<p>The dynamics and transport processes in the upper troposphere are of great importance for the global long-term distribution of greenhouse gases and pollution tracers, and hence for the anthropogenic impact on the Earth climate. Especially in the tropics, large amounts of carbon monoxide (CO), carbon dioxide (CO<sub>2</sub>), methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) are produced by e.g. biomass burning, anthropogenic and agricultural activities. These tracers are vertically transported by deep convective cells in the InterTropical Convergence Zone (ITCZ) into the Tropical Tropopause Layer (TTL). Long-range transport processes distribute the tracers globally, which have lifetimes of up to years and decades. It is crucial to understand the details of the transport processes and how the tracers are distributed throughout the upper troposphere and the lower stratosphere (UTLS).</p> <p>During several aircraft campaigns (CAFE Brazil 2022/2023, SouthTrac 2019, CAFE Africa 2018, OMO 2015, ESMVal 2012) CO, CH<sub>4</sub> and N<sub>2</sub>O have been measured nearly globally and especially in the tropics with quantum cascade laser absorption spectrometers deployed on the High Altitude and Long-range Aircraft (HALO). Combining these measurements, we can present a good overview of the large-scale distribution of the tracers in particular in the tropical troposphere up to altitudes of approx. 14 km.</p> <p>The in-situ aircraft measurements will be used to study interhemispheric transport processes and regional trace gas budgets at the base of the TTL. Therefore, they will be further combined and investigated with modelling data and back trajectories.&#160;</p>
Abstract. The Fast Infrared Hygrometer (FIRH), employing open-path tunable diode laser absorption spectroscopy at the wavelengths near the 1364.6896 nm line, was adapted to perform contactless humidity measurements at the Turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T), a unique turbulent moist-air wind tunnel. The configuration of the setup allows for scanning from outside the walls of the wind tunnel and at various positions without the need for repeated optics adjustments. We identified three factors which significantly influence the measurement – self-broadening of the absorption line, interference in the glass windows and parasitic absorption in the ambient air outside the wind tunnel – and developed correction methods which satisfactorily account for these effects. The comparison between FIRH and a reference hygrometer (dew-point mirror MBW 973) indicated a good agreement within the expected errors across the wide range of water vapour concentration 1.0–6.1×1017 cm−3 (equivalent to dew-point temperature of −5.4 to +21 ∘C at the temperature of 23 ∘C). High temporal resolution (∼2 kHz) allowed for studying turbulent fluctuations in the course of intensive mixing of two air streams which had the same mean velocity but differed in temperature and humidity, also including the settings for which the mixture can be supersaturated. The obtained results contribute to improved understanding and interpretation of cloud formation studies conducted in LACIS-T by complementing the previous characterizations of turbulent velocity and temperature fields inside the wind tunnel.
Abstract. The Fast Infrared Hygrometer (FIRH), employing open-path tunable diode laser absorption spectroscopy at the wavelengths near 1364.6896 nm line, was adapted to perform contactless humidity measurements at the Turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T), a unique turbulent moist-air wind tunnel. The configuration of the setup allows for scanning at various positions without the need for repeated optics adjustments. We identified three factors which significantly influence the measurement – self-broadening of the absorption line, interference in the glass windows and parasitic absorption in the ambient air outside the tunnel – and developed correction methods which satisfactorily account for these effects. The comparison between FIRH and a reference hygrometer (dew-point mirror MBW 973) indicated a good agreement within the expected errors across the wide range of water vapor concentration 1.0 . . . 6.1 cm−3 (equivalent to dew-point temperature of −5.4 . . . + 21 °C at the temperature of 23 °C). High temporal resolution (∼2 kHz) allowed for studying turbulent fluctuations in the course of intensive mixing of two air streams which had the same mean velocity but differed in temperature and humidity, including also the settings for which the mixture can be supersaturated. The obtained results complement the previous characterizations of turbulent velocity and temperature fields in LACIS-T. The variance of water vapor concentration exhibits a maximum in the center of the mixing zone which coincides with the steepest gradient.
<p>A narrow-band optical hygrometer FIRH (Fast Infrared Hygrometer, Nowak et al., 2016), based on absorption of laser light at wavelength &#955;=1364.6896 nm was used for contactless measurements of humidity inside the measurement volume of LACIS-T (turbulent Leipzig Aerosol Cloud Interaction Simulator, Niedermeier et al., 2020). LACIS-T is a multi-purpose moist-air wind tunnel for investigating atmospherically relevant interactions between turbulence and cloud microphysical processes under well-defined and reproducible laboratory conditions. Main goals of the experiment were:</p><p>1) characterization and evaluation of the FIRH hygrometer in controlled conditions,</p><p>2) characterization of fast turbulent humidity fluctuations inside LACIS-T.</p><p>&#160;</p><p>Collected results indicate, that FIRH can be used to characterize turbulent fluctuations of humidity in scales of tens of centimeters with the temporal resolution of 2 kHz and presumably more. Interestingly, scanning of LACIS-T measurement volume indicated existence of turbulence and wave-like features for the investigated measurement setup in its &#160;central part, where air streams of different thermodynamical properties, yet the same mean velocity mix intensively. , However, the setup for cloud measurements include an additional flow (i.e., an aerosol flow) in the central part strongly reducing the wave-like features. In other words, cloud process studies are most likely unaffected by these features.</p><p>Finally, the experiments proved that contactless measurements of humidity conducted from outside the measurement volume of LACIS-T are useful, on condition of corrections of glass window transmission and interferences.</p><p>&#160;</p><p>Niedermeier, D., Voigtl&#228;nder, J., Schmalfu&#223;, S., Busch, D., Schumacher, J., Shaw, R. A., and Stratmann, F. (2020): Characterization and first results from LACIS-T: a moist-air wind tunnel to study aerosol&#8211;cloud&#8211;turbulence interactions, Atmos. Meas. Tech., 13, 2015-2033, doi:10.5194/amt-13-2015-2020.</p><p>Nowak J., Magryta P., Stacewicz T., Kumala W., Malinowski S.P., 2016: Fast optoelectronic sensor of water concentration, Optica Applicata, vol. 46(4) , pp. 607-618 , doi: 10.5277/oa160408</p>
<p>The British Antarctic Survey (BAS) operates one of the most remote, advanced, and scientifically important research stations on the Antarctic continent &#8211; Halley. Located on the floating Brunt ice shelf, the station has provided meteorological and atmospheric observations since it was established in 1956. However, in the face of glaciological uncertainty, Halley Research Station had to close for the first time in its history during winter 2017. To overcome the subsequent data loss from the unmanned research station, engineering and science teams at BAS began automating the station.</p><p>In 2018-19, the Halley automation project began with scientific equipment adapted and the installation of an innovative micro-turbine electrical generator. Science experiments ran uninterrupted throughout the nine-month winter period, with the station preserving core science data streams such as Meteorology and Ozone Monitoring, Tropospheric Chemistry and Climate, and Space Weather and Upper Atmospheric Observations. The system proved its ability to withstand the Antarctic environment during the 2019 winter; unaffected by ambient temperatures as low as -55&#730;C and winds gusting up to 70 knots.</p><p>Work is ongoing to automate and reinstate the long-term atmospheric monitoring experiments at Halley. In December 2021, a new automated CO<sub>2</sub> and CH<sub>4</sub> analyser was installed in Halley&#8217;s Clean Air Sector (CAS) laboratory which will run continuously over the coming Antarctic winter. Halley&#8217;s coastal location provides an ideal platform to explore air-sea CO<sub>2</sub> exchange in the Southern Ocean region. The Southern Ocean is a globally important carbon sink, estimated to account for ~75% of global ocean CO<sub>2</sub> uptake but a sparsity of observations in the region has contributed to uncertainty around the inter-annual and seasonal nature of the Southern Ocean sink.</p><p>CO<sub>2</sub> mixing ratios have been measured at Halley at high temporal resolution since 2013. Before the installation of the new autonomous system at Halley, measurements were relocated to the German coastal Antarctic research station, Neumayer, at the end of 2017. Both the Halley and Neumayer records show short-term variability in CO<sub>2</sub> mixing ratios during the summer, with up to ~0.5 ppb decreases in CO<sub>2</sub> over the course of a day, about 1/6 of the average annual growth rate. Trajectory analysis suggests that these decreases in mixing ratio correspond to periods where the air sampled has spent time over the Southern Ocean, suggesting CO<sub>2</sub> uptake has occurred. This work will explore the possible drivers for the short-term variability in CO<sub>2</sub> mixing ratios. An overview of the automation work carried out so far at Halley and plans for future seasons will also be presented.</p>
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