Global and Seasonal Scintillation Morphology in the Equatorial Region Derived from ROCSAT-1 In-situ Data

The global/seasonal distributions of the scintillation occurrence rate are obtained from the in-situ density measurement of the ROCSAT-1 using a modified procedure reported by Wernik et al. (2007). A least-squares curve fitting in the optimal trust region is used to obtain the spectral slope for the density irregularity structure and the outer scale of the scintillation. The distribution of the S4 index for the weak scintillation (S4 < 0.3) is almost identical to that of the equatorial irregularity distribution reported in the literature. However, as the scintillation becomes stronger (0.3 < S4 < 0.6), the latitudinal distribution moves to the equatorial ionization anomaly (EIA) region. In addition, the distributions of the outer scale values that are useful for the study of the physical evolution of the irregularity structure are also obtained. The occurrence distribution of scintillation activity with several parameters such as dip-latitude, longitude, local time, solar activity, and geomagnetic activity during different seasons are presented and discussed in this paper

Scalar Gravitational Waves Can Be Generated Even Without Direct Coupling Between Dark Energy and Ordinary Matter

We point out, the scalar sector of gravitational perturbations may be excited by an isolated astrophysical system immersed in a universe whose accelerated expansion is not due to the cosmological constant, but due to extra field degrees of freedom. This is true even if the source of gravitational radiation did not couple directly to these additional fields. We illustrate this by considering a universe driven by a single canonical scalar field. By working within the gauge-invariant formalism, we solve for the electric components of the linearised Weyl tensor to demonstrate that both the gravitational massless spin-2 (transverse-traceless) tensor and the (Bardeen) scalar modes are generated by a generic astrophysical source. For concreteness, the Dark Energy scalar field is either released from rest, or allowed to asymptote to the minimum in a certain class of potentials; and we compute the traceless tidal forces induced by gravitational radiation from a hypothetical compact binary system residing in such a universe. Though their magnitudes are very small compared to the tensors', spin zero gravitational waves in such a canonical scalar driven universe are directly sensitive to both the Dark Energy equation of state and the eccentricity of the binary's orbit.Comment: 28 pages, 2 figure