Numerical Experiments of Conditional Symmetric Baroclinic Instability as a Possible Cause for Frontal Rainband Formation Part II. Effects of Water Vapor Supply

• Published in: Journal of the Meteorological Society of Japan Vol. 66; no. 1; pp. 39 - 54
• Main Authors: Saito, Sadamu, Tanaka, Hiroshi
• Format: Journal Article
• Language: English
• Published: Meteorological Society of Japan 1988
• ISSN: 0026-1165; 2186-9057
• DOI: 10.2151/jmsj1965.66.1_39

The main purpose of this paper is to study numerically how the low level water vapor supply modifies the circulation of conditional symmetric baroclinic instability (CSBI), and how the convective clouds are induced and controlled by CSBI circulation. The numerical model is basically the same as that used in Part I by the same authors, whereas the water vapor is supplied from the surface. Three cases of numerical experiment are considered: no water vapor supply, a small water vapor supply, and a large water vapor supply. Developments of clouds, rainfall and stratification are the main features inspected in the three cases. When the water vapor supply is moderate, a slantwise cloud is also developed due to the CSBI circulation, as in the case of no water vapor supply. However, nodal convective cells appear embedded in the slantwise cloud. A number of narrow, strong precipitation areas are embedded in the weak and wide-spread precipitation area and are associated with these nodal cells. Convective cells above the slantwise cloud (generating cells) are also developed in the mid-troposphere. When the water vapor supply increases, strong convective clouds rapidly grow at the convergence zone of CSBI circulation and at the slantwise convective unstable layer. The horizontal extension of the rainfall area becomes narrow but the rainfall intensity is greatly enhanced. One of the most important features of the CSBI circulation in rainband formation is to induce the slantwise convective unstable layer, which is appreciably enhanced as the rate of water vapor supply increases. At the same time, an increase of water vapor supply tends to activate cumulus clouds through the combined effect of low level convective unstable layer due to water vapor supply and flow convergence due to CSBI circulation.