1995 Volume 73 Issue 2B Pages 427-442
During the TOGA-COARE intensive observation period (IOP), many types of clouds were observed around Manus Island, Papua New Guinea, by X-band Doppler radars. This paper analyzes several characteristics of three types of tropical convective clouds, an isolated echo cell and two types of rainbands. The common characteristics, from the viewpoint of echo area, echo-top height and maximum reflectivity, in association with the development process are that 1) the peak of maximum reflectivity appeared in the early stage in the lower-level circulation, 2) the peak of the maximum echo top height appeared shortly after the maximum reflectivity caused by a development of upper-level circulation, and 3) the maximum echo area appeared at a later stage because of the appearance of anvil clouds.
In the case of the isolated echo, the above-mentioned characteristics were examined with kinematics in detail. The development of low-level circulation into upper-level circulation appeared successively and coexisted in the case of an isolated echo. In all cases, a strong reflectivity core appeared at the lower altitude, indicating the effectiveness of the warm-rain process. The echo-top height did not increase continuously to the maximum height; stable echo-top heights appeared during the echo development. This tendency was common to all cases of rainband. Anvil clouds contributed to the extension of the upper tropospheric cloud area in the later stage of its life cycle and formed a stratiform echo.
Rainbands are categorized as non-squall type from the GATE criteria (Barnes and Sieckman, 1984; Houze, 1977). Both rainbands developed parallel to the low-level shear vector. The first case was slow-moving: the rainband had a clear leading edge and continuous rear-to-front flow to maintain the circulation during the mature stage. The second case was relatively fast-moving: it had intermittent rear-to-front flow. These are somewhat different characteristics from rainbands during GATE. Convective outflows were also observed in all cases. In particular, gust fronts were observed in the rainband cases. The gust front in the second rainband had a thickness of 0.5 to 1.0km, and a propagation speed of 8 to 10m/s, which was slightly faster than the rainband's propagation speed.
