Revisions during 2007

8 June 2007

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5 June 2007 Introduction of Cycle 32r2 This version includes the following changes:

  • Three-minimization version of 4D- Var assimilation scheme (T95/T159/T255) with improved moist linear physics (cloud and convection)
  • Improved parametrization of the heterogeneous ozone chemistry
  • New short-wave radiation scheme ( RRTM-SW), plus McICA cloud-radiation interaction   and   MODIS albedo
  • Retuned ice particle size
  • Revised subgrid-orography scheme
  • Explicit numerical treatment of convection in the moist tangent linear model used in the calculation of tropical singular vectors

Cy32r2 will allow the monitoring of ASCAT and IASI data.   The change related to the ASCAT monitoring will also have an impact, albeit small, on the current use of scatterometer data, in particular the observations around the ice edge.

The impact of the main meteorological changes on the performance of the forecasting system has been tested in research mode for the months of July to November 2006, and in pre-operational runs for the period December 2006 to May 2007. The greatest impact is in the tropical troposphere which showed significant improvements at all forecast ranges. There are also moderate but statistically significant improvements in the extra-tropical troposphere, particularly in the first four days.

The EPS has been tested for December 2006. In the extra-tropics, ensemble spread is similar to the operational suite, while at 500 hPa the ensemble-mean error is reduced. In the tropics the spread at 850 hPa is increased, moving closer to the ensemble-mean error.

The new GRIB model identifiers are: 129 (atmospheric model), 116 (global wave model) and 216 (limited area wave model).

The monthly forecast system also runs with this new IFS cycle.

6 November 2007 Introduction of Cycle 32r3 The new cycle includes significant changes to the model physics, including the convection scheme, with a beneficial increase in model activity globally, but in particular in the tropics.

The main changes included in this cycle are:

  • New formulation of convective entrainment and relaxation timescale
  • Reduction in free atmosphere vertical diffusion
  • New soil hydrology scheme
  • New radiosonde temperature and humidity bias correction
  • Increase in number of radio occultation data from COSMIC
  • Assimilation of AMSR-E, TMI, SSMIS window channels (clear sky)
  • Assimilation of SBUV ( NOAA-17, NOAA-18) and monitoring of OMI ozone data

The impact of the new cycle on the performance of the forecasting system has been tested in research mode for the months of January to May 2007, and in pre-operational runs over the period June to September 2007. The new cycle shows improved scores for the extra-tropical southern hemisphere throughout the forecast range, and for the northern hemisphere in the first half of the forecast.   There is a substantial improvement to the lower tropospheric winds in the tropics compared to observations. Surface weather parameters have improved in the new system, in particular through a reduction in the biases of 2m temperature mainly over the Americas and better precipitation forecasts over Europe.

The main changes to the EPS included in this cycle are:

  • initial perturbation amplitude reduced by 30%
  • singular vectors targeted on tropical cyclones are computed with the new moist physics package in the tangent-linear and adjoint models (as used in the operational in 4D- Var since cycle 32r2).

The reduction of the initial perturbation amplitude resulted in a good match of spread and ensemble mean error. The magnitude of the reduction was based on preliminary experimentation over 13 summer cases and 13 winter cases. The EPS has also been evaluated in pre-operational runs during June to September 2007. Results confirm that the reduction in initial spread leads to a generally improved match between spread and average ensemble mean error throughout the forecast range for the extra-tropics, with slight over-activity towards day 15. Probabilistic skill is generally improved at mid-latitudes. Preliminary experimentation with the new moist physics package over 27 summer cases indicates an improved reliability of the tropical cyclone strike probability forecasts and neutral impact in the extra-tropics. ROC statistics indicate that these changes also had a beneficial impact on probabilistic precipitation forecasts over Europe.

The main technical changes included in this cycle 32r3 are:

  • Four new pressure levels will be introduced in the analyses and deterministic forecast runs: 600, 800, 900 and 950 hPa. These will be available through MARS and in the dissemination.
  • Corrections to the radiation post-processing in the IFS will correct/improve the following parameters:

            57         UVB                  Downward UV radiation at the surface

            58         PAR                  Photosynthetically active radiation at the surface

            59         CAPE                Convective available potential energy

The new cycle also includes changes in the hydrology of the land surface scheme which may have consequences for users of soil moisture (SM).  In the current operational system ( TESSEL) the land surface makes use of a single global soil type (loamy soil). Therefore, SM effectively ranges from field capacity (FC, with no stress on evaporation) to permanent wilting point ( PWP, where evaporation stops).

In the new cycle, the soil hydrology has been improved and a global distribution of soil type (based on the FAO soil texture data set) has been introduced. The implication is that effective soil moisture range between PWP and FC varies geographically. For instance the sandy soils will be dryer than before and the fine texture soils (clay) will have a higher soil moisture than before in line with observations.

This model change may have consequences for applications where soil moisture is used as initial condition for other models or for applications where soil moisture is used as a dryness indicator. For those applications it might be necessary to scale to the so-called soil moisture index defined as (SM- PWP) /(FC- PWP).  This is an index between 0 at the permanent wilting point to 1 at field capacity.  It is an indicator for the "wetness" of the soil and can be used as an intermediate step to scale soil moisture from one model to another in case these models use different soil characteristics.

More information can be found at

Cy32r3 soil hydrology changes

The web page provides a MARS-compute based script and guidelines to compute the soil moisture index.   Details about the availability of test data are also given.

The new GRIB model identifiers are: 130 (atmospheric model), 116 (global wave model) and 216 (limited area wave model).

The monthly forecast system also runs with this new IFS cycle.