Abstract
Thirty strong Madden-Julian Oscillation (MJO) events in boreal winter 1982–2001 are selected to investigate the triggering processes of MJO convection over the western equatorial Indian Ocean (IO). These MJO events are classified into three types, according to their dynamic and thermodynamic precursor signals in situ. In Type I, a remarkable increase in low-level moisture occurs, on average, 7 days prior to the convection initiation. This low-level moistening is mainly due to the advection of the background mean moisture by easterly wind anomalies over the equatorial IO. In Type II, lower-tropospheric ascending motion anomalies develop, on average, 4 days prior to the initiation. The cause of this ascending motion anomaly is attributed to the anomalous warm advection, set up by a suppressed MJO phase in the equatorial IO. In Type III, there are no clear dynamic and thermodynamic precursor signals in situ. The convection might be triggered by energy accumulation in the upper layer associated with Rossby wave activity fluxes originated from the midlatitudes.
Similar content being viewed by others
References
Bladé, I., and D. L. Hartmann, 1993: Tropical intraseasonal oscillations in a simple nonlinear model. J. Atmos. Sci., 50, 2922–2939, doi: 10.1175/1520-0469(1993)050<2922:TIOIAS>2.0.CO;2.
Gill, A. E., 1980: Some simple solutions for heat-induced tropical circulation. Quart. J. Roy. Meteor. Soc., 106, 447–462, doi: 10.1002/qj.49710644905.
Hendon, H. H., 1988: A simple model of the 40–50 day oscillation. J. Atmos. Sci., 45, 569–584, doi: 10.1175/1520-0469(1988)045<0569:ASMOTD>2.0.CO;2.
Holton, J., 2004: An Introduction to Dynamic Meteorology. 4th ed., Academic Press, 535 pp.
Hsu, H.-H., B. J. Hoskins, and F.-F. Jin, 1990: The 1985/86 intraseasonal oscillation and the role of the extratropics. J. Atmos. Sci., 47, 823–839, doi: 10.1175/1520-0469(1990)047<0823:TIOATR>2.0.CO;2.
Hsu, P.-C., and T. Li, 2012: Role of the boundary layer moisture asymmetry in causing the eastward propagation of the Madden-Julian oscillation. J. Climate, 25, 4914–4931, doi: 10.1175/JCLI-D-11-00310.1.
Hu, Q., and D. A. Randall, 1994: Low-frequency oscillations in radiative-convective systems. J. Atmos. Sci., 51, 1089–1099, doi: 10.1175/1520-0469(1994)051<1089:LFOIRC>2.0.CO;2.
Jiang, X.-A., and T. Li, 2005: Reinitiation of the boreal summer intraseasonal oscillation in the tropical Indian Ocean. J. Climate, 18, 3777–3795, doi: 10.1175/JCLI3516.1.
Kemball-Cook, S. R., and B. C. Weare, 2001: The onset of convection in the Madden-Julian oscillation. J. Climate, 14, 780–793, doi: 10.1175/1520-0442(2001)014<0780:TOOCIT>2.0.CO;2.
Kiladis, G. N., and K. M. Weickmann, 1992: Circulation anomalies associated with tropical convection during northern winter. Mon. Wea. Rev., 120, 1900–1923, doi: 10.1175/1520-0493(1992)120<1900:CAAWTC>2.0.CO;2.
Knutson, T. R., and K. M. Weickmann, 1987: 30–60 day atmospheric oscillations: Composite life cycles of convection and circulation anomalies. Mon. Wea. Rev., 115, 1407–1436, doi: 10.1175/1520-0493(1987)115<1407:DAOCLC>2.0.CO;2.
Lau, K.-M., and P. H. Chan, 1985: Aspects of the 40–50 day oscillation during the northern winter as inferred from outgoing longwave radiation. Mon. Wea. Rev., 113, 1889–1909, doi: 10.1175/1520-0493(1985)113<1889:AOTDOD>2.0.CO;2.
Lau, K.-M., and L. Peng, 1987: Origin of low-frequency (intraseasonal) oscillations in the tropical atmosphere. Part I: Basic theory. J. Atmos. Sci., 44, 950–972, doi: 10.1175/1520-0469(1987)044<0950:OOLFOI>2.0.CO;2.
Li, T., F. Tam, X. H. Fu, T. J. Zhou, and W. J. Zhu, 2008: Causes of the intraseasonal SST variability in the tropical Indian Ocean. Atmos. Oceanic Sci. Lett., 1, 18–23.
Liebmann, B., and C. A. Smith, 1996: Description of a complete (interpolated) outgoing longwave radiation dataset. Bull. Amer. Meteor. Soc., 77, 1275–1277.
Lindzen, R. S., and S. Nigam, 1987: On the role of sea surface temperature gradients in forcing low-level winds and convergence in the tropics. J. Atmos. Sci., 44, 2418–2436, doi: 10.1175/1520-0469(1987)044<2418:OTROSS>2.0.CO;2.
Ling, J., C. D. Zhang, and P. Bechtold, 2013: Large-scale distinctions between MJO and Non-MJO convective initiation over the tropical Indian Ocean. J. Atmos. Sci., 70, 2696–2712, doi: 10.1175/JAS-D-13-029.1.
Matthews, A. J., 2000: Propagation mechanisms for the Madden-Julian Oscillation. Quart. J. Roy. Meteor. Soc., 126, 2637–2651, doi: 10.1002/qj.49712656902.
Matthews, A. J., 2008: Primary and successive events in the Madden-Julian oscillation. Quart. J. Roy. Meteor. Soc., 134, 439–453, doi: 10.1002/qj.224.
Matthews, A. J., and G. N. Kiladis, 1999: The tropicalextratropical interaction between high-frequency transients and the Madden-Julian oscillation. Mon. Wea. Rev., 127, 661–677, doi: 10.1175/1520-0493(1999)127<0661:TTEIBH>2.0.CO;2.
Pan, L.-L., and T. Li, 2008: Interactions between the tropical ISO and midlatitude low-frequency flow. Climate Dyn., 31, 375–388, doi: 10.1007/s00382-007-0272-7.
Ray, P., C. D. Zhang, J. Dudhia, and S. S. Chen, 2009: A numerical case study on the initiation of the Madden-Julian oscillation. J. Atmos. Sci., 66, 310–331, doi: 10.1175/2008JAS2701.1.
Rui, H. L., and B. Wang, 1990: Development characteristics and dynamic structure of tropical intraseasonal convection anomalies. J. Atmos. Sci., 47, 357–379, doi: 10.1175/1520-0469(1990)047<0357:DCADSO>2.0.CO;2.
Saha, S., and Coauthors, 2006: The NCEP climate forecast system. J. Climate, 19, 3483–3517, doi: 10.1175/JCLI3812.1.
Seo, K. H., and K. Y. Kim, 2003: Propagation and initiation mechanisms of the Madden-Julian oscillation. J. Geophys. Res., 108, 4384, doi: 10.1029/2002JD002876.
Straub, K. H., 2012: MJO initiation in the real-time multivariate MJO index. J. Climate, 26, 1130–1151, doi: 10.1175/JCLID-12-00074.1.
Takaya, K., and H. Nakamura, 2001: A formulation of a phaseindependent wave-activity flux for stationary and migratory quasigeostrophic eddies on a zonally varying basic flow. J. Atmos. Sci., 58, 608–627, doi: 10.1175/1520-0469(2001)058<0608:AFOAPI>2.0.CO;2.
Uppala, S. M., and Coauthors, 2005: The ERA-40 re-analysis. Quart. J. Roy. Meteor. Soc., 131, 2961–3012, doi: 10.1256/qj.04.176.
Wang, B., and T. M. Li, 1994: Convective interaction with boundary-layer dynamics in the development of a tropical intraseasonal system. J. Atmos. Sci., 51, 1386–1400, doi: 10.1175/1520-0469(1994)051<1386:CIWBLD>2.0.CO;2.
Wang, L., K. Kodera, and W. Chen, 2012: Observed triggering of tropical convection by a cold surge: Implications for MJO initiation. Quart. J. Roy. Meteor. Soc., 138, 1740–1750, doi: 10.1002/qj.1905.
Yanai, M., S. Esbensen, and J.-H. Chu, 1973: Determination of bulk properties of tropical cloud clusters from large-scale heat and moisture budgets. J. Atmos. Sci., 30, 611–627, doi: 10.1175/1520-0469(1973)030<0611:DOBPOT>2.0.CO;2.
Zhao, C. B., T. Li, and T. J. Zhou, 2013: Precursor signals and processes associated with MJO initiation over the Tropical Indian Ocean. J. Climate, 26, 291–370, doi: 10.1175/JCLID-12-00113.1.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Mei, S., Li, T. & Chen, W. Three-type MJO initiation processes over the Western Equatorial Indian Ocean. Adv. Atmos. Sci. 32, 1208–1216 (2015). https://doi.org/10.1007/s00376-015-4201-0
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00376-015-4201-0