Neil R. Peacock

Bio: Neil R. Peacock is an academic researcher from University College London. The author has contributed to research in topics: Sea ice & Sea ice thickness. The author has an hindex of 3, co-authored 3 publications receiving 658 citations.

High interannual variability of sea ice thickness in the Arctic region.

Abstract: Possible future changes in Arctic sea ice cover and thickness, and consequent changes in the ice-albedo feedback, represent one of the largest uncertainties in the prediction of future temperature rise1,2. Knowledge of the natural variability of sea ice thickness is therefore critical for its representation in global climate models3,4. Numerical simulations suggest that Arctic ice thickness varies primarily on decadal timescales3,5,6 owing to changes in wind and ocean stresses on the ice7,8,9,10, but observations have been unable to provide a synoptic view of sea ice thickness, which is required to validate the model results3,6,9. Here we use an eight-year time-series of Arctic ice thickness, derived from satellite altimeter measurements of ice freeboard, to determine the mean thickness field and its variability from 65° N to 81.5° N. Our data reveal a high-frequency interannual variability in mean Arctic ice thickness that is dominated by changes in the amount of summer melt11, rather than by changes in circulation. Our results suggest that a continued increase in melt season length would lead to further thinning of Arctic sea ice.

Sea surface height determination in the Arctic Ocean from ERS altimetry

Abstract: [1] Accurate sea surface height measurements have been extracted from ERS altimeter data in sea ice - covered regions for the first time. The data have been used to construct a mean sea surface of the Arctic Ocean between the latitudes of 60 degreesN and 81.5 degreesN based on 4 years of ERS-2 data. An RMS value for the crossover differences of mean sea surface profiles of 4.2 cm was observed in the ice-covered Canada Basin, compared with 3.8 cm in the ice-free Greenland-Iceland-Norwegian Seas. Comparisons are made with an existing global mean sea surface (OSUMSS95), highlighting significant differences between the two surfaces in permanently ice-covered seas. In addition, we present the first altimeter-derived sea surface height variability map of the Arctic Ocean. Comparisons with a high-resolution coupled ocean - sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability. Quantitatively, we found that the observed variability was on average a factor of 3 - 4 greater than model predictions.

Ice shelf tidal motion derived from ERS altimetry

Abstract: [1] Ocean tides beneath floating ice shelves can affect heat and water circulations within the subshelf cavity, which may influence patterns of basal melting. Accurate tidal predictions are essential to eliminate vertical tide motions when mapping the flow speeds and thickness changes of floating ice. Global ocean tide solutions are typically accurate to 2–3 cm in amplitude. However, their coarse resolution limits their utility in coastal regions. Moreover, the absence of satellite and extensive gauge station data in the polar regions has resulted in significant differences between recent tide model solutions around the Antarctic continent. We use 9 years of high-resolution European Remote Sensing (ERS) satellite radar altimeter range measurements and a modified form of the orthotide method to generate tidal solutions for a series of ice shelves around the Antarctic Peninsula. We compare our tidal solution at George VI Ice Shelf on the western coast of the Antarctic Peninsula to direct measurements from British Antarctic Survey tide gauge records and contrast the results with solutions from the FES99 and Kantha2.0 (global) and the CATS01.02 (Antarctic) ocean tide models. The average root mean square vector difference between the tide gauge and tide model predictions of amplitude and phase was 10.9, 17.1, 4.2, and 15.4 cm for the ERS ice shelf, Kantha2.0, CATS01.02, and FES99 models, respectively. Tidal predictions derived from the ERS ice shelf model are closer to the tide gauge recordings than those of the global models, and the inclusion of ERS altimeter data may lead to improved global model performance.

Observations: Changes in Snow, Ice and Frozen Ground

Abstract: Contributing Authors: J. Box (USA), D. Bromwich (USA), R. Brown (Canada), J.G. Cogley (Canada), J. Comiso (USA), M. Dyurgerov (Sweden, USA), B. Fitzharris (New Zealand), O. Frauenfeld (USA, Austria), H. Fricker (USA), G. H. Gudmundsson (UK, Iceland), C. Haas (Germany), J.O. Hagen (Norway), C. Harris (UK), L. Hinzman (USA), R. Hock (Sweden), M. Hoelzle (Switzerland), P. Huybrechts (Belgium), K. Isaksen (Norway), P. Jansson (Sweden), A. Jenkins (UK), Ian Joughin (USA), C. Kottmeier (Germany), R. Kwok (USA), S. Laxon (UK), S. Liu (China), D. MacAyeal (USA), H. Melling (Canada), A. Ohmura (Switzerland), A. Payne (UK), T. Prowse (Canada), B.H. Raup (USA), C. Raymond (USA), E. Rignot (USA), I. Rigor (USA), D. Robinson (USA), D. Rothrock (USA), S.C. Scherrer (Switzerland), S. Smith (Canada), O. Solomina (Russian Federation), D. Vaughan (UK), J. Walsh (USA), A. Worby (Australia), T. Yamada (Japan), L. Zhao (China)

The HadGEM2 family of Met Office Unified Model climate configurations

Abstract: . We describe the HadGEM2 family of climate configurations of the Met Office Unified Model, MetUM. The concept of a model "family" comprises a range of specific model configurations incorporating different levels of complexity but with a common physical framework. The HadGEM2 family of configurations includes atmosphere and ocean components, with and without a vertical extension to include a well-resolved stratosphere, and an Earth-System (ES) component which includes dynamic vegetation, ocean biology and atmospheric chemistry. The HadGEM2 physical model includes improvements designed to address specific systematic errors encountered in the previous climate configuration, HadGEM1, namely Northern Hemisphere continental temperature biases and tropical sea surface temperature biases and poor variability. Targeting these biases was crucial in order that the ES configuration could represent important biogeochemical climate feedbacks. Detailed descriptions and evaluations of particular HadGEM2 family members are included in a number of other publications, and the discussion here is limited to a summary of the overall performance using a set of model metrics which compare the way in which the various configurations simulate present-day climate and its variability.

CryoSat-2 estimates of Arctic sea ice thickness and volume

Abstract: [1] Satellite records show a decline in ice extent over more than three decades, with a record minimum in September 2012. Results from the Pan-Arctic Ice-Ocean Modelling and Assimilation system (PIOMAS) suggest that the decline in extent has been accompanied by a decline in volume, but this has not been confirmed by data. Using new data from the European Space Agency CryoSat-2 (CS-2) mission, validated with in situ data, we generate estimates of ice volume for the winters of 2010/11 and 2011/12. We compare these data with current estimates from PIOMAS and earlier (2003–8) estimates from the National Aeronautics and Space Administration ICESat mission. Between the ICESat and CryoSat-2 periods, the autumn volume declined by 4291 km3 and the winter volume by 1479 km3. This exceeds the decline in ice volume in the central Arctic from the PIOMAS model of 2644 km3 in the autumn, but is less than the 2091 km3 in winter, between the two time periods.

Effects of Arctic Sea Ice Decline on Weather and Climate: A Review

Abstract: The areal extent, concentration and thickness of sea ice in the Arctic Ocean and adjacent seas have strongly decreased during the recent decades, but cold, snow-rich winters have been common over mid-latitude land areas since 2005. A review is presented on studies addressing the local and remote effects of the sea ice decline on weather and climate. It is evident that the reduction in sea ice cover has increased the heat flux from the ocean to atmosphere in autumn and early winter. This has locally increased air tempera- ture, moisture, and cloud cover and reduced the static stability in the lower troposphere. Several studies based on observations, atmospheric reanalyses, and model experiments suggest that the sea ice decline, together with increased snow cover in Eurasia, favours circulation patterns resembling the negative phase of the North Atlantic Oscillation and Arctic Oscillation. The suggested large-scale pressure patterns include a high over Eurasia, which favours cold winters in Europe and northeastern Eurasia. A high over the western and a low over the eastern North America have also been suggested, favouring advection of Arctic air masses to North America. Mid-latitude winter weather is, however, affected by several other factors, which generate a large inter-annual variability and often mask the effects of sea ice decline. In addition, the small sample of years with a large sea ice loss makes it difficult to distinguish the effects directly attributable to sea ice conditions. Several studies suggest that, with advancing global warming, cold winters in mid-latitude continents will no longer be common during the second half of the twenty-first century. Recent studies have also suggested causal links between the sea ice decline and summer precipitation in Europe, the Mediterranean, and East Asia.