo currents for many hours after the end of the storms. In this paper we define criteria to select a new simple type of ionospheric disturbance dynamo events that allow a simple interpretation over all longitude sectors. These events exhibit a weak auroral activity during at least 24 UT hours, on the day after the storm. We analyze the magnetic disturbances ''D dyn '' observed at equatorial latitudes in the three longitude sectors of such selected events. It is found for all the cases that the amplitude of the H component of the Earth's magnetic field is reduced, on the day after storm at equatorial latitudes, in agreement with the ionospheric disturbance dynamo model (Blanc and Richmond, 1980). The observation of H component decrease on the day after storm is longitudinally asymmetric. The observed signature of the ionospheric disturbance dynamo process in a specific longitude sector is strongly dependent on the magnitude, the start time, and the duration of the storm.Citation: Le Huy, M., and C. Amory-Mazaudier (2005), Magnetic signature of the ionospheric disturbance dynamo at equatorial latitudes: ''D dyn '',

This paper presents the results of the analysis of geomagnetic effects of solar flares (sfe) recorded at Ebre observatory (40.8° latitude N, 0.5° longitude E) during 33 years (1953‐1985). At Ebre, located near the focus latitude, two types of sfe can be observed: regular and reversed sfe. Regular sfe are those which have phase differences less than 90° with the regular diurnal magnetic variation of the day, SR. Reversed sfe are those which have phase differences greater than 90° with SR. From these 33 years, 140 sfe events were selected and a statistical study was performed. We found a local time dependence of the phase differences between the sfe and SR vectors. Morning hours have slightly positive values and afternoon hours have slightly negative ones. Reversed sfe, with a phase difference exceeding 90°, concentrate between 10 and 12 hours. Reversed sfe show a dominant equinoctial character. Also, a weaker correlation was found between solar activity with reversed sfe (r=0.47) than with regular sfe (r=0.68). Using data from 67 observatories, we performed a global study of a sfe case, seen at Ebre as reversed sfe. In this case, in the northern hemisphere, the sfe system was about 1 hour of local time eastward of the SR system and formed 4° higher in latitude. Finally, we present a model of two elliptical ionospheric equivalent current systems with focus offset about 1 hour in local time to explain the phase difference between the sfe and Sq magnetic vectors observed at Ebre. The parameters of this model have been fitted from the results of a previous statistical analysis from Ebre data. Spatial and temporal distribution of the sfe and Sq vector phases are calculated with this model, and conditions for reversed sfe occurrence are predicted.

Abstract. The penetration of disturbance electric fields from the polar region to the magnetic equator on the dayside of the Earth is examined with geomagnetic data on May 27, 1993. First, we examine a dayside equatorial disturbance that followed the rapid recovery of magnetic activity from a storm and that has the characteristics of overshielding caused by persistent region-2 field-aligned currents.