Extended Abstract (160K)15B.2A
Does the tropical atmosphere support large-scale radiative-convective overturning? (Formerly Paper Number P1.51)
Jialin Lin, SUNY, Stony Brook, NY; and M. Zhang and B. E. Mapes
Some recent modelling studies propose that the tropical atmosphere has negative effective static stability due to the contribution of the radiative heating. It means that the tropical atmosphere supports large-scale radiative-convective overturning. They propose that some important tropical disturbances, including the tropical cyclone and the Madden-Julian Oscillation, are driven by such large-scale radiative-convective overturning. In the current study, we test this hypothesis using the observed heat budget from four different sounding arrays during the Global Atmosphere Research Program (GARP) Atlantic Tropical Experiment (GATE) and the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE).
Observation from the four arrays show that the effective static stability is positive throughout the free troposphere. Decomposition in the frequency domain also shows that the effective static stability is positive at almost all sub-seasonal time scales. This means that the the tropical atmosphere does not support the large-scale radiative-convective overturning.
Although having a positive sign, the effective static stability is significantly smaller than the dry static stability and reduces to nearly zero (neutral) in the upper troposphere.
The effective static stability is reduced mainly by the convective heating, not the radiative heating. The radiative heating is not highly coherent with either the adiabatic cooling or the convective heating. The contribution of radiative heating is more significant for longer time scale but its phase is not well opposite to that of the adiabatic cooling. Furthermore, the radiative heating is not uniformly distributed in the troposphere. It is dominated by longwave cloud top cooling and cloud base warming.
Session 15B, Intraseasonal variability (Parallel with Sessions 15A and 15D)
Thursday, 2 May 2002, 4:00 PM-5:15 PM
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