A Long-Term Decrease of the Mid-Size Segmentation Lengths Observed in the He <Emphasis Type="SmallCaps">ii</Emphasis> (30.4 nm) Solar EUV Emission

Power spectra of segmentation-cell length (a dominant length scale of EUV emission in the transition region) from full-disk He?ii extreme ultraviolet (EUV) images observed by the Extreme ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during periods of quiet-Sun conditions for a time interval from 1996 to 2015 were analyzed. The spatial power as a function of the spatial frequency from about 0.04 to 0.27 (EIT) or up to 0.48 (AIA) Mm^?1 depends on the distribution of the observed segmentation-cell dimensions – a structure of the solar EUV network. The temporal variations of the spatial power reported by Didkovsky and Gurman (Solar Phys. 289, 153, 2014) were suggested as decreases at the mid-spatial frequencies for the compared spectra when the power curves at the highest spatial frequencies of 0.5 pix^?1 were adjusted to match each other. This approach has been extended in this work to compare spectral ratios at high spatial frequencies expressed in the solar spatial frequency units of Mm^?1. A model of EIT and AIA spatial responses allowed us to directly compare spatial spectral ratios at high spatial frequencies for five years of joint operation of EIT and AIA, from 2010 to 2015. Based on this approach, we represent these ratio changes as a long-term network transformation that may be interpreted as a continuous dissipation of mid-size network structures to the smaller-size structures in the transition region. In contrast to expected cycling of the segmentation-cell dimension structures and associated spatial power in the spectra with the solar cycle, the spectra demonstrate a significant and steady change of the EUV network. The temporal trend across these structural spectra is not critically sensitive to any long-term instrumental changes, e.g. degradation of sensitivity, but to the change of the segmentation-cell dimensions of the EUV network structure.     

GPS for real-time earthquake source determination and tsunami warning systems

We identify the key design aspects of a GPS-based system (and in the future, GNSS-based systems) that could contribute to real-time earthquake source determination and tsunami warning systems. Our approach is based on models of both transient and permanent displacement of GPS stations caused by large earthquakes, while considering the effect of GPS errors on inverted earthquake source parameters. Our main conclusions are that (1) the spatial pattern, magnitude, and timing of permanent displacement of GPS stations can be inverted for the earthquake source and so predict the 3D displacement field of the ocean bottom, thus providing the initial conditions for tsunami models, and (2) there are no inherently limiting factors arising from real-time orbit and positioning errors, provided sufficient near-field GPS stations are deployed. This signal could be readily exploited by GPS networks currently in place, and will be facilitated by the IGS Real-Time Project as it comes to fruition.     

Circulation on the north central Chukchi Sea shelf

Mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central Chukchi shelf. Previous studies indicated that Pacific waters crossed the Chukchi shelf through Herald Valley (in the west) and Barrow Canyon (in the east). We find a third branch (through the Central Channel) onto the outer shelf. The Central Channel transport varies seasonally in phase with Bering Strait transport, and is 0.2 Sv on average, although some of this might include water entrained from the outflow through Herald Valley. A portion of the Central Channel outflow moves eastward and converges with the Alaskan Coastal Current at the head of Barrow Canyon. The remainder appears to continue northeastward over the central outer shelf toward the shelfbreak, joined by outflow from Herald Valley. The mean flow opposes the prevailing winds and is primarily forced by the sea-level slope between the Pacific and Arctic oceans. Current variations are mainly wind forced, but baroclinic forcing, associated with upstream dense-water formation in coastal polynyas might occasionally be important.Winter water-mass modification depends crucially on the fall and winter winds, which control seasonal ice development. An extensive fall ice cover delays cooling, limits new ice formation, and results in little salinization. In such years, Bering shelf waters cross the Chukchi shelf with little modification. In contrast, extensive open water in fall leads to early and rapid cooling, and if accompanied by vigorous ice production within coastal polynyas, results in the production of high-salinity (>33) shelf waters. Such interannual variability likely affects slope processes and the transport of Pacific waters into the Arctic Ocean interior.     

Towards global space geodetic mapping of the dynamic deformation field after great earthquakes

GPS systems can be used as seismometers by sampling ground positions to detect travelling seismic waves. Data from dense geodetic networks near large earthquakes have been used to improve magnitude estimates, for tsunami warning, and to better understand the rupture processes. Here, we present 1 Hz GPS records of the March 11th, 2011, Mw = 9.0 Tohoku earthquake at unprecedented teleseismic distances. The spatial and temporal variations of the three‐dimensional GPS displacement vector field show various body waves, Love and Rayleigh surface waves along the direct path, and Love waves from the more than 31 000 km long major arc path. These results suggest that seismic wavefields can be mapped at teleseismic distances globally using space geodesy and could thus be used for source and structural studies. Data from numerous real‐time kinematic GPS networks could be combined to show the displacement field, giving unparalleled views of Earth's response to large earthquakes.     

High-pressure–low-temperature metamorphism of metasedimentary rocks, southern Menderes Massif, western Turkey

Kilometer-scale lenses of quartz-rich metasedimentary rocks crop out in a discontinuous belt along the southern margin of the Menderes Massif, Turkey, and preserve evidence for high-pressure–low-temperature (HP–LT) metamorphism related to subduction of a continental margin during Alpine orogeny. Kyanite schist, quartzite, and quartz veins contain kyanite + phengite + Mg-chlorite, and the veins also contain magnesiocarpholite. A deformed carbonate metaconglomerate juxtaposed with the quartzite-dominated unit does not contain HP index minerals, and likely represents the tectonized boundary of the siliceous rocks with adjacent marble. The HP–LT rocks (10–12 kbar, 470–570 °C) record different pressure conditions than the adjacent, apparently lower pressure Menderes metasedimentary sequence. Despite this difference there is disagreement as to whether these HP–LT rocks are part of the Menderes sequence or are related to the tectonically overlying Cycladic blueschist unit. If the former, the entire southern Menderes Massif experienced HP–LT metamorphism but the evidence has been obliterated from most rocks; if the latter, rocks recording different metamorphic-kinematic conditions experienced different tectonic histories and were tectonically juxtaposed during thrusting. Based on observations and data in this study, the second model better accounts for the differences in P–T-deformation histories of the southern Menderes Massif rocks, and suggests that the HP–LT rocks are not part of the Menderes cover sequence.     

Establishing a framework for Open Geographic Information science

When conducting research within a framework of Geographic Information Science (GISc), the scientific validity of this work can be argued as highly dependent upon the extent to which the methods employed are reproducible, and that, in the strictest sense, can only be fully achieved by implementing transparent workflows that utilize both open source software and openly available data. After considering the scientific implications of non-reproducible methods, we provide a review of both open source Geographic Information Systems (GIS) and openly available data, before describing an integrated model for Open GISc. We conclude with a critical review of this embryonic paradigm, with directions for future development in supporting spatial data infrastructure.     

Extension and Intensification of the Meso-American mid-summer drought in the twenty-first century

Recent global-scale analyses of the CMIP3 model projections for the twenty-first century indicate a strong, coherent decreased precipitation response over Central America and the Intra-America Seas region. We explore this regional response and examine the models’ skill in representing present-day climate over this region. For much of Central America, the annual cycle of precipitation is characterized by a rainy season that extends from May to October with a period of reduced precipitation in July and August called the mid-summer drought. A comparison of the climate of the twentieth century simulations (20c3m) with observations over the period 1961–1990 shows that nearly all models underestimate precipitation over Central America, due in part to an underestimation of sea surface temperatures over the tropical North Atlantic and an excessively smooth representation of regional topographical features. However, many of the models capture the mid-summer drought. Differences between the A1B scenario (2061–2090) and 20c3m (1961–1990) simulations show decreased precipitation in the future climate scenario, mostly in June and July, just before and during the onset of the mid-summer drought. We thus hypothesize that the simulated twenty-first century drying over Central America represents an early onset and intensification of the mid-summer drought. An analysis of circulation changes indicates that the westward expansion and intensification of the North Atlantic subtropical high associated with the mid-summer drought occurs earlier in the A1B simulations, along with stronger low-level easterlies. The eastern Pacific inter-tropical convergence zone is also located further southward in the scenario simulations. There are some indications that these changes could be forced by ENSO-like warming of the tropical eastern Pacific and increased land–ocean heating contrasts over the North American continent.     

CMIP3 projected changes in the annual cycle of the South American Monsoon

Nine models from the Coupled Model Intercomparison Project version 3 dataset are employed to examine projected changes in the South American Monsoon System annual cycle by comparing the 20th Century and SRES A2 scenarios. The following hypotheses are examined: (1) the warm season climate responses in the Southeast, Continental South Atlantic Convergence Zone (CSACZ) and Monsoon regions are related by regional circulation and moisture transport changes which, in turn, must be consistent with robust large-scale changes in the climate system, and (2) an increased threshold for convection in a warmer world may affect the timing of warm season rains. The present analysis reaffirms that the Southeast region is likely to experience increased precipitation through the warm season. Additional results exhibit more uncertainty due to large inter-model variance and disagreement in the A2 scenarios. Nevertheless several statistically significant results are found. In the Monsoon and to a lesser extent in the CSACZ region, the multi-model median suggests reduced precipitation during spring (Sep–Nov). These continental precipitation changes are accompanied by a southward shift of the maximum precipitation in the South Atlantic Convergence Zone. Changes in circulation include a poleward displaced South Atlantic Anticyclone (SAAC) and enhanced moisture transport associated with a strengthened northerly low level flow east of the Andes during spring. Moisture transport divergence calculations indicate unchanged divergence in the Monsoon region during spring and increased convergence in the Southeast throughout the warm season. The circulation and moisture transport changes suggest the increased precipitation in the Southeast during spring may be related to changes in the SALLJ and SAAC, which both enhance moisture transport to the Southeast. The seasonally dry Monsoon region is further affected by an increased threshold for convection in the warmer, more humid and stable climate of the 21st century, which combined with the circulation changes may weaken the onset of the rainy season. Although there is substantial variability among the models, and the results are represented by small changes compared with the multi-model variance, their statistical significance combined with their consistency with expected robust large scale changes provides a measure of confidence in otherwise tentative results. Further testing of the relationships presented here will be required to fully understand projected changes in the South American Monsoon.     

Effects of urbanization on streamflow in the Atlanta area (Georgia,USA): a comparative hydrological approach

For the period from 1958 to 1996, streamflow characteristics of a highly urbanized watershed were compared with less‐urbanized and non‐urbanized watersheds within a 20 000 km² region in the vicinity of Atlanta, Georgia: in the Piedmont and Blue Ridge physiographic provinces of the southeastern USA. Water levels in several wells completed in surficial and crystalline‐rock aquifers were also evaluated. Data were analysed for seven US Geological Survey (USGS) stream gauges, 17 National Weather Service rain gauges, and five USGS monitoring wells. Annual runoff coefficients (RCs; runoff as a fractional percentage of precipitation) for the urban stream (Peachtree Creek) were not significantly greater than for the less‐urbanized watersheds. The RCs for some streams were similar to others and the similar streams were grouped according to location. The RCs decreased from the higher elevation and higher relief watersheds to the lower elevation and lower relief watersheds: values were 0·54 for the two Blue Ridge streams, 0·37 for the four middle Piedmont streams (near Atlanta), and 0·28 for a southern Piedmont stream. For the 25 largest stormflows, the peak flows for Peachtree Creek were 30% to 100% greater than peak flows for the other streams. The storm recession period for the urban stream was 1–2 days less than that for the other streams and the recession was characterized by a 2‐day storm recession constant that was, on average, 40 to 100% greater, i.e. streamflow decreased more rapidly than for the other streams. Baseflow recession constants ranged from 35 to 40% lower for Peachtree Creek than for the other streams; this is attributed to lower evapotranspiration losses, which result in a smaller change in groundwater storage than in the less‐urbanized watersheds. Low flow of Peachtree Creek ranged from 25 to 35% less than the other streams, possibly the result of decreased infiltration caused by the more efficient routing of stormwater and the paving of groundwater recharge areas. The timing of daily or monthly groundwater‐level fluctuations was similar annually in each well, reflecting the seasonal recharge. Although water‐level monitoring only began in the 1980s for the two urban wells, water levels displayed a notable decline compared with non‐urban wells since then; this is attributed to decreased groundwater recharge in the urban watersheds due to increased imperviousness and related rapid storm runoff. Copyright © 2001 John Wiley & Sons, Ltd.