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RESEARCH PRODUCT

A tandem approach for collocated in-situ measurements of microphysical and radiative cirrus properties

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description

Abstract. Microphysical and radiation measurements were collected with the unique AIRcraft TOwed Sensor Shuttle (AIRTOSS) – Learjet tandem platform. It is a combination of a Learjet 35A research aircraft and an instrumented aerodynamic body, which can be detached from and retracted back to the aircraft during flight. Both platforms are equipped with radiative, cloud microphysical, trace gas (CO, N2O, O3 and H2O) and meteorological instruments to study the inhomogeneity of cirrus as well as other layer clouds. Sophisticated numerical flow simulations were conducted in advance in order to optimally integrate a Cloud Combination Probe (CCP) inside the AIRTOSS. The tandem platform was used for the first time at altitudes up to 36 000 ft (10 970 m) during the AIRTOSS – Inhomogeneous Cirrus Experiment (AIRTOSS-ICE). AIRTOSS is connected to the aircraft by a steel wire with a length of 4000 m. Ten flights were performed above the North Sea and Baltic Sea to probe frontal cirrus, in-situ formed cirrus, and anvil outflow cirrus. The cirrus microphysical and radiative properties displayed significant inhomogeneities resolved by both measurement platforms. Data collected with the CCP show that the maximum of the observed particle number size distribu- tions shifts with increasing altitude from 300 μm to 30  μm, which is typical for frontal, midlatitude cirrus. Theoretical considerations imply that cloud particle aggregation inside the studied cirrus is very unlikely. Consequently, diffusional growth was identified to be the dominant microphysical process. Measurements of solar downward irradiance at 670 nm wavelength on the Learjet and the sensor shuttle indicate a significant horizontal heterogeneity of the observed thin cirrus. Making use of the collocated irradiance measurements of the tandem platform, vertically resolved solar heating rates were derived. They varied by up to 6 K day−1 in and above the cirrus layer.