春季青藏高原西北侧一次平流层臭氧向对流层传输的模拟研究

利用NCEP/NCAR FNL客观分析资料和欧洲中期天气预报中心(ECMWF)的Interim再分析资料以及臭氧监测仪(OMI)的臭氧廓线资料,结合区域大气化学模式WRF-Chem对中国春季一次高空冷槽过境引起的对流层顶折卷过程(2012年3月19—21日)进行了分析,并从平流、湍流混合、对流输送等几个方面诊断分析了平流层臭氧向对流层的传输特征和细节。结果表明,发生于青藏高原西北侧的对流层顶折卷事件,其所在位置处于热带对流层顶向中纬度对流层顶的过渡区,由于陡峭的对流层顶南北梯度,在该区域发生的平流层-对流层物质交换(STE)比对流层顶东西方向折卷引起的物质交换要强烈和持久,跨越等熵面的物质交换和湍流混合对平流层-对流层物质交换有很大的贡献。大地形对平流层-对流层物质交换过程有显著的影响,且具有明显的日变化特征。早晚时段,大地形导致的爬坡上升气流显著,抑制了平流层空气与对流层空气的混合交换。午后,大地形热力作用增强,受背风坡局地环流的影响,靠近山顶处湍流混合作用对上对流层臭氧浓度升高的贡献显著增强,且地形越高,这种效应越显著。地形的湍流混合作用在2.5 km高度以上凸显,此高度之上地形平均高度每升高100 m,湍流混合的贡献增加约1%。

A simulation study of the transport of the stratospheric ozone to the troposphere over the northwest side of the Tibetan Plateau in spring

Using the NCEP/NCAR FNL data and the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim data and the Ozone Monitoring Instrument (OMI) ozone profile data,together with a regional atmospheric chemical model (WRF-Chem), a tropopause folding event caused by a cold trough during 19-21 March 2012 was analyzed.The contributions of advection, turbulence mixing and convective transport processes to the transport of the stratospheric ozone to the troposphere are diagnosed.The results show that the tropopause folding event occurred in the northwest side of the Tibetan Plateau is located in the transition zone between the tropical tropopause and the mid-latitude tropopause.Due to steep north-south gradient of the tropopause, the stratosphere and troposphere exchange (STE) in this region is more persistent and stronger than that caused by the east-west tropopause folding.Mass exchange across the isentropic surface and the turbulent mixing have significant contributions to the STE.The higher orography has a significant influence on the STE processes with its effect having an evident diurnal variation.In the morning and evening time, the upward motions due to forcing lift of the high orography are strong and inhibit the mass exchange between stratosphere and troposphere.In the afternoon, the thermal effect of the high orography enhances, and the turbulent mixing near the top of the mountain leads to significant ozone increases in the upper troposphere with the development of local circulation on the leeward slope of the high orography,and, the higher the orography is the more significant this effect is.The height of the orography of 2.5 km is critical in term of the turbulent mixing. Above this height, the contribution of turbulent mixing to ozone change increases about 1% when the average height of the orography rises 100 m.