Behavior of the scale height at the F2 layer peak derived from Digisonde measurements at two European stations M. Mosert a, * , R. Ezquer b,c , B. de la Morena d , D. Altadill e , G. Mansilla b , G. Miro Amarante f a CASLEO-CONICET, Avda. Espan ˜a 1512 Sur, 5400 San Juan, Argentina b Lab. de Iono ´ sfera, UNT, CONICET, Avda Independencia 1800, 4000 Tucuma ´ n, Argentina c GASuR, Fac. Reg. Tucuma ´ n, UTN, Rivadavia 1050, 4000 Tucuma ´ n, Argentina d INTA, Ctra. San Juan del Puerto-Matalascan ˜as Km. 33, 21130, Huelva, Spain e Observatori de l’Ebre, (CSIC-URL), Carretera de Lo ´ bservatori 8 E43896 Roquetes, Spain f ICTP, Strada Costiera 11, 34100 Trieste, Italy Received 29 December 2005; received in revised form 9 October 2006; accepted 23 November 2006 Abstract A new technique is presented to estimate the electron density topside profile from information derived from ground-based ionograms. The electron density above the F2 peak is approximated by an a-Chapman function with constant scale height (H m ). The scale height is derived from the shape of the bottomside profile near the F2 peak. Digisonde data obtained at two European stations: Ebro (40.4°N, 0.3°E) and El Arenosillo (37.1°N; 353.2°E) for different times of day, seasons, and periods of the solar cycle to study the variations of H m . The results of the analysis are in good agreement with those reported by other authors. A table of values is presented for typical hours of the day and different seasons and solar activity conditions. This study, once extended to a larger database, will support modeling H m as a function of time, season, latitude, solar activity and magnetic activity, and contribute to the formulation of the topside electron density in the IRI model. Ó 2006 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Middle latitude ionosphere; Topside electron density profile; Scale height 1. Introduction Electron density profiles derived from ground-based ionograms provide information up to the F2 layer peak, hmF2. Different true-height inversion programs are avail- able that calculate the bottomside profiles from the iono- gram echo traces (e.g., Huang and Reinisch, 1996; Titheridge, 1985). The information on the topside electron density distribution, usually derived from topside sounder and incoherent scatter radar (ISR) measurements, is scarce, compared with the bottomside. Reinisch and Huang (2001) introduced a new technique of estimating the topside profile from ground-based iono- grams, assuming an a-Chapman function with a constant scale height H m . The scale height is derived from the shape of the bottomside profile near the F2 peak and provides a good estimate for the electron density profile up to around 700 km. Recently Reinisch et al. (2004) have shown that the H m values, produced routinely by Digisondes, can be helpful in improving the formulation of the IRI topside electron density profile (Bilitza, 2001). The objective of the present paper is to analyze the behavior of the scale heights using the F2 layer Digisonde data at two European stations: Ebro (40.4°N, 0.3°E) and 0273-1177/$30 Ó 2006 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2006.11.029 * Corresponding author. Tel.: +54 264 421 3653; fax: +54 264 421 3693. E-mail addresses: mmosert@casleo.gov.ar (M. Mosert), rezquer@ herrera.unt.edu.ar, scytec@frt.utn.edu.ar (R. Ezquer), morenacb@inta.es (B. de la Morena), daltadill@obsebre.es (D. Altadill), amarante@ictp. trieste.it (G. Miro Amarante). www.elsevier.com/locate/asr Advances in Space Research 39 (2007) 755–758