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• The paper presented a simplified time domain approach to calculate lightning electric fields in the presence of the grounded tower-line-tower (TLT) structure. • The directly striking tower plays an important role in the increase of the electric field magnitude, while the neighbored tower and the associated grounded wire contributes to periodical superimpositions on the middle-and-late response of the electric fields. • The simulation results generally agrees with the measured electric field profiles. This study describes a method for calculating electric fields radiated by lightning in the presence of a tower-line-tower (TLT) structure, extending a previous method developed by Rachidi et al. (2002). The method involves using a lattice diagram to analyze current distribution and deriving expressions related to the current distribution along the lightning channel and the TLT structure. Expressions associated with the current distribution along the lightning channel and the TLT structure are derived. The impedances of the towers, the connected overhead grounded wire, and lightning channel were treated as constant values. The subsequent return stroke was analyzed in the paper. The lightning radiated electric fields at an intermediate distance of 15 km considering lightning striking to ground, one single object, and the TLT structure were presented and compared. The directly strike of lightning on a tower plays an important role in the increase of the electric field magnitude, while the neighbored tower and the associated grounded wire contributes to periodical superimpositions on the middle-and-late response of the electric fields. Detail discussion on the influences of the different parameters of the proposed method on the electric fields at 15 km and comparison to the measured data were also presented. [ABSTRACT FROM AUTHOR]

The US Corn Belt is a global hotspot of atmospheric ammonia (NH3), a gas known to adversely impact the environment and human health. We combine hourly tall tower (100 m) measurements and bi‐weekly, spatially distributed, ground‐based observations from the Ammonia Monitoring Network with the US National Emissions Inventory (NEI) and WRF‐Chem simulations to constrain NH3 emissions from April to September 2017–2019. We show that: (1) NH3 emissions peaked from May to July and were 1.6–1.7 times the annual NEI average; (2) average growing season NH3 emissions from agricultural lands were remarkably similar across years (3.27–3.64 nmol m−2 s−1), yet showed substantial episodic variability driven by meteorology and land management; (3) dry deposition was 40% of gross emissions from agricultural lands and exceeded 100% of gross emissions in natural lands. Our findings provide an important benchmark for evaluating future NH3 emissions and mitigation efforts. Key Points: Rare multiyear tall tower and ground‐based ammonia measurements were combined with WRF‐Chem to constrain emissions from the US Corn BeltMonthly ammonia emissions peaked in May through July and were 1.6–1.7 times the annual NEI averageEpisodic low WRF‐Chem bias versus tall tower observations underscore the importance of weather and land management as emission drivers [ABSTRACT FROM AUTHOR]

This data article describes a dataset of videos of lightning flashes to and around a tall tower (the Brixton tower) in Johannesburg, South Africa. The videos were collected during the 2015-2016 South African thunderstorm season and a total of 3623 .mp4 videos are available in the dataset. Three different cameras were used, two in a similar location and the third at a different location giving a 90 degree perspective. Each video is timestamped and labelled depending on the type of event seen (attachment to the tower, nearby the tower, far from the tower, intracloud etc.). This dataset provides ground-truth, timestamped evidence of lightning events a known location and of differing types and can benefit atmospheric research scientists as well as lightning detection operators, particularly with regards to evaluating detection networks operating in the area. As the dataset contains a significant number of labelled videos, it also of use to pattern or image recognition supervised machine learning techniques and researchers.

This paper presents in detail the instrumentation for coordinated optical and current measurements of lightning discharges to a 356-m-high meteorological tower and the observation results. The tower, which is located at Shenzhen, a lower latitude coastal city in south China, was equipped with a non-inductive current shunt at its top and a high-speed camera and electromagnetic field sensors at 440 m away from the tower base. A total of 24 discharges to the tower were well documented in the period of April to June of 2019. Three of them were analyzed in detail with the focus being given to the feature of upward leaders initiated from the tower: Case 1 - a connecting upward positive leader (connecting UPL) induced by a downward negative in a downward negative discharge, Case 2 - an upward positive leader (UPL) in the initial stage of an upward negative discharge, and Case 3 - an upward negative leader (UNL) in the initial stage of an upward positive discharge. All the three leaders had a stepping feature during their initial stages, each step producing an isolated but oscillated current pulse with a time scale of 1 μs. The connecting UPL had 5 steps during its initial 2.6 ms, with a step interval ranging in 0.1~1.5 ms and a current pulse peak in 1~5 kA. The UPL had also 5 steps but during its initial 200 μs, with a step interval ranging in 20~50 μs, a step length in 0.8~2.2 m, a current pulse peak in 0.5~2.2 kA, and a leader average speed in 0.4~1.1 × 105 m/s. The UNL had 8 steps during its initial 104 μs, with a step interval ranging in 13.6~22 μs, a step length in 3.9~7.1 m, a current pulse peak in 2.3~12.5 kA, and a leader average speed in 1.9~6.6 × 105 m/s.

The reliability of ERA5 reanalyses for directly predicting wind resources and energy production has been assessed against observations from six tall towers installed over very heterogeneous sites around the world. Scores were acceptable at the FINO3 (Germany) offshore platform for both wind speed (bias within 1%, r = 0.95−0.96) and capacity factor (CF, at worst biased by 6.70%) and at the flat and sea-level site of Cabauw (Netherlands) for both wind speed (bias within 7%, r = 0.93−0.94) and CF (bias within 6.82%). Conversely, due to the ERA5 limited resolution (~31 km), large under-predictions were found at the Boulder (US) and Ghoroghchi (Iran) mountain sites, and large over-predictions were found at the Wallaby Creek (Australia) forested site. Therefore, using ERA5 in place of higher-resolution regional reanalysis products or numerical weather prediction models should be avoided when addressing sites with high variation of topography and, in particular, land use. ERA5 scores at the Humansdorp (South Africa) coastal location were generally acceptable, at least for wind speed (bias of 14%, r = 0.84) if not for CF (biased by 20.84%). However, due to the inherent sea–land discontinuity resulting in large differences in both surface roughness and solar irradiation (and thus stability conditions), a particular caution should be paid when applying ERA5 over coastal locations.

Atmospheric ammonia (NH3) has increased dramatically as a consequence of the production of synthetic nitrogen (N) fertilizer and proliferation of intensive livestock systems. It is a chemical of environmental concern as it readily reacts with atmospheric acids to produce fine particulate matter and indirectly contributes to nitrous oxide (N2O) emissions. Here, we present the first tall tower observations of NH3 within the U.S. Corn Belt for the period April 2017 through December 2018. Hourly average NH3 mixing ratios were measured at 100 and 56 m above the ground surface and fluxes were estimated using a modified gradient approach. The highest NH3 mixing ratios (>30 nmol mol−1) occurred during early spring and late fall, coinciding with the timing of fertilizer application within the region and the occurrence of warm air temperatures. Net ecosystem NH3 exchange was greatest in spring and fall with peak emissions of about +50 nmol m−2 s−l. Annual NH3 emissions estimated using state‐of‐the‐art inventories ranged from 0.6 to 1.4 × the mean annual gross tall tower fluxes (+2.1 nmol m−2 s−1). If the tall tower observations are representative of the Upper Midwest and broader U.S. Corn Belt regions, the annual gross emissions were +720 Gg NH3‐N y−1 and +1,340 Gg NH3‐N y−1, respectively. Finally, considering the N2O budget over the same region, we estimated total reactive N emissions (i.e., N2O + NH3) of approximately 1,790 Gg N y−1 from the U.S. Corn Belt, representing ~23% of the current annual new N input. Key Points: Observations of NH3 from a tall tower (100 m) provide insights regarding regional emissions from the US Corn BeltAnnual NH3 emissions estimated using state‐of‐the‐art inventories were 0.6 to 1.4‐fold compared to the tall tower flux densityAnnual gross emission estimates for the Upper Midwest and broader US Corn Belt regions were +720 Gg NH3‐N y−1 and +1340 Gg NH3‐N y−1 [ABSTRACT FROM AUTHOR]

In this paper, we present an analysis of electromagnetic fields generated by a lightning return stroke to a tall tower in presence of a horizontally stratified two-layer ground. The electromagnetic fields are evaluated at a distance of 50 m from the tower for two observation points above and below the ground surface, by using the finite-difference time-domain method. The developed numerical model is validated using available experimental data obtained at the CN Tower in Toronto. To illustrate and discuss the effect of the soil stratification on the electromagnetic fields, we adopt two different cases characterized, respectively, by an upper layer less conductive than the lower level, and vice versa. The obtained results show, for the considered distance range (50 m), that the electromagnetic fields above ground at such close distance are nearly insensitive to the ground stratification. However, the underground electromagnetic fields are markedly affected by the properties of the soil layers. In the presence of a lower layer of higher conductivity, the horizontal electric field is characterized by a faster rise time, a significant decrease in amplitude and a bipolar wave-shape compared to that in the case of a homogeneous ground with the upper-layer characteristics. On the other hand, the presence of a lower layer with lower conductivity results in an increase of the peak value of the underground horizontal electric field. [ABSTRACT FROM AUTHOR]

Abstract In this study, the characteristics analysis on current of three sets of upward aborted leaders initiated from Zi-Feng tower in response to nearby lightning is performed. All of them had only an initial stage, not followed by any return-stroke sequences. With duration time of 83.3μs–590.6 μs, the measured current train is composed of a series of pulses. The pulses are close to a double exponential wave with the pulse width of about 7.7 μs ∼18.7 μs, and the rising time is on the order of sub-microseconds. The time interval between the neighboring pulses is about 18.6 μs The peak of pulse current ranges from 1.6 A to 226 A. With respect to the transferred charge of pulse, it ranges from 19 μC to 195.3 μC. Moreover, the possible reason for how the upward aborted leader starts is discussed. The presented statistical results may be of assistance in understanding initial continuous current and the initiation of upward leader at tall grounded objects, as well as in building more appropriate protective measures against lightning hazards. Highlights • Current characteristics of three sets of upward aborted leaders are analyzed. • The peak of pulse current ranges from 1.6 A to 226 A. • The transferred charge of pulse current ranges from 19 μC to 195.3 μC. • Possible reason for how the upward aborted leader starts is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Waveforms of vertical electric field observed at distances of 27, 57, and 101 km from the 634‐m tall Tokyo Skytree (Japan) struck by lightning have been reproduced using the 3‐D finite difference time domain method. Optically observed 3‐D lightning channels and currents directly measured in the tower were used. Distribution of current along the lightning channel was represented using the transmission line model, assuming a constant propagation speed v = 0.5c. Simulations with commonly assumed vertical channel did not allow us to reproduce the observed early (within 5 μs or so) field zero crossing when the 1‐D speed was set to be constant and equal to the 3‐D speed (v = 0.5c) used for the actual‐channel‐geometry case. It was, however, possible to achieve a good match for a vertical channel when the vertical component of 3‐D speed was evaluated for each nonvertical channel segment and used in the corresponding range of heights. [ABSTRACT FROM AUTHOR]

Abstract: Anthropogenic carbon dioxide (CO2) emissions dominate the atmospheric greenhouse gas radiative forcing budget. However, these emissions are poorly constrained at the regional (102–106 km2) and seasonal scales. Here we use a combination of tall tower CO2 mixing ratio and carbon isotope ratio observations and inverse modeling techniques to constrain anthropogenic CO2 emissions within a highly heterogeneous agricultural landscape near Saint Paul, Minnesota, in the Upper Midwestern United States. The analyses indicate that anthropogenic emissions contributed 6.6, 6.8, and 7.4 μmol/mol annual CO2 enhancements (i.e., departures from the background values) in 2008, 2009, and 2010, respectively. Oil refinery, the energy industry (power and heat generation), and residential emissions (home heating and cooking) contributed 2.9 (42.5%), 1.4 (19.8%), and 1.1 μmol/mol (15.8%) of the total anthropogenic enhancement over the 3‐year period according to a priori inventories. The total anthropogenic signal was further partitioned into CO2 emissions derived from fuel oil, natural gas, coal, gasoline, and diesel consumption using inverse modeling and carbon isotope ratio analyses. The results indicate that fuel oil and natural gas consumption accounted for 52.5% of the anthropogenic CO2 sources in winter. Here the a posteriori CO2 emission from natural gas was 79.0 ± 4.1% (a priori 20.0%) and accounted for 63% of the total CO2 enhancement including both biological and anthropogenic sources. The a posteriori CO2 emission from fuel oil was 8.4 ± 3.8% (a priori 32.5%)—suggesting a more important role of residential heating in winter. The modeled carbon isotope ratio of the CO2 source ( δ13Cs , −29.3 ± 0.4‰) was relatively more enriched in 13C‐CO2 compared to that derived from Miller‐Tans plot analyses (−35.5‰ to −34.8‰), supporting that natural gas consumption was underestimated for this region. [ABSTRACT FROM AUTHOR]

Simultaneous electric field and high-speed video camera records of two flashes, labeled 1593 and 1594, were obtained at the Lightning Observatory in Gainesville (LOG), Florida. Flash 1593 was an upward negative flash whose upward positive leader initiated from a 257-m high tower, located 8.8 km from LOG. It contained six leader/return-stroke sequences, all of which developed along the upward leader path and terminated on the 257-m tower. Flash 1594 was a three-stroke downward bipolar flash whose first stroke was positive and terminated on a 60-m tower. The two subsequent strokes were negative and terminated on the same 257-m tower as the six strokes of flash 1593. All strokes terminated on the 257-m tower exhibited very similar narrow bipolar electric field waveforms with damped oscillatory tails. Characteristics of those electric field waveforms are examined and compared to similar observations found in the literature. [ABSTRACT FROM AUTHOR]

Mountain-top observations of greenhouse gas mixing ratios may be an alternative to tall-tower measurements for regional scale source and sink estimation. To investigate the equivalence or limitations of a mountain-top site as compared to a tall-tower site, we used the unique opportunity of comparing in situ measurements of methane ( $$\hbox {CH}_{4}$$ ) and carbon dioxide ( $$\hbox {CO}_{2}$$ ) mixing ratios at a mountain top (986 m above sea level, a.s.l.) with measurements from a nearby (distance 28.4 km) tall tower, sampled at almost the same elevation (1009 m a.s.l.). Special attention was given to, (i) how local wind statistics and greenhouse gas sources and sinks at the mountain top influence the observations, and (ii) whether mountain-top observations can be used as for those from a tall tower for constraining regional greenhouse gas emissions. Wind statistics at the mountain-top site are clearly more influenced by local flow systems than those at the tall-tower site. Differences in temporal patterns of the greenhouse gas mixing ratios observed at the two sites are mostly related to the influence of local sources and sinks at the mountain-top site. Major influences of local sources can be removed by applying a statistical filter ( $$5{\mathrm{th}}$$ percentile) or a filter that removes periods with unfavourable flow conditions. In the best case, the bias in mixing ratios between the mountain-top and the tall-tower sites after the application of the wind filter was $${-}0.0005\pm 0.0010$$ ppm for methane (September, 0000-0400 UTC) and $$0.11\pm 0.18$$ ppm for $$\hbox {CO}_{2}$$ (February, 1200-1600 UTC). Temporal fluctuations of atmospheric $$\hbox {CH}_{4}$$ and $$\hbox {CO}_{2}$$ mixing ratios at both stations also showed good agreement (apart from $$\hbox {CO}_{2}$$ during summertime) as determined by moving bi-weekly Pearson correlation coefficients (up to 0.96 for $$\hbox {CO}_{2}$$ and 0.97 for $$\hbox {CH}_{4}$$ ). When only comparing mixing ratios minimally influenced by local sources (low bias and high correlation coefficients), our measurements indicate that mountain-top observations are comparable to tall-tower observations. [ABSTRACT FROM AUTHOR]

The understanding of scalar fluxes observed in the lower atmosphere is a challenging task, when the underlying surface is non-uniform. In this paper, we apply a micro-scale flow model with a two-equation closure scheme to analyse the influence of the surface heterogeneity on a flux measurement in the area surrounding the 122-m tower at Risø (Denmark), which is a mosaic of water, agricultural areas and forests. These heterogeneities are clearly reflected in the tower-based observations of the turbulence statistics from a profile of six sonic anemometers and are also reproduced by the flow model. Using the two-dimensional mode of the model, in combination with the footprint estimator, we calculate the scalar flux footprints for the 122 m eddy-covariance location and compare these results to analytical footprint estimators, which are only valid for homogeneous terrain, but are commonly applied also for heterogeneous terrain. Whereas the results by the analytical footprint estimator indicate smooth source areas regardless of the surface heterogeneities, the footprint estimator based on the micro-scale model indicates source hotspots, which have a stronger weight in the footprint. The hotspots coincide with areas, where the mean vertical velocity is positive. The positive mean vertical velocity is, in turn, related to topography and forest edge effects on the flow. Relative to the surface roughness estimated from a sonic anemometer, a higher value of the surface roughness was needed for the analytical footprint estimator in order to coarsely match the flow model-based footprint result. Although neither footprint model can be directly verified, the difference in the results underlines that the analytical model should be used with caution in heterogeneous areas. We also estimate the effect of the surface flux source-strength on the observed CO 2 flux. This step demonstrates a novel way of evaluating the CO 2 exchange with the surface, which is useful for constraining models of the surface source or sink. [ABSTRACT FROM AUTHOR]

This paper describes the first measurements of lightning currents from upward lightning events to a tall tower – the Sentech Tower – in Johannesburg, South Africa. The lightning activity in Johannesburg is described in context of other such sites around the world along with the high-speed camera setup and direct current measurement installation at the Sentech Tower, making up the project termed The Johannesburg Lightning Research Laboratory (JLRL). Measurements from the 2020–2021 lightning season are analysed in accordance with similar definitions used in other studies in Austria and Japan and the results are compared with the studies in these regions. A total of 42 lightning events to the tall tower are analysed. This resulted in 175 return strokes, 30 ICC fast pulses and 9 ICC Only events. The return stroke median current and median ICC fast pulse peak currents are comparable to the values seen in Austria and Japan at 7.51 kA and 3.75 kA, respectively. The median charge transfer is 41.36 C (35.51C for ICC Pulse events and 26.08C for ICC Only events) and is also similar to these studies. The return stroke multiplicity however, is higher for the Sentech Tower than elsewhere, with an average value of 6.41. Overall, the peak current distribution, charge transfer and inter-stroke time distribution showed agreement with the measurements made in Austria and Japan. However, the multiplicity of the events measured at the Sentech Tower appear to be twice as much as those seen in Austria and Japan. • The flash density is one of the highest of all locations where lightning studies have been conducted. • The first measurements of lightning currents in South Africa since Eriksson et al.'s work on the CSIR Tower. • The average peak current values of the subsequent return strokes and the average charge transfer appear to be similar to other upward lightning current measurements studies in Austria and Japan. • The multiplicity per event seems to be almost double that of Austria and Japan. [ABSTRACT FROM AUTHOR]

In this study, the spatial representativeness of eddy covariance (EC) methane (CH 4 ) measurements was examined by comparing parallel CH 4 fluxes from three short (6 m) towers separated by a few kilometres and from two higher levels (20 m and 60 m) at one location. The measurement campaign was held on an intensively managed grassland on peat soil in the Netherlands. The land use and land cover types are to a large degree homogeneous in the area. The CH 4 fluxes exhibited significant variability between the sites on 30-min scale. The spatial coefficient of variation ( CV spa ) between the three short towers was 56% and it was of similar magnitude as the temporal variability, unlike for the other fluxes (friction velocity, sensible heat flux) for which the temporal variability was considerably larger than the spatial variability. The CV spa decreased with temporal averaging, although less than what could be expected for a purely random process ( 1 / N ) , and it was 14% for 26-day means of CH 4 flux. This reflects the underlying heterogeneity of CH 4 flux in the studied landscape at spatial scales ranging from 1 ha (flux footprint) to 10 km 2 (area bounded by the short towers). This heterogeneity should be taken into account when interpreting and comparing EC measurements. On an annual scale, the flux spatial variability contributed up to 50% of the uncertainty in CH 4 emissions. It was further tested whether EC flux measurements at higher levels could be used to acquire a more accurate estimate of the spatially integrated CH 4 emissions. Contrarily to what was expected, flux intensity was found to both increase and decrease depending on measurement height. Using footprint modelling, 56% of the variation between 6 m and 60 m CH 4 fluxes was attributed to emissions from local anthropogenic hotspots (farms). Furthermore, morning hours proved to be demanding for the tall tower EC where fluxes at 60 m were up to four-fold those at lower heights. These differences were connected with the onset of convective mixing during the morning period. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports a set of experiments aiming at evaluating the capability of an innovative radar technique to measure the dynamic response of a 268m high tower, the Collserola tower located in Barcelona, and its guys; the tension force of some guys is also estimated from the obtained vibration frequencies. The applied procedure was based on the use of a coherent radar system: temporal samples acquired using different observation geometries were processed to retrieve the vibration characteristics of both the tower and its guys. This was attained by observing the tower in a fully remote sensing mode, i.e. several hundred metres from the object, without installing any reflector on the tower, and under micro-tremor and wind-induced excitation. During the campaigns, which were spread over three years, the investigated technique demonstrated its capability to measure the dynamic response for a number of different points of the tower with high repeatability. The performed experiments also allowed distinguishing and characterizing the different contributions of the tower and the guys. [Copyright &y& Elsevier]

• Return-stroke current measured at the Canton Tower were presented for the first time. • Quadratic relation was found between return stroke peak current and peak luminosity. • LLS-inferred peak current was overestimated by a larger factor for subsequent stroke. The lightning current on the 600-m high Canton Tower was measured directly for the first time, using a Rogowski coil installed at a height of 492 m above ground level. Return-stroke current measurements for three single-stroke downward negative flashes and two multiple-stroke upward negative flashes were presented and preliminarily analysed by combining the associated return-stroke luminosity and data of the lightning location system (LLS). The 10-90% rising time and the full width at half maximum (FWHM) of the first-stroke current were within a range of 6.0 to 9.3 μs and 68.1 to 96.9 μs, respectively. Subsequent-stroke currents were characterized by distinct sharp double peaks, and the typical 10-90% rising time of the initial peak was about 0.4 to 0.5 μs. The FWHM of the subsequent-stroke current ranged from 6.1 to 39.3 μs with AM (GM) value of 18.1 (15.0) μs. An approximately quadratic relation was found between the maximum peak current and the initial peak luminosity for subsequent strokes in the same upward flash. A total of 88% (14/16) of the subsequent strokes were misclassified as intracloud (IC) events by the LLS. The LLS-inferred peak current was overestimated by a larger factor for subsequent strokes than the first strokes. [ABSTRACT FROM AUTHOR]

Abstract: 222Rn concentration time series at 10 m and at 100 m have been measured hourly for one year at the meteorological station, El Arenosillo, on the Spanish southwest coast. A 222Rn flux characterization was also done. A seasonal analysis of atmospheric 222Rn concentration was performed and results for each season present evidence associated with the origin of air masses reaching the El Arenosillo station. An increase in 222Rn concentration was observed when the wind came from Morocco, the Sierra Morena and the Guadalquivir valley areas. On the other hand, a net 222Rn concentration decrease was found when the wind came from the Atlantic Ocean and the South of Portugal. Low 222Rn flux of 4 Bq m−2 h−1 was measured. This result makes this station a useful site for studies related to remote 222Rn source contributions because of low local 222Rn background. The measured annual average concentration of 222Rn gas at the El Arenosillo station is 3.51 ± 0.05 Bq m−3 at 10 m and 2.61 ± 0.05 Bq m−3 at 100 m. [Copyright &y& Elsevier]

Abstract: We present a method for the estimation of the spatial representativeness of tall tower eddy covariance measurements monitoring a heterogeneous landscape. The approach attributes the measured signal to the different ecosystems surrounding the tall tower site. For the identification of the ecosystems, remotely sensed vegetation index time series are used. Using 250m grid resolution defined by the available MODIS vegetation index data, we quantify the spatial distribution of winter and summer crops and we also provide an estimate on the fractional crop coverage for pixels with heterogeneous crop type. Using a state-of-the-art footprint model applicable in the mixed layer we calculate a footprint climatology for the 5-year period 2003–2007. With the synergy of the footprint analysis and the land cover classification scheme we quantify the representativeness of the eddy covariance measurement. It was found that the source region distribution is very similar from year to year. The biggest impact to the measurement originates generally within 1km radius from the tower. 75–80% of the measured signal originates from agricultural areas, while the contribution of pastures is also relevant. Though there are important other land use types in the region (e.g. forests, settlements) their contribution to the measured signal is rather small (<5% for forested regions, <2% for urban areas). Inside the source area the relative importance and spatial distribution of summer and winter crops is variable among the years, which may influence the measured signal due to the different timing of the intensive carbon uptake period and harvest. The presented methodology is used to estimate summer and winter crop-specific carbon dioxide exchange time series. The crop-specific carbon dioxide fluxes are markedly different in each year, and exhibit strong covariation with the crop-specific NDVI time series. The results further suggest that the applied footprint model provides accurate footprint estimates. [Copyright &y& Elsevier]

Abstract: We present an analysis of the electromagnetic fields at very close range from a tower struck by lightning. The electromagnetic fields are evaluated for observation points above, on the surface and below the ground plane characterized by a finite conductivity. The computations are obtained using the Finite-Difference Time-Domain (FDTD) technique, in which the so-called engineering models are incorporated to represent the spatial–temporal distribution of the current along the channel and along the strike object. The approach is tested using a set of simultaneously recorded data published in the literature consisting of the current measured at the top of the Peissenberg tower and the associated electric and magnetic fields and very good agreement has been found. Simulation results are performed for an observation point located 50m from the base of the channel (or tower, when present) and for three cases, namely (i) a lightning strike to ground, and (ii) a lightning strike to a 168-m tall tower, and (iii) a lightning strike to a 553-m tall tower. The effect of the presence of the tower and the effect of finite ground conductivity on the generated above-ground and underground electromagnetic fields are illustrated and discussed. It is shown that the underground electric fields are markedly affected by the ground conductivity. The underground electric field is predominantly horizontal with a negative polarity. The vertical electric field component is characterized by a bipolar wave-shape. The ground conductivity affects in a lesser degree the magnetic field penetrating into the ground. Above the ground and on the ground surface, the vertical electric field and the azimuthal magnetic field generated by a lightning return stroke initiated at ground level are nearly insensitive to the height of the observation point above ground. For the considered distance range (50m), they can be computed assuming the ground as a perfectly conducting plane. The magnetic field above ground at such close distance is virtually not affected by the ground conductivity. The presence of a tower results in a significant decrease of the vertical electric field in the immediate vicinity of the tower. Unlike the case of a ground-initiated return stroke, the above-ground vertical electric field associated with a return stroke to tall tower is very much affected by the ground conductivity. Depending on the value of this latter, this component could exhibit an inversion of polarity. [Copyright &y& Elsevier]

The reliability of ERA5 reanalyses for directly predicting wind resources and energy production has been assessed against observations from six tall towers installed over very heterogeneous sites around the world. Scores were acceptable at the FINO3 (Germany) offshore platform for both wind speed (bias within 1%, r = 0.95−0.96) and capacity factor (CF, at worst biased by 6.70%) and at the flat and sea-level site of Cabauw (Netherlands) for both wind speed (bias within 7%, r = 0.93−0.94) and CF (bias within 6.82%). Conversely, due to the ERA5 limited resolution (~31 km), large under-predictions were found at the Boulder (US) and Ghoroghchi (Iran) mountain sites, and large over-predictions were found at the Wallaby Creek (Australia) forested site. Therefore, using ERA5 in place of higher-resolution regional reanalysis products or numerical weather prediction models should be avoided when addressing sites with high variation of topography and, in particular, land use. ERA5 scores at the Humansdorp (South Africa) coastal location were generally acceptable, at least for wind speed (bias of 14%, r = 0.84) if not for CF (biased by 20.84%). However, due to the inherent sea–land discontinuity resulting in large differences in both surface roughness and solar irradiation (and thus stability conditions), a particular caution should be paid when applying ERA5 over coastal locations. [ABSTRACT FROM AUTHOR]

• 21-years long carbon dioxide flux dataset is presented from a Central Europen tall tower site. • net ecosystem production (NEP) increased during the years. • net biome production (NBP) estimation suggests that the region is a slight carbon source. • interannual variability is studied using a novel statistical method relying on monthly mean environmental factors. • major NEP anomaly during 2001-2003 is explained by the interaction of environmental variables. Eddy-covariance based carbon flux datasets spanning decades are becoming available worldwide due to the effort of associated scientists. Tall tower based monitoring stations are relatively rare, but provide important information about the carbon balance of a larger region surrounding the tower. In this study we report and analyze the 21-year-long dataset provided by the Hungarian tall tower site, Hegyhátsál. The daily and annual cycles of net ecosystem exchange (NEE), gross primary production, and total ecosystem respiration are presented. Footprint analysis reveals that the fluxes mostly originate from the surrounding arable lands; the main source region is located within 1 km around the tower. Long-term, mean NEE was -0.467 gC m-2 day-1, or -170 gC m-2 year-1, revealing that the complex region was a net carbon sink from the atmospheric perspective. Trend analysis indicates that overall, NEE decreased (i.e. became more negative, which means stronger sink) by 12 gC m-2 year-1, a trend that is explained by improved agrotechnology and climate change. Net biome production (NBP) was estimated using crop census data and assumptions about the management practices that affect lateral carbon flux. Long term mean NBP was -30 gC m-2 year-1, which indicates that the soils may be losing carbon, though this loss is within the range of uncertainty of the measurements (~50 gC m-2 year-1). Analysis of county-scale yield statistics suggested that the results can be representative to at least county scale (1651 km2). Interannual variability was analyzed by using environmental variables such as maximum and minimum temperature, precipitation, vapor pressure deficit, soil water content, and satellite based vegetation index aggregated at monthly and longer time intervals. The results indicate that environmental conditions in spring have a major role in the annual carbon balance. Moreover, water availability represented by soil water content rather than by precipitation is a major driver of the interannual variability of NEE. The statistical analysis suggested that the large positive NEE anomaly during 2001–2003 was caused by interplay among the environmental drivers, in particular maximum temperature, vapor pressure deficit and radiation in April, followed by a soil water content deficit during the growing season. This novel statistical analysis provides insight into the drivers of the carbon balance of a mixed agricultural region. [ABSTRACT FROM AUTHOR]