1.0
Tropospheric biennial oscillation and moisture transport over tropical Indian ocean and Pacific
Natalia A. Vjazilova, Russian Research Institute of Hydrometeorological Information, World Data Center, Obninsk, Russia
Some studies postulated, that the variability of the Asian monsoon is closely tied to the warm and cold phases of the Tropospheric Biennial Oscillation, and Warm and Cold Events of ENSO are extreme manifestation in this TBO. In this link between the Indian monsoon, Indian ocean and tropical Pacific the annual cycle of maximum convection is an active participant. Maximum convection or tropical precipitation anomalies can be viewed as a suppression or enhancement of the annual cycle in the movement of the tropical convergence zones. The goal of this study is to compare the annual cycle of moisture large-scale circulation in warm years of ENSO, El Nino, with strong deficit of rainfall over India (weak summer maximum convection) and during cold years, La Nina, with heavy rainfall, for period 1981 - 1998. The study based on composite for selected warm and cold years mean season precipitation, outgoing long-wave radiation, moisture content and moisture transport anomalies in low atmosphere. To show the role of moisture large-scale circulation anomalies in development of tropical ocean-atmosphere system anomalies and TBO the study of sea surface temperature anomalies, velocity potential and streamfunction anomalies at 200 gPa was added. NCAR/NCEP reanalysis and Xie-Arcin precipitation data set were used for study. A study had shown, that precipitation, precipitable water and moisture transport anomalies in low atmosphere, velocity potential and streamfunction anomalies at 200 gPa over the Indian ocean and Western Pacific, sea surface temperature anomalies during one composite year of quasi - biennial cycle of ENSO set up the conditions for the development of the opposite extreme in the following year. A comparison had shown, that the changes in the position and intensity of convective precipitation anomalies, precipitable water anomalies, moisture convergence in low atmosphere and upper inflow (outflow) area are found to be consistent with the change of moisture transport during all seasons both in selected warm and in cold years of ENSO. In turn, the improved precipitation can influence the large-scale circulation through condensation heating. That will result in further changes in moisture circulation. Through the interactions, both the large-scale circulation and precipitation are somewhat improved. The results had shown that annual cycle of moisture large-scale circulation may play an important role in development of TBO and is main part in the relationship between the Asian monsoon and ENSO.
Session 1, Opening Ceremony
Monday, 24 March 2003, 8:30 AM-10:00 AM