Low-Cloud Response To The East China Sea Kuroshio Fronts In Different Seasons

To investigate how the East China Sea Kuroshio front influence low cloud, we take some climatic analysis and case analysis using the CALIPSO satellite data and reanalysis data provided by the European Center for Medium-Range Weather Forecast(ECMWF). In the climatic analysis, eight tracks of CALIPSO over the East China Sea Kuroshio were composited to explore the physical mechanism during spring and winter. Low cloud top (LCT) is controlled by several elements. Cloud top/base height increases from north to south, and with a sharp transition across the SST front. In spring, there is fog on the north flank of front and low cloud on the south. The LCT increases with the difference between sea surface temperature and atmospheric temperature (SST-SAT). Instable marine boundary layer and ascending moion at 800hPa are both in favor of high LCT. The SST front induces a secondary circulation with ascending motion over the warm flank and descending motion over the cold flank. The upward motion can reach the mid-troposphere in spring. Composite analysis shows that low cloud responds obviously under northerly advection, and mid-level cloud responds under southerly advection. The frequency of mid-level clouds is more than both sides. The LCT is smoother on the cold flank, and when the air-sea interface and marine atmospheric boundary layer (MABL) are more stable. The maximum frequency of two cloud layers is over the SST front. Three typical cases representing different seasons were selected to study the differences of stratocumulus,stratus and sea fog over the East China Sea Kuroshio. The results show that stratocumulus, whose cloud top with poor smoothness is about 1.2-2.5km above the sea level and the cloud base height is about 0.7-2km, occurs after the upper trough. The characteristics include unstable air-sea interface and MABL, prevailing northerly winds and an inversion above the stratocumulus. Meanwhile, stratus, whose cloud top height is about 300-700m, takes place before the upper trough accompanied by intense cold advection. The characteristics contain stable air-sea interface and MABL, prevailing southerly winds and no subsidence in the cloud area. Sea fog occurs after the upper trough,along with low level warm advection. It’s above the centre of high pressure. The top of the fog is less than 700m, and is smoothest. Its bottom is grounded. The air-sea interface and MABL are also stable, but with strong subsidence. The sea surface prevails southerly wind, and the relative humidity is above 90%.The East China Sea Kuroshio Fronts influence the height and the morphological of low cloud by effecting MABL. The height of three types of low cloud are all decreasing from south to north, and have a sharp transition across the SST gradient zone. Sea fog and stratus are similar, and under certain conditions can be mutual conversion.