The ACT‐America project is a NASA Earth Venture Suborbital‐2 mission designed to study the transport and fluxes of greenhouse gases. The open and freely available ACT‐America data sets provide ...airborne in situ measurements of atmospheric carbon dioxide, methane, trace gases, aerosols, clouds, and meteorological properties, airborne remote sensing measurements of aerosol backscatter, atmospheric boundary layer height and columnar content of atmospheric carbon dioxide, tower‐based measurements, and modeled atmospheric mole fractions and regional carbon fluxes of greenhouse gases over the Central and Eastern United States. We conducted 121 research flights during five campaigns in four seasons during 2016–2019 over three regions of the US (Mid‐Atlantic, Midwest and South) using two NASA research aircraft (B‐200 and C‐130). We performed three flight patterns (fair weather, frontal crossings, and OCO‐2 underflights) and collected more than 1,140 h of airborne measurements via level‐leg flights in the atmospheric boundary layer, lower, and upper free troposphere and vertical profiles spanning these altitudes. We also merged various airborne in situ measurements onto a common standard sampling interval, which brings coherence to the data, creates geolocated data products, and makes it much easier for the users to perform holistic analysis of the ACT‐America data products. Here, we report on detailed information of data sets collected, the workflow for data sets including storage and processing of the quality controlled and quality assured harmonized observations, and their archival and formatting for users. Finally, we provide some important information on the dissemination of data products including metadata and highlights of applications of ACT‐America data sets.
Plain Language Summary
We describe the data collected and produced by the Atmospheric Carbon and Transport – America mission, including airborne and tower‐based measurements of greenhouse gases (e.g., carbon dioxide and methane) and modeled atmospheric mole fractions and regional carbon fluxes of greenhouse gases over North America. In this paper, we briefly describe the data collections and archival including the instruments and methodology used to generate, manage, and distribute the data, and the significance of these new measurements for the study of the North American carbon cycle.
Key Points
Atmospheric Carbon and Transport – America (ACT‐America) provides a unique, weather‐oriented collection of atmospheric CO2, CH4, trace gases, and meteorological properties measurements
ACT‐America data are free and open to the public from the Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC)
ACT‐America data are uniquely suited to improve the accuracy and precision of regional inverse greenhouse gas (GHG) flux estimates
During the SCOUT-O3/ACTIVE field phase in November–December 2005, airborne in situ measurements were performed inside and in the vicinity of thunderstorms over northern Australia with several ...research aircraft (German Falcon, Russian M55 Geophysica, and British Dornier-228. Here a case study from 19 November is presented in detail on the basis of airborne trace gas measurements (NO, NOy, CO, O3) and stroke measurements from the German LIghtning Location NETwork (LINET), set up in the vicinity of Darwin during the field campaign. The anvil outflow from three different types of thunderstorms was probed by the Falcon aircraft: (1) a continental thunderstorm developing in a tropical airmass near Darwin, (2) a mesoscale convective system (MCS), known as Hector, developing within the tropical maritime continent (Tiwi Islands), and (3) a continental thunderstorm developing in a subtropical airmass ~200 km south of Darwin. For the first time detailed measurements of NO were performed in the Hector outflow. The highest NO mixing ratios were observed in Hector with peaks up to 7 nmol mol−1 in the main anvil outflow at ~11.5–12.5 km altitude. The mean NOx (=NO+NO2) mixing ratios during these penetrations (~100 km width) varied between 2.2 and 2.5 nmol mol−1. The NOx contribution from the boundary layer (BL), transported upward with the convection, to total anvil-NOx was found to be minor (<10%). On the basis of Falcon measurements, the mass flux of lightning-produced NOx (LNOx) in the well-developed Hector system was estimated to 0.6–0.7 kg(N) s−1. The highest average stroke rate of the probed thunderstorms was observed in the Hector system with 0.2 strokes s−1 (here only strokes with peak currents ≥10 kA contributing to LNOx were considered). The LNOx mass flux and the stroke rate were combined to estimate the LNOx production rate in the different thunderstorm types. For a better comparison with other studies, LINET strokes were scaled with Lightning Imaging Sensor (LIS) flashes. The LNOx production rate per LIS flash was estimated to 4.1–4.8 kg(N) for the well-developed Hector system, and to 5.4 and 1.7 kg(N) for the continental thunderstorms developing in subtropical and tropical airmasses, respectively. If we assume, that these different types of thunderstorms are typical thunderstorms globally (LIS flash rate ~44 s−1), the annual global LNOx production rate based on Hector would be ~5.7–6.6 Tg(N) a−1 and based on the continental thunderstorms developing in subtropical and tropical airmasses ~7.6 and ~2.4 Tg(N) a−1, respectively. The latter thunderstorm type produced much less LNOx per flash compared to the subtropical and Hector thunderstorms, which may be caused by the shorter mean flash component length observed in this storm. It is suggested that the vertical wind shear influences the horizontal extension of the charged layers, which seems to play an important role for the flash lengths that may originate. In addition, the horizontal dimension of the anvil outflow and the cell organisation within the thunderstorm system are probably important parameters influencing flash length and hence LNOx production per flash.
During the SCOUT-O3/ACTIVE field phase in November-December 2005, airborne in situ measurements were performed inside and in the vicinity of thunderstorms over northern Australia with several ...research aircraft (German Falcon, Russian M55 Geophysica, and British Dornier-228. Here a case study from 19 November is presented in detail on the basis of airborne trace gas measurements (NO, NO sub(y), CO, O sub(3)) and stroke measurements from the German LIghtning Location NETwork (LINET), set up in the vicinity of Darwin during the field campaign. The anvil outflow from three different types of thunderstorms was probed by the Falcon aircraft: (1) a continental thunderstorm developing in a tropical airmass near Darwin, (2) a mesoscale convective system (MCS), known as Hector, developing within the tropical maritime continent (Tiwi Islands), and (3) a continental thunderstorm developing in a subtropical airmass ~200 km south of Darwin. For the first time detailed measurements of NO were performed in the Hector outflow. The highest NO mixing ratios were observed in Hector with peaks up to 7 nmol mol super(− 1) in the main anvil outflow at ~11.5-12.5 km altitude. The mean NO sub(x) (=NO+NO sub(2)) mixing ratios during these penetrations (~100 km width) varied between 2.2 and 2.5 nmol mol super(− 1). The NO sub(x) contribution from the boundary layer (BL), transported upward with the convection, to total anvil-NO sub(x) was found to be minor (<10%). On the basis of Falcon measurements, the mass flux of lightning-produced NO sub(x) (LNO sub(x)) in the well-developed Hector system was estimated to 0.6-0.7 kg(N) s super(− 1). The highest average stroke rate of the probed thunderstorms was observed in the Hector system with 0.2 strokes s super(− 1) (here only strokes with peak currents greater than or equal to 10 kA contributing to LNO sub(x) were considered). The LNO sub(x) mass flux and the stroke rate were combined to estimate the LNO sub(x) production rate in the different thunderstorm types. For a better comparison with other studies, LINET strokes were scaled with Lightning Imaging Sensor (LIS) flashes. The LNO sub(x) production rate per LIS flash was estimated to 4.1-4.8 kg(N) for the well-developed Hector system, and to 5.4 and 1.7 kg(N) for the continental thunderstorms developing in subtropical and tropical airmasses, respectively. If we assume, that these different types of thunderstorms are typical thunderstorms globally (LIS flash rate ~44 s super(− 1)), the annual global LNO sub(x) production rate based on Hector would be ~5.7-6.6 Tg(N) a super(− 1) and based on the continental thunderstorms developing in subtropical and tropical airmasses ~7.6 and ~2.4 Tg(N) a super(− 1), respectively. The latter thunderstorm type produced much less LNO sub(x) per flash compared to the subtropical and Hector thunderstorms, which may be caused by the shorter mean flash component length observed in this storm. It is suggested that the vertical wind shear influences the horizontal extension of the charged layers, which seems to play an important role for the flash lengths that may originate. In addition, the horizontal dimension of the anvil outflow and the cell organisation within the thunderstorm system are probably important parameters influencing flash length and hence LNO sub(x) production per flash.
We report on the retrieval of PAN (CH3C(O)OONO2) in the upper tropical troposphere from limb measurements by the remote-sensor MIPAS-STR on board the Russian high altitude research aircraft ...M55-Geophysica. The measurements were performed close to Araçatuba, Brazil, on 17 February 2005. The retrieval was made in the spectral range 775–820 cm−1 where PAN exhibits its strongest feature but also more than 10 species interfere. Especially trace gases such as CH3CCl3, CFC-113, CFC-11, and CFC-22, emitting also in spectrally broad not-resolved branches, make the processing of PAN prone to errors. Therefore, the selection of appropriate spectral windows, the separate retrieval of several interfering species and the careful handling of the water vapour profile are part of the study presented. The retrieved profile of PAN has a maximum of about 0.14 ppbv at 10 km altitude, slightly larger than the lowest reported values (<0.1 ppbv) and much lower than the highest reported in the literature (0.65 ppbv). Besides the NOy constituents measured by MIPAS-STR (HNO3, ClONO2, HO2NO2, PAN), the in situ instruments aboard the Geophysica provide simultaneous measurements of NO, NO2, and the sum NOy. Comparing the sum of in-situ and remotely derived NO+NO2+HNO3+ClONO2+HO2NO2+PAN with total NOy a deficit of 30–40% (0.2–0.3 ppbv) in the troposphere remains unexplained whereas the values fit well in the stratosphere.
During the TROCCINOX field experiments in February–March 2004 and February 2005, airborne in situ measurements of NO, NOy, CO, and O3 mixing ratios and the J(NO2) photolysis rate were carried out in ...the anvil outflow of thunderstorms over southern Brazil. Both tropical and subtropical thunderstorms were investigated, depending on the location of the South Atlantic convergence zone. Tropical air masses were discriminated from subtropical ones according to the higher equivalent potential temperature (Θe) in the lower and mid troposphere, the higher CO mixing ratio in the mid troposphere, and the lower wind velocity in the upper troposphere within the Bolivian High (north of the subtropical jet stream). During thunderstorm anvil penetrations, typically at 20–40 km horizontal scales, NOx mixing ratios were distinctly enhanced and the absolute mixing ratios varied between 0.2–1.6 nmol mol−1 on average. This enhancement was mainly attributed to NOx production by lightning and partly due to upward transport from the NOx-richer boundary layer. In addition, CO mixing ratios were occasionally enhanced, indicating upward transport from the boundary layer. For the first time, the composition of the anvil outflow from a large, long-lived mesoscale convective system (MCS) advected from northern Argentina and Uruguay was investigated in more detail. Over a horizontal scale of about 400 km, NOx, CO and O3 absolute mixing ratios were significantly enhanced in these air masses in the range of 0.6–1.1, 110–140 and 60–70 nmol mol−1, respectively. Analyses from trace gas correlations and a Lagrangian particle dispersion model indicate that polluted air masses, probably from the Buenos Aires urban area and from biomass burning regions, were uplifted by the MCS. Ozone was distinctly enhanced in the aged MCS outflow, due to photochemical production and entrainment of O3-rich air masses from the upper troposphere – lower stratosphere region. The aged MCS outflow was transported to the north, ascended and circulated, driven by the Bolivian High over the Amazon basin. In the observed case, the O3-rich MCS outflow remained over the continent and did not contribute to the South Atlantic ozone maximum.
We report on the retrieval of PAN (CH sub(3)C(O)OONO sub(2)) in the upper tropical troposphere from limb measurements by the remote-sensor MIPAS-STR on board the Russian high altitude research ...aircraft M55-Geophysica. The measurements were performed close to Aracaatuba, Brazil, on 17 February 2005. The retrieval was made in the spectral range 775-820 cm super(-1) where PAN exhibits its strongest feature but also more than 10 species interfere. Especially trace gases such as CH sub(3)CCl sub(3), CFC-113, CFC-11, and CFC-22, emitting also in spectrally broad not-resolved branches, make the processing of PAN prone to errors. Therefore, the selection of appropriate spectral windows, the separate retrieval of several interfering species and the careful handling of the water vapour profile are part of the study presented. The retrieved profile of PAN has a maximum of about 0.14 ppbv at 10 km altitude, slightly larger than the lowest reported values (<0.1 ppbv) and much lower than the highest reported in the literature (0.65 ppbv). Besides the NO sub(y) constituents measured by MIPAS-STR (HNO sub(3), ClONO sub(2), HO sub(2)NO sub(2), PAN), the in situ instruments aboard the Geophysica provide simultaneous measurements of NO, NO sub(2), and the sum NO sub(y). Comparing the sum of in-situ and remotely derived NO+NO sub(2)+HNO sub(3)+ClONO sub(2)+HO sub(2)NO sub(2)+PAN with total NO sub(y) a deficit of 30-40% (0.2-0.3 ppbv) in the troposphere remains unexplained whereas the values fit well in the stratosphere.
During the TROCCINOX field experiments in February-March 2004 and February 2005, airborne in situ measurements of NO, NO sub(y), CO, and O sub(3) mixing ratios and the J(NO sub(2)) photolysis rate ...were carried out in the anvil outflow of thunderstorms over southern Brazil. Both tropical and subtropical thunderstorms were investigated, depending on the location of the South Atlantic convergence zone. Tropical air masses were discriminated from subtropical ones according to the higher equivalent potential temperature (Theta; sub(e)) in the lower and mid troposphere, the higher CO mixing ratio in the mid troposphere, and the lower wind velocity in the upper troposphere within the Bolivian High (north of the subtropical jet stream). During thunderstorm anvil penetrations, typically at 20-40 km horizontal scales, NO sub(x) mixing ratios were distinctly enhanced and the absolute mixing ratios varied between 0.2-1.6 nmol mol super(-1) on average. This enhancement was mainly attributed to NO sub(x) production by lightning and partly due to upward transport from the NO sub(x)-richer boundary layer. In addition, CO mixing ratios were occasionally enhanced, indicating upward transport from the boundary layer. For the first time, the composition of the anvil outflow from a large, long-lived mesoscale convective system (MCS) advected from northern Argentina and Uruguay was investigated in more detail. Over a horizontal scale of about 400 km, NO sub(x), CO and O sub(3) absolute mixing ratios were significantly enhanced in these air masses in the range of 0.6-1.1, 110-140 and 60-70 nmol mol super(-1), respectively. Analyses from trace gas correlations and a Lagrangian particle dispersion model indicate that polluted air masses, probably from the Buenos Aires urban area and from biomass burning regions, were uplifted by the MCS. Ozone was distinctly enhanced in the aged MCS outflow, due to photochemical production and entrainment of O sub(3)-rich air masses from the upper troposphere - lower stratosphere region. The aged MCS outflow was transported to the north, ascended and circulated, driven by the Bolivian High over the Amazon basin. In the observed case, the O sub(3)-rich MCS outflow remained over the continent and did not contribute to the South Atlantic ozone maximum.
A lightning NOx (LiNOx) source has been implemented in the deep convection scheme of the Meso-NH mesoscale model following a mass-flux formalism coherent with the transport and scavenging of gases ...inside the convective scheme. In this approach the vertical transport of NO inside clouds is calculated by the parameterization of deep convective transport, thus eliminating the need for a-priori LiNOx profiles. Once produced inside the convective column, NO molecules are redistributed by updrafts and downdrafts and detrained in the environment when the conditions are favorable. The model was applied to three particular flights during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) campaign over the tropical area around Bauru on 3–4 March 2004. The convective activity during the three flights was investigated using brightness temperature at 10.7 μm observed from GOES-12 satellite. The use of a model-to-satellite approach reveals that the simulation appears rather realistic compared to the observations. The diurnal cycle of the simulated brightness temperature, CAPE, number of IC flashes, NO entrainment flux are in phase, with a succession of three marked peaks at 18:00 UTC (15:00 LT). These simulated peaks precede the observed afternoon one by about three hours. Comparison of the simulated NOx with observations along the flight tracks show that the model reproduces well the observed NOx levels when the LiNOx source is applied. The budget of entrainment, detrainment and LiNOx convective fluxes shows that the majority of the NO detrained back to the environment comes from lightning source inside the convective columns. Entrainment of NO from the environment and vertical transport from the boundary layer were not significant during the episode. The troposphere is impacted by detrainment fluxes of LiNOx from 4 km altitude to 16 km with maximum values around 14 km altitude. Detrainment fluxes vary between 75 kg(N)/s during nighttime to 400 kg(N)/s at the times of maximun convective activity. Extrapolation of the regional LiNOx source would yield a global LiNOx production around 5.7 Tg(N)/year which is within the current estimates but should not hide the overestimation of the number of flash rates by the model.
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