The Development of the South Asian Summer Monsoon and the Intraseasonal Oscillation

Man Li C. Wu Data Assimilation Office, Goddard Laboratory for Atmospheres, NASA/GSFC, Greenbelt, Maryland

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Siegfried Schubert Data Assimilation Office, Goddard Laboratory for Atmospheres, NASA/GSFC, Greenbelt, Maryland

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Norden E. Huang Oceans and Ice Branch, Goddard Laboratory for Hydrospheric Processes, Greenbelt, Maryland

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Abstract

Fourteen years (1980–93) of National Aeronautics and Space Administration reanalysis data are used to document and study the variability in the development of the South Asian summer monsoon associated with the Intraseasonal Oscillation (ISO). The focus is on the coupling of the large-scale upper-level divergent circulation with the low-level southwesterlies and the associated developing regions of moisture convergence and precipitation, which serve to define the onset times of the various regions of the South Asian monsoon.

The impact of the ISO on the development of the low-level southwesterlies is both local and remote, and depends on the strength and phasing of the ISO with the seasonal cycle. Of the 14 yr examined here, 6 showed a strong contribution to the northeastward progression and onset of the monsoon rains over India. In these cases, the ISO is initially (about 2 weeks prior to onset of rains over India) out of phase with, and therefore suppresses, the seasonal development of the regions of large-scale rising and sinking motion. As the ISO moves to the northeast, the rising branch enters the Indian Ocean and acts to enhance the latent heating in the region of the emerging Somali jet. At low levels the response takes the form of an anticyclonic circulation anomaly over the Arabian Sea, and a cyclonic circulation anomaly to the south, which acts to inhibit the eastward progression of the Somali jet. As the ISO moves in phase with and enhances the seasonal mean upper-level divergent circulation, there is an abrupt and intense development of the southwesterly winds leading to an unusually rapid northeast shift and intensification of the monsoon rains over India and the Bay of Bengal. The general northeast progression of the anomalies may be viewed as an initial suppression and then acceleration of the “normal” seasonal cycle of the monsoon.

Corresponding author address: Dr. Man Li C. Wu, Data Assimilation Office, Code 910.3, Goddard Laboratory for Atmospheres, NASA/GSFC, Greenbelt, MD 20771.

Email: mwu@dao.gsfc.nasa.gov

Abstract

Fourteen years (1980–93) of National Aeronautics and Space Administration reanalysis data are used to document and study the variability in the development of the South Asian summer monsoon associated with the Intraseasonal Oscillation (ISO). The focus is on the coupling of the large-scale upper-level divergent circulation with the low-level southwesterlies and the associated developing regions of moisture convergence and precipitation, which serve to define the onset times of the various regions of the South Asian monsoon.

The impact of the ISO on the development of the low-level southwesterlies is both local and remote, and depends on the strength and phasing of the ISO with the seasonal cycle. Of the 14 yr examined here, 6 showed a strong contribution to the northeastward progression and onset of the monsoon rains over India. In these cases, the ISO is initially (about 2 weeks prior to onset of rains over India) out of phase with, and therefore suppresses, the seasonal development of the regions of large-scale rising and sinking motion. As the ISO moves to the northeast, the rising branch enters the Indian Ocean and acts to enhance the latent heating in the region of the emerging Somali jet. At low levels the response takes the form of an anticyclonic circulation anomaly over the Arabian Sea, and a cyclonic circulation anomaly to the south, which acts to inhibit the eastward progression of the Somali jet. As the ISO moves in phase with and enhances the seasonal mean upper-level divergent circulation, there is an abrupt and intense development of the southwesterly winds leading to an unusually rapid northeast shift and intensification of the monsoon rains over India and the Bay of Bengal. The general northeast progression of the anomalies may be viewed as an initial suppression and then acceleration of the “normal” seasonal cycle of the monsoon.

Corresponding author address: Dr. Man Li C. Wu, Data Assimilation Office, Code 910.3, Goddard Laboratory for Atmospheres, NASA/GSFC, Greenbelt, MD 20771.

Email: mwu@dao.gsfc.nasa.gov

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  • Chen, T. C., and M. C. Yen, 1986: The 40–50 day oscillation of the low-level monsoon circulation over the Indian Ocean. Mon. Wea. Rev.,114, 2550–2570.

  • ——, R. Y. Tzeng, and M. C. Yen, 1988: Development and life cycle of the Indian monsoon: Effect of the 30–50 day oscillation. Mon. Wea. Rev.,116, 2183–2199.

  • Findlater, J., 1969: A major low-level air current near the Indian Ocean during the northern summer. Quart. J. Roy. Meteor. Soc.,95, 362–380.

  • ——, 1977: Observational aspects of the low-level cross-equatorial jet stream of the western Indian Ocean. Pure Appl. Geophys.,115, 1251–1262.

  • Gadgil, S., 1977: Orographic effects on the Southwest Monsoon: A review. Pure Appl. Geophys.,115, 1413–1430.

  • Gill, A. E., 1980: Some simple solutions for heat-induced tropical circulation. Quart. J. Roy. Meteor. Soc.,106, 447–462.

  • Gruber, A., and A. F. Krueger, 1984: The status of the NOAA outgoing longwave radiation data set. Bull. Amer. Meteor. Soc.,65, 958–926.

  • Hahn, D. G., and S. Manabe, 1975: The role of mountains in the South Asian monsoon circulation. J. Atmos. Sci.,32, 1515–1541.

  • Hart, J. E., G. V. Rao, H. V. de Boogaard, J. A. Young, and J. Findlater, 1978: Aerial observations of the East African jet. Mon. Wea. Rev.,106, 1714–1724.

  • Hartmann, D. L., and M. L. Michelsen, 1989: Intraseasonal periodicities in Indian rainfall. J. Atmos. Sci.,46, 2838–2862.

  • He, H., J. W. McGinnis, Z. Song, and M. Yanai, 1987: Onset of the Asian summer monsoon in 1979 and the effect of the Tibetan Plateau. Mon. Wea. Rev.,115, 1966–1995.

  • Hoskins, B. J., and M. J. Rodwell, 1995: A model of the Asian summer monsoon. Part I: The global scale. J. Atmos. Sci.,52, 1329–1340.

  • Huang, N. E., S. R. Long, and Z. Shen, 1996: The mechanism for frequency downshift in nonlinear wave evolution. Adv. Appl. Mech.,32, 59–117.

  • ——, and Coauthors, 1998: The Empirical Mode Decomposition and the Hilbert Spectrum for nonlinear and nonstationary time series analysis. Proc. Roy. Soc. Math. Phys. Eng. Sci.,A454, 1–93.

  • Joseph, P. V., J. K. Eischeid, and R. J. Pyle, 1994: Interannual variability of the onset of the Indian summer monsoon and its association with atmospheric features, El Niño, and sea surface temperature anomalies. J. Climate,7, 81–104.

  • Ju, J., and J. Slingo, 1995: The Asian summer monsoon and ENSO. Quart. J. Roy. Meteor. Soc.,121, 1133–1168.

  • Knutson, T. R., and K. M. Weickmann, 1987: 30–60 atmospheric oscillations: Composite life cycles of convection and circulation anomalies. Mon. Wea. Rev.,115, 1407–1436.

  • Krishnamurti, T. N., 1985: Summer monsoon experiment. Mon. Wea. Rev.,113, 1590–1626.

  • ——, and P. Ardanuy, 1980: The 10–20 day westward propagating mode and “breaks” in the monsoon. Tellus,32, 15–26.

  • ——, and Y. Ramanathan, 1982: Sensitivity of the monsoon onset to differential heating. J. Atmos. Sci.,39, 1290–1306.

  • ——, and D. Subrahmanyam, 1982: The 30–50 day mode at 850 mb during MONEX. J. Atmos. Sci.,39, 2088–2095.

  • ——, P. Ardanuy, Y. Ramanathan, and R. Pasch, 1981: On the onset vortex of the summer monsoon. Mon. Wea. Rev.,109, 344–363.

  • Kuma, K.-I., 1988: The role of the equatorial heat sources in the western Pacific Ocean on the onset of the Asian summer monsoons of 1986. J. Meteor. Soc. Japan,66, 399–417.

  • Lau, K. M., and L. Peng, 1990: Origin of low-frequency (intraseasonal) oscillations in the tropical atmosphere. Part III: Monsoon dynamics. J. Atmos. Sci.,47, 1443–1462.

  • ——, and S. Yang, 1996: Seasonal variation, abrupt transition, and intraseasonal variability associated with the Asian summer monsoon in the GLA GCM. J. Climate,9, 965–985.

  • ——, and ——, 1997: Climatology and interannual variability of the southeast Asian summer monsoon. Adv. Atmos. Sci.,14, 141–162.

  • Madden, R. A., and P. R. Julian, 1972: Description of global scale circulation cells in the Tropics with a 40–60 day period. J. Atmos. Sci.,29, 1109–1123.

  • Min, W., and S. Schubert, 1997: The climate signal in regional moisture fluxes: A comparison of three global data assimilation products J. Climate,10, 2623–2642.

  • Molod, A., H. M. Helfand, and L. L. Takacs, 1996: The climatology of parameterized physical processes in the GEOS-1 GCM and their impact on the GEOS-1 Data Assimilation System. J. Climate,9, 764–785.

  • Murakami, T., T. Nakazawa, and J. He, 1984: On the 40–50 day oscillations during the 1979 Northern Hemisphere summer. Part II: Heat and moisture budget. J. Meteor. Soc. Japan,62, 469–484.

  • ——, L. X. Chen, and A. Xie, 1986: Relationship among seasonal cycles, low-frequency oscillations, and transient disturbances as revealed from outgoing longwave radiation data. Mon. Wea. Rev.,114, 1456–1465.

  • Nigam, S., 1994: On the dynamical basis for the Asian summer monsoon rainfall–El Niño relationship. J. Climate,7, 1750–1771.

  • Ohring, G., A. Gruber, and R. G. Ellingson, 1984: Satellite determination of the relationship between total longwave radiative flux and infrared window radiance. J. Climate Appl. Meteor.,23, 416–425.

  • Park, C. H., S. Schubert, D. Lamich, and Y. Kondratyeva, 1996: Monsoon rainfall in EOS-1 assimilation: Sensitivity to input data. DAO Office Note 96-24, 17 pp. [Available from Data Assimilation Office, NASA/Goddard Space Flight Center, Greenbelt, MD 20771; also available online at.

  • Pearce, R. P., and U. C. Mohanty, 1984: Onsets of the Asian summer monsoon 1979–82. J. Atmos. Sci.,41, 1620–1639.

  • Pfaendtner, J., S. Bloom, D. Lamich, M. Seablom, M. Sienkiewicz, J. Stobie, and A. da Silva, 1995: Documentation of the Goddard Earth Observing System (GEOS) Data Assimilation System—Version 1. NASA Tech. Memo. 104606, Vol. 4, 58 pp. [Available from NASA/Goddard Space Flight Center, Greenbelt, MD 20771.].

  • Rodwell, M. J., and B. J. Hoskins, 1995: A model of the Asian summer monsoon. Part I: Cross-equatorial flow and PV behavior. J. Atmos. Sci.,52, 1341–1356.

  • Schubert, S. D., J. Pfaendtner, and R. Rood, 1993: An assimilated data set for Earth Science applications. Bull. Amer. Meteor. Soc.,74, 2331–2342.

  • ——, and Coauthors, 1995: A multiyear assimilation with the GEOS-1 System: Overview and Results. NASA Tech. Memo. 104606, Vol. 6, 207 pp. [Available from NASA/Goddard Space Flight Center, Greenbelt, MD 20771.].

  • Singh, S. V., R. H. Kripalani, and D. R. Sikka, 1992: Interannual variability of the Madden–Julian oscillations in Indian summer monsoon rainfall. J. Climate,5, 973–978.

  • Subbaramayya, I., and R. Ramanadham, 1981: On the onset of the Indian southwest monsoon and the monsoon general circulation. Monsoon Dynamics, J. Lighthill and R. P. Pearce, Eds., Cambridge University Press, 213–220.

  • Takacs, L. L., and M. J. Suarez, 1996: Dynamical aspects of climate simulations using the GEOS General Circulation Model. NASA Tech. Memo. 104606, Vol. 10, 70 pp. [Available from NASA/Goddard Space Flight Center, Greenbelt, MD 20771.].

  • ——, A. Molod, and T. Wang, 1994: Documentation of the Goddard Earth Observing System (GEOS) General Circulation Model-Version 1. NASA Tech. Memo. 104606, Vol. 1, 97 pp. [Available from NASA/Goddard Space Flight Center, Greenbelt, MD 20771.].

  • Wang, B., and X. Xu, 1997: Northern Hemisphere summer monsoon singularities and climatological seasonal oscillation. J. Climate,10, 1071–1085.

  • Webster, P. J., 1972: Reponse of the tropical atmosphere to local, steady forcing. Mon. Wea. Rev.,100, 518–541.

  • ——, 1983: Mechanics of monsoon low frequency variability: Surface hydrological effects. J. Atmos. Sci.,40, 2110–2124.

  • Yanai, M., and C. Li, 1994: Mechanism of heating and the boundary layer over the Tibetan Plateau. Mon. Wea. Rev.,122, 305–323.

  • Yang, S., and K. M. Lau, 1996: Precursor signals associated with the interannual variability of the Asian summer monsoon. J. Climate,9, 949–964.

  • Yasunari, T., 1981: Structure of an Indian summer monsoon system with a period around 40-days. J. Meteor. Soc. Japan,59, 336–354.

  • Young, J. A., 1987: Boundary layer dynamics of tropical and monsoonal flows. Monsoon Meteorology, C.-P. Chang and T. N. Krishnamurti, Eds., Oxford University Press, 461–500.

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