Indications of thin cirrus clouds in the stratosphere at mid-latitudes P. Keckhut, A. Hauchecorne, S. Bekki, A. Colette, C. David, and J. Jumelet Service d’Aéronomie/Institut Pierre-Simon Laplace, CNRS, Verrières le Buisson, France
Abstract. This study is devoted to the possible presence of cirrus clouds in the
stratosphere. 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 the
dynamical tropopause even when the cloud top is close to the thermal
tropopause. Ten cirrus cases are found to be unambiguously located above the
local dynamical tropopause according to high-resolution PV advection
calculations. The highest cloud detected above the local tropopause (nearly 3 km above) is observed inside air masses that originate
from the sub-tropical regions and are then transported rapidly to mid-latitudes
through isentropic transport. The details of the air mass history is described with a 3-D trajectory model. The back-plumes indicate that the
air mass, moist with respect to typical stratospheric air, was transported
from the subtropical troposphere to the lowermost stratosphere in 4 days
before detection above France. A continuous cooling of 5–10° along
the trajectory took place during its transit. This cooling could have been
partly responsible for the thin cirrus layer detected.
Citation: Keckhut, P., Hauchecorne, A., Bekki, S., Colette, A., David, C., and Jumelet, J.: Indications of thin cirrus clouds in the stratosphere at mid-latitudes, Atmos. Chem. Phys., 5, 3407-3414, doi:10.5194/acp-5-3407-2005, 2005.