Diagnosing the extreme surface melt event over southwestern Greenland in 2007

Abstract. Analysis of passive microwave brightness temperatures from the space-borne Special Sensor Microwave Imager (SSM/I) documents a record surface snowmelt over high elevations (above 2000 m) of the Greenland ice sheet during summer of 2007. To interpret this record, results from the SSM/I are examined in conjunction with fields from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis and output from a regional climate model. The record surface melt reflects unusually warm conditions, seen in positive summertime anomalies of surface air temperatures, downwelling longwave radiation, 1000–500 hPa atmospheric thickness, and the net surface energy flux, linked in turn to southerly airflow over the ice sheet. Low snow accumulation may have contributed to the record through promoting anomalously low surface albedo

An estimate of the suspended particulate matter (SPM) transport in the southern North Sea using SeaWiFS images, in situ measurements and numerical model results

A study is presented where satellite images (SeaWiFS), in situ measurements (tidal cycle and snapshot) and a 2D hydrodynamic numerical model have been combined to calculate the long term SPM (Suspended Particulate Matter) transport through the Dover Strait and in the southern North Sea. The total amount of SPM supplied to the North Sea through the Dover Strait is estimated to be 31.74 x 106 t. The satellite images provide synoptic views of SPM concentration distribution but do not take away the uncertainty of SPM transport calculation. This is due to the fact that SPM concentration varies as a function of tide, wind, spring-neap tidal cycles and seasons. The short term variations (tidal, spring-neap tidal cycle) have not been found in the satellite images, however seasonal variations are clearly visible. Furthermore the SPM concentration in the satellite images is generally lower than in the in situ measurements. The representativness of SPM concentration maps derived from satellites for calculating long term transports has therefore been investigated by comparing the SPM concentration variability from the in situ measurements with those of the remote sensing data. The most important constraints of satellite images are related to the fact that satellite data is evidence of clear sky conditions, whereas in situ measurements from a vessel can be carried out also during rougher meteorological conditions and that due to the too low time resolution of the satellite images the SPM concentration peaks are often missed. It is underlined that SPM concentration measurements should be carried out during at least one tidal cycle in high turbidity areas to obtain representative values of SPM concentration

Modelling currents and sediment transport phenomena in shelf seas and estuaries

Numerical models are an important tool for describing and understanding hydrodynamic and transport processes in the marine and estuarine environment. The success of these models is due to the fact that they are based on physical laws which describe in detail the processes involved. Two aspects of modelling, which are closely related, are highlighted. The first one focusses on the numerical aspects, while the second deals with validating the models through intercomparison with other models or analytical solutions and through field measurements. A2.50 vertical plane ice-ocean model and a 3D barotropic ocean model has been developed which simulates the wind induced currents in high latitude seas. The models solve the hydrodynamic and ice dynamic equations using finte different techniques. Because the domain of integration is very often smaller than the ocean basin non physical boundaries have to be introduced. Numerically this means that an open boundary condition has to be implemented. The Orlanski and the Camerlengo-O'Brien open boundary conditions have been introduced in an existing 2D depth averaged hydrodynamic model and have been validated by applying the model to some well defined test cases. It was found that the Camerlengo and O'Brien condition gave the best results. The Camerlengo-O'Brien open boundary condition has been used to simulate the flow behind a backward facing step in a long channel with the downstream boundaries open in order to investigate the quality of the results as a function of the advection scheme (1st order upstream and 3rd order QUICK).The 2.5D ocean model was validated by comparing the results to those of an other model and to an analytical solution. The 2.5D ice-ocean model was forced by a katabatic wind. It is shown that coastal polynyas can be formed by theses strong off coastal winds. The differences found between both model results have been summarized and explained. The 2.5D model has been applied to an (idealized) ocean covered by an ice layer and deal with the behaviour of an ocean in the vicinity of an ice edge and a continental slope.The second part is devoted to the study of mud transport in a part of the Scheldt estuary using field measurements and numerical models. The observations show the great variations in mud concentration found in the Scheldt estuary. The mud transport is simulated using a 2D and a 3D model. The 2D transport model is a Lagrangian model. The model has been validated by comparing the model results to the data obtained from a laboratory model. This experiment has shown that the model is able to reproduce qualitatively and quantitatively well the observations, but that the predictive capability of the model suffers from a good description and integration of the various physical processes which governs the mud transport. The 2D mud transport model has then been applied to a part of the Scheldt estuary. The results of the model have been compared to the results of two other mud transport models.The 3D mud transport model and several observations have been used to the study the mud transport in an access channel. It is shown that the high mud deposition in the access channels is mainly due to the density gradients existing between the river and the access channel and in the vertical plane