331 research outputs found
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Effect of ENSO phase on large-scale snow water equivalent distribution in a GCM
Understanding links between the El Nino-Southern Oscillation (ENSO) and snow would be useful for seasonal forecasting, but also for understanding natural variability and interpreting climate change predictions. Here, a 545-year run of the general circulation model HadCM3, with prescribed external forcings and fixed greenhouse gas concentrations, is used to explore the impact of ENSO on snow water equivalent (SWE) anomalies. In North America, positive ENSO events reduce the mean SWE and skew the distribution towards lower values, and vice versa during negative ENSO events. This is associated with a dipole SWE anomaly structure, with anomalies of opposite sign centered in western Canada and the central United States. In Eurasia, warm episodes lead to a more positively skewed distribution and the mean SWE is raised. Again, the opposite effect is seen during cold episodes. In Eurasia the largest anomalies are concentrated in the Himalayas. These correlations with February SWE distribution are seen to exist from the previous June-July-August (JJA) ENSO index onwards, and are weakly detected in 50-year subsections of the control run, but only a shifted North American response can be detected in the anaylsis of 40 years of ERA40 reanalysis data. The ENSO signal in SWE from the long run could still contribute to regional predictions although it would be a weak indicator onl
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Mechanisms for AMOC variability simulated by the NEMO model
We have investigated mechanisms for the Atlantic Meridional Overturning Circulation (AMOC) variability at 26.5° N (other than the Ekman component) that can be related to external forcings, in particular wind variability. Resolution dependence is studied using identical experiments with 1° and 1/4° NEMO model runs over 1960–2010.
The analysis shows that much of the variability in the AMOC at 26° N can be related to the wind strength over the North Atlantic, through mechanisms lagged on different timescales. At ~ 1-year lag the January–June difference of mean sea level pressure between high and mid-latitudes in the North Atlantic explains 35–50% of the interannual AMOC variability (with negative correlation between wind strength and AMOC). At longer lead timescales ~ 4 years, strong (weak) winds over the northern North Atlantic (specifically linked to the NAO index) are followed by higher (lower) AMOC transport, but this mechanism only works in the 1/4° model. Analysis of the density correlations suggests an increase (decrease) in deep water formation in the North Atlantic subpolar gyre to be the cause. Therefore another 30% of the AMOC variability at 26° N can be related to density changes in the top 1000 m in the Labrador and Irminger seas occurring ~ 4 years earlier
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GODIVA2: interactive visualization of environmental data on the Web
GODIVA2 is a dynamic website that provides visual access to several terabytes of physically distributed, four-dimensional environmental data. It allows users to explore large datasets interactively without the need to install new software or download and understand complex data. Through the use of open international standards, GODIVA2 maintains a high level of interoperability with third-party systems, allowing diverse datasets to be mutually compared. Scientists can use the system to search for features in large datasets and to diagnose the output from numerical simulations and data processing algorithms. Data providers around Europe have adopted GODIVA2 as an INSPIRE-compliant dynamic quick-view system for providing visual access to their data
The psychological effects of unemployment: a review of the literature
The literature on the psychological effects of unemployment is reviewed, with particular attention being paid to the somewhat scarce New Zealand literature on the subject. Studies conducted at the macrosocial level are discussed, followed by studies that focus on the individual, with respect to physical health, mental health and psychological well-being, and social attitudes. The differential effect of unemployment on various social groups is examined, and the methodological deficiencies in some of the studies reviewed are summarized. In conclusion, it is suggested that the documented psychological ill-effects of unemployment should make us view rising levels of unemployment with concern
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A perturbed biogeochemistry model ensemble evaluated against in situ and satellite observations
The dynamics of biogeochemical models are determined by the mathematical equations used to describe the main biological processes. Earlier studies have shown that small changes in the model formulation may lead to major changes in system dynamics, a property known as structural sensitivity. We assessed the impact of structural sensitivity in a biogeochemical model of intermediate complexity by modelling the chlorophyll and dissolved inorganic nitrogen (DIN) concentrations. The model is run at five different oceanographic stations spanning three different regimes: oligotrophic, coastal, and the abyssal plain, over a 10-year timescale to observe the effect in different regions. A 1-D MEDUSA ensemble was used with each ensemble member having a combination of tuned function parameterizations that describe some of the key biogeochemical processes,
namely nutrient uptake, zooplankton grazing, and plankton mortalities. The impact is quantified using phytoplankton phenology (initiation, bloom time, peak height, duration, and termination of phytoplankton blooms) and statistical measures such as RMSE, mean, and range for chlorophyll and nutrients. The spread of the ensemble as a measure of uncertainty is assessed against observations using the Normalised RMSE Ratio (NRR).We found that even small perturbations in model structure can produce large ensemble spreads. The range of 10-year mean surface chlorophyll concentration in the ensemble is between 0.14-3.69 mg m-3 at coastal stations, 0.43-1.11 mg m-3 on the abyssal plain, and 0.004-0.16 mg m-3 at the oligotrophic stations. Changing both phytoplankton and zooplankton mortalities and the grazing functions have the largest impact on chlorophyll concentrations. The in situ measurements of bloom timings, duration, and terminations lie mostly within the ensemble range. The RMSEs between in situ observations and the ensemble mean and median are mostly reduced compared to the default
model output. The NRRs for monthly variability suggest that the ensemble spread is generally narrow (NRR 1.21-1.39 for DIN and 1.19-1.39 for chlorophyll profiles, 1.07-1.40 for surface chlorophyll, and 1.01-1.40 for depth integrated chlorophyll).
Among the five stations, the most reliable ensembles are obtained for the oligotrophic station ALOHA (for the surface and integrated chlorophyll and bloom peak height), for coastal station L4 (for inter-annual mean), and for the abyssal plain station PAP (for bloom peak height). Overall our study provides a novel way to generate a realistic ensemble of a biogeochemical model by perturbing the model equations/parameterizations, which will be helpful for the probabilistic predictions
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Implications from opening Arctic sea routes
Summary for Policy Makers
The Arctic is warming faster than anywhere else on Earth; satellite observations have revealed the region is losing sea ice at a dramatic rate and this decline is expected to continue. This loss of sea ice is creating opportunities for shorter global trade links between East Asia and the UK via the Arctic. The Northern Sea Route and North West Passages are seasonally open most years, although specialised vessels are currently required. The Arctic shipping season will continue to extend tripling in length by mid-century, coinciding with the opening of the trans-polar sea route across the central Arctic Ocean, although there will still be sea ice present in the Arctic winter. Typically by mid-century voyages from East Asia to the UK could save 10 – 12 days by using trans-Arctic routes instead of the Suez Canal route. These findings suggest that trans-Arctic routes may provide a useful supplement to the traditional canal routes, but they will likely not replace them.
There are mixed views on whether trans-Arctic routes will become economically viable. The Russian government wishes to develop the Northern Sea Route as a commercial enterprise and offers substantial fee-based services such as ice breaking support and pilotage, which are certainly necessary for future investment and development of the route. However Arctic transport is also likely to grow due to increased destination shipping to serve natural resource extraction projects and cruise tourism.
The UK is well positioned, geographically, geopolitically, and commercially, to benefit from a symbiotic relationship with increasing Arctic shipping. The UK has a prominent role in Arctic science and a world leading maritime services industry based in London, including the International Maritime Organisation (IMO), one of the world’s leading financial centres, and Europe’s largest insurance sector. Arctic economic growth is focused in four key sectors — mineral resources, fisheries, logistics, and tourism — all of which require shipping, and could generate investment reaching $100bn or more in the Arctic region over the next decade. The UK had a fundamental role in preparing the UN IMO Polar Code which came into operation in January 2017. The Polar Code is an historic milestone in addressing the specific risks faced by Arctic shipping and acts to supplement the existing SOLAS and MARPOL conventions for protecting the environment whilst ensuring safe shipping in international waters.
Much of the investment into Arctic shipping projects is from China but northern European countries are also playing an increasing role. Potential opportunities for the UK include the development of UK based Arctic cruise tourism, and a UK based trans-shipment port — transferring goods from ice-classed vessels to conventional carriers. The UK has an active diplomatic role in many international organisations; this should be used to ensure that increased activity in the Arctic is accomplished in line with established UN maritime conventions, many of which were written with significant UK contributions. The UK’s leading role in Arctic science has wide reaching positive implications for international collaboration; this role requires continued investment into climate modelling centres, and science programs, that are essential to enhance predictions of the future Arctic
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Improved Arctic sea-ice thickness projections using bias corrected CMIP5 simulations
Projections of Arctic sea ice thickness (SIT) have the potential to inform stakeholders about accessibility to the region, but are currently rather uncertain. The latest suite of CMIP5 Global Climate Models (GCMs) produce a wide range of simulated SIT in the historical period (1979–2014) and exhibit various biases when compared with the Pan-Arctic Ice Ocean Modelling and Assimilation System (PIOMAS) sea ice reanalysis. We present a new method to constrain such GCM simulations of SIT via a statistical bias correction technique. The bias correction successfully constrains the spatial SIT distribution and temporal variability in the CMIP5
projections whilst retaining the climatic fluctuations from individual ensemble members. The bias correction acts to reduce the spread in projections of SIT and reveals the significant contributions of climate internal variability in the first half of the century and of scenario uncertainty from mid-century onwards. The projected date of ice-free conditions in the Arctic
under the RCP8.5 high emission scenario occurs in the 2050s, which is a decade earlier than without the bias correction, with potentially significant implications for stakeholders in the Arctic such as the shipping industry. The bias correction methodology developed could be
similarly applied to other variables to reduce spread in climate projections more generally
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Historical reconstruction of the Atlantic Meridional Overturning Circulation from the ECMWF operational ocean reanalysis
A reconstruction of the Atlantic Meridional Overturning Circulation (MOC) for the period 1959–2006 has been derived from the ECMWF operational ocean reanalysis. The reconstruction shows a wide range of time-variability, including a downward trend. At 26N, both the MOC intensity and changes in its vertical structure are in good agreement with previous estimates based on trans-Atlantic surveys. At 50N, the MOC and strength of the subpolar gyre are correlated at interannual time scales, but show opposite secular trends. Heat transport variability is highly correlated with the MOC but shows a smaller trend due to the warming of the upper ocean, which partially compensates for the weakening of the circulation. Results from sensitivity experiments show that although the time-varying upper boundary forcing provides useful MOC information, the sequential assimilation of ocean data further improves the MOC estimation by increasing both the mean and the time variability
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Inverse modeling of global and regional energy and water cycle fluxes using Earth observation data
The NASA Energy and Water Cycle Study (NEWS) climatology is a self-consistent coupled annual and seasonal cycle solution for radiative, turbulent and water fluxes over the Earth's surface using Earth observation data covering 2000-2009. Here we seek to improve the NEWS solution, particularly over the ocean basins, by considering spatial covariances in the observation errors (some evidence for which is found by comparing five turbulent flux products over the oceans) and by introducing additional horizontal transports from ocean reanalyses as weak constraints. By explicitly representing large error covariances between surface heat flux components over the major ocean basins we retain the flux contrasts present in the original data
and infer additional heat losses over the North Atlantic, more consistent with a strong Atlantic overturning. This change does not alter the global flux balance but if only the errors in evaporation and precipitation are correlated then those fluxes experience larger adjustments (e.g. the
surface latent heat flux increases to 85 +- 2 Wm). Replacing SeaFlux v1 with J-OFURO v3 ocean fluxes also leads to a considerable increase in the global latent heat loss as well as a larger North Atlantic heat loss. Furthermore, including a weak constraint on the horizontal transports of heat and freshwater from high-resolution ocean reanalyses improves the net fluxes over the North Atlantic, Caribbean and Arctic Oceans, without any impact on the global flux balances. These results suggest that better characterised flux uncertainties can greatly improve the quality of the optimised flux solution
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Improving seasonal forecasting through tropical ocean bias corrections
Initialisation shock is often discussed in the context of coupled atmosphere-ocean forecasting, but its detection has remained elusive. In this paper, the presence of initialisation shock in seasonal forecasts is clearly identified in the variability of the tropical thermocline. The specific source of shock studied here is the use of a bias correction procedure to account for errors in equatorial wind stress forcing during ocean initialisation. It is shown that the abrupt removal of the bias correction at the beginning of the forecast leads to rapid adjustments in the upper ocean, creating a shock that remains in the system for at least three months. By contrast, gradual removal of the correction term, over 20 days, greatly reduces the initialisation shock. Evidence is presented of substantial increases in sea surface temperature (SST) seasonal forecast skill, at around 3–7 months’ lead time, when the gradual removal approach is used.
Gains in skill of up to 0.05, as measured by the anomaly correlation coefficient for SST in the Nino4 region, are found, using a modest hindcast set covering four seasonal start dates. The results show that improvements in coupled initialisation aimed at reducing shocks may considerably benefit seasonal forecasting
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