Martin W. Miles

Analysis of merged SMMR‐SSMI time series of Arctic and Antarctic sea ice parameters 1978–1995

The most consistent means of investigating the global sea ice cover is by satellite passive microwave sensors, as these are independent of illumination and cloud cover. The Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) and the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSMI) provide information on the global sea ice cover from 1978 to present. The two instruments flew simultaneously during a 6-week overlap period in July and August 1987, thus enabling intercomparison of the two sensors. Brightness temperatures are corrected for instrument drift and calibration differences in order to produce continuous time series of monthly averaged Arctic and Antarctic sea ice extent and sea ice area through the use of the NOrwegian Remote Sensing EXperiment (NORSEX) algorithm, which relates brightness temperatures to ice concentration. Statistical analysis on the time series estimates the decreases in Arctic ice extent and ice area to be 4.5% and 5.7%, respectively, during the 16.8-year observation period. The overall trends established here serve to better define and strengthen earlier assertions of a reduced ice cover, based on analysis of SMMR and SSMI data taken separately. These results are consistent with GCM simulations that suggest retreat of the sea ice cover under global warming scenarios.

Recent Ice-Sheet Growth in the Interior of Greenland

A continuous data set of Greenland Ice Sheet altimeter height from European Remote Sensing satellites (ERS-1 and ERS-2), 1992 to 2003, has been analyzed. An increase of 6.4 ± 0.2 centimeters per year (cm/year) is found in the vast interior areas above 1500 meters, in contrast to previous reports of high-elevation balance. Below 1500 meters, the elevation-change rate is –2.0 ± 0.9 cm/year, in qualitative agreement with reported thinning in the ice-sheet margins. Averaged over the study area, the increase is 5.4 ± 0.2 cm/year, or ∼60 cm over 11 years, or ∼54 cm when corrected for isostatic uplift. Winter elevation changes are shown to be linked to the North Atlantic Oscillation.

A signal of persistent Atlantic multidecadal variability in Arctic sea ice

Satellite data suggest an Arctic sea ice-climate system in rapid transformation, yet its long-term natural modes of variability are poorly known. Here we integrate and synthesize a set of multicentury historical records of Atlantic Arctic sea ice, supplemented with high-resolution paleoproxy records, each reflecting primarily winter/spring sea ice conditions. We establish a signal of pervasive and persistent multidecadal (~60–90 year) fluctuations that is most pronounced in the Greenland Sea and weakens further away. Covariability between sea ice and Atlantic multidecadal variability as represented by the Atlantic Multidecadal Oscillation (AMO) index is evident during the instrumental record, including an abrupt change at the onset of the early twentieth century warming. Similar covariability through previous centuries is evident from comparison of the longest historical sea ice records and paleoproxy reconstructions of sea ice and the AMO. This observational evidence supports recent modeling studies that have suggested that Arctic sea ice is intrinsically linked to Atlantic multidecadal variability. This may have implications for understanding the recent negative trend in Arctic winter sea ice extent, although because the losses have been greater in summer, other processes and feedbacks are also important.

Barents Sea seasonal ice zone features and processes from ERS 1 synthetic aperture radar: Seasonal Ice Zone Experiment 1992

Sea ice features and processes in the Barents Sea were studied during the Seasonal Ice Zone Experiment 1992 (SIZEX92), a dedicated ERS 1 satellite synthetic aperture radar (SAR) field campaign carried out in March 1992. SIZEX92 was based around the research vessels Polarsyssel and Hakon Mosby. In situ oceanographic, meteorological, and ice measurements were made, coordinated with low-altitude aerial observations and ERS 1 SAR data acquired in near real time. Fifty-eight low-and full-resolution SAR scenes were obtained during SIZEX92, which provided a validation data set for ERS 1 SAR backscatter under winter conditions in the Barents Sea. Analysis of SIZEX92 data has provided geophysical insights, including a better understanding of Barents Sea ice edge freezing processes and ice edge development in response to atmospheric forcings. In particular, areas of new ice formation were found to be related to bathymetric features through their influence on the circulation of Arctic and Atlantic water masses. ERS 1 SAR image sequences revealed rapid, mesoscale variations in new ice areas and the ice edge in response to wind conditions. In addition to geophysical insight, SIZEX92 demonstrated some of the technical capabilities and limitations of ERS 1 SAR to identify new ice areas, the ice edge, ice floes, and ice types. Mapping new ice areas using satellite SAR data may be considered the most promising new application. The limitations of ERS-1 SAR-derived ice classification and ice motion estimates in the marginal ice zone are identified.

Surface air temperature variability and trends in the Arctic: new amplification assessment and regionalisation

Arctic amplification of temperature change is theorised to be an important feature of the Earths climate system. For observational assessment and understanding of mechanisms of this amplification, which remain uncertain, thorough and detailed analyses of surface air temperature (SAT) variability and trends in the Arctic are needed. Here we present an analysis of Arctic SAT variability in comparison with mid-latitudes and the Northern Hemisphere (NH), based on an advanced SAT dataset – NansenSAT. We define an index for the Arctic amplification as the ratio between absolute values of the Arctic (65–90°N) and NH 30-yr running linear SAT trends. It is demonstrated that the temperature amplification in the Arctic is characteristic not only for the recent warming but also the early 20th century warming (ETCW) and subsequent cooling. The amplification appears to be weaker during the recent warming than in the ETCW, simply because the index values reflect the more pervasive nature of the recent warming that reflects the background of anthropogenic global warming. We also produced a new Arctic regionalisation created from hierarchical cluster analysis, which identifies six major natural regions in the Arctic that reflect SAT variability. Statistical comparison with several climate indices shows that the Atlantic Multidecadal Oscillation (AMO) is the mode of variability that is most significantly associated with the amplified warming–cooling in the Arctic, with a stronger correlation during the ETCW and recent warming than during the intermediate period. Regionally, differences are identified in terms of annual and seasonal rates of change and in their correlations with modes of variability.

Anomalies in the seasonal cycle of sea level pressure in Iceland and the North Atlantic Oscillation

This letter presents an analysis of a new homogenized time series of daily mean sea level pressure (SLP) from Reykjavik and Stykkisholmur, Iceland from 1823–1999. Time series statistical techniques including harmonic analysis are used to identify the seasonal march of pressure and its variability through the record. The results are assessed regarding the North Atlantic Oscillation (NAO) index. In addition to the annual cycle, the seasonal march of SLP has an appreciable semi-annual cycle, as well as anomalies (abrupt rises and falls) occurring at remarkably distinct times in spring and winter. Multidecadal variability is apparent in the seasonal cycle and the anomalies. A shift in intraseasonal variability is observed in recent decades, including an extension of the winter Icelandic Low enhancement period into March. Increasing failure or delay of the “usual” abrupt pressure rise in Iceland in late February has contributed to the unusually positive winter NAO index values since the 1960s.

Global sea ice monitoring from microwave satellites

The global sea ice covers can be regularly and frequently monitored using satellite passive microwave sensors. Recent studies using passive microwave data have detected significant decreases in Arctic ice extent and ice area, with no significant changes in the Antarctic. The authors analyze microwave data through mid-1995, to identify changes in ice extent, ice area, and, for the first time, overall ice concentration. The authors find continued decreases in the Arctic ice extent and ice area, and establish a decrease in the ice concentration. They also include a seasonal analysis of the Arctic trends, which establishes the greatest decreases to be in summer and spring. The relatively large summer decreases imply a reduction in the multi-year ice area, suggesting reduced ice thickness, though observational data are lacking.

Exceptional 20th century glaciological regime of a major SE Greenland outlet glacier

The early 2000s accelerated ice-mass loss from large outlet glaciers in W and SE Greenland has been linked to warming of the subpolar North Atlantic. To investigate the uniqueness of this event, we extend the record of glacier and ocean changes back 1700 years by analyzing a sediment core from Sermilik Fjord near Helheim Glacier in SE Greenland. We show that multidecadal to centennial increases in alkenone-inferred Atlantic Water SSTs on the shelf occurred at times of reduced solar activity during the Little Ice Age, when the subpolar gyre weakened and shifted westward promoted by atmospheric blocking events. Helheim Glacier responded to many of these episodes with increased calving, but despite earlier multidecadal warming episodes matching the 20th century high SSTs in magnitude, the glacier behaved differently during the 20th century. We suggest the presence of a floating ice tongue since at least 300 AD lasting until 1900 AD followed by elevated 20th century glacier calving due to the loss of the tongue. We attribute this regime shift to 20th century unprecedented low sea-ice occurrence in the East Greenland Current and conclude that properties of this current are important for the stability of the present ice tongues in NE Greenland.

Unprecedented Retreat in a 50-Year Observational Record for Petermann Glacier, North Greenland

Abstract Petermann Glacier is a marine-terminating outlet glacier that had a 70 km-long floating ice tongue prior to a∼270 km2 calving event that was observed from satellite sensors in August 2010, shortening the ice tongue by∼27 km. Further, in July 2012, another 10 km was lost through calving. In order to understand these events in perspective, here the authors perform a long-term data analysis of Petermann Glacier calving-front variability and ice velocity for each year in the 1990s-2000s, supplemented by available observations from the previous three decades. Five major (on the order of 100 km2) calving events are identified, with∼153 km2 calved from 1959 to 1961,∼168 km2 in 1991,∼71 km2 in 2001,∼270 km2 in 2010, and∼130 km2 in 2012-as well as∼31 km2 calved in 2008. The increased frequency of major calving events in recent years has left the front terminus position retreated nearly 25 km beyond the range of observed in previous decades. In contrast, stable ice-dynamics are suggested from ice-velocity measurements made each year between 1993-2012, which are on average 1063 m yr-1, with limited interannual variability and no significant trend; moreover, there is no apparent relationship between ice-velocity variability and calving events. The degree to which the massive calving events in 2010 and 2012 represent natural episodic variability or a response to atmospheric and/or oceanic changes remains speculative; however, melt-induced weakening of the floating ice tongue in recent years is strongly suggested.

Incorporating the expansion method into remote sensingbased water quality analyses

1. An Introduction to the Expansion Method and to its Applications Emilio Casetti and John Paul Jones III 2. The Dual Expansion Method: An Application for Evaluating the Effects of Population Growth on Development Emilio Casetti 3. Paradigmatic Dimensions of the Expansion Method John Paul Jones III 4. A Contextual Expansion of the Welfare Model Janet E. Kodras 5. A Comparison of Drift Analyses and the Expansion Method: The Evaluation of Federal Policies on the Supply of Physicians Stuart A. Foster, Wilpen L. Gorr and Francis C. Wimberly 6. Personal Characteristics in Models of Migration Decisions: An Analysis of Destination Choice in Ecuador Mark Ellis and John Odland 7. Alternative Approaches to the Study of Metropolitan Decentralization Shaul Krakover 8. Long Wave Spatial and Economic Relationships in Urban Development Shaul Krakover and Richard L. Morrill 9. An Investigation of the Dynamics of Development Inequalities via Expanded Rank-Size Functions C. Cindy Fan 10. Identifying Hierarchical Development Trends in the Hungarian Urban System using the Expansion Method Darrick R. Danta 11. An Exploration of the Relationship between Sectoral Labor Shares and Economic Development Kavita Pandit 12. Production Function Estimation and the Spatial Structural of Agriculture Sent Visser 13. Incorporating the Expansion Method into Remote Sensing-Based Water Quality Analyses Marty Miles, Douglas A. Stow and John Paul Jones III 14. Innovation Diffusion Theory and the Expansion Method Michael Sonis 15. Spatial Dependence and Spatial Heterogegity: Model Specification Issues in the Spatial Expansion Paradigm Luc Anselin 16. Generating Varying Parameter Models using Cubic Spline Functions Robert Q. Hanham