Daytime geomagnetic disturbances at high latitudes during a strong magnetic storm of June 21–23, 2015: The storm initial phase

The high-latitude geomagnetic effects of an unusually long initial phase of the largest magnetic storm (SymH ~–220 nT) in cycle 24 of the solar activity are considered. Three interplanetary shocks characterized by considerable solar wind density jumps (up to 50–60 cm^–3) at a low solar wind velocity (350–400 km/s) approached the Earth’s magnetosphere during the storm initial phase. The first two dynamic impacts did not result in the development of a magnetic storm, since the IMF Bz remained positive for a long time after these shocks, but they caused daytime polar substorms (magnetic bays) near the boundary between the closed and open magnetosphere. The magnetic field vector diagrams at high latitudes and the behaviour of high-latitude long-period geomagnetic pulsations (ipcl and vlp) made it possible to specify the dynamics of this boundary position. The spatiotemporal features of daytime polar substorms (the dayside polar electrojet, PE) caused by sudden changes in the solar wind dynamic pressure are discussed in detail, and the singularities of ionospheric convection in the polar cap are considered. It has been shown that the main phase of this two-stage storm started rapidly developing only when the third most intense shock approached the Earth against a background of large negative IMF Bz values (to–39 nT). It was concluded that the dynamics of convective vortices and the related restructing of the field-aligned currents can result in spatiotemporal fluctuations in the closing ionospheric currents that are registered on the Earth’s surface as bay-like magnetic disturbances.     

The Earth’s passage of the April 11, 1997 coronal ejecta: geomagnetic field fluctuations at high and low latitude during northward interplanetary magnetic field conditions

An analysis of the low frequency geomagnetic field fluctuations at an Antarctic (Terra Nova Bay) and a low latitude (L’Aquila, Italy) station during the Earth’s passage of a coronal ejecta on April 11, 1997 shows that major solar wind pressure variations were followed at both stations by a high fluctuation level. During northward interplanetary magnetic field conditions and when Terra Nova Bay is close to the local geomagnetic noon, coherent fluctuations, at the same frequency (3.6 mHz) and with polarization characteristics indicating an antisunward propagation, were observed simultaneously at the two stations. An analysis of simultaneous measurements from geosynchronous satellites shows evidence for pulsations at approximately the same frequencies also in the magnetospheric field. The observed waves might then be interpreted as oscillation modes, triggered by an external stimulation, extending to a major portion of the Earth’s magnetosphere.     

The wetting ability of Si-bearing liquid Fe-alloys in a solid silicate matrix—percolation during core formation under reducing conditions?

The wetting characteristics of liquid Fe–Si alloys in a matrix of the respective predominating stable silicate mantle mineral (forsterite or silicate perovskite) at pressures of 2–5 and 25 GPa and temperatures of 1600–2000 °C were studied by determining the liquid metal–solid silicate contact angles. The median angle values from texturally equilibrated samples were found to be independent of pressure, temperature, silicate mineralogy and the Si content in the metal fraction and range between 130° and 140° which is far above the critical wetting boundary of 60°. This shows that within the studied range of conditions dissolved Si does not lower the surface energies between Fe-rich liquids and silicate mantle grains. As a consequence, under reducing conditions the presence of Si in the metal phase of planetary bodies would not have enhanced percolative flow as an effective metal–silicate separation process.     

Assessing the status of an artisanal shrimp fishery in a Ramsar wetland in Jamaica: The effects of seasonality,extreme La Niña episodes and elevated temperature on landings

An invasive crayfish, Cherax quadricarinatus, and several native shrimp species (Macrobrachium acanthurus, Macrobrachium faustinum, Macrobrachium carcinus, Xiphocaris elongata, and Atyidae sp.) found in the Black River Lower Morass (BRLM), a Ramsar Wetland in Jamaica, support subsistence and artisanal fisheries. Management of this fishery requires information on factors that influence their abundance. Consequently, we assessed the effects of seasonality, extreme and double La Niña episodes (in 2011) and elevated atmospheric temperature (in 2011 and 2012) on weekly Decapoda landing data, collected over a period of two years (2010–2012). The catch of native species showed a cyclical trend every 6 months, coinciding with the dry and wet seasons. The invasive crayfish landing showed a reverse trend during the first year, after which no pattern could be discerned. A dynamic factor analysis (DFA) model with two common trends and four explanatory variables (conductivity, mean weekly number of traps hauled, weekly mean water level, and mean dissolved oxygen) was the optimal model to characterize the variation in wet-weight landings. A generalized additive mixed model with an auto-regressive moving average (ARMA) error structure was used to show that the extreme and double La Niñas were associated with lower monthly atmospheric temperature. Sea surface temperature anomaly in region 3 (a proxy to ENSO) and the trend in temperature were then used to predict the wet weight of native shrimp (U-shaped relationship) and the invasive crayfish (reverse-j shaped relationship), respectively. The native shrimp (mean sustainable yield, MSY = 3469 kg and mean catch per fisher = 2.67 kg) and invasive crayfish (MSY = 11 kg and mean catch per fisher = 0.67 kg) are under fished, although populations of the native shrimp are possibly declining, whereas that of the invasive crayfish may be growing. The declining trend may have adverse implications for the stock of the native shrimp species, which has a higher economic value, if fishing pressure is not reduced/restricted or increased on the invasive crayfish, especially during seasonal and/or ENSO related declines in native shrimp stocks.     

A need for incentivizing field hydrology,especially in an era of open data: discussion of “The role of experimental work in hydrological sciences – insights from a community survey”*

The sharing of data and collection of new data are both essential, but they are not inherently complementary. When data are openly available, researchers may be motivated to use those data rather than collect more because field work has costs and risks. The competitive advantage to those who do not put resources towards fieldwork may discourage field hydrology. Allocating efforts towards generating field data, which benefits hydrological sciences, is not necessarily best for individual hydrologists, especially in an era of open data. The objective of this work is to open a conversation on whether individuals’ best interests may contrast with the community’s desire for new observations. If the community wants new field observations, there is a need to consider the shifting balance of incentives and disincentives for pursuing field studies in hydrology.     

Oceanographical patterns during a summer upwelling–downwelling event in the Northern Galician Rias: Comparison with the whole Ria system (NW of Iberian Peninsula)

Summer upwelling and downwelling processes were characterized in the Northern Galician Rias during July and August 2008 by means of sampling carried out onboard R/V Mytilus (CSIC) and R/V Lura (IEO). Thermohaline variables, dissolved oxygen, nutrients, chlorophyll, phytoplankton, ciliates and zooplankton abundances were measured at sections located in the Rias of Viveiro, Barqueiro and Ortigueira and their adjacent shelves. Ekman transport was calculated from QuikSCAT satellite, upwelling intensity estimated with upwelling index from the average daily geostrophic winds, and SST maps obtained from NASA GHRSST satellite. Ekman transport and SST behaviour showed two different patterns: (i) offshore and upwelling favourable conditions on 13–22nd of July; (ii) onshore and downwelling favourable conditions from 23rd July to 19th August. During upwelling, TS diagram showed an intrusion of Eastern North Atlantic Central Water affecting the continental shelf but not the rias. Nutrient salt concentrations increased with depth, reaching their maximum values near the mouth of Ortigueira Ria. During downwelling, coastal water increased its temperature (18.5–19.8 °C) and was retained inside rias; nutrients were nearly depleted, except for the innermost ria (estuarine zone) due to fluvial nutrient inputs. In this inner area, the maximum of chlorophyll-a (Barqueiro Ria) was observed. Low phytoplankton abundances were measured in both cases, even though a short increase in the plankton biomass was observed inside rias during upwelling, while under downwelling a small red tide of Lingulodinium polyedrum was detected. During the upwelling period Northern Rias tend to be mesotrophic systems as revealed by nutrient concentrations, chlorophyll levels and plankton abundances. On the contrary, in similar situations, the Western Rias behaves as eutrophics.