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Abstract. In this paper, variations in the ionospheric F2 layer's critical frequency are decomposed into their periodic and aperiodic components. The latter include disturbances caused both by geophysical impacts on the ionosphere and random noise. The spectral whitening method (SWM), a signal-processing technique used in statistical estimation and/or detection, was used to identify aperiodic components in the ionosphere. The whitening algorithm adopted herein is used to divide the Fourier transform of the observed data series by a real envelope function. As a result, periodic components are suppressed and aperiodic components emerge as the dominant contributors. Application to a synthetic data set based on significant simulated periodic features of ionospheric observations containing artificial (and, hence, controllable) disturbances was used to validate the SWM for identification of aperiodic components. Although the random noise was somewhat enhanced by postprocessing, the artificial disturbances could still be clearly identified. The SWM was then applied to real ionospheric observations. It was found to be more sensitive than the oftenused monthly median method to identify geomagnetic effects. In addition, disturbances detected by the SWM were characterized by a Gaussian-type probability density function over all timescales, which further simplifies statistical analysis and suggests that the disturbances thus identified can be compared regardless of timescale.

[1] We report accelerated particles observed by Solar Wind Ion Detectors (SWIDs) on Chang'E-1 spacecraft close to terminator regions of the Moon. As the spacecraft crosses the terminator, a stream of ions with energy of ∼200eV/q are detected. As the spacecraft moves to the anti-subsolar point of the Moon, the energy of these ions increase by 600 ∼ 1500eV. This phenomenon occurs at north/south pole when IMF B y component is dominant and negative/ positive. It is proposed these particles are scattered solar wind protons, accelerated by the convection electric field of the solar wind and E × B drift in the ambipolar electric field at the flank of the lunar wake. This mechanism allows a new portion of solar wind protons to enter the central lunar wake, and provides a possibility to study the property of proton scattering at the dayside of the Moon.

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Crystal-growth velocity in metallic melts has been reported by others to increase monotonically with undercooling. Nevertheless, such an observation is not predicted by conventional growth theory. In this work, the metallic melt of Zr 50 Cu 50 is studied to address the problem by measuring the growth velocity over a wide range of undercooling up to 325 K. A maximum growth velocity is observed at an undercooling of 200 K instead of the monotonic increase reported in the literature. We find that the planar or dendrite growth theories can explain the value of the maximum growth velocity, but the predicted location of the maximum in undercooling is far less than that seen by experiment. With the assistance of current results, a general pattern of crystal growth is established for melts of a variety of substances, where all sluggish crystal-growth kinetics is explained by the diffusion-controlled mechanism at deep undercooling.

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[1] The record-low thermospheric density during the last solar minimum has been reported and it has been mainly explained as the consequence of the anomalously low solar extreme ultraviolet (EUV) irradiance. In this study, we examined the variation of the energy budget to the Earth's upper atmosphere during last solar cycle from both solar EUV irradiance and geomagnetic energy, including Joule heating and particle precipitation. The globally integrated solar EUV power was calculated from the EUV flux model for aeronomic calculations (EUVAC) driven by the MgII index. The annal average of solar power in 2008 was 33 GW lower than that in 1996. The decrease of the globally integrated geomagnetic energy from 1996 to 2008 was close to 29 GW including 13 GW for Joule heating from Weimer (2005b) and 16 GW for particle precipitation from NOAA Polar-Orbiting Environmental Satellites (POES) measurements. Although the estimate of the solar EUV power and geomagnetic energy vary from model to model, the reduction of the geomagnetic energy was comparable to the solar EUV power. The Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) simulations indicate that the solar irradiance and geomagnetic energy variations account for 3/4 and 1/4 of the total neutral density decrease in 2008, respectively.