Enviscope (Germany)

Small changes in the equilibrium between water vapor and cirrus clouds in the upper troposphere and lower stratosphere (UTLS) can strongly influence atmospheric radiative forcing. Relative humidity with respect to ice (RHice) is a key parameter governing the formation and life cycle of cirrus clouds.We present RHice measurements in the UTLS over the North Sea and Germany during the TPEx Learjet campaign (7–20 June 2024), conducted from Hohn, Germany, as part of the TPChange research program. Two IAGOS capacitive hygrometers (ICHs) were deployed: one mounted on the Learjet fuselage and the other on an AIRTOSS (AIRcraft Towed Sensor Shuttle) trailing approximately 70–180 m below the aircraft. This setup enabled the resolution of fine vertical structures of RHice that cannot be captured by weather and climate models.By combining ICH RHice measurements with ECMWF ERA5 cloud ice water content along flight paths, we distinguish between cirrus and non-cirrus conditions, corroborated by the NIXE cloud probe onboard. Additionally, we examine the fine vertical structure of RHice across the extratropical tropopause and its relationship with cirrus clouds. These findings enhance our understanding of cirrus cloud occurrence and variability in this sensitive region, providing valuable insights for improving their representation in climate models.

<strong class="journal-contentHeaderColor">Abstract.</strong> A new modular multi-sensor aerological dropsonde system for high and fast-flying research aircraft has been developed for studying atmospheric processes. This new system allows to drop release containers with up to 4 sondes inside and data from up to 30 sondes can be transmitted simultaneously. After separation from the release container, the sondes enable high-resolution spatio-temporal profiling of temperature, humidity, pressure, and wind with a time resolution of 1.2 s corresponding to approximately 10 m vertical resolution. The modular design ensures simple integration of additional sensors without extensive flight tests and recertification for e.g. particle measurements and radioactivity. The standard meteorological sonde comprises sensor elements of a commercial Graw DFM-17 radiosonde, a 400 to 406 MHz band communication link to the aircraft, and an optional satellite communication module. By means of the satellite link, the data can be made ​​available worldwide in near real time and data loss is avoided when the dropping aircraft leaves the telemetry range. The main feature of the new system is the release container, which allows for dropping through standard dropsonde dispensers of both mid-size turbo-prop aircraft (e.g. Dornier Do 128-6) and jet aircraft (e.g. the Gulfstream 550 &ldquo;High Altitude and Long Range Research Aircraft, HALO&rdquo;). The release container ensures safe separation from the aircraft and protects its payload during deceleration from aircraft speed to fall speed before the sondes are released by an electro-mechanical mechanism. Operations in different campaigns have confirmed the reliability of the entire system and the quality of acquired data. Feasibility of the technical and operational approach for targeted observations of a mesoscale convective system in Argentina was demonstrated by HALO measurements during the SouthTRAC (TRAnsport and Composition of the southern hemisphere UTLS campaign) campaign. Moreover, a configuration consisting of one meteorological sonde coupled (a) with an optical counter for particle sizing was tested using a Dornier Do 128-6 aircraft during a Saharan dust episode over Germany and (b) with a radioactivity sensor was successfully dropped from a Learjet 35A.

Abstract. The instrumentation of the High Altitude and Long Range (HALO) research aircraft is extended by the new Broadband AirCrAft RaDiometer Instrumentation (BACARDI) to quantify the radiative energy budget. Two sets of pyranometers and pyrgeometers are mounted to measure upward and downward solar (0.3–3 μm) and thermal-infrared (3–100 μm) irradiances. The radiometers are installed in a passively ventilated fairing to reduce the effects of the dynamic environment, e.g., fast changes of altitude and temperature. The remaining thermal effects range up to 20 W m-2 for the pyranometers and 10 W m-2 for the pyrgeometers; they are corrected using an new efficient method that is introduced in this paper. Using data collected by BACARDI during a night flight, the thermal offsets are parameterized by the rate of change of the radiometer sensor temperatures. Applying the sensor temperatures instead of ambient air temperature for the parameterization provides a linear correction function (200–600 W m-2 K-1 s), that depends on the mounting position of the radiometer on HALO. Furthermore, BACARDI measurements from the EUREC4A (Elucidating the role of clouds-circulation coupling in climate) field campaign are analyzed to characterize the performance of the radiometers and to evaluate all corrections applied in the data processing. Vertical profiles of irradiance measurements up to 10 km altitude show that the thermal offset correction limits the bias due to temperature changes to values below 10 W m-2. Measurements with BACARDI during horizontal, circular flight patterns in cloud-free conditions demonstrate that the common geometric attitude correction of the solar downward irradiance provides reliable measurements in this typical flight sections of EUREC4A, even without active stabilization of the radiometer.

Abstract. Orographic gravity waves (i.e. mountain waves) can potentially lead to cross-isentropic fluxes of trace gases via the generation of turbulence. During the DEEPWAVE (Deep Propagating Gravity Wave Experiment) campaign in July 2014 we performed tracer measurements of carbon monoxide (CO) and nitrous oxide (N2O) above the Southern Alps during periods of gravity wave activity. The measurements were taken along two stacked levels at 7.9 km in the troposphere and 10.9 km in the stratosphere. A detailed analysis of the observed wind components shows, that both flight legs were affected by vertically propagating gravity waves with momentum deposition and energy dissipation between the two legs. Corresponding tracer measurements indicate turbulent mixing in the region of gravity wave occurrence. For the stratospheric data we identified mixing leading to a change of the cross-isentropic tracer gradient from the upstream to the downstream region of the Southern Alps. Based on the quasi-inert tracer N2O we identified two distinct layers in the stratosphere with different chemical composition on different isentropes. The CO-N2O relationship clearly indicates that irreversible mixing between these two layers occurred. Further we found a significant change of the N2O-Θ-profiles from the upstream to the downstream side above the Southern Alps with different gradients of the N2O-Θ-relation just above the tropopause. A scale-dependent gradient analysis reveals that this gradient change is triggered in the region of gravity wave occurrence. The power spectra of the in-situ measured vertical wind, Θ, and N2O indicate the occurrence of turbulence above the mountains associated with the gravity waves in the stratosphere. The estimated eddy dissipation rate based on the measured three dimensional wind indicates a weak intensity of turbulence in the stratosphere above the mountain ridge. The N2O-Θ-relation downwind the Alps modified by the gravity wave activity provides clear evidence that trace gas fluxes, which were deduced from wavelet co-spectra of vertical wind and N2O are at least in part cross-isentropic. Our findings thus indicate that orographic waves led to turbulent mixing on both flight legs in the troposphere and in the stratosphere. Despite only weak turbulence during the stratospheric leg, the cross isentropic gradient and the related composition change on isentropic surfaces N2O-Θ gradient change from upstream to downstream the mountain unambiguously conserves the effect of turbulent mixing by gravity wave activity before the measurements. This finally leads to irreversible diabatic trace gas fluxes and thus has a persistent effect on the UTLS trace gas composition.

Abstract. The impact of air masses from Asia influenced by the Asian monsoon anticyclone on the northern hemispheric stratosphere is investigated based on in-situ measurements. An statistical significant increase in water vapor of about 0.5 ppmv (11 %) and methane up to 20 ppbv (1.2 %) in the extra-tropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 by in-situ instrumentation in the northern hemisphere during the HALO aircraft mission TACTS and ESMVal. We investigate the origin of this water vapor and methane increase with the help of the three-dimensional Lagrangian chemistry transport model CLaMS. We assign the source of the moist air masses in the Asian region (North and South India, East China, South East Asia and tropical Pacific) based on tracers of airmass origin used in CLaMS. The water vapor increase is correlated to an increase of the simulated Asian monsoon air mass contribution from 10 % in August to 20 % in September, which corresponds to a doubling of the influence of air masses affected by the Asian monsoon region. Additionally, back trajectories starting at the aircraft flight paths are used to differentiate between transport from the Asian monsoon anticyclone and other source regions by calculating the Lagrangian cold point (LCP). The geographic location of the LCPs, which indicates the region where the imprint of water vapor concentration along these trajectories occur, can be exclusively attributed to the Asian monsoon region.

Abstract. A commercially available dry chemiluminescence (CI) instrument for fast and precise measurement of ozone (O3) is specified. The sensitivity is ~9000 counts s−1 per ppbv of ozone. Its precision is entirely determined by the number of photons reaching the detector (being a photomultiplier), i.e. is quantum-noise limited. The relative precision (ΔO3/O3 in %) thus follows Poisson statistics and scales with the square root of the measurement frequency f and with the inverse O3 mixing ratio: ΔO3/O3 ∝ f0.5 · O3−0.5. At typical O3 mixing ratios between 10 and 100 ppbv (and 1 bar), the precision is 0.3–1.0% at f = 10 Hz. The maximum measurement frequency is 50 Hz. The mechanical and electronic set-up as well as the instrument performance is described. Recommendations on the adequate inlet tube configuration (inlet tube length, sampling flow) and on the way of calibration at stationary ground-based platforms and onboard aircraft are given.

Abstract. A commercially available dry chemiluminescence (CI) instrument for fast and precise measurement of ozone (O3) is specified. The sensitivity is ~9000 counts s−1 per ppbv of ozone. Its precision is entirely determined by the number of photons reaching the detector (being a photomultiplier), i.e. is quantum-noise limited. The relative precision (ΔO3/O3 in %) thus follows Poisson statistics and scales with the square root of the measurement frequency f and with the inverse O3 mixing ratio: ΔO3/O3 ∝ f0.5 · O3−0.5. At typical O3 mixing ratios between 10 and 100 ppbv, the precision is 0.3–1.0% at f = 10 Hz. The maximum measurement frequency is 50 Hz. The mechanical and electronic set-up as well as the instrument performance is described. Recommendations on the adequate inlet tube configuration (inlet tube length, sampling flow) and on the way of calibration at stationary ground-based platforms and onboard aircraft are given.