Mesoscale surface circulation and variability of Southern Indian Ocean derived by combining satellite altimetry and drifter observations

High resoultion Eulerian mean velocity field has been derived by combining the satellite tracked surface drifter data with satellite altimetry and ocean surface winds. The drifter data used in this study includes Argos and surface drifter data from Global Drifter Program. Maps of Sea Level Anomaly(MSLA) weekly files with a resolution of(1/3)° in both Latitude and Longitude for the period 1993–2012 have been used. The Ekman current is computed using ocean surface mean wind fields from scatterometers onboard ERS 1/2,Quikscat and ASCAT. The derived mean velocity field exhibits the broad flow of Antarctic Circumpolar Current with speeds up to 0.6 m/s.Anomalous field is quite significant in the western part between 20° and 40°E and in the eastern part between 80°E and 100°E with velocity anomaly up to 0.3 m/s. The estimated mean flow pattern well agrees with the dynamic topography derived from in-situ observations. Also,the derived velocity field is consistent with the in-situ ADCP current measurements. Eddy kinetic energy illustrates an increasing trend during 1993–2008 and is in phase coherence with the Southern Annular Mode by three month lag. Periodic modulations are found in the eddy kinetic energy due the low frequency Antarctic Circumpolar Wave propagation.     

Observations of GRS 1915+105 from the USA Experiment on ARGOS

We present first results from a monitoring campaign of GRS 1915+105 undertaken with the USA X-ray timing experiment on the ARGOS satellite. A variety of behaviour has been observed, ranging from low, steady X-ray emission to rapid quasi-periodic flaring on timescales of approximately 10–120 seconds.     

Severity, duration and frequency of drought in SE England from 1697 to 2011

Severe droughts have affected much of Europe over the last 40 years. A limitation to current understanding of droughts is based around drought characteristics (e.g. frequency, severity and duration) as there are limited long series (>100 years) with well documented severe droughts. This is further complicated with future climate projections, and the potential implications that these will have on drought characteristics. This paper presents reconstructed drought series from 1697, 1726 and 1767 to 2011 for three sites in southeast England. Precipitation and temperature series are reconstructed to generate long drought series using the self-calibrated Palmer Drought Severity Index, enabling determination of drought characteristics. The reconstructions identify multiple drought-rich periods, 1730–1760 and 1890-present, with an increasing tendency towards more severe droughts during the latter period. Prolonged rainfall deficiencies are found to be the primary cause of severe droughts, with rising temperatures increasing soil moisture deficit, therefore intensifying drought conditions. Cycles at the 6–10 year period identify a sub-decadal to decadal signal during drought-rich periods. Analysis of the spatial variability of droughts finds that whilst severe events are predominantly regionally coherent, there are notable variations in severity and duration between sites, which are attributed to localised rainfall variability. This study extends the temporal range of previous drought studies and places recent drought events in a longer context improving upon existing ‘benchmark’ drought analyses in southeast England; with far-reaching implications for local, national and continental scale reduction of drought vulnerability and risk.     

Recombination of electrons with H3+ and H5+ ions

The dissociative recombination coefficients α for capture of electrons by H₃⁺ and H₅⁺ ions have been determined as a function of electron temperature T_e using a microwave afterglow-mass spectrometer apparatus. At ion and neutral temperatures T_u+ = T_n = 240 K, the coefficient α (H₃⁺) is found to vary slowly with T_e at first, decreasing from 1.6 × 10^?7 cm³/s at T_e = 240 K to 1.2 × 10^?7 cm³/s at T_e = 500 K, thereafter falling as T_e^?1 over the range 500 K ? T_e, ? 3000 K. These results, which have a ± 20% uncertainty, agree satisfactorily over the common energy range (0.03–0.36 eV) with the recombination cross sections determined in merged beam measurements by Auerbach et al. At T₊ = T_n = 128 K, the coefficient α(H₅⁺) is found to be (1.8 ± 0.3) × 10^?6 [T_e(K)/300]^?0.69 cm³/s over the range 128 K ? T_e ? 3000 K, with a more rapid decrease, as T_e^?1, between 3000 K and 5500 K. The implications of these results for modelling planetary atmospheres and interstellar clouds are briefly touched on.     

Trends in flood seasonality of the River Ouse (Northern England) from archive and instrumental sources since AD 1600

The last decade has witnessed an increase in the application of historical records (historical and documentary) in developing a more complete understanding of high-magnitude flood frequency; but little consideration has been given to the additional information that documentary accounts contain, particularly relating to flood seasonality. This paper examines the methods and approaches available in long-term flood seasonality analysis and applies them to the River Ouse (Yorkshire) in Northern England since AD 1600. A detailed historical flood record is available for the City of York consisting of annual maxima flood levels since AD 1877, with documentary accounts prior to this. A detailed analysis of long-term flood seasonality requires confidence in the accuracy and completeness of flood records; as a result the augmented flood series are analysed using three strategies: firstly, considering all recorded floods since AD 1600; secondly, through detailed analysis of the more complete record since AD 1800; and finally, applying a threshold to focus on high-magnitude flood events since AD 1800. The results identify later winter flooding, particularly in the second half of the twentieth century, with a notable reduction in summer flood events at York during the twentieth century compared to previous centuries. Flood generating mechanisms vary little between the periods considered, with a general pattern of stability in the ratio of floods incorporating a snowmelt component.     

European floods during the winter 1783/1784: scenarios of an extreme event during the ‘Little Ice Age’

The Lakagígar eruption in Iceland during 1783 was followed by the severe winter of 1783/1784, which was characterised by low temperatures, frozen soils, ice-bound watercourses and high rates of snow accumulation across much of Europe. Sudden warming coupled with rainfall led to rapid snowmelt, resulting in a series of flooding phases across much of Europe. The first phase of flooding occurred in late December 1783–early January 1784 in England, France, the Low Countries and historical Hungary. The second phase at the turn of February–March 1784 was of greater extent, generated by the melting of an unusually large accumulation of snow and river ice, affecting catchments across France and Central Europe (where it is still considered as one of the most disastrous known floods), throughout the Danube catchment and in southeast Central Europe. The third and final phase of flooding occurred mainly in historical Hungary during late March and early April 1784. The different impacts and consequences of the above floods on both local and regional scales were reflected in the economic and societal responses, material damage and human losses. The winter of 1783/1784 can be considered as typical, if severe, for the Little Ice Age period across much of Europe.     

Reconstruction of long-term precipitation records for Edinburgh: an examination of the mechanisms responsible for temporal variability in precipitation

Summary Recent dry years (combined dry winter and summer months) within the UK (2005 and 2006) have enhanced concerns relating to long term water resources and future water provision in large conurbations. This paper examines the mechanisms responsible for precipitation variability for five different areas in Edinburgh (precipitation regions) using composite historic precipitation records for the period 1861–2005. Trend analysis and principal component analysis (PCA) were undertaken to examine precipitation variability over time and space. Annual correlation co-efficients were derived for relationships between precipitation areas, atmospheric–oceanographic variations and geographic parameters. Stepwise regression models were constructed to specify annual precipitation, through atmospheric variations, for each of the precipitation areas. Significant downward trends in precipitation (p < 0.05) were noted in two out of the five precipitation areas, with one principal component representing precipitation variability over Edinburgh and the Pentland Hills. Precipitation variability is best explained by fluctuations in pressure, altitude and proximity to coast. Precipitation trends cannot be explained by changes in atmospheric circulation patterns. Authors’ addresses: N. Macdonald, Department of Geography, University of Liverpool, Liverpool L69 7ZT, United Kingdom; I. D. Phillips, J. Thorpe, School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston B15 2TT, United Kingdom.     

On the origin of the 511-keV emission in the Galactic Centre

Diffuse 511-keV line emission, from the annihilation of cold positrons, has been observed in the direction of the Galactic Centre for more than 30 yr. The latest high-resolution maps of this emission produced by the SPI instrument on INTEGRAL suggest at least one component of the emission is spatially coincident with the distribution of ∼70 luminous, low-mass X-ray binaries detected in the soft gamma-ray band. The X-ray band, however, is generally a more sensitive probe of X-ray binary populations. Recent X-ray surveys of the Galactic Centre have discovered a much larger population (>4000) of faint, hard X-ray point sources. We investigate the possibility that the positrons observed in the direction of the Galactic Centre originate in pair-dominated jets generated by this population of fainter accretion-powered X-ray binaries. We also consider briefly whether such sources could account for unexplained diffuse emission associated with the Galactic Centre in the microwave (the Wilkinson Microwave Anisotropy Probe 'haze') and at other wavelengths. Finally, we point out several unresolved problems in associating Galactic Centre 511-keV emission with the brightest X-ray binaries.     

A GIS Approach to Exploring Monetary Value on Enclosure Era Property-Related Maps

Historical enclosure era property-related maps can tell us a great deal about the life and times of communities in the past. This study offers a unique approach to studying the historical landscape by applying GIS techniques to the examination of an eighteenth-century English village. Using novel GIS applications relying on historical maps, the study explores various aspects of the village’s physical and social characteristics. In doing so, the study forges effective linkages between cultural and landscape variables to reveal aspects of the historical landscape in eighteenth-century Britain previously inaccessible to researchers. This, in turn, provides a much more comprehensive and sophisticated template for future use by historical geographers in a number of contexts.     

How effective is the new generation of GPM satellite precipitation in characterizing the rainfall variability over Malaysia?

We investigated the potential of the new generation of satellite precipitation product from the Global Precipitation Mission (GPM) to characterize the rainfall in Malaysia. Most satellite precipitation products have limited ability to precisely characterize the high dynamic rainfall variation that occurred at both time and scale in this humid tropical region due to the coarse grid size to meet the physical condition of the smaller land size, sub-continent and islands. Prior to the status quo, an improved satellite precipitation was required to accurately measure the rainfall and its distribution. Subsequently, the newly released of GPM precipitation product at half-hourly and 0.1° resolution served an opportunity to anticipate the aforementioned conflict. Nevertheless, related evidence was not found and therefore, this study made an initiative to fill the gap. A total of 843 rain gauges over east (Borneo) and west Malaysia (Peninsular) were used to evaluate the rainfall the GPM rainfall data. The assessment covered all critical rainy seasons which associated with Asian Monsoon including northeast (Nov. - Feb.), southwest (May - Aug.) and their subsequent inter-monsoon period (Mar. - Apr. & Sep. - Oct.). The ability of GPM to provide quantitative rainfall estimates and qualitative spatial rainfall patterns were analysed. Our results showed that the GPM had good capacity to depict the spatial rainfall patterns in less heterogeneous rainfall patterns (Spearman’s correlation, 0.591 to 0.891) compared to the clustered one (r = 0.368 to 0.721). Rainfall intensity and spatial heterogeneity that is largely driven by seasonal monsoon has significant influence on GPM ability to resolve local rainfall patterns. In quantitative rainfall estimation, large errors can be primarily associated with the rainfall intensity increment. 77% of the error variation can be explained through rainfall intensity particularly the high intensity (> 35 mm d^-1). A strong relationship between GPM rainfall and error was found from heavy (~35 mm d^-1) to violent rain (160 mm d^-1). The output of this study provides reference regarding the performance of GPM data for respective hydrology studies in this region.