Long Term Changes in UV and EUV Solar Radiation

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

San Jose

Congreso; 5ta COLAGE, Conferencia LatinoAmericana de Geofísica Espacial; 1998

ALAGE, Asociacion LatinoAmericana de Geofisica Espacial

There are hints which indicate that the total solar irradiance (TSI) would present the same long-term variations as the solar cycle length (SCL). This variation correspond to an 80-90 year periodicity called the Gleissberg cycle, and it is expected that, when SCL decrease, TSI increase and vice versa. In this work we use stratospheric, ionospheric and solar data analysis to show that there is UV and EUV solar radiation whose long-term varaitions do not depend on the sunspot number, Rz. We call these radiations UVr and EUVr. EUVr seems to have the long-term periodicity that SCL has. However, in this case it is expected that when SCL decrease EUV also decrease, and when SCL increase, EUV increase. Stratospheric temperature data shows the same behavior as ionospheric data. For this reason we assume that UVr would have the same long-term variation as EUVr. Through ionospheric data we estimate the long-term variation in EUVr to be around 2%. Although this variation is quite small in percentage terms, is much bigger than the 0.25% expected in TSI, so it should be taken into account in atmospheric processes involving long-term variations of the UV and EUV solar radiation (ionization processes, ozone depletion, stratospheric temperature variability, etc.).