Confidence Levels for the Cycles Found in Air Temperature Data

Poster (2009, April)

Recently, new cycles have been observed in air temperature data and proxy series using a wavelet-based methodology. Although many evidences attest the validity of this method applied to climatic data, no ... [more ▼]

Recently, new cycles have been observed in air temperature data and proxy series using a wavelet-based methodology. Although many evidences attest the validity of this method applied to climatic data, no systematic study of its efficiency has been carried out. Here, we estimate the confidence levels for this approach and show that the observed cycles are significant. [less ▲]

Greenland ice sheet surface mass balance projections from IPCC AR4 global models

Poster (2009, January 28)

Results from atmosphere-ocean general circulation models (AOGCM's) for the IPCC 4th Assessment Report are used to investigate surface mass balance (SMB) future projections of the Greenland ice sheet (GrIS ... [more ▼]

Results from atmosphere-ocean general circulation models (AOGCM's) for the IPCC 4th Assessment Report are used to investigate surface mass balance (SMB) future projections of the Greenland ice sheet (GrIS). The most efficient models for the GrIS climate modeling are chosen by comparison between the 1970-1999 outputs (averages and trends) from the Climate of the twentieth Century Experiment (20C3M) and reanalyses (ECMWF, NCEP) as well as observations (ice core measurements). The outputs from these most efficient models are after used to assess changes planned by the IPCC greenhouse gas emissions scenarios (SRES) for the 2070-2099 period. The GrIS SMB projections are estimated from changes in precipitation and temperatures from these AOGCM's outputs. However, large uncertainties remain in these SMB projections based on simplified physics and huge model outputs. High resolution simulations made with regional models (which simulate explicitly the SMB by taking into account the surface feedbacks) forced at their boundaries by a GrIS well-adapted AOGCM could bring more precise brief replies. [less ▲]

Hydrologic response of the Greenland ice sheet: the role of oceanographic warming

in Hydrological Processes (2009), 23(1), 7-30

The response of the Greenland ice sheet to ongoing climate change remains an area of great uncertainty, with most previous studies having concentrated on the contribution of the atmosphere to the ice mass ... [more ▼]

The response of the Greenland ice sheet to ongoing climate change remains an area of great uncertainty, with most previous studies having concentrated on the contribution of the atmosphere to the ice mass-balance signature. Here we systematically assess for the first time the influence of oceanographic changes on the ice sheet. The first part of this assessment involves a statistical analysis and interpretation of the relative changes and variations in sea-surface temperatures (SSTs) and air temperatures around Greenland for the period 1870-2007. This analysis is based on HadISST1 and Reynolds OI.v2 SST analyses, in situ SST and deeper ocean temperature series, surface-air-temperature records for key points located around the Greenland coast, and examination of atmospheric pressure and geopotential height from NCEP/NCAR reanalysis. Second, we carried out a novel sensitivity experiment in which SSTs were perturbed as input to a regional climate model, and document the resulting effects on simulated Greenland climate and surface mass balance. We conclude that sea-surface/ocean temperature forcing is not sufficient to strongly influence precipitation/snow accumulation and melt/runoff of the ice sheet. Additional evidence from meteorological reanalysis suggests that high Greenland melt anomalies of summer 2007 are likely to have been primarily forced by anomalous advection of warm air masses over the ice sheet and to have therefore had a more remote atmospheric origin. However, there is a striking correspondence between ocean warming and dramatic accelerations and retreats of key Greenland outlet glaciers in both southeast and southwest Greenland during the late 1990s and early 2000s. [less ▲]

Extreme snowmelt in Northern Greenland during summer 2008

in EOS : Transactions, American Geophysical Union (2008), 89(41), 391

Extreme snowmelt occurred during summer 2008 over the northern part of the Greenland ice sheet, according to the analysis of microwave data recorded by the Special Sensor Microwave Imager (SSM/I) on board ... [more ▼]

Extreme snowmelt occurred during summer 2008 over the northern part of the Greenland ice sheet, according to the analysis of microwave data recorded by the Special Sensor Microwave Imager (SSM/I) on board the F13 satellite of the U.S. Defense Meteorological Satellite Program (DMSP). New records of the number of melting days were also observed over large portions of the same areas (letters A and B in Figure 1). [less ▲]

Impacts of ice sheet mask and resolution on estimating the surface mass balance of the Greenland ice sheet

Poster (2008, April 15)

The impacts of the spatial resolution and a Greenland ice sheet (GrIS) mask on modelling the Surface Mass Balance (SMB) are studied with the regional climate model MAR coupled with a complex energy ... [more ▼]

The impacts of the spatial resolution and a Greenland ice sheet (GrIS) mask on modelling the Surface Mass Balance (SMB) are studied with the regional climate model MAR coupled with a complex energy balance/snowpack model. On the one hand, too coarse resolution prevents the model from resolving adequately the steep ice sheet margin and the ablation zone, not wider than 100 km in Greenland, where substantial seasonal melting occurs. The resolution affects also the precipitation modelling. On the other hand, a too large ice sheet mask (i.e. with low-altitude ice pixels in the model, where there is no ice in reality) leads to an overestimation of the run-off. In addition, due to the albedo feedback, biases in the ice sheet mask have also consequences on the surface energy balance. [less ▲]

A record negative Greenland ice sheet surface mass balance rate in 2007

Poster (2008, April 15)

Results made with the regional climate model MAR show a record surface melt (592 km³/yr = a global sea level rise of 1.6 mm/yr) of the Greenland ice sheet (GrIS) during summer 2007 compared with 1970-2006 ... [more ▼]

Results made with the regional climate model MAR show a record surface melt (592 km³/yr = a global sea level rise of 1.6 mm/yr) of the Greenland ice sheet (GrIS) during summer 2007 compared with 1970-2006. This record melt, detected also in the microwave satellite data, is associated with very low snowfall (508 km³/yr) inducing a negative Surface Mass Balance (SMB) rate of -65 km³/yr. Such a negative simulated SMB rate is unprecedented in the recent Greenland history. The summer 2007 is associated with a positive SST anomaly, a negative 2006-2007 GrIS winter accumulation and anomalous advection of warm air masses over the GrIS. Sensitivity experiments carried out by the MAR model evaluate the impacts of these anomalies on the Greenland climate and SMB. The main impacts of a warmer SST anomaly in the MAR model are more precipitation over Greenland due to an enhanced evaporation above the ocean and, an increase of surface melt induced by the advection of warmer oceanic air (>0°C) into the continent by the atmospheric part of MAR. A negative winter accumulation anomaly exposes ice and old snow (with a lower albedo) earlier than previous years in the ablation zone which significantly increases the melting given the albedo feedback. Finally, changes in the boundaries forcing of the MAR model test the consequence of the anomalous persistent southerly airflow during June and July. [less ▲]

Last century Greenland ice sheet surface mass balance projections from IPCC AR4 global models

Poster (2008, April)

Results from atmosphere-ocean general circulation models (AOGCM's) for the IPCC 4th Assessment Report are used to investigate surface mass balance (SMB) future projections of the Greenland ice sheet (GrIS ... [more ▼]

Results from atmosphere-ocean general circulation models (AOGCM's) for the IPCC 4th Assessment Report are used to investigate surface mass balance (SMB) future projections of the Greenland ice sheet (GrIS). The most efficient models for the GrIS climate modeling are chosen by comparison between the 1970-1999 outputs (averages and trends) from the 20C3M Experiment outputs, and the reanalyses (ECMWF, NCEP) as well as climatologies. The SMB is estimated from the summer temperature (from which is deduced the run-off) and annual snowfall from the well-adapted AOGCM's. It is validated with 1970-1999 results from the regional climate model MAR by interpolating the AOGCM's outputs on the MAR grid. However, large uncertainties remain in these SMB projections due to the simplified physic and coarse AOGCM's resolution. High resolution simulations made with the MAR model (which simulates explicitly the SMB by taking into account the surface feedbacks) forced at its boundaries by a GrIS well-adapted AOGCM could bring more precise brief replies. [less ▲]

Automatic 1958-2007 daily weather pattern classification applied to an analysis of climatic conditions of wildfires in eastern Belgium

Poster (2008, April)

The daily atmospheric circulation patterns classification is founded on a 100 km regular grid centred on Belgium. The geopotential heights of 500, 850 and 1000 hPa levels were extracted from the ERA-40 ... [more ▼]

The daily atmospheric circulation patterns classification is founded on a 100 km regular grid centred on Belgium. The geopotential heights of 500, 850 and 1000 hPa levels were extracted from the ERA-40 database on the period 1958-2002 and from ECMWF operational analysis until the end of year 2007. The classification was based on a similarity index calculated on the orientation of exaggerated slopes of different daily geopotential fields. Wildfire occurrences were analyzed in April and September (which are the two months with the most frequent wildfire-days in Belgium) together with monthly frequencies and persistences of daily atmospheric circulation pattern classes as well as with yearly variability of weather climate conditions. [less ▲]

Estimation of the Greenland ice sheet surface mass balance for the 20th and 21st centuries

in The Cryosphere [=TC] (2008), 2

Results from a regional climate simulation (1970–2006) over the Greenland ice sheet (GrIS) reveals that more than 97% of the interannual variability of the modelled Surface Mass Balance (SMB) can be ... [more ▼]

Results from a regional climate simulation (1970–2006) over the Greenland ice sheet (GrIS) reveals that more than 97% of the interannual variability of the modelled Surface Mass Balance (SMB) can be explained by the GrIS summer temperature anomaly and the GrIS annual precipitation anomaly. This multiple regression is then used to empirically estimate the GrIS SMB since 1900 from climatological time series. The projected SMB changes in the 21st century are investigated with the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). These estimates show that the high surface mass loss rates of recent years are not unprecedented in the GrIS history of the last hundred years. The minimum SMB rate seems to have occurred earlier in the 1930s and corresponds to a zero SMB rate. The AOGCMs project that the SMB rate of the 1930s would be common at the end of 2100. The temperature would be higher than in the 1930s but the increase of accumulation in the 21st century would partly offset the acceleration of surface melt due to the temperature increase. However, these assumptions are based on an empirical multiple regression only validated for recent/current climatic conditions, and the accuracy and time homogeneity of the data sets and AOGCM results used in these estimations constitute a large uncertainty. [less ▲]

Automatic 1958-2007 daily weather pattern classification applied to an analysis of climatic conditions of wildfires in eastern Belgium

Poster (2008)