Atmospheric tides below 80 km

Measurements and theory of diurnal and semidiurnal tidal oscillations between about 25 and 80 km are reviewed. At latitudes greater than about 30°, meridional (N-S) wind components are consistently in quadrature with and similar to the zonal (E-W) components. The tidal structures are interpreted as a superposition of quasi-steady higher-order modes excited in the troposphere by sources of limited extent (1,000–10,000 km). At latitudes less than about 30°, steady or quasi-steady diurnal and semidiurnal components are not necessarily the dominant components of the daily variation. At high latitudes diurnal phases generally show little change with height in comparison with observations at lower latitudes, in accord with the latitudinal properties of diurnal modes with positive and negative equivalent depths.     

Characterization of GNSS scintillations over Lagos,Nigeria during the minimum and ascending phases (2009–2011) of solar cycle 24

This study characterizes equatorial scintillations at L-band frequency over Lagos, Nigeria during the minimum and ascending phases of solar cycle 24. Three years (2009–2011) of amplitude scintillation data were used for the investigation. The data were grouped on daily, monthly, seasonal, and yearly scales at three levels of scintillation (weak (0.3 ? S₄ < 0.4), moderate (0.4 ? S₄ < 0.7), and intense (S₄ ? 0.7)). To ensure reliable statistical inferences, three data cut-off criteria were adopted. Scintillations were observed to have a daily trend of occurrence during the hours of 1900–0200 LT, and higher levels of scintillations were localized within the hours of 2000–2300 LT. On monthly basis, September and October recorded the highest occurrences of scintillation, while January recorded the least. Scintillations were recorded during all the months of 2011, except January. Surprisingly, pockets of scintillation events (weak levels) were also observed during the summer months (May, June, and July). Seasonally, equinoxes recorded the highest occurrences of scintillation, while June solstice recorded the least occurrences. Scintillation activity also increases with solar and geomagnetic activity. On a scintillation active day, the number of satellites available to the receiver’s view reduces as the duration of observation reduces. These results may support the development of future models that could provide real-time predictability of African equatorial scintillations, with a view to supporting the implementation of GNSS-based navigation for aviation applications in Africa.     

Probability distribution of complex monopulse ratio with arbitrary correlation between channels

The joint distribution of the real and imaginary parts of the monopulse ratio (MR) is obtained for a monopulse radar with arbitrarily correlated Gaussian noise and non-zero means in the sum and difference channels. The general result is used to consider thresholding and to develop the marginal density for the real part of the MR for the special case of real correlation between the channels.