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Gas flaring is a substantial global source of carbon emissions to atmosphere and is targeted as a route to mitigating the oil and gas sector carbon footprint due to the waste of resources involved. However, quantifying carbon emissions from flaring is resource-intensive, and no studies have yet assessed flaring emissions for offshore regions. In this work, we present carbon dioxide (CO2), methane (CH4), ethane (C2H6), and NOx (nitrogen oxide) data from 58 emission plumes identified as gas flaring, measured during aircraft campaigns over the North Sea (UK and Norway) in 2018 and 2019. Median combustion efficiency, the efficiency with which carbon in the flared gas is converted to CO2 in the emission plume, was 98.4 % when accounting for C2H6 or 98.7 % when only accounting for CH4. Higher combustion efficiencies were measured in the Norwegian sector of the North Sea compared with the UK sector. Destruction removal efficiencies (DREs), the efficiency with which an individual species is combusted, were 98.5 % for CH4 and 97.9 % for C2H6. Median NOx emission ratios were measured to be 0.003 ppmppm-1CO2 and 0.26 ppmppm-1CH4 , and the median C2H6:CH4 ratio was measured to be 0.11 ppmppm-1. The highest NOx emission ratios were observed from floating production storage and offloading (FPSO) vessels, although this could potentially be due to the presence of alternative NOx sources on board, such as diesel generators. The measurements in this work were used to estimate total emissions from the North Sea from gas flaring of 1.4 Tgyr-1 CO2 , 6.3 Ggyr-1 CH4 , 1.7 Ggyr-1 C2H6 and 3.9 Ggyr-1 NOx. [ABSTRACT FROM AUTHOR]

Gas flaring is a substantial global source of carbon emissions to atmosphere, and is targeted as a route to mitigating the oil and gas sector carbon footprint, due to the waste of resources involved. However, quantifying carbon emissions from flaring is resource intensive, and no studies have yet assessed flaring emissions for offshore regions. In this work, we present carbon dioxide (CO2), methane (CH4), ethane (C2H6), and NOx (nitrogen oxide) data from 58 emission plumes identified as gas flaring, measured during aircraft campaigns over the North Sea (UK and Norwegian) in 2018 and 2019. Median combustion efficiency, the efficiency with which carbon in the flared gas is converted to CO2 in the emission plume, was 98.4% when accounting for C2H6, or 98.7% when only accounting for CH4. Higher combustion efficiencies were measured in the Norwegian sector of the North Sea compared with the UK sector. Destruction removal efficiencies (DREs), the efficiency with which an individual species is combusted, were 98.5% for CH4, and 97.9% for C2H6. Median NOx emission ratios were measured to be 0.003 ppm per ppm CO2 and 0.26 ppm per ppm CH4, and the median C2H6:CH4 ratio was measured to be 0.11 ppm ppm-1. The highest NOx emission ratios were observed from Floating Production Storage and Offloading (FPSO) vessels, although this could potentially be due to the presence of alternative NOx sources onboard, such as diesel generators. The measurements in this work were used to estimate total emissions from the North Sea from gas flaring, of 1.4 Tg yr-1 CO2, 6.3 Gg yr-1 CH4, 1.7 Gg yr-1 C2H6, and 3.9 Gg yr-1 NOx. [ABSTRACT FROM AUTHOR]

In this essay, we highlight some challenges the atmospheric community is facing concerning adequate treatment of flows over mountains and their implications for numerical weather prediction (NWP), climate simulations, and impact modeling. With recent increases in computing power (and hence model resolution) numerical models start to face new limitations (such as numerical instability over steep terrain). At the same time there is a growing need for sufficiently reliable NWP model output to drive various impact models (for hydrology, air pollution, agriculture, etc.). The input information for these impact models is largely produced by the boundary layer (BL) parameterizations of NWP models. All known BL parameterizations assume flat and horizontally homogeneous surface conditions, and their performance and interaction with resolved flows is massively understudied over mountains—hence their output may be accidentally acceptable at best. We therefore advocate the systematic investigation of the so-called "mountain boundary layer" (MoBL), introduced to emphasize its many differences to the BL over flat and horizontally homogeneous terrain. An international consortium of scientists has launched a research program, TEAMx (Multi-Scale Transport and Exchange Processes in the Atmosphere over Mountains–Program and Experiment), to address some of the most pressing scientific challenges. TEAMx is endorsed by World Weather Research Programme (WWRP) and the Global Energy and Water Exchanges (GEWEX) project as a "cross-cutting project." A program coordination office was established at the University of Innsbruck (Austria). This essay introduces the background to and content of a recently published white paper outlining the key research questions of TEAMx. [ABSTRACT FROM AUTHOR]

The North Sea is Europe's key oil and gas (O&G) basin with the output currently meeting 3 %–4 % of global oil supply. Despite this, there are few observational constraints on the nature of atmospheric emissions from this region, with most information derived from bottom-up inventory estimates. This study reports on airborne measurements of volatile organic compounds (VOCs) emitted from O&G-producing regions in the North Sea. VOC source emission signatures for the primary extraction products from offshore fields (oil, gas, condensate, mixed) were determined in four geographic regions. Measured iso-pentane to n -pentane (i C 5 / n C 5) ratios were 0.89–1.24 for all regions, used as a confirmatory indicator of O&G activities. Light alkanes (ethane, propane, butane, pentane) were the dominant species emitted in all four regions; however, total OH reactivity was dominated by unsaturated species, such as 1,3-butadiene, despite their relatively low abundance. Benzene to toluene ratios indicated the influence of possible terrestrial combustion sources of emissions in the southern, gas-producing region of the North Sea, seen only during south or south-westerly wind episodes. However, all other regions showed a characteristic signature of O&G operations. Correlations between ethane (C 2 H 6) and methane (CH 4) confirmed O&G production to be the primary CH 4 source. The enhancement ratio (Δ C 2 H 6/Δ CH 4) ranged between 0.03–0.18, indicating a spatial dependence on emissions with both wet and dry CH 4 emission sources. The excess mole fraction demonstrated that deepwater oil extraction resulted in a greater proportion of emissions of higher carbon number alkanes relative to CH 4 , whereas gas extraction, typically from shallow waters, resulted in a less complex mix of emissions dominated by CH 4. The VOC source profiles measured were similar to those in the UK National Atmospheric Emissions Inventory (NAEI) for oil production, with consistency between the molar ratios of light alkanes to propane. The largest discrepancies between observations and the inventory were for mono-aromatic compounds, highlighting that these species are not currently fully captured in the inventory. These results demonstrate the applicability of VOC measurements to distinguish unique sources within the O&G sector and give an overview of VOC speciation over the North Sea. [ABSTRACT FROM AUTHOR]

The North Sea is Europe's key oil and gas (O&G) basin with the output currently meeting 3-4 % of global oil supply. Despite this, there are few observational constraints on the nature of atmospheric emissions from this region, with most information derived from bottom-up inventory estimates. This study reports on airborne measurements of volatile organic compounds (VOCs) emitted from O&G producing regions in the North Sea. VOC source emission signatures for the primary extraction products from offshore fields (oil, gas, condensate, mixed) were determined in four geographic regions. Measured iso-pentane to n-pentane (iC5 / nC5) ratios were 0.89-1.24 for all regions, used as a confirmatory indicator of O&G activities. Light alkanes (ethane, propane, butane, pentane) were the dominant species emitted in all four regions, however total OH reactivity was dominated by unsaturated species, such as 1,3-butadiene, despite their relatively low abundance. Benzene to toluene ratios indicated the influence of possible terrestrial combustion sources of emissions in the southern, gas-producing region of the North Sea, seen only during south or south-westerly wind episodes. However, all other regions showed a characteristic signature of O&G operations. Correlations between ethane (C2H6) and methane (CH4), confirmed O&G production to be the primary CH4 source. The enhancement ratio (ΔC2H6 / ΔCH4) ranged between 0.03-0.18, indicating a spatial dependence on emissions with both wet and dry CH4 emission sources. The excess mole fraction demonstrated that deepwater oil extraction resulted in a greater proportion of emissions of higher carbon number alkanes relative to CH4, whereas gas extraction, typically from shallow waters, resulted in a less complex mix of emissions dominated by CH4. The VOC source profiles measured were similar to those in the UK National Atmospheric Emissions Inventory (NAEI) for oil production, with consistency between the molar ratios of light alkanes to propane. The largest discrepancies between observations and the inventory were for mono-aromatic compounds, highlighting that these species are not currently fully captured in the inventory. These results demonstrate the applicability of VOC measurements to distinguish unique sources within the O&G sector and give an overview of VOC speciation over the North Sea. [ABSTRACT FROM AUTHOR]

ABSTRACT: Climate change caused by green house gas emissions is now following the trend of rapid warming consistent with a RCP8.5 forcing. Climate models are still unable to represent the mesoscale convective processes that occur at resolutions ∼O(3 km) and are not capable of resolving precipitation patterns in time and space with sufficient accuracy to represent convection. In this article, the UK Met Office precipitation observations are compared with the simulations for the period 1990–1995 followed by a simulation of a near‐future period 2031–2036 for a regional nested weather model. The convection‐permitting model, resolution ∼O(3 km), provides a good correspondence to the observational precipitation data and demonstrates the importance of explicit convection for future summer precipitation estimates. The UK summer precipitation is reduced slightly (∼10%) for 2031–2036 and there is no evidence of an increase in the peak maximum hourly precipitation magnitude. A similar pattern is observed over the whole European inner model domain. The results using the Kain–Fritsch convective parameterization scheme at a resolution ∼O(12 km) in the outer domain increase summer precipitation by ∼10% for the UK. The average precipitation rate per event increases, dry periods extend and wet periods shorten. As part of the change, 10‐m winds of <3 m s−1 become more common – a scenario that would impact on power generation from wind turbines through calmer conditions and cause more frequent pollution episodes. [ABSTRACT FROM AUTHOR]

An uncontrolled gas leak from 25 March to 16 May 2012 led to evacuation of the Total Elgin wellhead and neighbouring drilling and production platforms in the UK North Sea. Initially the atmospheric flow rate of leaking gas and condensate was very poorly known, hampering environmental assessment and well control efforts. Six flights by the UK FAAM chemically instrumented BAe-146 research aircraft were used to quantify the flow rate. The flow rate was calculated by assuming the plume may be modelled by a Gaussian distribution with two different solution methods: Gaussian fitting in the vertical and fitting with a fully mixed layer. When both solution methods were used they compared within 6 % of each other, which was within combined errors. Data from the first flight on 30 March 2012 showed the flow rate to be 1.3 ± 0.2 kg CH4 s-1, decreasing to less than half that by the second flight on 17 April 2012. δ13CCH4 in the gas was found to be -43 ‰, implying that the gas source was unlikely to be from the main high pressure, high temperature Elgin gas field at 5.5 km depth, but more probably from the overlying Hod Formation at 4.2 km depth. This was deemed to be smaller and more manageable than the high pressure Elgin field and hence the response strategy was considerably simpler. The first flight was conducted within 5 days of the blowout and allowed a flow rate estimate within 48 h of sampling, with δ13CCH4 characterization soon thereafter, demonstrating the potential for a rapid-response capability that is widely applicable to future atmospheric emissions of environmental concern. Knowledge of the Elgin flow rate helped inform subsequent decision making. This study shows that leak assessment using appropriately designed airborne plume sampling strategies is well suited for circumstances where direct access is difficult or potentially dangerous. Measurements such as this also permit unbiased regulatory assessment of potential impact, independent of the emitting party, on timescales that can inform industry decision makers and assist rapid-response planning by government. [ABSTRACT FROM AUTHOR]

An uncontrolled gas leak from 25 March to 16 May 2012 led to evacuation of the Total Elgin well head and neighbouring drilling and production platforms in the UK North Sea. Initially the atmospheric flow rate of leaking gas and condensate was very poorly known, hampering environmental assessment and well control efforts. Six flights by the UK FAAM chemically-instrumented BAe-146 research aircraft, were used to quantify the flow rate. Where appropriate, two different methods were used to calculate the flow rate: 1. Gaussian plume fitting in the vertical and 2. Direct integration of the plume. When both methods were used, they compared within 6 % of each other and within combined errors. Data from the first flight on 30 March 2012 showed the flow rate to be 1.3 ± 0.2 kg CH4 s-1, decreasing to less than half that by the second flight on 17 April 2012. δ13CCH4 in the gas was found to be -43 ‰, implying that the gas source was unlikely to be from the main high-pressure high-temperature Elgin gas field at 5.5 km depth, but more probably from the overlying Hod Formation at 4.2 km depth. This was deemed to be smaller and more manageable than the high-pressure Elgin field and hence the response strategy was considerably simpler. The first flight was conducted within 5 days of the blowout and allowed a flow rate estimate within 48 hours of sampling, with δ13CCH4 characterisation soon thereafter, demonstrating the potential for a rapid-response capability that is widely applicable to future atmospheric emissions of environmental concern. Knowledge of the Elgin flow rate helped inform subsequent decision making. This study shows that leak assessment using appropriately designed airborne plume sampling strategies is well suited for circumstances where direct access is difficult or potentially dangerous. Measurements such as this also permit unbiased regulatory assessment of potential impact, independent of the emitting party, on timescales that can inform industry decision-makers and assist rapid response-planning by government. [ABSTRACT FROM AUTHOR]

Although many LIDAR systems in the UK and Continental Europe observed ash during the 2010 Eyjafjallajökull eruption, no LIDAR was located in Iceland and the question regarding whether LIDARs have potential for near-field monitoring of explosive eruptions remained unanswered. A LIDAR was therefore deployed in southern Iceland in 2011, by the Icelandic Meteorological Office and the UK National Centre of Atmospheric Science, with the aim of using re-suspension of volcanic ash as a pilot near-field programme. When Grímsvötn erupted in 2011 it was moved to Keflavík Airport to monitor the atmosphere above the airport. Here we describe this successful redeployment. [ABSTRACT FROM AUTHOR]

Advances in computing are enabling atmospheric models to operate at increasingly fine resolution, giving rise to more variations in the underlying orography being captured by the model grid. Consequently, high-resolution models must overcome the problems associated with traditional terrain-following approaches of spurious winds and instabilities generated in the vicinity of steep and complex terrain. Cut-cell representations of orography present atmospheric models with an alternative to terrain-following vertical coordinates. This work explores the capabilities of a cut-cell representation of orography for idealized orographically forced flows. The orographic surface is represented within the model by continuous piecewise bilinear surfaces that intersect the regular Cartesian grid creating cut cells. An approximate finite-volume method for use with advection-form governing equations is implemented to solve flows through the resulting irregularly shaped grid boxes. Comparison with a benchmark orographic test case for nonhydrostatic flow shows very good results. Further tests demonstrate the cut-cell method for flow around 3D isolated hills and stably resolving flows over very steep orography. [ABSTRACT FROM AUTHOR]

In this paper, high-frequency pressure time series measured by microbarographs are used to extract information on the existence and characteristics of convective rolls in the convective boundary layer. Rolls are identified in radar and satellite data, and it is shown that the pressure signals associated with the rolls have been detected in an array of microbarographs. The methodology of obtaining further information on roll characteristics from the array, notably orientation and drift velocity, is discussed in some detail. It is shown that the pressure time series contain signals representing the roll motion, approximately normal to the mean wind, and signals representing turbulent structures that drift along the mean wind direction. As the along-wind signals may dominate the time series, care is needed to identify the roll motion. Filtering of the higher-frequency along-wind signals can isolate the roll motion details. Also, a new approach using “beam-steering diagrams” to discriminate rolls from gravity waves and turbulent eddies is tested in both a numerical model and an observational case. In the beam-steering diagram, multiple centers of signal cross correlation can be used to identify different features in a single set of time series from an array of stations. The observations and model show that an array of microbarographs are able to resolve rolls if they are properly distributed with their spacing being tuned according to roll wavelength. [ABSTRACT FROM AUTHOR]

The acoustic filter plate is a device giving a variable aperture, the diameter of which is proportional to the wavelength of the incident sound, thus producing a beamwidth for the transmitted sound that is independent of the wavelength. Previous experimental studies have demonstrated the effectiveness of the filter plate. However, it has been found that the performance of the device is seriously impaired at high frequencies and the purpose of this article is to provide an explanation for this high-frequency failure. The approach is numerical: The Helmholtz equation describing the propagation of sound through and around the filter plate is solved using the boundary integral element (BIE) method. Good qualitative agreement with the experimental results are obtained at moderate frequencies where the filter plate is operating normally and the reason for the high-frequency failure is demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, a state-of the art numerical weather prediction (NWP) model is used to simulate the near-field plume of a Plinian-type volcanic eruption. The NWP model is run at very high resolution (of the order of 100 m) and includes a representation of physical processes, including turbulence and buoyancy, that are essential components of eruption column dynamics. Results are shown that illustrate buoyant gas plume dynamics in an atmosphere at rest and in an atmosphere with background wind, and we show that these results agree well with those from theoretical models in the quiescent atmosphere. For wind-blown plumes, we show that features observed in experimental and natural settings are reproduced in our model. However, when comparing with predictions from an integral model using existing entrainment closures there are marked differences. We speculate that these are signatures of a difference in turbulent mixing for uniform and shear flow profiles in a stratified atmosphere. A more complex implementation is given to show that the model may also be used to examine the dispersion of heavy volcanic gases such as sulphur dioxide. Starting from the standard version of the weather research and forecasting (WRF) model, we show that minimal modifications are needed in order to model volcanic plumes. This suggests that the modified NWP model can be used in the forecasting of plume evolution during future volcanic events, in addition to providing a virtual laboratory for the testing of hypotheses regarding plume behaviour. [ABSTRACT FROM AUTHOR]

In the event of a volcanic eruption, the estimation of mass flux is a crucialtask for Volcanic Ash Advisory Centres (VAACs). Typically, thisestimate would be based upon a knowledge of the rise height of theplume and the background wind. Converting this information to a mass flux isperformed via a combination of historical data and idealised models of plume behaviour - the latterimplicitly rely on assumptions regarding plume entrainment (expressed in the form of entrainmentcoefficients). Such models typically have correspondingly idealised background wind profiles.We will describe a modification of a state-of-the-art numerical weather prediction (NWP)model that can simulate volcanic plumes. Rise heights and entrainment coefficientscan be extracted from the NWP simulations for arbitrary background wind profiles,allowing the mass flux inversion described above to have a much wider range ofapplicability. The method is also suitable to the modelling of other extreme convectiveevents, since in this approach the plume is buoyancy-driven. The inclusion of more complexphysical processes, such as those related to topography and microphysics, is also possible.Results will be given for idealised wind profiles (for comparison with theory) and formore complex cases. A further extension to this model framework, allowing the simulation ofdense volcanic plumes, will also be presented. [ABSTRACT FROM AUTHOR]

Volcanoes are a key natural source of CO2, but global estimates of volcanic CO2 flux are predominantly based on measurements from a fraction of world's actively degassing volcanoes. We combine high‐precision airborne measurements from 2016 and 2017 with atmospheric dispersion modeling to quantify CO2 emissions from Katla, a major subglacial volcanic caldera in Iceland that last erupted 100 years ago but has been undergoing significant unrest in recent decades. Katla's sustained CO2 flux, 12–24 kt/d, is up to an order of magnitude greater than previous estimates of total CO2 release from Iceland's natural sources. Katla is one of the largest volcanic sources of CO2 on the planet, contributing up to 4% of global emissions from nonerupting volcanoes. Further measurements on subglacial volcanoes worldwide are urgently required to establish if Katla is exceptional, or if there is a significant previously unrecognized contribution to global CO2 emissions from natural sources. [ABSTRACT FROM AUTHOR]

Volcanoes are a key natural source of CO2, but global estimates of volcanic CO2 flux are predominantly based on measurements from a fraction of world's actively degassing volcanoes. We combine high‐precision airborne measurements from 2016 and 2017 with atmospheric dispersion modeling to quantify CO2 emissions from Katla, a major subglacial volcanic caldera in Iceland that last erupted 100 years ago but has been undergoing significant unrest in recent decades. Katla's sustained CO2 flux, 12–24 kt/d, is up to an order of magnitude greater than previous estimates of total CO2 release from Iceland's natural sources. Katla is one of the largest volcanic sources of CO2 on the planet, contributing up to 4% of global emissions from nonerupting volcanoes. Further measurements on subglacial volcanoes worldwide are urgently required to establish if Katla is exceptional, or if there is a significant previously unrecognized contribution to global CO2 emissions from natural sources. Plain Language Summary: We discovered that Katla volcano in Iceland is a globally important source of atmospheric carbon dioxide (CO2) in spite of being previously assumed to be a minor gas emitter. Volcanoes are a key natural source of atmospheric CO2, but estimates of the total global amount of CO2 that volcanoes emit are based on only a small number of active volcanoes. Very few volcanoes that are covered by glacial ice have been measured for gas emissions, probably because they tend to be difficult to access and often do not have obvious degassing vents. Through high‐precision airborne measurements and atmospheric dispersion modeling, we show that Katla, a highly hazardous subglacial volcano that last erupted 100 years ago, is one of the largest volcanic sources of CO2 on Earth, releasing up to 4% of total global volcanic emissions. This is significant in a context of a growing awareness that natural CO2 sources have to be more accurately quantified in climate assessments, and we recommend urgent investigations of other subglacial volcanoes worldwide. Key Points: Subglacial volcanoes are underrepresented in terms of gas monitoring, but we show that they can be major emitters of CO2Katla volcano is found to be one of largest volcanic sources of CO2 on the planet, contributing up to 4% of all nonerupting volcanoesHigh‐precision airborne measurements combined with atmospheric modeling are a powerful method to monitor poorly accessible volcanoes [ABSTRACT FROM AUTHOR]

In its simplest form the filter plate is a circular metal plate which is thin at the center and has a thickness which increases towards the outer edge. Incident sound is transmitted through the thin central region while the outer region appears opaque. The effective diameter of the transparent region varies with wavelength in such a way as to produce a wavelength independent beamwidth for the transmitted sound. At high frequencies however, when the wavelength becomes comparable with or less than twice the outer thickness of the plate, this mode of operation is observed to break down and the beamwidth is no longer frequency independent. In order to gain a better understanding of the high frequency breakup of the transmitted beam, numerical solution of the problem has been carried out using the boundary integral element method. The method will be described and some results presented. [Work supported by ONR Code 425.] [ABSTRACT FROM AUTHOR]

Abstract: An isolated thunderstorm from the Convective and Orographically-induced Precipitation Study in southwest Germany and east France in 2007 is analyzed. On July 15, deep convection developed east of the Black Forest crest, although convective available potential energy (CAPE) was only moderate and convective inhibition (CIN) was high. Data analysis revealed that convection was triggered by updrafts penetrating the capping inversion of the planetary boundary layer as a result of low-level convergence. Although the numerical weather prediction model COSMO-DE of the German Weather Service (2.8km grid resolution) simulated a convergence line and the evolution of a line of low clouds in good agreement with radar and satellite observations, no precipitating deep convection developed from this line of clouds. For an improved representation of orographic effects, simulations with a finer grid resolution of 1km were performed. Despite almost optimal conditions, i.e. moderate amount of CAPE and almost vanishing CIN, the updrafts required to overcome CIN were not reached in both model configurations. Although both simulations did not initiate deep convection, the results suggest that in an air mass convection situation without mid-tropospheric forcing, the simulated location and timing of convergence lines with coexistent large values of CAPE and low values of CIN can be used as diagnostic parameters for deep convection nowcasting. [Copyright &y& Elsevier]