ALBERT

Description: We report calculations with first-principles density-functional theory and Landau–Devonshire theory that provide an atomic-scale mechanism for the composition- and pressure-induced relaxor ferroelectrics. A multiphase with coexisted cubic structures (MPCCS) is found to correspond to any of the composition- and pressure-induced relaxor ferroelectrics. On the other hand, a normal ferroelectric without relaxor behavior is structurally characterized by a single phase. Furthermore, the presence of the MPCCS in a composition- and pressure-induced relaxor increases the degrees of freedom of relaxors and no energy barriers are involved for the rotations of the polarization direction, leading to high electromechanical coefficients.

Description: During stratospheric sudden warming (SSW) periods large changes in the low latitude vertical drift have been observed at Jicarmarca as well as in other longitudinal sectors. In general a strengthening of the daytime maximum vertical drift with a shift from pre-noon to the afternoon is observed. During the January 2013 stratospheric warming significant longitudinal differences in the equatorial vertical drift were observed. At Jicarmarca the previously reported SSW behavior prevails, however no shift of the daytime maximum drift was exhibited in the African sector. Using the National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) the possible causes for the longitudinal difference are examined. The timing of the strong SSW effect in the vertical drift (15–20 January) coincides with moderate geomagnetic activity. The simulation indicates that approximately half of the daytime vertical drift increase in the American sector may be related to the moderate geophysical conditions (Kp=4) with the effect being negligible in the African sector. The simulation suggests that the wind dynamo accounts for approximately 50% of the daytime vertical drift in the American sector and almost 100% in the Africansector. The simulation agrees with previous findings that the migrating solar tides and the semidiurnal westward propagating tide with zonal wave number 1 (SW1) mainly contribute to the daytime wind dynamo and vertical drift. Numerical experiments suggest that the neutral wind and the geomagnetic main field contribute to the presence (absence) of a local time shift in the daytime maximum drift in the American (African) sector.

Description: The subsidy of carbon derived from macrophytes and associated periphyton to bacterioplankton and zooplankton in subtropical shallow eutrophic Huizhou West Lake in China was analyzed using carbon stable isotope signatures. A restored part of the lake dominated by macrophytes was compared with an unrestored phytoplankton-dominated part. Macrophytes, periphyton, seston, and zooplankton were sampled every two months to determine natural-abundance carbon isotope ratios ( δ 13 C). The δ 13 C of phytoplankton and bacterioplankton was determined from δ 13 C of fatty acid biomarkers. Macrophytes and associated periphyton had similar δ 13 C values and were the most enriched in 13 C of all measured organic carbon pools. A macrophyte–periphyton carbon isotopic signal was detected in particulate organic carbon, bacterioplankton, and zooplankton in the macrophyte-dominated lake part, which was demonstrated by a significant enrichment in 13 C compared with the unrestored part, while phytoplankton and dissolved organic carbon had similar δ 13 C values in both lake parts. A two-source (macrophytes–periphyton and phytoplankton) mixing model showed that macrophytes–periphyton potentially contributed 14–85% (average 55%) to bacterioplankton in the macrophyte-dominated lake part, depending on season. The macrophytes–periphyton contribution to zooplankton seasonally varied between 26% and 86%, with an average of 47%. The contribution of macrophytes–periphyton to bacterioplankton increased with increasing macrophyte biomass relative to phytoplankton biomass (indicated by chlorophyll a ). Carbon from macrophytes with associated periphyton subsidizes bacterioplankton and zooplankton, likely enhancing the cascading effects of planktonic food webs, providing an additional explanation for the stability of a clear-water state in shallow lakes dominated by macrophytes.

Description: [1]  Using multiple pairs of IMAGE ground magnetometers together with simultaneous measurements from two of the THEMIS spacecraft constellation, when they were flying over the magnetometers in magnetic conjunction and in close azimuthal separation, we are able to calculate the phase differences of Ultra Low Frequency (ULF) Field-Line Resonances (FLR), and, through that, their azimuthal mode number, wavelength and propagation characteristics. A Cross-Wavelet Technique is applied, that exposes the times and frequencies of common power between time series from azimuthally aligned magnetometers in space or on the ground, yielding their relative phase. Using the amplitude ratio and phase differences between ground stations with similar longitudes that are separated in latitude, a correction to the mode number calculation is demonstrated, accounting for the phase differences that arise from the L-shell separation of the THEMIS probes.

Description: The spatial distribution of 〉38 keV electron fluxes in the central plasma sheet (CPS) and the statistical relationship between the CPS electron fluxes and the upstream solar wind and interplanetary magnetic field (IMF) parameters are investigated quantitatively using measurements from the Geotail satellite (1998–2004) at geocentric radial distances of 9-30 RE in the night side. The measured electron fluxes increase with closer distance to the center of the neutral sheet, and exhibit clear dawn-dusk asymmetry, with the lowest fluxes at the dusk side and increasing toward the dawn side. The asymmetry persists along the Earth's magnetotail region (at least to Geotail's apogee of 30 RE during the period of interest). Both the individual case and the statistical analysis on the relationship between 〉38 keV CPS electron fluxes and solar wind and IMF properties show that larger (smaller) solar wind speed and southward (northward) IMF Bz imposed on the magnetopause result in higher (lower) energetic electron fluxes in the CPS with a time delay of about 1 hour, while the influence of solar wind ion density on the energetic electrons fluxes is insignificant. Interestingly, the energetic electron fluxes at a given radial distance correlate better with IMF Bz than with the solar wind speed. Based on these statistical analyses, an empirical model is developed for the first time to describe the 2-D distribution (along and across the Earth's magnetotail) of the energetic electron fluxes (〉38 keV) in the CPS, as a function of the upstream solar wind and IMF parameters. The model reproduces the observed energetic electron fluxes well, with a correlation coefficient R equal to 0.86. Taking advantage of the time delay, full spatial distribution of energetic electron fluxes in the CPS can be predicted about 2 hours in advance using the real-time solar wind and IMF measurements at the L1 point: 1 hour for the solar wind to propagate to the magnetopause and a 1 hour delay for the best correlation. Such a prediction helps us to determine whether there are enough electrons in the CPS available to be transported inward to enhance the outer electron radiation belt.

Description: Gravity waves have a significant impact on both the dynamics and energy budget of the Martian thermosphere. Strong density variations of spatial scales indicative of gravity waves have previously been identified in this region using in situ observations. Here we use observations from the NGIMS mass spectrometer on MAVEN to identify such waves in the observations of different atmospheric species. The wave signatures seen in CO 2 and Ar are almost identical, whereas the wave signature seen in N 2 , which is lighter and has a larger scale height, are generally smaller in amplitude and slightly out of phase with those seen in CO 2 and Ar. Examination of the observed wave properties in these three species suggest that relatively long vertical wavelength atmospheric gravity waves are the likely source of the waves seen by NGIMS in the upper thermosphere. A two-fluid linear model of the wave perturbations in CO 2 and N 2 has been used to find the best-fit intrinsic wave parameters that match the observed features in these two species. We report the first observationally based estimate of the heating and cooling rates of the Martian thermosphere created by the waves observed in this region. The observed wave density amplitudes are anti-correlated with the background atmospheric temperature. The estimated heating rates show a weak positive correlation with the wave amplitude, whereas the cooling rates show a clearer negative correlation with the wave amplitude. Our estimates support previous model-based findings that atmospheric gravity waves are a significant source of both heating and cooling.

Description: Cryospheric changes have great effects on alpine hydrology, but these effects are still unclear owing to rare observations and suitable models in the western cold regions of China (WCRC). Based on long-term field observations in the WCRC, a cryospheric basin hydrological model (CBHM) was proposed to evaluate the cryospheric effects on streamflow in the upper Hei river basin (UHR), and the relationship between the cryosphere and streamflow was further discussed with measured data. The Norwegian Earth System Model (NorESM1-ME) outputs were chosen to project future streamflow under scenarios RCP2.6, RCP4.5, and RCP8.5. The CBHM results were well validated by the measured precipitation, streamflow, evapotranspiration, soil temperature, glacier and snow cover area, and the water balance of land cover in the UHR. The moraine-talus region contributed most of the runoff (60%), even though it made up only about 20% of the area. On average, glacier and snow cover respectively contributed 3.5% and 25.4% of the fresh water to the streamflow in the UHR between 1960 and 2013. Because of the increased air temperature (2.9°C/54a) and precipitation (69.2 mm/54a) over the past 54 years, glacial and snowmelt runoff increased by 9.8% and 12.1%, respectively. The increase in air temperature brought forward the snowmelt flood peak and increased the winter flow due to permafrost degradation. Glaciers may disappear in the near future because of their small size, but snowmelt would increase due to increases in snowfall in the higher mountainous areas, and the basin runoff would increase slightly in the future.