Presentation on theme: "ENSO-Monsoon relationships in current and future climates Andrew Turner, Pete Inness and Julia Slingo The University of Reading Department of Meteorology."— Presentation transcript:
ENSO-Monsoon relationships in current and future climates Andrew Turner, Pete Inness and Julia Slingo The University of Reading Department of Meteorology Earley Gate, Reading, RG6 6BB, UK firstname.lastname@example.org pastpresentfuture 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). 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. Is the strengthened teleconnection due to a more realistic basic state and better ENSO evolution, or simply to the much larger ENSO amplitude? ENSO amplitude increases (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. 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 long- wave scheme. 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’ soil- moisture scheme to improve monsoon precipitation distribution. Run SPEEDY with idealised ENSO forcing (based on Spencer et al., 2004). Integrations will be made using HadCM3 at 2x and 4x CO 2, 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. 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. 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. Fig.1 Lag correlations between Nino-3 region SSTs and summer (a) Dynamical Monsoon Index (b) Indian Rainfall. Fig. 2 Power spectra of Nino- 3 region SSTs. Fig. 3 JJA 925hPa u-wind errorFig. 4 JJA zonal temp. error Fig. 5 Lag correlations between Nino-3 region SSTs and summer DMI Fig. 6 Idealised ENSO cycle of SSTs, to be applied to SPEEDY Fig. 7 21-year moving correlation between summer Nino-3 temperatures and All- India Rainfall 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.