RESEARCH ARTICLE


Long-Term Dependencies of Annual and Semiannual Components of NmF2 Over Concepción



Manuel A. Bravo, Alberto J. Foppiano *, Rodrigo Abarca del Río
Universidad Nacional de Tucuman - CONICET, Facultad de Ciencias Exactas y Tecnologia, Departamento de Fisica Av. Independencia 1800, 4000 Tucumán, Argentina


© 2011 Bravo et al. ;

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas, Universidad de Concepción, Avda. Esteban Iturra s/n, Barrio Universitario, Concepción, Chile; Tel: +56-41-2204136; Fax: +56-41-2220104; E-mail: foppiano@udec.cl


Abstract

In this work an attempt is made to determine whether the annual and semiannual components of the NmF2 observed over Concepción (36.8°S; 73.0°W), Chile, exhibit long-term trends. Monthly median hourly values of NmF2 determined from ionosonde observations are analyzed. Although the assessed trends for NmF2 and for the semiannual and annual components of NmF2, are hardly significant by any statistical test, they exhibit a systematic diurnal evolution. NmF2 trends are almost null during night time and negative from around noon to the early evening. The same can be said for trends of the amplitudes of the semiannual component. On the contrary, trends for the annual component are always positive and exhibit a rather irregular diurnal pattern. It seems reasonable then to particularly look for an explanation of the semiannual component long-term changes when concerned with long-term changes of NmF2. The semiannual variation is linked to composition and thermospheric wind effects, and solar zenith angle changes which may be connected to changes of the strength of the global circulation. But, more study is needed to envisage the changes on the semiannual component of NmF2 which may arise from eventual long-term changes of the global circulation

Keywords: Long-Term Trends, Ionosphere, NmF2, Annual Variation, Semiannual Variation.