Cycle 43r1 summary of changes

Horizontal

• Atmospheric (unchanged)
  • HRES: O1280
  • ENS Days 1 - 15: O640
  • ENS extended (Days 16 - 46): O320
• Wave (unchanged)
  • HRES-WAM: 0.125°
  • HRES SAW: 0.1°
  • ENS-WAM: 0.25°
  • ENS-WAM Extended: 0.5°
• Ocean (changed)
  • NEMO: 0.25°

Vertical (unchanged)

• Atmospheric
  • HRES: L137
  • ENS: L91

• Ocean (changed)
  • NEMO: 75

• HRES
• ENS
• HRES-WAM
• HRES-SAW
• ENS-WAM

Data Assimilation     

• The sea-surface temperature (SST) perturbations used in the EDA have been upgraded
• The EDA-derived background error estimates used in 4DVAR
• The weak constraint option of 4DVAR has been reactivated
• The land surface assimilation of SYNOP screen level observations now accounts for the vertical distance between the observations and model grid points
• A new ocean analysis/re-analysis (ORAS5) has been implemented.

Observations    

• Radiance assimilation will now take the viewing geometry more fully into account, by evaluating the radiative transfer along slantwise paths (instead of vertically).
• A better treatment of observation uncertainty for IASI and CrIS has led to updated observation error covariance matrices and a change of ozone anchor channels in bias correction.
• The channel selection for the hyperspectral infrared instrument CrIS has been revised and now uses 117 rather than 77 channels
• The aerosol detection scheme for IASI has been revised making it independent of the bias correction. The scheme is also applied to both CrIS and AIRS.

Model changes    

• A new CAMS ozone climatology is now used, consisting of monthly means of a re-analysis of atmospheric constituents (CAMSiRA) for the period 2003 to 2014.
• Changes to boundary layer cloud for marine stratocumulus and at high latitudes.
• Modifications to surface coupling for 2 metre temperature.
• Assimilation of snowfall from the NEXRAD RADAR network over the USA.
• New model output fields include four cloud and freezing diagnostics (for aviation), a new direct-beam solar radiation diagnostic and improvements to the sunshine duration diagnostic.

Medium-range ENS    

• The horizontal and vertical resolutions of the ocean model (NEMO v3.4.1) used by ENS is increased from 1 degree and 42 layers to 0.25 degree and 75 layers (ORCA025Z75).  An interactive sea-ice model (the Louvain-la-Neuve Sea Ice Model - LIM2) is introduced so that sea-ice cover evolves dynamically. Previously it was persisted for 15 days; over the next 30 days of the forecast, it was relaxed towards the climatology of the previous 5 years.
• Ocean initial conditions are taken from ORAS5 instead of ORAS4.
• A global fix for tendency perturbations in the stochastic model error scheme SPPT to improve global momentum, energy and moisture conservation properties.
• The land initial conditions of the ENS re-forecasts are taken from a new land surface simulation at the native ENS resolution (T_CO639, ~16km),  replacing the previous configuration that used ERA-Interim/Land (at T_L255 resolution,  ~80 km)

Upper Air

The new model cycle provides improved high-resolution forecasts (HRES) and ensemble forecasts (ENS) throughout the troposphere and lower stratosphere. In the extra-tropics, error reductions of the order of 0.5-1% are found for most upper-air parameters and levels. The improvement in the primary headline score for the HRES (lead time at which the 500 hPa geopotential anomaly correlation drops below 80%) is about 1 h.

Improvements are most consistently seen in verification against the model analysis. In the tropics, there is a small degradation (both against analysis and observations) of temperature near the tropopause in terms of root mean square error (RMSE) but not in terms of anomaly correlation. This is due to a slight cooling caused by a modification in the treatment of cloud effects in the vertical diffusion scheme, which overall leads to improved cloud cover. While there is a consistent gain for upper-air parameters on the hemispheric scale, some continental-scale areas, such as North America and East Asia, show statistically significant improvements only at some levels and for some parameters.

Increases in upper-air skill of the ENS are generally similar to the HRES, with a substantial gain for mean sea level pressure. The improvement in the primary headline score for the ENS (lead time at which the CRPSS of the 850 hPa temperature drops below 25%) is small (of the order of 0.5 h). The spread-error relationship is generally improved, partly due to reduced error and partly due to increased spread. For some parameters this improvement is quite significant, such as the 850 hPa wind speed in the tropics, where the under-dispersion is reduced by about 20% in the medium range.

Weather parameters and waves

The new model cycle yields consistent gains in forecast performance in the tropics and extra-tropics for total cloud cover, mostly due to a reduction of the negative bias in low cloud cover.  

Changes in precipitation over land areas are small and overall neutral.

The increase in forecast skill for 2m temperature is most pronounced in the short and medium range, where it amounts to ~1% reduction of the RMSE in the northern hemisphere extra-tropics, and up to 2% over some land areas such as Europe and North America. In the tropics there is an increase of 0.5-1% in the RMSE for 2m temperature, connected to a slight increase of the overall cold bias at low latitudes. In the ENS there is a significant improvement in 2m temperature amounting to a 3% reduction in the continuous ranked probability score (CRPS) in Europe.

There is an increase of the RMSE of 2m humidity by about 1% in winter associated with the introduction of limited evapotranspiration when the uppermost soil layer is frozen. This change contributes to the improvements in 2m temperature.  

10m wind speed shows error reductions of 0.5-1% over the ocean, leading to improvements in significant wave height and mean wave period, especially in the tropics and southern hemisphere. Over land areas, changes in 10m wind speed forecast skill are generally neutral to slightly positive.

Monthly forecast

Verification results show a modest positive effect on skill scores although the differences are not statistically significant. There is a substantial improvement in the skill scores for the Madden-Julian Oscillation (MJO), corresponding to a gain in lead time of 0.5-1 day at a forecast range of 4 weeks. Also, MJO spread is increased, bringing it closer to the RMSE. Verification of precipitation against analysis shows some degradation in the tropics which is not statistically significant, and a reduction of precipitation biases in the northwest Pacific.

Sea ice

The new cycle introduces a prognostic sea-ice model, leading to a significant reduction of the RMSE of sea ice fraction in the later medium range.

• Upgrade to the dynamical ocean model used for the medium-range ensemble and its monthly extension
• Changes to GRIB encoding
• Changes to forecast products
  • new model output

• Atmospheric: 147
• Ocean wave:  112
• Standalone ocean wave: 212