Abstract
Abstract. A new airborne tandem measurement platform for cloud-radiation interaction studies is introduced in this paper. It consists of a Learjet 35A research aircraft and the AIRcraft TOwed Sensor Shuttle (AIRTOSS), which is an instrumented drag-body towed by the Learjet. Currently, the AIRTOSS is instrumented with a Cloud Imaging Probe (CIP) for measuring cloud microphysical properties and an Inertial Navigation System (INS) for measurements of flight attitudes. The cable dragging AIRTOSS can be as long as four kilometres. Thus, truly collocated measurements in two altitudes above, in, and below clouds can be obtained. Results from first test flights with Learjet and AIRTOSS are reported here. The flights were performed from Hohn Airport, Germany. Specific manoeuvres were flown to test the aerodynamic behaviour of the drag-body and to investigate the suitability of AIRTOSS for high-precision irradiance measurements which require a stable flight attitude of AIRTOSS. The flight attitude data show that AIRTOSS is sensitive to several flight manoeuvres such as turns, altitude and airspeed changes, and also to changes of towing cable length. The effects of these manoeuvres on the attitude angles of AIRTOSS have been quantified. Maximum roll angle deviations were observed during turns. Even small changes in heading can lead to high roll angles (one degree change in heading causes a change in roll angle of about eight degrees). The pitch angle varies during climb or dive periods, extending or retracting of towing cable, acceleration or deceleration, and even when flying at too low or too high true airspeed depending on altitude. Values of pitch angle between −5° (dive) and 8° (climb and retracting towing cable) have been observed. While change in attitude is not problematic for cloud particle property measurements it is for radiation measurements. Here, the deviation from the horizontal should be no more than 3° to avoid large errors. When keeping the above mentioned flight parameters constant, sufficiently stable flight conditions can be maintained to perform high-quality irradiance measurements with AIRTOSS in future experiments. During this test campaign also observations of cloud microphysical data as for example droplet number concentrations and size distributions with the AIRTOSS in stratocumulus clouds were performed to prove the compliance with scientific needs. Simultaneous spectral cloud radiation measurements have been made. The measurements of internal operational data of AIRTOSS as well as the first atmospheric data demonstrate the suitability of this tandem platform for detailed cloud microphysics and radiation interaction studies.
Highlights
Clouds constitute an important factor in the global climate since they affect the radiation balance of the Earthatmosphere system in complicated but significant ways (cooling and warming of the atmosphere, as discussed in the IPCC report (Solomon et al, 2007))
As a result we find that the main misalignment related uncertainties of downwelling irradiances are: 1. independent of solar azimuth angles (SAA), 2. only weekly dependent on wavelengths of the solar radiation, 3. strongly influenced by solar zenith angles (SZA): the higher SZA the higher the uncertainty, and
A novel airborne tandem measurement configuration has been developed which allows truly collocated airborne atmospheric measurements at two different altitudes. It consists of a combination of a Learjet which tows a drag-body (AIRTOSS) with an adjustable cable length from 0 to 4 km
Summary
Clouds constitute an important factor in the global climate since they affect the radiation balance of the Earthatmosphere system in complicated but significant ways (cooling and warming of the atmosphere, as discussed in the IPCC report (Solomon et al, 2007)). W. Frey et al.: The AIRTOSS (AIRcraft TOwed Sensor Shuttle) attempted by using several aircraft in stack during numerous airborne experiments such as the Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment (CRYSTAL-FACE, Jensen et al, 2004) or the Tropical Composition, Cloud and Climate Coupling (TC4) mission (Toon, 2007). Frey et al.: The AIRTOSS (AIRcraft TOwed Sensor Shuttle) attempted by using several aircraft in stack during numerous airborne experiments such as the Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment (CRYSTAL-FACE, Jensen et al, 2004) or the Tropical Composition, Cloud and Climate Coupling (TC4) mission (Toon, 2007) These attempts of collocated airborne sampling have only partly been successful.
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