Evidence of convective transport in tropical West Pacific region during SHIVA experiment

Air masses in the convective outflows of four large convective systems near Borneo Island in Malaysia were sampled in the height range 11–13 km within the frame of the SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) FP7 European project in November and December 2011. Correlated enhancements of CO, CH4 and the short-lived halogen species (CH3I and CHBr3) were detected when the aircraft crossed the anvils of the four systems. These enhancements were interpreted as the fingerprint of vertical transport from the boundary layer by the convective updraft and then horizontal advection in the outflow. For the four observations, the fraction f of air from the boundary layer ranged between 15 and 67%, showing the variability in transport efficiency depending on the dynamics of the convective system

Airborne observations of peroxy radicals during the EMeRGe campaign in Europe

In this study, airborne measurements of the sum of hydroperoxyl (HO$_2$) and organic peroxy (RO$_2$) radicals that react with nitrogen monoxide (NO) to produce nitrogen dioxide (NO$_2$), coupled with actinometry and other key trace gases measurements, have been used to test the current understanding of the fast photochemistry in the outflow of major population centres. The measurements were made during the airborne campaign of the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) project in Europe on board the High Altitude and Long Range Research Aircraft (HALO). The measurements of RO$^∗_2$ on HALO were made using the in situ instrument Peroxy Radical Chemical Enhancement and Absorption Spectrometer (PeRCEAS). RO$^∗_2$ is to a good approximation the sum of peroxy radicals reacting with NO to produce NO$_2$. RO$^∗_2$ mixing ratios up to 120 pptv were observed in air masses of different origins and composition under different local actinometric conditions during seven HALO research flights in July 2017 over Europe. Radical production rates were estimated using knowledge of the photolysis frequencies and the RO$^∗_2$ precursor concentrations measured on board, as well as the relevant rate coefficients. Generally, high RO$^∗_2$ concentrations were measured in air masses with high production rates. In the air masses investigated, RO$^∗_2$ is primarily produced by the reaction of O$^1$D with water vapour and the photolysis of nitrous acid (HONO) and of the oxygenated volatile organic compounds (OVOCs, e.g. formaldehyde (HCHO) and glyoxal (CHOCHO)). Due to their short lifetime in most environments, the RO$^∗_2$ concentrations are expected to be in a photostationary steady state (PSS), i.e. a balance between production and loss rates is assumed. The RO$^∗_2$ production and loss rates and the suitability of PSS assumptions to estimate the RO$^∗_2$ mixing ratios and variability during the airborne observations are discussed. The PSS assumption for RO$^∗_2$ is considered robust enough to calculate RO$^∗_2$ mixing ratios for most conditions encountered in the air masses measured. The similarities and discrepancies between measured and PSS calculated RO$^∗_2$ mixing ratios are discussed. The dominant terminating processes for RO$^∗_2$ in the pollution plumes measured up to 2000 m are the formation of nitrous acid, nitric acid, and organic nitrates. Above2000 m, HO$_2$–HO$_2$ and HO$_2$–RO$_2$ reactions dominate the RO$^∗_2$ removal. RO$^∗_2$ calculations by the PSS analytical expression inside the pollution plumes probed often underestimated the measurements. The underestimation is attributed to the limitations of the PSS equation used for the analysis. In particular, this expression does not account for the yields of RO$^∗_2$ from the oxidation and photolysis of volatile organic compounds, VOCs, and OVOCs other than those measured during the EMeRGe research flights in Europe. In air masses with NO mixing ratios ≤ 50 pptv and low VOC/NO ratios, the RO$^∗_2$ measured is overestimated by the analytical expression. This may be caused by the formation of H$_2$O and O$_2$ from OH and HO$_2$, being about 4 times faster than the rate of the OH oxidation reaction of the dominant OVOCs considered

Shotgun metagenomic analysis of microbial communities in the surface waters of the Eastern South China Sea

Aims: The South China Sea (SCS) harbours a rich biodiversity. However, few studies have been published on its diverse communities, particularly its microbial counterparts. As key players behind many of the vital processes carried out in the ocean, microbes are the focus of this study, placing particular emphasis on community composition, structure, and function. Methodology and results: By employing next generation shotgun sequencing technologies (Illumina HiSeq2000), we assessed the taxonomic structure and functional diversity of the prokaryotic communities in surface waters collected from 3 representative sites in the Eastern SCS: Sarawak (Kuching), Sabah (Kota Kinabalu), and Philippines (Manila). Comparisons were undertaken to similar studies from coastal and open ocean environments. All 3 locations were dominated by members of the Proteobacteria (Alpha- and Gamma-) and Cyanobacteria (Synechococcus sp. and Prochlorococcus sp.). The highest proportion of Gammaproteobacteria was found in Sarawak, representing an approximate 20% of total sequences. Archaeal assemblages were made up largely of Euryarchaeota and unclassified sequences, while Crenarchaeota and Thaumarchaeota were present in much smaller proportions, except in the Philippines where Thaumarchaeota made up almost 40% of the entire taxa. Conclusion, significance and impact of study: The majority of the microbial communities adhered to a core set of functional genes across the different locations. However, differences existed particularly in Sarawak waters which are hypothesized to be due to local environmental parameters such as riverine influence. The results obtained from this study provide the first comparison of prokaryotic communities in the surface waters of the eastern SCS and will serve as a good platform for prospective studies in the field of environmental science

Irradiance and cloud optical properties from solar photovoltaic systems

Solar photovoltaic power output is modulated by atmospheric aerosols and clouds and thus contains valuable information on the optical properties of the atmosphere. As a ground-based data source with high spatiotemporal resolution it has great potential to complement other ground-based solar irradiance measurements as well as those of weather models and satellites, thus leading to an improved characterisation of global horizontal irradiance. In this work several algorithms are presented that can retrieve global tilted and horizontal irradiance and atmospheric optical properties from solar photovoltaic data and/or pyranometer measurements. Specifically, the aerosol (cloud) optical depth is inferred during clear sky (completely overcast) conditions. The method is tested on data from two measurement campaigns that took place in Allgäu, Germany in autumn 2018 and summer 2019, and the results are compared with local pyranometer measurements as well as satellite and weather model data. Using power data measured at 1 Hz and averaged to 1 minute resolution, the hourly global horizontal irradiance is extracted with a mean bias error compared to concurrent pyranometer measurements of 11.45 W m−2, averaged over the two campaigns, whereas for the retrieval using coarser 15 minute power data the mean bias error is 16.39 W m−2. During completely overcast periods the cloud optical depth is extracted from photovoltaic power using a lookup table method based on a one-dimensional radiative transfer simulation, and the results are compared to both satellite retrievals as well as data from the COSMO weather model. Potential applications of this approach for extracting cloud optical properties are discussed, as well as certain limitations, such as the representation of 3D radiative effects that occur under broken cloud conditions. In principle this method could provide an unprecedented amount of ground-based data on both irradiance and optical properties of the atmosphere, as long as the required photovoltaic power data are available and are properly pre-screened to remove unwanted artefacts in the signal. Possible solutions to this problem are discussed in the context of future work

Effects of transport on a biomass burning plume from Indochina during EMeRGe-Asia identified by WRF-Chem

The Indochina biomass burning (BB) season in springtime has a substantial environmental impact on the surrounding areas in Asia. In this study, we evaluated the environmental impact of a major long-range BB transport event on 19 March 2018 (a flight of the High Altitude and Long Range Research Aircraft (HALO; https://www.halo-spp.de, last access: 14 February 2023) research aircraft, flight F0319) preceded by a minor event on 17 March 2018 (flight F0317). Aircraft data obtained during the campaign in Asia of the Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales (EMeRGe) were available between 12 March and 7 April 2018. In F0319, results of 1 min mean carbon monoxide (CO), ozone (O$_3$), acetone (ACE), acetonitrile (ACN), organic aerosol (OA), and black carbon aerosol (BC) concentrations were up to 312.0, 79.0, 3.0, and 0.6 ppb and 6.4 and 2.5 µg m$^{−3}$, respectively, during the flight, which passed through the BB plume transport layer (BPTL) between the elevation of 2000–4000 m over the East China Sea (ECS). During F0319, the CO, O$_3$, ACE, ACN, OA, and BC maximum of the 1 min average concentrations were higher in the BPTL by 109.0, 8.0, 1.0, and 0.3 ppb and 3.0 and 1.3 µg m$^{−3}$ compared to flight F0317, respectively. Sulfate aerosol, rather than OA, showed the highest concentration at low altitudes (<1000 m) in both flights F0317 and F0319 resulting from the continental outflow in the ECS. The transport of BB aerosols from Indochina and its impacts on the downstream area were evaluated using a Weather Research Forecasting with Chemistry (WRF-Chem) model. The modeling results tended to overestimate the concentration of the species, with examples being CO (64 ppb), OA (0.3 µg m$^{−3}$), BC (0.2 µg m$^{−3}$), and O$_3$ (12.5 ppb) in the BPTL. Over the ECS, the simulated BB contribution demonstrated an increasing trend from the lowest values on 17 March 2018 to the highest values on 18 and 19 March 2018 for CO, fine particulate matter (PM$_{2.5}$), OA, BC, hydroxyl radicals (OH), nitrogen oxides (NO$_x$), total reactive nitrogen (NO$_y$), and O$_3$; by contrast, the variation of J(O$^1$D) decreased as the BB plume\u27s contribution increased over the ECS. In the lower boundary layer (<1000 m), the BB plume\u27s contribution to most species in the remote downstream areas was <20 %. However, at the BPTL, the contribution of the long-range transported BB plume was as high as 30 %–80 % for most of the species (NO$_y$, NO$_x$, PM$_{2.5}$, BC, OH, O$_3$, and CO) over southern China (SC), Taiwan, and the ECS. BB aerosols were identified as a potential source of cloud condensation nuclei, and the simulation results indicated that the transported BB plume had an effect on cloud water formation over SC and the ECS on 19 March 2018. The combination of BB aerosol enhancement with cloud water resulted in a reduction of incoming shortwave radiation at the surface in SC and the ECS by 5 %–7 % and 2 %–4 %, respectively, which potentially has significant regional climate implications

Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions

Significant reductions in stratospheric ozone occur inside the polar vortices each spring when chlorine radicals produced by heterogeneous reactions on cold particle surfaces in winter destroy ozone mainly in two catalytic cycles, the ClO dimer cycle and the ClO/BrO cycle. Chlorofluorocarbons (CFCs), which are responsible for most of the chlorine currently present in the stratosphere, have been banned by the Montreal Protocol and its amendments, and the ozone layer is predicted to recover to 1980 levels within the next few decades. During the same period, however, climate change is expected to alter the temperature, circulation patterns and chemical composition in the stratosphere, and possible geo-engineering ventures to mitigate climate change may lead to additional changes. To realistically predict the response of the ozone layer to such influences requires the correct representation of all relevant processes. The European project RECONCILE has comprehensively addressed remaining questions in the context of polar ozone depletion, with the objective to quantify the rates of some of the most relevant, yet still uncertain physical and chemical processes. To this end RECONCILE used a broad approach of laboratory experiments, two field missions in the Arctic winter 2009/10 employing the high altitude research aircraft M55-Geophysica and an extensive match ozone sonde campaign, as well as microphysical and chemical transport modelling and data assimilation. Some of the main outcomes of RECONCILE are as follows: (1) vortex meteorology: the 2009/10 Arctic winter was unusually cold at stratospheric levels during the six-week period from mid-December 2009 until the end of January 2010, with reduced transport and mixing across the polar vortex edge; polar vortex stability and how it is influenced by dynamic processes in the troposphere has led to unprecedented, synoptic-scale stratospheric regions with temperatures below the frost point; in these regions stratospheric ice clouds have been observed, extending over >106km2 during more than 3 weeks. (2) Particle microphysics: heterogeneous nucleation of nitric acid trihydrate (NAT) particles in the absence of ice has been unambiguously demonstrated; conversely, the synoptic scale ice clouds also appear to nucleate heterogeneously; a variety of possible heterogeneous nuclei has been characterised by chemical analysis of the non-volatile fraction of the background aerosol; substantial formation of solid particles and denitrification via their sedimentation has been observed and model parameterizations have been improved. (3) Chemistry: strong evidence has been found for significant chlorine activation not only on polar stratospheric clouds (PSCs) but also on cold binary aerosol; laboratory experiments and field data on the ClOOCl photolysis rate and other kinetic parameters have been shown to be consistent with an adequate degree of certainty; no evidence has been found that would support the existence of yet unknown chemical mechanisms making a significant contribution to polar ozone loss. (4) Global modelling: results from process studies have been implemented in a prognostic chemistry climate model (CCM); simulations with improved parameterisations of processes relevant for polar ozone depletion are evaluated against satellite data and other long term records using data assimilation and detrended fluctuation analysis. Finally, measurements and process studies within RECONCILE were also applied to the winter 2010/11, when special meteorological conditions led to the highest chemical ozone loss ever observed in the Arctic. In addition to quantifying the 2010/11 ozone loss and to understand its causes including possible connections to climate change, its impacts were addressed, such as changes in surface ultraviolet (UV) radiation in the densely populated northern mid-latitudes

Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions : (RECONCILE) ; activities and results

The international research project RECONCILE has addressed central questions regarding polar ozone depletion, with the objective to quantify some of the most relevant yet still uncertain physical and chemical processes and thereby improve prognostic modelling capabilities to realistically predict the response of the ozone layer to climate change. This overview paper outlines the scope and the general approach of RECONCILE, and it provides a summary of observations and modelling in 2010 and 2011 that have generated an in many respects unprecedented dataset to study processes in the Arctic winter stratosphere. Principally, it summarises important outcomes of RECONCILE including (i) better constraints and enhanced consistency on the set of parameters governing catalytic ozone destruction cycles, (ii) a better understanding of the role of cold binary aerosols in heterogeneous chlorine activation, (iii) an improved scheme of polar stratospheric cloud (PSC) processes that includes heterogeneous nucleation of nitric acid trihydrate (NAT) and ice on non-volatile background aerosol leading to better model parameterisations with respect to denitrification, and (iv) long transient simulations with a chemistry-climate model (CCM) updated based on the results of RECONCILE that better reproduce past ozone trends in Antarctica and are deemed to produce more reliable predictions of future ozone trends. The process studies and the global simulations conducted in RECONCILE show that in the Arctic, ozone depletion uncertainties in the chemical and microphysical processes are now clearly smaller than the sensitivity to dynamic variability

The NASA Airborne Tropical TRopopause EXperiment (ATTREX): High-Altitude Aircraft Measurements in the Tropical Western Pacific

The February through March 2014 deployment of the NASA Airborne Tropical TRopopause EXperiment (ATTREX) provided unique in situ measurements in the western Pacific Tropical Tropopause Layer (TTL). Six flights were conducted from Guam with the long-range, high-altitude, unmanned Global Hawk aircraft. The ATTREX Global Hawk payload provided measurements of water vapor, meteorological conditions, cloud properties, tracer and chemical radical concentrations, and radiative fluxes. The campaign was partially coincident with the CONTRAST and CAST airborne campaigns based in Guam using lower-altitude aircraft (see companion articles in this issue). The ATTREX dataset is being used for investigations of TTL cloud, transport, dynamical, and chemical processes as well as for evaluation and improvement of global-model representations of TTL processes. The ATTREX data is openly available at https:espoarchive.nasa.gov

Quasi-spherical ice in convective clouds

Homogeneous freezing of supercooled droplets occurs in convective systems in low and midlatitudes. This droplet-freezing process leads to the formation of a large amount of small ice particles, so-called frozen droplets, that are transported to the upper parts of anvil outflows, where they can influence the cloud radiative properties. However, the detailed microphysics and, thus, the scattering properties of these small ice particles are highly uncertain. Here, the link between the microphysical and optical properties of frozen droplets is investigated in cloud chamber experiments, where the frozen droplets were formed, grown, and sublimated under controlled conditions. It was found that frozen droplets developed a high degree of small-scale complexity after their initial formation and subsequent growth. During sublimation, the small-scale complexity disappeared, releasing a smooth and near-spherical ice particle. Angular light scattering and depolarization measurements confirmed that these sublimating frozen droplets scattered light similar to spherical particles: that is, they had angular light-scattering properties similar to water droplets. The knowledge gained from this laboratory study was applied to two case studies of aircraft measurements in midlatitude and tropical convective systems. The in situ aircraft measurements confirmed that the microphysics of frozen droplets is dependent on the humidity conditions they are exposed to (growth or sublimation). The existence of optically spherical frozen droplets can be important for the radiative properties of detraining convective outflows.Peer reviewe