Capsule summaryThe SOUTHTRAC-GW airborne mission explored the dynamics of gravity waves in the region of the Southern Andes and Antarctic Peninsula during the extraordinary southern hemisphere SSW of September 2019.

Abstract. Possible uncertainties of lidar measurements of middle-atmospheric temperatures, measured with the novel airborne Rayleigh lidar system ALIMA, are investigated on the basis of data from the SouthTRAC-GW campaign in September 2019 and corresponding simulations of photon counts of the ALIMA system. We evaluate uncertainties due to the attenuation by Rayleigh extinction and ozone absorption, (signal-induced) photon noise, the photon background, and the nonlinearity of photon counting detectors. Ozone absorption induces an altitude-dependent cold bias in the retrieved temperatures of 2 K between 25 km to 55 km. Rayleigh extinction introduces a similar uncertainty of 2 K below 25 km that can be decreased by a suitable correction. Photon noise can introduce uncertainties of ±25 K at high altitudes (above 70 km) for high temporal resolutions (1 min), but on average the photon noise influences the temperature by only 1 K to 2 K at 70 km and decreases downwards. Uncertainties related to the photon background and the nonlinearity of the detectors, with a dead time correction applied, play a minor role in the temperature uncertainty. The analysis of the photon background in the ALIMA measurements of six research flights of the SouthTRAC-GW campaign proves the assumption of a constant photon background with altitude as well as the Poisson distribution of the photon counts. The airborne operation of ALIMA is advantageous as the high flight altitudes reduce the Rayleigh extinction by up to 17 % and thus result in higher signal levels compared to a ground-based operation. Overall, our analysis reveals that temperatures can be retrieved from ALIMA measurements with a remaining uncertainty of ≤ 1 K if all known biases are corrected.

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Abstract. Clouds in the mixed-phase temperature regime impose a large uncertainty onto climate prediction models, in part due to incomplete knowledge of the degree of glaciation affecting cloud radiative properties. To achieve a better representation of these clouds, it is crucial to improve the understanding of ice nucleation and growth as well as microphysical properties determining the cloud phase. In this case study, we provide a rare data set of aircraft in situ measurements in a strong mid-latitude convective system extending from the boundary layer to the tropopause and aim to extend the sparse database of such measurements. Data were obtained with the research aircraft HALO and cloud properties were probed with the Cloud and Aerosol Spectrometer (CAS-DPOL) and the Cloud Imaging Probe grayscale (CIPg) during the CIRRUS-HL mission above Southern Germany in July 2021. Microphysical properties of the convective cloud system were measured along a 58-minute stepwise descent between the ground weather stations of Hohenpeissenberg and Munich at temperatures of -35 °C, -23 °C, -13 °C, -7 °C, and -1 °C. A phase identification (liquid/ice) of particles with diameters > 50 μm was achieved using the particle images of the CIPg. Based on recent work, clouds were categorized into four groups with different microphysical properties: Mostly Liquid, Coexistence, Secondary Ice, and Large Ice. High concentrations of large ice crystals were observed in upper layers at temperatures between -35 °C and -13 °C, confirming the importance of the Wegener-Bergeron-Findeisen process for mid-latitude convection. Exceptionally high vertical motions for mid-latitudes of up to +/ 4 ms-1 encountered in the convection promote various freezing and ice growth processes, which in this system led to high ice water contents of up to ~ 1.2 gm-3 and to instrument icing. In contrast, low-level clouds near -1 °C encountered at lower vertical velocities were predominantly composed of liquid droplets and contained precipitated large ice in low concentrations. We find that mechanisms initiating ice nucleation and growth strongly depend on temperature, relative humidity, and vertical velocity and variate within the cloud system. Our measurements represent a unique in-flight data set on microphysical cloud properties of a strong midlatitude convective event and invite for detailed cloud model evaluations and radar intercomparisons with focus on the mixed-phase temperature regime.