“EQUATORIAL TEC OVER SOUTH AMERICAN SECTOR WITH DIFFERENT MAGNETIC DECLINATION ANGLES” P. A. B. Nogueira *1, M. A. Abdu 1, J. R. Souza 1, I. S. Batista 1, E. B. Shume 1, R.Y.C. Cueva 1, C.V. Ely 1, G. J. Bailey 2. 1 Instituto Nacional de Pesquisas Espaciais, Caixa Postal 515, São José dos Campos, SP, Brasil; 2 Department of Applied Mathematics, University of Sheffield, Sheffield, S3 7RH, U.K

Abstract  TEC longitudinal variation;  Magnetic Declination Angles Dependence; São Luís (2.33° S, 315.8ºE, declination = -19 o ) in Brazil Arequipa (16.5°S, 288.5ºE, declination = 0.5 o ) in Perú  TEC variations for three solar activity levels;  TEC values over São Luís are larger than that ones over Arequipa;  SUPIM model has been used to investigate such difference.

TEC Longitudinal Variation It is well known:  TEC data show strong annual/semiannual, solar cycle, and 27-days variations. However, it is not known:  How is the TEC variation associated with different magnetic declination angles?

TEC Temporal Pattern and Magnetic Declination Angle Effect It is well known that the magnetic declination angle may affect:  The PRE vertical ExB drift (Batista et al., 1986);  The plasma bubble development (Abdu et al., 1981);  EEJ pattern (Shume et al., 2010).

GPS Receivers Station Arequipa: GPS Receiver ROGUE SNR-8000 São Luís GPS Receiver: Turbo Rogue ICS-400Z Allen-Osborne Associates Receivers.

TEC Seasonal Variation- 2001

Local Time Comparison: 0 – 6 LT

Local Time Comparison: 6 – 12 LT

Local Time Comparison: 12 – 18 LT

Local Time Comparison: 18 – 24 LT

foF2 Seasonal Variation- 2001

SUPIM MODEL

Observational Data vs Ionospheric Modelling

TEC Seasonal Variation- 2005

TEC Seasonal Variation

Changing SL GPS Receiver São Luís: GPS Receiver NetR K03649 Arequipa: GPS Receiver ROGUE SNR-8000

TEC Semiannual Variation Period

Summary TEC semiannual variation during daytime was establish, with two peak located over the equinoctial condition. The period of the TEC semiannual variation is better represented over high solar activity with period equal to ~185 days. The highest TEC magnitude was found over São Luís, the main reason for this feature could be attributed to the large negative declination angle over Brazil.

ACKNOWLEDGEMENT Paulo A. B. Nogueira acknowledges the supports from CNPQ for his PhD program.

Semiannual Variation

Olatunji (1967) found that this semiannual variation might be related to the variation of the noon solar zenith angle. However, Ross (1966) suggested that the variation of the intensity of the equatorial electrojet (EEJ) is mainly responsible for the semiannual TEC variation. Anderson et al. (2002) showed that during daytime, the vertical ExB drift velocity in the equatorial F-region is positively related to the EEJ intensity. For that it is necessary to consider the noon zenith angle and the daytime ExB drift simultaneously, and then the cause of the semiannual TEC variation might be the combination of these two factors. In the equinoctial months, because both the daytime ExB drift and the cosine of the noon zenith angle are larger simultaneously, the TEC has greatest values. On the other hand, for the summer (winter) months, the cosine of the noon zenith angle is larger (smaller), but the daytime ExB drift is smaller (larger). Therefore, the TEC values are smaller in these two seasons than in the equinoctial months. But, the TEC seasonal behavior in the Brazilian region would be an interesting discussion In the Brazilian region the cosine of the zenith angle at noon is the greatest at the equinoxes, moderate in summer and lower in winter solstice (with that a semiannual variation could be expected). Moreover, as the daytime F region electric fields are controlled by the E region dynamo process and the E region is controlled by tides, knowing that tidal winds have a semi-annual variation (Ma et al., 2003) then the F region should behave similarly. However, Shume et al. (2010) showed that the equatorial electrojet in the Brazilian region (São Luis), unlike that observed in Jicamarca, does not present a semiannual behavior (with peaks it the equinox) and an annual component dominates (maximum in summer solstices), (see also Muralikrishna e Abdu 1988).