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Natural variability of monsoon climates - WP 1000

Partners involved: the Met Office (lead contractor), UREADMY, CNRM, LMD, MPI

Summary

PROMISE aims to study the natural variability of monsoonal systems on seasonal, interannual and interdecadal timescales, using observations and model results. The analysis will include application of advanced statistical techniques. In addition, the interaction between various time and space scales will be investigated.

some key achievements:

  • the simulation of the mean and variability of monsoon climates using an atmosphere only GCM at a range of horizontal and vertical resolutions with an idealised El Nino/La Nina cycle. This study showed that the model has limited skill in reproducing observed interannual variability although reporducibility is quite high.

  • comparison of dynamical and statistical models used to predict monsoon rainfal anomalies over the Central Sahel. The results indicate that the GCM was less reliable than a simple regression. However, the GCM showed a better ability to simulate the variability of the large-scale African monsoon circulation.

  • the African monsoon onset has been studied through recurrent abrupt shift of the ITCZ which has been pointed out in the daily rainfall dataset for each year between 1968 and 1990. It has been found that the observed northward shift of the ICTZ is associated with westward travelling atmospheric circulation pattern in the monsoon layer, persistent up to 600hPa, at intraseasonal scale.

  • sepctral analysis of daily Sahelian rainfall indexes have highlighted rainfall fluctuations at intra-seasonal time-scale coherent with an intra-seasonal wind field pattern at 926 and 700hPa

  • The interannual variability of sea surface temperature in the tropical Indian Ocean has been studied to evaluate its relationship with monsoon systems and ENSO. It has been shown htat the Indian Ocean SST exhibits a strong ENSO-related interannual variability which accounts for most of the variance. The recently described dipole mode was found to exist only during the boreal autumn as a response to ENSO.

  • the impact of improving representation of oboundary layer turbulent mixin and convective transport was found to result in an improve simulation of the monsoon and its variability. Furthermore the teleconnection pattern of AIR with SST is greatly improved. However, the monsoon climatology was worsened wuggesting that the correct response to SST forcing is not the sufficient to correctly simulate the monsoon.

  • improved simulation of the Somali jet and intensit of West African rainfall distribution were achieved for a 20 year integration using a development version of the global climate model with better representaiton of convection

  • the vegetation scheme of the Hadley Centre climate model has been upgraded and will be used to examine the effect of vegetation seasonality on the simulation of monsoon climates

  • A set of statistical procedures in the PV-wave languate has been assembled for the analysis of intraseasonal variability in climate simulations.

Publications on this topic arising from PROMISE

Bader, J., M. Latif, and R. Schnur 2003 The Impact of Decadal-Scale Indian Ocean SST Anomalies on Tropical and Extra-Tropical Climate in preparation

Diedhiou, A., S. Janicot, A. Viltard and P. de Felice 2001 Energetics of easterly wave disturbances over West Africa and the tropical Atlantic : A climatology from the 1979-95 NCEP/NCAR reanalyses Climate Dynamics 18 487-500

Diedhiou, A., S. Janicot, A. Viltard and P. de Felice 2001 Composite patterns of easterly disturbances over West Africa and the tropical Atlantic : A climatology from the 1979-95 NCEP/NCAR reanalyses Climate Dynamics 18 241-253

Fontaine B., Philippon, N., Trzaska S. and Roucou P. 2002 Spring to summer changes in the West African monsoon through NCEP/NCAR reanalyses (1968-1998) Journal of Geophysical Research 107 10.1029-10.1037

Janicot, S. and B. Sultan 2001 Intra-seasonal modulation of convection in the West African monsoon Geophysical Research Letters 28 523-526

Molteni F 2003 Atmospheric simulations using a GCM with simplified physical parametrizations. I: model climatology and variability in multi-decadal experiments Climate Dynamics 20 175-191

Neale, R. B. and Slingo, J.M. 2003 The Maritime Continent and its role in the global circulation: A GCM study Journal of Climate 16 834 - 848

Poccard, I., S. Janicot and P. Camberlin 2000 Comparison of rainfall structures between NCEP/NCAR reanalysis and observed data over tropical Africa Climate Dynamics 16 897-915

Slingo, J. M. 2002 Monsoon Overview. Contribution to 'Encyclopedia of Atmospheric Sciences', Academic Press, 1356-1370

Sultan, B. and S. Janicot 2003 The West African monsoon dynamics. Part II: The pre-onset and the onset of the summer monsoon Journal of Climate in press

Sultan, B., S. Janicot and A. Diedhiou 2003 The West African monsoon dynamics. Part I: Documentation of intra-seasonal variability in press

Sultan, B. and S. Janicot 2000 Abrupt shift of the ITCZ over West Africa and intra-seasonal variability Geophysical Research Letters 27 3353-3356

Publications on this topic by PROMISE partners

Sperber, K. R., J. M. Slingo and H. Annamalai: Predictability and the relationship between subseasonal and interannual variability during the Asian Summer Monsoon. Q. J. R. Meteorol. Soc., in press.

Annamalai, H., J. M. Slingo, K.R. Sperber and K. Hodges, 1999: The mean evolution and variability of the Asian Summer Monsoon: Comparison of ECMWF and NCEP/NCAR Reanalyses. Mon. Weath. Rev., 127, 1157-1186

Ferranti, L., J. M. Slingo, T. N. Palmer and B. J. Hoskins, 1997: Relations between interannual and intraseasonal monsoon variability as diagnosed from AMIP integrations. Q. J. R. Meteorol. Soc., 123, 1323-1357.

Stephenson D.B., Douville H. and Kumar, K. (In press) Searching for a fingerprint of global warming in the Asian summer monsoon

Janicot, S. Spatio-temporal variability of West African rainfall. Part I : Regionalizations and typings. Journal of Climate, 5, 489-497.

Janicot, S. Spatio-temporal variability of West African rainfall. Part II : Associated surface and air masses characteristics. Journal of Climate, 5, 499-511

Fontaine, B. and Janicot, S Wind field coherence and its variations over West Africa. Journal of Climate, 5, 512-524.

Janicot, S. The West African monsoon of 1987 and 1988 : Pacific or Atlantic signal ? International Conference on Monsoon Variability and Prediction, Trieste, Italie, WCRP-84, WMO/TD-No 619, 765-772.

Janicot, S. The recent West African rainfall variability through empirical and modelling investigations. Global precipitations and climate change, NATO ASI Series, I, Vol.26, 135-150.

Fontaine, B. Janicot, S. and Moron, VRainfall anomaly patterns and wind field signals over West Africa in August (1958-1989). Journal of Climate, 8, 1503-1510. Abstract

Roucoup P. et al Vertical motion changes related to north-east Brazil rainfall variability : a AGCM simulation. Int. J. Climatology, 16, 879-891.

Fontaine, B. and Janicot, S. Near-global sea surface temperature variability associated with West African rainfall anomaly types. Journal of Climate, 9, 2935-2940.

Rowell, D.P., 1996: Reply to comments by Y.C. Sud and W.K.-M. Lau on `Variability of summer rainfall over tropical north Africa (1906-92): Observations and modelling' by D.P. Rowell, C.K. Folland, K. Maskell and M.N. Ward (April 4, 1995, 121, 669-704): Further analysis of simulated interdecadal and interannual variability of summer rainfall over tropical north Africa. Q. J. R. Meteorol. Soc., 122, 1007-1013

Rowell, D.P., Folland, C.K., Maskell, K. and Ward, M.N., 1995: Variability of summer rainfall over Tropical North Africa (1906-92): Observations and modelling. Q. J. R. Meteorol. Soc., 121, 669-704

Rowell, D.P., Folland, C.K., Maskell, K., Owen, J.A. and Ward, M.N., 1992: Modelling the influence of global sea surface temperatures on the variability and predictability of seasonal Sahel rainfall. Geophys. Res. Lett., 19, 905-908

For further information
see:
Description of the work package in the orginal proposal
Detailed first annual report (available only to PROMISE partners or by permission of the lead contractor)
Detailed second year report (available only to PROMISE partners or by permission of the lead contractor)
Detailed third year report (available only to PROMISE partners or by permission of the lead contractor)
Final report

or:
contact the lead contractor, Roy Kershaw at rkershaw@meto.gov.uk
contact Emily Black at emily@met.reading.ac.uk

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