M. Zöger

ACRIDICON–CHUVA Campaign: Studying Tropical Deep Convective Clouds and Precipitation over Amazonia Using the New German Research Aircraft HALO

AbstractBetween 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period...

ML-CIRRUS - The airborne experiment on natural cirrus and contrail cirrus with the high-altitude long-range research aircraft HALO

AbstractThe Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.In spring 2014, HALO performed 16 f...

HNO3 Partitioning in Cirrus Clouds

During the 1997 POLSTAR-1 winter campaign in northern Sweden a flight was performed across a cold trough of air (≃ 196 K) in the tropopause region. Measurements of total water vapour, nitric acid, particles and reactive nitrogen (NOy) were taken. The particle measurements indicate that about 3% of the particles in the moist tropospheric air were ice particles. Forward and backward facing NOy inlets were used simultaneously to determine condensed phase HNO3. The combined NOy and particle measurements reveal that less than 1% of a monolayer of NOy could have resided on the ice particles. This casts doubt on the hypothesis that sedimenting cirrus particles generally lead to a strong downward flux of NOy. In addition to the NOy measurements, independent HNO3 measurements were used to determine total HNO3. Although quantitative uncertainties do not allow to completely rule out that the NOy uptake on ice was limited by total HNO3, the combined NOy and HNO3 data suggest that there was low uptake of NOy on ice despite abundant HNO3 in the gas phase. Model studies indicate, that the most likely explanation of the measured nitric acid partitioning is given by HNO3 in ternary solution droplets coexisting with almost HNO3 free ice in the same air mass.

Static Pressure from Aircraft Trailing-Cone Measurements and Numerical Weather-Prediction Analysis

Accurate static-pressure measurements are a prerequisite for safe navigation and precise air-data measurements on aircraft. Pressure is also fundamental for wind and air temperature analysis in meteorology. Static-pressure measurement by aircraft is disturbed by aerodynamics and needs to be corrected using calibration. In this paper, a comparison has been made between static pressure measured by means of a trailing cone in the atmosphere behind two different jet aircraft at flight levels up to 450 and data from numerical weather predictions. The height is derived from differential Global Navigation Satellite System measurements. The Global Navigation Satellite System height is compared to numerical-weather-prediction geopotential height. The numerical-weather-prediction data were provided by the Integrated Forecast System of the European Centre for Medium-Range Weather Forecasts. When computing the geopotential with latitude-/height-dependent gravity, the pressure/height differences are −0.01±0.15  hPa an...

Ice particle sampling from aircraft - influence of the probing position on the ice water content

The ice water content (IWC) of cirrus clouds is an essential parameter determining their radiative properties and thus is important for climate simulations. Therefore, for a reliable measurement of IWC on board of research aircraft, it is important to carefully design the ice crystal sampling and measuring devices. During the HALO field campaign ML-CIRRUS in 2014, IWC was recorded by three closed path total water together with one gas phase water instrument. The hygrometers were supplied by inlets mounted on the roof of the aircraft fuselage. Simultaneously, the IWC is determined by a cloud 5 particle spectrometer attached under an aircraft wing. Two more examples of simultaneous IWC measurements by hygrometers and cloud spectrometers are presented, but the inlets of the hygrometers were mounted at the fuselage side (Geophysica, StratoClim campaign 2017) and bottom (WB57, MacPex 2011). This combination of instruments and inlet positions provides the opportunity to experimentally study the influence of the ice particle sampling position on the IWC. As expected from theoretical considerations, we found that the IWCs provided by the roof inlets deviate from those measured under the aircraft 10 wing. Caused by the inlet position in the shadow-zone behind the aircraft cockpit, ice particles populations with mean mass sizes larger than about 25 μm radius are subject to losses, which lead to strongly underestimated IWCs. On the other hand, cloud populations with mean mass sizes smaller than about 12 μm are dominated by particle enrichment and thus overestimated IWCs. In the range of mean mass sizes between 12 and 25μm, both enrichment and losses of ice crystal can occur, depending on whether the ice crystal mass peak of the in these cases bimodal size distribution is on the smaller or larger mass mode. 15 The resulting deviations of the IWC reach factors of up to 10 or even more for losses as well as for enrichment. Since the mean mass size of ice crystals increases with temperature, losses are more pronounced at higher temperatures while at lower temperatures IWC is more affected by enrichment. In contrast, in the cases where the hygrometer inlets were mounted at the fuselage side or bottom, the agreement of IWCs is -due to undisturbed ice particle sampling, as expected from theorymost frequently within a factor of 2.5, independently of the mean ice crystal sizes. Summarizing, in case IWC needs to be detected 20 1 Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-373 Manuscript under review for journal Atmos. Meas. Tech. Discussion started: 17 October 2017 c

Comparison of Static Pressure from Aircraft Trailing Cone Measurements and Numerical Weather Prediction Analysis

Accurate static pressure measurements are a prerequisite for safe navigation and precise air data measurements on aircraft. Pressure is also fundamental to assess winds and air temperature and, hence, important for meteorology. The direct static pressure measurement by aircraft is disturbed by the aircraft aerodynamics and needs to be corrected using proper calibration. In this paper we compare static pressure measured by means of a trailing cone (TC) in the undisturbed atmosphere behind two different jet aircraft (Dassault FALCON 20E and Gulfstream 550 “HALO”) at flight levels (FL) from 40 to 450 during 6 flights on different days with data from numerical weather predictions (NWP). The height is derived from differential Global Navigation Satellite System (GNSS) measurements. The GNSS height is compared to NWP geopotential height. The NWP data were provided by the Integrated Forecast System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The IFS model assumes constant gravity g. For constant g, the pressure differences (at same height) have mean values and standard deviations of 0.40±0.17 hPa for 159 individual measurements of 43±31 s duration each. The respective height differences (at same pressure) are -10±5 m on average over the same measurements. When computing the geopotential with latitude/height dependent gravity (which is 0.4 % smaller at FL 450 than at 0 km) the agreement becomes significantly better: -0.01±0.15 hPa for pressure, 0.6±2.8 m for height. This pressure accuracy implies NWP temperature errors <0.1 K on average below 10 km altitude. Standard deviations of random errors in the TC-NWP difference are 0.06 hPa and 1 m. The TC measurements provide a first quantification of the case-specific accuracy of NWP pressure geopotential relationships. The method of comparing operational pressure/GNSS measurements on aircraft with NWP analysis or predictions can be used to test the height keeping performance of aircraft after or during operation.