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Meteorological changes
Forecast
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- After consultation with our users, we have stopped archiving the Budget Values (shortName BV, paramId 128128).
Meteorological impact
Comparison of scores of model cycle 41r1 and cycle 40r1
Upper air
The new model cycle provides improved high-resolution (HRES) and ensemble forecasts (ENS) throughout the troposphere and in the lower stratosphere. In the HRES there is a significant reduction of forecast errors in the upper-air fields in the extra-tropics and tropics. Improvements are seen both in verification against the model analysis and verification against observations. They are largest and most significant in the tropics and southern hemisphere and smaller but still significant in the northern hemisphere. In the ENS improvements are largest and most consistent in Europe. In the southern hemisphere there is a deterioration of ENS temperature at 850 hPa which is, however, present only in the verification against the e-suite’s own analysis. It is due to a change in the analysis in the area resulting from a change in the usage of water vapour sounding data over sea ice.
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As in current operations, the AL field is not used in the forecast; it provides an indication of the total (broadband) albedo climatology (excluding snow and ice effects) for diagnostic use only. Users are advised to use the forecast field (FAL 243128) which also contains the snow and ice effects. FAL is a prognostic variable that changes during the forecasts.
You can read a detailed description of the albedo in the model.
ENS Leg B extended from 32 to 46 days on Mondays and Thursday (at 00UTC)
Both the monthly forecasts and re-forecasts are extended to 46 days. At this range forecast skill is relatively low and the forecasts should be used with care. However, results have shown that there is positive skill in some aspects of the forecasts in the 30-45 day range. Users are encouraged to read the review of extended-range performance in ECMWF Technical Memorandum 738 on 'Sub-seasonal predictions' for further information, before developing products using these forecasts. ECMWF will continue to investigate forecast performance and potential products for the 30-45 day range.
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An initial assessment of freezing rain is reported in the Autumn 2014 ECMWF Newsletter. Although the first evaluation for a number of case studies shows promise, further work is required to assess the ability of the IFS to predict the probability of freezing rain at different forecast ranges – feedback about these experimental products is welcome.
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As a weather hazard, fog is an extremely important, but difficult, variable to be able to predict. The visibility diagnostic includes information on the reduced visibility in fog. However, correctly predicting very low visibility (fog) is dependent on predicting the correct dynamic and thermodynamic conditions in the boundary layer and can be highly variable in space and time, often tied to orographic features that are not resolved by the model, and a probabilistic approach using the ensemble members will likely be of most benefit.
It should be stressed that this is a preliminary implementation of a "visibility" diagnostic, but there are plans for further evaluation and improvement in the future. Further evaluation and feedback is always welcome.
Ocean waves (wind waves and swell)
In IFS cycle 41r1 a new partitioning of ocean waves into wind waves and swell has been introduced. The new scheme splits the wave spectra into wind waves and up to three swell partitions (swell 1, 2 and 3, ranked by their respective energy). There is a new set of model output parameters (significant height, mean direction and mean period) to characterise each of the three swell partitions.
As originally implemented in IFS cycle 41r1, the new wind waves partition was different to that determined by the previous scheme, usually containing slightly more energy. The total swell, defined by all spectral components that are not wind waves, was also affected by the introduction of the new partitioning scheme, being significantly less smooth than before (this is a feature of how the new partitioning works). This had the unintended consequence that users were unable to use the new significant height of total swell field in the same way as before.
Therefore, starting with the forecast from 06 UTC on 19 May 2015, ECMWF reverted to the previous scheme to compute both total swell and wind waves parameters. The three new swell partition parameters based on the new scheme are still produced. However, the sum of their energy is not equal to the energy contained in the total swell (the difference being the extra wind waves energy). The new parameters remain experimental products and are not included in the Catalogue of ECMWF real-time products.
A full list of the new parameters introduced at IFS cycle 41r1 is provided in the table below. More detailed information about these parameters can be found in the parameter database.
Table of new parameters introduced at IFS cycle 41r1
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EMOSLIB has been updated to handle the new wave parameters. Users using these and/or the extended Limited Area wave model fields should use the new version 402, which can be selected with 'module' at ECMWF or which is available for download.
MARS
Users accessing the new wave fields and/or the extended Limited Area wave model fields should use the latest version of MARS ('mars -n'). The default version of MARS will be updated before the implementation of the new cycle.
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