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Changes to the Met Office seasonal prediction system

Notification of changes to the seasonal prediction system

GloSea system update: GloSea6 initial changes – February 2021

The GloSea system had a system upgrade in February 2021.  This was the first of two upgrades planned for ‘GloSea6 – a large ensemble Global Seasonal Forecasting System’.  This initial upgrade updated the Atmosphere, Land, Ocean and Sea Ice models.  GloSea6 uses more recent version of these model components.  Improvements include convection changes, the introduction of multi-layer snow and multi-layer sea ice and the introduction of icebergs.  It also updates the model forcings to use annually changing ozone in the hindcasts and solar irradiance variations in the hindcasts and forecasts.  This February 2021 update has not changed the ensemble size.  This is planned for a later date.

 

  •   Products with an issue date of February 2021  will be derived from the new system;
  •   Products for all future dates will be derived from the new system until further notice;
  •   Forecasts issued prior to February 2021, based on the former system (see below) will remain in place on the website;
  •   Corresponding changes will be made to the verification information.

GloSea5 Land Surface Initialisation – April 2019

From April 2019 GloSea5 will use a new approach for land surface initialisation. Initial conditions for soil moisture, soil temperature and snow will be generated by forcing the JULES land surface model with data from the Japanese Meteorological Agency’s atmospheric reanalysis (JRA-55). This approach allows us to create consistent land surface initial conditions for both the forecast and the full hindcast period (1993-2016). It also adds interannual variations to the soil moisture, whereas previously the soil moisture was initialised from a climatology.

 

  • Products with an issue date of April 2019 will be derived from the new system;
  • Products for all future dates will be derived from the new system until further notice;
  • Forecasts issued prior to April 2019, based on the former system (see below) will remain in place on the website;
  • Corresponding changes will be made to the verification information.

GloSea5 extended hindcast - November 2018

In November 2018 an extra year will be added to the hindcast set to make the total number 24 years . The new hindcast set will cover the years 1993 to 2016. This increase in hindcast length will be delivered to all users of our seasonal forecasts and is part of our contribution to the Copernicus Climate Change Service (C3S) Multi-model Seasonal Forecast Project.

GloSea5 extended hindcast - January 2017

In January 2017 the number of ensemble members in the GloSea5 hindcast set will be increased from 3 to 7. This increase applies to each start date (1st, 9th, 17th, and 25th of each month) and year (1993-2015)  in our hindcast set. These historical forecasts are used for bias correction of the forecast members and to estimate the skill of the system. Increasing the number of hindcast ensemble members will improve our estimation of the skill.

This increase in hindcast ensemble size will be delivered to all users of our seasonal forecasts and is part of our contribution to the Copernicus Climate Change Service (C3S) Multi-model Seasonal Forecast Project.  

GloSea5 extended hindcast - March 2016

In March 2016 the number of years in the GloSea5 hindcast set will be increased from 14 to 23. The new hindcast set will cover the years 1993 to 2015. This increase in hindcast length will be delivered to all users of our seasonal forecasts and is part of our contribution to the Copernicus Climate Change Service (C3S) Multi-model Seasonal Forecast Project.  
 
The hindcasts, or historical re-forecasts are used for bias correction of the forecast members and to give a lower bound on the skill of the system (as real time forecasts contain a larger number of ensemble forecast members). Three hindcast members continue to be produced for each year and are initialised on the same fixed calendar dates: 1st, 9th, 17th, and 25th of each month.

GloSea5-GC2 - February 2015

In February 2015 a new configuration of the coupled model was implemented in the GloSea5 prediction system; products from the new system will be made available around 10 February 2015 in the following way: 
 

  • Products with an issue date of February will be derived from the new system, GloSea5-GC2;
  • Products for all future dates will be derived from the new system until further notice;
  • Forecasts issued prior to February 2015, based on the former system (GloSea5, see below) will remain in place on the website;
  • Corresponding changes will be made to the verification information.

All future references to this new system in the context of real-time forecasts and hindcasts will use the name GloSea5, rather than the full GloSea5-GC2, unless in the context of comparisons with the previous version of the system when the distinction will be clearly made.

The main change in GloSea5-GC2 is the implementation of a new configuration of the coupled model (GC2.0), which consists of modular component configurations Global Atmosphere 6.0 (GA6.0), Global Ocean 5.0 (GO5.0), Global Sea Ice 6.0 (GSI6.0) and Global Land 6.0 (GL6.0). Key scientific advances to each of these constituents are:

  • GA6.0 - Implementation of a new dynamical core (ENDGame).
  • GO5.0 - Improvements to oceanic vertical mixing scheme to improve the mixed layer representation of the world's oceans, which is important to seasonal forecasting, marine ecosystems, and many other aspects of the climate system. Changes have also been made to the NEMOVAR assimilation scheme to improve the initialisation of sub-surface temperature and salinity.
  • GSI6.0 - Improvements to the albedo and surface roughness of the sea ice to achieve a more realistic seasonal cycle of sea ice.

GloSea5 - July 2013

Products from the new system will be made available around 15 July 2013 in the following way:

  • Products with an issue date of July will be derived from the new system (GloSea5).
  • Products for all future dates will be derived from the new system until further notice;
  • Forecasts issued prior to July 2013, based on the former system (GloSea4, see below) will remain in place on the website;
  • Corresponding changes will be made to the verification information.

The main improvements in the GloSea5 system are listed below:

  • Improvements to the model horizontal resolution for both the atmosphere and ocean components: the new atmosphere and land surface resolution is 0.833 ° by 0.556 ° (~50 km in mid-latitudes); the new resolution for the ocean and sea ice components is 1/ 4°;
  • Upgrade to ocean data assimilation: the new system uses NEMOVAR.

Upgrade to GloSea4 - November 2010

Products from the upgraded system will be made available on 3 December 2010 in the following way:

  • Products with an issue date of November 2010 will be removed and replaced with equivalent products from the upgraded system;
  • Products for all future dates will be derived from the upgraded system until further notice;
  • Forecasts issued with the former system prior to November 2010 will remain in place on the website;
  • Corresponding changes will be made to the verification information.

The main changes made to the GloSea4 system are listed below:

  • Improvements to the coupled-model (HadGEM3) physics, including a scheme to assimilate sea-ice concentrations: sea-ice in both forecast and hindcast mode, is now initialised from observed values rather than climatology;
  • Improvements to the model resolution for both the atmosphere and ocean components: the new atmosphere resolution is ~120 km in the horizontal and 85 levels (improving resolution of the stratosphere); the new ocean resolution is 1 ° and 75 levels. The ocean-atmosphere coupling frequency is 3 hours;
  • The hindcast period used has been updated to a more recent period, 1996 to 2009.