Longitudinal differences in the equatorial spread F characteristics between Vietnam and Brazil

We present the results of a comparative study of the equatorial spread F (ESF) and the F layer critical parameter, the base height of the F layer bottomside (h′F) over the two equatorial sites, Ho Chi Minh City – HCM (dip latitude: 2.9°N) in Vietnam and Sao Luis – SL (dip latitude: ∼2°S) in Brazil. The study utilizes simultaneous data collected by a CADI at HCM and a digisonde at SL during the year 2002 with the monthly mean solar 10.7 cm flux (F10.7) varying from ∼120 to ∼185. This study focuses on the quiet time seasonal behavior of the F layer parameters in the two widely separated longitude sectors, and addresses the question as to what can we learn from such comparative studies with respect to the ambient ionospheric and thermospheric parameters that are believed to control the ESF generation and hence its longitudinal occurrence pattern. The observed differences/similarities in the diurnal and seasonal patterns of the F Layer height vis-à-vis the ESF occurrences are evaluated in terms of the known longitudinal differences in the F layer heights, thermospheric meridional winds and the geomagnetic peculiarities of the two sites.     

Amplitude—frequency analysis of Chandler oscillations of the Earth’s pole

An approximate nonlinear spectral-correlation model of fluctuations of the amplitude—frequency characteristics of the Chandler self-excited oscillations of the Earth’s pole is considered. The sensitivity of the model parameters to the asymmetry and anisotropy of fluctuation-dissipative moments of forces and to the effect of harmonic gravitation-tidal moments of forces is studied at Chandler frequency and frequencies close to it. The results of analytical and statistical modeling of the stability of the amplitude—frequency characteristics are presented. The influence of fluctuation disturbances of the white noise type on spectral-correlation characteristics of the oscillations is investigated.