A new airborne tandem platform for collocated measurements of microphysical cloud and radiation properties

Atmospheric Measurement Techniques Discussions 01/2009; 2(1). DOI: 10.5194/amt-2-147-2009
Source: DOAJ


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 curves, 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 curve flight. 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 radiation measurements of the clouds 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.

Download full-text


Available from: Manfred Wendisch,
  • Source
    • "In addition to the new sensors that are capable of providing previously unavailable information on ice crystal properties or that avoid the more serious limitations, newly developed airborne platforms offer new approaches for measuring the microphysical properties of mixed phase clouds. For example unmanned airborne vehicles (UAVs) are now being instrumented to do long-range and long-duration measurements in cirrus es32 februAry 2012 | clouds, and instrumented sondes towed by an aircraft have allowed measurements of radiation fluxes from the aircraft flying above the cloud, while measurements of microphysics are made in the cloud by the towed vehicle (Frey et al. 2009). Wind tunnels also continue to be used to better understand measurement issues on aircraft, but in new ways. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The workshop on in situ airborne instrumentation: addressing and solving measurement problems in ice clouds, June 25-27, 2010, Oregon, aimed to identify unresolved questions concerning ice formation and evolution in ice clouds, assess the current state of instrumentation that can address these problems, introduce emerging technology that may overcome current measurement issues, and recommend future courses of action to improve our understanding of ice cloud microphysical. Eleven presentations were made covering measurement challenges associated measuring the composition and concentration of all the modes of ice nuclei (IN), measuring the morphology, mass, surface, and optical properties of individual ice crystals over all sizes, and measuring temperature, humidity, and winds in clouds accurately. It was found that cloud lifetimes are sensitive to the sedimentation velocity of the ice crystals, as are the rates of aggregation and riming that depend on the relative fall velocities of ice crystals and supercooled water droplets.
    Bulletin of the American Meteorological Society 02/2012; 93(2):Bulletin of the American Meteorological Society. DOI:10.1175/BAMS-D-11-00123.1 · 11.57 Impact Factor
  • Source
    • "t absorption remains to be explored , as well as the scales over which horizontal photon transport occurs in high‐cloud systems ( for example , by embedding the MAS cloud scene in the larger context of GOES retrievals ) . In the future , new measurement techniques such as a payload that can be lowered down into and below a cloud from an aircraft [ Frey et al . , 2009 ] will make apparent absorption measurements easier and will provide a link with cloud microphysics . [ 40 ] Acknowledgments . The first author was funded under the NASA TC 4 project ( NNX07AL12G ) , as were the deployment of MAS ( NNX08AR39G ) and CRS on board the NASA ER‐2 aircraft . Warren Gore and Antonio Trias ( NASA Ames Research C"
    [Show abstract] [Hide abstract]
    ABSTRACT: Coordinated flight legs of two aircraft above and below extended ice clouds played an important role in the Tropical Composition, Cloud and Climate Coupling Experiment (Costa Rica, 2007). The Solar Spectral Flux Radiometer measured up- and downward irradiance on the high-altitude (ER-2) and the low-altitude (DC-8) aircraft, which allowed deriving apparent absorption on a point-by-point basis along the flight track. Apparent absorption is the vertical divergence of irradiance, calculated from the difference of net flux at the top and bottom of a cloud. While this is the only practical method of deriving absorption from aircraft radiation measurements, it differs from true absorption when horizontal flux divergence is nonzero. Differences between true and apparent absorption are inevitable in any inhomogeneous atmosphere, especially clouds. We show, for the first time, the spectral shape of measured apparent absorption and compare with results from a three-dimensional radiative transfer model. The model cloud field is created from optical thickness and effective radius retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) Airborne Simulator and from reflectivity profiles from the Cloud Radar System, both on board the ER-2. Although the spectral shape is reproduced by the model calculations, the measured apparent absorption in the visible spectral range is higher than the model results along extended parts of the flight leg. This is possibly due to a net loss of photons into neighboring cirrus-free areas that are not contained within the model domain
    Journal of Geophysical Research Atmospheres 10/2010; 115(2010-D00J22):1-12. DOI:10.1029/2009JD013124 · 3.43 Impact Factor
  • Source
    • "Two types of 2D probes were developed for airborne measurements with upper detection limits of 0.8 mm and 6.4 mm, and with resolutions of 25 µm and 200 µm, respectively. In recent times, modernized versions (Cloud Imaging Probe, CIP; Precipitation Imaging Probe, PIP) became available for airborne measurements of droplet sizes and shapes extending from size diameters of 25 µm up to 1500 µm or even a few millimeters (De Reus et al., 2009; Frey et al., 2009). Most recently a two-dimensional video disdrometer (2DVD) has been developed for ground-based in situ measurements of precipitation drop size distributions, as well as of shape and terminal velocities of individual droplets under low-wind conditions (Kruger and Krajewski, 2002). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Since more than a hundred years ago the deformed shape of raindrops and their oscillations have been observed but investigations are still ongoing as the experimental and numerical techniques are being improved, and the demand from meteorological applications (e.g., weather radars) for more precise characterization of natural raindrops have increased. For laboratory measurements, the realistic simulation of atmospheric conditions is crucial so it is important that drops fall at their terminal velocities and appear as motionless in vertical wind tunnels. Experiments that are performed in fall shafts or vertical wind tunnels are complemented by ground-based and airborne field observations. On the theoretical side, raindrop deformation and oscillations are given by model computations. Comparing model axis ratios with different kinds of measurements allows one to conclude that the dynamic axis ratio of oscillating raindrops can be appropriately obtained from a force balance model. In the size range between 1 and 2.5mm diameter, which is of great importance from the point of view of radar meteorology, it is still questionable whether the dynamic axis ratios are equal to the equilibrium axis ratios in all cases. Equations which describe the oscillation frequencies of different modes are confirmed by laboratory measurements. Some experimental evidence hints at the co-existence of several modes of oscillations. It is, however, still not completely clear which modes can be active and how the existence of higher modes depends on the raindrop size. In this paper a review of the current knowledge about the time average axis ratio, the oscillation frequencies and modes, and the shape of freely falling raindrops is presented; besides an overview of the adopted experimental techniques is provided, and the remaining open questions are highlighted.
    Atmospheric Research 09/2010; 97(4). DOI:10.1016/j.atmosres.2010.03.024 · 2.84 Impact Factor
Show more