Ionospheric reflection of the magnetic activity described by the index g Beata Dziak-Jankowska a,⇑ , Iwona Stanisławska a , Tomasz Ernst b , Łukasz Tomasik a a Space Research Centre, Polish Academy of Sciences, ul. Bartycka 18A, 00-716 Warszawa, Poland b Institute of Geophysics, Polish Academy of Sciences, ul. Ksiecia Janusza 64, 01-452 Warszawa, Poland Received 5 November 2010; received in revised form 26 April 2011; accepted 27 April 2011 Available online 5 May 2011 Abstract Differences in the external part of the vertical geomagnetic component point to the existence of local inhomogeneities in the magne- tosphere or the ionosphere. Usually used magnetic indices are not sufficient to express the state of ionosphere, the common used global Kp index derived in the three-hour interval does not indicate much more rapidly changes appearing in ionosphere. Magnetic index g reflects ionospheric disturbances when other indices show very quiet conditions. Data of ionospheric characteristics (foE, foEs, h’E, h’F2) during 28-day long quiet day conditions (Kp = 0–2) in 2004 were analyzed. The correlations between strong local disturbances in ionosphere during very quiet days and high values of magnetic index g were found. The most sensitive to magnetic influence – ion- ospheric E layer data (foE characteristic) – reaches median deviations up to (+0.8 MHz and 0.8 MHz) during very low magnetic activ- ity (Kp = 0–1). The high peaks (2–2.7) of the magnetic index g correlate in time with large local median deviations of foE. Such local deviations can suggest local inhomogeneities (vertical drifts) in the ionosphere. The correlation in space is not trivial. The strong peak of g is situated between the positive and negative deviations of foE. Additional observation is connected with correlation in time of the high g value with the negative median deviations of h’F2 (in some cases up to 90 km). The analysis was based on one-minute data recorded at each of 20 European Magnetic Observatories working in the INTERMAGNET network and from 19 ionosondes for 2004. Iono- spheric data are sparse in time and in space in opposite to the magnetic data. The map of the magnetic indices can suggest the behavior of ionospheric characteristics in the areas where we have no data. Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Ionosphere; Magnetic indices; Sporadic E 1. Introduction The ionosphere is constantly changing and ionospheric disturbances have negative influence on radio transmis- sions. Especially hard to forecast and in principle unpredict- able are the ionospheric disturbances occurring under magnetically quiet time. For this reason monitoring and data collection are of importance for the subsequent analyz- ing and improving numerical forecast models of the state of the ionosphere that is significant for radiocommunications. Our knowledge of the spatial and temporal changes of the ionosphere is still incomplete. Magnetic indices usually used are not sufficient to express the state of the iono- sphere, e.g. the common used global Kp index derived in the three-hour interval does not indicate much more rap- idly changes appearing in ionosphere. Proposed by Ernst and Jankowski (2005) g index reflects ionospheric distur- bances when other indices show very quiet conditions. The advantage of the g is its simplicity of calculation and possibility to implication to only one station. Ernst and Jankowski (2005) conclude that the differences discovered in the external part of the vertical geomagnetic component point to the existence of local inhomogeneities in the mag- netosphere or the ionosphere. High local inhomogeneities and vertical drifts can be dri- ven by atmospheric waves (planetary, tidal, gravity and infrasonic) playing the most important role in forcing of the ionosphere under quiet geomagnetic conditions 0273-1177/$36.00 Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2011.04.029 ⇑ Corresponding author. Tel.: +48 22 4966 381. E-mail addresses: bdziak@cbk.waw.pl, bdziak@igf.fuw.edu.pl (B. Dziak-Jankowska). www.elsevier.com/locate/asr Available online at www.sciencedirect.com Advances in Space Research 48 (2011) 850–856