Comparing plasma bubble occurrence rates at CHAMP and GRACE altitudes during high and low solar activity

Based on the multi-year data base (2001–2009) of CHAMP Planar Langmuir Probe (PLP) data and GRACE K-Band Ranging (KBR1B) data, typical features of ionospheric plasma irregularities are studied at the altitudes of CHAMP (300–400 km) and GRACE (~500 km). The phenomena we are focusing on are the equatorial plasma bubbles (EPBs). Similar seasonal/longitudinal (S/L) distributions of EPB have been found at both CHAMP and GRACE altitudes during solar active and quiet years. Peak EPB occurrence rates, defined as number of events within an S/L bin divided by the number of passes over that bin, decrease from the high and moderate solar flux period (2001–2005) to the low solar flux period (2005–2009) from 80% to 60% and 60% to 40% at CHAMP and GRACE altitudes, respectively. On average the occurrence rate increases linearly with solar flux at about the same rate at CHAMP and GRACE. For high flux levels (P10.7>200) non-linear increases are observed at GRACE. The occurrence rate increases rapidly after 19:00 local time (LT) during high solar flux periods. Around solar minimum rates increase more gently and peak around 22:00 LT. The highest occurrence rates are encountered at latitudes around 10° north and south of the dip equator. Results from the two altitudes support the notion that EPBs form regions of depleted plasma along geomagnetic fluxtubes. It is shown for the first time that in regions of high occurrence rates EPBs are associated with fluxtubes reaching greater apex heights than those in regions of low rates

Succession of the sea-surface microlayer in the coastal Baltic Sea under natural and experimentally induced low-wind conditions

The sea-surface microlayer (SML) is located within the boundary between the atmosphere and hydrosphere. The high spatial and temporal variability of the SML's properties, however, have hindered a clear understanding of interactions between biotic and abiotic parameters at or across the air-water interface. Among the factors changing the physical and chemical environment of the SML, wind speed is an important one. In order to examine the temporal effects of minimized wind influence, SML samples were obtained from the coastal zone of the southern Baltic Sea and from mesocosm experiments in a marina to study naturally and artificially calmed sea surfaces. Organic matter concentrations as well as abundance, (3)H-thymidine incorporation, and the community composition of bacteria in the SML (bacterioneuston) compared to the underlying bulk water (ULW) were analyzed. In all SML samples, dissolved organic carbon and nitrogen were only slightly enriched and showed low temporal variability, whereas particulate organic carbon and nitrogen were generally greatly enriched and highly variable. This was especially pronounced in a dense surface film (slick) that developed during calm weather conditions as well as in the artificially calmed mesocosms. Overall, bacterioneuston abundance and productivity correlated with changing concentrations of particulate organic matter. Moreover, changes in the community composition in the field study were stronger in the particle-attached than in the non-attached bacterioneuston. This implies that decreasing wind enhances the importance of particle-attached assemblages and finally induces a succession of the bacterial community in the SML. Eventually, under very calm meteorological conditions, there is an uncoupling of the bacterioneuston from the ULW

Simulação do impacto das atividades florestais na fragilidade potencial em plantios de pinus.

Este trabalho, realizado em uma área com povoamento de Pinus taeda, teve por objetivo simular e mapear a influência do valor de impacto das atividades florestais na fragilidade potencial. Variáveis do solo, de declividade do terreno, valor de impacto e de cobertura vegetal foram utilizadas para gerar os mapas. Os resultados expressos pelo modelo adotado mostraram que as áreas mais frágeis apresentam em sua maioria declividades superiores a 75 % e textura que variam de arenosa a média, e as áreas menos frágeis apresentam predominantemente relevo plano (até 3 %) e textura argilosa. Quando simulado o impacto das atividades florestais sobre esse ambiente, verificou-se que na maior parte da área (78 %) todas as atividades florestais podem ser realizadas sem influência na degradação do meio ambiente e para algumas áreas (11 %) o ambiente foi considerado menos frágil, em razão da presença de cobertura vegetal

Extended description of tunnel junctions for distributed modeling of concentrator multi-junction solar cells

One of the key components of highly efficient multi-junction concentrator solar cells is the tunnel junction interconnection. In this paper, an improved 3D distributed model is presented that considers real operation regimes in a tunnel junction. This advanced model is able to accurately simulate the operation of the solar cell at high concentraions at which the photogenerated current surpasses the peak current of the tunnel junctionl Simulations of dual-junction solar cells were carried out with the improved model to illustrate its capabilities and the results have been correlated with experimental data reported in the literature. These simulations show that under certain circumstances, the solar cells short circuit current may be slightly higher than the tunnel junction peak current without showing the characteristic dip in the J-V curve. This behavior is caused by the lateral current spreading toward dark regions, which occurs through the anode/p-barrier of the tunnel junction

Geomagnetic data from the GOCE satellite mission

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) is part of ESA’s Earth Explorer Program. The satellite carries magnetometers that control the activity of magnetorquers for navigation of the satellite, but are not dedicated as science instruments. However, intrinsic steady states of the instruments can be corrected by alignment and calibration, and artificial perturbations, e.g. from currents, can be removed by their characterisation correlated to housekeeping data. The leftover field then shows the natural evolution and variability of the Earth’s magnetic field. This article describes the pre-processing of input data as well as calibration and characterisation steps performed on GOCE magnetic data, using a high-precision magnetic field model as reference. For geomagnetic quiet times, the standard deviation of the residual is below 13 nT with a median residual of (11.7, 9.6, 10.4) nT for the three magnetic field components (x, y, z). For validation of the calibration and characterisation performance, we selected a geomagnetic storm event in March 2013. GOCE magnetic field data show good agreement with results from a ground magnetic observation network. The GOCE mission overlaps with the dedicated magnetic field satellite mission CHAMP for a short time at the beginning of 2010, but does not overlap with the Swarm mission or any other mission flying at low altitude and carrying high-precision magnetometers. We expect calibrated GOCE magnetic field data to be useful for lithospheric modelling and filling the gap between the dedicated geomagnetic missions CHAMP and Swarm. Graphic Abstract: [Figure not available: see fulltext.]

Field-aligned current associated with low-latitude plasma blobs as observed by the CHAMP satellite

Here we give two examples of low-latitude plasma blobs accompanied by linearly polarized perpendicular magnetic deflections which imply that associated field-aligned currents (FACs) have a 2-D sheet structure located at the blob walls. The estimated FAC density is of the order of 0.1 μA/m<sup>2</sup>. The direction of magnetic deflections points westward of the magnetic meridian and there is a linear correlation between perpendicular and parallel variations. All these properties are similar to those of equatorial plasma bubbles (EPBs). According to CHAMP observations from August 2000 to July 2004, blobs show except for these two good examples no clear signatures of 2-D FAC sheets at the walls. Generally, perpendicular magnetic deflections inside blobs are weaker than inside EPBs on average. Our results are consistent with existing theories: if a blob exists, (1) a significant part of EPB FAC will be closed through it, exhibiting similar perpendicular magnetic deflection inside EPBs and blobs, (2) the FAC closure through blobs leads to smaller perpendicular magnetic deflection at its poleward/downward side, and (3) superposition of different FAC elements might result in a complex magnetic signature around blobs