Indications of thin cirrus clouds in the stratosphere at mid-latitudes

[摘要] This study is devoted to the possible presence of cirrus clouds in thestratosphere. Three months of lidar data collected in the south of France(44° N) for detection of stratospheric cirrus are carefully analyzed.Most of the cirrus clouds appear to be located in the troposphere below thedynamical tropopause even when the cloud top is close to the thermaltropopause. Ten cirrus cases are found to be unambiguously located above thelocal dynamical tropopause according to high-resolution PV advectioncalculations. The highest cloud detected above the local tropopause (nearly 3 km above) is observed inside air masses that originatefrom the sub-tropical regions and are then transported rapidly to mid-latitudesthrough isentropic transport. The details of the air mass history is describedwith a 3-D trajectory model. The back-plumes indicate that theair mass, moist with respect to typical stratospheric air, was transportedfrom the subtropical troposphere to the lowermost stratosphere in 4 daysbefore detection above France. A continuous cooling of 5–10° alongthe trajectory took place during its transit. This cooling could have beenpartly responsible for the thin cirrus layer detected.

[学科分类] 大气科学