Ionospheric disturbances detected by MEXART A. Carrillo-Vargas a , R. Pe ´rez-Enrı ´quez b,⇑ , Mario Rodrı ´guez-Martı ´nez b , R. Lo ´ pez-Montes b , G.A. Casillas-Pe ´rez c , E.A. Araujo-Pradere d a Universidad Nacional Auto ´noma de Me ´xico, Instituto de Geofı ´sica, Unidad Michoaca ´ n, Mexico b Universidad Nacional Auto ´ noma de Me ´xico, Campus Juriquilla, Centro de Geociencias, Blvd Juriquilla 3001, Juriquilla, Quere ´taro 76230, Mexico c Universidad Nacional Auto ´ noma de Me ´xico, Instituto de Geofı ´sica, Unidad de Co ´ mputo, Ciudad Universitaria C.P. 04510, Me ´xico D.F., Mexico d CIRES-University of Colorado 325 Broadway W/NP9. Boulder, CO, USA Received 14 June 2011; received in revised form 1 December 2011; accepted 4 December 2011 Available online 24 December 2011 Abstract The radio telescope MEXART was developed to make observations of interplanetary scintillation (IPS) produced by large scale dis- turbances associated with solar events. In this work it is shown that on occasion there are disturbances in the ionosphere that are related with these events and which cannot only contaminate the IPS but actually be the main contribution to the observed oscillations. This was the case of the event of 15 December 2006 observed by MEXART, which presented clear scintillation. The total electron content (TEC) of the ionosphere above Mexico was calculated for the same period. It was found that the variations in TEC were associated with the scintillations detected by MEXART. Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Interplanetary scintillation; Ionosphere disturbances; MEXART 1. Introduction The first evidence of interplanetary scintillation was observed in the 1950s, when the diameter of stellar radio sources was measured using radio telescopes (Readhead and Hewish, 1974). Several years later, during a set of observations of stellar radio sources developed in the Cam- bridge’s observatory by Hewish et al. (1964), unusual fluc- tuations were detected in the signal (at 178 MHz) of three sources: 3C119, 3C138 and 3C147. During the following days, these sources, in particular 3C138, showed an irregu- lar registry which was interpreted as a contamination by ionospheric scintillation. A more detailed analysis showed that these intensity fluctuations contained a time scale in the range of 1–2 s. Although ionospheric scintillation (IONS) had been known well enough at the time (Hewish, 1951; Little and Maxwell, 1952), this could not justify the rapid fluctuations observed in the intensity. Hewish et al. (1964) were the first to recognize that the radio signal from such sources presented ionospheric scintillation in addition to another scintillation associated with the plasma in the interplanetary medium, which is known as interplanetary scintillation (IPS) (Hewish et al., 1964; Readhead, 1971). The IPS can be observed in a wide frequency from 20 MHz upto over 10 GHz. The temporal scale depends on the observed frequency and of the scale in the irregular- ities of electronic density in the solar wind. Radio sources with an angular diameter smaller to 1 arcsec present an interplanetary scintillation in the frequency range of 0.1–3 Hz (Hewish and Duffet-Smith, 1987). For instance, the observations of IPS with the Ooty radio telescope (at 327 MHz) presented a power spectrum in the range 0.1– 5 Hz. The spectrum shows a knee at 1 Hz; and after this frequency the power falls faster until reaching the noise level at around 5 Hz (Manoharan and Ananthakrishnan, 0273-1177/$36.00 Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2011.12.017 ⇑ Corresponding author. Tel.: +52 442 238 1104; fax: +52 442 238 1101. E-mail addresses: armando@geofisica.unam.mx (A. Carrillo-Vargas), roman@geociencias.unam.mx (R. Pe ´rez-Enrı ´quez), mariorm@geociencias. unam.mx (M. Rodrı ´guez-Martı ´nez), rebeca@geociencias.unam.mx (R. Lo ´ pez-Montes), gacp@geofisica.unam.mx (G.A. Casillas-Pe ´rez), Eduardo.Araujo@noaa.gov (E.A. Araujo-Pradere). www.elsevier.com/locate/asr Available online at www.sciencedirect.com Advances in Space Research 49 (2012) 1570–1580