Sort Options:

• Sort By Last Name
• Sort By Title

Other:

• Print All

Sort by time-scale:

• Short
• Intermediate
• Long
• SHOW ALL

Systematic Errors in Parametrizations in Global NWP : Evaluation Against Observational Data and Budget Studies

Systematic Errors in Parametrizations in Global NWP: Evaluation Against Observational Data and Budget Studies

Sean Milton, Glenn Greed, Malcolm Brooks, Paul Earnshaw, Martin Willett & David Walters.
Met Office, Exeter, EX1 3PB, UK.

There are key advantages to using short-range NWP forecasts to study model systematic errors. Individual weather systems and their physical processes can be evaluated against detailed observational datasets (ARM, AMMA,TOGA-COARE etc.). Secondly, the systematic drift of the forecasts from the analysed state can be studied in detail in terms of budgets of heat, momentum, moisture and potential vorticity (PV). In the short-range (0-2 days) this can highlight local errors in parametrized or dynamical processes before errors arising from remote forcing make attribution difficult. The Met Office global NWP version of the Unified Model is close in formulation to that used for climate prediction, providing an ideal testbed for investigating errors in parametrized processes and their relationship to longer term systematic error growth (see contribution from Martin & co-authors for more discussion of climate aspects and idealised modelling). We focus here on examples from recent studies of systematic errors in NWP which use a combination of observational data and budget studies. These include some of the following (i) A continental summer warm bias in the extratropics investigated using observations from the ARM site at Southern Great Plains, (ii) West Africa - surface fluxes from the ARM mobile facility (situated in Niamey during the AMMA campaign of 2006) and radiative fluxes from the GERB instrument on Meteosat-8 are used to examine systematic errors in the surface energy and radiative balance during the dry and monsoon seasons. One key deficiency for this region is a lack of predictive capability for mineral dust aerosol. The performance of a dust parametrization developed for the climate model is evaluated in NWP mode, and (iii) Monsoons - the drift from analyses in the model's PV, thermal and momentum budgets are used to study the impact of potential deficiencies in parametrized processes on the evolution of the Monsoon flows and hydrological cycle over India and West Africa.