Model data for tropical nudging experiments

© Crown Copyright, Met Office

The accompanying data is made available under the terms of the Non-Commercial Government Licence (http://www.nationalarchives.gov.uk/doc/non-commercial-government-licence/version/2/).

We use the Hadley Centre Global Environmental Model version 3 with the Global Coupled model 2.0 configuration (HadGEM3-GC2; Williams et al., 2015). The model has a horizontal resolution of 0.83x0.55degrees and 85 levels with a lid at 85km. It employs interactive sea ice and ocean. We initialise the model using the observational conditions from the 1st September 2000 in all cases to prevent any differences in initial conditions. Model simulations are run for 3 months through to the start of December.

Model simulations are performed, nudging the tropics to the observationally-constrained reanalysis for the years 1993-2015 inclusive. For each year, a 20-member ensemble is produced using stochastic perturbations, giving 460 simulations in total. In each case, we nudge the tropical column at every timestep to ERA-Interim reanalysis (Dee et al., 2011) for the respective year. The tropical relaxation spans all vertical levels and extends +/- 19.5 degrees north/south of the equator, with an additional 8 degree latitude tapering. Temperature, along with the zonal and meridional components of wind are nudged at every timestep, with an e-folding timescale of 6 hours. Nudging moisture fields has little impact, so is not included. 

Data provided here is output for mean sea level pressure, geopotential height on the 200hPa pressure level, rainfall and sea ice.

Dee, D.P., Uppala, S.M., Simmons, A.J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M.A., Balsamo, G., Bauer, D.P. and Bechtold, P., 2011. The ERA‐Interim reanalysis: Configuration and performance of the data assimilation system. Quarterly Journal of the royal meteorological society, 137(656), pp.553-597. https://doi.org/10.1002/qj.828

Williams, K. et al. The Met office global coupled model 2.0 (GC2) configuration. Geosci. Model Dev. 88, 1509–1524 (2015). https://doi.org/10.5194/gmd-8-1509-2015