1,352 research outputs found
A Buys Ballot medal for Edward Lorenz : a reflection on the history of the prestigious award and evolving attitudes toward predictability
No full textSince 1893, the Royal Netherlands Academy of Arts and Sciences has awarded, once every 10 years, a golden Buys Ballot Medal to a scientist who has made outstanding contributions to the development of meteorology. The award was instituted in 1888 in honor of C. H. D. Buys Ballot (1817–90), upon his retirement as professor of physics at the University of Utrecht. Today, Buys Ballot is remembered best by Buys Ballot’s law, which gives the relation between wind and pressure. He derived this law from observations and published it in 1857.1 Buys Ballot was a pioneer both in weather forecasting and in recognizing the need for international cooperation in meteorology. He founded the Royal Netherlands Meteorological Institute (KNMI) in 1854 and served as its chief director until his death, and was first president (1873–79) of the International Meteorological Committee, a predecessor of the World Meteorological Organization (WMO)
Modelling the dynamics and boundary processes of Svalbard glaciers
No full textThe focus of this thesis is on improving our understanding of surface and basal processes in the context of glaciers in Svalbard. At the surface, interactions with the atmosphere and underlying snow determine the surface mass balance. A coupled model is applied to Nordenskiöldbreen, a tidewater glacier in central Svalbard, to quantify the surface mass balance and the significance of refreezing of percolating melt water. It is found that for 1989-2010, the annual mass balance was negative (-0.39 m w.e. yr-1) and that refreezing contributed substantially to the mass budget (0.27 m w.e. yr-1). Climate sensitivity experiments reveal that seasonal inhomogeneity in future warming leads to a relatively low sensitivity of the mass balance in a changing climate. Substantial uncertainty in mass balance modeling, as well as in the interpretation of local mass balance observations, stems from the lack of detailed knowledge of how snow accumulation varies in space and time. A novel inverse approach is presented to extract accumulation from radar data. The method involves iteratively running a coupled model to simulate the firn evolution, while calibrating accumulation. Resulting annual accumulation patterns for 2007-2012 along transect on Nordenskiöldbreen reveal strong variability both in space and time. Preferential snow deposition occurs on steep slopes in the lee of terrain undulations. Small-scale accumulation variability is shown to have a negative impact on the surface mass balance. The second part of the thesis focuses on subglacial conditions. At the ice-bed interface, the rate of basal motion depends on the interplay of stresses, thermodynamics and hydrology. Regardless of variability in the external climate forcing, internal interactions may lead to feedbacks inducing periodic changes, such as have been observed in surges on Svalbard. Cyclic behavior is studied in synthetic experiments using a 3-D ice-flow model (PISM). High- and low-frequency oscillations are identified and differ in terms of volume fluctuations and changes in the polythermal basal structure. The crucial role of parameters controlling basal sliding is discussed. In a next chapter, an inverse modeling approach is used to reconstruct distributed bed topography from surface height data. Detailed knowledge of basal topography is relevant both for estimating ice volume contained in ice masses as well as for accurate time-dependent dynamical modelling. Synthetic experiments illustrate robustness of the method, whereas application of the approach to Nordenskiöldbreen demonstrates applicability of the inverse approach in a real glacier setting. In a final chapter, ongoing work towards implementation of a new hydrology model in PISM is presented and discussed. The principle aim of a hydrology model is to compute water pressures, as sliding laws used in ice dynamical models commonly relate the degree of basal friction to the effective pressure of the ice. A linked-cavity drainage model is connected to englacial storage, which enables simulating spatio-temporal water pressure variations, sub-glacial water transport and an evolving drainage system capacity. We test model behavior and discuss the potential for coupling the hydrology model to ice dynamics and application at a wide range of spatial and temporal scales
Fouten in de representatie van straling in klimaatmodellen
No full textKlimaatmodellen zijn vrij goed in staat om de waargenomen temperatuurverdeling in de atmosfeer te repro- !"#&'()*+(,*-.+(&(/%0+%!*&2+3(455%(*2(6*/&,*-.(&*+'(700%5,(!4582(*&(!(40!&( zijn in hoge mate geijkt aan de hand van de waargenomen temperatuurverdeling. Klimaatmodellen zijn in staat het waargenomen temperatuurverloop nabij het aardoppervlak over de laatste eeuw vrij nauwkeurig te reproduceren. De relatief lage wereldgemiddelde temperatuur in de jaren vijftig en zestig van de vorige eeuw kan daarmee verklaard worden als een effect van toegenomen reflectie van zonnestraling door een vuilere atmosfeer. Sinds de jaren zeventig is de atmosfeer op veel plaatsen geleidelijk schoner geworden, waardoor meer zonnestraling het aardoppervlak bereikt. De temperatuurstijging nabij het aardoppervlak, die daar mede het gevolg van is, wordt goed berekend door de klimaatmodelle
De dikte van gletsjers en ijskappen
No full textGletsjers vullen dalen in de Alpen en bijna het gehele Antarctische continent wordt bedekt door een ijskap, maar hoe dik is dit ijs eigenlijk? Dit artikel geeft een globaal overzicht van de methoden die gebruikt worden om de ijsdikte te bepalen
Freezes, floes and the future [book review of A World Without Ice by Henry Pollack]
No full textThe story of Earth's glaciers and ice caps is key to understanding climate science, but this kaleidoscopic account lacks a strong narrative, argues Johannes Oerleman
Waar blijft de energie van het versterkte broeikaseffect
No full textAls het gaat om het detecteren van klimaatverandering is men teveel gepreoccupeerd met de atmosfeer. Men vergeet vaak dat de oceaan en de ijskappen een belangrijk onderdeel zijn van het klimaatsysteem. Dit wordt nog eens duidelijk, nu er wordt gezocht naar een verklaring voor het feit dat de globaal gemiddelde temperatuur van de atmosfeer nabij het aardoppervlak al geruime tijd (11 jaar) niet meer stijgt, ondanks de voortdurende stijging van de CO2-concentratie in de atmosfeer (figuur 1) (Kerr, 2009). Sommige “klimaatsceptici”, die geloven dat het allemaal niet zo’n vaart zal lopen met “de door de mens veroorzaakte opwarming van de aarde”, spinnen hier garen bij. Wetenschappers zoeken naar een verklaring. Die moet waarschijnlijk worden gezocht in de enorme warmtecapaciteit van de oceanen en de ijskappen. De waarnemingen zijn helaas nog onvoldoende nauwkeurig om deze verklaring te boekstaven
Estimating response times of Vadret da Morteratsch, Vadret da Palue, Briksdalsbreen and Nigardsbreen from their length records
No full textLength records of two pairs of glaciers are used to reconstruct the equilibrium-line altitude (ELA) and to estimate glacier response times. The method is based on the assumption that neighbouring glaciers should be subject to the same climatic forcing, and that differences in the length records are thus caused by differences in response times and climate sensitivities. By means of a control method, in which the difference between the reconstructed histories of the ELA is minimized, realistic response times are found. The pairs of glaciers studied are: (i) Vadret da Morteratsch and Vadret da Palu¨ in the Swiss Alps and (ii) Briksdalsbreen and Nigardsbreen in southern Norway. In both cases the reconstructed ELA histories of the individual glaciers are very similar, in spite of the large differences in the length records. Short e-folding response times are found for the steep glaciers: 4.4 years for Vadret da Palii, 5.0 years for Briksdalsbreen. For the larger glaciers with a more gentle slope the response times are substantially larger: 33.0 years for Vadret da Morteratsch, 34.8 years for Nigardsbreen
On the Dynamics and Water Mass Transformation of a Boundary Current Connecting Alpha and Beta Oceans
No full textA subpolar marginal sea, like the Nordic seas, is a transition zone between the temperature-stratified subtropics (the alpha ocean) and the salinity-stratified polar regions (the beta ocean). An inflow of Atlantic Water circulates these seas as a boundary current that is cooled and freshened downstream, eventually to outflow as Deep and Polar Water. Stratification in the boundary region is dominated by a thermocline over the continental slope and a halocline over the continental shelves, separating Atlantic Water from Deep and Polar Water, respectively. A conceptual model is introduced for the circulation and water mass transformation in a subpolar marginal sea to explore the potential interaction between the alpha and beta oceans. Freshwater input into the shelf regions has a slight strengthening effect on the Atlantic inflow, but more prominently impacts the water mass composition of the outflow. This impact of freshwater, characterized by enhancing Polar Water outflow and suppressing Deep Water outflow, is strongly determined by the source location of freshwater. Concretely, perturbations in upstream freshwater sources, like the Baltic freshwater outflow into the Nordic seas, have an order of magnitude larger potential to impact water mass transports than perturbations in downstream sources like the Arctic freshwater outflow. These boundary current dynamics are directly related to the qualitative stratification in transition zones and illustrate the interaction between the alpha and beta oceans
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