Long term decreasing of the ionospheric F2 Layer peak height at a southern low latitude station

NIEVES ORTIZ DE ADLER; ANA G. ELIAS; TERESITA HEREDIA

Praga

Workshop; 2nd Workshop on Long-term changes and trends in the atmosphere; 2001

IAGA - ICMA - CAWSES

The trend of the peak height of the ionospheric F2 layer, hmF2, during three solar cycles (1957-1986) at Tucuman (26.9°S, 65.4°W), located at the southern crest of the equatorial anomaly, has been estimated. hmF2 was calculated from M(3000) records at 12 LT using Shimazaki equation which has been tested with real height values obtained from rescaled ionograms. After filtering the effects of solar cycle variations, hmF2 shows a mean decrease of 0.3 km/year (9 km in 30 years). The decrease in hmF2 is qualitatively consistent, but larger than that estimated theoretically as a consequence of a cooling of the thermosphere produced by the increase in greenhouse gases concentration. A decrease of 14% in the maximum ionospheric electron density, NmF2, was observed at the same station for the same period in a previous work of the authors. The theory of a cooling in the thermosphere seems to be not enough to explain the simultaneous decrease in hmF2 and NmF2.