Abstract
Lidar measurements of midlatitude cirrus clouds over Buenos Aires, collected between 2002 and 2003 are compared with multiple tropopauses (MT) retrieved from rawinsonde temperature retrievals. Results derived from the rawinsondes display MT events with an annual cycle which are fewest in March. Comparison with lidar observations shows that cirrus clouds are mostly located closely below the first tro-popause, but when cloud top is above the first tropopause, in 25% of cases, the cloud base is not above it, resulting in a cirrus cloud crossing the inter-tropopause region. Compared with the distribution of the whole population of midlatitude cirrus clouds, cross-tropopause cirrus clouds display a similar geometrical thick-ness as inter-tropopause cirrus clouds.
Highlights
Cirrus clouds play an important but uncertain role in the Earth’s climate system 1
A field of view less than 1.5 mrad is normally used for both telescopes.To avoid possible, unwanted inclusion of altocumulus, i.e., of water clouds, we restricted the present campaign to clouds with a cloud base height ≥ 6 km, a criterion that coincides with the definition of cirrus clouds given by the International Coordination group on Laser Atmospheric Studies (ICLAS): cirrus clouds derived from lidar measurements are layers of particle above 6 km situated in an air mass with temperature of –25 ̊C or colder which in addition display a large temporal and spatial variability
These maximums may be correlated with the increase in multiple tropopauses (MT) frequency over the same period (Figure 1), but with its first maximum centered in July instead June
Summary
Cirrus clouds play an important but uncertain role in the Earth’s climate system 1. They cover about 30% of the Earth’s surface at any one time, and play an important role in the Earth’s climate system owing to their capability of trapping outgoing long-wave (greenhouse effect) and reflecting solar radiation (albedo effect) as well as in the troposphere – stratosphere exchange 2 Due to their ubiquitous nature and higher altitude, the properties of these ice clouds are difficult to characterize. Considering that the variability in the thermodynamic structure of the tropopause could affect the properties of the tropopause cirri, several recent analysis have focused on tropical and midlatitude tropopause cirri properties, bearing in mind that temperature inversion has a constraining effect on cloud altitude 2,14,15. Using this definition about the ratio defined by them, we studied the MT events but over Buenos Aires (EZE; 34.6S, 58.5W) during 2002-2003 and attempts to investigate the possible relationship between MT events and cirrus clouds occurrence
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