Two Current Systems in the Preliminary Phase of Sudden Commencements in the Magnetosphere

The geomagnetic variations of the preliminary impulse (PI) of the sudden commencement (SC) are known to show a time delay of the peak displacement and longer duration time in the higher latitudes in the pre-noon and post-noon sectors of the polar region. This peculiar behavior of the PI geomagnetic variation is associated with temporal deformation of the ionospheric PI field-aligned current (FAC) distribution into a crescent shape; its lower-latitude edge extends toward the anti-sunward direction, and its higher-latitude edge almost stays on the same longitude near noon. Numerical simulations revealed that the deformation of the FAC distribution is derived from different behaviors of the two PI current systems. The first current system consists of the FAC connected to the PI FAC in the lower latitude side of the ionosphere, the cross-magnetopause current, and the magnetosheath current (type L current system). The cross-magnetopause current is the inertia current generated in the acceleration front of the solar wind due to the sudden compression of the magnetosheath. Thus, the longitudinal speed of the type L current system in the ionosphere is the solar wind speed in the magnetosheath projected into the ionosphere. In contrast, the PI current system connected to the PI FAC at higher latitude (type H current system) consists of the upward/downward FAC in the pre-noon/post-noon sector, respectively, and dawn-to-dusk field-perpendicular current (FPC) along the dayside magnetopause. The dawn-to-dusk FPC moves to the higher latitudes in the outer magnetosphere over time. The FAC of the type H current system is converted from the FPC due to convergence of the return FPC heading toward the sunward direction in the outer magnetosphere; the return FPC is the inertia current driven by the magnetospheric plasma flow associated with compression of the magnetopause behind the front region of the accelerated solar wind. The acceleration front spreads concentrically from the subsolar point. Consequently, as the return FPC is converted to the FAC of the type H current system, it does not move much in the longitudinal direction over time because the dawn-to-dusk FPC of the type H current system moves to the higher latitudes. Therefore, the high-latitude edge of the PI current distribution in the ionosphere moves only slightly. Finally, we clarified that the FPC-FAC conversion of the type L current system mainly occurs in the region where the Alfvén speed starts to increase toward the Earth. A region with a steep gradient of the Alfvén speed like the plasmapause is not always necessary for conversion from the FPC to the FAC. We also suggest the possible field-aligned structure of the standing Alfvén wave that may occur in the PI phase.

Characterizing tundra snow sub-pixel variability to improve brightness temperature estimation in satellite SWE retrievals

Topography and vegetation play a major role in sub-pixel variability of Arctic snowpack properties but are not considered in current passive microwave (PMW) satellite SWE retrievals. Simulation of sub-pixel variability of snow properties is also problematic when downscaling snow and climate models. In this study, we simplified observed variability of snowpack properties (depth, density, microstructure) in a two-layer model with mean values and distributions of two multi-year tundra dataset so they could be incorporated in SWE retrieval schemes. Spatial variation of snow depth was parameterized by a log-normal distribution with mean (μsd) values and coefficients of variation (CVsd). Snow depth variability (CVsd) was found to increase as a function of the area measured by a remotely piloted aircraft system (RPAS). Distributions of snow specific surface area (SSA) and density were found for the wind slab (WS) and depth hoar (DH) layers. The mean depth hoar fraction (DHF) was found to be higher in Trail Valley Creek (TVC) than in Cambridge Bay (CB), where TVC is at a lower latitude with a subarctic shrub tundra compared to CB, which is a graminoid tundra. DHFs were fitted with a Gaussian process and predicted from snow depth. Simulations of brightness temperatures using the Snow Microwave Radiative Transfer (SMRT) model incorporating snow depth and DHF variation were evaluated with measurements from the Special Sensor Microwave/Imager and Sounder (SSMIS) sensor. Variation in snow depth (CVsd) is proposed as an effective parameter to account for sub-pixel variability in PMW emission, improving simulation by 8 K. SMRT simulations using a CVsd of 0.9 best matched CVsd observations from spatial datasets for areas > 3 km2, which is comparable to the 3.125 km pixel size of the Equal-Area Scalable Earth (EASE)-Grid 2.0 enhanced resolution at 37 GHz.

Weather & weather systems at Schirmacher Oasis (Maitri) during recent two decades - A review

Indian Antarctic station Maitri experiences varying external influences from interior of east Antarctica as well as moving depressions and cyclones along the coast. The relative position of circumpolar trough and strengthening of high pressure centre near pole influences variation of atmospheric pressure at Maitri. The diurnal, daily and seasonal variation of temperature mainly depend upon moving pressure systems, katabatic winds, change of solar insulation with change of seasons, reflectivity from clouds and snow surface. The katabatic winds prevail over Maitri which is highly directional from South- East sector due to increase of slope towards south. The blizzards are main weather at Maitri, fog and white out are occasional phenomena. The precipitation is mostly in form of snowfall but rain is very rare at Maitri. Heavy or moderate snowfall indicative of active front leading edge of warm air masses being transported southwards. Strong temperature variant near Schirmacher oasis give precipitation in form of snow. Fog occurred due to slow movement of relatively warm air from lower latitude over the colder surface. Winter season witnessed more snowfall accumulation at Maitri than other season. During summer rise of temperature accompanied with absorption of latent heat by ice pellets in low level of atmosphere results precipitation in form of water droplets. Highest number of blizzards occurs during winter season whereas lowest number of blizzards occurs during summer season. Normally due to cyclonic activities, warm air masses transported towards the Schirmacher oasis which causes rise of temperature at Maitri. Longer duration of the blizzards over the station depends upon strength of slow moving blocking anticyclone situated east of Maitri at lower latitude. Tremendous fluctuation of atmospheric electric field observed before onset is a pre-indication of commencement of blizzards.

Variationas of energy and aerodynamic terms at different stations of India

Variations and relative contributions of energy and aerodynamic terms to evaporation, from different stations of India are studied. Energy term shows higher value during first few weeks from the beginning of the year, at stations located at lower latitude, while its value retains high at stations lying on higher longitude except for Thiruvananthapuram. Aerodynamic term is found to be high at stations located at higher latitude, while except for Calcutta, its value is seen to be higher for the stations situated on higher longitude. Considerable variations in the percentage contribution of the energy and the aerodynamic terms are observed at stations situated at higher latitude. Stations situated at lower latitude show high and low value of percentage contribution of the energy and the aerodynamic terms In most of the weeks during the year. Relative shares of the energy term to evaporation are comparatively high at stations situated in higher longitude, while a higher percentage contribution of the aerodynamic term. is observed at stations located at lower longitude except for Nagpur.

A Unified Model for the Fan Region and the North Polar Spur: A Bundle of Filaments in the Local Galaxy

We present a simple, unified model that can explain two of the brightest, large-scale, diffuse, polarized radio features in the sky, the North Polar Spur (NPS) and the Fan Region, along with several other prominent loops. We suggest that they are long, magnetized, and parallel filamentary structures that surround the Local arm and/or Local Bubble, in which the Sun is embedded. We show that this model is consistent with the large number of observational studies on these regions and is able to resolve an apparent contradiction in the literature that suggests that the high-latitude portion of the NPS is nearby, while lower-latitude portions are more distant. Understanding the contributions of this local emission is critical to developing a complete model of the Galactic magnetic field. These very nearby structures also provide context to help understand similar nonthermal, filamentary structures that are increasingly being observed with modern radio telescopes.

Using conservation translocations to assess the impact of anthropogenic climate change on a cold-adapted reptile, the tuatara (Sphenodon punctatus)

<p>Anthropogenic climate change is progressing at a rate unprecedented in the past 65 million years and is a significant conservation concern. The associated biotic and abiotic impacts are expected to have substantial effects on global biodiversity, with some species potentially more vulnerable than others. The tuatara (Sphenodon punctatus) is a New Zealand endemic reptile and of particular interest as it is a slowly reproducing, range-restricted, cold-adapted ectotherm with temperature-dependent sex determination. Consequently, tuatara could be particularly vulnerable to rising air temperatures and conservation translocations have been key components of tuatara conservation efforts. Knowledge of how the tuatara might be affected by warmer climates will help inform where future conservation efforts are best directed, practices to avoid and which sites might be most suitable for the establishment of populations. The translocation of 176 adult tuatara in October 2012 from Stephens Island in New Zealand’s Cook Strait to four latitudinally distant North Island sites offered the opportunity to study the responses of tuatara in a range of environments. The comparatively warmer, drier climates of several sites provided surrogates for temporal climate change, enabling an assessment of how a warming climate might impact tuatara, and how they might respond. Using field observations, laboratory analysis and controlled experiments I investigated the short-term success of the translocations, the influence of translocation and climate on tuatara enteric bacterial communities and parasites, as well as how warmer climates might influence nocturnal activity, thermoregulatory opportunities and learning ability. I found several translocated populations to be progressing favourably, and found evidence that tuatara may exhibit enhanced growth at warmer, less densely-populated sites, suggesting that further translocations to lower latitude sites might be a viable conservation strategy. However, high population density at one translocation site was a concern and management recommendations were made to enable the dispersal of individuals. I detected Salmonella Saintpaul for the first time in a live tuatara, Campylobacter spp. was identified as a likely common commensal organism, and no measurable impact of translocation or climate on bacterial prevalence was observed, suggesting no substantial risk of climate warming to the susceptibility of tuatara to these bacteria. Tick populations were negatively impacted by translocation-associated factors following release but subsequently recovered at most sites and mites were not found on any translocated tuatara. Diurnal and nocturnal activities were positively influenced by air temperature, up to an upper threshold, and assessment of the site-specific thermal climates suggested that tuatara at warmer sites may benefit from increased opportunities for emergence and the attainment of preferred body temperatures throughout the year, though a higher frequency of restrictive air temperatures over summer may also reduce emergence opportunities. Experimental work showed that warmer air temperatures may enhance learning in tuatara, which could improve their ability to cope with challenging environments under climate change. However, body size was also an influential component of learning ability and further research is needed to build on these initial findings. I conclude that tuatara may experience overall benefits from further translocations to warmer sites and warming climates at currently cooler sites, which suggests that other cold-adapted reptiles with similar thermal tolerances may also see initial benefits under climate warming, though further monitoring is required to determine longer-term translocation success. Equally, while warmer air temperatures were not found to be detrimental to tuatara, they still pose a risk to population viability and further work is required on the impacts of associated abiotic factors like drought, and how populations of this long-lived species may be affected if and when climate warming exceeds the upper temperature rise of ~5°C predicted by the 2100s.</p>

Using conservation translocations to assess the impact of anthropogenic climate change on a cold-adapted reptile, the tuatara (Sphenodon punctatus)

<p>Anthropogenic climate change is progressing at a rate unprecedented in the past 65 million years and is a significant conservation concern. The associated biotic and abiotic impacts are expected to have substantial effects on global biodiversity, with some species potentially more vulnerable than others. The tuatara (Sphenodon punctatus) is a New Zealand endemic reptile and of particular interest as it is a slowly reproducing, range-restricted, cold-adapted ectotherm with temperature-dependent sex determination. Consequently, tuatara could be particularly vulnerable to rising air temperatures and conservation translocations have been key components of tuatara conservation efforts. Knowledge of how the tuatara might be affected by warmer climates will help inform where future conservation efforts are best directed, practices to avoid and which sites might be most suitable for the establishment of populations. The translocation of 176 adult tuatara in October 2012 from Stephens Island in New Zealand’s Cook Strait to four latitudinally distant North Island sites offered the opportunity to study the responses of tuatara in a range of environments. The comparatively warmer, drier climates of several sites provided surrogates for temporal climate change, enabling an assessment of how a warming climate might impact tuatara, and how they might respond. Using field observations, laboratory analysis and controlled experiments I investigated the short-term success of the translocations, the influence of translocation and climate on tuatara enteric bacterial communities and parasites, as well as how warmer climates might influence nocturnal activity, thermoregulatory opportunities and learning ability. I found several translocated populations to be progressing favourably, and found evidence that tuatara may exhibit enhanced growth at warmer, less densely-populated sites, suggesting that further translocations to lower latitude sites might be a viable conservation strategy. However, high population density at one translocation site was a concern and management recommendations were made to enable the dispersal of individuals. I detected Salmonella Saintpaul for the first time in a live tuatara, Campylobacter spp. was identified as a likely common commensal organism, and no measurable impact of translocation or climate on bacterial prevalence was observed, suggesting no substantial risk of climate warming to the susceptibility of tuatara to these bacteria. Tick populations were negatively impacted by translocation-associated factors following release but subsequently recovered at most sites and mites were not found on any translocated tuatara. Diurnal and nocturnal activities were positively influenced by air temperature, up to an upper threshold, and assessment of the site-specific thermal climates suggested that tuatara at warmer sites may benefit from increased opportunities for emergence and the attainment of preferred body temperatures throughout the year, though a higher frequency of restrictive air temperatures over summer may also reduce emergence opportunities. Experimental work showed that warmer air temperatures may enhance learning in tuatara, which could improve their ability to cope with challenging environments under climate change. However, body size was also an influential component of learning ability and further research is needed to build on these initial findings. I conclude that tuatara may experience overall benefits from further translocations to warmer sites and warming climates at currently cooler sites, which suggests that other cold-adapted reptiles with similar thermal tolerances may also see initial benefits under climate warming, though further monitoring is required to determine longer-term translocation success. Equally, while warmer air temperatures were not found to be detrimental to tuatara, they still pose a risk to population viability and further work is required on the impacts of associated abiotic factors like drought, and how populations of this long-lived species may be affected if and when climate warming exceeds the upper temperature rise of ~5°C predicted by the 2100s.</p>

Stable Silicon Isotopes Uncover a Mineralogical Control on the Benthic Silicon Cycle in the Arctic Barents Sea

Biogeochemical cycling of silicon (Si) in the Barents Sea is under considerable pressure from physical and chemical changes, including dramatic warming and sea ice retreat, together with a decline in dissolved silicic acid (DSi) concentrations of Atlantic inflow waters since 1990. Moreover, further expansion of the Atlantic realm (termed `Atlantification') is expected to shift phytoplankton community compositions away from diatom-dominated spring bloomsin favour of Atlantic flagellate species (coccolithophore-dominated). The changes in pelagic primary production will alter the composition of the material comprising the depositional flux, which will subsequently in influence the recycling processes at and within the seafloor. In this study we assess the predominant controls on the early diagenetic cycling of Si, a key nutrient in marine ecosystems, by combining stable isotopic analysis of pore water DSi and of operationally defined reactive pools of the solid phase. We show that low biogenic silica (BSi) contents (0.39-0.52 wt% or 92-185 μmol g dry wt-1) drive correspondingly low asymptotic concentrations of pore water DSi (~100 μM). However, while these surface sediments appear almost devoid of BSi, we present evidence for the rapid recycling of bloom derived BSi that generates striking transient peaks in sediment pore water [DSi], which is a feature that is subject to future shifts in phytoplankton community compositions. Using a simple mass balance calculation we show that the pore water DSi pool is supplemented by a lithogenic Si source (LSi), while our sediment pore water Si isotopic profiles also uncover a coupling of the iron (Fe) and Si cycles. This has previously been observed in lower latitude marine sediment systems and thus provides further support for a redox influence on oceanic pore water DSi. We suggest that a high LSi:BSi ratio and apparent Fe (oxyhydr)oxide influence could lead to a degree of stability in the annual background benthic flux of DSi despite the pressures on pelagic phytoplankton communities. Coupled with supporting isotopic evidence for the precipitation of authigenic clays in Barents Sea sediment cores, our observations have implications for the sink vs recycling terms in the regional Si budget.

Dynamical Splitting of Spot-producing Magnetic Rings in a Nonlinear Shallow-water Model

We explore the fundamental physics of narrow toroidal rings during their nonlinear magnetohydrodynamic evolution at tachocline depths. Using a shallow-water model, we simulate the nonlinear evolution of spot-producing toroidal rings of 6° latitudinal width and a peak field of 15 kG. We find that the rings split; the split time depends on the latitude of each ring. Ring splitting occurs fastest, within a few weeks, at latitudes 20°–25°. Rossby waves work as perturbations to drive the instability of spot-producing toroidal rings; the ring split is caused by the “mixed stress” or cross-correlations of perturbation velocities and magnetic fields, which carry magnetic energy and flux from the ring peak to its shoulders, leading to the ring split. The two split rings migrate away from each other, the high-latitude counterpart slipping poleward faster due to migrating mixed stress and magnetic curvature stress. Broader toroidal bands do not split. Much stronger rings, despite being narrow, do not split due to rigidity from stronger magnetic fields within the ring. Magnetogram analysis indicates the emergence of active regions sometimes at the same longitudes but separated in latitude by 20° or more, which could be evidence of active regions emerging from split rings, which consistently contribute to observed high-latitude excursions of butterfly wings during the ascending, peak, and descending phases of a solar cycle. Observational studies in the future can determine how often new spots are found at higher latitudes than their lower-latitude counterparts and how the combinations influence solar eruptions and space weather events.

Poleward migration of western North Pacific tropical cyclones related to changes in cyclone seasonality

The average location of observed western North Pacific (WNP) tropical cyclones (TCs) has shifted north over the last several decades, but the cause remains not fully understood. Here we show that, for the annual average, the observed northward migration of WNP TCs is related to changes in TC seasonality, not to a northward migration in all seasons. Normally, peak-season (July–September) TCs form and travel further north than late-season (October–December) TCs. In recent decades, related to less frequent late-season TCs, seasonally higher-latitude TCs contribute relatively more to the annual-average location and seasonally lower-latitude TCs contribute less. We show that the change in TC seasonality is related to the different responses of late-season and peak-season TC occurrence to a stronger Pacific Walker Circulation. Our findings provide a perspective on long-term trends in TC activity, by decomposing the annual-average statistics into seasonal components, which could respond differently to anthropogenic forcing.