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On 15 March 2005, the Meteorological Service of Canada (MSC) proceeded to the implementation of a four-dimensional variational data assimilation (4DVAR) system, which led to significant improvements in the quality of global forecasts. This paper describes the different elements of MSC's 4DVAR assimilation system, discusses some issues encountered during the development, and reports on the overall results from the 4DVAR implementation tests. The 4DVAR system adopted an incremental approach with two outer iterations. The simplified model used in the minimization has a horizontal resolution of 170 km and its simplified physics includes vertical diffusion, surface drag, orographic blocking, stratiform condensation, and convection. One important element of the design is its modularity, which has permitted continued progress on the three-dimensional variational data assimilation (3DVAR) component (e.g., addition of new observation types) and the model (e.g., computational and numerical changes). This paper discusses some numerical problems that occur in the vicinity of the Poles where the semi-Lagrangian scheme becomes unstable when there is a simultaneous occurrence of converging meridians and strong wind gradients. These could be removed by filtering the winds in the zonal direction before they are used to estimate the upstream position in the semi-Lagrangian scheme. The results show improvements in all aspects of the forecasts over all regions. The impact is particularly significant in the Southern Hemisphere where 4DVAR is able to extract more information from satellite data. In the Northern Hemisphere, 4DVAR accepts more asynoptic data, in particular coming from profilers and aircrafts. The impact noted is also positive and the short-term forecasts are particularly improved over the west coast of North America. Finally, the dynamical consistency of the 4DVAR global analyses leads to a significant impact on regional forecasts. Experimentation has shown that regional forecasts initiated directly from a 4DVAR global analysis are improved with respect to the regional forecasts resulting from the regional 3DVAR analysis.

In this paper, a weak constraint formulation of the digital filter based on the Dolph-Chebyshev window is introduced in a preoperational version of the 4DVAR analysis of Météo-France. The constraint is imposed only on the analysis increments to damp spurious fast oscillations associated with gravity-inertia waves. In the incremental formulation of 4DVAR, the analysis increments are obtained from a global model at a uniform low resolution with a simplified set of physical parameterizations, while the high-resolution forecast is obtained with a model that uses a variable-resolution grid having a higher resolution over France and the complete set of physical parameterizations. Both models have the same vertical resolution. In a set of preliminary experiments using the same background field and the same set of observations, it is shown that the weak constraint imposed only on the low-resolution increments manages to control efficiently the emergence of fast oscillations in the resulting high-resolution forecast while maintaining a closer fit to the observations than is possible if the digital filter initialization is applied externally on the final analysis increments. It is also shown that this weak constraint does not add any significant computer cost to the 4DVAR analysis. Finally, 4DVAR has been cycled over a period of 2 weeks and the results show that, compared to 3DVAR, the initial dynamical imbalances are significantly less in 4DVAR even if no constraint is imposed at all. However, it has been noted that the innovation statistics show a positive impact when a constraint is applied.

In this paper, the operational 3D variational data assimilation system (3D-var)

A meta-analysis was done to measure the effect of physical activity on the bone mass of healthy postmenopausal women. All studies published between 1966 and 1996, in French or English, were reviewed for inclusion from Medline search, bibliographies of relevant studies, review articles and books. Studies had to be prospective intervention trials, randomized or not, evaluating the effectiveness of an exercise program of any duration, frequency and intensity, with a control group. Studies had to measure bone parameters and involve healthy postmenopausal women over 50 years of age who were free of symptomatic osteoporosis at the time of study entry. Effect sizes (ES) were calculated for each bone parameter and site measured in every eligible study according to Hedges and Olkin. DerSimonian and Laird's model was used to estimate overall effect sizes when combining studies. All analyses were bone parameter and site specific. Of 217 papers extracted from the literature, 187 did not meet eligibility criteria and 12 others were rejected. The two main reasons for rejection were that both genders were combined in the analyses and no exercise group without drug interaction was present. Eighteen studies were included for meta-analysis. Taking into account the frequency, duration, compliance rate and average age of the subjects, the programs were judged of moderate intensity and focused on walking, running, physical conditioning and aerobics. A significant effect of physical activity was detected on the bone mineral density at the L2-4 level of the lumbar column in studies published after 1991 (ES = 0.8745, p < 0.05). No effect could be seen, however, on forearm and femoral bone mass. Although applied to a small number of studies, this meta-analysis suggests that exercise programs in a population of postmenopausal women over 50 years of age are effective for preventing spinal bone mineral density loss at the L2-4 level. However, such programs do not have any effect on the forearm or femoral bone mass.

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These results suggest that after 12 months, exercising can produce a significant increase above initial levels in the functional fitness, well-being, and self-perceived health of osteopenic women. Intensity of back pain can also be lowered by exercise. The exercise program succeeded in stabilizing spinal BMD but had no effect on femoral BMD.

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