Christine Amory-Mazaudier

Electrodynamic coupling of high and low latitudes: Observations on May 27, 1993

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. It lasted *0 3 hours. Second, we analyze a series of fluctuations with periods of 25-75 min, to determine the variations of amplitude and phase with magnetic latitude and magnetic local time. The fluctuations were highly coherent at all latitudes between the magnetic equator and the auroral zone, but the coherency decreasedin the polar cap. A northward fluctuation at the equator during midday hours accompanied auroral zone fluctuations that were southward before noon, eastward around noon, and northward after noon. The amplitudes decreased away from the auroral zone toward midlatitudes but were amplified under the equatorial electrojet. No detectablep hased ifferencesa re found, indicating that any temporal lags which might be inducedb y persistencein the region-2f ield-alignedc urrentsa re less than i min for fluctuations having periods like those examined here. A synoptic inversion analysis of the high-latitude magnetic data to estimate the time-varying high-latitude electric potential patterns shows that fluctuations of the high-latitude east-west potential gradient tended to be concentrated around midday, where they were in phase with fluctuations in the midday east-west potential gradient at the magnetic equator.

Midlatitude ionospheric plasma temperature climatology and empirical model based on Saint Santin incoherent scatter radar data from 1966 to 1987

Ionospheric plasma temperature variations have recently been studied based on incoherent scatter radar (ISR) observations at a lower midlatitude site, Shigaraki, in East Asia [Otsuka et al., 1998] and Millstone Hill, a typical subauroral midlatitude site in North America [Zhang and Holt, 2004]. The French Saint Santin ISR, with a geographic latitude slightly higher but an apex latitude 14° lower than Millstone, collected bistatic and quadristatic measurements for over two solar cycles beginning in September 1965. A database of these data, containing observations between 1966 and 1987, has been used in this study in order to establish the midlatitude ionospheric climatology, in particular that of the upper atmosphere thermal status, as well as empirical models for space weather applications. This paper presents, in comparison with the Millstone Hill results, variations of ion and electron temperatures (Ti and Te) with solar activity, season, time of the day, and altitude. The F2 region Te at St. Santin is found to be lower than at Millstone between March and July, when the St. Santin electron density Ne is relatively higher. The midday Te below 300 km increases with F10.7, as at Millstone Hill. Above 300 km it tends to decrease with F10.7 at St. Santin, while it increases in summer at Millstone Hill. Ti between 250 and 350 km peaks midway between spring and summer. We have also created St. Santin ionospheric models for Ne, Te, and Ti using a bin-fit technique similar to that used for the Millstone Hill models. Comparisons with corresponding IRI predications indicate good agreement in Ti at high solar activity, and above the F2 peak, Te from the IRI tends to be higher than both the St. Santin and Millstone Hill models.

Ionospheric local model and climatology from long-term databases of multiple incoherent scatter radars

Empirical ionospheric local models have been developed from long-term data sets of seven incoherent scatter radars spanning invariant latitudes from 25 to 75 in American, European and Asian longitudes at Svalbard, Tromso, Sondrestrom, Millstone Hill, St. Santin, Arecibo and Shigaraki. These models, as important complements to global models, represent electron density, ion and electron temperatures, and ion drifts in the E and F regions, giving a comprehensive quantitative description of ionospheric properties. A case study of annual ionospheric variations in electron density and ion temperature is presented based on some of these models. Clear latitudinal, longitudinal, and altitude dependency of annual and semiannual components are found.

Solar flare effects at Ebre: Regular and reversed solar flare effects, statistical analysis (1953 to 1985), a global case study and a model of elliptical ionospheric currents

This paperp resentsth e resultso f the analysiso f geomagnetice ffectso f solarf lares (sfe) recordeda t Ebre observatory(4 0.8o l atitudeN , 0.5o l ongitudeE ) during3 3 years( 1953- 1985). At Ebre, locatedn eart he focusl atitude,t wo typeso f sfe can be observedr:e gulara nd reverseds fe.R egulars fea ret hosew hichh avep hased ifferencelse sst han9 0o w ith the regular diurnal magnetic variation of the day, Sn. Reversed sfe are those which have phase differences greatert han 90o with Sn.F rom these3 3 years,1 40 sfe eventsw ere selecteda nd a statistical studyw as performed.W e founda local time dependencoef the phased ifferencesb etweent he sfe and S n vectors. Morning hours have slightly positive values and afternoon hours have slightly negative ones. Reversed sfe, with a phase difference exceeding 90 o, concentrate between1 0 and 12 hours.R everseds fe showa dominante quinoctiacl haracterA. lso, a weaker correlationw as foundb etweens olara ctivityw ith reverseds fe (r=-0.47)t han with regulars fe (r=-0.68).U sing data from 67 observatoriesw, e performeda globals tudyo f a sfe case,s een at Ebre as reverseds fe. In this case,i n the northernh emispheret,h e sfe systemw as about 1 hour of local time eastward of the S n system and formed 4 o higher in latitude. Finally, we presenta model of two elliptical ionospherice quivalentc urrent systemsw ith focus offset about1 hour in local time to explaint he phased ifferenceb etweent he sfe and Sq magnetic vectorso bserveda t Ebre. The parameterso f this model have been fitted from the resultso f a previouss tatisticaal nalysisf rom Ebre data. Spatiala nd temporald istributiono f the sfe and

Ionospheric disturbance dynamo associated to a coronal hole: Case study of 5–10 April 2010

q vector phasesa re calculatedw ith this model, and conditionsf or reverseds fe occurrence are predicted.

Solar flare effects at Ebre: Unidimensional physical, integrated model

In this paper we study the planetary magnetic disturbance during the magnetic storm occurring on 5 April 2010 associated with high-speed solar wind stream due to a coronal hole following a coronal mass ejection. We separate the magnetic disturbance associated to the ionospheric disturbance dynamo (Ddyn) from the magnetic disturbance associated to the prompt penetration of magnetospheric electric field (DP2). This event exhibits different responses of ionospheric disturbance dynamo in the different longitude sectors (European-African, Asian, and American). The strongest effect is observed in the European-African sector. The Ddyn disturbance reduces the amplitude of the daytime H component at low latitudes during four consecutive days in agreement with the Blanc and Richmonds model of ionospheric disturbance dynamo. The amplitude of Ddyn decreased with time during the 4 days. We discuss its diverse worldwide effects. The observed signature of magnetic disturbance process in specific longitude sector is strongly dependent on which Earths side faces the magnetic storms (i.e., there is a different response depending on which longitude sector is at noon when the SSC hits). Finally, we determined an average period of 22 h for Ddyn using wavelet analysis.

Signature of the coronal hole near the north crest equatorial anomaly over Egypt during the strong geomagnetic storm 5 April 2010

A great increase of the ionizing radiation during solar flares results in an immediate increase of the ionization production rate, electron densities and electric currents in the ionosphere, followed simultaneously by disturbances of the magnetic elements at ground level (solar flare effects (sfe)). In this paper an attempt is made to model sfe phenomena combining several semiempirical models derived from satellite and radar data obtained during the last two decades. The model allows us to quantify model values of the phase difference between the sfe and Sq vectors, for comparison to the measurable quantity. It explains the cause of the change in magnetic perturbation during a flare at Ebre Observatory (40.8° latitude N, 0.5° longitude E). Large phase shift of the magnetic vector observed before noon, result from a descent of the “center of gravity” of the conducting mass that, combined with a very different regime of neutral winds in the lower and in the middle parts of the dynamo region, produce a change in the direction of the integrated currents.

Geomagnetism during solar cycle 23: Characteristics

In this paper we study the ionospheric-magnetic disturbance during a strong magnetic storm on 5 April 2010 associated to a coronal hole. The Earth was under the influence of a high speed solar wind stream during four days, and IMF was southward during a very long period. The variation of the disturbed magnetic observations and GPS-TEC are compared with the variation of quiet days during the same month in order to obtain the characteristics of GPS-TEC and magnetic disturbances due to the coronal hole effect. We use multi-instruments as SCINDA-GPS station at Helwan, Egypt (29.86 N, 31.32 E) and ASW-MAGDAS station at Aswan, Egypt (23.59 N, 32.51 E) in the equatorial region. At the beginning of the storm our data highlights the effect of the prompt penetration of the magnetosphere electric field which strongly increases the TEC. During the recovery phase of the storm, we observe on TEC and magnetic data, the signature of the ionospheric disturbance dynamo due to wind produced by Joule heating in the auroral zone. It is the first time that we observe an anti-Sq circulation on magnetic data during four consecutive days associated to the high speed solar wind streams.

Correction to “Simulation of electric field and current during the 11 June 1993 disturbance dynamo event: Comparison with the observations”

On the basis of more than 48 years of morphological analysis of yearly and monthly values of the sunspot number, the aa index, the solar wind speed and interplanetary magnetic field, we point out the particularities of geomagnetic activity during the period 1996–2009. We especially investigate the last cycle 23 and the long minimum which followed it. During this period, the lowest values of the yearly averaged IMF (3 nT) and yearly averaged solar wind speed (364 km/s) are recorded in 1996, and 2009 respectively. The year 2003 shows itself particular by recording the highest value of the averaged solar wind (568 km/s), associated to the highest value of the yearly averaged aa index (37 nT). We also find that observations during the year 2003 seem to be related to several coronal holes which are known to generate high-speed wind stream. From the long time (more than one century) study of solar variability, the present period is similar to the beginning of twentieth century. We especially present the morphological features of solar cycle 23 which is followed by a deep solar minimum.

Hot O and nighttime ionospheric temperatures

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Simulation of electric field and current during the 11 June 1993 disturbance dynamo event: Comparison with the observations K.Z. Zaka, A. T. Kobea, V. Doumbia, A.D. Richmond, A. Maute, N.M. Mene, O.K. Obrou, P. Assamoi, K. Boka, J.P. Adohi, et al.