ABSTRACT:The Met Office has developed a 4D-Var data assimilation system, which was implemented in the global forecast system on 5 October 2004. This followed a development path based on the previous 3D-Var configuration, with many aspects kept in common. A 4D-Var capability was provided by the introduction of a linear perturbation forecast model based on the Unified Model, the non-hydrostatic grid-point model producing our operational forecasts.There were clear advantages in verification of forecasts compared to the equivalent 3D-Var configuration, with an improvement of 2.6% in a composite skill score verified against observations during pre-operational trials. The largest differences in model evolution occur in storm-track regions in the extratropics. Overall, improvements in verification scores as measured against observations were larger than those measured against analyses, particularly at upper levels. There is an improvement in verification of surface parameters (10 m wind, 1.5 m temperature and relative humidity) against analyses. The strongest impact on fitting observations is seen for satellite radiances with weighting functions peaking in the stratosphere and upper troposphere. The largest changes to assimilation increments occurred in the top model levels, particularly wind increments which became much larger near the model top.Similarities were found in the signal of 4D-Var versus 3D-Var for models at two different resolutions, from which we infer that low-resolution trials remain valid for exploring some aspects of 4D-Var before confirmation in full-scale tests.  Crown

A new humidity analysis variable has been successfully introduced into the Met Office's variational data assimilation system. The new variable uses a transformation consisting of a nonlinear normalization and a link with temperature increments that is a function of background (forecast) humidity. The normalization (which is the more important aspect) makes the new variable's errors more symmetrical and thus better represented by the variational cost function. As in the previous operational system, water vapour and cloud are combined into a single total water variable for the analysis step. The transform is now operational in both global and limited-area systems. The forecast improvements -to the mass as well as the humidity fields -are largest in the Southern Hemisphere and there is a better fit of both background and analysis to humidity-sensitive satellite channels. The results suggest that the transformation is particularly beneficial for the use of satellite data. The transform reduces the problem of negative humidities in the analysis which were more prevalent over the ocean.

SUMMARYA set of four experiments is described which measure the expected beneficial aspects of incremental fourdimensional variational (4D-Var) compared to 3D-Var data assimilation systems: allowing for the time of each observation in the full and increment fields with which it is compared, and using time-evolved covariances. Judging each scheme by the overall accuracy of resulting numerical weather prediction forecasts compared to observations, each aspect is shown to provide benefit.On other measures of analysis quality, such as the fit of short-period forecasts and analyses to observations, the benefits of 4D-Var are less clear; it is sometimes worse. Perhaps 4D-Var is improving the analysis of growing modes, which are more important for forecasts, without improving all aspects of the analysis.Our basic 4D-Var was not provided with many observations distributed in time, and had very simple parametrizations. There is an expectation of enhanced benefits as these aspects are developed.

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We compared telesonography to usual patient care in a rural clinic in the Dominican Republic. A total of 108 low-income Dominican and Haitian patients volunteered to participate. The patients were randomly assigned to either telesonography or control groups. Patients in the telesonography group were scanned and sonographic images and Request for Interpretation (RFI) forms were sent by email to six volunteer radiologists in the USA. Completed RFI forms were transmitted back to the clinic at the radiologists' earliest convenience. Patients in the control group received an ordinary ultrasound referral, which required travel to a tertiary medical centre where their scans were completed by a local sonographer. Sonographic reports from the control group were hand delivered to the referring physician at patient follow-up. The telesonography system provided a four-fold increase in the proportion of patient follow-ups and a six-fold increase in the proportion of returned radiological reports. In the telemedicine group, the median total elapsed time from referral to report return was 17.8 h (interquartile range, IQR 12.2-27.1) and the median time to patient follow-up was 67.1 h (IQR 45.9-113.7). The latter was similar in the control group, where the median total elapsed time was 76.7 h (IQR 65.8-144.7). The pilot study demonstrated that store-and-forward telesonography reduced time to diagnosis and increased the continuity of care compared to the usual ultrasound referral system in the region of the Dominican Republic which was studied.