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Implementation timeline
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Meteorological content
In this model cycle single precision for ENS (forecast up to d+46 and hindcast) and HRES (forecast) will be introduced. The will be increased to 137 to bring it in line with HRES.Meteorological impact
Evaluation of 47r2
The two changes at 47r2 were a reduction to single precision in our HRES and ENS forecasts and (with the computational savings made) an increase from 91 to 137 levels in the ENS forecast. Our deterministic and ensemble analyses, including background forecasts, remain at double precision, and so are unaffected.title | CURRENT EVALUATION >> |
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Score cards
The change to single precision is neutral in terms of HRES skill (less than a 0.3% change is typical for the troposphere, and the frequency of statistically significant differences is in line with what one might expect by chance), but there are benefits of the increased levels in the ENS.
The ensemble score card is overwhelmingly positive and statistically significant (occasional negative changes are small in magnitude.)
Scorecards presenting the new cycle performance are regularly updated:Tropical Cyclones in the Ensemble (all basins)
The ensemble scores for Tropical Cyclones show reduced intensity errors (largely associated with reduced bias: ~2hPa mean reduction in central pressure) in the medium-range, increased spread, and improved reliability as measured by the spread-error agreement. The cycle is neutral in terms of track errors.
Root mean square errors in the ensemble mean of tropical cyclone (TC) intensities and locations, along with the standard deviation (spread) of TC intensities and locations amongst the ensemble members. Results are based on all TC basins for the periods 20191125-20200228 and 20200510-20201130. The numbers at the top of the top panel indicate the number of TCs which could be evaluated at each lead time.
Tropical Cyclone Activity/Probability products (medium and extended ranges)
In tandem with the reduction in mean central pressure for tropical cyclones in the ENS in 47r2, referenced above, there are also modest increases, on average, in tropical cyclone counts, as represented on tropical cyclone activity / genesis / strike probability charts, for medium range (here) and extended range (here). For the extended range users are encouraged to reference tropical cyclone activity anomaly charts: such products should be more consistent through cycle changes because we are normalising against the model climates for the respective cycles.
ENS vertical profile product at 20°S 90°W (VT = 20210123 at 12UTC)
The extra levels mean that sharper inversions can be resolved. For example, the ensemble vertical profile product now uses 34 model levels below 700hPa instead of the previous 22. The 47r2 test profile, which uses the new mapping of model levels, shows little obvious change although the thermal inversion is indeed a little sharper at 47r2. Users will need to ensure that they extract the correct model levels when creating their own forecast products. Over the testing period, the root-mean-square-error of the ensemble-mean T850 is reduced in the subtropics.
ENS vertical profile tephigram product for forecasts started on 20210121 at 0UTC and at lead time 60h, for temperature (red) and moisture (dewpoint, green). Shaded bands denote the minimum, 25th and 75th percentiles and maximum for temperature and dewpoint distributions at each level. The median value is shown by a thin solid line. A thick solid line represents HRES and a thick dashed line represents the Control.
Zonal-mean Temperature bias in Control forecast (day 10)
The extra levels also allow the ENS to better resolve gravity waves in the vertical, and this helps reduce the cold bias in the upper troposphere / lower stratosphere, e.g. by about 33% at day10. This improvement persists into the extended range.
Zonal means of mean temperature errors at a lead time of 10 days in the ensemble control forecast. More saturated colours indicate statistical significance at the 5% level using a t test accounting for temporal correlation. Evaluated over all forecasts started 20191125-20200228 and 20200510-20201107.
Madden Julian Oscillation (assessment of bivariate index)
In the extended range we also see the amplitude of the Madden-Julian Oscillation (MJO) being better sustained (amplitude loss by day 15 is now ~15% rather than previously ~20%), increased MJO spread and improved scores. Changes come mostly from improvements in tropical zonal winds at 200hPa.Score differences (47r2 minus 47r1) for the Wheeler and Hendon (2004) bivariate Real time Multivariate Madden Julian Oscillation (RMM) index based on reforecasts initialised at the start of each month for the period 1989-2016. The differences shown are for ( i ) the fair version of the Continuous Rank probability Skill Score (FCRPSS), (ii) the bivariate anomaly correlation (CORR), (iii) the bivariate root mean square error (RMSE), (iv) the bivariate spread of the ensemble with respect to ensemble mean, (v) amplitude of the RMM index, and (vi) the phase of the RMM index. Bivariate scores are calculated following Gottschalck et al. (2010) and verified against the RMM index constructed from the ERA5 analysis. Triangles indicate increased (pointing up) and decreased (pointing down) values, which are significant when the shading is with more saturated.
Indicators related to convection
The introduction of more levels in ENS has slightly changed the values of some convective indicators. CAPE and CAPE-shear are slightly higher, on average, in the 47r2 ENS than they were in the 47r1 ENS. Lightning density is also slightly higher in 47r2 - global data for April 2021, for example, showed an increase of 20%. Meanwhile values of these parameters in HRES have not changed. Whilst it is difficult to verify the value increases seen in ENS, a significant plus for users is that HRES and ENS representations of CAPE, CAPE-shear and Lightning Flash Density become more compatible. The plots below show examples of differences between 47r2 and 47r1, for CAPE and CAPE-shear daily maxima, in the Model Climate.Day 2 differences (47r2 minus 47r1) in the (20-year) Model Climate (M-Climate) values, for a valid date of 6 May, for CAPE-shear (mean only), and CAPE (mean, and 95th (Q95) and 99th (Q99) percentiles), based in both cases on the daily maxima of hourly values. Red colours mean that the 47r2 ENS is delivering higher values of these parameters in some systematic sense. Standard units apply to the legends (m2/s2 for CAPE-shear, J/kg for CAPE).