The University of Reading Department of Meteorology ENSO-Monsoon relationships in current and future climates Earley Gate, Reading, RG6 6BB, UK Andrew Turner, Pete Inness and Julia Slingo a.g.turner@rdg.ac.uk past Previous work (Turner et al., 2004) has shown that warming (improving) the basic state in the tropical Pacific of a coupled GCM produces a better monsoon climate and a stronger, better timed monsoon-ENSO teleconnection (Fig. 1). Fig.1 Lag correlations between Nino-3 region SSTs and summer (a) Dynamical Monsoon Index (b) Indian Rainfall. present The SPEEDY model (Molteni, 2003) provides a quick way of running simple experiments with reasonable skill. • The Simplified Parametrizations, primitivE-Equation DYnamics model is designed to run on only a few vertical levels, T30 L8 resolution in this configuration. 45mins/year runtime on a workstation as an AGCM, forced by the HadISST dataset. • Main errors with the model include low speed jets (Fig. 3) and upper tropospheric warm bias (Fig. 4), likely related to poor longwave scheme. Fig. 3 JJA 925hPa u-wind error Fig. 4 JJA zonal temp. error • The tropical Pacific is too cool in HadCM3 and is warmed using a system of limited-area flux adjustments, devised by Inness et al. (2003). • The revised model, HadCM3FA, has a better climate in the tropical Pacific Ocean (less confined warm pool, reduced zonal temperature gradient, weaker trade winds). • Indian monsoon climate is improved, having less precipitation and a weaker flow. Fig. 2 Power spectra of Nino• ENSO amplitude increases 3 region SSTs. (Fig. 2); the combination of this enlarged amplitude and stronger teleconnection (Fig. 1) increases the monsoon variability. • Enhanced biennial power in HadCM3FA, likely due to stronger coupling. Is the strengthened teleconnection due to a more realistic basic state and better ENSO evolution, or simply to the much larger ENSO amplitude? • SPEEDY monsoon simulation gets the gross features but fails in the detail. Monsoon winds are too weak, lacking stationary wave patterns, and precipitation is wrongly distributed. • East African highlands are important in focussing and maintaining the Somali Jet (Rodwell and Hoskins, 1995; Slingo et al., 2004). Their poor representation at T30 resolution impacts on the monsoon flow. • Envelope orography (Wallace et al., 1983) better emphasises the East African Highlands and makes some improvement to the Somali Jet. The monsoon-ENSO teleconnection is also strengthened (Fig. 5), but still mis-timed. Fig. 5 Lag correlations between Nino-3 region SSTs and summer DMI future Once the SPEEDY model is tuned correctly it will be used to evaluate the effect of ENSO amplitude on the monsoon-ENSO teleconnection. Other considerations include coupling with an Indian Ocean mixed-layer model, and use of a ‘bucket’ soilmoisture scheme to improve monsoon precipitation distribution. • Run SPEEDY with idealised ENSO forcing (based on Spencer et al., 2004). Fig. 6 Idealised ENSO cycle of SSTs, to be applied to SPEEDY • SST anomalies of varying amplitude (Fig. 6) will be applied to a background climatology of current and also future climates, further testing the role of the basic state. The changing nature of the monsoon-ENSO teleconnection in recent years (Fig. 7) together with a likely warmer basic state after climate change provide motivation for further work with the Unified Model. Fig. 7 21-year moving correlation between summer Nino-3 temperatures and AllIndia Rainfall • Integrations will be made using HadCM3 at 2x and 4x CO2, to look at the changing nature of the monsoon-ENSO teleconnection with climate change, as well as changes to the monsoon variability and climate. References: Inness, P. M., Slingo, J. M., Guilyardi, E. and Cole, J. (2003), “Simulation of the Madden-Julian Oscillation in a coupled general circulation model. Part II: The role of the basic state” J. Clim. 16: 365-382; Molteni (2003), “Atmospheric simulations using a GCM with simplified physical parametrizations. I: model climatology and variability in multi-decadal experiments” Clim. Dyn. 20: 175-191; Rodwell, M. J. and Hoskins, B. J. (1995), “A Model of the Asian Summer Monsoon. Part II: Cross-Equatorial Flow and PV Behavior” J. Atmos. Sci. 52: 1341-1356; Slingo, J. M., Spencer, H., Hoskins, B., Berrisford, P. and Black, E. (2004), “The Meteorology of the Western Indian Ocean, and the influence of the East African Highlands” submitted, Proc. Roy. Soc; Spencer, H., Slingo, J. M. and Davey, M. K. (2004), “Seasonal predictability of ENSO teleconnections: the role of the remote ocean response” Clim. Dyn. 22: 511-526; Turner, A. G., Inness, P. M. and Slingo, J. M. (2004), “The Role of the Basic State in Monsoon Prediction” submitted, Q. J. R. Meteorol. Soc.; Wallace, J. M., Tibaldi, S. and Simmons, A. J. (1983), “Reduction of systematic forecast errors in the ECMWF model through the introduction of an envelope orography” Q. J. R. Meteorol. Soc. 109: 683-717.