Internal Structure of ITCZ Mesoscale Convective Systems and Related Environmental Factors in the Western Pacific: An Observational Case Study

Abstract

The case study in this paper describes the characteristics of the observed internal structure of the ITCZ precipitating system and related environmental factors in the western Pacific. We deployed the R/V Mirai for a 10-day period in June 2000 at (7 N, 140 E) to determine the detailed structure of the western Pacific ITCZ by obtaining various data including C-band Doppler radar data and 3-hourly radiosonde data.
In the present case, four mesoscale convective systems (MCSs) passed over the vessel continuously. The leading edge of the MCSs elongated meridionally, which was orthogonal to the low-level wind shear. The internal structure was similar to the typical two-dimensional structure, including a leading convective edge and a following stratiform precipitating area with a melting convergence. However, the detailed structure was rather three-dimensional. The subsystem in the northern end of the MCSs included an earlier-dissipating weak stratiform precipitating area. This could have occurred as a result of the introduction of the subtropical dry air to the northern end of the MCSs, by the combined effect of the melting convergence and large-scale wind profile. The initialization processes of the MCSs are also discussed. These results suggest that, to form and maintain the western Pacific ITCZ MCSs, the combination of the environmental meridional moisture contrast and the dynamics in the stratiform region of the MCSs is also important as well as the large-scale disturbances.