観測船啓風丸によりTOGA COARE集中観測期間中、1992年11月に観測された赤道付近の対流

Abstract

During the TOGA COARE IOP (Tropical Ocean-Global Atmosphere, Coupled Ocean-Atmosphere Response Experiment, Intensive Observation Period), 7.5-minute-interval weather radar observations and 6-hourly radiosonde observations were conducted by the Keifu Maru, a research vessel of the Japan Meteorological Agency (JMA) at a point of (0.5S, 154.5E), near the center of the Intensive Flux Array (IFA), from 3 to 16 November, 1992. The radar echo intensity is digitized on a 2.5km mesh over a square of 500km×500km.The observed equatorial convection was documented focusing on mesoscale precipitation systems (MPSs). According to the radar echo coverage, the observation period was divided into four periods. On 3-4 November, convection was inactive and organization of MPSs was suppressed. On 5-8 November, convection was activated and echoes were organized into MPSs with a horizontal scale of about 100-300km. The convection showed diurnal variation with enhancement in the midnight to early morning (14-20 UTC, 00-06 Local Time (LT)). Major MPSs formed as convective cells at early night around 10 UTC (20 LT) and matured into large echoes with embedded strong echoes around midnight to early morning (14-20 UTC, 00-06 LT), then dissipated into scattered weak echoes by the morning around 23 UTC (09 LT). Life histories of major MPSs were similar those of mesoscale precipitation features (MPFs) presented by Leary and Houze (1979). On 10-12 November, an active convective event containing larger MPSs occurred for 1.5 days associated with the westward passage of a large (1500-2000km) scale rapid westward-moving cloud disturbance. The MPSs moved eastward but the field of development of the MPSs seemed to move westward, corresponding to the westward passage of the large-scale cloud disturbance. The MPSs took the form of a multiple-line structure oriented northeast to southwest with a length over 300-500km in the developing stages. The longer lifetime of MPSs covered up the diurnal variation of convection. On 13-14 November, convection was completely suppressed.The nighttime enhancement of convection on 5-8 November suggests that even over an open warm water pool region, intense convection circumstantially behaves as diurnal cyclic through the nighttime appearances of MPSs depending on large-scale conditions. Tightly bound and successively westward appearances of eastward-moving MPSs on 10-12 November implies an interaction between the grouped MPSs and the westward-moving large-scale cloud disturbance. Characteristics of the large-scale cloud disturbance were examined.