Monitoring Changes of Ice Streams Using Time Series of Satellite-Altimetry-Based Digital Terrain Models

The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar sea represent its gateways to the world's oceans. Satellite radar altimeter data provide an opportunity for mapping surface elevation at kilometer-resolution with meter-accuracy. Geostatistical methods have been developed for the analysis of these data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is the key for a time-series analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics of the ice-stream/ice-shelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice. In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric problem.     

Post-collisional extension of the East Greenland Caledonides: a geophysical perspective

Crustal extension during and following continental collision is well documented in the Arctic Caledonian fold belt. However, models for the post-collisional extension of the Caledonides are mainly based on geoscientific data from Scandinavia. For a more complete understanding of the evolution of the Caledonides, knowledge of the crustal structure of East Greenland is vital. Seismic and gravity studies have revealed a pronounced Moho topography and a west-dipping lower crustal reflector beneath the fjord region of East Greenland. These deep crustal structures are related to Late Caledonian extensional structures at the surface. The observations can be satisfactorily explained by applying simple shear or eduction models proposed for upper crustal extension in Scandinavia to the complementing lower crustal structures in East Greenland. However, exhumation of the Caledonian Northeast Greenland eclogite province cannot be accomplished by these models. Instead, a synthesis of geoscientific data has shown marked differences in the crustal structure of East Greenland north and south of about 76°N, indicating a different crustal evolution of the northern and southern parts of the East Greenland Caledonides.     

Low‐frequency modulation and trend of the relationship between ENSO and precipitation along the northern to centre Peruvian Pacific coast

The relationship between El Niño Southern Oscillation (ENSO) and precipitation along the Peruvian Pacific coast is investigated over 1964–2011 on the basis of a variety of indices accounting for the different types of El Niño events and atmospheric and oceanographic manifestations of the interannual variability in the tropical Pacific. We show the existence of fluctuations in the ENSO/precipitation relationship at decadal timescales that are associated with the ENSO property changes over the recent decades. Several indices are considered in order to discriminate the influence of the two types of El Niño, namely, the eastern Pacific El Niño and the central Pacific El Niño, as well as the influence of large‐scale atmospheric variability associated to the Madden and Julian Oscillation, and of regional oceanic conditions. Three main periods are identified that correspond to the interleave periods between the main climatic transitions over 1964–2011, i.e. the shifts of the 1970s and the 2000s, over which ENSO experiences significant changes in its characteristics. We show that the relationship between ENSO and precipitation along the western coast of Peru has experienced significant decadal change. Whereas El Niño events before 2000 lead to increased precipitation, in the 2000s, ENSO is associated to drier conditions. This is due to the change in the main ENSO pattern after 2000 that is associated to cooler oceanic conditions off Peru during warm events (i.e. central Pacific El Niño). Our analysis also indicates that the two extreme El Niño events of 1982/1983 and 1997/1998 have overshadowed actual trends in the relationship between interannual variability in the tropical Pacific and precipitation along the coast of Peru. Overall, our study stresses on the complexity of the hydrological cycle on the western side of the Andes with regard to its relationship with the interannual to decadal variability in the tropical Pacific. Copyright © 2014 John Wiley & Sons, Ltd.     

Spatio-temporal regression kriging for modelling urban NO2 concentrations

ABSTRACT

Recently developed urban air quality sensor networks are used to monitor air pollutant concentrations at a fine spatial and temporal resolution. The measurements are however limited to point support. To obtain areal coverage in space and time, interpolation is required. A spatio-temporal regression kriging approach was applied to predict nitrogen dioxide (NO₂) concentrations at unobserved space-time locations in the city of Eindhoven, the Netherlands. Prediction maps were created at 25 m spatial resolution and hourly temporal resolution. In regression kriging, the trend is separately modelled from autocorrelation in the residuals. The trend part of the model, consisting of a set of spatial and temporal covariates, was able to explain 49.2% of the spatio-temporal variability in NO₂ concentrations in Eindhoven in November 2016. Spatio-temporal autocorrelation in the residuals was modelled by fitting a sum-metric spatio-temporal variogram model, adding smoothness to the prediction maps. The accuracy of the predictions was assessed using leave-one-out cross-validation, resulting in a Root Mean Square Error of 9.91 μg m^?3, a Mean Error of ?0.03 μg m^?3 and a Mean Absolute Error of 7.29 μg m^?3. The method allows for easy prediction and visualization of air pollutant concentrations and can be extended to a near real-time procedure.     

Trends of persistent organic pollutants in the suspended matter of the River Rhine

Recently amended European (EU) water policies call for an adequate monitoring of the chemical status of sediments and suspended matter (SM) in rivers. In this study, we focus on long‐term time series of particle‐bound hexachlorobenzene (HCB) and selected polychlorinated biphenyls (PCB‐138 and PCB‐153) that were monitored biweekly to monthly at eight stations in the River Rhine catchment. Our aims are (1) to detect trends in the concentration series HCB, PCB‐138 and PCB‐153, (2) to estimate the uncertainty of loads caused by SM collection techniques and load calculation procedures and (3) to detect trends in the subsequently calculated annual load series. HCB concentration in the SM for the period 1995–2008 significantly (p < 0·01) decreased at six of the eight monitoring stations. Decreasing PCB‐138 and PCB‐153 concentrations are significant at six of the eight and seven of the eight monitoring stations, respectively. A two‐way analysis of variance (ANOVA) that tested the effect of two collection techniques and four load calculation procedures on annual loads indicates homogeneity of the methods at four of the five monitoring stations. At Weil, only the loads of HCB, PCB‐138 and PCB‐153 are significantly affected by the collection technique. The trend analysis of an extended series (1985–2007) of annual HCB loads at Koblenz showed a significant decrease from about 110 kg year^?1 to about 15–23 kg year^?1; however, in the shorter period (1995–2007) only at two of the eight monitoring stations decreasing trends of annual contaminant load could be detected. We conclude that any of the tested load calculation procedures can be applied, as loads do no differ systematically. Although a high uncertainty in load estimation exists (e.g. maximum percentage error of E = [18·1, 122·5]% for HCB), the monitoring programme at the Rhine is adequate for analysing the long‐term chemical status of SM. Copyright © 2011 John Wiley & Sons, Ltd.     

Observed spatiotemporal characteristics of drought on various time scales over the Czech Republic

This paper analyses the observed spatiotemporal characteristics of drought in the Czech Republic during the growing season (April to September) as quantified using the Standardised Precipitation Evapotranspiration Index (SPEI) on various time scales. The SPEI was calculated for various lags (1, 3, 6, 12, and 24 months) from monthly records of mean temperature and precipitation totals using a dense network of 184 climatological stations for the period 1961–2010. The characteristics of drought were analysed in terms of the temporal evolution of the SPEI, the frequency distribution and duration of drought at the country level, and for three regions delimited by station altitude. The driest and the wettest years during the growing season were identified. The frequency distribution of the SPEI values for seven drought category classes (in per cent) indicates that normal moisture conditions represent approximately 65 % of the total SPEI values for all time scales in all three regions, whereas moderate drought and moderate wet conditions are almost equally distributed around 10.5 %. Differences in extremely dry conditions (5 %) compared with extremely wet conditions (1.5 %) were observed with increasing SPEI time scales. The results of the non-parametric Mann–Kendall trend test applied to the SPEI series indicate prevailing negative trends (drought) at the majority of the stations. The percentage of stations displaying a significant negative trend for the 90, 95, 99, and 99.9 % confidence levels is approximately 40 %. An Empirical Orthogonal Functions (EOF) analysis was used to identify the principal patterns of variability of the SPEI during the growing season that accounted for the highest amount of statistical variance. The variance explained by the leading EOF range 66 to 56 %, whereas for EOF2 and EOF3, the value is between 7 and 11 % and between 4 and 7 %, respectively, for the SPEI is calculated for 1- to 24-month lags.     

Comparative Study Of The Dust Polarimetric Properties In Split And Normal Comets

Our polarimetric database contains six comets, C/1975 V1 (West), 16P/Brooks 2,C/1988 A1 (Liller), D/1996 Q1 (Tabur), C/1999 S4 (LINEAR), and C/2001 A2(LINEAR), which can be related to the group of split comets. Comets West, S4(LINEAR) and A2 (LINEAR) were observed during splitting. We compare thepolarimetric measurements of the dust particles in these comets, sometimes togetherwith available photometric and colorimetric data, with those in normal comets. Weconclude that there is no significant evidence for differences of polarization betweentidally split comets (e.g., Brooks 2), dissipating comets (e.g., Tabur), non-tidally splitcomets (e.g., West) and normal comets. The total disintegration of Comet S4 (LINEAR), however, did produce significant changes in the observed properties of dust.     

A heat flow and physical properties package for the surface of Mercury

European Space Agencies fifth cornerstone mission BepiColombo includes a ‘Surface Element’ to land a scientific payload on the surface of Mercury. The current strawman payload includes a heat flow and physical properties package (HP³), focussing on key thermal and mechanical properties of the near-surface material (down to a depth of 2–5 m) and the measurement of heat flow from Mercury's interior, an important constraining parameter for models of the planet's interior and evolution. We present here an overview of the HP³ experiment package and its possible accommodation in a self-inserting ‘mole’ device. A mole is considered to be the most appropriate deployment method for HP³, at least in the currently-assumed case of an airbag-assisted soft landing architecture for the Mercury Surface Element.