Clezio Marcos Denardini

Understanding space weather to shield society : A global road map for 2015-2025 commissioned by COSPAR and ILWS

There is a growing appreciation that the environmental conditions that we call space weather impact the technological infrastructure that powers the coupled economies around the world. With that co ...

Competition between winds and electric fields in the formation of blanketing sporadic E layers at equatorial regions

In the present work, we analyze the competition between tidal winds and electric fields in the formation of blanketing sporadic E layers (Esb) over São Luís, Brazil (2° 31′ S, 44° 16′ W), a quasi-equatorial station. To investigate this competition, we have used an ionospheric E region model (MIRE) that is able to model the Esb layers taking into account the E region winds and electric fields. The model calculates the densities for the main molecular and metallic ions by solving the continuity and momentum equations for each of the species. Thus, the main purpose of this analysis is to verify the electric fields role in the occurrence or disruption of Esb layers through simulations. The first results of the simulations show that the Esb layer is usually present when only the tidal winds were considered. In addition, when the zonal component of the electric field is introduced in the simulation, the Esb layers do not show significant changes. However, the simulations show the disruption of the Esb layers when the vertical electric field is included. In this study, we present two specific cases in which Esb layers appear during some hours over São Luís. We can see that these layers appear when the vertical electric field was weak, which means that the tidal components were more effective during these hours. Therefore, the vertical component of the electric field is the main agent responsible for the Esb layer disruption.

E region electric field dependence of the solar activity

We have being studying the zonal and vertical E region electric field components inferred from the Doppler shifts of type 2 echoes (gradient drift irregularities) detected with the 50 MHz backscatter coherent radar set at Sao Luis, Brazil (SLZ, 2.3°S, 44.2°W) during the solar cycle 24. In this report we present the dependence of the vertical and zonal components of this electric field with the solar activity, based on the solar flux F10.7. For this study we consider the geomagnetically quiet days only (Kp ≤ 3+). A magnetic field-aligned-integrated conductivity model was developed for proving the conductivities, using the IRI-2007, the MISIS-2000, and the IGRF-11 models as input parameters for ionosphere, neutral atmosphere, and Earth magnetic field, respectively. The ion-neutron collision frequencies of all the species are combined through the momentum transfer collision frequency equation. The mean zonal component of the electric field, which normally ranged from 0.19 to 0.35 mV/m between the 8 and 18 h (LT) in the Brazilian sector, show a small dependency with the solar activity. Whereas the mean vertical component of the electric field, which normally ranges from 4.65 to 10.12 mV/m, highlights the more pronounced dependency of the solar flux.

Equatorial sporadic E -layer abnormal density enhancement during the recovery phase of the December 2006 magnetic storm: A case study

Sporadic layers appear in the equatorial region (Esq) between 90 and 130 km mainly due to irregularities in the electrojet equatorial (EEJ) current. In the present work, we have analyzed the behavior of the frequency parameters associated with these sporadic layers, covering the days before, during, and subsequent to, the intense magnetic storm that occurred on December 14, 2006. The parameters used in our analyses are the top frequency (ftEs) and blanketing frequency (fbEs) of the Es layer as measured over São Luís, Brazil (2.33°S, 44.2°W, dip: −4.5°) by digital ionosonde. A tentative association between these parameters and X-ray data measured by sensors on board the GOES satellite was carried out. Also, we investigated the effects on the dynamics of the equatorial electrojet using magnetometer data related to the presence of these Es layers. Our analyses show that there are notable changes in the fbEs, which are characterized by the occurrence of peaks that exceed the ambient background values.

A conductivity model for the Brazilian equatorial e-region: initial results

This paper presents results from a new model of field-line-integrated ionospheric conductivity for the Brazilian equatorial region. It was developed aiming to calculate zonal electric fields at E-region heights in the equatorial region. The present model is based on a constant neutral atmosphere model and on an empirical electron densities model (which also gives the ion composition) adjusted by E-region electron density measured by digisonde. It is also based on a geomagnetic field model that we approximate with a dipole which is not located at the centre of the Earth due to the large magnetic declination angle in the Brazilian sector. We have also considered the eccentric dipole having an inclination of 20o with respect to the Earth rotation axis. The conductivities are calculated for the year 2002 and the results from the present model are compared to those obtained from the conductivity model of the Kyoto University.

Detection of three distinct regions in the equatorial electrojet in the Brazilian sector

Em dezembro de 1999 realizou-se uma campanha de coleta de dados do eletrojato equatorial, usando-se o radar de espalhamento coerente (RESCO), em Sao Luis, sob o equador magnetico. Neste artigo, selecionamos o periodo de 11 a 19 de dezembro, que cobre uma etapa magneticamente calma e outra relativamente perturbada. Para este periodo, 16 espectrogramas foram obtidos a cada dia de observacao, onde cada espectrograma corresponde a uma faixa de amostragem em altura. A primeira faixa de amostragem esta centrada em 97,4 km de altitude, enquanto a ultima corresponde a altura central de 115,6 km, e cada faixa possui uma extensao de 2,6 km. Mapas Diarios de Variacao Temporal de Intensidade foram gerados para o referido periodo. Pela analise dos espectrogramas e considerando a intensificacao do eletrojato equatorial ao entardecer de alguns dias, foi possivel observar tres regioes distintas como ja foi mencionado por Pfaff et al (1987) e Kudeki et al (1987). Na verdade, nossas observacoes concordam com os resultados da Campanha Condor de observacao do eletrojato. Usamos os indices de atividade auroral AU e AL, alem do indice Dst, relacionado a corrente anelar, para avaliar a resposta do eletrojato equatorial as perturbacoes magneticas.

The Embrace Magnetometer Network for South America: First Scientific Results

The present work is the second of a two-part paper on the Embrace Magnetometer Network. In this part, we provide some of the first scientific findings that we have already achieved with this network. We identified the diurnal and the seasonal natural variations of the H component. We provided the precise determination of SSC and SI. We showed that the ∆H amplitudes derived from the Embrace MagNet during intense magnetic storm are in very good agreement with the Dst index. We showed that it is possible to investigate of the effects of the Sq systems response to the X-class solar flares occurring during daytime under magnetically quiet conditions.

Statistical study of incoherent integration applied to simulated power spectra of radar signals backscattered from equatorial electrojet irregularities

Spectral analysis of radar echoes through spectral moment estimation allows to identify the characteristics of plasma irregularities from equatorial electrojet. The curve fitting using the maximum likelihood estimator (MLE) was chosen as the technique to obtain the plasma irregularity information. The implication of applying distinct number of incoherent integration to simulated Type 1 plasma irregularity radar spectra is investigated. The response of the fitting is evaluated using the covariance matrix of the MLE. A statistical study of incoherent integration applied to equatorial electrojet plasma irregularity spectra is presented in order to determine its effects over the estimation of Doppler velocities. The optimal values of incoherent integrations in relation to the goodness of the fitting are obtained in order to better determine the Type 1 plasma irregularity characteristics.