THE TURBULENT STRUCTURE AND SEASONAL VARIATION OF NOCTURNAL COLD DRAINAGE FLOW INTRUDING A PLAIN AND COASTAL AREA.

通过对1997年4月26日夜间排涝冷流的观测个例分析，揭示了高知平原发生在陆风中的重力流特征。根据SODER资料测得的排水冷流深度约为75-80m，流速约为3.5m/S，确定了研究冷流特征的三个点。1997年4月至今(1998年3月)在佐冈小学较靠近山区的地点进行观测，结果表明：(1)在上坡气流(谷风)爆发前，气温突然升高，混合比有较大波动；这种现象与沿山坡的热对流有关。2.冷流由沿山坡侵入和谷底在日落前后排入平原的气团组成。3.从两个热力气象要素(气温[T]、混合比[Q])的直方图看，夏季各模式为24ﾟC，Q为16(g/kg)，冬季为7ﾟC，3 g/kg。

The observational case study of the nocturnal drainage cold flow on 26 April 1997 shows the characteristics of the gravity current which intduded into land breeze occurred in the Kochi Plain. From the soder measurements the depth and speed of the drainage cold flow is about 75-80m and about 3.5m/s, respectively.The three points for investigating the feature of the cold flow are settled. The observations from April 1997 to the present (March 1998) at Saoka primary school, the points existed nearer the mountainous area, indicate the turbulent characteristics and the seasonal variations as follows :1.the simultaneous abrupt increase of air temperature and large fluctuation of mixing ratio before onset of the upslope flow (valley wind) are found. The phenomena are associated with the thermal convection along the side slope of mountain.2.The cold flows consisted of the air mass intruded along the side slope and along the valley bottom drained into the plain at around the sunset time of Kochi.3.From the histograms of the two thermal meteorogical factors (air temperature [T], mixing ratio [q] in the calm condition), each modes are 24ﾟC in T,16 (g/kg) in q during summer season, and 7ﾟC in T,3 (g/kg) during winter season.